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GSA 2003 Guidelines for Preventing Progressive CollapsePCADG | Beam (Structure) | Column
GSA 2003 Guidelines for Preventing Progressive CollapsePCADG
Description: GSA
for New Federal Office Buildings and Major Modernization Projects June 2003
Preface................................................................................................................................ iii Section 1. General Requirements..................................................................................... 1-1 1.1 1.2 1.3 1.4 1.5 Purpose.................................................................................................. 1-1 Applicability ......................................................................................... 1-1 Guideline Philosophy............................................................................ 1-2 How To Use This Document ................................................................ 1-3 Documentation Requirements............................................................... 1-5
Section 2. Definitions....................................................................................................... 2-1 2.1 2.2 2.3 General Terms....................................................................................... 2-1 Frangible/Non-frangible Façade ........................................................... 2-5 Alternate Analysis Techniques ............................................................. 2-5
Section 3. Exemption Process.......................................................................................... 3-1 Section 4. Reinforced Concrete Building Analysis and Design ...................................... 4-1 4.1 New Construction ................................................................................. 4-1 4.1.1 Design Guidance....................................................................... 4-2 4.1.2 Analysis..................................................................................... 4-4 4.1.2.1 Analysis Techniques ..................................................... 4-5 4.1.2.2 Procedure ...................................................................... 4-5 4.1.2.3 Analysis Considerations and Loading Criteria ............. 4-5 4.1.2.3.1 Typical Structural Configurations......................... 4-6 4.1.2.3.2 Atypical Structural Configurations ....................... 4-8 4.1.2.4 Analysis Criteria ........................................................... 4-9 4.1.2.5 Material Properties...................................................... 4-13 4.1.2.6 Modeling Guidance..................................................... 4-14 4.1.3 Redesign of Structural Elements............................................. 4-16 4.1.3.1 Procedure .................................................................... 4-16 Existing Construction.......................................................................... 4-17
Section 5. Steel Frame Building Analysis and Design .................................................... 5-1 5.1 New Construction ................................................................................. 5-1 5.1.1 Design Guidance....................................................................... 5-2 5.1.1.1 Local Considerations .................................................... 5-2 5.1.1.2 Global Considerations................................................... 5-6 5.1.2 Analysis..................................................................................... 5-7 Page i
TABLE OF CONTENTS 5.1.2.1 Analysis Techniques ..................................................... 5-7 5.1.2.2 Procedure ...................................................................... 5-7 5.1.2.3 Analysis Considerations and Loading Criteria ............. 5-8 5.1.2.3.1 Typical Structural Configurations......................... 5-8 5.1.2.3.2 Atypical Structural Configurations. .................... 5-11 5.1.2.4 Analysis Criteria ......................................................... 5-12 5.1.2.5 Material Properties...................................................... 5-20 5.1.2.6 Modeling Guidance..................................................... 5-22 5.1.3 Redesign of Structural Elements............................................. 5-24 5.1.3.1 Procedure .................................................................... 5-24 Existing Construction.......................................................................... 5-27
Section 6. Resources ........................................................................................................ 6-1 Appendix A. Appendix B. Appendix C. Appendix D. Atypical Structural Configurations...................................................... A-1 Design Guidance...................................................................................B-1 Example Calculations ...........................................................................C-1 Structural Steel Connections................................................................ D-1
the U. Army Corps of Engineers. GSA subsequently identified the need to update the November 2000 Guidelines to address the progressive collapse potential of steel frame structures. Inc. Department of State. initially released in November 2000. Houghton & Partners. Inc. with assistance provided by Myers. Preparation of the updated Guidelines was performed by Applied Research Associates. Gumpertz and Heger. Bruce Hall. focused primarily on reinforced concrete structures. planning and construction of new buildings and major renovation projects.. initiated this work in 1999 and served as the GSA Project Manager.S. Mr. Simpson. General Services Administration (GSA) developed the “Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects” to ensure that the potential for progressive collapse is addressed in the design..S. P. of the Office of the Chief Architect.E. Inc.. and the U. Page iii .S.PREFACE Preface The U. The Guidelines.
