NlSTlR 7133 

NIST-SFPE Workshop for Development of a National 

R&D Roadmap for Structural Fire Safety Design and 

Retrofit of Structures: Proceedings 

NmNational Institute of Standards and Technology Technology Administration U.S. Department of Commerce 

NlSTlR 7133 

NET-SFPE Workshop for Development of a National 

R&D Roadmap for Structural Fire Safety Design and 

Retrofit of Structures: Proceedings 

Kathleen H. Almand 

Society of Fire Protection Engineers 

and 

Long T. Phan 

Therese P. McAllister 

Monica A. Starnes 

John L. Gross 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

April 20,2004 

U. S. Department of Commerce 

Donald L. Evans,‘ Secretary 

Technology Administration 

Phillip J. Bond, Under Secretary for Technology 

National Institute of Standards and Technology 

Arden L. Bement, Director 

NIST-SFPE Workshop for Development of a National R&D Roadmap 

for Structural Fire Safety Design and Retrofit of Structures: 

Proceedings 

Table of Contents 

Abstract 

Acknowledgements 

Executive Summary 

3 

3 

4 

1. 

1.1 

1.2 

1.3 

2. 

2.1 

2.2 

2.3 

3. 

3.1 

3.2 

3.3 

4. 

4.1 

4.2 

4.3 

5. 

5.1 

5.2 

5.3 

5.4 

INTRODUCTION 5 

Background 5 

NIST R&D program in fire safety design and retrofit of structures 6 

NIST-SFPE workshop on structural fire safety design and retrofit 

of structures 7 

STATEMENT OF NEED 

Code enforcement perspective 

Architectural perspective 

Engineer’s Perspective 

FRAMEWORK FOR STRUCTURAL FIRE ENGINEERING AND DESIGN 

METHODS 

Overview 

Discussion 

Needed Actions 

RELATIONSHIP BETWEEN STRUCTURAL FIRE PROTECTION 

DESIGN AND OTHER ELEMENTS OF FIRE SAFETY DESIGN 

Overview 

Discussion 

Needed Actions 

ANALYSIS TOOLS 

Design Fires 

5.1.1. Overview 

5.1.2. Discussion and Needed Actions 

Thermal Analysis 

5.2.1 Overview 

5.2.2 Discussion and Needed Actions 

Structural Analysis 

5.3.1 Overview 

5.3.2 Discussion and Needed Actions 

Existing Buildings 

5.4.1. Overview 

5.4.2 Discussion and Needed Actions 

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12 

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14 

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15 

15 

15 

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6. BEST PRACTICES AND SUPPORTING TECHNICAL DATA 19 

6.1 Overview of Current International Codes and Standards 19 

6.2 Discussion 19 

6.3 Needed Actions 20 

7. 

8. 

9. 

9.A 

9.B 

9.c 

9.D 

9.E 

9.F 

9.G 

9.H 

RESEARCH PRIORITIES FOR ROADMAP DEVELOPMENT 22 

RECOMMENDATIONS 25 

APPENDICES 26 

Workshop Prospectus 27 

Steering Committee Members 29 

Workshop Agenda 30 

Workshop Facilitators and Recorders 32 

Workshop Attendance 33 

Workshop Breakout Notes 37 

Research and Development Priorities 55 

White Papers 60 

White Paper 1. 

Challenges Facing Engineered Structural Fire Safety - A Code 

Official’s Perspective 

By Jonathan C. Siu 61 

White Paper 2. 

The Need for Structural Fire Safety Design Methods - An Architect’s Perspective 

The Who, What, Where, When and How of Doing Fire Safety Design 

By David S. Collins 70 

White Paper 3. 

Framework for Structural Fire Engineering and Design Methods 

White Paper 4. 

Relationship Between Structural Fire Protection Design and Other Elements of 

Fire Safety Design 

White Paper 5. Design Fire Scenarios 

By Morgan J. Hwley 107 

White Paper 6. 

Analysis Tools and Design Methods: Current Best Practices 

By James Milk 118 

White Paper 7. 

Thermal and Structural Analysis Methods and Tools - Gaps in Knowledge and 

Priority Area for Research fiom a Practice Perspective 

By Barbara Lane 146 

White Paper 8. 

Evaluation and Retrofit of Existing Buildings for Structural Fire Safety 

By Frederick W. Mower and Robert H. Iding 

White Paper 9. 

International Status of Design Standards for Structural Fire Safety 

By Andy Buchanan 168 

By Gregory G. Deierlein and Scott Hamilton 75 

By Craig BeyIer 100 

158 

2 
Abstract 

This report describes the results of the workshop sponsored by the National Institute of Standards 

and Technology’s Building and Fire Research Laboratory that was held on October 2,3,2003 in 

Baltimore, MD. The workshop was planned to assist with the development of a research and 

development roadmap for structural fire safety design and retrofit of structures,. This report 

summarizes the content of nine contextual white papers prepared for the workshop and the 

process and results of the industry discussion and prioritization that took place. 

Acknowledgements 

This workshop and the related activities of the Society of Fire Protection Engineers in its 

organization and report were supported through a contract from the National Institute of 

Standards and Technology. The workshop was led by a devoted industry steering team who 

guided its agenda and resulting productivity. Team members are: 

Lou Gerschwinder, American Institute of Steel Construction 

Jim Rossberg, American Society of Civil Engineers 

Steve Szoke, Portland Cement Association 

Pravin Gandhi, Underwriters Laboratories, Inc. 

Chris Marrion, Amp Fire 

Kathleen Almand, Society of Fire Protection Engineers 

Robert Duval, National Fire Protection Association 

In addition, the thoughtful contributions from each of the white paper authors whose work formed 

the basis of the discussion of the workshop are acknowledged: 

Jonathan Siu, City of Seattle 

Dave Collins, the Preview Group 

Carig Beyler, Hughes Associates, Inc. 

Greg Deierlein, Stanford University 

Morgan Hurley, Society of Fire Protection Engineers 

James Milke, University of Maryland 

Barbara Lane, Arup Fire 

Robert Iding, Wiss, Janney, Elstner, and Associates 

Frederick Mower, University of Maryland 

Andrew Buchanan, University of Canterbury 

Finally, the editors would like to acknowledge the assistance from Elle Andracsek, SFPE staff for 

logistical oversight of the workshop. 

Disclaimer 

Certain trade names or company products are mentioned in the text to specify adequately the 

experimental procedure and equipment used. In no case does such identification imply 

recommendation or endorsement by the National Institute of Standards and Technology, nor does 

it imply that the equipment is the best available for the purpose. 

3 
Executive Summary 

The National Institute of Standards and Technology’s Building and Fire Research Laboratory, as 

the national laboratory responsible for research into building fires, initiated a program prior to the 

events of September 1 1,200 1 to put structural fire protection on a stronger scientific footing. The 

catastrophic collapses of the World Trade center underscored the need to accelerate this effort. 

As part of this effort, NIST commissioned the Society of Fire Protection Engineers to organize an 

industry workshop calling on the expertise of the global fire safety engineering community. The 

purpose of the workshop, held on October 2 and 3,2003 in Baltimore, MD, was to provide 

industry input for use in the development of a detailed R&D roadmap for structural fire safety 

design and retrofit of structures. Sixty individuals attended the workshop including structural and 

fire protection engineers, architects, academia, research and testing laboratory representatives, 

regulatory offices and representatives of insurance and industry associations. 

Nine white papers were commissioned in advance of the workshop to outline the issues and 

research needs associated with implementing improved structural fire safety design and retrofit 

methodologies. These papers, providing the perspective of industry users and international 

experts in the field, set the context for a vigorous one and half day series of discussion sessions 

where needs for further research and improved practices were identified and prioritized. Two 

tiers of top priority recommendations were developed, ranging from the need for more research 

quality experimental data of the behavior of structural components and materials at elevated 

temperatures to the need to specifjr professional responsibilities for structural fire protection over 

the life of the building. 

The general consensus of the workshop participants on research needs are summarized as 

follows: 

Obtain research-quality laboratory and real data, including construction and use of 

large-scale structural fire test facilities, of engineering material properties at elevated 

temperature and performance of structural components under load and fire 

conditions. 

Develop performance goals, criteria and methodologies for implementation in codes 

ind standards, including quantification of safety provided by current prescriptive and 

performance-based methods, practice guidelines for the enforcement and engineering 

communities, risk-based methodology for design fires, benchmark problems for 

validation of analysis tools, standardized test methods, and limit states and failure 

criteria. 

Specify professional responsibilities for structural fire protection over the life of the 

building. 

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4 
1. INTRODUCTION 

1.1 Background 

In the wake of the collapse of buildings in the World Trade Center (WTC) complex on September 

1 1,200 1, the National Institute of Standards and Technology (NIST), under the authority of the 

National Construction Safety Team Act (Public Law [P.L.] 107-23 l), formally initiated the 

federal building and fire safety investigation of the WTC disaster on August 21,2002. The 

investigation aims to achieve the following four objectives: 

1. 

2. 

3. 

4. 

Determine why and how WTC 1 and WTC 2 collapsed following the initial impacts of 

the aircraft and why and how WTC 7 collapsed. 

Determine why the injuries and fatalities were so high or low depending on location, 

including technical aspects of fire protection, occupant behavior, evacuation, and 

emergency response. 

Determine what procedures and practices were used in the design, construction, 

operation, and maintenance of WTC 1,2, and 7. 

Identify areas in the current national building and fire model codes, standards, and 

practices that warrant revision. 

The fast three objectives are short-term and addresses issues specific to the collapse of WTC 1,2, 

and 7. The fourth objective is long-term and addresses deficiencies in design practice related to 

building and fre safety. 

Current building design practice does not consider fire as a design condition for purposes of 

evaluating structural performance in the presence of an uncontrolled fire. Instead, fire endurance 

ratings of building members or subassemblies, derived from standard fire endurance tests (e.g., 

ASTM E-1 19), are specified prescriptively in building codes. In addition, there is no accepted set 

of verified tools to evaluate the fire performance of entire structures and to achieve engineered 

fire safety. While current prescriptive methods appear to work satisfactorily in typical 

compartment fres, the adequacy of such methods in large, uncontrolled fires is questionable. 

Thus, there is widespread recognition of the need to develop and implement significantly 

improved tools, practices, and standards that explicitly consider structural fire loads in the design 

of new structures and the retrofit of existing structures. 

Balancing the competing demands for fire safety and economy in a rational manner requires the 

development of performance-based methods to measure and predict the behavior of hll-scale 

structures under fire conditions. Such performance-based methods must consider the following 

five key deficiencies in the current building fire safety design practice: 

First, while the current standard fire endurance test methods, which stipulate a prescribed 

time-temperature exposure, are adequate to compare relative performance of structural 

components, they do not provide information about the actual performance (i.e., load carrying 

capacity) of a component in a real fire environment (e.g., involving fire of building contents, 

hydrocarbon pool fires, or a combination thereof). 

Second, the role of structural connections, diaphragms, and redundancy in enabling load 

transfer and maintaining overall structural integrity (i.e., preventing progressive collapse) 

during fire is ignored in structural design. Current structural fire protection design methods 

are based on fire endurance tests of single components and do not account for the behavior of 

connections or the complex two- and three-dimensional behavior of the entire structure. 

5 
Third, current analytical tools are inadequate to evaluate the effectiveness of alternative 

design, retrofit, and fire protection strategies to enhance structural fire endurance (including 

alternate cementitious spray or board systems, intumescent coatings, high-performance frre 

protective coatings, active suppression systems, and more sensitive sensing and monitoring). 

No practical analytical tools exist today that couple the fire dynamics to the structural system 

response, and the resulting transient, multi-dimensional heat transfer through structural 

components made with multiple materials. 

Fourth, there is a need to better model and predict the fre hazards to structures and to 

develop design criteria for evaluating fire hazards from internal and external fires (e.g., due to 

accidents or terrorist threats). This includes deterministic and probabilistic models for 

specifying the magnitude, location, and spatial distribution of fire hazards on structures (e.g., 

design fire scenarios defined by the probability of exceeding established criteria by 2% in 50- 

years); determination of reliability-based load factors for combined dead, live, and fire loads 

and resistance factors for loss in structural strength and stiflhess; and methods for load and 

resistance factor design (LRFD) under fire conditions. 

Fifth, there is a lack of knowledge about the fire behavior of structures built with innovative 

structural materials (e.g., high-strength concrete or steel structures) or passive fire protection 

materials. 

1.2 NIST R&D Program in Fire Safety Design and Retrofit of Structures 

As part of the NIST response plan for the WTC disaster, NIST has initiated a major R&D project 

in fire safety design and retrofit of structures. The project aims to develop and implement 

significantly improved standards, tools, and practical guidance for the structural fire safety design 

and retrofit of structures in partnership with key stakeholders by integrating knowledge of 

modem fire science and fire protection engineering with knowledge of modem structural 

reliability methods and structural engineering. Specifically, the project aims to produce the 

following eight key products in three major areas, including Structural Fire Safety Design of New 

Buildings, Analysis of Structural Fire Performance, and Fire Safety Evaluation and Retro@t of 

Existing Buildings, over a multi-year period: 

Structural Fire Safetv Desim of New Buildings 

Best practices for structural fire dety design of structures. 

Guidelines/pre-standards for fire safety design of structures. 

Analysis of Structural Fire Performance 

0 

0 

0 

Best practices tools for analyzing structural fire performance. 

Load and resistance factor methodology for structural fire safety. 

Selected verifiedvalidated predictive tools for analyzing structural performance in real fires. 

Structural Fire Safetlv Evaluation and Retrofit of Existing Buildings 

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0 

e 

Guidelinedpre-standards for structural fire safety evaluation of existing buildings. 

Best practices for fire safety retropt of structures. 

Guidelinedpre-standards for fire safety retrofltting of structures. 

6 
1.3 NIST-SFPE Workshop on Structural Fire Safety Design and Retrofit of Structures 

As part of this R&D project, in June 2003, the Building and Fire Research Laboratory (BFRL) of 

NIST commissioned the Society of Fire Protection Engineers (SFPE) to organize an industry 

workshop to provide input for the development of a detailed roadmap that will identify the R&D 

gaps for each of the products identified above. A steering team, (Appendix B) consisting of 

representatives of the design and construction industry, was formed to assist in the planning of the 

workshop. The team met five times by teleconference over a five month period. Its’ activity 

included: 

Commissioning nine white papers (Appendix 9.1) from authors with acknowledged 

expertise and leadership in various aspects of structural fire safety design and retrofit and 

the industry context for it. The purpose of the white papers was to outline the issues and 

research needs associated with implementing improved structural fire safety design and 

retrofit methodologies. 

Recommending invited participants (Appendix 9.E) for the workshop who would 

represent the following sectors of the industry: fire safety design, structural design, 

architecture, code enforcement, academia, research, and professional and industry 

associations. 

Developing detailed workshop plan which included a workshop agenda designed to 

encourage full participation from workshop participants (Appendix 9.C). Breakout 

sessions were planned to group individuals by their area of expertise: design fires, 

thermal analysis, structural design, and existing buildings. 

Selecting sixteen recorders and facilitators from participants (Appendix 9.D) 

Developing an outline of a final report to guide discussion at the workshop to the goals of 

the project. 

White papers were sent to all participants in advance of the workshop. Input from participants 

was sought to gain consensus on a recommended roadmap and provide guidance to NIST for their 

R&D program. The workshop was held at the Radisson Lord Baltimore Hotel on October 2-3, 

2003. Sixty individuals (Appendix 9.E) participated with a breakdown of employment as: 

0 Structural engineering - 8 

Architecture - 3 

Academia-9 

0 

0 Regulatory officials - 5 

Insurance- 1 

Fire protection engineering - 8 

Research and testing - 6 

NIST-6 

Associations - materials, professional - 14 

The workshop was divided into 3 sessions, each started with a presentation of the session white 

papers to all participants. The participants were assigned to four breakout groups: Design Fires, 

Thermal Analysis, Structural Analysis, and Existing Buildings. Each discussed the session topic 

according to its particular group focus. Group assignments were made for relatively even 

representation of all disciplines and background in each group. The groups convened at the end 

of each session to share identified issues and needs. In the sections that follow, a summary of the 

white papers is followed by a summary of the participants’ discussion points. The workshop was 

opened with an overview of the NIST WTC response plan by S. Sunder, leader of the NIST WTC 

investigation. Products developed are the summary presentations by each white paper author 
(Appendix 9.H), notes taken within each breakout sessions regarding issues and priorities for 

research and design guidance (Appendix 9.F), and priorities for the NIST roadmap developed by 

individual breakout groups and by the group as a whole (Appendix 9.G). 

8 
2. STATEMENT OF NEED 

2.1 Code Enforcement Perspective 

Jonathan Siu presented the perspective of the code official when confronted with the need to 

review and approve building designs based on structural fire safety design principles. The code 

official must balance the sometimes conflicting demands of the developer and designer, and user 

and societal goals. In his view, the fire protection engineer often represents the concerns of the 

developer in terms of seeking approval for a design that does not comply with the building code 

in effect - either to reduce costs or because the architectural design does not itself conform to the 

structures envisaged by the codes. The movement to a performance-based approach for structural 

fire safety requires a paradigm shift in code enforcement away from considering engineered 

solutions as equivalents to existing prescriptive code provisions, to a new design approach based 

on mutually agreed upon performance goals. In order to meet these challenges, the enforcement 

community seeks well validated engineering information which can support a performance 

approach. Key issues are the selection of performance standards, understanding their 

implementation, selection of an accepted design event (i.e. size, location and duration of design 

fires) and the influence of active fire protection systems on the design event, and validation of 

computer models used for design and analysis. These issues remain a barrier to the ready 

acceptance of performance-based structural fire safety analysis and design in the enforcement 

community. 

2.2 Architectural Perspective 

Dave Collins presented the perspective of the architectural community with respect to the current 

state of the practice in fire safety design. Typically, the architect of record is responsible for many 

aspects of fire safety design, including the protection of the structure, through the interpretation 

and application of prescriptive code requirements, for which there is a well-established 

framework. The architect is often in the unique position of both specifying these features and 

finding alternative means to satisfy their intent when unique architectural aspects of the design 

demand other solutions. A concern of the architectural community in moving away from 

prescriptive code requirements of any kind is a determination of the performance levels currently 

offered by code complying buildings and a means to assure equivalent performance in 

“engineered” solutions. 

2.3 Engineer’s Perspective 

A specific white paper was not prepared on this topic. However, there was discussion throughout 

the workshop regarding the role of structural and fire protection engineers in the structural fire 

safety design process. It was acknowledged that there is a need for structural engineering 

expertise in structural fire safety design, but concern was expressed by many regarding a business 

practice model and fee structure for this role. Fire protection engineers have more experience in 

assisting the architectural community with unique fire safety situations; design and evaluation of 

structural fire safety must be broadened to include the structural engineer for this aspect of fire 

safety design. 

9 
3. FRAMEWORK FOR STRUCTURAL FIRE ENGINEERING AND DESIGN 

METHODS 

3.1 Overview 

Greg Deierlein presented the structural engineering context for the implementation of fire safety 

as an integrated component of structural design. The author noted that fire represents a small 

component of the risk to a structure; further, the primary hazards presented by a fire event are not 

structural, and speculated that this may be the reason why this aspect of structural design has not 

been further developed and integrated in the overall design of the structure, but rather left to 

prescriptive code requirements satisfied in the architectural design. Using the seismic analogy, an ' 

overall fiamework for incorporating fire risk into structural design was proposed, including the 

elements of fire hazard analysis, structural analysis, damage assessment, and loss and risk 

assessment. An example was given of how a risk-based approach to fire safety design could be 

integrated in parallel with other design loads. This performance-based methodology provides a 

fiamework to identlfy research and development needs in a systematic way. These needs include: 

the further development and refinement of a risk-based design fiamework that is consistent with 

models and approaches common to both the structural and fire protection engineering 

communities; validated models for each element of the design process which have a probability 

basis; and a focus on risk communication and perception. 

3.2 Discussion 

Workshop participants raised several issues with respect to the integration of fire into the 

structural design context. There is a lack of understanding that fire is different than other natural 

disaster events. The current level of safety inferred by prescriptive building and fire codes, if 

considered acceptable, must be defined. This may be accomplished using methods developed for 

a performance-based approach. Similarly, since ASTM El 19 tests are generally accepted as 

providing adequate safety, new approaches and levels of acceptable performance should be . 

defined and correlated to this system. Early applications of the approach may include signature 

buildings, existing or historic buildings, and unique buildings with respect to structure, fire loads, 

etc. Perhaps a separate performance-based code that would be applicable only for signature or 

high-risk structures is needed. Simple tools and methods will also be required (as opposed to full 

probabilistic analysis) if the methods are to see widespread use. It is believed that a significant 

amount of information can be obtained by analyzing the performance of structures in real fires. A 

probabilistic approach may not account for certain loads such as terrorism and arson and may 

need to be addressed. Additionally, for the structural engineer to take on additional liability for 

fue safety design, responsibilities, business practices, and fee structure will need to be developed. 

For implementation, standards are needed and documentation of non-U.S. approaches would be a 

useful first step. Finally, education of the structural engineers must accompany this initiative. 

3.3 Needed Actions 

Based on their discussions, workshop participants identified the following (non-prioritized) 

needed actions to integrate structural fue safety design into the structural engineering context: 

0 Archive and mine existing real fire performance data to provide an immediate source of 

data and identi@ gaps in needed information 

Identi@ the full range of accidental fire hazards, in addition to those considered in 

building codes that may result in hazard to the building structure 

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Communicate the concept of risk-based analysis and design as an essential part of 

rational fire design 

Provide education for the engineering profession on the structural fire performance 

Develop funding resources for implementation of the roadmap 

Leverage resources with other disaster resistance programs 

Understand building performance in fire conditions 

Develop specialized design and analysis tools for signature and high-risk buildings which 

recognize their unique vulnerability to fire 

Develop data on risk-based design of structures for fire conditions and probabilities of 

event occurrence 

Incorporate the concept of the difference between large impact events over large area 

(seismic) versus individual building fire (times number of buildings per year are affected) 

in risk-based approaches to design and analysis 

Define the relationship between fie safety engineering and structural engineering 

through the use of probability/event tree analysis 

Normalize ASTM E- 1 19 with respect to engineering based design fires 

Review and compare international codes vs. U.S. codes 

Develop a significant structural code which considers the unique fire hazards that may 

apply to these structures and provisions for their protection 

Use analytical tools to determine how well existing practice provides structural fire 

protection and structural safety 

Develop minimum criteria the context for structural fire safety design in the overall fire 

design context and clarifies the differences between guides, standards and codes 

Develop minimum criteria for a fire safety design go/no go decision to aid in determining 

whether fire safety design is needed for a specific building (a minimum structural fire 

safety level that is calculation based) 

Define true cost vs. construction cost - i.e. include maintenance costs, business 

interruption costs, and other “soft” costs that related to the fire condition 

Consider fire hazards to structures in the context of other hazards 

Society (through building codes) must decide on the method used for fire safety 

evaluation 

Of these action items, the archiving and mining of actual fire performance data was 

considered of high importance in the roadmap. 

11 
4. RELATIONSHIP BETWEEN STRUCTURAL FIRE PROTECTION 

DESIGN AND OTHER ELEMENTS OF FIRE SAFETY DESIGN 

4.1 Overview 

Craig Beyler summarized the current elements of comprehensive fire safety design for buildings, 

including passive and active fire protection, detection and alarm, smoke management, egress 

systems, contentshinish control and manual fire fighting. Current structural fire protection 

requirements are based upon assumed fire load densities defined by occupancy as well as building 

height and area. Structural response is not calculated using advanced analytical methods but 

rather assumed based on the results of a standard fire endurance test. There are significant 

science and engineering methods available to apply to this engineering problem; a context within 

a rational fwe safety design method is required to allow them to be implemented. Traditional 

code requirements implicitly require that overall structural failures need to be prevented in the 

absence of active fire protection, manual firefighting, or fire barriers; however, inherent 

assumptions made in implementing this goal may be too conservative in some instances and 

unconservative in other instances. Thus some assessment of the overall system performance and 

reliability, on a performance basis, is needed to enable performance oriented structural fire safety 

design. It was noted that structural performance itself has an impact on barrier integrity. Global 

fire risk models are available internationally which rigorously account for the performance and 

reliability of all structural fire design features but much research is needed to quantifjdprovide 

input data for these methods. The primary research need is the development of an overall design 

methodology framework. Additional research needs include the performance of structural and 

fue barriers, reliability and effectiveness models for sprinkler systems and fire departments, and 

analysis and test methods to support a_ risk-based design method. 

. 4.2 Discussion 

Workshop participants onwagain questioned whether these approaches would be used for all 

buildings or for signature buildings only. The issue of acceptable levels of risk and who 

determines them was raised as was code equivalent safety. The definition of failure or limit states 

and a performance envelope are key parameters for a performance approach. Data are required on 

fuel loads as well as accepted methods for defining them for use in fire safety design. 

4.3 Needed Actions 

Based on their discussions, workshop participants identified the following needed actions to 

integrate structural fire safety design into the fire protection engineering context: 

Define characteristic fire loads for the design and analysis of structural fire performance. 

Provide professional training for engineers to enable competent structural fire safety 

design. 

Develop all the needed steps in the process - tools, methods, codes, design guidelines - to provide rational methods and a consensus framework for structural fire protection 

design. 

Develop outreach program to disseminate the approach to authorities, ownerddesigners 

and the public to ensure successful implementation. 

Consider changes in the assignment of professional liability for design engineers as a 

result of the move to a calculation-based approach to structural fire safety design. 

Provide a performance-based option in building codes to enable this new design 

approach. 

0 

12 
0 Maintain the option for prescriptive design approach and quantify the level of protection 

provided by current prescriptive code requirements using performance-based calculation 

methods to serve as a performance benchmark. 

Specify performance goals in the building code for both prescriptive and performancebased options. 

Establish general procedures and identify roles for the design and enforcement 

community in design and maintenance (change of use) of structures in fire. 

Develop and implement more training and education programs for all parties involved in 

designlconstruction process in this aspect of fire safety design. 

Conduct outreach program to develop understanding by all parties in the design process 

that interaction between disciplines early in the design process will optimize the frnal 

design. 

Identify those building conditions (complexity, size, function) that should require 

calculated fire resistance rather than a prescriptive solution. 

Building code performance goals should not require consideration of extreme events in 

buildings. 

Provide guidance about the types of tools and procedures that should be used in 

calculating fire resistance (fire load estimation, thermal analysis, structural analysis) - 

guidance should include the level of complexity and types of tools currently available. 

Of these action items, quantifj7ing the level of protection provided by current 

prescriptive code requirements was considered of high importance in the roadmap. 

13 
5. ANALYSIS TOOLS 

Structural fire safety design of new buildings is typically a three-step process: assessment of 

the thermal input to the structure (i.e. design fire); assessment of the thermal response of the 

structure and its fire protection; and assessment of the structural response to the design fire. 

Each of these three topics is addressed separately in sections 5.1 to 5.3 that follow. Section 

5.4 addresses the approach to analysis of structural fire safety in existing buildings. 

5.1 Design Fires 

5.1.1 Overview 

Morgan Hurley summarized the current methods available to predict the fire boundary 

condition. The application and limitations of closed form algebraic equations and 

computerized fire models relevant to the modeling of fully-developed enclosure fires, 

window flames and fire plumes were reviewed. The presenter also addressed probabilistic 

issues including uncertainty in model inputs, active intervention fiom sprinklers and manual 

fire fighting and extreme events. Knowledge gaps were identified in the areas of fire load 

data and he1 characteristics, active intervention, long narrow enclosure fires, window flames 

with varying fuels, and validation of computer models for more complex geometries and 

scenarios. 

5.1.2 Discussion and Needed Actions 

Workshop participants extended the discussion on design fires by exploring the topic of frre 

modeling. It was agreed that one-zone models were the most relevant to the post flashover 

condition and that the focus should be on enhancing those models, rather than. on more 

complex models such as NIST’s Fire Dynamics Simulator (FDS). 

Based on their discussions, participants identified the following research needs: 

Improve models and analysis tools for fire loads and their effects. Priorities identified 

were: the integration of modeling of heat release rate into fire-development models; 

modeling of mixed types of combustible materials; and effect of today’s internal 

floor and wall covering combustibility on fire severity. 

Improve models and analysis tools related to ventilation effects. Priorities identified 

were: predicting the size of broken glass openings based on window types; effects of 

glazing characteristics and number of panes on ventilation opening; estimating the 

impact of numerous openings on different walls with various characteristic 

dimensions; quantifying stack effects; quantifying the impact of mechanical 

ventilation and air-conditioning systems and wind regimes on ventilation 

characteristics. 

Develop tools to quantify the effect of active intervention in the form of sprinklers 

and fire fighters. 

Develop partial safety factors indicating the respective influence of fire loads and 

boundary conditions and their geometrical features and material properties. 

Improve models and analytical tools that analyze the effects of the building 

envelope’s thermal construction (both thermal mass and insulation properties) 

Improve models and analysis tools for compartment geometry, specifically tall 

compartments, long and narrow compartments, and concave compartments. 

0 

14 
Improve models and analysis tools for propagation of fully developed fires into other 

spaces. 

Develop criteria for software validation and benchmarking (by experimental evidence 

and between models), and identi@ limits of model validity. 

Improve models and analysis tools for fire spread through window flames. 

Identify and collect data and information needs for fire modeling, specifically a 

survey of fire loads and their surface areas, including data for various spaces in 

typical occupancies 

Collect real fire statistical data. 

None of these research needs were identified as of high priority by workshop participants as 

a whole. 

5.2 Thermal Analysis 

5.2.1. Overview 

James Milke presented a survey of heat transfer analysis methods currently available for 

analyzing the thermal response of a fire-exposed assembly. Lumped heat capacity, steady state 

heat balance, and semi-infinite slab closed form methods were reviewed with limitations for each 

described. Graphical methods using temperature profiles on cross-section of structural elements 

based on ASTM E-1 19 standard fire exposure, shown as thermal isotherms, were reviewed. 

Numerical finite element and finite different methods were also reviewed, with a focus on 

numerical codes developed specifically for the fire condition. The major limitation of all 

methods identified is the lack of accurate material property data for input, including assumptions 

regarding homogeneity, moisture movement and gross physical changes (spalling, lack of 

integrity). 

5.2.2 Discussion and Needed Actions 

Workshop participants concurred with the assessment that current thermal analysis methods are 

adequate with a few exceptions noted below: 

Thermal analysis methods that respond to unique boundary conditions such as plastics or 

wood burning adjacent to structural elements 

Thermal analysis methods for timber structures 

Thermal analysis methods to account for water spray on structural elements 

Thermal analysis methods that explicitly account for joints or seams in membranes (for 

example suspended ceiling systems) 

Thermal analysis methods that account for openings in membranes such as fire doors 

Thermal analysis methods that account for geometry that changes with time in the fire 

event - eg. spalling, intumescent coatings 

Thermal analysis methods that explicitly account for moisture migration 

Workshop participants also identified a range of material property data needs to be used in 

existing thermal analysis models: 

Wide public availability of material property data in a form suitable for modeling, 

including results of proprietary tests 

Standard test methods for determining material properties at elevated temperatures 

15 
Specific Elevated Temperature Material Properties 

a) cooling phase properties (when are not reversible) 

b) new materials (new concretes) 

c) glass (windows and structural) 

d) material stickability 

e) material contact resistance 

They also noted that there is a need to interface thermal analysis methods with Computational 

Fluid Dynamic (CFD) models for fire’exposure. 

Of these research needs, the development of standard methods for determining material 

properties at elevated temperatures was considered to be of high importance by workshop 

participants. 

5.3 Structural Analysis 

5.3.1 Overview 

James Milke reviewed elementary mechanics approaches for evaluating the performance of 

structural elements at elevated temperatures, along with limitations for each method. Steel, 

timber, concrete were treated separately for beams and columns (flexural and compression 

behavior) A comparison by Hosser et al. was described which rated the various methods 

available using criteria related to application and accuracy. The currently available numerical 

analysis methods, which are primarily finite element methods, developed specifically for 

analyzing the response of structural components to elevated temperature exposure were also 

presented. A review of a limited number of fe analysis applications was also presented. 

These are limited by assumptions regarding connection behavior and this area is the subject of 

several current research initiatives internationally. Research needs identified include the need for 

a coupling of thermal and mechanical effects, connection behavior, mechanical and thermal 

properties at elevated temperatures for structural materials, and experimental validation. 

5.3.2 Discussion and Needed Actions 

Workshop participants reviewed currently available numerical analysis methods and identified 

several limitations in terms of validation. There was a consensus that, in comparison with other 

materials, steel behavior is better understood and predicted by current analysis methods. The 

connection between blast effects and fire was also noted as an area of interest. Finite element 

analytical tools (ABAQUS, ANSYS, LS-DYNA, etc) provide for the most accurate prediction of 

structural response under fire conditions. These tools are very useful for research or for design 

studies by specialized consulting firms. However, such sophisticated analytical tools require a 

high degree of knowledge by the user, and are costly to develop and interpret the results. 

Consequently, finite element analytical tools are probably not suitable for routine design 

applications. However, when they are used, the analytical tools that use explicit integration 

schemes are likely preferable to those that use implicit integration. Structural element based 

models (fiame models) are likely to be most suitable for routine analysis of structural response 

under fire conditions. Such models are very commonly used at present for structural analysis 

under other load conditions (gravity, wind, seismic) and could potentially be extended to include 

structural fire response analysis. Commercial software developers would likely incorporate fire 

response analysis into their frame analysis programs if the basic modeling information were 

available and if sufficient demand exists for such models. 

16 
The following research needs were identified: 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Develop criteria for failure or limit states for predicted structural response under fire. That is, 

what level of deformation, force or other measures of structural response predicted by a 

structural analysis model will be considered as failure? 

Develop structural analysis models, starting at the material level, and then work up towards 

the system level. 

Develop structural analysis models (for materials, members, connections, etc) which must be 

accompanied by experimental research for understanding, calibration and validation of 

models. 

Conduct research-quality structural fire experiments. 

Incorporate certain aspects of the response of concrete structures at high temperature, 

including larger strength reduction of high strength concrete, spalling, post tensioned systems 

and anchorage, into the analysis methods. 

Construct structural-fire test facilities in the US to develop the needed research quality 

experimental data. Such facilities must have the capabilities to apply complex structural 

loads to elements, connections, subassemblies, etc at elevated temperature and at realistic 

scales. 

Conduct a limited number of full-scale building tests under fire conditions to enhance 

understanding of system response and to validate structural analysis models (tests similar to 

those conducted at Cardington). There may be a possibility of conducting such tests on 

existing buildings that are scheduled for demolition. 

Develop a set of "benchmark" problems for validation as structural element based models are 

developed for predicting structural fire response. 

Develop a structural analysis method with specific capabilities unique to fire. 

Develop more complete temperature dependent material properties (substantial data already 

exists for steel and concrete under simple stress conditions; need additional data for material 

response under complex states of stress, and rate dependent response) 

Develop connection response models (inadequate data available at present to develop reliable 

connection response models; substantial research is needed on connection behavior at 

elevated temperature). 

Model element (beams, columns, braces, etc) behavior under complex 3-dimensional loading 

(e.g., biaxial bending plus compression) and elevated temperatures and temperature 

gradients; models should include plasticity and post-peak (unloading) response (substantial 

experimental data and model development work are needed here) 

Improve 3 -dimensional modeling capability, including floor slabs and membranekatenary 

action (there is some data available on membrane action in slabs, but more is needed) 

Of these research needs, workshop participants identified the need to define failurehimit 

states, the need to develop benchmark problems for model verification, and the need for 

large scale structural-fire experimental facilities in the U.S. as having high priority. 

5.4 Existing Buildings 

5.4.1. Overview 

Fred Mowrer and Bob Iding described the general approach to analysis of structural fire safety in 

existing buildings, noting that approaches are similar to those used for new buildings, but that 

factors such as undocumented design basic, presence of archaic building systems and materials, 

concealment of design details, and unknown condition of concealed elements complicate the 

17 
analysis. The seismic retrofit analogy was explored, noting that fire differs from seismic design 

in that seismic loads can be predicted based on statistical data; in fire, both the frequency and the 

magnitude of fires are influenced by human interactions and design decisions. Key elements in 

an analysis of existing buildings which merit further research are the identification of relevant fire 

scenarios to be considered, means to incorporate uncertainties into analysis and design, and 

development or adaptation and use of non destructive evaluation technologies for the fire 

condition. 

5.4.2 Discussion and Needed Actions 

Workshop participants discussed lessons to be learned from seismic retrofit analysis procedures. 

Tools and methods to evaluate existing structures are needed, as well as a prescribed means to 

utilize design documentation that may exist. Consideration should be given to load paths, nonvisible structural redundancy, and he1 load assessments. Masonry was identified as an area 

where more information is needed. A multihazard approach to retrofit was recommended. 

The following research needs were identified: 

Collect data fiom full scale buildings tests measuring effective properties of existing 

materials and existing fuel loads which focus on the performance of archaic (not new) 

materials and systems 

Develop performance metrics for multihazard building robustness 

The development of- performance metrics for multihazard building robustness was 

considered to be a high priority need by workshop participants. 

18 
6. BEST PRACTICES AND SUPPORTING TECHNICAL DATA 

6.1 Overview of Current International Codes and Standards 

Andy Buchanan presented an overview of the international status of design standards for 

structural fire safety, beginning with a review of the international performance based regulatory 

environment and the context of structural fire design within overall firesafety design. The review 

included current available information on loads for structural fire design, fire severity and 

standard fire exposures, fire resistance of building elements, failure criteria, and material specific 

design standards. It was concluded that the Eurocodes represent the best current source of 

accepted, authoritative information on structural fire design. 

Barbara Lane presented a practice perspective on design methods, analysis tools and regulatory 

frameworks needed to implement structural fire safety design. Changes to building codes to 

identify accepted methods and performance criteria for regulators and designers are needed. For 

routine application of an engineering approach, simple, validated analysis tools are needed and 

are available in many situations. Gaps include structural system-specific methods (e.g. ribbed 

slabs), the acceptance by the regulatory community of these methods, and available guidance on 

their application. Similarly, there must be validation and guidance for regulatory approval of 

more advanced methods, including compartment fire models, heat transfer to compartments, and 

structural response to fires. Availability of information on structural fire performance was 

identified as a key need for the design community; this includes both the development of a robust 

research base and an information management system to make it easily accessible for routine use. 

The development of consensus failure and performance criteria for structural fire safety is a key 

design need, as are simple design approaches for connection behavior at elevated temperatures. 

Fred Mowrer and Bob Iding discussed design approaches to building retrofit for fire. There is a 

need for standards which are unique to the retrofit problem which include retrofit trigger criteria, 

codification of fire loadings, and approved retrofit technologies to enhance the structural andor 

thermal performance of the overall structure. An evaluation methodology and checklist of 

critical assessment features and retrofit techniques was presented. Needs identified included an 

assessment of non destructive testing methods, an engineering guide to retrofit options, and 

evaluation of a multihazard approach to retrofit. 

6.2 Discussion 

Workshop participants discussed the need for best practices and design methods in the areas of 

design fire exposures, thermal analysis methods, structural design, and retrofit of existing 

buildings. 

For design fire exposures, more accurate statistics are required to calibrate currently available 

Eurocodes design fire loads and a probabilistic approach must take into account other mitigating 

measures (e.g. a post flashover fire may not occur). 

Although methods are available for thermal analysis, there is no generally accepted design 

criteria. There is also a need for standardized validation criteria for software and its applicability, 

and standardized fire test methods for material properties at elevated temperatures. 

The Eurocodes were considered a good starting point for structural fire design. However, the 

applicability to U.S. design practices of the data that support the provisions of the Eurocodes is 

unknown and must be established before the Eurocodes can be accepted in the U.S. The issue of 

19 
design responsibility over the life of the structure was addressed: i.e. as changes in occupancy or 

geometry occur, this may have impacts on structural fire safety. 

There is little knowledge available on retrofit of existing structures for fire, nor standard 

inspection procedures. Owner incentives may need to be provided; education is a major 

component of retrofit best practices and must extend beyond the engineering community. 

6.3 Needed Actions 

The following needs for best practiceddesign guides and standards were’ identified: 

Design Fires 

0 

Develop design fires using risk-based methodology to account for various fire scenarios; 

validation with fire tests 

Develop a catalogue of standard or benchmark fire loads for generic occupancies 

Thermal Analysis 

0 

0 

0 

0 

Develop a design guide using existing thermal analysis methods 

Standardize validation of thermal analysis computer models and clear definition of its 

applicability 

Publish available material property data in a form suitable for model input 

Codify thermal analysis methodology - agreement on acceptable methods for various 

applications and limitations 

Publish model output, available in a form suitable for use by various groups (engineers, 

authorities having jurisdiction, etc) 

Standardize test methods to evaluate thermal properties of materials 

I 

Structural Design 

0 

Research results to supporthalidate existing Eurocode methods 

Develop and validate of connection design methods for the fire condition - 

Develop codes of practice to assign responsibility for structural fire design over the life of 

the building 

Develop design methods to account for interaction of structure and the compartment (ie 

when the structural barrier itself become involved in the fire scenario) 

Upgrade of Existing Buildings 

0 Establish design and performance criteria for structural fire safety retrofit 

Develop and implement owner incentives to upgrade the structural fire safety of existing 

buildings 

Implement education programs to overcome the perception (cultural) that structural fue 

protection doesn’t change with time 

Develop guidelines for the enforcement and engineering communities - e.g. “Evaluation 

And Remediation Of Structural Fire Performance Of Existing Buildings” 

Workshop participants identified the following as having the highest priorities from the 

above list: 

0 Design Fires - Develop design fires using risk-based methodology to account for 

various fire scenarios; validate with fire tests 

20 
Structural Design - Develop and validate connection design methods for the fire 

condition 

Structural Design - Develop codeq of practice to assign responsibility for structural 

fire design over the life of the building 

Upgrade - Develop guidelines for the enforcement and engineering communities - e.g. “Evaluation And Remediation Of Structural Fire Performance Of Existing 

Buildings” 

V 

21 
7. RESEARCH PRIORITIES FOR DEVELOPMENT OF NATIONAL ROADMAP 

Workshop participants identified the following research needs as having the highest priority for 

development of best practices for structural fire safety design and retrofit of structures (shown 

with the number of votes given by participants as a percentage of the total votes cast. Note that 

this list represents the highest priority items only, other items received less than 1% votes): 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

Build and utilize structural-fire experimental facilities in U.S. to apply complex 

structural loads to large-scale components at elevated temperature - 6% 

Develop more research quality experimental data on the behavior of the following 

structural components and material properties at elevated temperature - 6% 

a) multi-axial stress and rate effects (creep) of materials 

b) structural connections 

c) members under complex loading 

d) subassemblies 

e) structural systems 

Quantify level of protection provided by current prescriptive code requirements - 5% 

Collect actual fire performance data - 5% 

Define failure/limit states for structural response in fire - 5% 

Develop guidelines for enforcement and engineering communities on evaluation and 

remediation of structural fwe performance of existing buildings - 5% 

Specify performance goals in the building code for prescriptive and performance- based 

options - 4% 

Develop performance metrics for multihazard building robustness - 3% 

Develop a risk based methodology for design fires and the data to support it; place 

into a standard - 3% 

Develop standard methods for determining material properties at elevated 

temperatures - 3% 

Investigate fire performance of structural connections to and develop and validate 

engineering methods to predict this performance - 3% 

Develop benchmark problems for verification of analytical tools - 2% 

Specify professional responsibilities for structural fire protection over the life of the 

building - 2% 

Table 7.1 shows these priorities for actions mapped against the expected products of NIST 

Research and Development program in structural fire safety of new and existing buildings. 

22 
Expected Products 

Structural Fire Safety Design of New Buildings 

Needed Actions 

Best practices for fire safety design 

of structures’. 

Guidelineslpre-standards for fire 

safety design of structures. 

Analysis of Structural Fire Performance 

Best practices tools for analyzing 

structural fire performance. 

Load and resistance factor 

methodology for structural fire 

safety. 

Selected verifiedhalidated 

predictive tools for analyzing 

structural performance in real fikes. 

3. Quantify level of protection provided by current 

prescriptive code requirements - 5% 

5. Define failure/limit states for structural response 

in fire - 5% 

7. Specify performance goals in the building code s for prescriptive and performance-based options - 

4% 

8. Develop performance metrics for multihazard 

building robustness - 3% 

9. Develop a risk based methodology for design 

fires and the data to support it; place into a 

standard - 3% 

13. Specify professional responsibilities for 

structural fire protection over the life of the 

building - 2% 

1. Build and utilize structural-fire experimental 

facilities in U.S. to apply complex structural 

loads to large scale components at elevated 

temperature - 6% 

2. Develop more “research quality” experimental 

data on structural response at elevated 

temperature - 6% 

4. Collect actual fire performance data - 3% 

10. Standard methods for determining material 

properties at elevated temperatures - 3% 

1 1 .Investigate fire performance of connections - 3% 

12. Develop benchmark problems for verification of 

analytical tools - 2% 

Steel, concrete, and steel-concrete composite construction 

23 
Table 7.1 (continued) 

Structural Fire Sdety Evaluation and Retrofit of Existing Buildings 

Guidelinedpre-standards for 

structural fire safety evaluation of 

existing buildings. 

Best practices for fre safety 

retrofit of structures. 

Guidelinedpre-standards for fre 

safety retrofitting of structures. 

3. Quantify level of protection provided by current 

prescriptive code requirements - 5% 

5. Define failurehimit states for structural response 

in fire - 5% 

6. Develop guidelines for enforcement and 

engineering communities on evaluation and 

remediation of structural fire performance of 

existing buildings - 5% 

7. Specify performance goals in the building code 

for prescriptive and performance-based options - 

4% 

8. Develop performance metrics for multihazard 

building robustness - 3% 

9. Develop a risk based methodology for design 

fires and the data to support it; place into a 

standard - 3% 

13. Specify professional responsibilities for 

structural fire protection over the life of the 

building - 2% 

24 
8. RECOMMENDATIONS 

The top 13 research needs identified by workshop participants can be grouped into the following 

three main categories: 

Obtaiddevelop research-quality real and experimental data on structural fire performance 

(priorities # 1,2,4, 11 and 12 - total 22% votes) 

Codifjdstandardize performance goals, criteria and methodologies for structural fire 

design and analysis (priorities ## 3, 5, 6, 7, 8,9, and 10 - total 28% votes) 

Specify professional responsibilities for structural fire protection of buildings (priority # 

13 - total 2% votes) 

Of the above three categories of research needs, the top two - collection of structural fire 

performance data and codificatiodstandardization of performance goals and criteria to provide 

guidance for structural fire design and analysis - received the most number of votes (22% and 

28%, respectively). Thus, there appeared to be a general consensus that better data and an 

accepted design and regulatory frame work are most needed for progress in structural fire safety. 

25 
9. APPENDICES 

26 
Appendix 9. A: 

Workshop Prospectus 

National R&D Roadmap for Structural Fire Safety Design and Retrofit of Structures 

Need 

Current building design practice does not consider fire as a design condition for purposes of 

evaluating structural performance. Instead, structural fire endurance ratings are specified in 

building codes. In addition, there is no accepted set of verified tools to evaluate the fire 

performance of entire structures and to achieve engineered fire safety. Thus, there is widespread 

recognition of the need to develop and implement significantly improved tools, practices, and 

standards that explicitly consider structural fire loads in the design of new structures and the 

retrofit of existing structures. Background information on this need is attached. 

Expected Products of NIST R&D 

The National Institute of Standards and Technology (NIST) recently initiated a major R&D 

project to develop and implement significantly improved standards, tools, and practical guidance 

for the fire safety design and retrofit of structures in partnership with key stakeholders. The 

project will integrate knowledge of modem fire science and fire protection engineering with 

knowledge of modern structural reliability methods and structural engineering. Specifically, the 

project aims to produce the following key products over a multi-year period: 

Structural Fire Safety Design of New Buildings 

Best practices for fire safety design of structures*. 

Guidelinedpre-standards for fire safety design of structures. 

Analysis of Structural Fire Performance 

0 Best practices tools for analyzing structural fire performance.. 

Load and resistance factor methodology for structural fire safety. 

Selected verifiedvalidated predictive tools for analyzing structural performance in real fires. 

Structural Fire Safety Evaluation and Retrofit of Existing; Buildings 

Guidelinedpre-standards for structural fire safety evaluation of existing buildings. 

Best practices for fire safety retrojit of structures. 

Guidelinedpre-standards for fire safety retroJitting of structures. 