This update includes lessons learned and adds a separate section pertaining to structural steel buildings. new or existing facilities is described in Sections 4 and 5.1 Purpose The purpose of these Guidelines is to: • • • Assist in the reduction of the potential for progressive collapse in new Federal Office Buildings Assist in the assessment of the potential for progressive collapse in existing Federal Office Buildings Assist in the development of potential upgrades to facilities if required To meet this purpose. and for assessing the potential for progressive collapse in existing buildings. General Requirements 1. The previous guidelines. The analysis and design guidance for considering non-exempt. The primary users of the document will be architects and structural engineers. The use of a simplified analysis approach (hereafter referred to in these Guidelines as a “Linear Procedure”) should typically be limited to consideration of low-to-medium-rise facilities.2 Applicability These Guidelines should be used by all professionals engaged in the planning and design of new facilities or building modernization projects for the GSA. these Guidelines provide a threat independent methodology for minimizing the potential for progressive collapse in the design of new and upgraded buildings.S. “Progressive Collapse Analysis and Design for New Federal Office Buildings and Major Modernization Projects”. It should be noted that these Guidelines are not an explicit part of a blast design or blast analysis.SECTION 1 – General Requirements Section 1. or private concern. While mandatory for GSA facilities. these Guidelines may also be used and/or adopted by any agency. The requirements contained herein are an independent set of requirements for meeting the provisions of Interagency Security Committee (ISC) Security Criteria regarding progressive collapse. The procedures presented herein are required for the treatment of progressive collapse for U. The exemption process contained in these Guidelines applies to the majority of the construction types currently in the GSA building inventory as described in Section 3. November 2000 focused primarily on analysis and design for progressive collapse of reinforced concrete structures. organization. A Linear Procedure implies the use of either a static or dynamic linear-elastic Page 1-1 . It applies to in-house Government engineers. General Services Administration (GSA) facilities. and the resulting design or analysis findings cannot be substituted for addressing blast design or blast analysis requirements. 1. architectural/engineering (A/E) firms and professional consultants under contract to the GSA.
The Guidelines take a flexible and realistic approach to the reliability and safety of Federal buildings.3 Guideline Philosophy These Guidelines address the need to protect human life and prevent injury as well as the protection of Federal buildings.) Number of stories Seismic zone Detailed description of local structural attributes [discrete beam-to-beam continuity. etc. However. as illustrated in Figure 1. and nonlinear structural response. a Nonlinear Procedure may be required.. Special attention should be taken for facilities that contain atypical structural configurations and/or high-rise buildings that may exhibit complex response modes for the case where a primary vertical element is instantaneously removed. steel frame building. existing facilities shall be evaluated to determine the potential for progressive collapse. and connection resilience. The approach described below utilizes a flow-chart methodology to determine if the facility under consideration might be exempt from detailed consideration for progressive collapse. and/or exhibit an atypical structural configuration (as defined in Section 2.1 and elaborated on in Appendix A). functions and assets. The ISC Security Criteria requires all newly constructed facilities to be designed with the intent of reducing the potential for progressive collapse.1. when analyzing buildings that have more than 10 stories above grade.1] Page 1-2 . the assessment team will require experience and demonstrated expertise in structural dynamics. In other words. project engineers should consider using a more sophisticated analysis method hereinafter referred to as a “Nonlinear Procedure”. It should be noted that if a Nonlinear Procedure is utilized. 1. as defined under Section 2. A Nonlinear Procedure implies the use of static or dynamic finite element analysis methods that capture both material and geometric nonlinearity. Similarly. Additionally. As such. Typically such facilities consist of buildings and specialty structures that are nominally 10 stories above grade or less. If a complex structural response to the analysis process contained in these Guidelines is anticipated. This process is based on ascertaining certain critical documentation to ensure that resources are spent wisely regarding this issue.SECTION 1 – General Requirements finite element analysis. abnormal loading. a series of questions must be answered that identify whether or not further progressive collapse considerations are required. Critical documentation consists of identifying all of the following information: • • • • • Building occupancy Building category (e. the approach must be based on the intent of these Guidelines and use the same allowable extents of collapse area as that presented in Section 4 and Section 5 in the evaluation of the potential for progressive collapse. the applied procedure will require approval by the project Contracting Officer Technical Representative (COTR). regardless of the required level of protection determined in the facility-specific risk assessment.g. reinforced concrete building. connection redundancy.
As such. prescribed as it is not feasible to rationally examine all potential sources of collapse initiation.) there are always scenarios that will be capable of initiating a collapse.e. and project engineer should be thoroughly familiar with the provisions of these Guidelines. albeit a simplified methodology. Rather. etc.4 How To Use This Document The intent of this document is to provide guidance to reduce and/or assess the potential for progressive collapse of Federal buildings. impact design. as it applies to their specific facility. structural irregularities. These Guidelines and the provisions made herein would undoubtedly reduce the extent of this initially collapsed area. blast design. seismic design. respectively.. for new or existing construction. Regardless of other specific design requirements. however. It should be noted that the use of a Linear Procedure. the architect/engineer may apply methods appropriate to the facility at hand. providing the acceptance criteria accounts for the uncertainties in behavior in the form of appropriate Demand-Capacity Ratios. The objective is to prevent or mitigate the potential for progressive collapse. provisions of these Guidelines should serve to help arrest the progression of the collapse and should reduce the extent of the damage. A threat independent approach is. The approach taken (i. is not intended for and not capable of predicting the detailed response or damage state that a building may experience when subjected to the instantaneous removal of a primary vertical element. No special value is placed on using more robust columns that can survive a particular threat or the use of larger spans to avoid multiple column failure from a specific point threat.] The outcome of these answers leads to either (1) an exemption (no further consideration required) or (2) the need to further consider the potential for progressive collapse. These Guidelines present the methodology and performance criteria for these determinations without prescribing the exact manner of design or analyses. say a building is rammed by an 18-wheeler taking out 3 columns and collapsing several structural bays over 2 floors. architect. the removal of a column or other vertical load bearing member) is not intended to reproduce or replicate any specific abnormal load or assault on the structure. For example. The detailed analysis required in the latter case is intended to reduce the probability of progressive collapse for new construction and identify the potential for progressive collapse in existing construction. not necessarily to prevent collapse initiation from a specific cause.SECTION 1 – General Requirements • Description of significant global structural attributes [single point failure mechanism(s).e. The owner. More importantly. a high or low potential for progressive collapse). fire design. etc. Page 1-3 . however. may. a Linear Procedure. (e. 1. as provided for in these Guidelines. The strategy places a premium on well designed continuity as well as post event capacity. ductility and robustness as compared with just using key element resistance.. However.g. with proper judgment. be used for determining the potential for progressive collapse (i.. member removal is simply used as a “load initiator” and serves as a means to introduce redundancy and resiliency into the structure.
1 or Section 5. recommendations and costs. linear static-dynamic .2 New or Existing Construction ? The potential for progressive collapse is high.SECTION 1 – General Requirements Progressive Collapse Analysis and Design Guidelines Exemption Process (Facility Exemption Consideration) Section 3 No further consideration for progressive collapse is required Yes Is the facility exempt from further consideration for progressive collapse ? Report New Construction Section 4. Yes No The potential for progressive collapse is high and the facility has not met the requirements for minimizing the potential for progressive collapse. Analysis .2 or Section 5. nonlinear static-dynamic Analysis .1.1 Design No Existing Construction Section 4. recommendations and costs. Prepare report that documents findings. Overall flow for consideration of progressive collapse. Figure 1. Prepare report that documents findings. linear static-dynamic . Page 1-4 . nonlinear static-dynamic No Does the structure meet the requirements for minimizing the potential for progressive collapse ? Does the structure meet the requirements for minimizing the potential for progressive collapse? Yes The potential for progressive collapse is low and the facility has met the requirements for minimizing the potential for progressive collapse.