Workshop to Develop R&D Roadmap 

NIST plans to hold a three-day workshop3 to develop a detailed roadmap that will identi@ the 

R&D gaps to be filled to achieve each of the products identified above. Workshop participations 

will include representatives from engineering practice, relevant standards and codes committees, 

and technical groups as well as experts in structural reliability, fire protection engineering, and 

structural fire analysis. While the focus of the workshop is on U.S. practice and codes and 

standards, a limited number of international experts will be invited to provide perspective on 

important recent developments in these areas elsewhere around the world. 

Steel, concrete, and steel-concrete composite construction 

Afternoon of the first day, full second day, and until noon the third day. 

27 
The workshop will also invite representatives fiom codes and standards organizations to develop 

and present a framework in which the above R&D products will fit and that maximizes their 

value to the private sector codes and standards development effort. 

Background 

Balancing the competing demands for fire safety and economy in a rational manner requires the 

development of performance-based methods to measure and predict the behavior of fill-scale 

structures under fire conditions. 

Five key factors must be considered in developing such performance-based methods: 

0 First, while the current standard fire endurance test method, which stipulates a prescribed 

time-temperature exposure, is adequate to compare relative performance of structural 

components, it does not provide any indication about the actual performance (Le., load 

carrying capacity) of a component in a real fire environment (e.g., involving fire of building 

contents, hydrocarbon pool fires, or a combination thereof). 

0 Second, the role of structural connections, diaphragms, and redundancy in enabling load 

transfer and maintaining overall structural integrity (i.e., preventing progressive collapse) 

during fire is ignored in structural design. Current design methods are based on fire 

endurance tests of single components and do not account for the behavior of inter-component 

connections or the complex two- and three-dimensional behavior of the entire structure. 

Third, there is a need to evaluate the effectiveness of alternative design, retrofit, and fire 

protection strategies to enhance structural fire endurance (including alternate cementitious 

spray or board systems, intumescent coatings, high-performance fire protective coatings, 

active suppression systems, and more sensitive sensing and monitoring). No practical, highlevel models exist today that couple the fire dynamics to the structural system response, and 

the resulting transient, multi-dimensional heat transfer through structural components made 

with multiple materials. 

0 Fourth, there is a need to better model and predict the fire hazard to structures fiom internal 

and external fires (e.g., due to accidents or terrorist threats). This includes deterministic and 

probabilistic models for specifying the magnitude, location, and spatial distribution of fire 

hazards on structures (e.g., design fire scenarios, extreme events such as 10% in SO-years and 

2% in 50-years); determination of reliability-based load factors for combined dead, live, and 

fire loads and resistance factors for loss in structural strength and stiffness; and methods for 

load and resistance factor design (LRFD) under fire conditions. 

Fifth, there is a lack of knowledge about the fire behavior of structures built with innovative 

structural materials (e.g., high-strength concrete or steel structures) or passive fire protection 

materials. 

28 
Appendix 9.B 

Steering Committee Members 

Lou Gerschwinder, American Institute of Steel Construction 

Jim Rossberg, American Society of Civil Engineers 

Steve Szoke, Portland Cement Association 

Pravin Gandhi, Underwriters Laboratories, Inc. 

Chris Marrion, Amp Fire 

Kathleen Almand, Society of Fire Protection Engineers 

Robert Duval, National Fire Protection Association 

29 
Appendix 9.C 

Fire Safety Design and Retrofit of Structures 

Workshop Agenda 

October 2,3 

Versailles Room 

Radisson Lord Baltimore Hotel 

Baltimore, MD 

Thursday, October 2,2003 

7:OO 

8:OO 

wo 

9:15 

10:15 

10:45 

12:15 

1 :oo 

2:oo 

3:OO 

500 

5:45 

I 

Registration opens (continental breakfast provided) 

Opening remarks, NIST 

Keynote presentations - Architect and Code Official Perspectives on Need for 

Structural Fire Safety Design Methods - Jonathan Siu, City of Seattle and 

Dave Collins, AIA 

Plenary 1 - Context for Structural Design for the Fire Condition - Greg 

Deierlein, Stanford University and Craig Beyler, Hughes Associates 

Break 

Breakout sessions 1 - Goal: To gain consensus on the context and identify 

means for the integration of structural design for the fire condition within fire 

safety design and within framework for reliability based structural design 

Reconvene to summarize breakout sessions- key observations and required 

actions 

Lunch 

Plenary 2 - State of the Art in Structural Design for the Fire Condition -New 

and Existing Buildings - Morgan Hurley, SFPE, Jim Milke, University of 

Maryland, Barbara Lane, Amp Fire, Fred Mowrer, University of Maryland, and 

Bob Iding, WE 

Breakout sessions 2 - Goal: To identifl and prioritize gaps in analysis 

methods and their technical basis (research needs) for the four components of 

structural design for the fire condition: design fires, thermal analysis methods, 

structural analysis methods, and evaluation and retrofit techniques. 

Reconvene to summarize break out sessions - key gaps in research, datu, 

vu Iidation 

Adjourn 

5~45 - 7:OO Reception 

Friday, October 3,2003 

7:30 Continental breakfast 

30 
8:OO 

8:30 

1o:oo 

10:30 

1 l:oo 

12:oo 

12:30 

Plenary 3 - International status of development and adoption of design 

standards for structural fire safety and the overall codes and standards context - 

Andy Buchanan, University of Canterbury 

Breakout sessions 3 - Goal: to identi@ and prioritize gaps in best practices, 

design guidelines, standards etc. for the four components of design for the 

structural condition: design fires, thermal analysis methods, structural analysis 

methods, and evaluation and retrofit techniques. 

Break 

Reconvene to summarize breakout sessions - key gaps in best practices, 

standards, guidelines 

General prioritization of results of Breakout sessions 1,2 and 3 

Discussiodsynthesis & Wrap-up 

Adjourn 

31 
Appendix 9.D 

Workshop Facilitators and Recorders 

Four groups - A, By C, D assigned as follows 

Breakout Sessions Facilitators 

1. Context 

A,B Fire Safety Design Paul Sullivan 

Milosh Puchovsky 

C,D Structural Design Bruce Ellingwood 

Jim Rossberg 

2. State of the Art 

A Design Fires 

B Thermal Analysis 

C Structural Analysis 

D Evaluation and Retrofit 

'3. Design Guides and Standards 

A Design Fires 

B Heat Transfer Design 

C Structural Design 

D Evaluation and Retrofit 

Rachel Becker 

Jean Marc Franssen 

Asif Usmani 

Bob Weber 

Beth Tubbs 

Bob Berhinig 

Charlie Carter 

Bob Duvall 

Recorders 

Chris Marrion 

Scott Nacheman 

Steve Szoke 

John Ruddy 

Chris Marrion 

Pravin Ghandi 

Mike Englehardt 

Ramon Gilsanz 

Farid Alfawhakiri 

Tom Izbicki 

Steve Szoke 

Dave McKinnon 

32 
Appendix 9. E 

WORKSHOP ATTENDANCE 

John Abruzzo 

LZA Technoloyg Inc. 

641 6* avenue 

New York, NY 1001 1 

Farid Alfawakhiri 

American Institute of Steel Construction 

One East Wacker Drive, Suite 3 100 

Chicago, IL 

alfawakhiri@aisc.org 

Hosam Ali 

FM Global Corporation 

1 15 1 Boston-Providence Turnpike 

Nonvood, MA 

hosam.ali@finglobal.com 

Kathleen Almand 

SFPE 

73 1 5 Wisconsin Avenue, Suite 1225 W 

Bethesda, MD 

kalmand@sfpe.org 

Jonathan Barnett 

Worcester Polytechnic Institute 

Center for Firesafety Studies, 100 Institute 

Road 

Worcester, MA 

jbarnett@wpi.edu 

Rachel Becker 

Department of Civil Engineering, TechnionIsrael Institute of Technology 

National Building Research Institute 

Technion City, Haifa 

becker@tx.technion.ac.il 

Robert Berhinig 

Underwriters Laboratories Inc 

333 Pfingsten Road 

Northbrook, IL 

robert.m.berhinig@us.ul.com 

Craig Beyler 

Hughes Associates 

36 10 Commerce Drive, Suite 8 17 

Baltimore, MD 

cbeyler@haifire.com 

Andy Buchanan 

University of Canterbury 

Private Bag 4800 

Christchurch, NZ 

andy@civil.canterbury .edu.nz 

Doug Carpenter 

Combustion Science and Engineering 

8400 Old Annapolis Road 

Columbia, MD 2 1045 

dcarpenter0,csefire .corn 

Charlie Carter 

American Institute of Steel Construction 

One East Wacker Drive, Suite 3 100 

Chicago, IL 

carter@aisc.org 

Dave Collins 

The Preview Group 

8 10 Llum Street 

Cincinatti, OH 

pregrp@aol.com 

Gene Corley 

Construction Technology Laboratory 

5400 Old Orchard Rd 

Skokie, IL 

gcorley@ctlgroup.com 

Mark Cummings 

Fire Risk Management Inc 

Customs House, 2nd Floor 1 Front Street 

Bath, ME 

wmark@firerishgt .com 

Greg Dierlein 

Stanford University 

Terman Engineering Center 

Stanford, CA 

ggd@stanford.edu 

Robert Duvall 

National Fire Protection Association 

1 Batterymarch Park 

Quincy, MA 

bduval@nfpa.org 

33 
, 

Bruce Ellingwood 

Civil and Environmental Engineering, 

Georgia Institute of Technology 

790 Atlantic Drive 

bruce. el lingwood@ce.gatech .edu 

Atlanta, GA 30332-0355 

Mike Englehardt 

PRC-Ferg Struct Engr, University of Texas 

at Austin 

1 University Station Stop R7200 

Austin, TX 

mde@mail .utexas.edu 

Jean Marc Franssen 

University of Liege 

6 Quai Banning 

Liege, 

jm.fianssen@ulg.ac.be 

Pravinray Gandhi 

Underwriters Laboratories Inc 

333 Pfingsten Road 

Northbrook, IL 

pravinray . d . gandhi@us .ul . corn 

Lou Gerschwindner 

American Institute of Steel Construction 

One East Wacker Drive, Suite 3 100 

Chicago, IL 

1 fg@psu . edu 

Ramon Glisanz 

Gilsanz, Murray &Steficek 

41 E. 11th Street 

New York, NY 

ramon.gilsanz@gmsllp.com 

John Gross 

Building and Fire Research Laboratory, 

NIST 

100 Bureau Drive, Stop 861 1 

Gaithersburg, MD 

William Grosshandler 

Building and Fire Research Laboratory, 

NIST, 100 Bureau Drive, Stop 866 1 

Gaithersburg, MD 

Ronald Hamburger 

Simpson Gumpertz & Heger Inc. 

The Landmark @ 1 Market, Suite 600 

San Francisco,, CA 

roham burger@@ .corn 

Morgan Hurley 

Society of Fire Protection Engineers 

73 15 Wisconsin Avenue, Suite 1225W 

Bethesda, MD 

mhurley@sfpe.org 

Robert Iding 

WE 

2301 Rose Street 

Berkeley, CA 

riding@wje.com 

, 

Jerry Isenberg 

Weidlinger and Associates Inc. 

375Hudson St 

New York, NY 

isenbergawai .corn 

Thomas Izbicki 

Dallas Fire Department 

8908 High Meadows Drive 

Plano, TX 

tizbick@mail .ci .dallas.tx.us 

Venkatesh Kodur 

National Research Council of Canada 

1500 Montreal Rd, M-59hRC 

Ottawa, Ontario 

venkatesh. kodur@nrc .gc.ca 

Bill Koffel 

Koffel Associates 

3300 North Ridge Road, Suite 275 

Ellicott City, MD 

kaihq@aol.com 

Joel Kruppa 

CTICM 

Domaine de Saint Paul-BP64 

Saint Remy-Les-Chevreuse, 

j kruppa@cticm .corn 

34 
Barbara Lane 

Arup Fire 

13 Fitzroy Street 

London, UK 

barbara. lane@arup .com 

Jon Magnusson 

Magnusson Klemencic Associates 

1301 Fifth Avenue, Suite 3200 

Seattle, WA 

jmagnusson@mka.com 

Chris Marrion 

ARUP Fire Engineering 

155 Avenue of the Americas 

New York, NY 

Chris .marrion@arup .corn 

Terri McAllister 

Building and Fire Research Laboratory, 

NIST, 100 Bureau Drive, Stop 86 1 1 

Gaithersburg, MD 

David McKinnon 

Canadian Steel Construction Council 

201 Consumers Road, Suite 300 

Toronto, Ontario 

david.mackinnon@cisc-icca.ca 

Tom McLane 

Applied Technology Council 

21 11 Wilson Blvd, Suite 700 

Arlington, VA 

tmclane@atcouncil .org 

Jim Milke 

UMD 

Fire Protection Engineering, University of 

Maryland, 01 5 1 Glenn Martin Hall 

College Park, MD 

milke@eng.umd.edu 

Fred Mowrer 

UMD 

Fire Protection Engineering, University of 

Maryland, 01 5 1 Glenn Martin Hall 

College Park, MD 

fmowrer@eng .umd.edu 

Scott Nacheman 

LZA Technology 

14 East Jackson Blvd, Suite 1100 

Chicago, IL 

snacheman@Izatechnology .com 

Bud Nelson 

consultant 

4217 Kings Mill Lane 

Annandale, VA 

hnelson444@aol.com 

Long Phan 

Building and Fire Research Laboratory, 

NIST100 Bureau Drive, Stop 86 1 1 

Gaithersburg, MD 

lphan@nist .gov 

Robert Polk 

NASFM 

c/o Melissa Klein, 13 19 F St NW, Suite 301 

Washington, DC 

bpo I k@sc. rr. com 

Max Porter 

Civil Engineering, Iowa State University 

4 16A Town Engrg. Bldg. 

Ames, Iowa 

mporter@iastate.edu 

Nadine Post 

ENR, McGraw Hill 

122 1 Avenue of the Americas 

New York, NY 

postn@mcgrawhill.com 

Kuldeep Prasad 

Building and Fire Research Laboratory 

NIST, 100 Bureau Dr., Stop 8661 

Gaithersburg, MD 20899 

kprasad@nist.gov 

Milosh Puchovsky 

NFPA 

1 Batterymarch Park 

Quincy, MA 

mpuchovsky@nfpa.org 

35 
James Rossberg 

American Society of Civil Engineers 

1801 Alexander Bell Drive 

Reston, VA 

j rossberg@asce. org 

John Ruddy 

SA11 

2424 Hillsboro Rd, Suite 202 

Nashville, TN 

jruddy@saii.com 

Jonathan Siu 

City of Seattle 

700 5th Avenue, Suite 2000 

Seattle, WA 

j onathan .siu@ci. Seattle. wa.us 

Bruce Spiewak, Architect 

375 Morgan Lane, Unit #405 

West Haven, CT 

bruces@conncode.com 

Monica Starnes 

Building and Fire Research Laboratory, 

NET, 100 Bureau Drive, Stop 861 1 

Gaithersburg, MD 

Paul Sullivan 

Robert W. Sullivan Associates 

343 Commercial St, 302 Union Wharf 

Boston, MA 

pds@rwsullivan. com 

Shyam Sunder 

BFRL, NIST 

100 Bureau Drive, Stop 861 1 

Gaithersburg, MD 

Steve Szoke 

Portland Cement Association 

5420 Old Orchard Road 

Skokie, IL 

sszoke@cement.org 

Beth Tubbs 

International Code Council 

244 Brookway Drive 

Northbridge, MA 

btubbs@iccsafe.org 

Asif Usmani 

School of Engineering, University of 

Edinburgh, The Kings Building 

Edinburgh, 

asif.usmani@ed.ac.uk 

Bob Weber 

Consultant 

9784 Ice Box Canyon Court 

Las Vegas, NV 

r.d.weber@cox.net 

Robert Wills 

American Iron and Steel Institute 

907 Spyglass Circle 

Birmingham, AL 

rwills@steel.org 

Wei Zhang 

Combustion Science and Engineering 

8400 Old Annapolis Road 

Columbia, MD 2 1045-2 129 

wzhang@csefire.com 

36 
Appendix 9.F 

Workshop Breakout Notes 

Note: No written summaries of Group B, Breakout session 2 and Group B and C, breakout 

session 3 were submitted by workshop participants 

37 
Groups A and B, Breakout Session 1 

Discussion: Context for Fire Safety Design for Fire Conditions 

Paper by: Craig Beyler 

General 

- 

- 

Where do we want to be at the end of this process regarding fire/structures? 

Guidelines for ‘exceptional’ versus ‘everyday’ projects? - What is needed for each? i.e. 

‘everyday’ projects typically prescriptive based design - How will codes be impacted? What 

is needed. for this approach? Larger projects - what tools/methods/data, etc are needed? - Should look at structural engineer’s process for this. 

Today’s paradigm 

- 

- 

- 

- 

- 

- 

- 

Working wlauthorities, insurers, designers, owners, public - all with various issues/concerns. 

Fire/structures studies are safety and economics driven. 

Looking to move from equivalencies to understanding overall performance. 

More knowledge needed in undertaking flrre/structures studies 

Performance criteria - ‘as -safe’ as code design. How safe is this though? 

Who decides what level of risk is acceptable? 

Objectives/risk - fire protection engineers may frame this, however, public should decide 

what level of risk is acceptable. How does this process happen though? 

Need capability to predict the ‘performance envelope’ of buildings or structure so we know 

what we have, i.e., does a 2 hour fire rated column fail at 2 hrs and 1 minute, or continue to 

bear its load? 

Should we look at providing a conservative first estimate, and refine the 

process/tools/information as knowledge level increases? 

May want to look into using the Eurocodes as a starting point. 

- 

- 

- 

Limitations 

FireRuel Load 

- 

- 

The fire/fuel load is not defined for fire as it is for other loads. 

How should this be defined? 

o Lb/f? or energylunit area? 

o Duration? 

o Maximum heat release rate 

- Need to improve deterministic approach to determining this, and develop probabilistic 

approach that is simplified. 

Performance Design Criteria 

- What is failure? 

- 

- How is this defined? Local? Global? Failure of structure? Failure of compartmentation? 

Comparative analysis - against what code requires, versus ‘absolute’ analysis which would 

be driven more by objectives/performance criteria. 

Calculation methods 

- Are ‘approved’ calculation methods available? 

38 
Different types of models - large models available treating all phenomenon, while small 

models available for sub-system assessment. 

Scaling is a factor. 

RisWdecision making tools are important and needed. 

Validation of models is important and needed. 

Should predict structural performance to failure so one knows what they have and not just to 

say 2 hours, as may fail at 2 hrs and 1 minute. 

Effect of compartment (Le. compartment size) on fire induced environment is important. 

Data/Information 

- 

- 

- 

Is datdinformation available to undertake these assessments? 

Data is needed including for materials effects and response. 

Process, assumptions, model information, etc. needed as well. 

Performance codes/standards/Guidelines . 

- Are they available? - Methodology for desigdanalysis is needed. 

MarketinglSelling 

- 

- 

- Towhom? 

Challenges exist with regards to selling to authorities, public, owneddesigners. 

How do we markedsell this? 

Authorities - acceptability of process, tools, results, etc. 

Public - level of safety provided 

Owneddesign team - benefits 

- cost-effective solutions, 

- aesthetics, 

- 

- 

- Benefits 

assessing whether code required protection is adequate 

being able to provide equivalent levels of safety between buildings 

Vision for tomorrow 

Vision for tomorrow should include developing: 

- Methodologies 

- FireLoads 

- Address the above - 

- Tools 

FPE’s assist Structural engineers with defining fire loads 

Steps 

Steps to getting there should include the following: 

- Defineloads 

- Training 

- Data 

- Codes/guidelines 

- ‘Marketing’/selling 

- Tools 

39 
Priorities 

- Defining fuel loads 

- Probabilities 

- Reliability 

- Liability 

40 
Group A, Breakout Session 2 

Design Fires (for structural fire safety design) - Analysis Methods 

Paper by: Morgan Hurley 

Aim of workshop: Identifjl and prioritize gaps in analysis methods and their technical basis 

(research needs). The group was requested to focus on analysis during this session, as session 3A 

would be devoted to design and codes. 

The discussion included the following items: 

1) State-of-the-art 

2) 

3) Priorities 

Gaps in methods, validation, and data 

1) State of the art 

The White Paper by Morgan Hurley summarized the state-of-the-art on modeling of realistic 

fires, while referring-to an extensive list of 45 references. Three main types of design fires have 

been discussed: 

0 Post flashover ventilation-controlled compartment fires, which are relevant for the design of 

the general structure and its parts. 

Window flames that stem from flashed over ventilation-controlled compartment fires, which 

are relevant for the design of external steel construction. 

Fire plumes, which are relevant for the design of structural elements when exposed to 

localized fuels in large compartments. 

Two additional White Papers (Andy Buchanan, Barbara Lane) have devoted some sections to the 

topic of fire modeling. 

Three types of modeling tools have been distinguished: 

1-zone models, for which there are some well known available computer models. It was 

mentioned that these models are sufficiently accurate but conservative, and are thus the most 

adequate for the sake of structural design. Being based on simple equations they are 

sufficiently simple and in essence there should be no difficulty for most design offices to 

write their own computer code, and integrate it into their design procedures. 

Fire dynamics simulators (FDS) using computational fluid dynamics (CFD). These are 

usually developed for simulating the initial stages of fire development, and do not seem to 

41 
add significant information for the post flashover stage. The group decided thus that there is 

no need to discuss research needs in this area. 

Algebraic formulations and standardized graphs. These are simplistic approximations to 

realistic fires that may be used in very simple cases, but are not suitable for the cases where a 

performance-based or fire safety engineering approach would usually be applied. It was thus 

agreed that there is no need for NIST to devote research efforts in this direction. 

The group has consequently reached consensus that the 1-zone models are the most adequate for 

the sake of structural design in the anticipated performance-based fire safety engineering 

environment. It thus devoted the discussion to this type of fire modeling in the context of its 

ability to predict the main features of the post-flashover temperature-time curve, which are 

significant for structural design (slopes during heating and cooling, Tmax, time fiom flashover to 

Tmax, duration of Tmax). 

Time-Temperature 

Generic Curves 

’ 

r 

t 

2) Gaps in methods, validation, & data 

A. Gans & research needs 

Towards the discussion the facilitator prepared a preliminary list of the gaps and needs for further 

research that have been raised in the mentioned white papers, as well as, in some other papers 

(mainly: V. Babrauskas, “Fire modeling tools for FSE: are they good enough?”, J. Fire Protection 

Eng. 8,87-95 (1996)). 

In its discussion the group reached consensus that NIST research in this area should be devoted to 

items that are needed for advancement of design tools, rather than to the general refinement of the 

scientific basis of fire modeling. Consequently, many items on the list have been graded as 

42 
insignificant, as explained below, and only five items were identified as requiring further 

research, with two of them gaining high priority, while the other three medium to low priority, as 

indicated below. 

The list of items and the ensuing discussion and decisions were: 

A. I) Fire loads & their effects (integrating modeling of heat release rate into fire-development 

models; mixed types of combustible materials; internal coverings ’ combustibility): The group 

stated that the fire of interest is ventilation-controlled, and as such, only fire loads’ energy content 

is significant. Consequently, HRR is of no interest, and combustible covering materials should be 

added to the fire load. Combustible construction and its time dependent contribution to the fire 

load was raised as a significant topic to be mentioned later, under item 7. 

A.2) Ventilation (size of broken glass areas depending on window types, glazing characteristics, 

and number of panes; numerous openings on drfferent walls with various characteristic 

dimensions; stack eflects; existence of mechanical ventilation and air-conditioning systems; wind 

regime around the building): It was agreed that, as design tools should be conservative, the 

possible variations in the size of broken glass areas should be incorporated into the safety factors 

and/or design scenarios, and there is no need to gather information on actual windows’ behavior. 

In addition, it was stated that multiple openings are represented sufficiently well in the current 

models, stack effects are rare and usually not relevant in most buildings, mechanical ventilation 

and air conditioning systems are blocked during fire by means of dampers and do not contribute 

to the fire ventilation, and wind has almost no effect on fully developed fires. It was thus 

concluded that this item is well represented in existing models and needs no further research. 

A. 3) Effects of intervention means (sprinklers andfire fighters): Activated sprinklers prevent the 

development of a fully developed fire and as such there is no need in their incorporation in 

models for structural design. Fire fighters’ intervention may reduce the fire severity, and would 

lead to unconservative design. Taking into account the lack of uniformity in fire fighting 

intervention, it seems that this cannot be incorporated into the fire modeling. 

A. 4) Partial Safety Factors @or fire loads, for geometrical features, for material properties): It 

was argued that this topic should be discussed by the Design Tools group, and not by the Analysis 

group. No further discussion ensued. 

A.5) EHects of building envelope’s thermal construction (location of mass and insulation): It was 

agreed that these may affect the fire growth rate and maximal temperature and their incorporation 

into the models is needed. However, the item has been identified as of low priority. 

. 

43 
A.6) Compartment geometry (tall compartments, long and narrow compartments, concave 

compartments): There was consensus that the knowledge regarding the fire behavior in these 

types of compartments needs further research, but the item was regarded as of medium priority. 

A. 7) Propagation offilly developedflres into other spaces: This item has been recognized as of 

high priority. Modeling should include spread of fire due to heat transfer through barriers, as well 

as via existing openings (doors and windows) and those developing with time by perforation, 

degradation, breakage or dismantling of separation elements (walls and floors). The group 

concluded that it would be best to integrate the fire modeling with the construction fireperformance modeling (thermal and structural) so that time-dependent damage to building 

elements on one hand, and exposure of structural combustible materials on the other hand and 

their contribution to the growth of fire, would automatically be incorporated in the predictions. It 

was also suggested that a methodology should be established for the incorporation of tested fire 

properties of building separation elements into the models. 

A. 8) Validation and benchmarking @y experimental evidence and between models), and 

identification of validity limits of models: It was suggested to use the term Calibration instead of 

Validation as the models are not intended to be accurate, but rather a pessimistic representation of 

possible real fires. The item was considered as of high priority. It was also suggested to 

recommend that the activity will be linked as much as possible with information derived from 

real fire, as mentioned in item B.2 below. 

A.9) Window Flames: There was consensus that this item is currently covered by very little 

research, and the only available model is the one developed by Margaret Law and implemented in 

the EC 1, Part 2: Actions on Fire. Further research is required. 

44 
B. Data and Information Needs 

B.I) HRR - Data for various spaces in typical occupancies: The group argued that this 

information is not relevant for the modeling of fully developed fires, and its gathering is not 

important in the context of structural fire design. 

B.2) Fire loads and their surface areas - Data for various spaces in Vpical occupancies: The 

group recognized that there is an urgent need to gather statistically valid information on the fuel 

loads (in energetic terms) in the various typical spaces of most typical occupancies. It was 

suggested that the information should be then used as a basis for the codification of the Fire 

Loads in a standard. Data should include distributions in order to enable evaluation of 

probabilities and partial safety factors. 

B. 3) GIming breakage during fire (linked to window type, gIass properties and number of panes): 

As mentioned in A2 above, the group concluded that although not fully available, this 

information will be of no significance for structural design. The size of openings should be taken 

as maximal window area in most design cases, as this pessimizes the fire. When longer and cooler 

fires may be more threatening to the structure, the designer should consider scenarios with 

parametrically smaller openings. 

B. 4) ReaI$re statistical data: the group suggests that NIST should develop a methodology for the 

extraction of valid information from real fires. The methodology should address, on one hand, 

how to extract more information from existing information bases on past fires, and, on the other 

hand, how to handle the interrogation and extraction of information from future fires. 

3) Conclusions 

The following research and data needs and priorities were identified: 

High priori@: 

Items A.7 - Integration of fire analysis and models with fire performance of the construction in 

order to enable the prediction of the time-dependent fire spread beyond the compartment of origin 

as well as the fire load imposed by combustible construction. 

Item A.8 - Validation and benchmarking (by experimental evidence and between models), and 

identification of validity limits of models. 

45 
Item B.2 - Collection of statistically valid data regarding fuel loads distributions (in MJ) per floor 

and envelope area, and their surface areas. Information should be specific for the various spaces 

in as many as possible of the typical occupancies. 

I Item B.4 - Development of methodologies for the extraction of valid information fiom real past 

and fbture fires. Implementation of the methodologies for the existing information bases, and in 

future fires. 

Medium to low priority: 

Item AS - Effects of building envelope’s thermal construction (location of mass and insulation. 

Although of low priority this item can easily be integrated into item A.7. 

Item A.6 - Compartment geometry (tall compartments, long and narrow compartments, concave 

compartments). 

46 
Group C, Breakout Session 2 

Discussion: Structural Analysis - Issues And Needs 

Paper by: James Milke 

0 Need better definition of “failure” or limit states for predicted structural response under fire. 

That is, what level of deformation, force or other structural response quantity predicted by a 

structural analysis model will be taken as failure? 

Possible limit states: 

- global collapse of structure; 

- local collapse of structure; ‘ 

- 

- 

excessive deformation that will impair fire rated compartment walls; 

excessive deformation that will lead to excessive repair costs. 

In a performance based design approach, various limit states may need to be considered, 

corresponding to various performance objectives. Associating predicted structural response 

quantities (deflection, force, etc) with corresponding damage conditions in the structure will 

be a particularly difficult task (the same has proven true for performance based seismic 

engineering). 

Development of structural analysis models should start at the material level, and then work 

up towards the system level. That is, models should be developed for: 

- material response ( simple and complex states of stress) 

- member response (simple and complex loading conditions) 

- connection response 

- subassembly response (frame subassembly of two or more members with 

connections) 

- frame response 

- 3-dimensional system response 

By starting at the material level and working upwards to more complex behaviors, we 

progressively build our knowledge, modeling capability, and our ability to use and interpret 

the results of the models. 

0 Development of structural analysis models (for materials, members, connections, etc) must 

be accompanied by experimental research for understanding, calibration and validation of 

models. 

Need “research” quality structural-fire experiments: 

- apply complex structural loads to elements, connections and subassemblies under 

elevated temperatures; 

- thorough instrumentation 

- test elements to “failure” 

Whereas a great deal of test data is available for standard ASTM El 19 fire endurance 

47 
tests, these standard tests do not, in general, provide the type of loading, data collection 

and analysis needed for development of structural analysis models. 

Certain aspects of the response of concrete structures merit investigation. These include: 

- high strength concrete (need very large load capacity test facilities to obtain 

meaningfkl data at realistic scales) 

- spalling behavior 

- post-tensioned systems and anchorages - behavior during cool-down (may be critical in some cases). 

Need structural-fire test facilities in the US to develop the needed research quality 

experimental data. Such facilities must have the capabilities listed above; i.e., apply mplex 

structural loads to elements, connections, subassemblies, etc at elevated temperature and at 

realistic scales. It appears that no such facility exists in the US. 

Need a limited number of fill-scale building tests under fire conditions to enhance 

understanding of system response and to validate structural analysis models (tests similar to 

those conducted at Cardington). There may be a possibility of conducting such tests on 

existing buildings that are scheduled for demolition. 

Finite element models (ABAQUS, ANSYS, LS-DYNA, etc) provide for the most accurate 

prediction of structural response under fire conditions. Finite element models are very useful 

tools for research or for design studies by specialized consulting fms. However, such finite 

element models require a high degree of knowledge by the user, and are costly to develop 

and to interpret the results. Consequently, finite element models are probably not suitable for 

routine design applications. However, when finite element models are used, models that use 

explicit integration schemes are likely preferable to those that use implicit integration. 

Structural element based models (fiame models) are likely to be most suitable for routine 

analysis of structural response under fire conditions. Such models are very commonly used at 

present for structural analysis under other load conditions (gravity, wind, seismic) and could 

potentially be extended to include fire structural response analysis. Commercial software 

developers would likely incorporate fire response analysis into their fiame analysis programs 

if the basic modeling information were available and if sufficient demand exists for such 

models. 

As structural element based models are developed for predicting structural fire response, 

need to develop a set of “benchmark” problems for validation. Benchmark problems of 

selected elements, fiames and systems would be solved by more advanced and exact methods 

(fmite element, etc) and be used to evaluate the accuracy of the simpler element based 

models. 

Required attributes of a structural analysis model capable of predicting response under fire 

conditions: 

- need to model large deformations 

(such modeling capability already exists; no significant research needs for this) 

need temperature dependent material properties 

(substantial data already exists for steel and concrete under simple stress conditions; 

- 

48 
need additional data for material response under complex states of stress, and rate 

dependent response) 

(inadequate data available at present to develop reliable connection response models; 

substantial research needed on connection behavior at elevated temperature). 

need to model element (beams, columns, braces, etc) behavior under complex 3- 

dimensional loading (e.g., biaxial bending plus compression) under elevated 

temperatures and temperature gradients; models should include plasticity and postpeak (unloading) response 

(substantial experimental data and model development work needed here) 

need 3-dimensional modeling capability, including floor slabs and 

membranekatenary action 

(some data available on membrane action in slabs, but need more) 

- need connection response models 

- 

- 

49 
Group D, Breakout Session 2 

Discussion: State of the Art in Evaluation and Retrofit for Fire Safety 

Paper by: Fred Mowrer and Bob Iding 

Issues: 

What triggers a retrofit? 

Look at seismic retrofit as an example 

Code trigger by architect/ structural. Fire - change of use 

Code lacks triggers to upgrade - building official call vs. scoping engineering standarddguides 

What is retrofit? 

Consider use of other strategies - existing and life safety, seismic 

Needs: 

20 year roadmap/plan 

New procedures/standards -tools to evaluate the fire resistance of archaic materials, criteria to 

access structures 

Tools that would be relevant for both new and retrofit conditions - analysis, evaluation 

Methodology to use of existing construction documents 

Education 

Thermal analysis of archaic materials 

Plan of Action: 

Develop design guides/standards/tools - retrofit for unsafe buildings, optional upgrades - convince the architedengineer and owner of value 

Develop evaluation checklist, assessment criteria - elements, connection. load paths, non visible, 

Develop existing building performance objectives - levels, measurement, validations. Develop 

means to make fuel load assessment. 

Carry out fill scale building testing - develop test criteria, consider available buildings, fuel loads 

Develop performance measures - metrics, multihazard robustness, redundancy 

50 
Group A, Breakout Session 3 

Discussion: Design Fires 

Paper by: Morgan Hurley 

Attendance 

Beth Tubbs, Facilitator 

Farid Alfawakhiri, Recorder 

Jonathan Barnett 

Rachel Becker 

Craig Beyler 

Doug Carpenter 

David Collins 

Joel Kruppa 

Chris Marrion 

Bud Nelson 

Long Phan 

Robert Thomas 

Wei Zhang 

Opening 

Beth Tubbs opened the session at 850 am 

The goal of the session was to identi@ and prioritize gaps in best practices, design guidelines, 

standards, etc for the Design Fires for use in the structural design for the fire condition: 

(1) Current design methods, codes and standards 

(3) Priorities 

(2) Gaps 

Discussion 

It is important to develop meaningful codes and standards that would allow more routine structural 

design for fire - this will improve AHJ confidence and streamline the approval process. 

Eurocodes contain provisions for design fires. 

More accurate statistics are required to calibrate the codes 

Current state - there is no de or standard in US for design fires 

Methods of establishing fire (energy) loads were discussed 

Eurocodes use 80 % fiactile fire loads for occupancies 

Discussion went on whether the client (and the design team) or the code/standard establish the 

design fire load 

Factors that would affect fire loads and load factors were discussed - probabilistic approaches were 

discussed 

It is important to develop a probabilistic standard on fu-e loads based on the current state of 

knowledge, and then maintain and update the standard as more research is done in this field. 

51 
Flipchart Outlines 

Questions 

What do code officials (or other stakeholders) need 

Should it be probabilistic 

In a code or standard 

Methodology or more of a list 

Fire load studies 

Fatom that affect fue lo& 

Ventilatiodopenings 

Active protection systedhteraction 

Combustibility of construction 

Use/occupanc y 

Heighvarea 

Level of compartmentation 

Separation between buildings 

52 
Group D, Breakout Session 3 

Discussion: 

Paper by: 

Robert Duvall - Facilitator 

David MacKinnon - Recorder 

Note: Group believes upgrade is a better term than retrofit. 

Gaps 

Retrofit Best Practices, Guides and Standards 

Fred Mowrer and Bob Iding 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

No case studies available 

Few engineers, if any, have ever done a structural retrofit for fire performance 

Fire performance is not being considered when doing other, multi-hazard (seismic, etc) 

upgrades for other purposes. . 

Triggers 

o West coast, seismic 

o East coast, any time you do an upgrade, maybe for a change in tenancy if a problem 

is identified 

No standardizedpublished inspection procedures 

o Criteria - 

o Could trigger upgrade 

o Method to prioritize problems 

o Check list 

o 

o 

Primarily a self regulatory process but could be adopted by a community that has 

severe problem 

No guideline for redundancy and toughness 

Same (maybe) procedures for inspection of fire protection materials 

Existing Building Codes have triggers, are focused on reuse, assume building fire protection 

features are as per code when built 

Owner incentives to evaluate building 

o 

o Disclosure 

o But no published criteria 

o Financing institution 

o Internally driven 

o 

o 

o Employees 

Evaluation upon sale of building 

Due diligence, comprehensive, price negotiation 

Quality Index for Fire, rating like LEEDS, part of structural evaluation (NYC) 

Knowledge of practicing structural engineers 

Even if not regulated will be used by owners and purchasers but building department will not 

get involved unless legislated 

Life Safety work is being done in hospitals, self-evaluation, plan for improvements, effects 

accreditation. Hospitals are now more open, and want to know what is wrong with their 

building. Not presently regulated. 

Understanding of responsibility, who responsible for what. 

Fire safety inspections are not focused on consequences of degraded structural fire protection 

53 
o 

o 

o 

Perception that once regulatory agencies sign off on building, owners no longer need 

to think about structural fire protection. 

Accountability: owner required to maintain and operate a facility that meets 

requirements 

Insurance companies do evaluation of life safety systems and fire hazards but don’t 

go into hidden things like structural fire protection issues. Perception is that when 

structure is built, it is OK and nothing ever changes. Only visual inspection are 

conducted (if done at all), protection materials are not measured or tested. 

Design Guidelines and Standards 

Guideline for the evaluation and remediation of structural fire performance of existing 

buildings. 

o Toughness/robustness 

o Egress routes 

o Redundancy 

o Keeping fire separated from critical elements 

o Systems, components, connections 

o Fire spread, barriers, all passive systems 

o Roles of design team members - who is responsible for what 

o Communication of findings, legal issues, professional codes of ethics 

0 

0 

0 

Tools to identifj. weak links in structural fire performance. 

Guidelines to identify problem components based on consequence of failure 

Document that describes when a structural engineer should be called in to evaluate structural 

fire protection 

o Need measures? - Affected area. 

o Upgrades are complaint driven 

o 

o Tax incentives, etc. 

Owner and allied professions need guidance 

0 Non-technical guide for communities who want to upgrade their building stock 

54 
Appendix 9. G 

National R&D Roadmap for Structural Fire Safety Design and Retrofit of 

Structures 

Research and Development Priorities 

Workshop participants identified the following research needs as having the highest priority for 

development of best practices for structural fire safety design and retrofit of structures (shown 

with the number of votes given by participants as a percentage of the total votes cast. Note that 

this list represents the highest priority items only). On the following pages, under Research and 

Development Needs, the entire list of research needs are presented, with the number of votes 

received by each. 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

Need structural-fire experimental facilities in U.S. - 35 

a) apply complex structural loads to large scale components at elevated temperature 

Need more “research quality” experimental data on structural response at elevated 

temperature - 34 

f) material behavior - need some additional data on multi axial stress and rate effects 

(creep) - 1 

g) connection behavior - need substantial work - little data available at present) - 3 

h) member behavior under complex loading - need substantial work - current data 

mostly for simple loading - 1 

i) subassembly behavior - need substantial data - 6 

j) system behavior - need additional data to supplement Cardington - 9 

Quanti@ level of protection provided by current prescriptive code requirements - 32 

Actual fire performance data - 32 

Need definition of failure/limit states for structural response in fire - 29 

Guideline needed - for public community and engineering community 

“Evaluation and remediation of structural fire performance of existing buildings” - 29 

Specify performance goals in the building code for prescriptive and performance-based 

options - 2 1 

Develop performance metrics for multi-hazard building robustness - 18 

Design Fires: needs - risk based methodology - 18 

- 

- data to support with future considerations - 12 

development of a standard - 7 

Standard methods for determining material properties at elevated temperatures - 16 

Fire performance of connections for codes and standards - 15 

Need benchmark problems for model verification - 14 

Whose role is fire protection including over the life of the building - 13 

55 
Research and Development Needs 

Listed below are the research and development needs identified by workshop participants 

accompanied by the number of “votes” assigned to each during the general prioritization session. 

IA - Context for fire safety design 

Defrne loads 

Tools 

Data- 1 

Codeddesign guidelines 

Marketinghelling - authorities, ownerddesigners, public - 6 

Probabilities 

Reliability 

Liability 

Training- 1 

IB - Context for fire safety design 

Provide a performance based option in building code - 1 

Maintain option for prescriptive design option - 5 

Quantify level of protection provided by current prescriptive code requirements - 32 

Specify performance goals in the building code for prescriptive and performance-based options - 21 

Establish general procedures and identify roles (design team and enforcement) 

Implement more training and education programs for all parties involved in desigdconstruction 

process 

Enhance interaction between disciplines early in design process - 8 

Identify those building conditions (complexity, size, fhction) that should require a calculated fire 

resistance 

Building code performance goals should not require consideration of extreme events 

Provide direct reference to the types of tools and procedures that should be used in calculating 

fire resistance (fire load, thermal analysis, structural analysis) 

IC - Context for Structural Design 

New buildings - current practice seems ok but we don’t really know 

Existing buildings -we don’t know 

Poor data available on performance of active systems, performance of structural components and 

barriers - 1 

Lack of understanding that fire is different than natural disaster events. - 2 

Need Actual Fire Performance data - 32 

Identification of fire hazards (accidental) - 1 

Risk communication - rational fire design 

Professional education component 

Develop funding resources - 7 

Capitalize on other disaster resistance programs 

Understand building performance 

Tools for signature buildings 

Measure of what is intended to be applied 

Limited data on risk based design and probabilities - 1 

Large impact over large area (seismic) versus individual building fire (times no. of buildings) 

56 
ID - Context for Structural Design 

Understanding of the relationship between fire safety engineering and structural engineering - “probability/event tree - 2 

Normalization of E-1 19 - 4 

Review/comparison of Int’l codes vs. us 

Significant structure code? 

Reverse engineering from existing to new; use analytical tools to verify existing practice 

Context/preamble of effort within societal beliefs (public perception) - difference between 

guidedstds and codes 

Handling the unpredictable 

Develop a fire safety go/no go - 4 

Define true cost vs. cost - Le. cost to society 

Structural engineering and fire safety engineering collectively define the unknown” 

Multi hazard considered with fire 

“Society” selection of method 

IIA - Design Fires 

Compartment fire model gaps: 

1) integration with construction performance in order to enable: 

a. fire spread to other compartments (via thermal conduction, holes, dismantled 

partitions, openings) - 10 

. b. involvement of combustible construction materials (with time) - 3 

2) Calibration, benchmarking (experimental, between models). An identification of 

limitations - 8 

3) geometry (tall, long, concave) 

4) envelope (mass and insulation) 

Window flames 

Data: fuel loads (per typical spaces) - 5 

Methodology for gathering statistical information from past and future fires. 

IIIA - Design Fires 

Current status - Non existent in USA 

Gaps - lack of data and methodology - 8 

Needs - risk based methodology - 18 

- 

- 

data to support with future considerations - 12 

development of a standard - 7 

Establish benchmark fire loads for generic occupancies - 4 

IIB - Thermal Analysis 

Analysis methods are adequate for modeling conduction 

- are not ok for 

o 

o Wood 

o Water spray on structures 

o Membranes (joints0 

o Fire doors 

FRP or wood burning around the structure - define boundary conditions 

57 
o Changing geometry (spalling, intumescent materials) - 1 

o Moisture movement 

Material Properties availability - 7 

Elevated Temperature Material Properties - 2 

thermal and boundary conditions 

cooling phase (Properties are not reversible0 

new materials (new concretes) 

glass (windows and structural) 

proprietary results 

material stickability 

Standard Methods for determining material properties at elevated temperatures - 16 

Contact Resistance 

Interface CFD fue modeling to the structure - 2 

IIIB - Thermal Analysis 

Lack of a design guide for thermal analysis methods - 6 

Standardized validation of sohare - clear definition of software applicability - 5 

Lack of published material property data - 3 

Acceptance of codified thermal analysis methodology (i.e. sprinkler hydraulics, smoke control, 

etc) - published software output, published results tailored to various groups (engineers, AHJ. 

Standardized fire test methods 

Etc) - 6 

IIC - Structural Analysis Methods 

Need definition of failurellimit states for structural response in fire - 29 

Need to develop structural element based models (i.e. kame analysis type models).for routine 

analysiddesign of structural fire response - 2 

Need benchmark problems for model verification - 14 

Need more “research quality” experimental data on structural response at elevated temperature - 

material behavior - need some additional data on multi axial stress and rate effects 

(creep) - 1 

connection behavior - need substantial work - little data available at present) - 3 

member behavior under complex loading - need substantial work - current data 

mostly for simple loading - 1 

subassembly behavior - need substantial data - 6 

system behavior - need additional data to supplement Cardington - 9 

Need structural-fire experimental facilities in U.S. - 35 

b) apply complex structural loads to large scale components at elevated temperatures 

Need limited number of full scale “Cardington-like” tests to evaluate system behavior - use 

actual buildings - 8 

58 
IIIC - Structural Analysis Methods 

Euro codes methods seem good but need to validate supporting data - 5 

Connections - 15 

Whose role is fire protection including over the life of the building - 13 

Interaction of structure and the compartment - 4 

IID - Retrofit 

Identify what data is needed - 2 

Identify what data is not available - 2 

Database collection - fbll scale buildings tests, properties of existing materials, he1 loads - 9 

Analyze data 

Develop performance metrics for multihazard building robustness - 18 

Validate the results 

Start over 

IIID - Retrofit 

Develop and publish criteria for retrofit 

Owner incentives to upgrade 

Perception (cultural) - structural fir protection doesn’t change with time 

Guideline needed - public community and engineering community 

Evaluation and remediation of structural fire performance of existing buildings 

59 
, 

Appendix 9.H 

White Papers 

1. Challenges Facing Engineered Structural Fire Safety - a Code Officials’ Perspective 

-Jonathan Siu, P.E., SE 

2. Challenges Facing Engineered Structural Fire Safety - the Architect’s Perspective - Dave Collins, AIA 

3. Framework for Structural Fire Engineering and Design Methods - Greg Deierlein, 

Ph.D. and Scott Hamilton 

4. Relationship between Structural Fire Protection Design and Other Elements of Fire 

Safety Design - Craig Beyler, Ph.D. 

5. Design Fire Scenarios - Morgan Hurley, P.E. 

6. Analysis Tools and Design Methods: Current Best Practices - Jim Mike, Ph.D. 

7. Thermal and Structural Analysis Methods and Tools - Gaps in Knowledge and 

Priority Areas for Research fiom a Practice Perspective - Barbara Lane, Ph.D. 

8. Evaluation and Retrofit of Existing Buildings for Structural Fire Safety - Fred 

Mowrer, Ph.D., and Bob Iding, Ph.D. 

9. International Status of Design Standards for Structural Fire Safety - Andy Buchanan, 

Ph.D. 

60 
White Paper 1 

Challenges Facing Engineered Structural Fire Safety - A Code Official’s Perspective 

Jonathan C. Siu, PE, SE’ 

INTRODUCTION 

In 1973, construction was completed on two highrise office buildings-the 62-story First 

Interstate Bank building in Los Angeles, California, and the 38-story One Meridian Plaza 

building in Philadelphia, Pennsylvania. Fifteen years later, on May 4, 1988, a fire destroyed four 

floors of the First Interstate building after burning for four hours. Nearly three years later, on 

February 23, 1991, a fire burning for over 19 hours gutted eight floors of the One Meridian Plaza 

building. Although the resources of the Los Angeles Fire Department were severely challenged, 

they were successful in controlling the first fire, and the resultant damage to the structure was 

very minor. In the One Meridian Plaza fire, the Philadelphia Fire Department was unable to 

control the fire before the onset of major structural damage. Due to fear of imminent structural 

collapse, firefighting personnel were pulled out of the building eight hours before an automatic 

fire sprinkler system finally controlled the fire. Shortly after the 9-1 1 terrorist attacks in 2001, the 

World Trade Center 7 building, completed in 1987, became the first modern fire-protected steel 

highrise building to collapse due primarily to fire damage. In all three cases, the buildings were 

built in accordance with the latest prescriptive codes in effect at the time of construction. 

After each of these three major fires, the question has been raised whether prescriptive building 

codes provide adequate protection for the structure. It can be argued that the code-required 

(prescriptive) fire protection for the structure in the first two fires performed adequately, since 

neither structure collapsed, and no loss of life occurred as a result of damage to the structure. On 

the other hand, even though the First Interstate building was put back into complete service 

within a few months, the economic losses along with the attendant costs to society in all three 

cases would argue equally that the prescriptive building code requirements are lacking. 

The First Interstate and One Meridian Plaza fires eventually resulted in changes being made to 

the prescriptive codes to require automatic fire sprinkler systems to be installed throughout all 

new highrise buildings. Changes to the building codes are currently being discussed in various 

forums as a result of the World Trade Center 7 collapse. At the same time, the organizations that 

promulgate building codes are trying write codes that are more “performance-based” and less 

prescriptive, to increase design flexibility. Increasingly, analysis and reports from fire protection 

engineers are being provided to code officials in lieu of traditional fire protection of structures. 

In the atmosphere of increasing demand for fire protection engineering and the increasing 

sophistication of the analytical tools available to the fire protection engineer, it must be 

recognized that code officials will ultimately decide what will be permitted for protection of 

structures. There are many challenges facing the code official (and by extension, the fire 

protection engineer) before engineered fire protection can become widely accepted. The four 

example buildings below will be used to illustrate how engineered fire protection is being used in 

lieu of prescriptive code requirements in the city of Seattle, Washington, and will also serve as 

examples of the challenges facing the code official. 

61 
EXAMPLES OF ENGINEERED STRUCTURAL FIRE PROTECTION IN SEATTLE 

The Department of Design, Construction and Land Use (DCLU) is the agency in the City of 

Seattle government that regulates construction. DCLU enforces the Seattle Building Code (SBC), 

a locally-amended version of the Uniform Building Codem. The SBC allows alternate materials 

and methods to be used in lieu of prescriptive code requirements, on the condition the alternates 

provide protection equivalent to that required by the code. The four projects discussed below are 

examples of structures where engineered fire protection was approved by DCLU as an alternate 

for the protection ordinarily required by the code. 

1. Glasdsteel bridge; Seattle City Hall 

Earlier in 2003, the City of Seattle completed construction of a new City Hall building. One 

of the more striking architectural features of the new building is a bridge spanning the public 

lobby space, used as one of the routes connecting the City Council offices to their meeting 

chamber. The bridge floor and rails are constructed of glass panels with steel supports, and 

the entire structure is stabilized laterally with steel rods. Given the type of construction of the 

building, the prescriptive provisions of the SBC require any structure supporting floor loads 

to be protected by 3-hour fire rated construction. For most steel structures, this protection is 

provided by spray-applied fireproofing. However, that method would have destroyed the 

architecture of the bridge. Instead, the fire protection engineer was able to demonstrate that 

an “expected” fire, uncontrolled by sprinklers, and placed in the “worst” location would not 

raise the temperature of the steel to the point where the bridge would collapse. 

2. Mesh structure; Seattle Central Library 

As of this writing, the new Central Library for the City of Seattle is under construction. A 

steel mesh structure on the outside of the building provides support for the exterior glazing, 

as well as lateral bracing for the building against earthquakes and wind. In one portion of the 

building, the mesh structure is canted at an angle such that it also acts as part of the roof 

framing, transferring vertical loads to the primary frame of the building. The SBC requires 

secondary roof framing members (those not directly connected to columns) to have a 

protection rating of two hours, although there are allowances in the code to lessen the 

protection if the structure is far enough away from potential fire sources. Again, sprayed-on 

fireproofing was not acceptable to the architect, and given the nature of the mesh structure, 

sprinkler protection of the structure was impractical. The ultimate resolution was the product 

of teamwork between the fire protection engineer and the structural engineer. Once the fire 

protection engineer was able to show how many members of the mesh structure would be 

expected to fail under fire conditions, the structural engineer was able to demonstrate the 

highly redundant structure was capable of transferring the loads around the failed portion. As 

added protection, the sprinkler system was designed to provide a greater density of water onto 

the source of he1 (primarily bookshelves) below the canted portion of the mesh structure, in 

order to control any fire before it would endanger the structure. 

3. Roof fiaming and walkways; Fred Hutchinson Cancer Research Center Building 

A four-story atrium connects two wings of the Fred Hutchinson Cancer Research Center 

Building, which is nearing completion at the time of this writing. The roof of the atrium is 

constructed of glass supported by a steel beam grid. Walkways supported by steel beams 

cross the atrium to connect the wings at each floor level. Mid-span support for the walkways 

and the roof grid is provided by a group of four steel columns. The architectural design 

62 
4. 

called for the roof and the walkway beams to be unprotected, whereas the SBC required them 

to be protected for two hours (roof) or three hours (walkways). The fire protection engineer 

considered the likely fuel loading in the atrium and was able to convince the code official the 

design fire would not damage the structure. 

Columns; Space Needle 

The Space Needle at the Seattle Center was constructed in the early 1960’s as the centerpiece 

of the 1962 World’s Fair, and is Seattle’s defining landmark. Originally, the only occupied 

space in the,structure was on the restaurant and observation levels in the saucer-shaped 

structure at the top. The main columns are in a tripod configuration, and constructed of steel 

sections with flanges in excess of 1% inches thick. Each leg of the tripod consists of two 

steel sections. In the 1980’s, a lower restaurant level was added, being attached to the inside 

of the tripod structure. In the 1990’s, a new retail and ticketing structure was constructed at 

the ground level, enclosing the base of the tripod. Because the columns were no longer fully 

open to the atmosphere, DCLU was concerned that heat from a fire would build up 

sufficiently to damage the columns. Although the SBC would have required 3-hour rated 

protection to be provided for the columns, the fire protection engineer demonstrated the 

columns would not heat up enough to fail under design fire conditions, due to their large size. 

The common thread running through the four cases above is the desire of the architect to leave 

the steel structure exposed, without code-required (prescriptive) fire protection. In each case, the 

fire protection engineer was able to demonstrate the structure would not be damaged by a design 

fire. However, also common to each case, the code official for DCLU had to decide what the 

goals were, what parameters needed to be addressed, and whether the fire protection engineer had 

adequately addressed the issues. 

CHALLENGES FACING THE CODE OFFICIAL 

I. The Balancing Act. When a building is built, the main stakeholders are the developer, the 

designers, the users of the building, and society in general. The code official is placed in the 

position of balancing the needs of these stakeholders, and managing the impacts and risks 

associated the compromises made to maintain that balance. 

On the developer’s side, while many are interested in more than their bottom line, ultimately, 

any building and therefore any solutions to building code issues must make economic sense 

to them. In the example of the Central Library steel mesh above, protecting the mesh with a 

sprinkler system would have been acceptable by the code, but would not have been 

economically feasible to the owneddeveloper (in this case, the City of Seattle) as it would 

have taken hundreds of extra sprinkler heads to provide adequate coverage of the structure. 

As another stakeholder, in many building designs, the architect is focused on the aesthetics of 

the space, or the need to make an architectural/artistic “statement”. The unprotected 

structures in all four cases above are expressions of this artistic nature of architecture. 

Another example is in old, historic buildings where certain architectural features such as large 

timber beams and columns must remain exposed to preserve the historic character of the 

building. 

The third set of stakeholders, the users of the building, want to be safe but my experience is if 

they are lessees or owners, they are also very concerned with the economics of the building. 

63 
Many times the concern to minimize dollar costs of construction override safety concerns. In 

those cases, they are essentially willing to gamble that a fire, an admittedly somewhat rare 

event, won’t affect them. This is usually less of an issue with new construction, but is a 

larger issue in older (lower rent) existing buildings. 

Finally, society demands life or economic losses in a single event be minimized-buildings 

must provide some level of life safety for occupants as well as property protection. (Note that 

since the World Trade Center collapses, there has also been a heightened public concern for 

the safety of emergency responders.) Public outcry does not occur over the many, many 

deaths in fires in single family residences each year, but single events with large losses of life 

such as the 911 1 terrorist attacks will generate an outcry. This is recognized in the building 

codes, which require higher levels of protection for buildings housing large numbers of 

people. On the economics side, the loss of a large building such as One Meridian Plaza leads 

to other societal impacts--economic strain on businesses (those formerly housed by the 

building and those dependent on the business generated by the building), not to mention the 

cost of demolition and rebuilding. Again, society is willing to endure many small losses, but 

does not tolerate large single losses. On the other hand, similar to the developer’s need, 

society wants solutions to make economic sense. In general, the public is not willing to pay 

the price for complete safety- such construction would not be attractive or affordable. 

However, after a large-loss event, there is a danger that societal demands will be used to 

inappropriately influence (i.e., politicize) changes to codes. 

Even though many code officials recognize their role in balancing the stakeholder needs, they 

also view their main purpose for existence in the construction process as representing the 

needs of society and the users of the building. Thus, they tend to err on the side of life safety 

for the occupants of buildings. Fire protection engineering consultants are viewed by many 

code officials as advocates for the developer or architect, and not necessarily for safety. This 

lack of trust by the code official is due to many factors that may include: 

o Lack of code official expertise. Many code officials lack the expertise to properly 

evaluate engineered fire protection proposals. Because they are not comfortable making 

the evaluation, they are more likely to depend on the prescriptive codes rather than 

shifting paradigms, as discussed in the next section. 

Credibility of the fire protection engineer. The profession of fue protection engineering 

is relatively new to most code officials. As a whole, code officials don’t know what type 

of training or other exams a fire protection engineer must take in order to be called an 

“engineer”. Is there a core set of courses a college graduate in fire protection engineering 

must take, regardless of where he/she goes to school? In most states, there is not a 

separate professional license for fire protection engineers. Is there a nationally 

recognized standardized testing program for licensure? Because there isn’t the “comfort 

level” with the fxe engineering professionals as there is with other design professionals 

(architects or engineers), the code official is less likely to approve engineered solutions 

for structural fire protection. In addition, as in any profession, there are those fire 

protection engineers who are credible, and those that aren’t. The code official has to 

discern whether or not the fire protection engineer is knowledgeable and credible. To 

establish credibility, the fire protection engineer must be able to explain what the 

prescriptive code requires, why it’s required (what’s the intent of the code), and most 

importantly, how their proposal is justified, or how the proposal mitigates the hazards the 

prescriptive code is trying to address. An engineered fire protection proposal that is not 

adequately justified is unlikely to inspire code official confidence in the engineer. 

o 

64 
Another reason for code official reluctance to deviate fiom the prescriptive code is the fear of 

litigation or media exposure. It is my opinion that this fear is somewhat irrational, as lawsuits 

involving building code decisions are practically non-existent. Even so, it is viewed by many 

code officials (with encouragement from their attorneys in many cases) as being a safer 

course to stay with the strict wording in the code. Additionally, in hidher mind’s eye, any 

failure reflects poorly on the professionalism of the code official, and failures resulting from 

poor code provisions are easier to live with than failures resulting from risky decisions. 

II. The Paradigm Shift. In order for code officials to consider engineered structural fire safety 

solutions, they must be prepared to consider new methods that are not neatly codifiedperformance requirements. The prescriptive code requirements are familiar, and easy to 

enforce. Deciding whether performance goals are met requires judgment, and the knowledge 

of the goals. Unfortunately, this shift is difficult for many code officials, as many do not 

have a professional background that prepares them to make these judgments. 

These first two challenges are not under the control of the fire protection engineer. However, 

there are other challenges that hinder wider acceptance of engineered solutions, even for the 

professionally-trained code officials who are willing to make the paradigm shift. 

III. Performance Standards. The code official’s first challenge from a technical standpoint (as 

opposed to philosophical) when presented with a proposal for engineered fire protection is to 

determine what standards must be met. Attempts are being made in various forums to define 

performance standards to which buildings can be designed and evaluated. One example is in 

the ICC Performance Code for Buildings and Facilities”, promulgated by the International 

Code Council. This code sets general standards indicating occupant lives, property, and fire 

fighters and emergency responders are to be protected. A more specific performance 

standard for structures in fire is stated as follows: 

“Structural members and assemblies shall have a fire resistance appropriate to 

their function, the fire load, the predicted fire intensity and duration, the fire 

hazard, the height and use of the building, the proximity to other properties or 

structures, and any fire protection features.” ($170 1 -3.1 1) 

Performance requirements relevant to this discussion are stated in the Building Construction 

and Safety Code” (NFPA 5000”) promulgated by the National Fire Protection Association as 

follows: 

“Buildings shall be designed and constructed to reasonably prevent structural 

failure under fire conditions for a time sufficient to protect the occupants.” 

($ 5.2.2.3) 

““Buildings shall be designed and constructed to reasonably prevent structural 

failure under fire conditions for a time sufficient to enable fire fighters and 

emergency responders to conduct search and rescue operations.” (95.2.2.3) 

While the standards in both these codes are of some help to the code official, they are still 

vague, and don’t provide a basis for evaluating or approving a particular proposal. What is 

“appropriate”? What is “reasonable” prevention of failure? As a result, there is still much 

left to be decided and negotiated with the fire protection engineer on a particular building. 

65 
IV. Design Event. The most difficult challenge facing the code official is evaluating the design 

event being proposed. To do this, there are at least three questions that need to be answered: 

o What is the size of the design fire? For designing exiting systems for building 

occupants, the prescriptive building codes assume there is one fire burning at a time, 

and it does not fully involve a floor in the building. This may be a reasonable design 

event for engineered structural fire protection, but in reality, the First Interstate and 

the One Meridian Plaza fires fully involved floors, and more than one floor was 

burning at the same time. Preliminary studies of World Trade Center 7 indicate a 

strong possibility a larger-than-normal fuel load (a ruptured diesel fuel line for 

emergency generators) was a contributing factor in the collapse of the’ building. 

However, these are extraordinary events, and I do not think they represent reasonable 

design events, especially given the performance standards in the codes. In each of 

the four examples of engineered fire protection in Seattle, the fire protection engineer 

assumed a localized fire, with fuel provided by expected furnishings or hazards 

(books and bookshelves, combustible furniture, retail goods, etc.) None were in an 

environment that was likely to have high fuel loads. 

o What is the duration of the design fire? The prescriptive codes require protection for 

structures ranging fiom a rating of zero to a rating of three hours, depending on the 

size and use of the building. (Note that these ratings are based on a standardized fm 

test, and don’t necessarily reflect how long the structure would last in a real fire.) 

Emergency systems are generally required to operate for two hours. The NFPA 

5000 code says the goal is to “reasonably” avoid structural failure until occupants 

are evacuated and search and rescue operations are accomplished. In a large 

building, search and rescue operations could amount to several hours. In the First 

Interstate fire, search and rescue operations were not started until the fire was 

knocked down, nearly four hours after it had started. The design fire durations used 

to just@ the unprotected steel in the Seattle examples were built around the expected 

fuel load. For example, for the City Hall glass bridge design, the fire protection 

engineer analyzed the structure for a fire in the adjacent office area, and a 

furniturekiosk fire immediately below the bridge. The furniture/kiosk fire was 

determined to be the worst case fiom the standpoint of heat impingement on the 

‘structure. However, the duration of the design fire was less than 10 minutes since the 

fuel for the fire was consumed in that time, and therefore, the heat released by the fire 

decreased. 

o What other assumptions are associated with the design event? While the prescriptive 

codes generally assume the only protection for structures is the passive protection 

(e.g., sprayed-on fireproofing or gypsum wallboard enclosures), they do allow fire 

sprinkler systems to substitute for one hour of required protection. Some fire 

protection engineers will try to justify performance-based designs by saying fire 

sprinkler systems will control the fire before it gets hot enough to affect the structure. 

There is some merit to this idea-if sprinklers are operating properly, then, no fire 

protection is really needed for the structure. However, there is debate among code 

officials as to how much these active systems should be relied upon. The question is, 

how subject to failure (human-caused or otherwise) are they? The First Interstate fire 

+started on a floor that had operable sprinklers-the problem was they had been shut 

off and drained in order to work on the system. With this in mind, there is a question 

as to whether or not it should be assumed that the sprinkler system is operable when 

engineering fire protection of structures. For the examples in Seattle, DCLU required 

66 
a “belt and suspenders” approach-the design fire was assumed to be burning 

without being controlled by sprinklers, but the sprinklers were still required in order 

to further reduce the hazard. 

V. Validation of Models. Another hindrance to code official acceptance of engineered 

structural fire protection is the lack of data to validate the models and assumptions made by 

the engineers. Sophisticated programs and modeling techniques are available and can be 

used by the engineer to calculate, for example, whether or not a certain component of a 

structure will fail given a specific fire in a specific room configuration. For the glasdsteel 

bridge in Seattle City Hall, the engineer used a computer program to model the spread of heat 

fiom the fire source through the open lobby area up to and across the ceiling where the 

structure is attached. However, the results of engineered structural fire protection have not 

been tested in real-life situations enough (if at all) to assure the code official the solutions will 

really work, as opposed to working in a computer program or in a limited, controlled test. 

The three fires discussed in the introduction are the ‘only major fires in modem highrise 

buildings resulting in any kind structural damage. From an overall societal standpoint, this is 

good news. However, these fires are not tests of engineered solutions, but of the prescriptive 

code provisions, and so do not contribute to any sort of validation of fire engineering 

methods. In fact, it can be argued that the prescriptive solutions met the performance goals 

discussed above-one only collapsed after seven hours of uncontrolled burning, and the other 

two did not collapse at all despite long fire exposures. Based on the performance of these 

buildings, many code officials will prefer to rely on the tested prescriptive solutions than on 

theoretical and unvalidated engineered solutions. 

The lack of data to validate models also means factors of safety are unknown. Structural 

engineering uses factors of safety ranging from 1 ?4 to 6 to account for uncertainties in loading 

or material properties. When a fire protection engineer shows the code official a particular 

beam will not be affected by a particular fire, the code oficial does not know if there is any 

sort of safety factor built in to the engineer’s analysis to account for uncertainties in the 

design fire or the structural materials. Even if the engineer does provide a safety factor, there 

is no standard to guide the code official as to what factor is appropriate. 

FURTHER STUDY 

In my view, the challenges discussed above must be addressed before research on specific issues 

will be usefbl. Without the standards, research provides data, but not information to the code 

official. Once the code oficial is willing to use hidher judgment, he/she needs a standard basis 

on which to manage the risk of his/her decisions. As a possible model for engineered structural 

fire safety, here are some examples that may be used in seismic design by structural engineers 

that attempt to address these same challenges. 

67 
Issue 

Performance Standard 

Design Event 

t 

Model Validation 

Factor of Safety (examples) 

Notice that there are several levels of performance standards, depending on the design event, and 

even the most extreme design, while based on a remote event, is not based on the largest, worstcase event. This is a concept that I have not seen in the engineered structural fire safety proposals 

presented to the DCLU. 

Structural Engineering Example 

Collapse prevention in a major event. Local collapses may 

occur, but global collapse does not. 

Life safety in a moderate event. Building may be heavily 

damaged, but occupants can evacuate the building. 

Light damage in minor event. Limited to cosmetic and minor 

non-structural damage only. 

Major event: Earthquake with 2% chance of exceedance in 

50 years (1 in 2500 year event) 

Moderate event: Earthquake with 10% chance of exceedance 

in 50 years (1 in 450 year event) 

Minor event: Earthquake with 50% chance of exceedance in 

Tested several times a year by Mother Nature 

Specific structural components: Varies with materials used 

for construction. Ranges from 2 to 6 or more. 

Global overturning: 1.5 

50 years (1 in 100 year event) 

Once the code officials and fire protection engineers can come to an agreement as to what are the 

appropriate standards, design events, models, and factors of safety, then there two areas of 

research that would have been helpful to DCLU in evaluating the proposals in the four-examples 

above: 

1. Effectiveness of fire sprinkler system protection of structures. As discussed in the challenges 

above; sprinklers are a primary component in any engineered structural fire safety design 

presented to DCLU. Usually, they end up as adding some extra safety factor as part of the 

“belt and suspenders” approach. However, a preliminary request was made on the Fred 

Hutchinson building to use sprinklers to “wet” the columns supporting the stairs, walkways, 

and roof in the atrium, in lieu of providing code-required 3-hour rated protection. DCLU 

raised many objections to this concept, and ultimately, the architect provided an approved 

intumescent paint for protection, hidden by some architectural finishes. However, for the 

expected fuel load in the atrium, it is probable the sprinklers would have been adequate. 

There is a question, though, about how far this concept can be pushed. Further research is 

also required on the reliabili~ of sprinkler systems if they are to be used as the sole source of 

protection of structures. 

2. Validation of computer models of heat releasekpread. DCLU approved the Seattle City Hall 

glass bridge on the basis of such a model, as discussed above, and similar models have been 

used to justify other engineered fire safety designs (not necessarily structural). 

68 
CONCLUSION 

Engineered structural fire protection is increasingly being utilized as an option to prescriptive 

code requirements for protection of steel structures. As a result, code officials first are in need of 

guidance as to the standards by which the engineering solutions can be evaluated. Second, in 

order to raise the confidence level of code officials in engineering solutions, research is needed to 

validate the models used by the engineer as justification for deviating from the prescriptive code. 

Once those have been developed, the philosophical barriers still need to be overcome, but at least 

the fire protection engineer is dealing from a sound technical basis. Technical research can then 

be guided by the standards. 

REFERENCES: 

“First Interstate Bank Building Fire, Los Angeles, California,” Technical Report Series; United 

States Fire Administration 

“Highrise Ofice Building Fire, One Meridian Plaza, Philadelphia, Pennsylvania, ” Technical 

Report Series; United States Fire Administration 

“World Trade Center Building Performance Stu+ ”, Chapter 5; Federal Emergency Management 

Agency 

Uniform Building Code TM; International Conference of Building Officials 

ICC Performance Code for Buildings and FacilitiesTM; International Code Council 

Building Construction and Safety CodeT* (NFPA 5000TM); National Fire Protection Association 

69 
White Paper 2 

The Need for Structural Fire Safety Design Methods 

An Architect’s Perspective - The Who, What, Where, When and How of doing fire safety 

design. 

David S. Collins, FAIA 

A premise: Most of the public assumes that there is structural fire safety involved in the design 

of most major buildings. Do we actually understand the risks we face each time .we walk into a 

building or structure? The architect’s role in development of construction documents and the 

subsequent process of making a building that is safe and will remain safe has varied over time. 

Our understanding, and by that I mean the entire construction industry’s understanding, of the 

necessary level of fire safety and the means to design to achieve it isn’t absolute, nor is it as clear 

as most of us would like. 

A standard of care: The typical approach to frre safety design in virtually 100% of major 

projects constructed today is to rely heavily on a standard of care that has been established 

through the model building codes. That standard has been an evolving, moving target which 

responds relatively rapidly to changes in technology and materials development, largely fueled by 

the materials or systems manufacturing communities, and even responds to disasters with or 

without adequate justification. 

Examining the earliest standards, we know that the value was placed on the ability of the builder 

to adequately deliver the project that the owner wanted. The penalties for the lack of 

performance were rather severe, and were simply aimed at the collapse of the structure. An 

interesting part of Hammurabi’s Code is the admonition to the fire fighter to not take any property 

while fighting the fire. 

If fire break out in a house, and some one who comes to put it out cast his eye upon the 

property of the owner of the house, and take the property of the master of the house, he shall be 

thrown into that self-same fire. 

Registration laws throughout the United States and much of the world put the responsibility on 

the design professional that they approve to be responsible for designing buildings and structures 

in a safe and sanitary manner. Even the building regulatory system recognizes this approach by 

referencing “referenced design professionals” directly into the codes. 

However, there is a prevailing attitude within our culture that anyone may build or modify his 

own home without the benefit of a design professional. The statistical results might point out the 

fallacy of that attitude. Unfortunately, many of the laws have reinforced this and enforcement 

allows anyone to build their own home with or without the expertise to determine what is 

necessary or even what is needed. There is little wonder that when these same persons are 

working in positions of responsibility within corporations and businesses that they may also take 

a rather cavalier attitude toward the elements of a building structure that may be vital to saving 

their lives or the lives of the employees and customers that may be in the space. 

70 
Later in this paper I will discuss the issues that further compound the design professional’s 

inability to actually determine whether their original design is carried out, leaving to question if 

there is a valid system for delivery of safe structures. 

There is typically a team involved in the design of any project. In the simplest of them, the team 

may be the architect and the owner making all the decisions. Other more complex projects may 

involve large numbers of consultants. Focusing only on active fire protection systems, the team 

may use a consultant, or even a system vendor to assist in the decision making process. The level 

of involvement and ability to influence the design decisions depend largely on the scope of the 

project and the ability of the owner and team leader to see the need for added participation. 

ARCHITECTURAL TEAM 

Non-Structural 

Consultants - Fire Safety, Sprinkler Designer, Sprinkler Installer 

Structural 

Manufacturers - DOW, 3M 

Agencies - UL, Warnock Hersey 

Associations - AISVAISC, PCAPCI, Gypsum Association, NF&PA 

Structural fire resistance is almost exclusively based on the standards within the code and the 

specifications of the materials provided in the listings. There is very little to guide the designer in 

making a choice of materials or methods except for the information provided by the specific 

manufacturer and the various agencies that may also be a part of the manufacturer’s product 

approval process. Compounding the problems for designers is a confusing network of jargon 

associated with various materials and the information that is provided with respect to the 

’ performance characteristics. 

For example, there are rules associated with performance of a structural member relating to the 

coverage of the reinforcement of the concrete beam or the thickness of coverage for the fire 

protected steel beam. The basis for measurement of the performance is the ASTM E 1 19 test 

procedure which has been under review and has received criticism from various materials 

interests for several years. Such debate raises questions in the minds of the designer and the 

specifier regarding the basis for their decision making. 

Building codes have also contributed to the level of confusion regarding the appropriateness of 

protection features. Terminology such as “fire-retardant”, “fireproof ’, “fire blocking”, “fire 

stopping”, “combustible”, “limited combustible” and “fire resistant” are used in various contexts 

to the point that ASTM E176 says that fireproof is “an inappropriate and misleading term” which 

was used (and still is today) to describe buildings of a certain characteristic. 

All too often the designer depends on the fire protection contractor to provide the necessary 

design document in order to obtain a building permit. This practice, in my opinion, is paramount 

to allowing the building contractor to design the building. Again, later in the paper the issues of 

delivery will be further explored. 

WHAT 

No standard existed in Hammurabi’s Code for the fire safety of a structure or the manner of 

building it except that the walls must be stable to prevent them from falling and killing the 

71 
members of the owner’s household. With the advent of modem building codes the creation of 

standards for fire protection came into play more and more. 

Earliest versions of the modem building codes we use today included both the passive and active 

fire protection features. The codes have vacillated between which of these systems is the more 

important to providing the level of safety felt to be appropriate. Hearings are held on a tri-annual 

basis to determine what changes are necessary to the codes to achieve what? 

This systematic process of review and modification could be seen as facilitating changes that 

aren’t necessary, but the reality is that a very high percentage of proposals never make it beyond 

being introduced for an initial hearing. At the recent International Code Council’s Committee 

meetings in Nashville, there were 598 changes considered to the building and fire codes that in 

some way would affect how buildings are designed. Of these changes, well over half were 

rejected by the committee. 

’ 

What are we hoping to achieve with constantly changing the standard of care we call a building 

code? 

WHERE 

We are accustomed to the environment we are working in where the need for fire protection is 

fairly well laid out in the model buildings codes. Other interests also may initiate additional 

requirements for protection due to the nature of the property being protected. Insurance 

companies will often ask for additional levels of protection in order to offset a perceived 

exposure. 

Various standards are in existence which is also usefbl to provide guidance for certain special 

types of facilities such as fireworks and explosives. Other conditions such as medical and 

environmental dangers are not as well explained or understood as part of the development of . 

safety features in building design. 

The codes tell us specifically the aspects of the structure that must be protected by passive means. 

Is there evidence to show that these means are inadequate for normal exposures? At a recent 

conference in Washington, DC, sponsored by the TISP (The Infiastrkture Security Partnership), 

the conclusion was that there was no need for such a change. 

. 

Perhaps one of the most difficult parts of the process of designing for fire resistance is in existing 

structure that are unpredictable. I have been involved in three major projects over the past five 

years that involved issues of the predictability of existing construction fire resistance parameters 

and fire safety design issues. 

0 Shillito Lofts Apartments 

Federal Reserve Bank 

University of Cincinnati Medical Sciences Building 

In each there were unique problems associated with the existing structure that’were major 

challenges to the design team now charged with retrofitting the buildings for ongoing use. 

WHEN 

Decisions regarding the use of materials and their application to create a fire resistive structure 

can come at any time during the preliminary design process. There are guides for such decision 

72 
making, which again leads us back to the building code as the font for all knowledge on the 

subject 

The AIA is involved with the development of MASTERSPEC" as a primary service to architects 

in preparation of their construction documents. Some interesting excerpts from that document 

include: 

Several methods, both active (sprinklers) and passive, are possible for protecting steel structures 

>om fire. Designing forjire protection might include dividing a building into is0 Iated modules 

with a limited number of penetrations forjire-rated doorways, electrical conduits, and ducts. 

Modules could be protected.. . . 

Specijic3re-resistance design decisions can aflect the cost, scheduling, and complexity of 

sprayed3re-resistive material applications. Careful design forf;re protection can avoid some 

common problems. For example, to forestall problems with warranty limitations and with the 

vulnerability of roof assemblies protected by applied sprayedfire-resistive materials when 

subject to construction, maintenance, or repair activities on the rooj roof- ceiling designs might 

be limited to those assemblies protected by materials other than sprayed3re-resistive 

materials.. . . 

There is always the listed assemblies to fall back upon as the most easy means of acceptance. 

A general outline of the specification section from MASTERSPEC* on sprayed fire -resistance 

materials would include the following: 

General 

Related documents 

Summary 

Definitions 

Submittals 

Qualifications 

Delivery, storage, and handling 

Project conditions 

Coordination 

Warranty 

Products 

Manufacturers 

Concealed sprayed fire -resistive materials 

Exposed fire-resistive materials 

Exposed foamed magnesium oxychloride fire-resistive materials 

Exposed intumescent mastic fire-resistive coatings 

Auxiliary fire-resistive materials 

Execution 

Examination 

Preparation 

Installation, general 

Installation, concealed sprayed fire-resistive materials 

73 
Installation, exposed sprayed fire -resistive mat4erials 

Field quality control 

Cleaning, protecting and repair 

HOW 

The methods by which the contracts are executed are often the most important part of the entire 

process fi-om my perspective. AIA has taken positions on the various means of delivering 

designs. Following this section are various statements regarding those methods and the federal 

governments documents for securing design services as well as the ABA's model procurement 

procedures. 

Generally, the procedures follow one of the following procedures. 

0 Qualifications based Selection 

Fee Based Selection 

Methods of Delivery 

Design Bid Build 

0 Design Build 

0 Multi Prime Contractors 

0 Construction Management 

0 Quality Control 

0 Value Engineering 

Bibliography: 

The American Institute of Architects - http://www.aia.org 

The Infi-astructure Security Partnership - http://www.tisp.orq 

The American Institute of Architects Public Policies: 

Government Procurement: ArchitectEngineer Selection 

Government Procurement: Project Delivery 

Position Statement: Design/Build 

Position Statement: Design/Bid/ Build 

United States Code 

TITLE 10 - ARMED FORCES ' 

TITLE 41 - PUBLIC CONTRACTS 

Federal Acquisition Regulation Part 36- Selected Provisions on Two-Phase designBuilding Selection Proceuder4es 

The American Bar Association - http://www./abanet.orpl 

Model Procurement Code for State and Local Governments 

74 
White Paper 3 

Framework for Structural Fire Engineering and Design Methods 

Gregory G. Deierlein & Scott Hamilton 

Stan ford University 

PREFACE 

This paper was developed for the NIST/SFPE workshop to develop a National 

R&D Roadmap for Fire Safety Design and Retrofit of Structures. The scope is to 

review overall methodology aspects of structural fire engineering within the 

context of design methods, procedures and standards for structural engineering, 

including probabilistic and risk aspects. Many sources of material were reviewed 

in preparing this paper, only a portion of which are formally referenced in the 

paper. Other sources, which are not specifically referenced, but are useful 

background are listed in the bibliography 

INTRODUCTION 

In the broad scheme of things, structuraZ$re engineering encompasses only a small but essential 

aspect of fire protection engineering and risk management. By definition, structural fire 

engineering should involve close coordination between fire protection engineers and structural 

engineers, but this has not generally been the practice in the United States. Instead, requirements 

for structural fire protection are largely handled through prescriptive building code provisions, 

which are often employed under the architect’s scope of work. There are other reasons for the 

lack of coordination. Compared to other structural loadings, fires are usually not a primary 

structural design consideration, except for instances where fire considerations impose constraints 

on the design, such as relating to the choice of structural materials for high hazard facilities or 

minimum thickness of floor slabs for thermal barriers. Moreover, as compared to other design 

loads, the life safety and economic losses due to fires are usually governed by “non-structural” 

considerations (smoke, burning of contents, egress, etc.) where the structural response is not a 

major factor. This is in contrast to most other load effects (gravity, wind, earthquake), where the 

losses begin with the structural response, Le., where excessive structural deformations or collapse 

will precipitate events that lead to significant economic losses, injuries, and potentially casualties. 

In these cases, the external hazards (the loads) are largely pre-determined, such that the only way 

to affect performance is through structural design. In fires, on the other hand, there are many 

factors associated with fire ignition, suppression, fuel loads, compartmentalization, etc., which 

can be altered through fire protection engineering that affect the imposed risk (through fire loads) 

on the structure. This is illustrated in Figure 1, where the topic “provide structural stability” is 

one of many “leaves” in the fire safety concepts tree. Indeed, one of the important incentives for 

performance-based building codes is to tailor structural fire protection requirements based on 

other measures taken to reduce the chance of structurally significant fires. 

75 
In terms of overall economic and life-safety risks, the “optimum” structural performance targets 

for fire conditions should be considered relative to other risks and overall cosvbenefit 

considerations. Assessment and design procedures 

for structural fire engineering should permit 

alternative approaches to achieving the desired 

safety, which has the potential to dramatically 

change current practice. Evidence, which will be 

cited later, suggests that for certain construction 

types and occupancies, structural risks from fire are 

considerably smaller than from other hazards. Thus, 

in some cases, it may be appropriate to relax 

structural fire requirements from current practice, 

provided that one can quantify and demonstrate the 

benefits of such changes. The first priority for 

research and development should be to develop 

procedures, models and criteria to assess 

performance in terms of meaningfhl economic and 

life-safety metrics. The next priority would then be 

to develop minimum building code requirements, 

considering relative risks to other hazards and 

codbenefits of alternative fire protection measures. 

Ideally, the performance framework should inform 

rather than mask fire risk management decisions. 

Risk is often conceived of as the probability or 

likelihood of an event coupled with the 

consequences resulting from that event. However, 

translating this general concept of risk into a 

quantifiable methodology is not straightforward. In 

particular, how one defines the “event” and 

“consequences” depends upon ones perspective. In 

NRE SAFETV CONCEPTS TRE 

.’ -1 

t 

Manzge ?ire impacf 

4 4 

Manege axposed 

peIsons and property 

I I 

Provide mute I’ 

I I I 

I 

I 

I 

Figure 1 - Conceptual framework for fire 

safety (Buchanan 2001) 

the most general sense, the event of interest should be the likelihood fire ignition with the 

consequences being injuries, deaths, and economic losses resulting from fire. Alternatively, from 

the standpoint of structural frre engineering, the “event” could be conceived of as excessive 

structural deflections with the “consequences” being breach of a barrier between fire 

compartments. While this general concept of risk can help guide the discussion, the risk 

framework needs much more specificity to articulate and quantify the many events and 

consequences that make up fire engineering. Ideally, the framework will permit one to achieve 

desired outcomes of reduced risk through alternative means, e.g., providing the means to trade-off 

measures that affect the likelihood of a structurally significant fire (e.g., use of sprinklers) against 

other measures to limit the impact of such a fire (e.g., thermal insulation of structural members). 

Indeed, this is is one of the motivations behind the ICC Performance Code (2001). Quoting from 

the User’s Guide to this code, “Under prescriptive codes, the typical failure rates of systems are 

sometimes compensated for by requiring redundancy. One of the perceived advantages of a 

performance based design is that it might allow the designer to minimize redundancy in order to 

achieve efficiency by increasing the reliability of the systems and/or strategies used to implement 

the design.” (pg. 119, ICC 2001). 

Performance-based engineering and standards should ultimately enable more transparent and 

direct assessment of risks, which in turn will lead to more informed and effective risk 

management. This goal, however, is not equally recognized or embraced by all those working on 

76 
performance-based engineering. To many, performance-based engineering simply represents the 

move away from prescriptive design requirements to ones that are more scientifically based. This 

view is particularly appealing to researchers (including the author) interested in developing and 

applying technologies to simulate structural response to extreme loadings. Simulation 

technologies are an essential part of performance-based engineering, however, they are only part 

of the overall goal to provide a methodology that can inform risk decision-making. An equally 

important challenge to performance-based methods is the development of statistical data and 

models to characterize hazards and uncertainties throughout the entire process - from the fire 

hazard through to the consequences of fire. Quantification of risk should be in terms of 

parameters or metrics that can inform the relevant decision makers, including building owners, 

building code oficials (representative of society at large and emergency responders), insurance 

and finance organizations, and other stakeholders. 

Overview of Paper Organization: With the objective to contribute to establishing an overall 

framework for performance-based structural fire engineering, this paper is structured along the 

following lines. First, the key structural behavioral effects and design parameters associated with 

fires are briefly reviewed. These effects, along with models and criteria to assess them, will be 

dealt in greater detail in other papers at the workshop. The discussion here is intended to set the 

stage for this paper’s main emphasis on a methodology for performance assessment and design. 

Second, the issue of “acceptable risk” is discussed, with the objectives to first consider how to 

phrase the question of risk and then look at fire risks relative to the failure probabilities implied 

by current practice for other structural loadings. Third, the concepts of the International Code 

Council’s proposed Performance Code (ICC 200 1) are summarized and discussed. Next, and 

perhaps most central to this paper, a comprehensive framework for performance-based structural 

fire engineering is introduced. The proposed framework is modeled after a comparable 

framework for performance-based earthquake engineering under development by the Pacific 

Earthquake Engineering Research (PEER) center. Apart ftom providing a methodology for codes 

and standards development, the framework provides an effective means to organize research for 

developing the data, models and criteria necessary for implementing the framework. Following 

the presentation of the detailed methodology, some concepts are proposed to envision adaptations 

of the framework for simplified design provisions appropriate building code implementation. 

Included is some discussion of design approaches taken by the Eurocodes and recent initiatives of 

the Americaq Institute of Steel Construction. Finally, the paper concludes with a summary of 

recommendations for research and development priorities. 

BEHAVIORAL EFFECTS AND DESIGN PARAMETERS 

Fire effects on structures primarily have to do with structural response of materials, members and 

systems under high temperatures that occur during a “structurally significant” (post-flashover) 

fire. An accurate structural fire assessment will generally require information describing the time 

history of elevated temperatures in all of the structural members and the applied gravity loads. 

Temperature distributions in the structural members are, in turn, a hnction of (a) the fire 

compartment(s) temperatures, often described through a time versus temperature curve, (b) 

spreading of the scenario (or design basis fire) to adjacent compartments through convection and 

or destruction of compartment boundaries, and (c) heat transfer models to relate temperatures in 

the compartment to those in the structural members and connections. Generally speaking, the fire 

temperature response can %e calculated independently of the structural response, with the 

77 
exception of cases where excessive structural deformations or collapse lead to breaching of’fire 

barriers and fire spread and growth. 

The basic effects of high temperatures on steel and concrete are thermal expansion, reduced 

stiffness (elastic modulus), and reduced strength. In addition, concrete may be subject to 

temperature induced cracking and spalling, which depend on the build up of internal pressure 

associated with the formation of water vapor from inherent moisture and whether the vapor can 

be dissipated. Studies of high strength concrete (50 to 120 MPa) have shown it to have a higher 

rate of strength loss under high temperatures and more susceptibility to spalling due to higher 

cement paste density (Buchanan 200 1). 

ACCEPTABLE RISK 

In debating minimum standards for structural safety, the establishment of an “acceptable risk” 

level will invariably arise. Though relevant to the issues in performance-based codes, phrasing 

the issue in terms of “acceptable risk” can be more distracting than it is helpful. In a report on 

organizational and societal considefations for performance-based earthquake engineering, Peter 

May (a political scientist at the University of Washington) writes, “The notion of acceptable risk, 

while common in engineering, is one of the more disputed notions within the risk literature 

itself.” (May 2002). Quoting risk scholar Baruch Fischhoff, May goes on to note, “Many debates 

turn on whether the risk associated with a particular configuration of a technology is acceptable. 

Although these disagreements may be interpreted as reflecting conflicting social values or 

confused individual values, closer examination suggests that the acceptable-risk question itself 

may be poorly formulated.” 

May argues against attempting to establish “acceptable risk” in an absolute sense, because this 

approach is not consistent with how risk management decisions are made. Rather than focusing 

on what risk is “acceptable”, May argues that development of performance-based guidelines and 

standards should emphasize tools and strategies to evaluate risk in a manner to permit the 

stakeholder to make informed choices about how to manage the risk. The question of “acceptable 

risk” should be recast into a “discussion of desired safety goals, the costs involved of achieving 

these, and the trade-offs imposed”. Thus, the “challenge is not only one of assembling collective 

views about safety but also of effectively communicating the trade-offs in attempting to achieve 

different levels of safety”. 

While heeding May’s caution not to become pre-occupied with defining what the “acceptable 

risk” is, it is nonetheless useful to contrast structural fire safety risks with those implied by 

current building codes and standards for other hazards. 

Gravity loads and wind: In a recent reassessment of wind loading provisions, Ellingwood and 

Tekie (1999) propose matching the strength limit state under combined gravity and wind loads to 

the implied safety under gravity loads. As a basis, they use provisions developed in about 

twenty-five years ago (Galambos et al., 1982; Ellingwood et al., 1982; Ravindra & Galambos, 

1978), which established the still current ASCE 7 (2003) gravity load combination of 1.2D + 

1.6L and design resistance factors for steel structures (AISC-LRFD 1999). They report the mean 

annuaIprobabiIity of failure (UaPf) under dead and live loads to be approximately UaPf= 

0.0007 (7 x 1 04), where “failure” is defined as the strength limit state associated with exceeding 

the nominal plastic yield strength of a structural member. Their proposal for a new gravity plus 

78 
wind load combination (1.2D + 0.5L + 1.6W) targets a comparable failure rate (MAPf= 0.0007). 

The specific load factors are chosen to result in a failure probability of (0.0007) where the 

nominal wind load is based on wind speeds with a roughly 500-year recurrence interval 

(approximately 0.002 mean annual probability of exceedence). The difference between the wind 

load probability and the failure probability is the result of the load factors, the statistical 

combination of three loads (D, L and W), and the resistance factor applied to the nominal 

strength. Their load combination recommendation has since been adopted into ASCE 7 (2003). 

Earthquakes: The target failure probability under combined gravity loads and earthquakes is 

more difficult to quantify due to-the assumptions regarding dynamic inelastic behavior that are 

built into the earthquake loading and design provisions. Given the fact that the earthquake risk to 

buildings is dominated by the earthquake hazard, a first-order approximation to the failure 

probability implied by current codes is the return period associated with “maximum considered 

earthquake” under which structures are not expected to collapse. Roughly speaking, the 

“maximum considered earthquake” used as the basis for ASCE 7 (2003) is based on a 2,500 year 

return period, which translates to an annual probability of exceedence of 0.0004 (4x IO-‘). While 

this is about half the failure probability associated with the gravity and wind load fimits, one must 

remember that the definition of “failure” is different in this case. For earthquakes, the target 

performance under the maximum considered earthquake is structural collapse, as opposed to the 

yielding limit state used to evaluate failure probabilities for other loads. Thus, in terms of overall 

structural collapse, the associated failure probability for gravity and wind loads is probably less 

than that for earthquakes. 

. Nuclearpowerplants: Another reference point to gage minimum performance targets are the 

failure rates for nuclear power plants - an area which as received significant attention and 

scrutiny. The target safety goal for standards of the Nuclear Regulatory Commission are based 

on a mean reactor core damage probability of IO-’ per year from all causes (Cornel1 2003). Using 

as the design basis and earthquake hazard recurrence rate of I 0-‘, the expected failure rate from 

seismic effects is estimated at 

gravity and wind load limit states and 0.0004 for collapse under earthquakes), the reactor core 

failure target from all events is about four to seven times less, and the failure target fiom seismic 

effects is about 40 to 70 times less. One should be cautious about making a literal comparison of 

these rates, since the definitions of “failure” are different for each situation, and the standards 

applied in design and construction are more stringently controlled for nuclear power facilities. 

Nevertheless, the comparisons provide some basis to evaluate what is deemed “acceptable”. 

Comparing these to the figures cited above (0.0007 for 

Fire: How do the limits mentioned above compare to the structural risks due to fire? In a paper 

looking at load factor combinations for fire, Ellingwood and Corotis (1 99 1) cite a mean annual 

probability of a structurally significant (flashover) fire in modern office buildings of about IO? 

This is based on an assumed mean annual ignition probability of IO-‘ for a 100m’ office building 

and a conditional probability of flashover given ignition of IO-’. They go on to propose a load 

combination for combined gravity and fire effects, which reduces the probability of failure by 

another order of magnitude - down to MAP’ = IO-’, which is generally held to be the minimum 

threshold for perceiving risks. The proposed load combination of 1 .OD + 0.5L + 1 .OF (where F 

denotes the fire-induced effects) represents the “arbitrary point in time” gravity loads, with a 

mean annual exceedence probability of about IO-’. Similar criteria to this are used in ASCE 7 

(2002) for design against “extraordinary events” (e.g., blast or fire) with assumed mean annual 

probabilities of occurrence of I 0-6 to IO? 

79 
Risk Informed Deckbn Making: Taken at face value, the statistics cited above indicate the 

probability of occurrence of a significant fire occurring is roughly one to two orders of magnitude 

less than the probability of structural failure for other hazards. Thus, one might conclude that the 

structuraZ fire hazard is a non-issue. This is in stark contrast to current practice, where structures 

are designed to resist the rare structurally significant fire events. The obvious question is, why 

should one design against a hazard with such a low probability of occurance relative to other 

significant hazards? In light of the comments made previously about “acceptable risk”, the point 

here is not to attempt an answer to this question. But it is important to raise this question, since 

the notion of “risk informed” and “risk consistent” decision-making is central to the gains to be 

realized through performance-based design. 

There are many arguments one can make for and against using calculated risk to argue for 

changes in current practice. Complicating these discussions is the fact that the risk argument 

would suggest relaxing current practice, which in light of September 11 is contrary to the 

direction of public sentiment on fire safety. Without going into great detail, the following are 

some factors to consider in advancing risk-informed decision-making: 

0 Accuracy of failure probabilities: To have any credence, failure probabilities need to be 

backed up with solid data and verifiable models to quanti6 all significant aspects of the 

fire safety problem, from the likelihood of fires through to evaluation of their 

consequences. This is a key challenge throughout performance-based engineering 

methodologies and technologies. 

0 Identzfiing stakeholders and their interests: Collective consensus on minimum safety or 

other issues, requires that the key constituencies be identified and their concerns voiced 

in a productive manner. Firefighters, for example, will not necessarily see their 

individual risk mitigated by a low probability of the occurrence of a significant fire, as 

compared to the structural performance given a fire. 

Communication of risk andperformance metrics: Measurements of risk and performance 

need to reflect the ways that stakeholders relate to risk. For some stakeholders, a 

rigorous probabilistic presentation (i.e., mean annual probabilities or expected values) are 

appropriate, whereas for others, scenario descriptions would be more effective. 

Benefit-cost tradeofls: Risk decisions are best made in the context of considering tradeoffs of benefits and costs, For example, increasing the risk of one consequence may be 

considered acceptable if it results in reductions of other risks or improvements in other 

performance, e.g., trading off fire insulation of a steel frame in favor of sprinklers and 

improved alarms to detect and suppress the likelihood of a fully developed fire. 

Quality and assurance in design, construction and operations: Performance-based 

design solutions often involve increased reliance on predictable and reliable performance. 

For structural fire engineering this could range from accurate calculations of fire loads 

and heat transfer in design to reliable operation of fire suppression equipment. Thus, 

80 
acceptance of the calculated risk will often require increased trust in the process of 

design, construction and operation. 

Comprehensive assessment of performance and consequences: A common dilemma in 

developing building code provisions concerns the tradeoff between crafting general 

provisions that are practical to apply versus provisions that are best tailored to a specific 

situation. As a result, building codes tend to emphasize a “one size fits all” approach, 

which are too conservative in some cases and not conservative enough in others. One can 

imagine, for example, that in setting minimum failure probabilities for structural collapse, 

one would need to know the consequences of collapse. To some extent, codes address 

this through the designation of building “use groups” or “performance groups”. Ideally, 

performance-based approaches should articulate performance metrics that will provide 

more accurate and comprehensive measures of performance in terms of a common set of 

metrics related to safety (injuries and casualties) and economic losses. 