the conclusion as to whether or not adequate standoff is sufficient to justify an exemption from further consideration of progressive can be determined from Table 3.gov. When the criteria are satisfied (i. (3) a description of both the global and local structural attributes as they may affect progressive collapse and (4) the level of protection required.5 Documentation Requirements The entire evaluation process shall be documented to a level such that the conclusions can be independently verified by in-house designers or outside firms and professionals under contract to the GSA. STANDGARD may also be used for reporting on new and upgraded building designs. Answers to subsequent questions in the flow diagram will require either a similar or even a higher level of supporting detail. the methodology for existing construction outlined in Section 4. the potential for progressive collapse is low). and can be easily compared to other assessed buildings as part of a common database. (2) a description of the overall construction type.1 or Section 5.e.2. a redesign must be executed. reinforced concrete building vs. if the facility is determined not to be exempt from further consideration for progressive collapse.. depending on the material category of a given building (e.. This process provides design guidance and evaluation guidance for determining the potential for progressive collapse.1. This generally will involve providing adequate support for the “answers” to each question in the process in the form of a report. For existing construction. as applicable. if the facility is determined not to be exempt from further consideration for progressive collapse. If the facility is determined to be exempt.2 or 5. Information on STANDGARD and access to the program may be obtained at the website www. the process concludes with documentation of the exemption process. For example. The potential for progressive collapse determined in this process (whether low or high) must be quantified and the analysis procedure and results documented. to ensure that such reports contain the same type of information for each building assessed. Page 1-5 . For the exemption process. shall be executed. steel frame building). 1.1. the process concludes with documentation of the analysis procedure and results. particularly as to structural considerations. From this information.gsa. The STANDGARD (Standard GSA Assessment Reporter & Database) software program shall be used for preparing progressive collapse assessment reports for all existing GSA buildings.SECTION 1 – General Requirements The first step of the process is to evaluate the facility using the methodology outlined in Section 3 of these Guidelines to determine if the facility might be exempt from further consideration for progressive collapse.g. the answer to each question in the flow diagram should be supported by a written description and graphics (as may be appropriate) to fully describe the conclusion.oca. For new construction. as applicable. the initial consideration in the exemption process will generally require the following supporting information: (1) the site plan showing minimum defended standoff distances. If the potential for progressive collapse is found to be high for a given design. the methodology for new construction outlined in Section 4. shall be executed.
In particular. and connection resilience (as defined in Section 2. using a general description such as those used in Appendix D. judicious configuring of weld orientations. coupled with connection redundancy to ensure a multiplicity of clearly defined load paths. In particular. similar to the language used to characterize the term “symmetric reinforcement” in Section 2.. the reporting analyst shall first describe the beamto-column connection type. as well as how they are achieved or not achieved individually and collectively for assessments of existing buildings. connection redundancy. and to achieve a resilient and robust design. Favorable attributes include the use of creative detailing of the geometry of connection elements (i.SECTION 1 – General Requirements The written description of global attributes shall include column spacing. and any significant structural irregularities. The reporting analyst shall then describe those connection attributes (favorable or otherwise) that directly affect the connection’s ability to maintain independent structural beam-to-beam continuity across a removed column.1 for reinforced concrete buildings. building height and number of stories. and/or orientation of bolt groups) to achieve discrete beam-to-beam continuity across a column. The written description of local attributes shall include a detailed summary of essential connection elements and a detailed description and sketch of the geometry of those elements as they affect the ability to maintain structural continuity across a removed vertical element.1) are achieved in any proposed new or retrofit upgrade design. the project engineer is required to explicitly describe how the essential attributes of discrete beam-to-beam continuity across a column. selection of weld types. for steel frame buildings.e. and with increased torsional strength and minor-axis bending strength to provide overall connection resilience. Page 1-6 .
Definitions The following definitions apply to terms used throughout these Guidelines.1 General Terms Abnormal Loads – Loads other than conventional design loads (dead. live. without rupture. Connection Redundancy – A beam-to-column connection that provides direct. 2.) for structures such as air blast pressures generated by an explosion or impact by vehicles.Section 2. and its primary use of proven ductile properties of a given construction material. etc.) that may be used to determine the potential for progressive collapse in a given facility. General terms are defined in Section 2.2. and alternate analysis methods are discussed in Section 2. nonlinear. Connection Resilience – A beam-to-column connection exhibiting the ability to withstand rigorous and destructive loading conditions that accompany a column removal. dynamic finite element analysis. Allowable Extent of Collapse (Exterior Consideration) – The extent of damage resulting from the loss in support of an exterior primary vertical load-bearing member that extends one floor above grade (one story) shall be limited. Requirements and further discussion of this topic is included in Section 2. Defended Standoff Distance – The defended standoff distance is the range between a point along the defended perimeter and the nearest structural element.. Explicit limitations for damage to primary and secondary structural components are defined in Sections 4 and 5. its robustness.1. etc. seismic.The extent of damage resulting from the loss in support of an interior primary vertical load-bearing member that extends one floor above grade (one story) shall be limited. etc. multiple load paths through the connection. Defended Perimeter – The defended perimeter is the line that defines the boundaries of defended standoff zones (Figure 2. A detailed discussion of atypical structural configurations is presented in Appendix A. wind. Explicit limitations for damage to primary and secondary structural components are defined in Sections 4 and 5. Alternate Analysis Techniques – Sophisticated analysis methods (e.3.3. Parking within this defended zone must be limited Page 2-1 .g. frangible/non-frangible façade is described in detail in Section 2.1). This ability is facilitated by the connection’s torsional and weak-axis flexural strength. Allowable Extent of Collapse (Interior Consideration) . Atypical Structural Configuration – A structural configuration that has distinguishing features or details.