INTERNATIONAL CODE COUNCIL’S - PERFORMANCE CODE 

Building code provisions can generally be considered to serve three basic purposes. First, the 

codes articulate minimum standards and criteria by which buildings should be designed and 

constructed. Implied by these minimum requirements are desired levels of performance for 

hnctionality and safety. Second, the codes and underlying specifications establish the 

responsibilities and limits of liability between the various parties (e.g., design professionals, code 

officials, manufacturers, and contractors) involved in the design and construction. For example, 

ASTM material testing standards provide a basis upon which the design engineers, material 

manufacturer, and contractor share a common view of the properties of a specified construction 

material or product. Third, the codes and standards provide a compendium of validated models 

and criteria for designing to meet the implied performance. 

Current building codes have evolved in a way that has not clearly distinguished between these 

three different purposes, the result being that the performance targets implied by the codes are not 

apparent through the maze of specified procedures and prescriptive design requirements. This is 

particularly true for fire and earthquake engineering, where the underlying phenomena and 

science are so complex that, until quite recently, prescriptive “deemed to comply” provisions 

provided the only practical way to do routine design. The difficulty is that much like legacy 

software code, which was originally designed with a simpler purpose in mind, building codes and 

standards are being challenged to the point that a major overhaul is needed. 

81 
The ICC Performance Code (ICC 2001) outlines a new fiamework that articulates the 

performance intent and design standards through a hierarchical organization of (a) performance 

objectives, (b) hctional statements, and (c) performance requirements. Shown in Table 1 is a 

conceptual representation of acceptable performance targets, where the performance target 

(describe in terms of mild, moderate, high or severe damage) is specified as a fbnction of building 

performance group (occupancy and function for a facility) and the magnitudeflikelihood of hazard 

events. The basic concept is to accept more severe damage under less frequent hazard events in 

less important buildings. This table is an adaptation of one originally developed with earthquake 

hazards in mind (SEAOC Vision 2000), and the representation is not as well suited to structural 

fire engineering - the main reason being that significant fires tend to be binary events as opposed 

to the continuum hazard implied by the vertical column in the table. Nevertheless, this graphic 

provides a concise way to characterize the basic performance tradeoffs in risk decision-making. 

Following below are some specific 

details and discussion of the ICC 

Performance Code (200 1) related to 

structural fire performance. 

ICC - General Requirements: The 

following is a summary of some 

general performance and riskacceptance concepts proposed in the 

ICC Performance Code approach: 

Performance Group Risk 

Factors: These are factors to 

articulation the risk to . 

occupants in a facility, taking 

into account the nature of the 

hazard, the number of 

Table 1 - Maximum level of tolerable damage based on 

performance group and design hazard event (ICC 2001). 

PERFORWCE W4U€#PS i 

building occupants, the length of time the building is normally occupied, whether or not 

people sleep in the facility, familiarity of the occupants with the facility layout and means 

of egress, the vulnerability state of the occupants (particularly with respect to ability to 

egress). Risk to the occupants, together with the importance of the facility’s function to 

the community, are used to establish the performance group of a facility between use 

group I, 11, 111, or IV. Note that the performance group categories are geared toward 

minimum life safety considerations and, with the possible exception of Category IV 

(essential facilities), do not consider economic loss issues. 

0 Structural Performance: Structural performance of facilities is distinguished between 

four levels, which are characterized as follows: 

o Mild - no structural damage, safe to occupy, comparable to what FEMA 356 

(2003) would classiQ as “immediate occupancy”. 

o Moderate - moderate but repairable localized structural damage, some delay in 

re-occupancy, major nonstructural systems operational, low likelihood of life 

loss, and very low likelihood of multiple life loss. Structure will retain nearly all 

pre-hazard event strength and stifiess. 

o High - Significant structural damage, but no large falling debris. Repair is 

technically possible, but may not be economical with significant delays in re82 
0 

Load Type 

Wind 

Floods 

Snow 

occupancy. Significant nonstructural damage, including light debris and 

disruption to egress. Injuries locally significant with risk to life, but moderate in 

numbers. This might be considered comparable to what FEMA 356 terms “life 

safety”. 

Mean Return Period of Loads (approx. mean annual probability) 

Small Medium Large Very Large 

50 yr (0.02/yr) 75 yr (0.0 I3/yr) 100 yr (O.OI3/y) IOOyr (O.OI3/y) 

100 yr (0. Ol/yr) 500 yr (0.002/’) case specific case specific 

Severe - Substantial structural damage, but no collapse. Significant degradation 

in strength and stiffness in lateral system, large permanent deformation, and more 

limited degradation to vertical system. Structure is not safe to re-occupy, and 

repair may not be technically possible, Significant risk to life may exist, and an 

additional event (such as an earthquake aftershock) could cause collapse. This 

state is similar to the FEW 356 designation of “collapse prevention”. 

Earthquake 

ICC - Structural Stability: On the topic of structural Stability, Chapter 5 of the ICC states the 

objective, “To provide a desired level of structural performance when structures are subjected to 

the loads that are expected during construction or alteration and throughout their intended life. 

(pg. 19, ICC 200 l).” The jhctional statements make additional general statements to the effect 

that the structural design should limit the threat to life safety, injury protection, and 

property/amenity protection to levels consistent with Table 1. The performance requirements 

state that structures “shall remain stable and not collapse during construction or alteration and 

throughout their lives” and “shall be designed to sustain local damage, and that structural system 

as a who shall remain stable and not be damaged to an extent disproportionate to the original 

local damage” (the latter point addressing the issue of progressive collapse). Note that these 

functional statements are very explicit in stating that structures “shall not collapse” and do not 

make any mention of probabilities or uncertainty. On the other hand, performance requirements 

on functionality provide more latitude through statements such as, structures “shall have a low 

probability of causing damage or loss of amenity through excessive deformation, vibration or 

degradation .” 

25 yr (O.O4/yr) 72 yr (O.OI4/’) 475 yr (0.002/y) 24 75 yr (0.0004/yr) 

Specific reliability levels for “shall not collapse” and “low probability” are left ambiguous, except 

by specified relations between the expected load magnitudes (small, medium, large, and very 

large) and anticipated mean return periods. These are summarized in Table 2, along with a 

conversion fiom mean return period to mean annual probabilities of exceedence. A literal 

comparison of Tables 1 and 2 (e.g., the expectation of severe damage under very Zarge loads for 

Performance Group 11) indicates that the implied damage return periods varies dramatically by 

load type, suggesting need for more explicit thinking about failure probabilities for load effects 

and their combinations under extreme events. Fire loading is absent from this list of loads and 

specified return periods in the ICC Performance Code, although fire and other extreme loadings 

(blast, wind borne debris) are cited as considerations for design. 

83 
ICC on Fire Performance: The users guide to the ICC Performance Code acknowledges that the 

relationships between magnitude of event and level of damage given in Table 1 are not 

appropriate for fire loads for the reason mentioned previously. The code also expresses the view 

that the life safety risks from fire should be less than for other loads. Quoting from the Users 

Guide, “Generally, society has a very low tolerance for death or serious injury caused by fires, 

especially in larger numbers in a single incident.” (pg. 13 1, ICC 200 1). Whether or not one 

agrees with this statement is a topic for discussion. However, the ICC Performance Code uses 

this sentiment as justification to establish a single life-safety performance level of mild impact for 

all fire events. Referring back to Table 1, this implies performance criteria required for fires 

equal to that associated with small and frequent events for wind, earthquake and other loads listed 

in Table 2. 

Specific criteria concerning fires and fire safety appear in other chapters of the ICC Performance 

Code. Highlights of those provisions most directly associated with structural fire are summarized 

below: 

Limiting Fire Impact and Fire Impact Management (Chapters 6 & 17) 

Objective (1701.1): “TO provide an acceptable level of fire safety performance when 

facilities are subject to fires which could occur... during construction or alteration and 

throughout the intended life” 

Functional Statements (I 701.2): “. . .design with safeguards against the spread of fire so that 

no person not directly adjacent to or involvedin ignition of a fire shall suffer serious injury or 

death from a fire and so that the magnitude of property loss is limited as follows:” 

Performance Group I - High Damage 

Performance Group II - Moderate Damage 

Performance Groups II & IV - Mild Damage 

The hctional statements also stipulate that, “Buildings and facilities shall be designed 

and constructed so that the firefighters can appropriately perform rescue operations, protect 

property, and utilize fire-fighting equipment and controls.” 

Performance Requirements (1 701.3): “Facilities . . . shall be designed, constructed, and 

operated to normally prevent any fire from growing to a stage that would cause life loss or 

serious injury ... Facilities shall be designed to sustain local fire damage and the facility as a 

whole will remain intact and not be damage to an extent disproportionate to the original local 

damage” 

Structural members and assemblies (I 701.3.11). “Structural members and assemblies shall 

have a fire resistance appropriate to their hnction, the fire load, the predicted fire intensity 

and duration, the fire hazard, the height and use of the building, the proximity to other 

properties or structures, and any fire protection measures” 

Magnitude of fire event (I 701.3.15). 

ignition, growth and spread potential of fires and fire effluents that could occur . . .” “Design fire events shall realistically reflect the 

Engineering analyses of potential $re scenarios (I 701.3.15.3). “Quantification of the 

magnitudes of design fire events shall be based on engineering analyses of potential fire 

scenarios that can be expected to impact a building throughout its intended life . . .” 

84 
Relationship of design $re to tolerable damage. “When determining (assigning) the 

magnitude of a design fire event, the physical properties of the fire and its effluents shall 

only be considered in terms of how they impact the levels of tolerable damage.” 

Safety Factors. “Design fires and fire scenarios shall be chosen to provide appropriate 

factors of safety to provide adequate performance by accommodating for the following 

factors: 

1. Effects of uncertainties arising fiom construction activities 

2. Variations in the properties of materials and the characteristics of the site. 

3. Accuracy limitations inherent in the methods used to predict the fire safety of the 

building. 

4. Variations in the conditions of facilities, systems, contents and occupants.’ 

Emergency Responder Safety (Chapter 21) 

Objective: “To protect emergency responders from unreasonable risks during 

emergencies.’’ 

Functional Statements: “. . . protect against unanticipated structural collapse.” 

Performance Requirements: “ Buildings and structures shall be designed, constructed, 

loaded and maintained so that the potential for structural collapse is predictable based on 

the construction method, building condition, and fire size, location and duration.” 

Regarding this performance requirement, the ICC User’s Guide (pg. 173, ICC 200 1) 

notes, “The committee realizes that it is neither economically feasible nor even realistic 

to design and build structures and facilities in such a manner that collapse or failure could 

be eliminated in every instance regardless of the incident circumstances. 

Observations on ICC Fire Provisions: The ICC Performance Code outlines a reasonably good 

framework to describe the minimum acceptable performance criteria; however, there is clearly 

room for discussion and refinement as to what the performance the criteria should target. In 

particular, one can question that blanket assertion regarding the public’s risk tolerance for fire and 

the requirement that structures be designed for “mild impact” for all fires. Statements made in 

later sections of the code, such as the discussion of safety factors under fire management and 

safety of emergency responders, seem more realistic in their performance expectations, given the 

low probabilities and large uncertainties associated with severe fires. Beyond providing a basic 

framework to describe minimum acceptable Performance, the current version of the code does not 

provide much specificity on methods and criteria to assess performance. As such, there is 

considerable room for research and development to move the code from its present form to the 

stage of implementation in design practice. 

PERFORMANCE-BASED METHODOLOGY FRAMEWORKS 

85 
In many respects, the challenges faced with performance-based fire engineering are similar to 

those of performance-based earthquake engineering. Hazards in both cases are low-probability 

high-consequence events, quantification of which involves complex nonlinear behavior with 

considerable uncertainties. As such, current design methodologies for both earthquakes and fire 

rely on prescriptive semi-empirical techniques, which do not offer information to inform risk 

management decisions and may not provide cost-effective design solutions. 

Considerable progress has been made over the past ten years to develop performance-based 

approaches for earthquake engineering and fire protection engineering; although, for a variety of 

reasons, these developments have largely occurred separately in the structural (earthquake) 

engineering and fire protection engineering communities. In spite of this, the development of the 

performance-base approaches share many features, beginning with a more scientific definition of 

the hazard and accurate simulations of the structural response to that hazard. One of the 

persistent challenges in both arenas is to develop strategies for translating descriptions of 

structural response to meaningful performance measures for risk management and stakeholders. 

Since one of the goals of structural fire engineering is to integrate it more into the mainstream of 

structural engineering, it is proposed to consider structural fire engineering in the context of a 

performance-based earthquake engineering methodology that is gaining acceptance among 

structural engineers. The following discussion begins with an overview of a methodology for 

earthquake engineering that has developed over a number of years, most recently through 

concerted efforts of the Pacific Earthquake Engineering Research (PEER) Center and the FEMA 

ATC-58 project. These latest efforts build on concepts that were first envisioned for seismic loss 

assessment on a regional scale (e.g., HAZUS) and for performance assessment and design of steel 

buildings (e.g., see Cornel1 et al. 2002 for the probabilistic underpinnings of the assessment 

procedure in the FEMA-SAC Guidelines). Following a brief overview of the methodology for 

earthquakes, a complementary approach for fire engineering is proposed. 

Performance Framework for EARIWQUAKE Engineering: As outlined in Table 3, the 

proposed fiamework for performance-based earthquake engineering characterizes the 

performance assessment process into four steps, each of which emphasizes a different discipline 

focus. Data between each step is organized into four generalized variables, defined as Intensity 

Measure, Engineering Demand Parameters, Damage Measures, and Decision Variables. 

Unambiguous articulation of these variables is key to the framework organization. 

86 
TABLE 3: ATTRIBUTES OF PBEE (I 

VARIABLE 

IM 

IM-+EDP 

DM+DV 

DISCIPLINE 

seismology & 

geotechnical 

engineering 

structural & 

geotechnical 

engineering 

structural, mech. 

& elec. engrg.; 

construction; 

architecture; 

loss modeling 

construction & 

cost estimating; 

loss modeling 

ARTHQUAKE) METl 

PARAMETERS 

fault location 

type and length of 

rupture (magnitude of 

event) 

sitehoil conditions 

foundation and 

structural system 

dynamic mass & 

damping 

... 

deformation sensitive 

component fragilities 

(walls, beams, 

columns) 

acceleration sensitive 

component fragi 1 ities 

(equipment, contents) 

occupancy 

time of earthquake 

post-eq recovery 

resources 

ODOLOGY 

EXAMPLES 

PGA, PGV 

Aires intensity 

... 

story drift 

floor accelerations 

component forces 

& deformations 

... 

component 

strengtwde formatio 

n limits 

damage (repair) 

states 

hazards (falling, 

blocked egress, 

chemical release, 

etc.) 

collapse 

fatalities 

direct $ losses 

repair 

time/downtime 

The Intensity Measure (IM) describes the seismic hazard at the building site in terms of a seismic 

hazard determined from a probabilistic seismic hazard analysis considering the seismologic 

parameters summarized in Table 3. Current practice is to define IM in terms of spectral 

acceleration for the first mode period of the structure, Sapl), which relects important aspects of 

the ground motion amplitude and frequency content. However, alternative IWs are sometimes 

used, such as peak ground ground velocity (PGY). The best IM is one that best reflects the 

damaging features of earthquake ground motions, i.e., those aspects of the ground motion which 

correlate best to the resulting building response and damage. Determination of IM is largely in 

the discipline of engineering seismology. For routine design, the IM’s are codified in the form of 

hazard maps, which are incorporated in building codes and standards; whereas, for unique or 

important structures, the IM’s would be determined from a site-specific hazard analysis. 

Given the ground motion intensity, the next step is to conduct structural analyses (static or 

dynamic inelastic analyses) to simulate the building response and determine the Engineering 

Demand Parameters, EDPs. The EDPs are response measures that can later be related to Damage 

Measures (DM), which describe the consequences of the response. Two common EDPs are peak 

interstory drift ratios and floor accelerations; other more localized EDPs include element forces, 

hinge rotations and generalized strains. The DMs quanti@ the damage and consequences of the 

damage as they affect cost of repairs, safety, and other considerations. For example, DMs for 

87 
architectural wall partitions include relationships between peak inter-story drifts (the EDP) and 

damage states ranging from minor (hairline cracking, requiring spackling and painting of walls), 

moderate (replacement of some wallboards, taping, spackling and painting) to severe (demolition 

and full wall replacement). DMS for structural elements may describe similar damage states, in 

addition to the impact of the damage on the performance of the overall structural frame. DMS for 

building contents and equipment may relate to damage and the consequences of damage, such as 

hazards posed by toppling heavy equipment or hazardous chemical release. 

Given a full description of the damage state through the DMS, the final step is to quantify 

Decision Variables (DVs), which express the performance in terms relevant to the owner and 

other stakeholders. The DVs include risk of casualties (deaths and serious injuries), direct dollar 

loss (repair costs and lost inventory), and downtime (duration of repairs). Recognizing the large 

uncertainties in each step of the performance evaluation, the DV. are described in a probabilistic 

sense, as an annual mean rate of exceedence or alternative metric that describes the uncertainties. 

For example, the direct dollar losses could be described as the mean annual probability that the 

direct dollar loss exceeds a percentage of the replacement cost of the facility; mathematically, this 

can be expressed as O(DY) = O(doZlar Ioss > PA replacement cost). An alternative would be to 

express the DV in terms of a scenario, e.g., given the occurrence of an earthquake of magnitude 

M on a nearby fault., there is a Y% confidence the direct dollar loss will not exceed X% of the 

replacement cost. 

Underlying the proposed methodology is the recognition of there being significant uncertainties 

and variability in each stage of the process. Thus, descriptions of each variable and the models 

relating them should be formulated to include both the characteristic value (e.g., a mean or 

median response) and the uncertainty associated with each quantity. Based on the total probability 

theorem, uncertainties in the assessment process are tracked through the following framework 

equation: 

A(DV) = Ilk;cDVI DM) dG(DM1 EDP) dG(EDP1IM) dA(IM) 

where the term G[DV IDMj' represents the conditional probability that DV exceeds a given value, 

conditioned on DM; dG[DM IEDP] is the derivative of the conditional probability for DM with 

respect to EDP; and similarly for dG[EDPIIMJ The last term on the right, dO@w, is the 

derivative of the seismic hazard curve, which defines the mean annual frequency (MAF) of 

exceeding a specified IM, e.g., a 0.002 U4F (or 10% in 50 year chance) of exceeding a specified 

spectral acceleration level. 

The form of Equation (1) implies that the intermediate variables (OMS and EDPs) are chosen 

such that the conditional probabilities are independent of one another and conditioning 

information need not be carried forw&d. This implies, for example, that given the structural 

response described by EDP, the damage measures (DMS) are conditionally independent of the 

ground motion intensity (IM), Le., there are no significant effects of ground motion that influence 

damage and are not reflected in the calculated EDPs. The same can be said about the conditional 

. independence of the decision variables (DV) from ground motion IM or structural EDP, given 

G(DylDA4). Likewise, the intensity measure (IM) should be chosen such that the structural 

response (EDP) is not also further influenced by, say, magnitude or distance, which have already 

been integrated into the determination of dil(IW. Apart from facilitating the probability 

calculation, this independence of parameters serves to compartmentalize discipline-specific 

knowledge necessary to evaluate relationships between the key variables. 

88 
Performance Framework for FZm Engineering: Much like performance-based earthquake 

engineering, performance-based fire engineering is based on the premise of achieving 

performance goals set by various interested parties-owners, regulators, code officials, society, 

etc. As noted by Custer and Meacham (1997), despite the various efforts and huge volume of 

research world wide, to date there is not a single, generally accepted framework, for performancebased fire engineering. It is therefore proposed, that the aforementioned methodology for 

earthquake engineering provides a generic framework to model the various aspects and 

complexities of performance-based fire engineering as well. The overall goals would be the same 

as in performance-based earthquake engineering, i.e., the ability to relate design decisions to 

quantifiable risk assessment of life safety and economic factors. Note that the framework itself 

does not dictate specific target risk levels, rather the focus is only on a methodology to evaluate 

the risks in a scientifically quantifiable way. 

Summarized in Table 4 is a framework for performance-based fire engineering, which is 

analogous to the earthquake-engineering framework in Table 3. Items listed in the table focus 

mainly on the structural engineering aspects of fire engineering, but the general framework is 

envisioned as extendable to the broader concerns of fire protection engineering. A key feature of 

this fiamework is separation of the performance-assessment into four unique processes, where 

information between the processes is described unambiguously in terms of the four general 

variables, IM; EDP, DM and D?? As with the earthquake framework, one of the motivations of 

this approach is to clearly articulate the role of the various professional disciplines and the 

handoff of information from one discipline to another. 

Referring to Table 4, the first step is a probabilistic fire hazard analysis, which culminates in the 

probabilistic definition of a fire intensity measure, IM. For structural fire engineering, the 

obvious IM would be a description of temperatures in the structural members. However, 

alternative measures such as maximum compartment temperature or normalized heat load are 

other candidate I.s. For the purposes of probabilistically characterizing the uncertainties in IM, 

it is preferable for the primary IM hazard variable to be a scalar quantity (e.g., maximum 

temperature), as opposed to a vector of multiple variables (e.g., maximum temperature plus time 

to maximum temperature). One might envision that the internal temperatures are described by a 

probabilistically determined characteristic maximum temperature, supplemented by descriptions 

of the spatial (and perhaps temporal) temperature gradients throughout the structural members. 

As summarized by the parameters in Table 4, calculation of the temperature depends on the 

likelihood of a flashover fire and characterization of the compartment gas temperature 

(compartment geometry and boundary materials, he1 load, and ventilation) and heat transfer into 

the structural members (thermal insulation, thermal mass, structural configuration, etc.). An 

example of the process by which one could develop a probabilistic fire ZM hazard curve 

(expressed in terms of material temperature) are presented later. As with IMs to characterize 

earthquake hazards, one could imagine codified ways to determine the structural temperature IM 

in several ways - ranging from tabulated values for certain classes of building occupancies and 

configurations, to parametric fire curves, or by case-specific assessment by fire scientists and 

engineers. 

89 
PROCESS 

m 

m 

.A 

a 

4 

TABLE 4: Attributes of Probabilistic PBFE (fire) Methodol. 

VARIABLE 

IM 

IM+EDP 

EDP+DM 

% 

d 

.& 

m 

i4 

DISCIPLINE 

Fire science and 

fire protection 

engineering 

structural 

engineering 

Structural and fire 

prot. engineering; 

construction; 

architecture; 

loss modeling 

construction & 

cost estimating; 

risk assessment; 

loss modeling 

PARAMETERS 

- likelihood of 

structurally significant 

fire (plume, preflashover, & post 

flashover ) 

compartment geometry 

and thermal properties 

- ventilation 

- he1 load & burning 

rate 

- fire insulation 

- structural 

configuration and fire 

exposure 

- structural model 

- fire scenario & steel 

temperature 

distribution 

- steel mechanical and 

thermal properties 

- applied gravity loads 

- damage fiagility 

curves af smoke and 

thermal barriers 

- damage fragility 

curves of structural 

components 

- collapse hazard 

(either local, global, or 

progressive) 

- occupancy 

- hazardous contents 

- alarms and egress 

efficiency 

- fire 

duratiodendurance 

- external risk factors 

(e.g., impact on 

neighboring buildings) 

- ... 

EXAMPLES 

maximum steel 

temperature 

compartmentgas 

time-temperature 

curve 

load ... normalized heat 

component 

forces 

inelastic 

deformations 

deflections 

... 

strengthlimit 

states 

structural 

damage (repair) 

states 

barrierbreach 

local or global 

collapse 

casualties 

(occupants, first 

responders) 

direct $ losses 

repair duration & 

downtime 

Given the maximum steel temperature (IM) and guidance on likely fire scenarios (e.g., 

distributions of the steel temperatures among various compartments, various steel members, and 

gradients through members), structural engineers can then perform analyses to determine the 

effects of thermal expansion and degradation of material properties on EDP demand measures, 

90 
such as induced memberkonnection forces, deflections, and inelastic deformations. The EDPs 

are next related to DMs, such as the impact of structural deformations and induced forces on the 

structural elements and firelsmoke barriers. Note - it should be emphasized that the present 

discussion and parameters in Table 4 are limited to structural fire protection - a subset of the 

broader issues related to fire endurance of the barriers themselves and other fire protection and 

egress systems in the building. 

Finally, information from the DAh is next used in loss modeling and risk analyses to determine 

the DVs. In terms of life safety (casualty) risks, this would include the risk to building occupants 

from (a) smoke/fre, associated with breaches in the fire barriers and blocked egress, and (b) 

injuries fiom local or global structural collapse. Risks to emergency responders relate more to 

risks from structural collapse, although sudden breach of major barriers also presents a life safety 

risk to emergency responders. The two other DVs related to economic consequences (repair costs 

and associated downtime) can likewise be determined from the DMs. 

An important feature of the comprehensive evaluation, from EDPs through to DVs, is that it 

provides generalized performance metrics that feed directly into quantitative risk assessment, 

thereby avoiding the need for ad-hoc judgments to relate the structural performance to the 

consequences. For example, current building codes typically differentiate fire insulation 

requirements for buildings based on the building height and floor area to account for the 

consequences of a structural collapse. In moving towards performance-based approaches, the 

goal should be comprehensive approach provides for consistent evaluation through to the final 

decision metrics, whereby the end result is a direct measure of consequences (e.g., probabilistic 

measure of fatalities, injuries, or economic losses). One would not want to, for example, apply 

advanced models and data to evaluate likelihood of collapse, only to then resort to ad-hoc 

judgments of the consequences of the collapse (e.g., to decide how much more unacceptable is 

the collapse of a two, ten, or twenty story building). 

Implementation of the proposed methodology will require models and data to calculate the 

necessary parameters. Further, since the intent is to rigorously account for the many uncertainties 

in the process, the models and data should be formulated so as to provide the conditional 

probabilities required for Equation (1). These conditional probabilities should account for both 

intrinsic variabilities in the underlying data and phenomena (aleatory variability) and those 

associated with lack of data or modeling simplifications (epistemic uncertainties). Although not 

comprehensive, many of the major parameters that would need to be considered are listed in 

Table 4. 

Evaluation of Fire Intensity Measure: To demonstrate the process of evaluating the fire hazard 

IM in the performance-methodology, the following discussion example is presented to determine 

the maximum temperature in a steel beam. In terms of Eq. 1 (the total probability equation), the 

goal is to define X(IM), i.e., a ‘‘fire hazard curve” which describes the mean annual probability of 

exceeding a specified steel temperature. Calculation of A(1M) can be broken down into the 

following equation, which is another application of the total probability equation: 

A(IA4) = [IdG (IM I F0))dG (FO I F)A(F) 

where, h(F), is the probability of ignition, dG[FO IF] is the conditional probability of flashover, 

given ignition, and dG[IM IF01 is the conditional probability of the steel reaching a certain 

temperature, given flashover. The integrations of Eq. 2 imply taking account of all possible fire 

event scenarios and the uncertainties in all aspects of the problem. Data for the last two terms of 

Eq. 2 are available from a number of sources (e.g., Buros 1975, Ellingwood 1991, CIB 1983); in 

91 
this example the following values are assumed P(F0IF) = 1x10-2 and P(F) = 8.1~10~. As 

ignition and flashover are discrete (binary) events, the integrations involving F and FO turn out to 

be simple multiplications to give MP[FO] = 8 x lo". The remaining discussion treats the 

conditional probability of the steel temperature, given flashover, i.e., dG[IM I FO]. 

Assuming flashover has occurred, calculation of the resulting steel temperature (Zw is based on 

fire duration, fire gas temperature in a compartment, heat flux imposed upon the inside surfaces 

of a compartment, or enclosure boundary, and heat transfer into the steel member. These in turn 

are based on the processes of the fuel consumption, the ventilation rate, and the heat transfer 

process. Fuel consumption and the ventilation rates are based on the type of fuel, amount of fuel, 

distribution of fuel, geometry of compartment, ventilation area and shape, and the thermal 

characteristics of the compartment boundaries. Components of heat transfer are geometry of 

compartment, ventilation area and shape, and the thermal characteristics of the compartment 

boundaries. Clearly, it is dificult, if not impossible to precisely quantify all of these variables - 

hence, the motivation to describe the variables and the resulting structural material temperature in 

a probabilistic sense. 

1000 1 I I I I I I 

0 30 60 90 120 150 180 210 240 

Figure 2 - Time versus temperature relationship for fue 

compartment gases and steel beam (unprotected and insulated) 

As show in Figure 2, a standard way to calculate steel temperature is through a two-step process - 

the first involving calculation of gas temperature in a compartment, and the second the steel 

temperature from the gas temperature. Given the time dependency of both processes, the 

calculations are interconnected. This interconnection is the primary reason for choosing the steel 

temperature, rather than gas temperature, as the IM. Otherwise, had gas temperature been chosen 

for the scalar IM, we would have been faced with the need to estimate the maximum steel 

temperature with only information about the peak gas temperature (as opposed to the full time 

versus gas temperature relationship). 

The compartment gas temperature can be modeled using a parametric fire equation, such as one 

from Appendix A of Eurocode 1 (equation A.l, ECS 2001), where the gas temperature is given as 

92 
a function of a variable that accounts for ventilation, enclosure properties, fuel load, and other 

parameters related to fire activation and growth (equations A.2 to A.12 of Eurocode 1). 

Parameters, which have a significant outcome on the results (e.g., ventilation, fuel load, and 

enclosure properties), are specified as random variables, where the mean values are based on 

characteristic values for the specific structure, combined with coefficients to describe the 

variability. In some cases, data are available to describe the random variables, e.g., Eurocode 1 

includes data to describe the fire load in terms of a Gurnble distribution. However, for most 

variables probabilistic descriptions are not generally available, which presents an important 

research and development need to apply the probabilistic model with confidence. 

Using the compartment gas temperature, the next step is to calculate the steel temperature using a 

standard heat transfer equations, which take into account any insulation on the beam. Key 

variable parameters in these equations include (a) the ratio of exposed surface area to volume of 

the steel member, (b) thermal convection and emissivity coefficients, (c) insulation thickness, 

specific heat, and thermal connectivity of insulation - each of which can be probabilistically 

described with characteristic (mean) values and variability coefficients. As with the gas 

temperature calculations, there is a need for more complete characterization and reporting of 

statistical properties of key parameters. 

Models and random variables for the gas temperature and heat transfer can be combined and 

evaluated through Monte Carlo simulation or other reliability methods. Shown in Figure 3, is an 

example of the resulting steel temperature (134) curve that would result fiom the process just 

described. This specific example shown is of a W24 steel beam in a typical office building 

(Hamilton et al. 2002). The result of the Monte Carlo analysis is used to determine the 

conditional probability, dG[IM IFO], which is the probability of reaching a specified maximum 

steel temperature (Tvte,l = IM) given the gas temperature curve associated with flashover, FO. 

The conditional probabilities are related to the mean annual steel temperature hazard curves for 

an unprotected and protected beam shown in Fig. 3 by integrating (or in this instance multiplying) 

dG[IM (FO] with the probabilities of ignition and flashover. 

There are a number of interesting observations to note from Figure 3. First, the combined 

probabilities of ignition and flashover result in a probability of a flashover fire of 5 x AT5, which 

is in itself quite low relative to other structural hazards mentioned before. Further reduction in 

probabilities below this point (i.e., the sloping of the temperature hazard curves) reflect the 

Figure 3 - Hazard curve for maximum steel temperature (maximum steel temperature 

versus mean annual probability of exceedence) 

93 
variations of assumed fire load in the Monte Carlo analyses. Second, assuming a “critical design 

temperature” of about 54OoC (when the strength and stiffness of steel drops to about half its 

original value) we see that the probability of the unprotected beam reaching this temperature is 

equivalent to the probability of flashover, whereas for the protected beam, the insulation reduces 

the probability of reaching this temperature by about an order of magnitude. Thus, from a risk 

perspective, the cost of the fireproofing would be judged against the perceived benefit of reducing 

the probability of reaching the critical temperature fiom about lo‘’ to lo6. An additional factor 

not apparent in these numbers is that the unprotected beam reaches the critical temperature in 

about 35 minutes versus about 100 minutes for the protected beam. 

Finally, certain stakeholders, such as first responders, are likely to view risk performance not in 

terms of the total probability, but rather, from the standpoint that a flashover fire has already 

occurred. This would imply disaggregating the O(Iw hazard into the pre- and post-flashover 

components, and processing the downstream calculations for EDP, DM and DV independently of 

the I34 probability. Referring back to Eq. 2, this can be handled by setting P(FOIF)P(F) = 1, 

which essentially would shift the vertical intercept of the fire hazard curve in Fig. 3 to be 1. Here 

the role of themal insulation would be to reduce the probability of the beam reaching its critical 

temperature fiom 1 to 0.1. 

Evaluation of EDP-DM-Dk Given the maximum steel temperature hazard, as described by the 

A(I@ fire hazard curve of the type shown in Fig. 3, the next step would be to calculate the effect 

of the increased temperature, together with other simultaneous loads, on the structure. This step 

entails structural analysis, the output of which would be EDPs (see Table 4), including 

deflections, forces and inelastic deformations in member and connections, and indices for local 

and/or global collapse. Following the probabilistic fiamework equation, Equation (l), the 

analyses should be conducted to describe the demand parameters (response quantities), 

conditioned on the maximum steel temperature, resulting in the conditional probability 

relationship dG(EDP( IW. The variability in this step results from assumptions regarding 

member temperature distributions, structural modeling assumptions, gravity load magnitudes and 

distributions, and material properties at elevated temperatures. Thus, given the maximum steel 

temperature (scalar fire IM), one must still make choices regarding the distribution of 

temperatures through the member, the distribution throughout a compartment, and the 

distributions in adjacent compartments. 

Analyses relating IM (steel temperature) to EDP (response), can either be simplified component 

based analyses or comprehensive nonlinear analyses. The type of analysis will affect the choice 

of EDPs. A simplified component analysis would consist of calculating the member forces and 

deflections (the EDPs) for the specified temperature and mechanical loading. These would then 

be related to performance criteria, described in terms of discrete damage measures (DW. For 

example, do the imposed member forces exceed the strength calculated at the elevated 

temperature, thereby suggesting the onset of local collapse? What are the deflections, which may 

cause damage to adjacent fire barriers? If warranted, a more detailed and in depth nonlinear 

analysis of the entire structure could be performed, which explicitly models nonlinear 

temperature effects (thermal strains and degradation of material properties). For comprehensive 

analyses, emphasis would be to track performance via the deflections and inelastic deformations, 

e.g., permanent sag, or displacement of beams, local buckling of members, or runaway 

deflections - the latter signifying the onset of local or global collapse. 

Once the EDPs are determined, DMs can be calculated, reflecting damage to structural elements 

and thermal barriers, and the life safety and economic implications of this damage. A significant 

94 
difference between earthquake and fire damage concerns the relationship of nonstructural to 

structural damage. In earthquakes, essentially all damage to structural and non-structural 

components (and building contents) can be related to the structural motion (deformations and 

accelerations). This is not the case for fires, where most of the nonstructural and content damage 

is due to heat and other fire load effects, which are related to but distinct from the heat induced 

structural deformations. Thus, the most important aspects of the structural DM evaluation (DMs 

caused by structural EDPs) are likely to be those associated with (a) life safety implications of 

structural forces and deformations imposed on nonstructural heavsmoke barriers from the 

structural frame, (b) localized failures in a fire affected region that lead to progressive collapse, 

and thereby impose life safety and economic losses much larger than those caused by the fire 

itself, and (c) permanent inelastic damage to structural components and systems, which impact 

post-fire repair costs. 

ISSUES IN CODIFYING PBFE DESIGN PROVISIONS 

The methodology just described is intended to outline a rigorous assessment method, which is 

based on detailed simulation of the fire growth, heat transfer, structural performance, and 

consequences of the performance. Obviously, such a detailed methodology would not be applied 

routinely in design; but, rigorous methodologies of this sort are important for developing and 

calibrating simplified methods and criteria .for engineering practice. Equally important, the 

detailed breakdown of the assessment into its constituent parts provides a systematic way to 

organize research and development necessary to develop the data and technologies necessary to 

do accurate assessments. 

There are a number of ways that the detailed procedures could be simplified for codification in 

design standards, while preserving important features of a performance-based approach. For 

example, much in the same way that load and resistance factors are applied to establish limit state 

checks with a defined probability of exceedence, so too might such methods be applied to target 

specified limit states or performance points for structural fire engineering. As noted previously, 

Ellingwood and Tekie (1 999) have proposed gravity load combinations for use in conjunction 

with a fire analysis. They assumed the fire loading and associated limit state as extreme events, 

and hence they limited their consideration to uncertainties in the gravity load effects. A more 

complete methodology, would take a account of the statistics and models for fire ignition, growth, 

and heat transfer to develop temperature intensity hazard information, such as discussed above. 

Codified procedures could be developed to include load and resistance type factors (partial safety 

factors) on the fire temperatures and structural resistances to target specified failure probabilities. 

Such procedures could be modeled after an approach described by Cornel1 et al. (2002), which 

determines factors of this sort for a simplified probabilistically based assessment for steel 

structures under earthquakes. 

RESEARCH AND DEVELOPMENT NEEDS 

Listed below is a summary of research and development needs to hrther the development of 

performance-based assessment and design procedures for structural fire engineering. Many of the 

needs related to validated models and data, which should be envisioned to determine both 

characteristic values supplemented by appropriate uncertainty measures and statistics. The 

modeling needs and format should be clearly formulated ahead of time in terms of inputloutput 

variables, so as to fit into the overall performance assessment methodology. 

95 
Methodology Development: Much work is needed to further develop and refine the 

methodology framework proposed herein to organize data, models, and criteria into a 

consistent methodology to' apply for the assessment of fire hazards on structures. The 

framework should be one that relates to models and approaches common to the structural 

engineering and fire protection engineering communities. The methodology should 

establish language and terminologies, with clear definitions to facilitate information 

sharing between disciplines. One approach would be to adopt the four general terms 

proposed for performance-based earthquake and fire engineering (IM, EDP, DM and 

DO, and to describe these in very specific terms within the context of structural fire 

engineering. Early research on the methodology should investigate significance and 

sensitivity of the outcome to model parameters, so as to guide research needs on 

validated models (see next item). 

0 . Validated Models: 

o Fire IgnitiodFlashover: Probabilistic models, statistics and criteria to characterize 

risk of fire ignition and flashover as a fbnction of occupancy, construction 

type/quality, fire suppression systems, and other salient features of buildings. 

Models should be scientifically based, and to the extent possible should reflect clear 

cause-effect relationships between the input parameters and the fire risk. 

Mechanisms should be developed and put in place to continually track and update 

these models as a function of recorded fire events. 

o Compartment Temperatures: Validated models, statistics and criteria timetemperature compartment temperatures as a function of (a) fire load (combustible 

materials), (b) ventilation, (c) size and geometry of compartment, (d) thermal 

properties of the compartment enclosure, (e) fire suppressiodfire fighting, and other 

salient compartment characteristics. Parametric curves in the Eurocodes are a good 

starting point, but these should be examined and validated based on US construction. 

o Multi-compartment fire scenarios: Validated models and approaches to quantify 

multi-compartment fire scenarios, accounting for such factors as (a) risk of 

simultaneous ignitions due to earthquakes or other outside influence, (b) intercompartment spread through compartment boundaries by convection, including the 

statistical probabilities of unanticipated openings in compartment enclosure (c) intercompartment spread through building facades, and (d) effectiveness and reliability of 

fire suppression measures. 

o Heat Transfer: Validated heat transfer models and data to relate compartment 

temperatures to temperatures in structural members. For steel framed structures, this 

should include data on common thermal insulation materials and heat transfer in 

beams cast integrally with concrete slabs or other heat sinks. For structural concrete, 

the models should describe temperature gradients through concrete and in embedded 

steel reinforcing, taking into account concrete cracking and the potential for spalling. 

o Structural Materials & Elements: Validated models to simulate performance of 

structural materials, members and subassemblies under high temperatures. Primary 

emphasis should be on materials and systems most common to construction, 

including structural steel framing, composite steel beam and composite deck floor 

systems, structural concrete with mild and post-tensioned reinforcement, and other 

structural construction materials at elevated temperatures. 

96 
o Simulation Models: Development and validation of computer modeling techniques 

for structural systems, taking into account three-dimensional large deformation 

response under temperature effects (thermal expansion plus material degradation). 

Validation could be through both comparisons to sophisticated finite element models 

and to selective large-scale system tests. 

Risk Decision-Making: 

o Articulation of safety and performance metrics. Determine appropriate decision 

variables (DVs) and metrics to describe fire performance to key decision makers. 

o Risk Communication and Perception: Investigate and implement ways to 

communicate risk to key stakeholders, with an emphasis on relative risk and costbenefit decision making. 

o Educational materials and guidelines to help inform building code officials, 

owners, insurers and other stakeholders about structural fire hazards and the 

benefits and costs of alternative strategies to manage risk. 

Building-Code Implementation: Proactively pursue the development and implementation 

of building code provisions, along the lines that has been done for earthquake 

engineering. Involve appropriate professional organizations (ASCE, SFPE, SEA, ATC), 

industry groups (AISC, ACI, fire protection industry), practitioners and researchers 

involved in structural and fire protection engineers, and key stakeholder groups (building 

code officials, fire safety officials). 

REFERENCES 

AISC-LRFD (1999>, Load and Resistance Factor Design Specification for Structural Steel 

Buildings, AIS C, Chicago. 

ASCE (2002), Minimum Design Loads for Buildings and Other Structures, SEIIASCE 7-02, 

ASCE, Reston, VA. 

Buchanan, A.H. (200 l), Structural Design for Fire Safe@ Chichester: John Wiley & Sons, Ltd. 

Burros, R.H., Probability of Failure of Buildingfrom Fire. Journal of the Structural Division, 

ASCE, 1975. lOl(ST9): p. 1947-1960. 

CIB W14. A Conceptual Approach Towards a Probability Based Design Guide on Structural 

Fire Safety. in CIB W14 Workshop ‘Structural Fire Safety”. 1983: Fire Safety Journal. 

Cornell, C.A., Jalayer, F., Hamburger, R.O., Foutch, D.A. (2002), “Probabilistic Basis for 2000 

SAC Federal Emergency Management Agency Steel Moment Frame Guidelines,” JSE, ASCE, 

128(4), pp. 526-533. 

Cornell, C.A. (2003), Personal discussion with G. Deierlein, August, 2003. 

97 
Custer, R.L.P. and B.J. Meacham, Introduction to Performance-Based Fire Safety. 1997: Society 

of Fire Protection Engineers. 260. 

Deierlein, G.G., H. Krawinkler, and C.A. Cornell (2003) A pame work for performance-based 

earthquake engineering. in 7th PaciJic Earthquake Engrg. Conference. Christchurch, NZ. 

ECS (European Committee for Standardization) 2001, Eurocode 1 - Actions on Structures. 

Brussels. 

Ellingwood, B.R., Tekie, P.B. (1 999), “Wind Load Statistics for Probability-Based Structural 

Design,” JSEJ ASCE, 125(4), pp. 453-463. 

Ellingwood, B.R., MacGregor, J.G., Galambos, T.V., Cornell, C.A. (1982), “Probability Based 

Load Criteria: Load Factors and Load Combinations,” JSE, ASCE, 108(5), 

Galambos, T.V., Ellingwood, B., MacGregor, J.G., Cornell, C.A. (1 982), “Probability based load 

criteria: assessment of current design practice,” JSE, ASCE, 108(5), 959-977. 

Krawinkler, H. A General Approach to Seismic Performance Assessment. 2002. Hong Kong 

ICC (200 1 ), Performance Codes for Buildings and Facilities, International Code Council, Falls 

Church, VA, 195 pgs. 

Kruppa, J. (2000), “Recent Developments in Fire Design,” Progress in Structural Engineering 

and Materials, J. Wiley & Sons, Vol. 2, pp. 6-15. 

. May, P. (200 l), “Organizational and Societal Considerations for Performance-Based Earthquake 

Engineering,” PEER 2001/04, Pacific Earthquake Engineering Research Center, Richmond, CA. 

(www.peer.berkeley.edu), 52 pg. 

BIBLIOGRAPHY (resources reviewed for preparation of this paper, but not specifically cited) 

Anchor, R.D., Malhortra, H.L., Purkiss, J.A. (1986), Design of Structures Against Fires, Elsevier, 

251 pp. 

Armer, G.S.T., O’Dell, T., Eds. (1997), Fire, Static and Dynamic Tests of Building Structures, E 

& F Spon, NY. 

ASCEISFPE (2003), Stanabd Calculation Methods for Structural Fire Protection, 

ASCEEEYSFPE 29-99, ASCE, Reston, VA. 

ASCE (19921, Structural Fire Protection, ASCE MmuaI No. 78, ASCE, Reston, VA. 

Bailey, C.G., I.W. Burgess, and R.J. Plank, Computer simulation of afill-scale structuraljke 

test. Structural Engineer, 1996. 74(6): p. 93-100 

Barry, T.F. (2002), Risk-Informed Perjiormance-Based Industrial Fire Protection, Tennessee 

Valley Publishing, Knoxville, ‘I”. 

98 
Brannigan, V .M. Fire Scenarios or Scenario Fires? Can Fire Safety Science Provide the Critical 

Inputs for Performance Based Fire Safety Analyses? in Sixth (6th) International Symposium. 

International Association for Fire Safety Science. 1999. Poitiers France: IAFS S. 

Bukowski, R.W. and V. Babrauskas, Developing Rational, Performance-based Fire Sa$ety 

Requirements in Model Building Codes, in Fire Safety Engineering in Pursuit of Performancebased Codes: Collected Papers. 1996, National Institute of Standards and Technology. p. 40. 

Council on Tall Buildings (1 992), Fire Safety in Tall Buildings, Eds. Sfintesco, D., Scawthron, 

C., Zicherman, J., McGraw Hill, 348 pp. 

Hamilton, S .R. (2003), Perjormance-Based Fire Engineering For Steel Framed Structures: A 

Probabilistic Methodology, Draft PhD Thesis, Stanford University. 

Hamburger, R.O., et al., A Practical Approach to Protecting Infiastructure. Modem Steel 

Construction, 2002.42(6): p. 55-57 

Harmathy, T.Z. (1 993), Fire Safety Design & Concrete, Longman Scientific, 4 12 pp. 

Martin, D.M. A Natural Fire Safety Concept for Buildings-2. in Second Cardington Conference. 

1996. Cardington, England: E. & F. N. Spon. 

Mehaffey, J.R. and T.Z. Harmathy, Failure Probabilities of Constructions Designed for Fire 

Resistance. Fire and Materials, 1984. 8(2): p. 96-104 

Ove Amp & Partners (2003), Strategy for Integrating Structural and Fire Engineering of Steel 

Structures, Draft report commissioned by the American Institute of Steel Construction. 

‘Conner, D. J., Structural Engineering Design for Fire Safeq in Buildings. The Structural 

Engineer, 1995. 73(4): p. 53-58. 

Pettersson, O., Magnusson, S-E., Thor, J. (1 976), “Fire Engineering Design of Steel Structures,” 

English translation by L.J. Gruber, Swedish Institute of Steel Construction, Stochholm, Sweden 

Robinson, J.T. and D.J. Latham. Fire Resistant Steel Design--The Future Challenge. in Second 

International Conference Design of Structures Against Fire. 1986. Birmingham, England: 

Elsevier Applied Science Publishing 

Shields, T.J. and G.W.H. Silcock, Buildings and Fire. 1987, Essex: Longman Scientific & 

Technical. 

Technical Committee 3, Model Code on Fire Engineering. 200 1, European Convention for 

Constructional Steelwork: Brussels. 

Vamvatsikos, D. and C.A. Cornell, Incremental Dynamic Analysis. Earthquake Engineering and 

Structural Dynamics, 2002.3 l(3): p. 491-5 14. 

Wang, Y.C. (2002), Steel and Composite Structures -Behavior and Design for Fire Safety, Spon 

Press, NY. 

99 
White Paper 4 

Relationship Between Structural Fire Protection Design 

and Other Elements of Fire Safety Design 

Craig Beyler 

Hughes Associates, Inc. 

Fire Science and Engineering 

INTRODUCTION 

Broadly stated, the goals of fire safety design are to limit life loss (both civilian and firefighter), 

property loss, and enterprise interruption costs. These goals are achieved by limiting the spread of 

fire and by limiting the extent of smoke and heat spread to people, building contents, and building 

systems. The general methods for controlling these hazards include passive fire protection, active 

fire protection, manual firefighting, detection and alarm, egress systems, smoke management 

systems, and contentdfmish control. 

Few of these fire protection methods act in only one way. For instance, active fire protection 

systems, like sprinklers, limit the spread of fire, limit the production (and hence spread) of heat 

and smoke, as well as detect the fire. Passive fire protection systems like firewalls are designed to 

limit fire spread, but also serve to limit smoke and heat spread, and facilitate firefighting. Even 

egress systems, like stair enclosures, function to limit the exposure of people to smoke and heat, 

while also playing a role in fire department access and safe staging for firefighting. Detection and 

alarm systems function to alert occupants, as well as the fire department. Smoke management 

systems provide people and property protection from smoke and heat, while facilitating 

firefighting. Contentdfmish controls limit the initiation and spread of fire within spaces, while 

lessening the severity of the fire exposure to passive fire protection features and limiting the 

challenge to active fire protection systems. The multiple roles of individual fire safety systems 

and the time-dependent interaction of these systems in defining the fire hazard and risk are the 

sources of the complexity in assessing fire safety performance. 

ELEMENTS OF EIRE SAF'ETY DESIGN 

To facilitate further discussions of the interaction of structural fire protection design with the 

other elements of fire safety design, each element of fire safety design will be reviewed for those 

less familiar with fire protection engineering practice. 

Passive Fire Protection 

Passive fire protection includes both the provision of fire resishce to structural elements and 

systems, as well as building construction features designed to limit fire spread. It is understood 

that in most buildings, many elements function both structurally and as a barrier to fire spread. 

The most common examples of this duel function are floor systems and bearing walls. 

Building elements are classified as structural fiame, bearing walls, nonbearing walls and 

partitions, floor construction, and roof construction. Each element classification has its own fire 

resistance rating requirements. There are many instances when characterizing structural elements 

is less than straightforward, and the value of making such distinctions is less than clear. Current 

100 
approaches to structural fire protection call for fire resistance ratings based on these 

classifications. 

In addition to the requirements for fire resistance ratings for structural elements/assemblies, 

limitations on building height and area, and requirements for horizontal and vertical fire barriers 

are called for in current regulations. The goal is to prevent the spread of fire beyond defined 

limits. In order to be effective, these barriers need to prevent the passage of flame, limit heat 

transfer, and must remain in place. In the latter regard, there is an additional relationship between 

limiting fire spread and structural fire protection, since excessive deflections in the structure can 

lead to loss of integrity of fire barriers against flame passage. If a fire barrier is built integrally 

with a structural beam, the deflection of the beam due to fire exposure can lead to damage to the 

integrity of the barrier. 

Active Fire Protection 

While in general, active fire protection includes any type of fire suppression system, for most 

buildings the automatic fire protection is provided by fire sprinkler systems. Most sprinkler 

systems are designed to control a fire to a limited area. Final extinguishment relies upon the 

intervention of firefighters. Sprinkler systems are hydraulically designed based upon one or more 

available water supply sources (e.g., municipal mains, elevated tanks, pumped storage). If the fire 

grows beyond the design capabilities of the supporting hydraulic system, then fire control is no 

longer expected. 

Detection and Alarm 

Detection and alarm systems are designed to detect the presence of a fire and communicate with 

building occupants and emergency services concerning the fire. Modern fire alarm systems 

should be thought of as a computer-based emergency monitoring and communication system. 

Smoke and heat detectors, valves, flow switches, fans, and emergency lighting are monitored. In 

the event of a fire, the system provides information to the emergency services and building 

occupants. The monitoring functions provide centralized information to emergency responders 

upon their arrival. Of course, detection and alarm systems do nothing themselves to suppress or 

mitigate fires. 

Smoke Management Systems 

These systems generally operate upon detection of a fire to control the movement of smoke 

within the building. These systems support safe evacuation of building occupants, limit heat and 

smoke damage, and support manual firefighting efforts. Most systems make use of the building 

WAC systems, though in single story warehouse and industrial facilities, natural vents that 

remove smoke through roof vents through the action of buoyancy are often used. In tall buildings, 

stairway pressurization systems are widely used to maintain smoke-free conditions within the 

egress paths and additional zoned areas of supply and exhaust are used to further limit smoke 

spread. 

Egress Systems 

Provisions are made in all buildings for safe means for occupant escape in the event of a fire. The 

exit pathways are bounded by fire rated construction and are often protected by smoke 

management systems. Emergency lighting is provided to support evacuation. The alarm system is 

an integral part of the emergency egress system, notieing occupants and, in some cases, 

managing the evacuation process. General design practice provides for multiple exit paths in most 

cases. 

101 
ContentdFinish Control 

Building and fire codes generally limit the contents and use of a facility based upon the 

occupancy of the building with the goal of limiting building use consistent with the provided fire 

protection. The use of combustible materials as wall linings is generally regulated. Fuel loads are 

not limited, but are assumed to be characteristic of the occupancy. These assumed fuel loads 

underlie the fire resistance ratings required by building regulations. 

Manual FireJighting 

The local fue department provides manual fire suppression and occupant evacuation support for 

all buildings. Some buildings or facilities provide an in-house fire brigade as the initial first aid 

firefighting. Support for firefighting operations generally includes hydrants and standpipe 

systems, with additional support fiom active, passive, detection and alarm, and smoke 

management systems for both firefighting and rescue operations. Whether the fire is limited by 

passive fire protection systems or controlled by automatic systems, the fire department is 

generally relied upon for the ultimate extinguishment of a fire. 

Each of these fire protection systems has a defined capability and finite reliability. Multiple 

systems work together to achieve fire safety and multiple means provide redundant capabilities to 

limit fire, heat, and smoke in the building. The recognition of finite reliability and the need for 

redundant design are the basis for the balanced design approach implicit in most codes. No single 

system should be relied upon solely to achieve fire protection objectives. 

INTEGRATION OF RATIONAL STRUCTURAL FIRE PROTECTION IN FIRE 

SAFETY DESIGN 

The required structural performance in fire will be determined by occupant egress, firefighting, 

and property protection considerations. However, the required resistance of the structure to fire to 

achieve these objectives will also be determined by the other means to limit or control the fire. In 

the current code requirements, these interactions give rise to what are known as trade-offs. The 

classic example of a structural fire protection trade-off is the lessening of hourly rating 

requirements if sprinklers are provided. Currently, such trade-offs are numerous and are 

introduced on an ad hoc basis with no firm foundation in terms of assuring equivalent or better 

performance. The performance of the basic requirements is not known and the effect of the tradeoff on performance is not determined. 

There are two levels at which rational structural fire protection design can be integrated with fire 

protection design. The first and most ambitious is through the implementation of an overall 

rational fire safety design method. The second and less ambitious method is to design rational 

structural fire protection to prevent structural collapse within the current code environment. Both 

approaches will be discussed here, beginning with the simpler approach. However, it is 

instructive to review the current basis and methods of assuring structural performance in fires. 

Current Structural Fire Protection Design 

The roots of the current method of protecting structures from fire date back over a century to the 

era of urban conflagrations and associated building collapses (AISI, 197 1). Building components 

and assemblies (floor assemblies, columns, bearing and nonbearing wall assemblies, penetration 

protection assemblies, door assemblies) are exposed to a standard fire exposure, assumed to 

represent the severity of natural fires. The standard test method, ASTM E- 1 19, uses a component 

or assembly with a length scale of roughly ten feet. Based on ad hoc structural and thermal test 

102 
endpoints, a fire resistance rating, in hours, is determined. No engineering data is generated fiom 

the testing. 

The required fire resistance rating is assumed to be determined by the fire load density alone (not 

ventilation or thermal properties of the boundaries), based on the 1920s work of Ingberg at NIST 

(then NBS). Required fire resistance ratings are set based upon the anticipated he1 load for the 

occupancy, as well as the height and area of the building. 

The current design method makes no use of modern structural analysis methods, of modem fire 

dynamics, or of modem heat transfer analysis. It assumes that the performance of a less than real 

scale component test is representative of real scale structural performance and ignores the central 

role of ventilation in compartment fire dynamics. Clearly, we can do better with little or no new 

science. However, there is a need to develop design methods, performance criteria, engineering 

data, and a code infrastructure to allow rational structural fire protection to be implemented. 

Simple Approach to Integration 

The basic goal of structural fire protection is to prevent extensive building collapse due to a fire 

in a building. This can be realized if the damage to the structure is limited to that area directly 

affected by fire. This means that loss of load carrying capability by secondary structural members 

in the fire is not inherently problematic and loss of primary structural members in the fire area is 

acceptable as long as load redistribution to the remaining structure is effectively accomplished. If 

the fire area is well defined, this can in principle be accomplished without the provision of fire 

resistance and without consideration of the role of fire protection measures. However, even in this 

simplified approach, fire barriers, active systems, and firefighting will be the means for defining 

and limiting the fire area, and in fact the structural system must be designed to allow fire barriers 

to fulfill their intended fbnction. 

More typically, structural members will be provided fire resistance through the provision of some 

form of thermal resistance to fire. Taking credit for the residual strength of the structural 

members exposed to fire then requires that the thermal exposure to the members be properly 

characterized and the thermal performance of fireproofing materiaWassemblies needs to be 

known. 

Inherent in the balanced design philosophy is the realization that performance must be assured 

when all systems perform as designed and that defined levels of safety must be achieved even in 

the event of at least one system failure. For structural fire protection, the current code 

requirements implicitly require that structural failures need to be prevented in the absence of 

active fire protection, manual firefighting, or fire barriers. This implicit requirement dates back to 

the development of fire resistance rating requirements that are linked to occupancy via expected 

fuel loads and the fire severity linked to the consumption of that fuel load as determined by the 

work of Ingberg at NIST in the 1920s. The ability to pass the E-1 19 test for the required duration 

is assumed to assure that there will be no structural failure without respect to the physical extent 

of the fire exposure beyond the structural assembly tested in the furnace. Clearly, in the light of 

our modem understanding of structural fire protection, this assumption may be exceedingly 

conservative in some instances and exceedingly non-conservative in other instances. 

In determining the system failures appropriate for design, it is worth considering the nature of 

system failures expected for various systems. For active fire protection systems, it is generally 

appropriate to consider that when the system is successful, the fire does not grow to become 

structurally significant. However, when system failures occur, the fire generally will approximate 

the fire severity expected without the protection system. Thus, for active fire suppression systems, 

103 
the most significant metric is the success or failure probability, given a fire start. Based upon 

available studies, the success probability is in the range of 0.9 to 0.95 (Bukowsi, Budnick, and 

Shemmel, 1999). For manual firefighting, the success probability is a function of the fire size on 

arrival, manpower, water supply, and passive fire protection system capabilities (Marchant et al., 

200 1, Sardqvist, 2000). For manual firefighting, it is unlikely that a single success probability can 

be used to assess performance. For fire barriers, the success probability is a hnction of the fire 

severity, the presence and quality of penetrations, and the general quality of the construction. 

While we speak of the passive fire protection as a system, for the most part the individual fire 

barriers are largely independent systems, so that passive fire protection also cannot be 

characterized by a single success probability, even if made appropriately dependent on fire 

severity and conskction. Setting appropriate deterministic design points for structural fire 

protection design is desirable for simplicity of use, but determination of the design points requires 

some assessment of the total fire protection system performance and reliability. 

In addition to assuring protection from structural collapse, it is important to assure that structural 

deformations will not cause failures in fire barrier performance. Fire barrier and structural 

protection are often very much integrated. Deformations of a beam that do not have serious 

structural consequences may cause failure in the performance of a floor or wall system that acts 

as a fire barrier. Systems susceptible to this behavior must be avoided or protected to prevent fire 

barrier failure due to structural deformations. 

Fire areas are generally determined by the fire barriers present. The likelihood of various fire 

areas can be determined using the Building Firesafety Engineering Method (Fitzgerald, 1986). 

This method assesses the performance of automated, manual firefighting and fire barrier 

performance through network diagrams. While the method as developed by Fitzgerald uses 

subjective probabilities, statistical and analytical methods of assessment can be used at any 

desired level of detail. 

In particular, a simplified approach to determining the frequency of a structurally significant fire 

exposure for a series of compartments separated by fire barriers can be assessed. Here we 

consider a sprinkler system, fire department operations, and fire barriers as the available means of 

limiting a fire. We begin with the frequency at which established fires occur, FD. One would 

expect the fiequency of reportable fires to be deduced from fire statistics. A fire will be prevented 

from becoming a significant threat to the structure if it is extinguished by a sprinkler system with 

likelihood, PSP, or if the fire department is able to control the fire in its early stage of 

development, Pm. This likelihood is, of course, dependent upon the available means to detect a 

fire and the capabilities of the fire service. Thus the frequency of a structurally significant fire, 

Fss in the compartment is 

The characteristics of the fully developed fire are determined by the fuel load, the ventilation, and 

the bounding surfaces thermal properties. The fully developed fire environment exposes both the 

structural elements in contact with this compartment as well as the fire barriers that form the 

compartment. Spread to an adjacent compartment is largely dependent upon the ability of fire 

barrier to resist the thermal insult in the first compartment, PB,JZ, augmented by sprinklers, PspJ, 

and the fire department, Pm2, to defend the fire barrier. This can be expressed as 

Typically, the probability of success of the sprinkler system in the second compartment would be 

very low. The probability of the fre department defending the fire barrier will depend upon the 

104 
barrier performance, the extent of the barrier, and the fire department capabilities. This analysis 

process can be extended recursively to additional compartments. To a first approximation, time 

dependent analysis is limited to the submodels for defining the component probabilities. The 

result of this process is a frequency distribution for the fire area. The structural element 

temperatures and resulting structural response need to be assessed for fire areas with frequencies 

above a threshold value. Acceptable consequences would need to be assured, based upon the 

frequency of the fire area involvement. 

Global Integration of Structural Fire Protection Design with Total Fire Safeq Design 

The integration of structural fire protection design with an overall rational fire protection design 

can be approached through a comprehensive risk assessment methodology, such as CESARERISK (Beck, 1997), FIRECAM (Yung et a1 1997), FIERA (Hadjisophocleous and Torvi, 2000), 

or the Carlton University (Hadj isophocleous and Fu, 2003) building risk assessment models. The 

performance of the suite of fire safety features needs to be understood both individually and 

together. This means that designers of individual fire protection systems are provided with 

performance and reliability requirements. 

Creating such a methodology requires analytical tools such as CESARE-RISK, which models the 

performance of the total fire safety system for a set of code provisions. CESARE-RISK was 

developed to assess expected building performance under existing code provisions and to assess 

the equivalency of alternate deemed to satis@ requirements. Since there are currently no 

established research projects in the U.S. to develop such a global fire safety risk model, it is clear 

that rational structural fire protection design should not wait for the development of the global 

risk model approach. The elements of the simpler structural fire protection methodology will be 

able to be integrated into a global fire risk model when such methodologies are developed and 

validated. 

NEEDED RESEARCH 

The primary research need is the development of the overall design methodology framework. 

This includes the development of the design approach and the methods for determining 

component probabilities and probability distributions. This effort should be scheduled early in the 

development process to assure that the outcomes of component development efforts will clearly 

fulfill the needs of the overall methodology. Additional research required includes the 

development of validated models for the following: 

1. compartment fire time-temperature histories; 

2. heat transfer to and through structural and barrier assemblies; 

3. mechanical response of structural and barrier assemblies; 

4. structural response of the building system; 

5. sprinkler reliability and effectiveness model; 

6. fire department effectiveness model; and 

7. suite of fire test methods to support design method. 

BENEFITS OF A RATIONAL STRUCTURAL FIRE PROTECTION METHODOLOGY 

This method of integration with the overall fire safety design is simple and straightforward. It has 

the benefit that realistic structural fire exposures and realistic structural response methodologies 

105 - 
can be applied to enhance the reliability of the design performance with a minimum of 

interactions with other frre safety systems design. Clearly, the interactions with fire barrier 

performance cannot be avoided. Since much of the enhanced response methodologies are equally 

applicable to fire barrier design, it seems efficient and natural to extend structural fire protection 

design methods to include all fire resistance aspects of building design. The incremental 

developmental work is incremental and the benefits in extending design reliability are substantial. 

REFERENCES 

AIS1 (1 97 l), Fire Protection Through Modern Building Codes, American Iron and Steel Institute, 

New York. 

Beck, V. (1 997), “Performance-based Fire Engineering Design and its Application in Australia,” 

Fijih International Symposium for Fire Safety Science, International Association for Fire Safety 

Science, pp 23-40. 

Bukowski, Budnick, and Shemmel(1999), “Estimates of the Operational Reliability of Fire 

Protection Systems,” Third International Conference on Fire Research and Engineering, Society 

of Fire Protection Engineers, Bethesda MD, pp 87-98. 

Fitzgerald, R. (1 986), “Risk Analysis Using the Engineering Method for Building Firesdety,” 

First International Symposium for Fire Safety Science, Hemisphere Publishing Co., Washington, 

pp 993-1002. 

Hadjisophocleous, G., Torvi, D. (2000), FIERAsystem: A New Computer Model for Fire 

Evaluation and Risk Assessment of Industrial Buildings,” Sixth International Symposium on Fire 

Safety Science, IAFSS, p 1 194. 

Hadjisophocleous, G., Fu, Z. (2003), “A Fire Risk Assessment Model for Commercial 

Buildings,” Fourth International Seminar on Fire and Explosion Hazards, Londondeny Northern 

Ireland, in press. 

Marchant, R., Kurban, N., Wise, S. (2001), “Development and Application of the Fire Brigade 

Intervention Model,” Fire Technology, 37, pp 263-278. 

Sardqvist, S., Holmstedt, G. (2000), “Correlation Between Firefighting Operation and Fire Area: 

Analysis of Statistics,” Fire Technology, 36, pp 109-1 30. 

Yung, D., Hadjisophocleous, G.,, Proulx, G. (1997), “Modeling Concepts for the Risk-cost 

Assessment Model FIRECAM and its Application to a Canadian Government Office Building,” 

Fijih International Symposium on Fire Safety Science, IAFSS, pp 6 19-630. 

106 
White Paper 5 

Design Fire Scenarios 

Morgan J. Hurley, P.E. 

Technical Director 

Society of Fire Protection Engineers 

INTRODUCTION 

Fire resistance is typically designed into structures to protect against failure in the event of fire. ' 

The design of fire resistance of structures has historically been based on prescriptive requirements 

that have their basis in research conducted in the early 1900's. These methods typically prescribe 

minimum fire resistance ratings for individual structural elements based on a number of building 

characteristics such as occupancy type and building height. 

While structures that are designed based on these requirements have a history of excellent 

performance in fires, by not considering the fire exposures to which structures might be exposed 

and structural response at elevated temperature, these prescriptive requirements do not provide a 

true measure of structural performance in fire. Additionally, it is clear from fire experience that 

structures built according to existing methods do not necessarily perform the same in fires.' 

The most effective way to determine true structural performance in fire is through an engineering 

approach. The first step in engineering structural fire resistance is to determine the fire boundary 

conditions to which a structure could be exposed. After determining the fire boundary conditions, 

the thermal response of the structure can be predicted. Finally, with knowledge of the thermal 

response of the structure, the structural response analysis can be conducted with the use of 

elevated temperature material properties. 

FIRE SCENARIOS 

While the number of possible fire scenarios in a building is essentially limitless, it is typically 

only necessary to consider fully-developed fires for purposes of structural fire resistance design. 

There are three types of fue scenarios which may need to be considered: fully-developed, or postflashover compartment fires, fire plumes and flames from windows which expose exterior 

structural elements. 

Post-flashover fires are fires in compartments where all combustible materials within the 

compartment are involved in the fire. This scenario would be applicable to enclosures where the 

fuel load is distributed within the compartment. Window flames are flame projections fi-om 

windows where there is a post-flashover fire inside the building; this scenario is only of interest if 

there are exterior structural elements that may be exposed to flame projections from the windows. 

For cases where fuel is localized, the enclosure is very large, or where there is no enclosure, it 

may be necessary to consider exposures from fire plumes. 

Enclosure Fires 

The vast majority of design situations will involve the exposure of structural elements in 

enclosure fires. Fires in enclosures may be characterized in three phases. The first phase is fire 

growth, when a fire grows in size and heat release rate from a small incipient fire. If there are no 

actions taken to suppress the fire, it will eventually grow to a maximum size. This maximum size 

107 
is a function of either the amount of fuel present or the amount of air available through ventilation 

openings. As all of the fuel is consumed, the fire will decrease in size and the temperature in the 

compartment will decrease. These stages of fire development can be seen in Figure 1. 

Fully Developed 

Time 

Significant effect on structure 

Figure 1 - Phases of Fire Development 

The size (magnitude) of the fire and the relative importance of these phases (growth, fully 

developed and decay) are affected by the size and shape of the enclosure, the amount, 

distribution, form and type of fuel in the enclosure, the amount, distributiop and form of 

ventilation of the enclosure and the form and type of materials forming the roof (or ceiling), walls 

and floor of the enclosure. 

The significance of each phase of an enclosure fire depends on the fire safety system component 

under consideration. For components such as detectors or sprinklers, the fire growth stage is 

likely to be the most significant because these components are typically intended to activate early 

in the course of the fire. The fire growth stage usually proves no threat to the structure, and is 

hence typically neglected in designs of structural fire resistance. The threat of fire to the structure 

is primarily during the duration of the fully-developed fire and the cooling phase? 

For enclosure fires, the surface temperature of non-insulated structural materials, including 

reinforced concrete and timber, can conservatively be approximated as the gas temperature in the 

compartment, which simplifies the thermal analysis to a conduction problem. The temperature of 

uninsulated steel will lag the gas temperature in the compartment? Hence, the decay phase can 

typically be neglected for uninsulated steel, but may need to be considered for design of structural 

fire resistance of concrete, insulated steel, or timber. 

108 
Window Flames 

Exterior structural elements may be exposed by flames which issue from windows. The scenario 

that is typically considered is a post-flashover fire, which results in flame projections Erom any 

windows in the compartment. The shape and temperature distribution of the flame projection is a 

function of burning rate in the compartment and any air flow through the compartment which is 

not created by buoyancy of fire gasses.’ 

Fire Plumes 

In some scenarios, burning will be limited to an object or group of objects with no significant 

impact from an enclosure. Where discrete objects bum adjacent to or near a structural element, 

the local fire exposure may be more significant than the hot gas layer that develops in the area of 

consideration. Some examples are open parking garages, large warehouses, and bridges and 

overpasses. 

CURRENT METHODS 

The methods that are presently available to predict fire boundary can be classified into two 

categories: computerized fire models and closed-form algebraic equations. Closed-form 

algebraic equations predict compartment fire temperature based on input data relating to the 

amount of fuel in the compartment and .compartment characteristics such as compartment 

geometry, ventilation geometry and thermal characteristics of the construction materials. 

With a few exceptions, computer fire models predict the temperature in a compartment as a 

function of a user-defined fire! Therefore, most computer fire models require the user to predict 

the burning rate in the enclosure independent of the model. Hence, the quality of predictions 

made using computer fire models is limited by the ability of the modeler to estimate the heat 

release rate of the fire. However, NIST’s Fire Dynamics Simulator holds some promise here, as 

it is capable of predicting the burning rate in a compartment fire. 

Enclosure Fires 

Historically, the basis for fire resistance in buildings has been the standard time-temperature 

curve, which specifies temperature as a function of time. A structural element is rated, in hours, 

where the rating corresponds to the length of time before the element, with any protection, 

reached prescribed failure criteria based on temperature or ability to support a specified load 

when subjected to the standard time-temperature curve. Methods are available to calculate the 

fire resistance of an element without having to expose it to a full scale test.7 Building codes 

specify minimum fire ratings as a function of building characteristics such as building use, 

whether or not sprinklers are provided, and the building height and area. 

The current method of designing structural fire resistance based on exposure to the standard timetemperature curve is based on the concept of “equal area” under the standard time-temperature 

curve. Specifically, two fires with different time-temperature histories would be considered to 

have equal severity if the areas under their time-temperature curves are equal? 

The standard time-temperature curve has two limitations: 

109 
The standard time temperature curve does not consider factors that would influence 

the temperature and duration of a fire in a compartment, such as ventilation, fuel 

load, and thermal properties of materials of construction. 

Two identical time-temperatye curves in different furnaces may result in different 

heat transfer to tested elements? Radiation from furnace walls is believed to be the 

dominant mode of heat transfer in a test furnace: and furnaces with walls that have a 

low thermal inertia will result in a more severe exposure than furnaces with walls 

with a greater thermal inertia, since the walls will heat more quickly. Also, the type 

of fuel used in furnaces is not specified, so furnaces which use different types of he1 

may have different emissive characteristics, resulting in differing radiation heat 

transfer fiom furnace gasses. 

There are several methods available to determine the time in the standard test that would have the 

same heating effect as a compartment fire.". 11, 12, 13* These methods overcome, at least 

to a certain extent, the limitation that the standard time temperature curve does not consider 

factors that would influence the temperature and duration of a fire in a compartment. However, 

the other limitation identified above persist. Additionally, long, narrow compartments are not 

satisfactorily correlated by these methods. l8 

15, 16, 

Designing based on the actual fire exposure that could occur in a compartment would overcome 

both of the limitations identified above. There are several methods available to predict the timetemperature bound7 conditions of a fully-developed fire in an 

enclosure. Most of these methods have their basis in fires involving 

wood cribs. There is one exception:3* 24 which allows for the consideration of pool fires. 

16,19,20,21,22 23,2 ,25,26,21,28 

Many hydrocarbon-based materials, such as plastics, have approximately twice the heat of 

combustion of wood (in other words - burning one kg of a plastic can liberate twice the energy as 

burning an equal mass of wood). However, use of methods developed based on wood cribs is 

reasonable for most design scenarios, since more energy is required to cause wood to release 

flammable vapors than is needed for plastic^^^ which results in longer burning durations. In 

ventilation limited fires the rate of air flow into the enclosure will govern the heat release rate 

inside the enclosure, and fuel vapors that cannot bum inside the enclosure will bum outside once 

they encounter fiesh air. Additionally, most compartments of interest contain primarily cellulosic 

materials. 

Each of the methods identified above that can be used to model fully-developed enclosure fires is 

subject to the following limitations: 

The methods are only applicable M compartments with fuel uniformly distributed 

over their interior. (Sparse distributions, or concentrated fuel packages should be 

considered using the methods applicable to fire plumes.) 

The methods are only applicable to compartments having vents in their walls. 

Only natural ventilation is considered as would occur through wall vents such as 

windows and doors. (The effect of forced ventilations, and wind and stack-effect 

flows in tall buildings are not addressed.) 

Large fires are considered with heating effects felt uniformly through the 

compartment. 

Concern has been expressed that fires in lon narrow enclosures exhibit different burning 

behavior than fires in other types of enclosures! Specifically, for ventilation controlled burning 

110 
in long, narrow enclosures, the burning occurs at the fuel closest to the ventilation opening, and 

only moves away from the opening as the fuel is depleted. Hence, the assumption of uniform 

conditions throughout the enclosure does not hold, and predictive methods that were developed 

based on fires in compartments that are not long and narrow may not accurately predict burning 

behavior in long, narrow enclosures. However, analysis of data from experiments conducted in a 

compartment with dimensions of 5.5 m (width) x 23 m (length) x 2.7 m (height)31 reveals that 

some methods do satisfactorily predict the temperature and duration of fires in long, narrow 

enclosures .4 

With one excepti01-1,~~ all of the methods identified above for calculating the time-temperature 

history for a fire in a compartment are relatively simple, closed form equations, and even the 

exception has a closed form approximation which provides predictions to within 3-5% of 

predictions made using the computer program.24 Simple, closed form equations are possible 

because of the assumptions made to solve the fundamental conservations equations, e.g., uniform 

conditions throughout the compartment. Indeed, even the computer model referenced above23 

assumes a uniform temperature in the enclosure. 

Many computer models exist that predict fire temperatures for user-defined heat release rates. 

Use of most computer fire models for predicting post-flashover fire boundary conditions requires 

the modeler to estimate the burning rate in the compartment using other methods. Given that the 

heat release rate in a post-flashover compartment fire is a function of the characteristics of the 

enclosure, it is difficult to apply these models without making additional simplifLing 

assumptions. For example, by assuming that burning in the compartment is stoichiometric or 

ventilation limited, a burning rate could be estimated as a constant multiplied by the ventilation 

characteristics of the enclosure. Pool fires could be modeled using burning rate correlations that 

were developed for open air burning; however, these correlations neglect thermal feedback to the 

fuel fiom the enclosure. 

Field models such as NIST’s Fire Dynamics Simulator (FDS) allow abandoning the assumption 

that compartment gasses are well stirred?* Instead of modeling the enclosure as one zone, field 

models model an enclosure as many rectangular prisms, and assumes the conditions are uniform 

throughout each of these cells. 

FDS contains pyrolysys models for solid and liquid fuels. The pyrolysys rate of the fuel is 

predicted by FDS as a function of the modeled heat transfer to the fuel, and thermally thick, 

thermally thin and liquid fuels can be treated. Combustion is modeled by FDS using a mixture 

fraction model. 

While FDS holds promise in calculating heat release rates in fires, it presently must be used with 

caution, since a number of simplifications are used due to computational, resolution, and 

knowledge limitations. As stated in the FDS User’s Guide, “The various phenomena (associated 

with modeling combustion) are still subjects of active research, thus the user ought to be aware of 

the potential errors introduced into the cal~ulation.”~~ Any errors that are present with pool-like 

or slab-like fuels would likely be magnified when considering crib-like fuels such as furniture. 

Window Flames 

The state of the art in modeling fire exposures from window flames is contained in design guide 

published by the American Iron and Steel Institute (AISI).34 The AIS1 guide is a condensed 

version of work published by Ove Arup & Partners.35 

111 
The AISI guide provides a multi-step process as follows: 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

Define the room geometry 

Determine the fire load 

Determine whether a fire would be fuel or ventilation controlled 

Determine the burning rate 

Determine the fire temperature 

Model the geometry of the window flame 

Determine the flame temperature at the point nearest to the steel member 

Calculate the heat transfer to the steel member 

Determine the temperature of the steel member 

The AISI guide provides different methods for cases with and without through draft. If there is 

no through draft, the burning rate is calculated as the lesser of the burning rates for fuelcontrolled and ventilation controlled burning. If there is through draft, the AISI guide assumes 

that the fire would be fuel-controlled. 

For ventilation controlled fires, the AISI guide uses Law’s burning rate correlation? For fuel 

controlled fires, the AISI guide suggests that the fire duration would be approximately 20 

minutes, and the fuel controlled burning rate can be determined by dividing the mass of fuel by 

the duration of burning. The burning rate for fuel controlled fires is a function of the fuel surface 

area;22 however, fuel surface area is difficult to estimate for real buildings, and 20 minutes is 

consistent with Harmathy’s finding that the burning duration for fuel controlled fires is typically 

in the range of 6-25 minutes.22 

Correlations are provided for flame geometry for cases of through draft and no through draft. 

The AISI guide contains procedures for calculating the flame temperatures, heat transfer and steel 

element temperatures for a variety of orientations of steel elements with respect to windows. 

Maximum temperature criteria are given which are consistent with ASTM E- 1 19; however, the 

calculated temperatures could be used to determine material properties for purposes of conducting 

a structural analysis. Similarly, thermal analyses of structural elements that are constructed of 

materials other than steel would be possible by using the flame heating characteristics in a 

thermal analysis. 

A limitation of the method contained in the AISI guide is that it is predicated on cellulosic fuels. 

For compartments that contain primarily cellulosic fuels, this may be acceptable. While 

designing based on cellulosic fuels would be conservative for determining temperatures and 

burning durations in compartment fkes, the opposite is true for window flames. Because 

cellulosic fuels require more energy to produce volatile vapors than do hydrocarbon-based fuels, 

the mass loss rate for hydrocarbon-based fuels would be greater less than the mass loss rate for 

cellulosic fuels. Any fuel that does not burn in the compartment because of ventilation 

limitations would bum outside of the compartment. The excess volatiles associated with noncellulosic fuels, which would not be predicted by the AISI method, would burn outside the 

compartment, providing a more severe exposure to the exterior elements. 

Lattimer also provides a method for predicting the heat flux from a window flame to surfaces 

above the window? In Lattimer’s method, the heat flux to surfaces above the window can be 

estimated from graphs of heat flux vs. heat release rate. No correlation is given, and there is 

much scatter in the data, although a bounding analysis would be possible. 

112 
Fire Plumes 

The state of the art in calculating fire hazards from fire plumes has been summarized by Be~le2~ 

and by Latti~ner.~~ Be~ler~~ summarizes available methods for determining the temperature and 

velocity of fire plumes and ceiling jets as a function of fire heat release rate, height above the 

plume source, and for ceiling jets, radial distance from the plume centerline. Beyler also 

summarizes methods of calculating the heat flux from an impinging fire plume on a ceiling. This 

information could be used in a heat transfer analysis to determine the thermal response of 

structural elewnts exposed to fire plumes or ceiling jets. 

Lattin~er~~ summarizes methods of estimating the heat flux from localized fires, i.e., not flashedover compartments, to surfaces. Specifically, Lattimer provides methods of estimating heat 

fluxes from area fires, wall and ceiling fires and the aforementioned window flames to surfaces. 

Lattimer considers six geometric exposure scenarios, specifically, flat vertical walls, flat ceilings, 

parallel flat vertical walls, comer walls, comer walls with a ceiling and horizontal I-beams. 

Predictive methods and comparison with data are provided. 

PROBABILISTIC ISSUES 

Although the use of fully-developed fire scenarios eliminates much of the variability in fire 

scenario development, e.g., first item ignited, fire growth rates, etc., this approach is not without 

uncertainty. Any of the input variables used in predictive methods could vary. Additionally, 

manual or automatic intervention would be expected for fires in most buildings. Also, extreme 

events, such as terrorist attacks, may not be considered since they may introduce additional fuel 

or ventilation openings. 

Uncertainty in Model Inputs 

All predictive methods require as input information about the fuel source, for example, mass of 

fuel or type of fuel, and information regarding the geometry being modeled. Models involving 

hlly developed enclosure fire scenarios, including flames issuing from windows, require 

information regarding compartment and window geometry. Many models of fully developed 

enclosure fires also require thermal properties of the materials that line the enclosure. There may 

be uncertainty in each of these parameters. 

Thermal properties of the enclosure linings generally have the least amount of uncertainty, since 

the materials of construction are typically selected early in the design of a building and would not 

be expected to change significantly. Also, predictive methods are typically not highly sensitive to 

variations in these properties. 

Compartment and ventilation geometry could similarly be considered as invariant. However, 

these factors could change over the life of a building due to remodeling. Also, some serious fwe 

losses have occurred during construction or remodeling.38' 39 

Fuel characteristics are the property that could be expected to vary the most. Several documents 

contain information regarding fire loads in different occupancies. Most design guides derive this 

information from a CIB report:' which presents fire loads in MJ/m2 for a variety of occupancies 

at 80%, 90% an 95% confidence values. These values could be converted to a mass per unit area 

basis by dividing by an effective heat of combustion. Several researchers have also published 

surveys of fire loads. 41,42,43 

113 
In addition to the total amount of fuel, the surface area also influences burning the rate. For 

ventilation controlled fires this is typically neglected, although the fuel surface area must be 

considered for fires which might be fuel controlled. There is limited data available on the surface 

area of fuel as a function of occupancy, although Harmathp reports that for furniture, the surface 

area to mass ratio is generally between 0.1 and 0.4 m2/kg, and is most often the range of 0.12 to 

0.18 m2/kg. 

For deterministic evaluations, it would be prudent to use bounding or reasonably conservative 

values. One caution that must be considered is that reported surveys generally only consider 

“normal” occupancy characteristics, and do not include the fire loads that might be present during 

times of construction or renovation. 

Similarly, methods of predicting fire exposures from fire plumes require input values such as heat 

release rate or dimension from the fire source. When selecting input values for these methods, 

bounding or reasonably conservative input values would generally be used. 

Intervention 

Intervention, such as sprinkler suppression or fire service response, would be expected in many 

buildings. If either of these systems functions as intended, the burning duration would be 

decreased. However, sprinklers are not 100% effective; the actual effectiveness in somewhere in 

the vicinity of 95%? Similarly, the fire service can’t be relied upon to extinguish all fires. 

If the sprinkler system were relied upon when designing on a deterministic basis, the design 

would not be safe approximately 5% of the time. While the fire service could be expected to 

extinguish some fraction of the remaining 5%, there would still be some fires that would continue 

until burnout. 

To adequately consider both fire resistance and intervention would require designing on a risk 

basis. For example, acceptance criteria could be stated in a form of x amount of loss per unit 

time. Designs could then be evaluated on a risk basis as follows: 45 

Risk = c Risk, = c [c x (Loss, x R, + Loss, (1 - R, >11 

Where Riski = 

Loss, = 

Risk associated with scenario i 

Loss associated with scenario i ifthe design succeeds 

LOSS, = 

F, = 

Rk = 

Loss associated with scenario i ifthe design fails 

Frequency of scenario i occurring 

Probability of design succeeding 

The Eurocode’6 contains an approach for accounting for interventions where the design fire load 

is reduced by a factor (0.0- 1 .O). This results in a design fire load that is less than the actual fire 

load. This is only a quasi risk-based method, as it does not explicitly consider the actual 

frequency and consequences of fires. 

114 
Extreme Events 

Buildings are typically designed based upon the types of fires that might reasonably be expected 

to occur. However, there are some types of events that may fall outside of the design basis of 

most buildings; for example, collisions with aircraft or bombings. These types of scenarios might 

ignite multiple simultaneous fires or a single fire with a large burning area and may change the 

building characteristics that affect fire performance. Extreme events are, by definition, high 

consequence/low probability events. 

KNOWLEDGE GAPS 

There is sufficient information available to predict with reasonable precision the fire boundary 

conditions to which most structures could be exposed. However, research could be used to 

reduce the uncertainties in designs or analyses, resulting in more cost effective use of resources 

without compromising safety. These include the following, which are not listed in any ranked 

order: 

Fire Load 

While some information is available on fire loads in some occupancies, the information displays 

international differences4' and is in some cases, dated. Given that the fuel load is a critical input 

into design fire calculations, reducing the uncertainty would be beneficial. For designs in which 

fires would be fuel controlled, additional data relevant to the fuel surface area would be 

beneficial. Additionally, beyond mass or calorific value per unit area, little information is 

available on fuel characteristics, such as how well they can be approximated as wood cribs or 

pools. 

Intervention 

While there is an accepted approach for considering the impact of active systems on fire 

resistance in Europe, this approach is not without shortcomings. Development of a true riskbased approach to structural fire resistance would allow an apples to apples comparison of active 

and passive systems. 

Long-Narrow Enclosures 

Because of the burning phenomena in long-narrow enclosures, the heat transfer boundary 

conditions are not uniform throughout the enclosure. Although some methods do reasonably 

predict the temperature and duration of fires in long, narrow enclosures, they do not consider the 

non-uniform conditions in the enclosure. Additional research is needed to quantitatively 

understand burning phenomena in ,long, narrow enclosures. 

Window Flames 

Much of the work on flames issuing from windows is limited by the types of fuels considered. 

Research is needed to provide methods that have broader ranges of applicability. 

Predictive Methods 

There are a number of relatively simple methods available to predict fire boundary conditions. 

Some evaluation of these methods has occurred: however, additional evaluation may be needed. 

115 
Evaluation is also needed of more complex methods, such as the methods used in NIST’s Fire 

Dynamics Simulator. 

While existing methods can be used with confidence in most design or analysis situations, the 

need for more complex methods should also be explored. 

REFERENCES 

Hurley, M. “Why Should We Practice Performance-Based Design,” Fire Protection Engineering, 

Buchanan, A. Structural Design for Fire Safety. John Wiley and Sons, U.K. 2001. 

1 

Summer, 2003, p. 60. 

3.“Rational Fire Safety Engineering Approach to Fire Resistance in Buildings,” CLB W 14 Report 269, 

200 1. International Council for Research and Innovation in Building and Construction, Rotterdam. 

Bethesda, MD, In Process. 

SFPE Engineering Guide to Fire Exposures to Structural Elements, Society of Fire Protection Engineers, 

Fire Safe Steel -A Design Guide, American Iron and Steel Institute, Washington DC, 1979. 

Babrauskas, V. “Fire Modeling Tools for Fire Safety Engineering: Are They Good Enough?” JournaZ of 

Fire Protection Engineering, 8,2, 1996, pp. 87-96. ’ ASCEBFPE 29, “Standard Calculation Methods for Structural Fire Protection,” American Society of 

Civil Engineers, Reston, VA, 1999. 

Engineers, New York: 1992. 

lo Fire Protection through Modern Building Codes, American Iron and Steel Institute, Fifth Edition. 198 1 , l1 Kawagoe, K, Takashi, S, Sekine, T, “Estimation of Fire Temperature-Time curve in Rooms”. Occasional 

Report No. 1 1 , Building Research Institute, Tokyo: 1963. 

l2 Law, M. “A Relationship between Fire Grading and Building Design and Contents.” Fire Research Note 

No 877, Joint Fire Research Organisation, 197 1. 

l3 Law, M. “Prediction of Fire Resistance”. Symposium No.& Fire Resistance Requirements for Buildings 

- a New Approach. Department of the Environment and Fire Office’s Committee Joint Fire Research 

Organisation, London 1973 HMSO. 

l4 Pettersson, 0, Magnusson, S. & Thor J., “Fire Engineering Design of Steel Structures”, Swedish Institute 

of Steel Construction, 1976. 

l5 Harmathy, T, & Mehaffey, J., “Post-Flashover Compartment Fires”, Fire and Materials, Vol. 7 No.2, 

l6 Eurocode 1 - Basis of design and actions on Structures Part 2.2 Actions on structures - Actions on 

structures exposed to fire. ENV 1991-2-2: 1995, CEN. 

17 Fire Engineering Design Guide, Buchanan, A., Editor, Centre for Advanced Engineering, Christchurch, 

New Zealand, 200 1. 

l8 Law, M. “A Review of Formulae for T-Equivalent,” Fire SrIfetv Science - Proceedings - of the F@h 

International Symposium, International Association for Fire Safety Science, London, 1997. 

l9 Lie, T “Fire Temperature-time Relationships”, SFPE Handbook of Fire Protection Engineering, 2”d 

Edition, National Fire Protection Association, Quincy, MA: 1995. 

2o Magnusson, S. E., Thelandersson, S, “Temperature-time curves of complete process of fire 

development”, ACTA Polytechnica Scandinavica, Civil Engineering and Building Construction Series 

N0.65, Stockholm, 1970. 

21 Harmathy, T. “A New Look at Compartment Fires, Part I,” Fire Technology, 8, #2, 1972. 

23 Babrauskas, V., COMPF2-A Program for Calculating Post-Flashover Fire Temperatures (Tech Note 

991). IrJ. S.] Natl. Bur. Stand. (1979). 

24 Babrauskas, V. “A Closed-Form Approximation €or Post-Flashover Compartment Fire Temperatures,” 

Fire Safety Journal, 4, 198 1 , pp. 63-73. 

25 Ma, Zhongcheng, Miikelilinen, Pentti,. “Parametric Temperature-Time Curves of Medium Compartment 

Fires for Structural Design,” Fire Safety Journal, 34, (2000), 361-375. 

Lie, T (Ed.) Structural Fire Protection, ASCE Manual and Report #78, American Society of Civil 

Drysdale, D. Introduction to Fire Dynamics, Wiley, Chichester, UK: 1999. 

1983 pp. 49-61. 

Hmathy, T. “A New Look at Compartment Fires, Part 11,” Fire Technology, 8, #4,1972. 

116 
26 Law, M. “A Basis for the Design of Fire Protection of Building Structures,” The Structural Engineer, 

Vol. 61A, No. 5, January, 1983. 

27 Thomas, P. & Heselden, A. “Fully Developed Fires in Single Compartments, A Co-operative Research 

program of the Conseil International du Batiment (CIB Report No. 20),” Fire Research Note No. 923, Fire 

Research Station, Borehamwood, UK, 1972. 

28 Tanaka, T., Sato, M. & Wakamatsu, T. “Simple Formula for Ventilation Controlled Fire Temperatures,” 

13* Meeting of the UJNR Panel on Fire Research and Safety, March 13-20, 1996,” NISTIR 6030, National 

Institute of Standards and Techno logy, Gaithersburg, MD, 1997. 

29 Karlsson, B. & Quintiere, J. Enclosure Fire Dynamics, CRC Press, Boca Raton, FL: 1999. 

30 Thomas, I. & Bennets, I. “Fires in Enclosures with Single Ventilation Openings - Comparison of Long 

and Wide Enclosures,” Fire Safety Science - Proceedings of the Sixth International Symposium,” 

International Association for Fire Safety Science, London: 1999. 

Station Collaborative Project,” British Steel, Rotherdam, UK, 1994. 

32 McGrattan, .K., et al. “Fire Dynamics Simulator (Version 3) - Technical Reference Guide”, NISTIR 

6783, National Institute of Standards and Technology, Gaithersburg, MD 2002. 

33 McGrattan, K. et al., “Fire Dynamics Simulator (Version 3) - User’s Guide,” NISTIR 6784, National 

Institute of Standards and Technology, Gaithersburg, MD 2002. 

34 Fire Safe Structural Steel - A Design Guide. American Iron and Steel Institute, Washington DC, 1979. 

35 Ove Amp & Partners, “Design Guide for Fire Safety of Bare Exterior Structural Steel,” Technical 

Reports and Designer’s Manual, London, 1977. 

36 Lattimer, B. “Heat Fluxes fkom Fires to Surfaces,” SFPE Handbook of Fire Protection Engineering, 

National Fire Protection Association, Quincy, MA, 2002. 

Beyler, C. “Fire Plumes and Ceiling Jets,” Fire Safety Journal, 11, 1, 1986, pp. 53-76. 

38 Klem, T. J., Fire Investigation Report. One Meridian Plaza, Philadelphia, Pennsylvania. Three Fire 

Fighter Fatalities. February 23, 199 1. National Fire Protection Assn., Quiricy, MA, 199 1. 

39 ‘Smoke Caused Most Damage’ in Broadgate Fire. New Builder, No. 90,6 (July 1 1, 1991). 

40 Thomas, P., et al. “Design Guide - Structural Fire Safety.” Fire Safety Journal, Vol. 10, No. 2, March, 

41 Kumar, S. & Rao, V. “Fire Loads in Office Buildings,” Journal of Structural Engineering, March, 1997, 

42 Narayanan, P. “Fire Severities for Structural Engineering Design,” Study Report No. 67, BRANZ, 

Wellington, New Zealand, 1996. 

43 Caro, T. & Mike, J. “A Survey of Fuel Loads in Contemporary Office Buildings,” NIST-GCR-96-697, 

National Institute of Standards and Technology, Gaithersburg, MD, 1996. 

44 Budnick, E. “Automatic Sprinkler System Reliability,” Fire Protection Engineering, Winter, 200 1, pp. 

45 SFPE Engineering Guide to Performance- Based Fire Protection Analysis and Design of Buildings, 

National Fire Protection Association, Quincy, MA, 2000. 

Kirby, B. et al., “Natural Fires in Large-Scale Compartments - A British Steel Technical, Fire Research 31 

37 

1986, pp. 75 - 137. 

pp. 365-368. 

7-12. 

117 
White Paper 6 

Analysis Tools and Design Methods: Current Best Practices 

J. Milke, P.E., Ph.D. 

Abstract 

A variety of analytical tools are available to assess the thermal and structural response of fireexposed building assemblies. The available calculations apply to many different types of 

building assemblies, including floor- and roof-ceiling assemblies, columns, walls and trusses. 

The building assemblies may be comprised of any of the principal structural materials, i.e. steel, 

concrete, concrete and clay masonry and wood, as well as protection materials and veneers. 

Significant constraints in the application of such tools include the limited availability of material 

property data and the limited understanding of these analytical tools by practicing engineers. 

1. Introduction 

Assessing the response of building assemblies containing structural members consists of 

evaluating the thermal response and structural response of the assembly. A thermal response 

analysis considers the heat transfer to the assembly resulting from the heating conditions provided 

by the defined fire exposure. The structural response analysis determines the effect of the 

temperature changes induced within the structural assembly as a result of the fire exposure. A 

variety of analytical tools are available to assist with these evaluations. 

This review intends to provide an overview of the analytical tools available to assess the thermal 

and structural response of structural assemblies. This overview will outline the technical basis, 

assumptions, limitations and capabilities associated with the variety of analytical tools. 