a prescreening system. if parking is allowed in this zone. window systems. In addition.1. Minimum Defended Standoff Distance Defended Standoff Distance Defended Standoff Distance Defende d Figure 2. an automatic vehicle identification (AVI). Refer to Section 2. for steel frame beam-to-column connection applications. security countermeasures (i.) that has an ultimate. as a minimum. retaining walls. High Potential for Progressive Collapse – The facility is considered to have a high potential for progressive collapse if analysis results indicate that the structural member(s) and/or connections are not in compliance with the appropriate progressive collapse analysis acceptance criteria. etc. planters. vehicle barriers capable of stopping the Medium Level Protection vehicle explosive threat (defined in the ISC Security Criteria) must be in place. Vehicle barriers such as bollards. clearly defined beam-to-beam continuity link across a column. In order for the perimeter to be considered defended.2 for a more detailed description. Exemption Procedure .0 psi..A facility exemption process is offered for both new and existing construction.e. cil Fa Perimet er ity Defended Standoff Distance Page 2-2 .. This process presents the designer/analyst with an outlet to further consideration of progressive collapse if the facility possesses structural and/or site characteristics that enable the facility to be considered a low potential for progressive collapse. regardless of the actual or potential damage state of the column. unfactored flexural capacity that is less than 1. etc. system.to cleared employees or other controlled parking as defined by the ISC Security Criteria. unless a Higher Level of Protection is specified. etc. Illustration depicting defended perimeter and defended standoff distances. that is capable of independently transferring gravity loads for a removed column condition. landscaping.) must be in place. Discrete Beam-to-Beam Continuity – A distinct. can be designed to stop a vehicle of the specified weight and speed consistent with the criteria. to reduce the potential for the delivery of an explosive device into this defended area.An exterior façade system (wall systems. Frangible Façade .
Major damage. the primary non-structural elements that are considered are all elements (including their attachments) that are essential for life safety systems or elements that can cause substantial injury if failure occurs. The facility or protected space will sustain a significant degree of damage. ISC Low and Medium/Low Level Protection . ceilings or heavy suspended mechanical units. Such facilities may be exempt from any further consideration of progressive collapse. but the structure should be reusable. the primary structural elements are the essential parts of the building’s resistance to abnormal loads and progressive collapse.2 for a more detailed description. Non-Frangible Facade – An exterior façade system (wall systems. ISC Medium Level Protection . and assets may receive minor damage. Primary Non-Structural Elements – As defined by the ISC Security Criteria. including. in recognition of the improved response information that can be obtained from such procedures when employed by highly trained analysts. Primary Structural Elements – As defined by the ISC Security Criteria. Building components. but not limited to.) that has an ultimate.ISC Higher Level Protection . and the main lateral resistance system. The facility or protected space will sustain a high level of damage without progressive collapse. girders.A Linear Procedure is a simplified analysis approach.Moderate damage. It is generally a more accurate analysis approach than are Linear Procedures to characterizing the damage state of a structure. roof beams. repairable. and implies the use of either static or dynamic elasto-plastic finite element analysis methods that capture both material and geometric nonlinearity.A Nonlinear Procedure is a more sophisticated analysis approach. window systems.1) are permitted. repairable. less restrictive acceptance criteria (Table 2. will require replacement. Occupants may incur some injury. Refer to Section 2. Low Potential for Progressive Collapse –The facility is considered to have a low potential for progressive collapse if analysis results indicate that the structural member(s) and/or connections are in compliance with the appropriate progressive collapse analysis acceptance criteria. unfactored flexural capacity that is greater than or equal to 1. Building elements other than major structural members may require replacement. including structural members.Minor damage. Nonlinear Procedure . and implies the use of either a static or dynamic linear-elastic finite element analysis. Page 2-3 . Some casualties may occur and assets may be damaged.0 psi. including columns. The facility or protected space may globally sustain minor damage with some local significant damage possible. or the building may be completely unrepairable. When such procedures are used. Casualties will occur and assets will be damaged. etc. requiring demolition and replacement. Linear Procedure .