2. Thermal Analysis Methods 

The thermal response of a fire-exposed assembly is evaluated by a heat transfer analysis. A thermal 

response analysis is conducted to determine the temperature distribution throughout the construction 

assembly or at selected locations. Possible locations of interest can be proposed given the basic 

objectives of fire resistant assemblies, e.g. the unexposed side of the assembly or positions of loadcarrying structural members within assemblies. Heat transfer within a solid, non-porous assembly 

occurs via conduction, with convection and radiation boundary conditions. In assemblies comprised 

of porous media (wood, concrete, masonry, gypsum board, etc.), coupled heat and mass transfer 

considerations become increasingly important. Consequently, heat transfer within the porous 

materials is by conduction, convection and radiation. 

Several possible approaches are available to solve a conduction heat transfer problem. Exact 

solutions are often impractical, especially given the non-linear, unsteady boundary conditions 

typically associated with fire, in addition to the temperature-dependent material properties and 

complex geometries associated with building assemblies. Consequently, virtually all heat transfer 

analyses of fire-exposed building assemblies involve approximations, which simplifL the governing 

equations, the geometry, or both. Calculation methods range from applying simple algebraic 

equations to computer models. 

The analytical methods incorporated into design guides are all relatively simple, requiring the 

application of algebraic equations or graphs. In these analyses, changes in materials caused by 

decomposition, dehydration or phase changes or changes in geometry are neglected or included 

118 
implicitly by use of effective values for the thermophysical properties. In contrast, finite element 

and finite difference models are available that permit temperature-dependent material properties 

and varying boundary conditions. 

2. I Lumped Heat Capacity Analysis 

One of the elementary methods to assess the thermal response of a structural component follows a 

lumped heat capacity analysis. This approach is based on a simplification of the phenomenon, 

assuming that any incident heat from the fire causes a uniform temperature increase throughout 

the exposed object. This assumption is most appropriate for exposed objects with high thermal 

conductivities, uniform exposure conditions around the entire perimeter and length of the object 

and relatively thin-walled sections, such as steel columns in the middle of a compartment,. The 

assumption of uniform temperature is less appropriate for partially exposed steel members such 

as steel beams in contact with a deck, steel columns partially embedded in a wall, concrete 

assemblies and timber assemblies. 

The lumped heat capacity approach can be applied to steel columns that are unprotected or protected 

with insulating-type fireproofing materials. The heat flow through the protection material is assumed 

to be steady-state such that a linear temperature gradient is assumed through the fireproofing 

material. 

With the noted assumption of uniform temperature and constant properties, the lumped heat 

capacity analysis involves the application of an algebraic equation to determine the temperature 

rise in the exposed object during a small time step (a maximum time step of 10 sec is stipulated by 

the Eurocodes [2001]). For the case of time-varying exposure conditions or temperaturedependent properties, as typically experienced in fires, the algebraic equation needs to be applied 

repeatedly, dividing the fire exposure into several small time steps. The lumped heat capacity 

analysis can be applied to evaluate the temperature rise in unprotected, partially protected or 

completely protected steel members [Malhotra, 1 9821 [Pettersson, et al., 1 9761 [Eurocodes, 200.11. 

The lumped heat capacity approach can be used either to determine the temperature of the steel after 

a given period of exposure or determine the time for the steel to reach a critical temperature. A 

spreadsheet routine can be formulated to perform the iterative calculations associated with the 

lumped heat capacity approach [Gamble, 19891 [Berger, 19891. 

The lumped heat capacity method is valid for any specified time-temperature relationship. The 

heating conditions associated with the fire are described in terms of a time-temperature relationship 

for protected and unprotected columns. For protected columns, the fire exposure conditions are 

addressed by assuming that the temperature of the outer surface of the protection material is equal to 

the fire temperature, and the temperature of the inner surface of the insulation is equal to the steel 

temperature. For unprotected columns, convective and radiative heat transfer parameters need to be 

specified. The convection heat transfer coefficient is often assumed to be constant throughout the 

duration of the exposure, typically with a value of 20 to 25 W/m2-"C. A single radiation parameter is 

often cited, accounting for the emissivity and view factor associated with radiation fiom flames, 

smoke, and compartment enclosure surfaces. [Pettersson, et al., 1976]FCCS, 19851. 

Evaluation of the predictive capability of the lumped heat capacity approach for steel columns 

protected with a spray-applied cementitious material was conducted by Berger [ 19891. The 

analysis consisted of comparing predicted versus measured temperatures for steel columns 

exposed to the standard fire exposure. Comparing the predicted versus measured times for the 

steel column to reach 538°C is provided in Table 2.1. 

119 
A comparison of the predicted temperature with those measured for one protected steel column 

assembly is provided in Figure 2.1. The good agreement is best indicated by the similarity of the 

slope of the predicted temperatures with the trend in the measured temperature points throughout 

the exposure. The good agreement of the slope and data trend indicates that for the design 

evaluated, a proper combination of material properties and exposure conditions were used and the 

lumped heat capacity analysis was appropriate. 

Table 2.1 Comparison of Predicted Time from Lumped Heat Capacity Analysis and 

Measurements for Protected Steel Column to Reach 53 8OC 

W12X106 3.8 200 203 

W 14x228 1.4 123 140 

I W14X233 I 2.9 I 225 I 251 

Figure 2.1. Predicted Temperature for W 1 OX49 Protected Steel Column 

600 

A 500 

0, 400 

3 E 300 

c 

g 200 

1 00 

0 

0 6 12 18 24 30 36 42 48 54 60 66 

Time (min) 

Test 

- Calc 

Predictions of temperature rise in steel beams by’the lumped heat capacity approach are prone to 

be inherently less accurate than those for steel columns milke, 19981. As noted previously, a 

steel beam in contact with a slab only has 3 “sides” exposed to a fire and also will lose heat to the 

120 
slab. Consequently, the temperature of a steel beam exposed to fire is likely to vary appreciably 

from the bottom flange to the top flange, stretching the validity of the uniform temperature 

assumption. Nonetheless, for many engineering applications, the lumped heat capacity approach 

can provide a reasonable estimate of the average temperature rise of a steel beam [Smith and 

Stirland, 1983 3. Heat losses to the slab may be compensated for by reducing the heat transfer 

parameters from the fire. However, if the temperature gradient across the beam is important, 

another analytical approach will need to be applied. 

Graphs summarizing the trends in temperature rise of protected columns exposed to natural fires 

are presented by Pettersson, et al. [ 19761. Indicated in the graphs is the influence of two fire 

parameters (ventilation and fuel load) and two parameters of the column assembly (steel column 

shape and protection thickness) on the temperature rise of the steel. 

Limitations 

Limitations of the lumped heat capacity analysis include the following: 

The heat transfer parameters are “effective” properties, supported by agreement with results 

obtained in standard tests. The values for these properties may vary appreciably for analyses 

with natural fires. 

Moisture movement and heat absorption are not addressed [Pettersson, et al., 19761 

[Malhotra, 19821. ECCS [1985] provides a calculation for a time lag to account for moisture 

loss. 

The steady state assumption of the heat transfer through the insulation is inappropriate for 

fires with high rates of temperature change. 

2.2 Steadv-State Heat Balance 

An upper limit of the temperature rise of a structural member can be determined using a steady 

state heat balance. This approach has been documented for two applications: 

1. temperature rise of exterior steel columns and beams exposed to radiant energy fiom a 

compartment fire and flames projecting out of wall openings. 

2. temperature rise of fire-exposed, water-filled steel columns. 

The temperature of the steel is determined from an energy balance, where the incoming heat fiom 

the compartment fire is equal to the heat leaving the steel [Law, 1978][AISI, 19791 [Schleich, 

19931 [Eurocodes, 200 11. The incoming heat from the exposing fire is estimated considering 

radiation heat transfer from the gases inside the compartment and fiom flames projecting fiom 

compartment openings such as windows. Convective heating is also considered for steel sections 

engulfed in flames projecting from the window. The heat leaving from the steel structural 

member consists of radiative and convective heat losses to the environment. Conduction losses to 

adjoining building assemblies are neglected. As with the lumped heat capacity approach, this 

method assumes a uniform steel temperature. 

In the analysis for water filled columns [Schleich, 19931, incoming heat from the compartment 

fire is estimated considering radiation and convection heat transfer fiom the gases inside the 

compartment. Heat losses include convection to the circulating water. 

These methods could be modified to address the temperature rise of the exterior steel or waterfilled column as a function of time. This would involve an iterative calculation similar to that in 

121 
, 

the lumped heat capacity approach. As input, the temperature history of the fire within the 

compartment needs to be provided along with the time for flames to initially project fiom the 

compartment opening. The temperature history of the fire is well within the state-of-the-art of 

compartment fire modeling. However, predicting the time for flames to project fiom the 

Compartment opening is more difficult. In particular, either the compartment opening needs to be 

assumed “open” throughout the exposure or breakage of a closed window needs to be assessed. 

Limitations 

Limitations of the lumped steady-state heat balance analysis include the following: 

the analysis provides an upper limit temperature which may substantially overestimate the 

temperature expected for the steel, especially where the peak temperature conditions are 

short-lived. 

predicting window breakage to create the compartment opening involves appreciable 

uncertainty. 

0 

2.3 Semi-infmite dab (therm&-thick slab) 

The semi-infinite slab approximation simplifies the heat transfer phenomenon by assuming that the 

effect of the incident heat on the exposed side dissipates before reaching the unexposed side due to 

the thickness and thermal properties of the floor, roof or wall slab. As a result, the temperature on 

the unexposed side of such a slab does not increase appreciably above the initial value. In this 

situation, the temperature near the exposed surface is dependent solely on the exposure conditions 

and is independent of conditions on the unexposed side. Even though no actual slab is infinitely 

thick, a slab can be considered to be suflciently thick for engineering purposes to permit the semiinfinite assumption if: 

X 

2& > 

(2-1) 

For thermally thick walls, simplified expressions are available in the literature for temperatures near 

the exposed surface if the exposure can be characterized as imposing a constant heat flux on the 

surface or a constant surface temperature. In the simplified expressions, the material properties of 

the exposed structural element are assumed constant. The effect of temperature dependent 

properties can be included in the analysis by evaluating the material properties at an average 

temperature for the portion of the slab under investigation. The semi-infinite slab approximation 

has been applied to wood slabs [Schaffer, 19771 for the period before charring is initiated. 

. 

Limitations 

Limitations of the semi-infinite slab analysis include: 

0 

0 

the fire exposure must provide a steady (or near-steady) heat flux, which is uniform across 

the entire exposed surface. 

the analysis is not relevant if materials undergo changes in composition, experience 

significant moisture movementlevaporation or have significant variations in property values 

between the exposed and unexposed surfaces 

122 
As an alternative to the semi-infinite slab approximation involving the exponential function for an 

exposure consisting of a constant heat flux, a quadratic temperature profile was proposed in 

Eurocode 5, part 1.2 for timber structures. Janssens and White [ 19941 found that the quadratic 

profile provided a reasonable, but conservative fit to experimental data for slabs of eight different 

wood species exposed to ASTM E 1 19 conditions. 

2.4 Graphical solutions 

Numerous graphical solutions of the temperature distribution within fire-exposed structural 

members have been presented in the literature. However, 'most of the graphical solutions are 

limited to cases involving the standard ASTM El 19 exposure. A limited number of graphical 

solutions apply to exposures from natural fires, e.g. the graphs attributed previously to Pettersson, 

et al. [ 19761. 

Lie [1972] provided a series of graphs for one-dimensional analyses of the temperature 

distribution in walls or slabs exposed on one or two sides to the ASTM Ell9 exposure. The 

graphs can also be used for two-dimensional assemblies such as columns or beams by applying 

the principle of superposition. Because the material properties are assumed to be constant, 

average properties need to be identified. In addition, the constant property assumption effectively 

limits the analysis to slabs and beams composed of relatively inert materials, such as concrete, 

steel, or wood before charring. 

The temperature distribution within concrete slabs is presented graphically based on data from 

tests with the ASTM E119 exposure [PCI, 19771. Graphs are provided for three aggregates: 

siliceous, carbonate and sand-lightweight. According to the review by Hosser, et al. [ 19941, the 

graphical analysis included in the PCI guide provides the best agreement with actual data when 

compared to predictions from three methods evaluating the thermal response of concrete 

assemblies using graphs or tables. The other two methods included graphical analyses by ISE 

[1978] and IBD [1981]. 

Graphs or tables of the fire resistance of masonry walls as a function of equivalent solid thickness 

and concrete aggregate type are also available WCMA, 19961. The fire resistance evaluation is 

based solely on the temperature rise on the unexposed surface. Consequently, the solutions 

actually indicate the time required for the average temperature of the unexposed surface of the 

walls to increase by 250'F when the wall is exposed to the fire environment consistent with 

ASTM El 19. 

Limitations 

Limitations of the graphical analyses are: 

0 most of the graphical methods apply for exposures associated with the standard test 

graphical solutions cannot be readily incorporated into computer-based methods which 

require temperature of the assembly as input. 

only conduction heat transfer is addressed; mass transport (i.e., effect of moisture 

evaporation, migration, etc.) is neglected. 

Graphical methods cannot be applied for materials which undergo decomposition or phase 

change. 

123 
2.5 Numerical Analvses 

Numerous algorithms are available to evaluate the thermal response of heated objects. These 

algorithms are based on finite difference or finite element formulations. Finite difference 

formulations simplify both the geometry and the governing equation. The geometry is 

approximated by a grid of nodes while the derivatives in the governing equation are replaced by 

algebraic expressions. Finite element models also approximate the geometry, though utilize the 

actual governing partial differential equation in the formulation [Minkowycz, et al., 19881. 

Lie and Harmathy [ 19721 formulated one of the first finite difference models that analyzed the 

heating of circular reinforced concrete columns exposed to the standard fire. In addition, finite 

difference models were applied for concrete floor slabs [Lie, 19781, square reinforced concrete 

columns [Lie, el al., 19841 and concrete-filled tubular steel columns Lie [1984]. Ahmed and 

Hurst have applied a one-dimensional, finite difference analysis of the coupled heat and mass 

transfer through carbonate and siliceous aggregate concrete slabs and multi-layered gypsum 

wallboard-and-stud assemblies [ 19951. Dehydration and evaporation phenomena and changes in 

porosity were considered by the model. Mehaffey and Takeda [1995] formulated a finite 

difference model to analyze the heating of wood stud walls exposed to the standard fire. In 

Mehaffey and Takeda’s model, dehydration and porosity of gypsum wallboard is accounted for 

through the use of effective properties. Milke and Vizzini developed a finite difference model to 

investigate the thermal response of fire-exposed anisotropic slabs, such as graphite-reinforced 

epoxy composites [ 19901 and glass-reinforced thermoplastic composites [ 199 11. PATHOS-2 is a 

one-dimensional finite difference model developed principally for the evaluation of fire-exposed 

structures on off-shore platforms [PCL, 19921. In a recent review of thermal analysis programs 

by Sullivan, et al. [1994], FIREWS [OM, 19851 and CEFICOSS [Franssen, 19871 were 

identified as contemporary finite difference models. FIRETRANS can be used to address onedimensional problems involving slabs exposed to fire. Heating 7 [Childs, 19991 is a threedimensional finite difference model which can be applied to address the heat transfer through a 

wide variety of assemblies. Time-varying boundary conditions and temperature-dependent 

material properties can be addressed with Heating 7. Several finite difference models have been 

formulated to assess the heat transfer through light frame walls [Clancy, 1999][Collier and 

Buchanan, 2002][Cooper, 19971 [Sultan, 1996][Sultan, et al., 200 13 [Takeda and Kouchleva, 

200 11. 

Several examples can be found where finite element analyses have been applied in recent efforts 

to analyze the thermal response of fire-exposed building assemblies such as steel beams, partially 

and fully-protected steel columns, wall assemblies, and floor systems [Moss, 20021. Finite 

element models that have been developed specifically to address the thermal response of fueexposed building assemblies include FIREST3 [Bresler, Iding and Nizamuddin, 19771, TASEF-2 

[Sterner and Wickstrom, 19901, SUPER-TEMPCALC [Anderberg, 19881, STABA-F [Rudolph, 

et al., 19861 and Imperial College’s model [Terro, 19911, and SAFIR pranssen, et al., 20001. 

Another finite element model, HADAPT Famont, et al., 20011 was applied for a twodimensional analysis of a composite steel beam and concrete floor slab, though it is not clear 

whether that model is generally applicable or limited to the situation analyzed in that reference. 

SAFE is capable of addressing two- and three-dimensional heat transfer as the first step of a 

thermo-mechanical analysis. FIRES-T3, TASEF-2, SAFIR and SUPER-TEMPCALC can be 

used to evaluate the thermal response of assemblies with voids. 

Some of the applications have involved consideration of exposure to the standard fire whereas 

others have involved exposure to natural fires. Milke [ 1992) and Sullivan, et al. [ 19941 provide 

124 
reviews of the first five finite element models developed to evaluate thermal response from fire 

(FIRES-T3, TASEF-2, SUPER-TEMPCALC, STABA-F and Imperial College’s model). 

Shape 

W6X16 

Results of predictions by FIRES-T3 are included in Table 2.2. A comparison of the predicted 

time for a variety of column assemblies to reach 538°C by Milke using FIRES-T3 and that 

determined in ASTM El 19 tests are included in Table 4.2. 

h (cm) Test (min.) Model (min.) 

1.9 58 62 

Being formulated specifically to address heating due to fire exposure, the finite element models 

include three special features: 

3.8 

7.6 

time-varying exposure conditions 

0 temperature-dependent properties 

one- or two-dimensional analyses (a three-dimensional analysis may be conducted using 

FIRES-T3) 

112 111 

210 232 

Approximately 25 years ago when FIRES-T3, TASEF-2, and SUPER-TEMPCALC, these three 

special features made these models unique. However, several commercially-available algorithms 

are available with capabilities to address two- and three-dimensional analyses and temperaturedependent properties. 

W 1 OX49 

W12X106 

W14X228 

Table 2.2 Comparison of FIREST3 Predicted and Measured Times for Protected Steel 

Columns to Reach 538°C wilke, 20021. 

8.3 29 1 283 

9.5 355 346 

1.9 70 77 

5.6 217 205 

3.8 200 199 

1.4 123 129 

W8X28 I 3.5 I 122 I 116 

W14X233 I 2.9 I 225 I 227 

There are two drawbacks to the applicability of numerical models to predict the. thermal response 

of any building assembly to fire. One difficult aspect of applying a numerical model to address 

the thermal response of fire exposed building assemblies is associated with acquiring the input 

data. “Boundary conditions” associated with the exposure must be stipulated. Material properties 

need to be available as a function of temperature. 

Another shortcoming of the heat transfer analysis algorithms is that they are applicable primarily 

to inert materials. Where assemblies experience moisture migration, phase changes, dehydration, 

125 
decomposition or changes in geometry, specific algorithms will need to be identified or 

developed to model the thermal response of such assemblies. Results for the available models 

often deviate appreciably from measured temperatures in the area of 100 to 200°C where 

concrete, gypsum, wood and other moisture containing materials are included despite the use of 

effective properties to account for the change in enthalpy [Sullivan, et al., 19941. Ahmed and 

Hurst’s model has much better predictive capabilities within this range of temperatures [ 19951. 

Limitations 

Limitations of the numerical analyses include: 

0 

the material is considered to be homogeneous, with changes permitted only to account for 

variation in properties due to temperature 

material properties which vary with temperature may not be known, especially for protection 

materials 

surface movement (recession or expansion) is not addressed, except in PATHOS 2. 

moisture migration and pressure build-up in pores is not addressed, except in the model by 

Ahmed and Hurst [1995] and in some thermal response models for non-fire purposes [Milke, 

19913. 

neither spalling nor cracking is considered. 

heat transfer parameters (convection coefficient and surface radiation properties) are semiempirically or empirically defined. 

0 

3. Structural Analysis Methods 

An analysis of the structural response of fire-exposed building assemblies addresses the 

consequences of the induced elevated temperatures on the integrity of load-carrying members. The 

temperature profile resulting from the thermal response analysis is used to determine material 

property values as well as assess thermally-induced stresses or curvature. The remainder of the 

input consists of parameters that are needed for typical structural analyses at ambient temperature, 

e.g. load levels (including load combinations), end conditions, and mechanical properties of 

structural member. Numerous calculation methods are available to analyze the structural 

response of a heated assembly, ranging from algebraic equations to finite element computer 

models. 

Most of the analysis methods are limited to the response of a single structural member. In these 

cases, adjoining members are accounted for through the specification of end conditions. 

However, recently a limited number of calculation methods have been documented which address 

the response of a structural frame to fre. 

3. I Elementary Mechanics Approaches 

All of the existing design guides for evaluating fire resistance reference algebraic equations 

developed from elementary mechanics to evaluate the structural response of fire-exposed 

assemblies. Most of the algebraic equation based methods address buckling and moment capacity 

analyses of individual components. Buchanan [2001] provides a good overview of the variety of 

algebraic-equation based methods. A deflection analysis with algebraic equations of a simple 

frame is outlined by Pettersson, et al. [1976]. The principal difference of applying these 

equations for fire resistance evaluations as compared to ordinary structural calculations is the 

adjustment of material property values to reflect their dependence on temperature. 

126 
Flexural Members 

Most of the analyses of the fire resistance of flexural members consist of evaluating a reduction in 

moment capacity resulting fiom a reduction in strength. The premise of conducting the moment 

capacity analysis in assessing fire resistance is that the assembly maintains integrity as long as the 

moment capacity exceeds the applied moment. In some publications, a deflection analysis is 

described, where a limiting deflection is established, typically expressed as a fraction of the span 

of the beam. Considering a maximum allowable deflection of 1130th of the span, critical 

temperatures determined fi-om deflection analyses are generally comparable to those determined 

from moment capacity analyses [ECCS, 19831. 

The algebraic equations for moment capacity analyses are similar to those presented for room 

temperature analyses in elementary mechanics. Algebraic equation-based analyses for moment 

capacity have been proposed for a variety of flexural assemblies (beams and slabs) comprised of 

steel, concrete and timber. Evaluation of moment capacity is dependent on the response of the 

material(s) to fire and whether the assembly is comprised of a homogeneous material or a composite. 

Steel Beams 

In fire resistance calculations, the yield strength of the steel is evaluated at the steel temperature 

determined from the thermal response analysis. Twilt [1988] proposed the use of an effective 

yield stress based on 0.5% permanent strain because additional strain is acceptable in fire 

conditions as opposed to ambient temperature conditions. 

Plastic analyses are outlined in several publications [Pettersson, et al., 19761 [Malhotra, 19821 

[ECCS, 19851 [Buchanan, 20011. In the plastic analysis, the applied moment is changed to 

account for load redistribution as a result of the formation of plastic hinges. In addition, the 

plastic analysis requires that the elastic section modulus be replaced by the plastic section 

modulus and the yield strength by the ultimate strength. 

Table 3.1 summarizes critical beam temperatures at which the moment capacity is exceeded for 

steel beams with various end conditions based on an elastic or plastic analysis [ECCS, 1985). The 

results also indicate the effect of load level and load application on the critical temperature. 

Timber Beams 

The moment capacity analysis for timber members is conducted considering a reduction in the 

section modulus to account for charring. Variations on the analysis are included in the literature, 

differing in how they account for the charring. The simplest method assumes that the charring depth 

is uniform for each exposed side of the timber member. In reality, rounding at the comers (arris 

rounding) causes a further reduction in the section modulus which should be accounted for in the 

analysis [Buchanan, 19941. Consequently, some of the methods using algebraic equations account 

for the arris rounding through an empirically defined factor [Schaffer, et al., 19861 [Lie, 19771. Yet 

another estimates the size of the rounded cross-section and requires that the section modulus be 

determined for this rounded shape. Another empirical factor may also be included to account for a 

reduction in material properties. 

127 
Table 3.1. Critical Temperatures of Steel Beams [ECCS, 19851 

type of statically end 

analysis determinate? load' conditions2 

Plastic Yes or No any Any 

Elastic Yes any Any 

Elastic No distr. f-f 

Elastic No point f-f 

Elastic No distr. f-p 

Elastic No point f-p 

Elastic No distr. conup 

Critical Steel Temperature (OC) 

Load level, proportion of allowable load 

0.3 0.4 0.5 0.6 0.7 

585 540 490 430 360 

605 565 525 475 425 

640 605 575 545 510 

605 565 525 475 425 

650 615 590 560 535 

615 580 545 505 465 

650 615 590 560 535 

An essential input for the analysis of timber members is the charring rate. Information on charring 

rates is available from a variety of sources [white, 20021 [Buchanan, 20021, however virtually all of 

these rates have been determined empirically based on the exposure of wood specimens to the 

standard time-temperature curve exposure. Several models have been developed over the last 60 

years to estimate the pyrolysis of wood for structural fire protection purposes [Janssens, 20021. 

Janssens has recently developed the model CROW to estimate charring behavior. 

Concrete Beams and Slabs 

Wade reviews the performance of concrete structural members under fire conditions [1991a, 

199 1 b]. The moment capacity analysis formulated for reinforced and prestressed concrete 

flexural members accounts for the composite nature of the assembly. The analysis of concrete 

slabs and beams is based on methods of analysis used in room temperature concrete design 

adapted for fire resistance analyses, with support from large-scale test data from the Portland 

Cement Assdciation pleischmann and Buchanan, 20021. 

When considering the positive moment capacity, the strength of the concrete in a slab is assumed 

to remain unchanged fiom that at ambient temperature. However, the strength of the steel is 

reduced commensurate with the temperature at the position of the reinforcement. In addition, thin 

beams, such as in concrete single or double tee beams, experience an increase in temperature as a 

result of fire exposure. In some analysis methods, any portion of concrete which attains a 

threshold temperature of at least 65OOC for siliceous aggregates or 760°C for carbonate 

aggregates is neglected based on a substantial loss in strength occurring at that temperature [PCI, 

19771 [CRSI, 19801. 

Negative moment analyses for continuous and other statically indeterminate sections are 

appreciably more complex. If the temperature is in excess of the threshold value noted in the 

previous paragraph, that portion of concrete on the lower edge of the beam or slab is neglected to 

reduce the negative moment arm [PCI, 1977 ][CRSI, 19801. The strength of the concrete and 

reinforcing steel is reduced given the temperatures at the centroid of the equivalent stress block 

and reinforcement location. Development lengths of steel reinforcement need to be evaluated, 

128 
accounting for the redistribution of moments. The tlmst due to expansion of the slab is evaluated 

to determine its effect on adjoining structural members. 

Limitations 

Limitations of the algebraic equations for flexural members are: 

the analysis for a steel beam assumes a uniform temperature of the beam (as determined from 

the lumped heat capacity analysis. In reality, a temperature distribution will be present on the 

beam with the bottom flange being at the greatest temperature and the top flange at the lowest 

temperature. Because of the temperature gradient in the beam, an additional positive 

curvature will be induced [Boring, 19791 [Eurocodes, 200 11. The moment analysis can be 

formulated by considering a composite beam comprised of small isothermal sections of the 

steel beam. 

the analysis for concrete members does not consider failure other than by moment capacity, 

neglecting shear and anchorage failure [Pettersson, 19861 

the negative moment analysis for concrete slabs bases the values for slab deflections with 

varying restraint and location of line of action for thrust force on limited experimental data 

[CRSI, 19801. 

mass transport phenomena and pore pressure build-up are not considered 

Compression Members 

The structural response of fire-exposed compression members depends on the anticipated mode 

of failure, as in the structural analysis of compression members at ordinary temperature. Short 

columns are expected to fail as a result of the applied stresses exceeding the strength of the heated 

compression member. In contrast, long, slender columns are expected to fail by loss of stability 

or buckling, where the applied stress exceeds the critical elastic buckling stress. Generally, 

columns which are “stout” or “slender” for the purpose of an ordinary temperature structural 

analysis retain those definitions in elevated temperature analyses. 

Buckling Analyses 

Buckling or stability analyses of steel or timber columns involve the application of the Euler 

buckling equation, developed from elementary principles of mechanics. The effective length 

modifies the actual length of the column based on the end conditions. The values of effective 

length used in design applications are more conservative than the theoretical values. 

Steel Columns 

Using the results of a thermal response analysis to determine the temperature of a fire-exposed 

steel column, Euler’s equation can be applied with the modulus of elasticity decreased as a 

hnction of the steel temperature. Euler’s equation can only be applied where the column 

achieves a uniform temperature through the cross-section and along the length. AISC uses a 

revised form of Euler’s equation and defines the slenderness ratio accordingly to permit it to be 

used for structural steel of any strength [AISC, 19931. 

ECCS developed a buckling analysis of fire-exposed steel columns by adapting an empiricallyderived set of buckling curves for ambient temperature conditions. Equations were developed via a 

regression analysis to describe the ambient temperature buckling behavior. The buckling curves for 

129 
fire-exposed steel columns, presented in Figure 3.1, were determined by multiplying the 

dimensionless buckling load by the ratio of yield stress at elevated temperature to that at ambient 

temperature. The advantage of the ECCS equation is that it implicitly accounts for actual steel 

column behavior including the effect of residual stresses and buckling near the plastic limit. 

c. I. '1 I' I .. 1 ._ I -, .. 

1.4 .. .. . .. 0 0.2. 0.4 0.6 0.8. I .o 1.2 

:A * .. 

Figure 3.1 Buckling Curves for Steel Columns [Milke, 2002, p. 4-2321 (from ECCS, 1985) 

Timber Columns 

As with timber beams, the cross-section of a fire-exposed timber column needs to be reduced to 

account for charring. A similar analysis is used for the columns as for the beams wherein the 

buckling load for a charred section is determined accounting for strength reduction and arrises via 

empirical factors. As with the analyses for beams, the charring rate needs to be known. 

Concrete Columns 

Allen and Lie [1974] evaluated the buckling of reinforced concrefe columns by conducting an 

analysis of the Strains through the cross-section at mid-span. Stress resultants were applied to 

determine the strain distribution through the cross-section and the total strain was related to the 

curvature in the column. Buckling behavior was concluded when the radius of curvature decreased 

without limit. The analysis compared favorably with experimental data [Harmathy, 19931. 

Frannsens and Dotreppe [2003] outline a simplified buckling analysis for reinforced concrete 

columns exposed to conditions associated with the standard test. 

130 
Limitations 

Limitations of the algebraic equations for compression members are: 

0 the analysis for a steel column assumes a uniform cross-section temperature of the column. 

Partially protected columns will not have uniform temperatures because of the varying 

exposure conditions around the perimeter. 

the analysis for columns of any material assume that the temperature or degree of charring is 

uniform along the length of the column. 

all columns are concentrically loaded. 

0 

0 

Comparison of Elementarv Mechanics Approaches 

Hosser, et aZ. [1994] presented a comprehensive comparison of a variety of the elementary 

mechanics approaches to estimate the fire resistance of assemblies included in design guides fiom 

North America and Europe, such as those described previously in this section. The comparison was 

organized according to methods for structural members of a particular material: concrete, steel or 

wood. The comparison and ranking of methods was based on the following eight factors: 

0 

application: types of members and end conditions addressed 

verification: agreement with experimental data 

precision (referred to as “accuracy” by Hosser, et aZ.): degree of approximation 

physics: extent of theoretical basis of method (versus empirically-derived method). 

completeness: level of documentation to describe basis of method 

input existent: availability of input data 

user fiiendliness: level of training required to apply method. Algebraic equations receive better 

ratings than computer models 

approval/standard experience: recognition of method in standard or regulation 

Hosser et al., emphasized the verification and application factors by weighting these factors greater 

than the others. Least important were the physics and user-friendliness factors. 

Concrete 

The following four methods to evaluate the fire resistance of concrete beams or slabs were included 

in the comparison. 

PCI IpCI, 19771 

ISE FSE, 19781 

SWE purocode, 19901 

IBD[Hertz,1981] 

All four methods can be applied to analyze the integrity of fire-exposed beams or slabs. In addition, 

ISE and SWE can be applied for combined slab-beam cross-sections. All four methods address the 

moment capacity of the member, though fiom varying perspectives. All methods except SWE can 

be used to evaluate reinforced or prestressed concrete members. According to the ranking developed 

by Hosser, et al., the PCI method received the best rating (with IBD being a close second), while the 

ISE method was worst. 

131 
Steel 

The following seven methods evaluating the fire resistance of steel columns and beams were 

included in the review. 

ECCS 119831 

SIA[1985] 

Combined ECCS and SIA 

NORDTEST [ 19851 

Bongard [ 19741 

- DTU[1982] 

Lie and Stanzak [ 19741 

Lie and Stanzak‘s method evaluates fire resistance by comparing the temperature rise of a steel 

section fiom a thermal response analysis to a predetennined critical temperature. The NORDTFBT 

method involves a means of interpolating standard test results. The approach by Bongard was 

considered to be outdated by Hosser, et d., though the basis for that opinion was not provided. 

The ECCS method is the basis for the approach included in Eurocode Part 3. Of the other four 

methods which account for temperature rise, load levels and structural pdormance, the ECCS and 

SIA methods were highly rated, with the combination ECCS and SLA method being the highest rated 

(obtaining almost a pedect.score). However, in a comparative analysis of the predicted tire 

resistance by the methods, the ECCS method was observed to overestimate the fire resistance for 

stout columns. 

wood 

A detailed review was conducted of the following seven methods which evaluate the fire resistance 

of wood columns and beams. 

Seekamp/Stanke [ 19691 

0 Klement/Rudolphi/Stanke [ 19721 

0 Meyer-Wns [ 19761 

Meyer-Wns/Haksever [ 19791 

ScheedSchatz [ 19851 

0 White [2002] 

Stiller [ 19831 1 

All of the methods address the fire resistance of wood members given the fire exposure associated 

with the standard test. The latter three methods are applicable to beams or columns, although the 

methods by Klement, et d., and Meyer-Ottens and Haksever are only applicable to columns and 

those by Seekamp and Stanke and Meyer-Ottens apply only to beams. Methods are applicable to 

solid wood sections, laminated wood sections or a combination thereof. All of the methods consider 

the amount of charring resulting fiom the fire exposm, although methods by Klement, et d., and 

Meyer-Ottens and Haksever consider rounding of the comers. A reduction in material properties in 

heated, uncharred regions is considered by Klement, et al., and Meyer-Wns and Haksever. 

The method by Stiller was rated best, with the method by Klement, et d. being second. Hosser, et 

al., indicate that Stiller’s method is the more recently developed method and improves on the other 

methods. Its principle strength is the timedependent predictions of charring and stresses. The 

132 
methods by Scheer and Schatz and White received the lowest ratings due to over-simplification of 

. the equations. 

3.2 Numerical Analvses 

Most contemporary studies of the structural analysis of fire-exposed structural members or frames 

have been conducted by finite element models. Sullivan, et al., [ 19941 indicate that most of the 

existing finite element models used for structural fire protection analyses were developed 

originally for research applications. Considering the fourteen papers presented in the area of 

structural fire protection at the Fourth IAFSS Symposium [Kashiwagi, 1994land the International 

Conference on Fire Research and Engineering [Lund, 19951, the majority of papers involved 

either the development or application of finite element models. Few recent structural analyses 

have been conducted with a finite difference model. 

FASBUS-II is one of the early finite element model developed in the U.S. to evaluate the 

structural response of complex building assemblies such as floor assemblies consisting of a twoway concrete slab, steel deck and steel beam [Jeanes, 19821. Input for FASBUS-I1 includes the 

temperature distribution, temperature-dependent mechanical properties, geometry, end conditions 

and loading. The output of FASBUS-I1 includes deflections, rotations and stresses in the 

components of the assembly which then need to be compared to performance limits. Use of 

FASBUS-I1 has not been indicated in the literature for over 10 years. 

Sullivan, et al. [ 19941 and Franssen, et al. [ 19941 provide extensive reviews and comparisons of 

existing finite element models for structural fire protection applications. According to Sullivan, 

et al., all of the models make the follcrwing assumptions: 

Navier-Bernoulli hypothesis: plane sections remain plane 

0 Perfect composite action is assumed for steel-concrete assemblies, neglecting any slippage 

between the steel and concrete 

torsion is neglected 

0 moisture effects are neglected 

Sullivan, et al. [ 19941 reviewed the following eight finite element models: 

FASBUS-I1 [Jeanes, 19821 

FIRES-RCII [Iding, et al., 19771 

CONFIRE [Forsen, 19821 

STEELFIRE [Forsen, 19831 

CEFICOSS [Franssen, 19871 

LUSAS [1988] 

SheffieldMethercott [ 19881 

BRE [Yong, 19901 

The review of the models was conducted by a literature survey, comparing the formulation and 

basis of each of the models. The capabilities of each of the models is reviewed in terms of the 

maximum number of nodes or elements, types of elements, materials and types of assemblies 

which can be modeled. The following comments were provided Sullivan, et al. based on the 

review: 

133 
the predictive capability of the structural models is less than that for the thermal finite . 

element models due to: 

inadequate material models 

uncertain material property values at elevated temperature 

sensitivity of the structural analysis, given the accumulating error from material 

models and thermal response analysis 

stress history is ignored 

transient thermal creep in concrete is ignored, having its greatest impact on concrete columns 

the effect of creep in steel appears to be of second order importance. Creep is generally 

compensated for by defining other mechanical properties as “effective” properties. 

programs are limited to two-dimensional analyses 

programs are based on Navier-Bernoulli assumption of small displacements. Hence, large 

displacements are not accurately modeled. 

Weaknesses in the programs included: 

poor documentation 

poor user-fiiendliness 

Comparisons of predictions and measurements have been included in the literature. Examples of 

such comparisons for steel columns, beams and frames are provided in Figures 3.2 and 3.3. 

Franssen, et al. [1994] reviewed five models, of which only one, CEFICOSS, was also reviewed 

by Sullivan, et al. The other four models reviewed by Franssen, et al., include DIANA, LENASMT, SAFE and SISMEF. In addition to a literature survey of the formulation and limitations of 

each model, eight numerical tests were conducted to compare the output from each model. The 

tests included simulation of Lee’s frame bee, et al., 19681, a uniformly loaded column and an 

eccentricity loaded column. Heating conditions were varied in the eight tests ranging from the 

standard exposure to one which uniformly heats the structural member. In general, the agreement 

between the models is reasonable. The output, in terms of maximum load or failure temperature 

varies for any two models by less than 6% for any of the tests. Greater disagreement was noted in 

the predicted displacements by the models. These differences are attributed to different methods 

of addressing residual stresses. 

While not finite element formulations, other computer-based structural models which can be coupled 

to finite element thermal analyses do exist. All of the following methods were included in the review 

by Sullivan, et al., except SAWTEF: 

STABA-F Ipudolph, et al., 19861 

ISFED Fowler, et al., 19891 

BFIRE [Sullivan, et al. , 19941 

FIRESTRUCT [ON, 19851 

SOSMEF pirdi, 19881 

SAWTEF [Cramer and Shrestha, 19931 

These methods accept temperature input to evaluate material properties and thermal strain. A 

moment or curvature analysis is conducted to evaluate the performance of the fire-exposed member. 

134 
Figure 3.2 Predicted Deformations of Structural Frame [ Schleich, 1993 , p. 601 

135 
Figure 3.3 Comparison Predicted and Measured Fire Resistance of Steel Structural Members 

[Schleich, 1993, p. 601 

SAWTEF is applied to analyze the integrity of fire-exposed wood trusses. SAWTEF accounts for 

material property changes with temperature, both for the wood and metal connecting plates. Stress 

resultants are determined for the wood members and connector plates and displacements are 

determined for each connection point. 

SAFIR is one of the few models that can conduct a thermo-mechanical analysis, where the results of 

the heat transfer analysis are provided for the structural analysis. This does not mean that the 

analysis is hlly coupled, as the geometry is not redefined, etc., however, this is a promising first step 

toward that end. 

Since the mid-9O’s reviews, development and application of finite element models have been 

described in several papers. As an example, VULCAN has been applied to model the structural 

response of the floor assemblies in the Cardington test Bug, et al., 20021. Existing models 

ABAQUS and ANSYS have also been applied for structural fire protection analyses [Spyrou, et al., 

20021 [Gillie, et al., 20021 [Cameron and Usmani, 20021 [Zhao and Kruppa, 20021. 

136 
3.3 Frame Analvses 

Recently, methods to analyze the effect of fire exposure on a building fiame have been developed. 

The frame analyses range from algebraic-equation based methods to finite element analyses, As 

indicated in the review of finite element models by Franssen, et al., [ 19941, Lee’s fiame is used 

extensively as a test case in the documentation for several models. 

Pettersson, et al. [1976] include a frame analysis via algebraic equations used to determine 

displacement. The frames consist of beams supported by one or two columns at mid-span. The 

analysis assumes that each beam or column has a uniform temperature (though the temperature of the 

beam is not required to be that of a column). A pinned connection between the structural members is 

assumed. The analysis considers the compatibility’of the deformation of each member by requiring 

that the change in length of the column is equal to the beam deflection at the point of contact. 

Schleich, et al., [1986] describe the application of CEFICOSS [Franssen, 19871 for a fi-ame analysis. 

The fiame consists of a single beam and column, where one end of the column is connected to an end 

of the beam. Reasonable agreement is indicated between predicted and measured results. 

El-Rimavi, et al. , [ 19941 describe the application of another finite element model, NARR2, for the 

evaluation of a large building fiame involving numerous beams and columns. The large fiame is 

divided into several subfi-ames for computational ease. Good agreement is noted between 

predictions of deflections and force resultants obtained involving simulations of the full building 

he and subhes. Slightly greater failure temperatures were determined for semi-rigid 

connections as compared to rigid connections. 

Liew and Ma [2002] apply the model FAIlTS to assess the response of a steel frame with concrete 

floor slabs to fire exposure. The principal intent of their analysis is to assess the response of the 

frame to varying levels of fireproofing provided to the steel columns and beams. 

One of the current areas of research activity and modeling involves the analysis of connections. 

Many of the previous efforts involving frames assumed that the integrity of the connection was 

maintained throughout the duration of the exposure. Papers by Franssen and Brauwers [2002] (see 

Figure 3.4) and Spyrou, et al., [2002] recently analyzed the performance of connections in steel 

frame buildings. 

Limitations 

The principal limitation associated with frame analyses are related to the rigidity of the connection. 

0 Limited information is available concerning the effect of elevated temperature on the rigidity of 

the connection. 

Other than the Cardington tests, no other data is available on the performance of fire-exposed 

frames with which to compare results from models. 

4. Summary and Research Needs 

A wide variety of calculation methods for structural fire protection have been reviewed in the 

previous sections. The available calculations apply to many different types of building 

assemblies, including floor- and roof-ceiling assemblies, columns, walls and trusses. The 

building assemblies may be comprised of any of the principal structural materials, i.e. steel, 

concrete, concrete and clay masonry and wood, as well as protection materials and veneers. In 

137 
fact, in a previous survey of experts in structural fire protection conducted almost 20 years ago, a 

strong majority indicated that techniques were available at that time to assess the fire resistance 

for engineering purposes of any type of structural member [Milke, 19851. 

Several published evaluations of the predictive capabilities of the methods have been conducted. 

In general, the predictive capability of the methods is acceptable for engineering purposes. 

However, all calculations from a particular method should not be expected to agree perfectly with 

measured parameters. For example, calculated stresses may be in good agreement with 

measurements while agreement of displacements is disappointing. Even so, many of the tools do 

appear to adequately capture the first-order effects of fire resistance assessments to qual@ as 

candidates for use in design applications. The adequacy of the engineering tools for fre 

resistance assessments is indicated by the incorporation of analysis procedures into the Eurocodes 

documents. 

Significant constraints in the application of such tools include the limited availability of material 

property data and the limited understanding of these analytical tools by practicing engineers. 

However, as in virtually any area of engineering, numerous “unknowns” or gaps in the state of 

knowledge remain. These gaps have been identified in the previous sections, often as limitations 

of a particular calculation method. Some of the gaps indicate a lack of understanding, while 

others relate primarily to a lack of data. The impact of the unknowns varies, though many of 

them relate to issues of second order importance. One principal effect of the unknowns is to limit 

the applicability of the calculation methods to selected types of building assemblies. Even though 

many of the unknowns are individually of second order importance, together they may have 

significant impact in certain applications. Thus, if the gaps can be addressed, “anomalies” in the 

predictions may be resolved and broaden the applicability of the calculation methods. The gaps 

are summarized in the following sections. 

4. I Material Effects 

Material response to fire is a principal area of weakness in evaluating the response of building 

assemblies to fire exposure and serves as a major constraint to the application of analytical 

methods for fue resistance assessments. Except for the principal structural materials and a 

limited number of protection materials, material property data at elevated temperature are sparse. 

Part of the problem concerning material property data is the shortage of standard test methods for 

conducting such analyses for a wide variety of materials for the wide range in temperatures 

relevant to fire resistance analyses. 

Other issues include the inability to predict crack initiation and development, adherence of 

protection materials to structural members and ablation and intumescence of protection materials, 

though attempts have been made at assessing such behavior putler, et al., 19951. Aspects of heat 

absorption and moisture migration are often neglected or are incorporated implicitly into other 

material properties. A model for spalling behavior of concrete is not available. Char rates 

typically cited for wood members are independent of the stress state and are only valid for the 

standard fire exposure. 

In some cases, the deficiencies simply restrict the ability of calculation methods to be applied for 

that material, such as intumescent materials. In other cases, the gaps may be of second order 

significance, given the recognition given to existing design guides that ignore the gaps and the 

presence of some of these same gaps in structural engineering calculations for ambient 

temperature conditions. 

138 
Two approaches can be proposed to narrow these gaps in material effects. One approach is to 

conduct fimdamental research to narrow or eliminate the gap. Such research could result in 

improved material models. The second approach is to continue conducting large-scale tests 

involving fire exposure to develop “effective” properties and implicitly address complex issues 

such as adherence of protection materials or cracks. 

4.2 nermal Response 

A principal limitation in heat transfer analyses is the lack of coupling to mechanical analyses. While 

output from some heat transfer models is easily provided as input, geometric changes are neglected. 

Further, assemblies are treated from an idealistic perspective, Le. crack formation is neglected as is 

the loss of adherence of fireproofing materials. A model for intumescent protection materials is 

lacking. While models have been developed for research applications that couple heat and mass 

transfer for moisture containing materials, such has not been applied for structural fire protection. 

An improved basis for heat transfer parameters, especially convection, is needed. As indicated in the 

previous section, the dearth of material property data, especially at elevated temperature for 

protection materials is a significant barrier. 

While some of the shortcomings can be improved via model development, most of the 

shortcomings are due to the lack of experimental data. The majority of the experimental data 

needed relates to material behavior and can be conducted via small-scale tests. However, 

developing an improved understanding of heat transfer in fully-developed fires requires largescale experiments. 

4.3 Structural Response 

As with the shortcomings for thermal response analysis, the shortcomings for structural response 

can be divided into the need for additional data and the need for improved models. The principal 

issue relating to modeling again addresses the need for a coupled thermo-mechanical model. 

Data needs again involve material property values at elevated temperature, improved 

understanding of the role of stress on spalling and charring, creep, and the performance of 

connections in frames exposed to fires. 

As noted for thermal response analyses, the data needs involve conducting small- and large-scale 

experiments. Much of the material behavior aspects can be explored via small-scale tests, while 

understanding the performance of connections involves a larger-scale experiment. 

5. References 

ACI, 1981, Guide for Determining the Fire Endurance of Concrete Elements, Report No. 216, 

American Concrete Institute. 

AISC, 1993, Load & Resistance Factor Design Specijkation for Structural Steel Buildings, 

AISI, 1979, Fire-Safe Structural Steel, A Design Guide, Washington, DC, American Iron and 

American lnstitute of Steel Construction, Chicago, IL. 

Steel Institute. 

Ahmed, G.N. and Hurst, J.P., 1995, “Modeling the Thermal Behavior of Concrete Slabs 

Subjected to the ASTM El 19 Standard Fire Condition,” .I of Fire Protection Engineering, 7, 

4, 125-132. 

139 
Allen, D.E. and Lie, T.T., 1974, “Further Studies of the Fire Resistance of Reinforced Concrete 

Columns,” Technical Paper No. 416, NRCC 14047, Ottawa: Division of Building Research, 

National Research Council of Canada. 

ASTM, 1995, “Standard Test Methods for Fire Tests of Building Construction and Materials,” 

ASTM E 1 19, Philadelphia, American Society of Testing and Materials. 

Anderberg, Y ., 1988, “Modeling Steel Behaviour,” Fire Safety J , 13, 1, 1 7-26. 

Berger, G., 1989, “Estimating the Temperature Response of Wide Flange Steel Columns in the 

ASTM El 19 Test,” College Park, University of Maryland. 

Bongard, W., 1974, “Brandsicherheit im Stahlbau - Teil V: Unverkleidete Stahlkonstruktionen - 

Brandverhalten und Verwendungsbereich,” Europaische Konvention fiir Stahlbau (EKS), 

EKS -1u-74-2-D . 

Boring, D.F., 1979, “An Analytical Evaluation of the Structural Response of Simply Supported, 

Thermally Unrestrained Structural Steel Beams Exposed to the Standard Fire Endurance 

Test,” M.S. Thesis, Columbus, Ohio State University. 

Buchanan, A., 2001, “Structural Design for Fire Safety,” John Wiley, New York. 

Butler, K.M., Baum, H.R., Kashiwagi, T., 1995, “Heat Transfer in an Intumescent Material Using 

a Three-Dimensional Lagrangian Model,” Proceedings of International Conference on Fire 

Research and Engineering, Society of Fire Protection Engineers, 26 1-266. 

Cameron, N. and Usmani, A., 2002, “Analysis of the Structural Behaviour of Floor Slabs Under 

Thermal Effects using Fundamental Principles,” Proceedings of the 2“d International Workshop 

on Structures in Fire, Canterbury, New Zealand, 1 15- 126. 

Childs, Kenneth, 1999, Heating 7.3 User’s Manual, Oak Ridge National Laboratory, Oak Ridge, 

TN. 

Clancy, P., 1999, “Time and Probability of Failure of Timber Framed Walls in Fire, PhD Thesis, 

CRSI, 1980, Reinforced Concrete Fire Resistance, Chicago, Concrete Reinforcing Steel Institute. 

Collier, P.C.R. and Buchanan, A.H., 2002, “Fire Resistance of Lightweight Timber Framed 

Walls,” Fire Technology, 38, p. 125-145. 

Cooper, L.Y., 1997, “The Thermal Response of Gypsum Panel Steel Stud Wall Systems Exposed 

to Fire Environments, NISTIR 6027, National Institute of Standards and Technology. 

Cramer, S., and Shrestha, 1993, User’s Manual - SAWTEF Ver 1.1, Structural Analysis of Wood 

Trusses Exposed to Fire, University of Wisconsin - Madison and USDA Forest Products 

DTU, 1982, “Mdthode de Prdvision par le Calcul du Comportement au Feu des Structures en 

Victoria University of Technology. 

Laboratory. 

Acier - Document Technique Unifi6, Construction Metallique, No. 10. 

El-Rimawi, J.A., Burgess, I.W. and Plank, R.J., 1994, “Model Studies of Composite Building 

Frame Behaviour in Fire, Proceedings of Fourth International Symposium of Fire Safety 

Science. 

ECCS, 1983, Technical Committee 3, European Recommendations for the Fire Safety of Steel 

Structures, European Convention for Constructional Steelwork, Amsterdam, Elsevier. 

140 
ECCS, 1983, Technical Committee 3, Design Manual on the European Recommendations for the 

Fire Safety of Steel Structures, European Convention for Constructional Steelwork, Brussels, 

Elsevier. 

Eurocodes, 2001, “Design of Steel Structures, Part 1.2 General Rules, Structural Fire Design,” 

Eurocodes 3, CEN, Brussels. 

Fleischmann, C., and Buchanan, A., 2002, “Analytical Methods for Determining Fire Resistance of 

Concrete Members,” SFPE Handbook of Fire Protection Engineering, 3“‘ edition, P.J. DiNenno 

(Ed.), Quhcy, NFPA. 

Forsen, NE., 1982, A Theoretical StuaFy on the Fire Resistance of Concrete Structures’ - 

CONFIRE, Cement and Concrete Research Institute, SINTEF, Report No. STF 65 A82062, 

The Norwegian Institute of Technology. 

Forsen, NE., 1983, STEELFIRE - Finite Element Program for Nonlinear Analysis of Steel 

Frames Exposed to Fire, Multiconsult AS Consulting Engineers, Norway. 

Frannsen, J.M., 1987, Etude du Comportement au Feu des Structures Mixtes Ancier - Bkton, 

(CEFICOSS), A Study of the Behaviour of Composite Steel-Concrete Structures in Fire, 

Theses de Doctorate, Universite de Liege, Belgique. 

J-M. Franssen, J-B. Schleich, L-G Cajot, D. Talamona, B. Zhao, L. Twilt and K. Both, 1994, “A 

Comparison Between Five Structural Fire Codes Applied to Steel Elements,” Proceedings of 

Fourth International Symposium of Fire Safety Science. 

Franssen, J.-M., Kodur, V.K.R, and Mason J., 2000, “User’s Manual for SAFIR: A Computer 

Program for Analysis of Structures Submitted to Fire,” University of Liege, Belgium. 

Franssen, J.-M., and Brauwers, L., 2002, “Numerical Determination of 3D Temperature Fields in 

Steel Joints,” Proceedings of the 2& International Workshop on Structures in Fire, Canterbury, 

New Zealand, 1-20. 

Franssen, J.-M. and J.-C. Dotreppe, 2003, “Fire Tests and Calculation Methods for Circular Concrete 

Columns, Fire TechnoZogy, 39,89-97. 

Gamble, W.L., 1989, “Predicting Protected Steel Member Fire Endurance Using Spread-Sheet 

Programs,” Fire Technology, 25,3,256-273. 

Gerlich, J.T., 1995, “Design of Loadbearing Light Steel Frame Walls for Fire Resistance,” Fire 

Engineering Research Report 95/3 , Christchurch, University of Canterbury. 

Gillie, M., Usmani, A., and Rotter, M., 2002, “Bending and Membrane Action in Concrete Slabs,” 

Proceedings of the 2* International Workshop on Structures in Fire, Canterbury, New Zealand, 

95-1 14. 

Harmathy, T.Z., 1993, Fire Safety Design & Concrete, N.Y., John Wiley. 

Hertz, K., 198 1 , “Simple Temperature Calculation of Fire Exposed Concrete Constructions,” 

Institute of Building Design, Report No. 159, Technical University of Denmark. 

Hosser, D., Dorn, T., and Richter, E., 1994, “Evaluation of Simplified Calculation Methods for 

Structural Fire Design,” Fire Safety .I, 22,249-304. 

Huang, Z., Burgess, I., Plank, R., Bailey, C., 2002, “Comparison of BRE Simple Design Method for 

Composite Floor Slabs in Fire with Non-linear FE Modeling,” Proceedings of the 2nd 

International Workshop on Structures in Fire, Canterbury, New Zealand, 83-94. 

141 
Iding, R., Bresler, B., Nizamuddin, Z., 1977, FIRES-RCII, A Computer Program for the Fire 

Response of Structures - Reinforced Concrete Frames, Fire Research Group, Report 

No.UCB FRG 77-8, Berkeley, University of California. 

Iding, R., Nizamuddin, Z., Bresler, B., 1977, Ere REsponse of &-uctures - Thermal 3- 

Dimensional Version, UCB FRB 77-1 5, Berkeley, University of California. 

ISE, 1978, “Design and Detailing of Concrete Structures for Fire Resistance,” London, Institution 

of Structural Engineers. 

Janssens, M., 2002, “Modeling of the Thermal Degradation of Structural Wood Members Exposed to 

Fire,” Proceedings of the 2“d International Workshop on Structures in Fire, Canterbury, New 

Zealand, 2 1 1-222. 

Janssens, M., and White, R., 1994, J of Fire and Materials, 18,263-266. 

Jeanes, D.C., 1982, “Predicting Fire Endurance of Steel Structures,” ASCE preprint 82-033. 

Kashiwagi, T., (ed), 1994, Fire Safety Science - Proceedings of the Fourth International 

Klement, E., Rudolphi, R., and Stanke, J., 1972, “Das Brandverhalten von Holzstiitzen unter 

Law, M., 1978, “Fire Safety of External Building Elements - The Design Approach,” AISC Eng 

Lee, S.L., Manuel, F.S., and Rossow, E.C., 1968, “Large Deflections and Stability of Elastic 

Lie, T.T., 1972, Fire and Buildings, London, Applied Science Publishers. 

Lie, T.T., 1977, Canadian J of Civil Engineering, 4, 161-169. 

Lie, T.T., 1978, “Calculation of the Fire Resistance of Composite Concrete Floor and Roof 

Lie, T.T., 1984, “A Procedure to Calculate Fire Resistance of Structural Members,” Fire and 

Lie, T.T., ed, 1992, Structural Fire Protection, NY, American Society of Civil Engineers. 

Lie, T.T., and Harmathy, T.Z., 1972, “A Numerical Procedure to Calculate the Temperature of 

Protected Steel Columns Exposed to Fire,” Fire Study No. 28, NRCC 12535, Ottawa, 

Division of Building Research, National Research Council of Canada. 

Lie, T.T. and Stanzak, W.W., 1974, “Structural Steel and Fire - More Realistic Analysis. ASCE 

National Structural Engineering Meeting, Cincinnati. 

Lie, T.T., Lin, T.D., Allen, D.E., Abrams, M.S., 1984, “Fire Resistance of Reinforced Concrete 

Columns,” Technical Paper No. 378, Ottawa, Division of Building Research, National 

Research Council of Canada. 

Liew, J.Y.R, and Ma, K.Y., 2002, “Advanced Analysis of Steel Framework Exposed to Accidental 

Fire,” Proceedings of the 2“‘ International Workshop on Structures in Fire, Canterbury, New 

Lund, P.D., (ed), 1995, Proceedings of International Conference on Fire Research and 

Symposium, IAFSS. 

Druckbeanspruchung, Bauen mit Holz,” Heft 5 und 6. 

J, 2nd Quarter. 

Frames,” J of Eng. Mech. Div. ASCE, 94, EM2,521. 

Slabs,” Fire Technology, 14, 1,284. 

Materials, 8, 1,40-48. 

Zealand, 303-3 18. 

Engineering, Society of Fire Protection Engineers. 

LUSAS, 1988, Advanced Procedures Training Course, FEA, United Kingdom. 

142 
Malhotra, H.L., 1982, Design of Fire-Resisting Structures, N.Y., Chapman and Hall. 

Markstein, G.H., 1976, “Radiative Energy Transfer from Turbulent Difision Flames,” 

Combustion and Flame, 27,5 1-63. 

Mehaffey, J.R. and Takeda, H., 1995, “Predicting Heat Transfer Through Wood Stud Walls 

Exposed to Fire,” International Conference on Fire Research and Engineering, Society of 

Fire Protection Engineers. 

Meyer-Ottens, C., 1976, “Feuenviderstandsdauer unbekleideter Halzbal ken mit Rechteckquerschnitt,” Bauen mit Holz, Heft 5. 

Meyer-Ottens, C., and Haksever, A., 1979, “Brandverhalten von brettschichtverleimten. 

Holzstutzen,” Forschungsbeitrage fur die Baupraxis, Berlin. 

Milke, J.A., 1985, “Overview of Existing Analytical Methods for the Determination of Fire 

Resistance,” Fire TechnoIogy, 2 1, 1,59-65. 

Milke, J., 1992, “Sohare Review: Temperature Analysis of Structures Exposed to Fire,” Fire 

Technology, 28,2, 184-1 89. 

Milke, J.A., 2002, “Analytical Methods for Determining Fire Resistance of Steel Members,” SFPE 

Handbook of Fire Protection Engineering, 3rd edition, P.J. DiNenno (Ed.), Quincy, NFPA. 

Milke, J.A., and Vizzini, A.J., 1990, “Modeling and Evaluation of the Thermal Response of Fire 

Exposed Composites,” Proceedings of the 5* AMASME Thermophysical and Heat Transfer 

Conference, Seattle, WA. 

Milke, J.A., and Vizzini, A.J., 1991, “Thermal Response of Fire-Exposed Composites,” J of 

Composites Technology and Research, I3,3, 145- 1 5 1. 

Milke, J.A., and Vizzini, A.J., 1993, “The Effects of Simulated Fire Exposure on Glass-Reinforced 

Thermoplastic Materials,” JI of Fire Protection Engineering, 5,3, 1 13-124. 

Moss, P. J., 2002, Structures in Fire: Proceedings of the Second International Workshop,” 

Canterbury, New Zealand. 

NCMA, 1966, “Estimating the Fire Resistance of Concrete Masonry,’’ Herndon, VA, National 

Concrete Masonry Association. 

Nethercot, D.A., 1988, Private Communication to Sullivan, Terro and Moms, [1994], August 1, 

1988, and August 20,1990. 

NORDTEST, 1985, Nordtest Method NT FIRE 021 Insulation of Steel Structures: Fire Protection. 

OM, 1985, Large PaneI Systems - Prediction of Behaviour in Fire Tests, A report submitted to the 

Building Research Establishment, Report No. 14404/JB/CW, Ove Amp and Partners, Building 

Research Station, June. 

Palm Computing Ltd. (PCL), PATHOS 2 Manual, Revision 2.01, Berkshire, U.K., May 1992. 

Pettersson, O., Magnusson, S.E. and Thor, J., 1976, “Fire Engineering Design of Structures,” 

Publication 50, Swedish Institute of Steel Construction. 

Pettersson, O., 1986, “Structural Fire Behavior,” Proceedings of First International Symposium of 

Fire Safety Science. 

Pettersson, O., Magnusson, S-E., and Thor, J., 1976, Fire Engineering Design of Steel Structures, 

Publication 50, Stockholm, Swedish Institute of Steel Construction. 

143 
PCI, 1977, Design for Fire Resistance of Precast Prestressed Concrete, Chicago, Prestressed 

Concrete Institute. 

Rudolph, K., Richter, E., Hass, R., and Quast, U., 1986, Principles for Calculation of Load-Bearing 

and Deformation Behaviour of Composite Structurd Elements under Fire Action (STABA-F), , Proceedings of 1 st International Symposium of Fire Safety Science. 

SchafTer, E.L., 1977, “State of Structural Timber Fire Endurance,” Wood and Fiber, 9,2,145- 190. 

Scheer, C., and Schatz, T., 1985, “Bemessingshilfen - Brandschutz im Holzbau,” Bauen mit Holz, 

Heft 3 and 4. 

Schleich, J.B., 1993, International Fire Engineering Design for Steel Structzrres: State of the Art, 

Brussels, International Iron and Steel Institute. 

Schleich, J.B., Dotreppe, J.C., and Franssen, J.M., 1986, ‘Numerical Simulations of Fire Resistance 

Tests on Steel and Composite Structural Elements. on Frames,” Proceedings of First 

International Symposium of Fire Safety Science. 

SIA, 1985, “Schweizerischer Ingenieur- and Architecktenverein: Feuerwiderstand von 

Stahlbauteilen,” Heft 82, Zurich. 

Seekamp, H. and Stanke, J., 1972, “Das Brandverhalten von belasten Holzstiitzen unter 

Druckbeanspruchung,” Bauen mit Holz, Heft 5 und 6. 

Smith, I.A. and Stirland, C., 1983, “Analytical Methods and Design of Fire Safe Steel 

Structures,” International Seminar on Three Decades of Structural Fire Safety, 

Borehamwood, U.K. 

Spyrou, S., Davison, B., Burgess, I., and Plank, R, 2002, “Experimental and Analytical Studies of 

Steel Joint Components at Elevated Temperatures,” Proceedings of the 2“d International 

Workshop on Structures in Fire, Canterbury, New Zealand, 2 1-33. 

Sterner, E., and Wickstrom, U., 1990, “TASEF-Temperature Analysis of Structures Exposed to 

Fire,” Fire Technology SP Report 1990: 05, Boras, Swedish National Testing Institute. 

Sullivan, P.J.E., Terro, M.J., and Morris, W.A., 1994, “Critical Review of Fire Dedicated 

Thermal and Structural Computer Programs,” Jof Applied Fire Science, 3,2, 1 13-135. 

Sultan, M., 1996, “A Model for Predicting Heat Transfer through Non-insulated Unloaded SteelStud Gypsum Board Wall Assemblies Exposed to Fire,” Fire Technology, 32,3,239-259. 

Sultan, M., Alfawakhiri, F., and Benichou, N., 2001, “A Model for Predicting Heat Transfer 

through Insulated Steel-Stud Wall Assemblies Exposed to Fire,” Proceedings of Fire and 

Materials Conference, Interscience Communications, 495-506. 

Takeda, H., and Kouchleva, S., “A Model to Predict Fire Resistance of Wood-Framed 

Floor/Ceihg Assemblies, 200 1, Proceedings of Fire and Materials Conference, Interscience 

Communications, 505-5 16. 

Terro, M.J., 1991, “Numerical Modelling of Thermal and Structural Response of Reinforced 

Concrete Structures in Fire,” Ph.D. Thesis, Department of Civil Engineering, Imperial 

College of Science, Technology and Medicene. 

Towler, K., Khoury, G., and Sullivan, P.J.E., 1989, Computer Modelling of the Eflect of Fire on 

Large Panel Structures, Final Report Submitted to the Department of the Environment by 

Fire Safety Design Consultants, United Kingdom. 

Twilt, L., 1988, “Strength and Deformation Properties of Steel at Elevated Temperatures: Some 

Practical Implications,” Fire Safety .I, 1 3, 1,9- 16. 

144 
Virdi, K.S., 1988, Validation of Computer Model for Predicting the Structural Response of Steel 

&Section Columns Heated Non-uniformly to Elevated Temperatures, Report submitted to the 

Building Research Establishment, Fire Research Station, Report No. 042.9080 1 , London, 

Department of Civil Engineering, City University. 

White, R.H., 2002, “Analytical Methods for Determining Fire Resistance of Timber Members,” 

SFPE Handbook of Fire Protection Engineering, 3rd edition, P.J. DiNenno (Ed.), Quincy, 

NFPA. 

Yong, W., 1990, Building Research Establishment, Private Communication to Sullivan, Terro and 

Morris, [ 19941. 

Zhao, B., and Kruppa, J., “Numerical Modeling of Structural Behaviour of Open Car Parks under 

Natural Fire,” Proceedings of the 2nd International Workshop on Structures in Fire, Canterbury, 

New Zealand, 3 3 7-3 50. 

145 
White Paper 7 

Thermal and structural analysis methods and tools - gaps in knowledge and priority area 

for research from a practice perspective 

Barbara Lane, Ph.D., Arup Fire 

Introduction 

This NIST workshop is being held to create a detailed research and development roadmap for 

Fire Safety Design and Retrofit of Structures. 

This paper addresses thermal and structural analysis methods and tools only. Specifically this 

paper aims to create a list of knowledge gaps in this field, which are priority areas for research, 

from an Engineering Practitioners perspective. 

The information presented in this paper is based on expertise within Arup Fire from related 

design projects and research, which also form part of existing commissioned surveys such as that 

carried out for the American Institute of Steel Construction 2003. 

The paper has been written as a discussion.point only and therefore does not contain a literature 

review of this field as a preamble to the gaps identified. 

The following is a list of gaps in the current ability of practitioners to successfully carry out fire 

safety design of structures. 

Regulatory Guidance and Control - 

In order to ensure the success of structural fire engineering design methods - from complex finite 

element analysis to single element analytical methods, the acceptance by the regulatory 

authorities is essential. As well as a general understanding and acknowledgement of the rigorous 

validation behind such analyses, an ability to review proposed solutions is required. 

Currently there exists no good practice guide for structural fire engineering design methods. It 

seems key that authorities should have accepted codes of practice that provide a step by step 

guide to evaluating proposed design methods. For example minimum levels of input and 

corresponding output, key structural items and materials to be considered, peer reviewed data 

sources and design methods, basic test scenarios - specific fires that amply evaluate the structural 

response, etc. 

Initial reviews of the current state of the US building regulatory system indicate that it is not yet 

ready to support widespread application of performance-based structural fire protection. This is 

largely due to the individualized nature of performance-based projects. The performance-based 

design concept requires that building projects be analyzed individually and that their specific 

details be considered in the development of fire protection strategies. It is difficult for a 

regulatory system based largely on standard test methods and fire ratings to evaluate buildings 

that have been designed to meet unique pefiormance criteria. Also however there is no back up 

information for authorities even if they did decide to approach such a problem. 

Similarly for designers, a good practice guide is essentia1 to limit abuse of analytical and 

numerical methods for passive fire protection designs. 

146 
Possible Ways Forward 

The following is a list of possible changes or additions to building codes that may be necessary to 

support engineered structural fire protection. 

1. Regulatory support for defining project goals, objectives, and performance 

criteria. In order to evaluate the adequacy of a given design, both the building 

designers and the regulatory officials must understand the goals, objectives, and 

performance criteria of the project and must compare these to the expected 

performance of the design. If a standardized method of defining this information is 

not available then regulatory control of projects will be very difficult and regulatory 

bodies will be reluctant to allow performance-based fire protection approaches. 

2. Regulatory Support for Defining Design Fire Scenarios. Along with a system of 

defining goals, criteria, and objectives, codified design fire data may be necessary. 

Structural engineers will require guidance in choosing appropriate thermal 

environment data for structural fire analyses, and regulatory officials will need a way 

of ensuring that appropriate design fires have been utilized for a given project. 

Regulatory Support and Approval for Analytical Methods. In order to allow 

nationwide application of performance-based techniques, a system of identification 

of approved and appropriate analysis methods must be developed. This will inform 

and instruct structural engineers in the correct use of appropriate tools for given 

situations and will help authorities to ensure that appropriate methods have been 

utilized correctly. This may be accomplished by code references to existing or future 

design guides. 

3. 

Approved Simple Analysis Methods 

While advanced, non-linear analysis methods are available and may be the most accurate ways to 

evaluate theoretical structural behavior at fire temperatures, their complexity and the level of 

knowledge required to apply them correctly require a great deal of knowledge on the part of the 

engineer. They are also still relatively rare for real structural assessments. 

Because of this, these tools are a long way from being widely accepted for structural design 

projects. However, if a performance-based approach to structural design for fire conditions is to 

be widely accepted, methods to accomplish the required analysis must be evaluated, approved, 

and made available to engineers. Application of simple methods, developed from complex 

assessments of structures in fire, is a logical and reasonable approach to this issue. 

Various simple analysis methods exist that could be used to determine certain aspects of 

structural fire behavior. These include spreadsheet applications, parametric and linear equations, 

and graphical approaches. Topics such as the strength and deformation of horizontal members at 

elevated temperatures are relatively well covered in the range of existing simple approaches, and 

some research exists validating or disputing these approaches. However, numerous specific 

topics exist for which simple analysis methods do not accurately represent real behavior, or 

simply do not exist. 

Possible Wavs Forward - - __ ~ -~ ~ - ~~ 

A specific list of topics for which fbture research regarding simple analytical methods is required 

should be developed. A full understanding of simple approaches to analyzing structural response 

to fire temperatures requires research into each of these topics. However, the most important 

147 
work in this area will be the validation and justification of the use of simplified methods to 

represent the highly complicated, nonlinear structural behavior associated with fires in buildings. 

As mentioned previously, approval and acceptance of complex nonlinear analysis tools by the 

regulatory bodies and the practicing engineers for general structural design projects will be very 

difficult to attain. Such goals for simplified methods are more reasonable, initially. However, 

widespread acceptance of simplified analytical methods will require the completion of several 

tasks: 

1. 

2. 

Validation of different simple analytical methods for specific design purposes (for 

example, validation of a tool for the analysis of ribbed concrete slabs, etc.). 

Regulatory acceptance of the validation of various models. 

3. 

4. 

Regulatory dissemination of approved simple analytical methods. 

Availability of regulatory and industry guidance on the proper use of available 

simplified analytical methods for the benefit of authorities having jurisdiction and 

engineers alike. 

If the above four tasks can be accomplished, great strides will have been taken towards the 

accomplishment of widespread acceptance of engineered structural fire safety approaches. 

Information Availability 

A large amount of data exists worldwide regarding various aspects of the behavior of structural 

components under fire conditions. However, this data is not organized or linked together in a 

way that provides structural engineemwith easy access to appropriate answers for specific 

questions that arise during the design and analysis of structures exposed to real fire temperatures. 

Also, many research efforts do not get published for public use, so an engineer may not be able to 

use the information they contain. Thus, an engineer may not have access to state-of-the-art 

information regarding the specific hctions the engineer needs to perform, such as those that 

make up the performance-based structural engineering process. 

. 

Possible Wws Forward 

The engineering world in general has long been devoted to the dissemination of knowledge 

amongst its members. The current lack of access to pertinent data is due largely to the separation 

that has long existed between structural and fire protection engineers. This gap has prevented or 

discouraged the efficient trade of information between these fields. However, the performancebased approach to structural fire protection requires that structural engineers have access to the 

knowledge of the fire protection engineering community, and that this and structural engineering 

information be easily and efficiently accessed. 

To this end, the following are general recommendations for advances that may help bring needed 

information to engineers designing structures for fire safety: 

1. Information Management. Develop and make widely available a database system 

dedicated to the dissemination of structural fire engineering information. This 

database should provide access to information covering all aspects of the process of 

designing and analyzing structures at fire temperatures, and should provide the 

engineer with guidance in choosing appropriate methods, data, and other critical 

information. 

148 
2. Research Support and Publication. Encourage global contribution to the body of 

knowledge regarding structural fire safety issues by identifying gaps in that 

knowledge, making these gaps known to researchers and engineers, and sponsoring 

research efforts, and also by providing a forum for dissemination of new knowledge 

(such as a database system as discussed above). 

3. Availability of Existing Research. Collect information regarding existing research, 

both published and unpublished, and make this information available to engineers. 

Author Submission of Past Research. Encourage the availability of past research 

efforts by providing an easy and efficient way for authors to submit information 

regarding their existing work to a forum such as that discussed above. 

4. 

Compartment Fire Models 

Computer Fire Models have been traditionally divided in two groups, Zone Models (ZM) and 

Computational Fluid Dynamics (CFD) or Field Models. 

Zone models treat compartments as a control volume sub-divided into two smaller control 

volumes. All heat transfer related quantities within these codes are established in an empirical 

manner. 

The main aspect that differentiates CFD codes is the way by which turbulence is modeled. Thus, 

CFD codes can be divided into three groups, Reynolds Averaged Navier-Stokes (WINS) models, 

Large Eddy Simulation (LES) models and Direct Numerical Simulation (DNS) models. 

Specific limitations of these models relating to structural design follow. 

Characteristic time scales for the heating of solids are in general considered much larger than the 

time scales for fire growth. Thus it has been an accepted approach to ignore the fire growth period 

and conduct all structural analysis under conditions corresponding to a post-flash over or fully 

developed fire. Within a fire scenario it is possible that flashover might be attained within the 

compartment of origin before any structural element has undergone significant heating, 

nevertheless none of the adjacent compartments will be expected to have reached fully developed 

conditions. Furthermore, growth beyond the compartment of origin will generally be within the 

same time scales as the heating of structural elements. If the objective is to integrate CFM’s with 

structural analysis, significant effort is necessary to establish realistic timescales and 

characteristic conditions of fire growth beyond the compartment of origin. Experimental 

validation should follow because little or no useful data exists. 

It is of importance to note that extensive experimental data has been gathered on the evolution of 

the temperatures within a compartment but very little information exists on the evolution of the 

heat fluxes imposed on a compartment surface. This data is of immediate need if any validated 

integration of Fire and Structural Engineering is to be achieved. 

Time scales more relevant to structural behavior imply in most cases fully developed fires. None 

of the existing CFD codes has been properly validated under these conditions. The data available 

for post-flashover, fully developed fires is generally in the form of average punctual 

measurements of temperature, which is more suited for the validation of Zone Models than of 

CFD codes. Combustion and soot models are greatly sensitive to the burning conditions therefore 

the capability of existing model to provide reasonable predictions under fully-developed fire 

conditions remains untested. 

149 
Independent of the model used all numerical tools are severely limited by an improper definition 

of the fundamental properties of materials controlling fire growth. An analysis of the input 

variables for all flammable materials shows a systematic dependence of simple and very 

approximate databases. The errors that can be induced by an improper or incomplete selection of 

material properties can be more important &an those generated by an improper use of the 

parameters of the turbulence model. 

Possible Wavs Forward 

The following is a list of specific research areas regarding compartment fire models for which 

future effort is required: 

1 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

Establish realistic timescales and characteristic conditions of fire growth beyond the 

compartment of origin plus experimental validation so as usefid data exists for 

modelers. 

Validate existing CFD codes for time scales more relevant to structural behavior 

(fully developed fires). 

Validations of combustion and soot models to provide reasonable predictions under 

fully-developed fire conditions. 

Further validation of empirical constants with detailed and quantitative 

measurements is required for zone models, specifically entrainment rates and their 

validation under conditions other than fiee axis-symmetric or line fires. 

For zone models, of the constant properties in each zone, complicated geometries 

would be treated in the same way as less complicated ones. The absence of velocity 

fields and lack of turbulence modeling implies that the convective heat transfer will 

not be affected by complicated geometries. The use of zone model for very 

complicated geometries requires validation. 

Establish sensitivity of heat fluxes to the different numerical parameters and physical 

models. 

Validation of wall functions and heat transfer models with detailed quantitative 

measurements. 

Validation of turbulence models for transitional flows, re-circulation areas and 

regions close to walls. 

Evaluation of the effect of fire retardants on soot production. 

Effect of soot dep.osition on soot concentrations in fire related environments. 

Extension of soot models to flames generated by materials typical of fires. 

Quantitative evaluation of the effect or roughness on existing turbulence models and 

convective heat transfer. 

Development of more efficient numerical schemes to speed computations and allow 

modeling of more complex environments. 

Establish sensitivity of heat fluxes to the different numerical parameters and physical 

models. 

Thermal and Mechanical Properties of Structural Materials 

While numerous sources for thermal and mechanical material properties exist, some gaps are 

evident in the body of data. This conclusion is based on the following observations: 

150 
1. Information is greatly limited regarding values and temperature dependence of 

numerous specific steel properties. Those observed here are: 

Temperature-dependent tensile strength of steel 

Temperature-dependent shear modulus of steel 

Temperature-dependent density of steel 

Temperature-dependent Poisson’s Ratio of steel 

2. Information is greatly limited regarding values and temperature dependence of 

numerous specific concrete properties necessary for analysis of composite 

construction. Those observed here are: 

Temperature-dependent compressive strength and elastic modulus for 

concrete 

Temperature-dependent shear modulus of concrete 

Temperature-dependent density of concrete 

Temperature-dependent Poisson’s Ratio of concrete 

Mass loss rate at elevated temperatures 

3. Information is greatly limited regarding the temperature dependence of passive 

protection material properties. Specifically, no resources reviewed here included 

mathematical expressions to describe the temperature-dependence of protective 

material properties. Parameters which require further research and would benefit 

from correlation to mathematical expressions are: 

Temperature-dependent protection material thermal conductivity. 

Temperature-dependent protection material specific heat. 

Temperature-dependent protection material density. 

Temperature-dependent protection material rate of thermal expansion. 

Additionally, material property data for intumescent coatings is difficult to obtain, 

and the information that is available is greatly limited and frequently proprietary. 

Available property information is largely limited to traditional materials. Recent 

tendencies toward performance-based building design have increased the use of more 

novel, high performance materials such as high-strength steels, concretes, and 

composite materials, as well as both common and novel insulation materials. The 

availability of thermal and mechanical properties are, in general, lacking for these 

materials. 

4. 

5. Advanced research on material properties is often not readily available. In order to 

analyze a complex structural assembly or a novel material, the engineer needs access 

to sources of appropriate and accurate information regarding a wide range of material 

properties. 

Possible Ways Forward 

Based on the observations presented above, the following are recommendations for future 

research efforts in regard to structural material thermal and material properties: 

151 
Steel Properties. Several steel properties require exploration to accurately 

determine temperature dependence. These are: 

Tensile Strength 

Shear Modulus 

Density 

Poisson's Ratio 

In addition to simply understanding the temperature dependence of the above steel properties, the 

industry would greatly benefit from the correlation of mathematical expressions describing this 

temperature dependence. 

2) Concrete Properties. Several concrete properties require exploration to determine 

temperature dependence for use in the analysis of composite elements. These are: 

Shear Modulus 

Poisson's Ratio 

Density 

Mass Loss Rate 

Mathematical expressions for the above would prove very beneficial to the field. Also, 

mathematical expressions describing the temperature dependence of the modulus of elasticity of 

concrete and the strength and modulus of elasticity of reinforcing steel are required. 

3) Protection Material Properties. Several protection material properties require 

exploration to determine temperature dependence. These are: 

Thermal Conductivity 

Density 

Specific Heat 

Coefficient of Thermal Expansion 

Formal mathematical representations of these temperature dependent properties could serve to 

increase the accuracy with which the performance of protective materials under fire conditions is 

predicted in structural analysis. The ability to model intumescent paints are of particular interest. 

Development of Tests for Material Properties. Where accepted tests do not exist 

for determining specific thermal or mechanical properties identified as necessary for 4) 

analysis and not currently available (see above), new test methods will need to be 

developed or existing test methods adapted. 

Novel Materials. Additional research is necessary to define the high-temperature 

behavior of novel and high-performance materials. These may include but are not 

limited to the numerous high strength steels and alternative metals that are emerging, 

high-strength concretes, composite materials, and insulation materials. 

Availability of Material Property Information. Compilation of the full range of 

available research, either into comprehensive overview sources or a network or 

database of specific sources, is necessary to ensure that those practicing 

performance-based structural analysis and design have access to inputs that the 

analysis requires. 

Material Property Model Validation. Existing and future research efforts must 

continue to be confirmed and refined through comparison to actual structural fire 

behavior. This can be accomplished through parametric studies of large- and small5) 

6) 

7) 

152 
scale fire tests, as well as through analysis of real structure fires. Such research can 

help refine the general understanding of material behavior and can lead to more 

accurate prediction of actual structural fire performance. 

Heat Transfer Analvsis Methods 

Heat transfer to unprotected structural steel can generally be calculated by hand or spreadsheet 

because its high conductivity and homogeneity make simple calculations accurate. 

Input to any calculation or computer program always requires an estimate of the emissivity and 

the convective heat transfer coefficients. These are both areas that still need investigating. 

Unprotected steel acts as a large heat sink and the effect of this on fire temperatures is not well 

understood. It is known that in a standard furnace a lot more fuel is pumped into the furnace to 

maintain the fire temperature when testing unprotected steel. 

Moisture migration is essentially a concrete problem and the nuclear industry has spent a huge 

effort in understanding pore pressures and migration of water. This level of accuracy is probably 

not required for fire calculations although it is critical in helping to determine spalling of 

concrete, which is not well currently understood. 

Heat transfer through thin film intumescents is not well understood and needs to be quantified. 

Various tools are available for predicting heating conditions in sophisticated projects where the 

design fire is not a relatively simple post-flashover fire involving the whole Compartment. A 

common example of such a tool is FDS (Fire Dynamics Simulator, developed by NIST), a 

computational fluid dynamics code that has become an industry standard in predicting 

compartment fire behavior. Unlike simpler zone models, FDS can be beneficial in compartments 

with large floor plates and when fire spreads from one compartment to another. Also, FDS and 

similar models are useful for predicting temperature distributions throughout a compartment, 

information which is necessary for the prediction of localized heating effects and performance 

under uneven heating conditions. 

The current method of utilizing FDS or other computational fluid dynamics models in structural 

analyses is to record time-temperature relationships for specific points in a structure (i.e. air 

temperatures near structural members) and then input them into the structural analysis, at which 

point a heat transfer analysis must be included to calculate material temperatures. In order to 

accomplish this, the output of the FDS model needs to be coupled with the heat transfer model, or 

the mesh used in both the FDS model and the structural analysis model need to be very similar if 

not exactly the same. The boundary condition between the fire temperature and the steel surface 

is difficult to model accurately and assumptions must be made about convection at this boundary. 

Additional work is required to refine this process. 

Possible Wavs Forward 

1. Coupling of Computational Fluid Dynamics, Thermal and Mechanical Analyses. 

Possibly the most important needed development is the streamlining of the 

interaction of fire models, heat transfer models, and structural analysis models. The 

industry will benefit greatly if a link can be developed between fire behavior 

prediction and structural analysis such that an engineer can efficiently move fkom 

nodal time-temperature curve predictions to material temperatures and the resulting 

structural response. This is challenged by numerous issues, not the least of which is 

the difficulty inherent in modeling thermal boundary conditions close to physical 

objects (e.g. structural members). However the immediate urgency of this seems 

153 
remote as currently there remains so much that is not understood fiom uncoupled 

thermal-structural modeling. 

Material Thermal Properties. Additional research regarding thermal properties of 

construction materials is needed, as discussed above. Specifically, thin film 

intumescents require significant fbrther work. 

Heat Sink Behavior. The effects of heat sink behavior on fire temperatures must be 

better understood and quantified through physical testing and parametric studies. 

2. 

3. 

Non-Linear Analvsis Methods 

Simple analytical methods are generally favorable in the everyday design environment due to 

their relative ease of use and their time and cost efficiency. However, such methods are generally 

incapable of considering numerous complex structural behavior issues. Advanced analysis 

methods, specifically finite element models, are available for complicated situations or when 

increased detail and accuracy is required in an analysis. 

In general, commercially available finite element codes have all the capabilities necessary to 

perform any non-linear analysis; structural response to fire is just one of these. The software 

packages developed in universities and research institutes are frequently less functional but are 

generally designed specifically for modeling some aspect of structural fire behavior. 

Commercial software packages are readily available and have the advantage of being tested on a 

number of highly non-linear and sophisticated problems by the writers and users around the 

world. Upgrades and improvements are released on a regular basis. One disadvantage is the 

computing power necessary to run such models. With the advent of very powerful personal 

computers this is becoming less of an issue. The initial investment in buying the FE program and 

the computer to run it may be considerable. 

Several research institutions have developed special-purpose non-linear structural mechanics 

codes to model structural behavior in fire. Vulcan at the University of Shefield and SAFIR at the 

University of Liege are probably two of the most advanced. However, research codes are 

generally designed to deal with the structural fire problem specifically. Therefore, such codes 

may be improved and modified much more readily for a specific problem than commercial codes. 

However commercial codes are by their broader use subject to constant scrutiny and 

improvement. 

While significant capabilities exist in available finite element codes, the accuracy of their 

analyses depends on their appropriate application. A good deal of effort has gone towards 

validation of models and analysis techniques, especially with the availability of significant data 

sources, such as the Cardington tests, but many situations and details exist for which modeling 

techniques or capabilities are lacking or have not been validated. Some of these details are 

discussed below. 

One of the main drawbacks to advanced analysis methods is the difficulty inherent in their 

regulation. Advanced knowledge is required to utilize these models, and likewise to understand 

their use and the results they produce. Most regulatory officials are not intimately familiar with 

the methodologies implemented in advanced models, and thus may be uncomfortable in allowing 

their application to projects or in assessing their predictions. 

Possible WQVS Forward 

While advanced finite element models are currently the most accurate way to simulate complex 

material and structural behaviors, such as those experienced during a building fire, several aspects 

154 
of the use of these models require additional work. The following is a list of future work efforts 

designed to fill various gaps noted in the current knowledge regarding the use of finite element 

models in analyzing structures at fire temperatures. 

Regulatory Guidance and Approval. The structural design community, traditionally 

dedicated to prescriptive guidance and support, will require that regulatory bodies 

indicate approved advanced analysis methods. Also, regulatory guidance on applying 

these methods appropriately will most likely be required. 

Coupling Thermal and Mechanical Analyses. As noted, the coupling of thermal and 

mechanical analyses would be a very significant step forward in performance-based 

structural fire engineering, and could greatly streamline the process of moving from a 

prediction of fire compartment temperatures to a prediction of mechanical structural 

response. This is seen as a long term objective. 

Model Validation. Significant available research (the Cardington tests, for example) is 

available for use in validating advanced structural analysis methodologies, and this is a 

critical goal. However, additional aspects of structural fire behavior may not be evident 

from currently available test data, and thus additional testing is required in order to fully 

validate advanced models and approaches. Aspects that require future investigation 

include: 

Mathematical representations of thermal and mechanical material properties. 

Brittle rupture of steel members. 

Representation of mechanical behaviors of concrete slabs. 

Fracture of concrete reinforcement. 

Cracking and fiacture of concrete members and slabs. 

Accurate modeling of connections. 

Failure Criteria / Performance Criteria 

A significant obstacle hindering the development and acceptance of performance-based design in 

the US is the availability of information for use in establishing performance criteria for structural 

fire design. Regardless of the availability of validated and approved analysis methodologies and 

material property data sources, structural analysis cannot be carried out without defined 

performance (or failure) criteria definitions. An understanding of the performance of a structure 

during a given fire is only half of the performance-based structural fire engineering approach. The 

necessary other half involves defining acceptable performance and comparing actual performance 

with this, thus determining if the structure performs adequately in the fire. 

Some guidance is currently available for the basic process of defining general failure criteria. 

However, most of this guidance simply suggests that building performance should be adequate in 

terms of prevention of collapse and aiding of life safety. There are currently no defined failure 

criteria for structural fire engineering assessments. In the UK, common practice is to use one of 

the following to demonstrate stability and maintenance of compartmentation throughout the 

design fire duration: 

155 
0 

0 

0 

Beam deflections do not exceed the rates stated in the standard furnace test BS 476 (one 

example is beam spad20). 

Rapid increases in beam deflections do not occur during the design fire duration. 

Column instability does not occur during the design fm period. 

However, the above criteria are not standardized, and thus a method of justifying their application 

is not currently in place. Such an approach could provide a model for the definition of 

performance criteria in the US, however. 

Possible Ways Forward 

In order to provide engineers and regulatory officials with guidance in determining appropriate 

performance criteria for performance-based structural design, the following achievements are 

viewed as necessary: 

1 Experimental study (particularly full-scale tests) into appropriate definitions 

regarding failure modes and limiting values of material parameters for determination 

of structural failure under fire conditions. 

Consensus regarding the definition of structural failure during fire. 

Codification (and thus widespread availability) of either numerical values for 

parameter limit states or approaches to defining specific and appropriate 

performance criteria for use by engineers and regulatory officials. 

Given the lack of current knowledge regarding this subject, a forum of international 

experts may be in order for the review of the topic. Note that such conversations 

have already occurred in the UK with no measurable results. 

2 

3 

4 

Connection Analysis and Design 

The specific effects of connection performance on the fire performance of structures are not well 

understood. Additionally, practical tools do not yet exist to guide designers in their choice of 

connection detailing. Traditionally, connection performance has not been analyzed implicitly, 

and overall frame behavior has been assumed to be indicated by the performance of individual 

members. -However, depending on connection details, factors such as load and moment 

redistribution can play a very significant role in building fire performance by transferring loads 

away fiom components that are nearing or have reached failure. Thus, a true representation of 

real structural fire performance might not be obtained unless the behavior and performance of the 

associated connections is specifically considered. 

\ 

Most connection analysis is accomplished through advanced fmite element modeling, since this 

approach can take into account the highly nonlinear nature of connection behavior at high 

temperatures. However normally gross simplifications are made to reduce computational time so 

these response tends not to be modeled explicitly. Some recent work has led to relatively simple 

methods that can be used to approximate beam-column connection performance. Validation of 

this work for different connection details is required. 

There is currently little code advice in regard to the fire protection of connections. Generally, 

codes spec@ that connections must be protected to the same degree as the surrounding structural 

elements. Some research aimed at understanding the fire performance of connections has been 

undertaken, especially given the apparent importance of connection performance in WTC Towers 

1 and 2 and in the Cardington tests. However, a great deal of additional research will be required 

to fully understand the behavior of the various connection types commonly used. 

156 
Possible Wuvs Forward 

Further research is needed to increase the understanding of how real structures perform in fire. 

Although testing of components greatly increases the understanding of their behavior in fire, 

many component tests do not model the complex structural interactions that are found in normal 

building structures and are greatly impacted by connection conditions. Topics regarding 

connection design for which future research is needed include: 

1) Simple analytical methods for considering the effects of elevated temperatures on 

structural connections. 

Performance of fin plateslshear plates in fire, for beam column and beam to beam 

joints. A review of minimum edge distances is required. 

* 

3) Forces and strains generated within connections in the cooling cycle. 

4) 

5) 

6) 

Minimum slab reinforcemeqt and connectivity needed to satisfy fire conditions. 

Shear stud performance and shear force distribution during the fire cycle. 

Development of realistic 3 -dimensional finite element models of connections 

subjected to series of loads and restraints in simulated real fire conditions. 

7) Review of the need for column stiffener plates, where the bottom flange is connected 

to the column. 

Conclusions 

This paper summarizes specific items, which require research and development, to ensure robust 

fire safety design of structures. This ranges from simple analytical methods to complex finite 

element analysis of structures in fire. 

This list is from a practitioner’s point of view, such that design methods, which are robustly 

validated, can be presented to authorities having jurisdiction for careful review and consideration. 

The overall aim being, the improved design of structures for fire. 

Acknowledgements 

The author wishes to acknowledge Arup Fire staff, specifically Matt Johann and Susan Lamont, 

plus Dr Jose Torero at the University of Edinburgh, for their contributions to project work that 

allowed this paper to be written. 

157 
White Paper 8 

Evaluation And Retrofit Of Existing Buildings For Structural Fire Safety 

Frederick W. Mowrer, Department of Fire Protection Engineering, University of Maryland 

Robert H. Iding, Wiss Janney Elstner Associates, Inc. 

Introduction 

This white paper addresses structural fire safety in existing buildings. In many respects, the 

analysis of structural fire safety in existing buildings is no different fiom the analysis of new 

buildings. The same basic principles apply to both. But evaluation of structural fire safety in 

existing buildings is generally more complicated than in new buildings for a number of reasons, 

including one or more of the following: 

Undocumented design basis; 

0 Presence of archaic building systems and materials with unknown structural and thermal 

performance characteristics; 

0 Concealment of design details; 

0 Unknown condition of concealed structural elements and fireproofing systems. 

Assuming these issues can be addressed in a satisfactory manner, retrofit options must be 

considered. In this respect, the analysis of existing buildings may also be more complicated than 

for new buildings because the designer must identify retrofit options that are compatible with the 

existing design as well as cost effective. 

In this paper, design approaches to the evaluation and retrofit of buildings for structural fire dety 

are addressed. An analogy is made to the seismic retrofit of structures. Issues related to the 

evaluation and retrofit of structures for improved fire performance are addressed. 

Recommendations are made for the research and development that is necessary to implement a 

code of practice for the retrofit of structures for improved fire performance. 

Design approaches 

There are three general aspects to the analysis of structural fire safety in both new and existing 

buildings. These include: 

0 Evaluation of the thermal conditions resulting fiom design basis fires, commonly 

expressed in terms of time-temperature histories; 

Evaluation of the thermal response of structural elements and assemblies, including 

effects of fire resistance treatments, to the imposed fire conditions; 

Evaluation of the structural response of structural elements, assemblies and frames 

resulting fiom their thermal response. 

0 

158 
There are two general approaches to the analysis of structural fire safety in both new and existing 

buildings, These include: 

Prescriptive approach 

Performance-based design 

In the prescriptive approach that has traditionally been applied to structural fire safety, the 

relationship between thermal performance and structural response is evaluated by subjecting 

representative building elements and assemblies to standardized exposure conditions and 

obtaining a standard fire resistance rating for the element or assembly. In the prescriptive 

approach, structural design for fire is basically just a matter of specifying and selecting structural 

elements and assemblies that have been tested and meet the standard fire resistance rating 

requirements mandated by prevailing building regulations. 

The prescriptive approach assumes that there is an implicit relationship between the mandated 

fire resistance requirements, the fire resistance test performance of rated elements and assemblies, 

and the expected performance of these elements and assemblies under actual fire conditions in the 

field. Unfortunately, the exact nature of this relationship is not known, in large part because only 

isolated elements and assemblies are tested, without consideration of the impact on the entire 

structural frame. Consequently, applying this prescriptive code approach to retrofitting an 

existing structure would not be very useful and would amount to little more than searching for 

and correcting code violations. 

In performance-based structural design for fire, the relationship between fire-induced thermal 

exposure conditions and structural response to these exposure conditions is addressed explicitly. 

The performance-based design process generally includes the following steps: 

Identify possible fire scenarios; 

Calculate fire temperatures and durations for these scenarios; 

Calculate temperatures of structural elements; 

Calculate the structural response of each member; 

Calculate the structural response of the building as a whole. 

In the design process, several trial design concepts are evaluated until a final configuration is 

chosen which gives the desired fire response. In the retrofit process, the existing building is 

evaluated structurally and several retrofit concepts are also evaluated until one meeting 

requirements of practicality and desired fire response is found. The performance-based design 

approach can be used to evaluate existing buildings and serve as a basis for analysis and design of 

retrofit options. The general methodology of the performance-based approach is the same for 

designing new buildings or for evaluating existing buildings. 

The seismic retrofit analogy 

There is a well-established code of practice for seismic retrofit of existing buildings that has 

evolved over the last 50 years [ 11. Some of this methodology may be useful for developing a 

similar code of practice for retrofitting buildings for improved fire performance. Some cost 

159 
savings would probably be realized if seismic and fire retrofit options were considered together. 

It should be recognized, however, that there are significant differences between the hazards and 

risks of fires and earthquakes that will prevent the wholesale adoption of the seismic retrofit 

methodology for fire. Of most significance, earthquakes are an extrinsic hazard, while fires are 

an intrinsic hazard. In seismic design, designers have no control over the magnitudes or 

frequencies of earthquakes; they rely on statistical data for these parameters. In fire design, both 

the frequency and the magnitude of fires are influenced by human interactions and design 

decisions. They have both random and intentional aspects. In this respect, fire design is more 

analogous to blast design than to seismic design. Despite these important differences, the seismic 

retrofit code of practice can serve as a useful starting point for a fire retrofit code of practice. 

Under the seismic retrofit code of practice, seismic retrofit design can follow either a 

performance-based or a prescriptive code approach. Using the newer performance-based 

approach, risk analysis is used to establish an earthquake return period, from which acceleration 

history and lateral forces are determined. The structure is then modified to resist these lateral 

forces without collapsing. Often the structure is also required to withstand a smaller earthquake 

with a shorter return period without suffering serious structural damage. Additional requirements 

of ductility and connection detailing may be imposed. The actual design of ahseismic retrofit is 

primarily a matter of common sense, general design experience and intuition, and good 

engineering judgment, backed by calculations to test and evaluate trial retrofit configurations. 

However, attempts to establish a code of practice have been made by FEMA [ 11 and others. 

There are also publications suggesting standard details for reinforcing connections and other 

aspects of seismic retrofit design. 

. Establishing a methodology for retrofit for improved structural performance in fire could follow a 

similar pattern: 

1. Develop criteria for determining when retrofit is required or desirable. 

2. CodifL fire loadings. Two levels of design fire intensity and duration may be useful: one 

with a higher probability of occurrence for which structural damage would be minor, and 

another with a more remote possibility for which only avoidance of structural collapse is 

desired. Much of the work needed to establish these fire loadings has already been done 

PI. 

3. Calculate thermal and structural response for proposed retrofit schemes and verify that 

the structure performs in an acceptable manner. There is an extensive literature on 

analysis techniques suitable for this purpose [3]. 

4. Develop additional requirements that would improve a building’s survivability when 

subjected to extreme initiating events, such as fire coupled with earthquake, explosion or 

impact. Among these would be flexibility or ductility requirements, toughness 

requirements, and improved redundancy, as discussed later in this paper. 

Most of this fire retrofit methodology is the same for design of new buildings. However, retrofit 

gives rise to many special difficulties since the designer must work around and with existing 

structure. As with seismic design, good solutions are based on common sense and good 

engineering judgment. Many of the methods developed for seismic retrofit would not be useful 

because they deal with dynamic properties of buildings, energy absorption, horizontal 

diaphragms, and other properties not related to fire performance. Furthermore, some seismic 

160 
retrofit techniques, such as wrapping columns with fiber-reinforced plastics, may increase fire 

hazards without providing any structural benefits under fire conditions. However, some of the 

techniques used to improve connections and to tie together all parts of the buildings to better 

resist non-gravity loading could find application to fire retrofit. For example, the FEMA code of 

practice [ 13 presents details for the following: 

Cover plates, gusset plates, knee braces, and boxing members to increase connection 

strength; 

Supplemental frames and braces to add redundant load paths for lateral loads; 

Lateral bracing methods for unsupported flanges of long-span trusses or beams; 

Encasing steel members in concrete to create stronger composite members; 

Increasing strength and toughness of slabs and diaphragms with overlays; 

Methods for anchor bolts and other improved connection of trusses and beams at their 

supports. 

Seismic retrofit often does not give consideration to how effective these methods would be if 

exposed to fire. However, many of the methods are only intended to give additional strength for 

a seismic lateral load which would not be on the structure at the time a fire occurs, so lack of fire 

resistance is not always a problem. Fire retrofit must always consider performance of the retrofit 

under elevated temperatures, the magnitude of which will be coupled with the materials and 

methods used to insulate structural elements fiom the fire conditions. 

Evaluation of existing conditions 

After the potential need to retrofit a structure for fire is recognized, the next step is to evaluate the 

existing conditions. This includes evaluation of both the existing structural design as well as the 

thermal protection and fire endurance of the existing structural elements and assemblies. 

The retrofit evaluation process requires identification of the design basis for the existing building. 

To the extent such documentation is available, structural design drawings, calculations, 

specifications and test data can be used to evaluate the expected structural performance of the 

existing building. Such documentation should be verified by visual inspections and surveys to 

determine if the as-built condition is the same as the design documentation indicates. 

A significant issue with respect to verification of the existing conditions is accessibility. In many 

existing buildings, structural elements and assemblies have been encapsulated or covered by other 

materials. In some cases, these materials serve only an aesthetic function, while in other cases, 

these materials may also serve a fireproofing or thermal insulation function. Regardless of their 

purpose, the presence of such materials may prevent the direct visual inspection of some or all of 

the structural elements and connections in an existing building. Depending on the importance 

associated with verification of existing conditions, removal and replacement of materials covering 

structural elements may be necessary. Ironically, if the covering materials are serving a 

fireproofing function, the removal and replacement of such materials for visual inspection may 

have a negative impact on post-inspection fire performance. 

161 
Because the basic structure as well as the thermal insulation materials may be concealed from 

view, it would be desirable to develop nonvisual, nondestructive methods to evaluate the existing 

condition of a structure as well as of the fireproofrng materials protecting the structural elements 

and assemblies. It may be possible to adapt ultrasonic, magnetic or other nondestructive 

evaluation methods for this purpose. This issue should be explored further. 

Evaluation of expected performance of existing buildings and structural elements 

Analysis of the fire performance of an existing building ultimately depends on calculation of its 

fire response. In this respect, evaluation of existing buildings may be easier than evaluation of 

new buildings because the structural design and construction of an existing building is already 

established while the design of a new building may not be. While both new and existing 

buildings may require analysis of a multitude of fire scenarios, the basic design of an existing 

structure is established, at least before retrofit options are evaluated. Once structural retrofit 

options are considered, the picture once again becomes more complicated in terms of the number 

of variables that need to be considered. 

Evaluation of the expected fire performance of existing buildings will generally follow the 

performance-based design process outlined above. As a first step, the effects of losing one or 

more structural elements to fire-induced failures can be considered without actually calculating 

the fire conditions leading to such failures. This would permit identification of those elements 

that are critical to the overall stability of a structure or, expressed differently, those elements that 

would cause disproportionate damage or collapse if they were to fail. Such identification of the 

critical structural elements may influence the selection of retrofit options and focus retrofit 

activities on the most critical structural elements. 

Once the critical structural elements are identified and prioritized, the performance of these 

elements under different fire conditions can be evaluated. In a performance-based analysis, the 

postulated fire conditions should bear some relationship with the actual fire conditions expected 

under different fire scenarios. Evaluation of the expected fire conditions would be the same as 

for new buildings. 

Retrofit / repair alternatives 

Retrofitting buildings to improve their structural fire safety can generally take one of two forms, 

or in some cases a combination of both. The options generally include: 

Enhance the structural performance of the structural elements and assemblies; 

Enhance the thermal performance of the fire resistant materials and assemblies protecting 

the structural elements. 

Retrofitting buildings to improve their structural performance in fire is a relatively new field. 

Cases in which the actual structure of a building has been modified solely for the purpose of 

improving its fire performance have been very rare. However, the same methodology used in the 

performance-based design of new buildings for structural fire safety is directly applicable. In 

applying this methodology, the following principles should be usefbl: 

162 
1. Build in more redundancy if it is lacking. Add members to give alternate load paths or 

strengthen connections to mobilize other portions of the building to increase redundancy. 

2. Move or isolate particularly bad fire scenarios so important members are not impacted. 

3. Strengthen connections to give better flexibility and ductility to the building so that it 

may accommodate the large distortions that are caused by fire. The structural system 

should be well tied together and tough. Unlike seismic retrofit, energy absorption is not 

important -just the ability to move without breaking joints and to permit redistribution 

of loads away from areas of local failure. Moment-resistant joints are preferred and can 

add considerable redundancy to the structure. Add thermal protection to connections if 

they can be exposed to fire. 

4. Add bracing where necessary to prevent local collapse of floor assemblies or other 

structural members from leading to instability in primary structural members. An 

example of this would be a light truss floor system that braces walls or columns. 

5. Repair damaged or improperly designed elements that affect fire resistance. Examples 

would be reinforcing bars that have become exposed due to spalling, walls or other loadbearing elements that have been removed, or areas of defective fireproofing. 

In many cases, the basic structure will not require retrofitting, but the level of thermal insulation 

will need to be increased to meet current structural fire safety goals and objectives related to fire 

endurance. In evaluating the current level of fire resistance and the alternatives available for 

upgrading this level, the fundamental question will be whether to add additional layers of thermal 

insulation to the existing installation or to remove the existing thermal insulation and replace it 

with new materials. In either case, environmental impacts need to be considered, particularly for 

fibrous materials that may contain asbestos or other fibers with potential health or environmental 

consequences. 

. 

For the addition of new thermal insulation to an existing installation, a number of issues need to 

be considered, including: 

1. Is it better to use contour or membrane protection? In many existing installations, 

contour protection has been adhered to the structural elements, then the insulated 

assembly has been enclosed in finish materials, which may impart additional fire 

resistance. In some cases, the simplest and most cost-effective upgrade may be to simply 

add additional membrane protection to the existing assembly. This is analogous to the 

component additive method [4] used to evaluate the fire resistance of timber structures. 

In other cases, adding additional contour protection may be the simplest and most costeffective alternative. 

2. Are there adhesion or cohesion issues related to the application of new contour protection 

to old? Contour protection materials are typically adhered to steel or concrete substrates. 

If these materials are applied to similar existing contour protection materials, the 

adhesion of the new material to the old must be considered along with the continued 

adhesion of the old material to the substrate as well as the continued cohesion of the old 

material as it is subjected to new stresses imposed by the addition of the new material. 

The quality of the upgrade will depend on all of these issues. 

163 
3. What are the Derformance evaluation issues for the composite assembly? Large-scale 

testing is still generally used to evaluate the fire resistance of insulated building 

assemblies. This is true at least in part because it is still difficult to predict or calculate 

all of the factors that can cause the delamination or differential movement of components 

in a fire resistive assembly. Consequently, the option to add additional thermal insulation 

to an existing installation may require extensive and expensive fire testing to evaluate the 

expected performance of such composite assemblies until correlations can be established 

similar to those used in the component additive method. 

For the replacement of an existing installation with a new one, issues that need to be considered 

include: 

1. 

2. 

What issues are associated with the removal and disposal of existing; fireDroofing 

materials? In many existing buildings, the fireproofing systems may contain asbestos or 

other fibers that may have health or environmental consequences. The removal and 

disposal of these materials must be handled properly, which may incur high costs and 

make this option less cost effective than alternative methods. Encapsulation of existing 

fireproofmg may be a more cost-effective and environmentally-friendly solution. 

What issues are associated with adhesion of new material to the existing; substrate? If the 

existing fireproofing material is removed fiom its substrate for replacement by new 

material, the substrate may require reconditioning in order for the new material to 

properly adhere. 

Some guidance for retrofit designers 

It is generally recognized by structural fire designers that certain features of a structure can cause 

problems during a fire. These features should be carefully scrutinized in order to focus the design 

or retrofit effort on the most critical elements. Among these are the following: 

1. Look for lack of redundancy. A structure that will perform well in a severe fire will 

permit gravity loads that must be supported during the fire to be carried to the 

foundations using several load paths. That is, if one large member is removed, the weight 

it supported will redistribute to other nearby members and collapse will not occur. 

Identify critical, irreplaceabIe members, which if softened or buckled in a fire would 

cause more than a local failure, Le. lead to progressive collapse of the entire building. 

The types of members to look for include nonrepetitive long-span trusses and beams, 

columns with large tributary areas, cantilevers, and members necessary for lateral 

stability of trusses or buckling stability of columns. Structural assemblies that tend to 

have a high degree of redundancy are composite floor slabs and moment fiames. When 

conducting calculations keep in mind that the live load on the structure at the time of a 

fire is almost always less than the full design load and this reduction contributes to 

redundancy. 

2. Look for weak connections. Connections are very important and are critical in holding a 

building together during the large movements that occur in a fire. They must be ductile 

or flexible so they do not break due to these large distortions in the building. This quality 

in a structural component is called toughness. In addition, strong connections give 

continuity to mult-span beams and other flexural members, reducing bending moments 

and therefore increasing fire resistance. Strong and flexible connections also permit these 

flexural members to develop into a catenary when they fail in bending and sag, increasing 

the fire endurance even more. The types of connections that often perform poorly in a 

164 
3. 

4. 

5. 

6. 

7. 

fire are simple bearing connections and shear tabs. Best are moment-resistant framing 

connections in steel or welldetailed, ductile moment connections in concrete. 

Beware of very large, very stiff structural elements. When such elements are exposed to 

fire, they may expand against weaker restraining members surrounding them, breaking 

connections and perhaps causing other types of failure.. Earthquake retrofitting often 

introduces these types of elements (diaphragms, braces, etc.) and it is important to make 

sure restraining elements have sufficient flexibility, ductility and stability to 

accommodate the expansion if the stiff elements can be exposed to fire. When 

conducting calculations keep in mind that braces under elevated temperature will 

eventually buckle but not actually fail, since the thermal force is self-limiting and often 

leads to a stable post-bucking reaction, limiting the force on adjacent structure. In fire, 

buckling of a brace is sometimes a good thing since it limits the damage its expansion can 

cause to the rest of the structure. 

Pay particular attention to light members. These members have notoriously low fire 

resistance. Determine how these members would fail and be sure the failure will be 

strictly local and not spread to other parts of the structure. For example, the collapse of a 

floor assembly in a single bay probably would remain local. Light trusses are particularly 

problematical since they are dificult to fireproof and have very little fire resistance 

without fire protection. 

Check that important braces will not fail in fire. Such failures can undermine the stability 

of primary structural members, even ones that are cool and not involved in the fire. 

Fireproofing'of these braces may be necessary. Examples of such braces are those that 

give lateral stability to trusses and beams. 

Pay special attention to prestressed concrete members. Prestressed concrete members are 

particularly vulnerable to fire because prestressing steel loses strength quickly at elevated 

temperatures. Check for adequate cover. 

Watch for high risk or high temperature fire sources located close to particularly critical 

members, such as fuel tanks or fuel lines near large trusses or nonredundant columns. 

. 

Recommendations for further research and development 

Based on the foregoing discussion of issues, the following recommendations are made for 

research that is needed to develop a code or standard of practice for the evaluation and retrofit of 

existing buildings for structural fire safety: 

0 A survey should be conducted of nondestructive evaluation technologies that might be 

adapted for evaluating the existing conditions of inaccessible structural elements and 

thermal protection in buildings. The more promising of these technologies should be 

evaluated for adaptation €or this purpose. 

An engineering guide should be developed that describes the general retrofit options that 

could be applied to buildings designed with different structural systems. Research should 

be performed to address the relative costs and benefits of these different retrofit options. 

Research should be performed to evaluate how retrofit design for fire can be coordinated 

with seismic retrofit design to cost-effectively address both issues together. 

The following recommendations are made to advance the practice of structural fire safety design 

for both new and existing buildings: 

165 
Methods should be developed for building codes for structural design to give more 

consideration to fire loads. Ultimately, fire should be a design load condition, just as 

gravity, wind, earthquake and other thermal loads are. 

Computer software for structural analysis and design for fire should be developed and 

distributed to structural fire safety designers. Research should be conducted to determine 

how fire loading can be incorporated into widely used commercial structural design 

programs. 

Workshops and training courses should be developed to introduce practicing engineers 

and building officials to structural design for fire, particularly the newer performancebased methods. 

Design for structural fire safety should be incorporated into structural engineering 

curricula and given the same emphasis as design for other extreme events is currently 

given. 

Research funding should be provided to support graduate students interested in 

developing expertise in structural fire safety design. Research performed by such 

graduate students would advance the state of knowledge while the graduate students 

would become the educators of future structural fire safety designers as well as leaders in 

the field of structural fire safety design. 

Summary and conclusions 

Evaluation of structural fire safety in existing buildings presents many of the same challenges as 

in new buildings. These challenges include: 

0 

0 

Identification of the relevant fire scenarios to be analyzed; 

Uncertainties in the calculation of expected fire conditions and structural response, 

including both parameter and modeling uncertainties; 

Lack of information on the high-temperature properties of building materials, particularly 

those materials used to insulate structural steel fiom fue temperatures; 

A general lack of design practices, educational opportunities and designers educated and 

experienced in the field of structural fire design. 

0 

0 

Evaluation of structural fire safety in existing buildings also presents many challenges different 

from those associated with new buildings. These challenges include: 

0 Identification of existing structural and thermal conditions, including adaptation of 

nondestructive evaluation technologies and methods for this purpose; 

Lack of design information on different retrofit options including the relative costs and 

benefits of the different options; 

Lack of a code of practice specifically for retrofitting for structural fire performance 

analogous to the code of practice that has been developed for seismic retrofit. 

0 

0 

It is recommended that methods for evaluation and retrofit of existing buildings for structural fire 

safety be developed in concert with the development of retrofit methodologies for other hazards, 

166 
such as wind and earthquake. In this way, the relative costs associated with fire retrofits would 

be minimized, while the relative benefits could be maximized. It is also recommended that 

structural fire safety design be incorporated into structural engineering curricula. 

References 

1. 

2. 

3. 

4. 

NEHRP, Handbook of Techniques for the Seismic Rehabilitation of Existing Buildings, 

FEMA-172, June 1992. 

Buchanan, Andrew H., Structural Design for Fire Safety, John Wiley & Sons, LTD, 

Chichester, 200 1. 

Iding, Robert H., “Calculation of Structural Response to Fires,” Fire Protection 

Engineering, Society of Fire Protection Engineers, Spring 2003. 

White, Robert H., “Analytical Methods for Determining Fire Resistance of Timber 

Members,” Section 4 I Chapter 1 1, SFPE Handbook of Fire Protection Engineering, 3“‘ 

Edition, National Fire Protection Association, Quincy, MA, 2003. 

167 
White Paper 9 

International Status Of Design Standards 

For Structural Fire Safety 

Dr. Andy Buchanan 

Department of Civil Engineering, University of Canterbury, New Zealand 

ABSTRACT 

This paper describes international design standards for structural fire safety. These standards 

range fiom very simple prescriptive documents to sophisticated codes which allow advanced 

methods of analysis under a wide range of realistic conditions. The paper focuses on the 

Structural Eurocodes which are the most comprehensive suite of documents for structural fire 

design at the present time. 

168 
INTRODUCTION 

The purpose of this paper is to benchmark the international status of development and adoption of 

design standards for structural fire safety, and the overall codes and standards context. Some of 

this paper is based on the author’s book, Structural Design for Fire Safety (Buchanan, 2001). 

LEGISLATIVE ENVIRONMENT 

The legislative environment is very different in different countries. Many countries are moving at 

various speeds to adopt performance based codes, or to move from a prescriptive code 

environment to a more performance based environment. 

Performance based codes 

Until recently, most structural design for fire safety has been based onprescriptive building 

codes, with little or no opportunity for designers to take a rational engineering approach to the 

provision of fire safety. Many countries have recently adopted performance bused building codes 

which allow designers to use any fire safety strategy they wish, provided that adequate safety can 

be demonstrated. In general terms, a prescriptive code states “how a building is to be constructed” 

whereas a performance based code states “how a building is to perform” (Buchanan, 2001). 

Performance based design is not totally new. Even within prescriptive codes, there is the 

opportunity for performance based selection of structural assemblies. For example, if a code 

specifies a floor with a fire resistance rating of 2 hours, the designer has the freedom to select 

from a wide range of listed systems which have sufficient fire resistance. 

In the development of new codes, many countries have adopted a multi-level code format as 

shown in Figure 1. At the highest levels, there is legislation specifying the overall goals, 

functional objectives and required performance which must be achieved in all buildings. At a 

lower level, there is a selection of alternative means of achieving those goals. The three most 

common options are either to comply with a prescriptive “acceptable solution”, to comply with an 

“approved calculation method”, or to carry out a “performance based alternative design” from. 

first principles, using all the information available. 

Standard calculation methods have not yet been developed for widespread use, so compliance 

with performance based codes in most countries is usually achieved,by simply meeting the 

requirements of “acceptable solutions” (“deemed-to-satisfy” solution), or alternatively carrying 

out a “performance based alternative design” based on fire engineering principles. Alternative 

designs can often be used to justify variations from the Acceptable Solution in order to provide 

cost savings or other benefits. 

The code environment in England, Australia and some Scandinavian countries, is similar to that 

in New Zealand (described by Buchanan, 1994,2000). Moves towards performance based codes 

are being taken in the United States (IFCI 2000). Codes are different around the world, but the 

objectives are similar; that is to protect life and property from the effects of fire. 

169 
Functional objectives 

Performance requirements . 

Eurocodes 

For more than twenty five years, European countries have been working on a new coordinated set 

of structural design standards known as the Structural Eurocodes. These are comprehensive 

doduments which bring together diverse European views on all aspects of structural design, for all 

main structural materials. The Eurocodes are being prepared by the European Committee for 

Standardization (CEN) under an agreement with Commission of the European Community. The 

Eurocodes recognize the need for member countries to set national safety standards which may 

vary fiom country to country, so each country’s national standard will comprise the full text of 

the Eurocode, with local modifications in a supporting document. More details are given later in 

this paper. 

Structural Design for Fire Conditions 

Design objectives 

Fire safety objectives must be established before making any design. The overall design needs to 

set objectives for property protection and safety of occupants and fire fighters. Design for fire 

safety is often split into active andpassive fire protection. A major component of passive fire 

protection isfire resistance, which is only one component of the overall fire safety strategy. 

Structural design for fire safety is a subset of fire resistance. ’ 

Structural elements can be provided with fire resistance for either controZZing the spread of@re or 

preventing structuraZ coZZapse, or both, depending on the functional requirements for the 

particular building. This paper concentrates on the latter. 

Design process 

Structural design for fire conditions is conceptually similar to structural design for normal 

temperature conditions. Before making any design it is essential to establish clear objectives, and 

determine the severity of the design fire. The design can be carried out using either working stress 

170 
or ultimate strength (LRFD) format. The main differences of fire design compared with normal 

temperature design are that, at the time of a fire: 

the applied loads are less 

internal forces may be induced by thermal expansion 

strengths of materials may be reduced by elevated temperatures 

cross section areas may be reduced by charring or spalling 

smaller safety factors can be used, because of the low likelihood of the event 

deflections are not important (unless they affect strength) 

different failure mechanisms need to be considered 

0 

0 

0 

0 

0 

0 

0 

The above factors may be different for different materials. 

Design equation 

The fundamental step in designing structures for fire safety is to veri@ that the fire resistance of 

the structure (or each part of the structure) is greater than the severity of the fire to which the 

structure is exposed. This verification requires that: 

fire resistance 2 fire severity 

where $re resistance is a measure of the ability of the structure to resist collapse, fire spread or 

other failure during exposure to a fire of specified severity, and 

fzre severiq is a measure of the destructive impact of a fire, or a measure of the forces or 

temperatures which could cause collapse or other failure as a result of the fire. 

As shown in Table 1, there are three alternative methods of comparing fire severity with fire 

resistance. The verification may be in the time domain, the temperature domain or the strength 

domain, using different units, which can be confusing if not understood clearly. 

Table 1. Three alternative methods of comparing fire severity with fire resistance 

FIRE RESISTANCE 2 FIRE SEVERITY 

Domain Units 

Time minutes Time to failure 2 Fire duration. as calculated or 

Temperature “C Temperature to 2 Maximum temperature 

reached during the fire 

Strength kN or Load capacity at 2 Applied load during 

or hours specified by code 

cause failure 

kN.m elevated temperature the fire 

Loads for structural fire design 

The most likely loads at the time of a fire are much lower than the maximum design loads 

specified for normal temperature conditions. For this reason, different design loads and load 

combinations are used. Most codes refer to an “arbitrary point-in-time load” to be used for the 

fire design condition. Loads and load combinations are given, for example, by ASCE (1995) and 

the Eurocode (EC 1,2002). 

171 
Fire Severity 

Fire Severity For Design 

The fire severity to be used for design depends on the legislative environment and on the design 

philosophy. In aprescriptve code, the design fue severity is usually prescribed by the code with 

little or no room for discussion. In aperformunce based code, the design fire is usually 

recommended to be a complete burnout, or in some cases a shorter time of fire exposure which 

only allows for escape, rescue, or firefighting. The equivalent time of a complete burnout is the 

time of exposure to the standard test fire that would result in an equivalent impact on the 

structure. 

Standard fire exposure 

Most countries around the world rely on full size fire resistance tests to assess the fire 

performance of building materials and structural elements. The time temperature curve used in 

fire resistance tests is called the standardfire. Full size tests are preferred over small scale tests 

because they allow the method of construction to be assessed, including the effects of thermal 

expansion, shrinkage, local damage and deformation under load. 

The most widely used standard test specifications are ASTM El 19 (ASTh 1995) and IS0 834 

(IS0 1975). Other national standards include British Standard BS 476 Parts 20-23 (BSI 1987), 

Canadian Standard CANAJLC-S 10 1 -M89 (ULC 1989) and Australian Standard AS 1530 Part 4 

(SAA 1990). The standard time temperature curves from ASTM El 19 and IS0 834 are compared 

in Figure 2. They are seen to be rather similar. All other international fire resistance test standards 

specifL similar time temperature curves. 

The ASTM El 19 curve is defined by a number of discrete points The IS0 834 specification (IS0 

1975) defines the temperature T (“C) by the following equation: 

T = 345 loglo (8 t + 1) + To 

where t is the time (minutes) and 

To is the ambient temperature (“C) 

Figure 2 also shows two alternative design fres from the Eurocode (EX1 2002). The upper curve 

is the hydrocarbon fire curve, intended for use where a structural member is engulfed in flames 

from a large pool fire. The temperature T (“C) is given by 

T = 1080 (1 - 0.325e 

where t is the time (minutes) 

To is the ambient temperature (“C) 

- 0.675e -2.5t ) + TO 

The lower curve is intended for design of structural members located outside a burning 

compartment. Unless they are engulfed in flames, exterior structural members will be exposed to 

lower temperatures than members inside a compartment. The temperature for external members is 

given by 

T = 660 (1 - 0.687e - 0.3 13e”.*‘ ) + TO 

172 
Figure 2. Standard time temperature curves 

1000 

800 

600 

400 

- IS0 834 

--- ASTM El 19 

External fire 

Hydrocarbon fire 

-- -- ---- -.-.- 

” 

0 30 60 90 120 150 180 

Time (min) 

Realistic fire exposure 

If a fire in a typical room is allowed to grow without intervention, assuming sufficient fuel and 

ventilation, temperatures will increase with increasing radiant heat flux to all objects in the room. 

At a critical level of heat flux, all exposed combustible items in the room will begin to burn, 

leading to a rapid increase in both heat release rate and temperature. This transition isflashover, 

after which the fire is often referred to as a “post flashover fire”, “fully developed fire” or “full 

room involvement”. 

The most widely referenced time temperature curves for post-flashover fire exposure are those of 

Magnusson and Thelandersson (1970) shown in Figure 3, often referred to as the “Swedish” fire 

curves. They are derived from heat balance calculations for the burning rate of ventilation 

controlled fires. A group of curves, such as the one shown, is provided for different ventilation 

factors, with fuel load as marked. Note that the units of fuel load are MJ per m2 of total internal 

surface area (not MJ per m2 of floor area which is more often used in design calculations). In a 

similar approach, Lie (1995) performed heat balance calculations for post flashover fires with a 

range of ventilation factors and different wall lining materials. Computer programs for calculating 

temperatures in post flashover room fires include COMPF2 (Babrauskas, 1979), Ozone (Franssen 

et a1 1999). FASTLite (Buchanan 1997) and CFIRE (Yii, 2003). 

The Eurocode (EC 1,2002) gives an equation for “parametric” fires, allowing a time- temperature 

relationship to be produced for any combination of fuel load, ventilation openings and wall lining 

materials, to give an approximation to the Swedish curves shown above. The Eurocode equation 

for temperature T (“C) is 

173 
7200 ! 

1000 00 

Q) 800 3 

5 600 

E 

e 400 

200 

0 

L 

* 

Q 

0 7 2 3 4 5 6 

Time (hours) 

Figure 3. Time temperature curves for given ventilation factor and different fuel loads (MJ/m2 

of total surface area) (Magnusson and Thelandersson 1970) 

T = 1325 (1 - O.324eaa2 '* - 0.204e-'.''* - 0.472e'19 '*) [11 

where t* is a fictitious time (hours) given by t* = r t 

t is the time (hours) and 

r= FJ0.04 )' 

( b/1160)2 

where b is dthermal inertia = d(kpc,) (WS~*~/~'K) 

Fv is the ventilation factor 

A, is the area of the window opening (m) 

At is the total internal surface area of the room 

Hv is the height of the window opening 

F, = A, dHv / At (dm> 

(m2) 

(m) 

Equation 1 is a good approximation to the IS0 834 standard fire curve for temperatures up to 

about 13OO0C, so the Eurocode parametric fire curve is close to the IS0 834 curve for the special 

case where r = 1. 

The duration of the burning period 

latest version (2002) simplified as: 

(hours) in the Eurocode has been increased by 50% in the 

= 0.0002e,/FV = 0.0002 E / (Av dHv) 

where e, is the he1 load (MJ / m2 total surface area) 

or E is the total energy content of the fuel 0 

174 
The Eurocode uses a basic decay rate of 625°C per hour for fires with a burning period less than 

half an hour, decreasing to 250°C per hour for fires with a burning period greater than two hours, 

all modified by the r factor. Recent research using the COMPF2 program and many test fire 

results has shown that the temperatures in the Eurocode formula are often too low and the rate of 

decay is often inappropriate, leading to proposals for empirical modifications (Feasey and 

Buchanan 2000). 

Time equivalence 

The concept of equivazent fre severity is used to relate the severity of an expected real fire to the 

standard test fire. This is important when designers want to use published fire resistance ratings 

from standard tests with estimates of real fire exposure. There are several methods of comparing 

real fires to the standard test fire, the most common being the time equivalence formula given in 

Eurocode 1 (EC1,2002), which gives the equivalent time & (min) as 

where ef is the fuel load (MJlm2 of floor area) 

w is the ventilation factor, given by 

is a parameter to account for different compartment linings 

"."I I 1 + bva, 

H, is the compartment height (m) 

a,= A, I Af 

b, = 12.5 (1 + 10 a, - a: ) 

Af is the floor area of the compartment (m') 

A, is the area of vertical openings in the walls (m') 

Ah is the area of horizontal openings in the roof (m2) 

0.05 2 a, 50.25 

ah = Ah 1 Af ah 0.20 

. 

The equivalent fire severity is very useful where the details of the compartment are known, and 

where the designer wishes to use published fire resistance ratings for selection of construction 

elements. 

FIRE RESISTANCE 

Fire resistance is a measure of the ability of a building element to resist a fire, usually the time 

for which the element can meet certain criteria during exposure to a standard fire resistance test. 

Individual materials do not possess fire resistance. Fire resistance is a property assigned to 

building; elements which are constructed from a single material or a mixture of materials. AJire 

resistance rating is the fire resistance assigned to a building element on the basis of a test or some 

other approval system. Some countries use the termsfire rating, fire endurance rating orfire 

resistance ZeveZ which are usually interchangeable. 

175 
Failure criteria 

The three failure criteria for fire resistance are stability, integrity and insulation. To meet the 

stability criterion in a standard fire resistance test, a structural element must perform its load 

bearing function and carry the applied loads for the duration of the test, without structural 

collapse. The integrity and insulation criteria are intended to test the ability of a barrier to contain 

a fire, to prevent fire spreading from the room of origin. To meet the integrity criterion, the test 

specimen must not develop any cracks or fissures which allow smoke or hot gases to pass through 

the assembly. To meet the insulation criterion, the temperature of the cold side of the test 

specimen must not exceed a specified limit, usually an average increase of 14OOC and a 

maximum increase of 180°C at a single point. 

An increasing international trend is for fire codes to specify the required fire resistance separately 

for stability, integrity and insulation. For example a typical load bearing wall may have a 

specified fire resistance rating of 60/60/60, which means that a one hour rating is required for 

stability, integrity and insulation, respectively. If the wall was non load-bearing, the specified fire 

resistance rating would be - /60/60. A fire door with a glazed panel may have a specified rating 

of - /30/ - , which means that this assembly requires an integrity rating of 30 minutes, with no 

requirement for stability or insulation. 

Approvals 

Most countries require that fre resistance tests be certified by a recognized testing laboratory or 

approvals agency. In North America, independent testing organizations such as Underwriters 

Laboratories (UL 1996) and Southwest Research Institute (SW 1996) maintain registers of fre 

resistance ratings. Most of these ratings are based on standard tests. Ratings based on these 

approvals are listed in some national building codes (eg NBCC 1995, UBC 1997). Small 

countries may need to use approvals from other countries, so that in New Zealand for example, a 

register of approved listings is maintained by the national standards organization (SNZ 199 1). 

Some trade organizations (eg. ASFPCM 1988, Gypsum Association 1994) maintain industry 

listings of approvals for products manufactured or used by their members. Listings generally fall 

into three categories; generic ratings, proprietary ratings, or calculation methods. 

Generic fire resistance ratings, or “tabular ratings” are listings which assign fire resistance to 

typical materials such as concrete or steel. Generic ratings are derived from full-scale fire 

resistance tests carried out over many years, and are widely used because they can be applied to 

commonly available materials in any country. However, generic ratings make no allowance for 

the size and shape of the fire exposed member or the level of load. 

Proprietary fre resistance ratings apply to proprietary products made by specific manufacturers, 

so they may be more accurate than generic ratings, but cannot be applied to similar products from 

other manufacturers. 

As fire engineering develops, it is becoming feasible to assess fire resistance of structural 

members and some assemblies by calculation. Some listing agencies and national design codes 

now include approved calculation methods for assessing fire resistance. Calculation methods 

must be based on full scale fire resistance test results of similar assemblies. Calculations can be 

used for predicting insulation and load-bearing response, but not integrity. 

An increasing number of listed fire resistance ratings are based on expert opinion. The opinion 

will state whether the assembly would be considered likely to pass a test, based on observations 

of similar successful tests, calculations, and the considered experience of the testing and 

approving personnel. 

176 
MATERIALS STANDARDS 

In most countries the materials standards for structural design provide methods of assessing or 

calculating fire resistance . 

Europe 

By far the most comprehensive international documents for structural design of buildings and 

structures in fire conditions are the Structural Eurocodes. The main codes are listed below, with 

details in the list of references: 

EN 199 1 Eurocode 1 Basis of design and actions on structures; 

EN 1992Eurocode 2 Design of concrete structures; 

EN 1993 Eurocode 3 Design of steel structures; 

. EN 1994 Eurocode 4 Design of composite steel and concrete structures; 

EN 1995 Eurocode 5 Design of timber structures; 

EN 1996Eurocode 6 Design of masonry structures; 

EN 1997Eurocode 7 Geotechnical design; 

EN 1998 Eurocode 8 Design provisions for earthquake resistance of structures; 

EN 1999Eurocode 9 Design of aluminum alloy structures. 

All of these have substantial fire sections, (1 00 pages or more). Most are nearing completion, 

published in final draft form, and will go to a formal vote this year after final editing and 

translation into French and German. Most of the structural Eurocodes include the following 

statement: 

“A full analytical procedure for structural fire design would take into account the behaviour 

of the structural system at elevated temperatures, the potential heat exposure and the 

beneficial effects of active and passive fire protection systems, together with the uncertainties 

associated with these three features and the importance of the structure (consequences of 

failure). 

At the present time it is possible to undertake a procedure for determining adequate 

performance which incorporates some, if not all, of these parameters and to demonstrate that 

the structure, or its components, will give adequate performance in a real building fire. 

However, where the procedure is based on a nominal (standard) fire the classification system, 

which call for specific periods of fire resistance, takes into account (though not explicitly), 

the features and uncertainties described above.” 

Design can then be at various levels in a hierarchy, as shown in Figure 4. which identifies the 

prescriptive approach and the performance-based approach. In general terms, the most simple 

designs will be at the far left hand side of Figure 4 (using tabulated data for single members in a 

prescriptive environment), with the most sophisticated designs being at the right hand side of 

Figure 4 (using advanced calculation models for entire structures). 

177 
/f/ 

Member analysis 

Analysis of parts of the 

structure 

I 

Tabulated data Simplified calculation 

YES YES 

Standard fire only 

NO YES 

methods 

Standard fire and 

parametric fire 

Standard fire and 

BElglH (iiaraiwe) 

Figure 4. Alternative design procedures in the Structural Eurocodes (EC2,2002) 

Global structural 

Table 2 (abbreviated fiom EC2,2002) further illustrates the applicability of alternative methods 

of verifjling fire resistance. 

parametric fire 

NO NO 

Table 2. Summary table showing alternative methods of verification for fire resistance. 

I analysis 

I Advanced calculation 

models 

YES 

Only the principles are given 

YES 

Only the principles are given 

YES 

Only the principles are given 

178 
All the structural Eurocodes include the following sections: 

o Fire exposure 

o Verification methods 

o Methods of structural analysis 

o Mechanical properties 

o Thermal properties 

o Tabulated data 

o Simple‘ calculation methods 

o Advanced calculation methods 

0 Basis of design 

0 Material properties 

0 Design procedures 

0 Construction details 

The fire exposure allows for standard or realistic fire design curves to be used. The simple 

calculation methods are for predicting the behavior of single members based on simple 

assumptions. The advanced calculation methods provide the principles for computer analyses 

based on fundamental physical behavior, for both thermal analysis and mechanical behavior. 

These analyses need to take into account factors such as transient temperature gradients, variation 

of thermal properties with temperature, axial and flexural restraint, thermally induced forces, and 

thermally induced deformations, throughout the duration of the expected fire. The effects of creep 

are not explicitly included in the advanced calculation methods, but the stress-strain relationships 

have been modified to include creep in an indirect way. 

The Eurocodes include information which does not generally appear in other fire codes, such as 

comprehensive expressions for thermal and mechanical properties at elevated temperatures, and 

stress-strain relationships at elevated temperatures. This is very useful for any analytical 

modeling of fire behavior of structures. The tabulated listings in the Eurocodes are far more 

extensive than most other codes, the particular benefit to designers being that the tables include 

the improved fire resistance for members which are loaded below their design capacity at the time 

of a fire. 

European countries 

All of the major European countries have been involved in development of the Eurocodes, but 

they have also been maintaining parallel development of national codes which are used for 

everyday design. The transition to design office use of the Eurocodes is expected to be slow in 

most countries, depending on the rate at which the existing national codes are phased out. 

In the United Kingdom, a comprehensive recent publication is Structural Response and Fire 

Spread Beyond the Enclosure of Origin (BSI 2003) which is a “Published Document” in support 

of BS 7974 Application of Fire Safety Engineering Principles to the Design of Buildings (BSI, 

2001). BS 7974 is currently the most comprehensive code of practice for specific fire engineering 

design in any country. 

The Published Document (1 50 pages) is complementary to the Structural Eurocodes, and 

provides data and guidance for calculating the fire exposure and fire resistance (structural and 

non-structural) for a wide range of materials and assemblies. The document recognizes that 

detailed structural analysis of complex load-bearing structural frames is beyond the scope of such 

a guidance document. 

179 
North America 

Structural design for fire safety in the United States has not moved as quickly as in Europe. 

Existing building codes include prescriptive requirements for fire resistance which have not 

changed greatly in recent years. The current movement fiom regional to national building codes 

(IBC, NFPA codes) has not been accompanied by significant changes in design for fire resistance. 

However the need for change has been recognized and several background documents have 

recently been published (ASCEISFPE 1999, SFPE 2003% SFPE 2003b) which will eventually 

lead to code changes. The collapse of the World Trade Center towers in 2001 has obviously given 

new impetus for change (FEMA, 2002). 

Industry groups for particular materials (steel, concrete and timber industries) are also developing 

standards and guidance documents for structural fire resistance. 

Canada 

Most design standards (concrete, wood and steel) in Canada refer to the National Building Code 

of Canada (NBCC, 1995) for fire resistance specifications. The 2004 edition of the NBCC will 

include a few changes with respect to fire resistance. New design equations are proposed for fire 

resistance of concrete filled steel columns with bar reinforced concrete and steel fiber reinforced 

concrete filling. The prescriptive fire resistance ratings tables for walls and floors are being 

expanded with some additional assemblies, based on recent fire tests. A new standard for fiber 

reinforced plastics (FRP) is CSA-S806 which was published in 2002, including design charts for 

the fire resistance design of FRP-reinforced concrete slabs. 

Australia and New Zealand 

The Australian and New Zealand fire codes permit specific fire engineering design in a similar 

performance based environment. However, the minimum fire ratings specified by the Australian 

prescriptive documents are much higher than in New Zealand. The fire requirements in the 

structural design codes are rather simplistic; using tabulated values for reinforced concrete, for 

example, or specifling that standard tests should be used for establishing fire resistance ratings. 

All fire resistance values are based on standard fire exposure, with little or no mention of realistic 

fires. Alternative calculations are permitted but, unlike Europe, very little guidance is given 

(Buchanan, 2000). As in many other countries, the structural timber standards include a 

calculation method based on a constant rate of charring under standard fire exposure. A useful 

Guide for the Design of Fire Resistant Barriers and Structures has recently been published in 

Australia (England et al. 2000). 

180 
CONCLUSIONS 

Structural design is only part of the overall provision of fire safety. Structural fire safety must 

be provided as part of a comprehensive fire safety strategy. 

It is possible to use simple methods for specifying the required fire resistance, and to use 

tabulated data for compliance. The more simple the method, the more conservative the 

underlying assumptions need to be, and the less the accuracy of predicted behaviour. 

For large or prestigious buildings where the consequences of failure are most serious, the 

need for advanced structural design for fire safety becomes very important. 

Structural design for fire conditions must consider many different fire scenarios, with realistic; 

assessment of possible fire conditions. 

Maturing analytical tools for advanced structural analysis, combined with developing 

knowledge of material properties under elevated temperatures, are allowing the development 

of sophisticated methods for structural design for fire safety. 

Structural analysis and design of buildings in fire conditions is far more complex than for 

normal temperature conditions. It is necessary for design to be restricted to those with 

advanced knowledge of structural engineering, suitable analytical tools, and knowledge of 

thermal and mechanical material properties. 

The Structural Eurocodes provide the best current source of peer-reviewed information on 

principles and details for structural fire resistance. 

ACKNOWLEDGEMENTS 

Thanks to many people who provided information for this paper, including Jean-Marc Franssen, 

Venkatesh Kodur, Jurgen Koenig and Jim Milke. 

181 
REFERENCES 

ASCE, 1995. Standard for Load and Resistance Factor Design (LRFD) for Engineered Wood 

Construction. AF&PA/ASCE 16-95. American Forest and Paper Association, American 

Society for Civil Engineers, New York. 

ASCEISFPE, 1 999. Standard Calculation Methods for Structural Fire Protection, Document 29- 

99, American Society of Civil Engineers. 

ASFPCM, 1988. Fire Protection for Structural Steel in Buildings. Association of Specialist Fire 

Protection Contractors and Manufacturers, U.K. 

ASTM, 1995. Standard Test Methods for Fire Tests of Building Construction and Materials. 

El 19-95a. American Society for Testing and Materials. 

Babrauskas, V. 1979. COiWF21 A Program for Calculating Post-Flashover Fire Temperatures. 

NBS Technical Note 99 1. National Bureau of Standards. 

BSI, 1987. Fire Tests on Building Materials and Structures. BS 476 (Parts 1 to 23). British 

Standards Institution, UK. 

BSI, 200 1. Application of Fire Safety Engineering Principles to the Design of Buildings - Code of 

Practice. BS 7974:200 1. British Standards Institution, UK. 

BSI, 2003. Application of Fire Safety Engineering Principles to the Design of Buildings - Part 3: 

Structural Response and Fire Spread Beyond the Enclosure of Origin (Sub-system 3). 

Published Document PD 7974-3. British Standards Institution, UK. 

Buchanan, A.H. 1994. Fire Engineering for a Performance Based Code. Fire Safety Journal, Vol. 23, 

Buchanan, A.H. 1997. Modeling Post Flashover Fires with FASTLite. Journal of Fire Protection 

Buchanan, A.H. 2000. (Editor) Fire Engineering Design Guide. Centre for Advanced 

Buchanan, A.H. 2001. Structural Design for Fire Safety. John Wiley & Sons, Ltd. U.K. 

EC 1,2002. Eurocode 1 : Actions on Structures. ENV 1991, Part 1-2: General Actions - Actions on 

Structures Exposed to Fire. European Committee for Standardization, Brussels. 

EC2,2002. Eurocode 2: Design of concrete structures. ENV 1992, Partl-2: General rulesStructuralfire design, European Committee for Standardization, Brussels. 

EC3,2002. Eurocode 3: Design of steel structures. ENV 1993, Partl-2: General rules- Structural 

$+e design, European Committee for Standardization, Brussels. 

EC4,2003, Eurocode 4: Design of Composite Steel and Concrete Structures. ENV 1994, Part 1- 

2: General Rules - Structural Fire Design. European Committee for Standardisation, 

Brussels. 

EC5, 1994. Eurocode 5: Design of Timber Structures. W 1995, Part 1-2: General Rules - 

Structural Fire Design. European Committee for Standardization, Brussels. 

EC6, 1995. Eurocode 6: Design of Mmonry Structures. ENV 1996, Part 1-2: General Rules - 

Structural Fire Design. European Committee for Standardization, Brussels. 

England, J.P. et al. 2000. Guide for the Design of Fire Resistant Barriers and Structures. Building 

Control Commission, Melbourne, Victoria, Australia. 

Feasey, R. and Buchanan, A.H. Post-flashover Fires for Structural Design. Fire Safety Journal. 

FEW, 2002. World Trade Center Building Performance Study: Data Collection, Preliminary 

Observations, and Recommendations, FEMA Report 403, Federal Emergency 

Franssen, J.-M., Kodur, V.K.R. and Mason J. (2002) User’s manual for SAFIR200Ifree: A 

computer program for analysis of structures at elevated temperature conditions. 

University of Liege, Belgium. 

Draft Final Report, Part 2. Profil Arbed Centre de Recherches, Luxemberg. 

NO. 1,pp 1-16. 

Engineering. Vol9, No 3, pp 1-1 1. 

Engineering, University of Canterbury, New Zealand. 

V0137, 83-105,2002. 

Franssen, J-M. et al. 1999. Competitive Steel Buildings Through Natural Fire Safety Concept. 

182 
Gypsum Association, 1994. Fire Resistance Design Manual, 14th Edition. Gypsum Association, 

IFCI, 2000. International Building Code. International Fire Code Institute, USA. 

ISO, 1975. Fire Resistance Tests - Elements of Building Construction. IS0 834 - 1975. 

Lie, T.T. 1995. Fire Temperature-Time Relations. Chapter 4-8. SFPE Handbook of Fire 

Magnusson, S.E. and Thelandersson, S. 1970. Temperature-Time Curves of Complete Process of 

USA. 

International Organization for Standardization. 

Protection Engineering. Second Edition. Society of Fire Protection Engineers, USA. 

Fire Development; Theoretical Study of Wood Fuel Fires in Enclosed Spaces. Acta 

Polytechnica Scandinavica. Civil Engineering and Building Construction Series 65. 

NBCC, 1995. National Buildbzg Code of Canada. National Research Council of Canada. Ottawa. 

SAA, 1990. Fire Resistance Tests of Elements of Structure. AS 1530.4-1990. Standards 

SFPE, 2003a. Structural Design for the Fire Condition - the Role of the Design Professional. 

SFPE, 2003 b. SFPE Engineering Guide to Fire Exposures to Structural Elements, Society of Fire 

SNZ, 199 1. MP9. Fire Properties of Building Materials and Elements of Structure. 

SWRI, 1996. Directoly of Listed Products. Department of Fire Technology, Southwest Research 

UBC, 1997. Uniform Building Code. International Conference of Building Officials, Whittier, 

UL, 1996. Fire Resistance Directory. Underwriters Laboratories Inc, USA. 

ULC, 1989. Standard Methods of Fire Endurance Tests of Building Construction and Materials. 

Yii, 2003. Modelling the EfJects of Fuel Types and Ventilation Openings on Post-Flashover 

Association of Australia. 

Society of Fire Protection Engineers, USA (draft for comment). 

.Miscellaneous Publication No. 9. Standards New Zealand, Wellington. 

Institute, San Antonio, Texas. 

California, USA. 

CANAJLC-S 10 1 -M89. Underwriters Laboratories of Canada, Ontario. 

Compartment Fires. Fire Engineering Research Report 03/1 , University of Canterbury, 

New Zealand. 

183