e. Another example includes exposed perimeter columns. Secondary Non-Structural Elements – As defined by the ISC Security Criteria.Progressive Collapse . a blast consultant should have a minimum of 5 years of demonstrated experience in the design and assessment of facilities subjected to blast loads as well as in the testing and evaluation of hazard mitigating products. and/or 2) may significantly depend on panel zone participation from the column’s web to achieve its rotational capacity.e. Symmetric Reinforcement – Symmetric reinforcement is defined here as having continuous (i. etc. Secondary Structural Elements – As defined by the ISC Security Criteria. Hence. the secondary structural elements are all other load bearing members (not included in the primary structural elements category). the total damage is disproportionate to the original cause.Progressive collapse is a situation where local failure of a primary structural component leads to the collapse of adjoining members which. Single Point Failure Mechanism – A structural feature in which a localized structural failure can lead to a widespread collapse of the structure. the secondary non-structural elements are all elements not covered in primary non-structural elements. Page 2-4 . across a column.. transferring load to the load bearing members supporting the girder). leads to additional collapse. Robustness – Ability of a structure or structural components to resist damage without premature and/or brittle failure due to events like explosions. and light fixtures.3). such as floor beams. due to its vigorous strength and toughness. impacts. in turn. A primary example includes the use of transfer girders (i. To be considered qualified. slabs. such as partitions. no lap splices across a column) and equal amounts of main reinforcing steel in both the compressive and tension faces of a reinforced concrete girder or beam. and demonstrated experience with accepted design practices for blast resistant design and with referenced technical manuals (Figure 3. furniture. hence. beams or girders that typically provide vertical support for intermediate columns or load bearing members located above. Qualified Blast Engineer/Consultant – Consultant should have formal training in structural dynamics. Traditional Moment Connection – A ‘traditional’ moment connection is defined here as a steel frame moment-resisting beam-to-column connection that 1) typically joins beam or girder flanges directly to the face of a column flange in the field by using either a complete joint penetration (CJP) groove weld in a T-joint configuration. fire or consequences of human error..
A non-frangible façade system is quantified by having a static flexural capacity equal to 1. where no operational security countermeasures are in place to screen vehicles that could enter this area with an explosive device. action.0). The procedure (i. Examples of this process are shown in Appendix C. The façade system that has the largest capacity shall be used to specify the type of façade system (i. operational security countermeasures in place.2 Frangible/Non-frangible Façade Façade systems that constitute at least 25% of the wall area per structural bay shall be evaluated for flexural capacity. Unfactored. Unfactored Capacity – The calculated flexural. Any façade system that occupies less than 25% of the wall area per structural bay shall be disregarded for this consideration.e. The concern for this situation is that an explosive device could be brought into the facility and placed at a vulnerable location. and axial capacities with no use of a capacity reduction factor (i. 2.e.Typical Structural Configuration – A typical structural configuration consists of a structural layout that is generally simple and contains no atypical structural configuration arrangements. Ultimate.) for determining the flexural capacity of the façade system should correspond with the construction details of the actual façade system.0 psi. Uncontrolled Public Areas – These are areas located at the ground floor or entry level that are utilized by retail and other users and have no. or inadequate.. φ = 1. based on a uniform distributed load acting inward (towards the interior of the building). such as next to a column.. based on a uniform distributed load acting inward.e. boundary conditions. When such procedures are used. ultimate strengths should be used in the determination of the capacity. etc. A frangible façade system is quantified by having a static flexural capacity that is less than 1. less restrictive acceptance Page 2-5 ..3 Alternate Analysis Techniques Nonlinear Procedure A Nonlinear Procedure implies the use of either static or dynamic finite element analysis methods that capture both material and geometric nonlinearity. 2. Uncontrolled Parking – Public parking or a parking area located within the footprint of the building under consideration. It is generally a more sophisticated analysis approach than are Linear Procedures in characterizing the performance of a structure. frangible or non-frangible).0 psi or greater. shear.
The values listed are for typical elements in conventional construction (i.1.1.1 provides the maximum allowable ductility and/or rotation limits for many structural component and construction types to limit the possibility of collapse. until only recently. infrequent usage of Nonlinear Procedures was. Empirically determined damage criteria must be utilized to predict the potential collapse of a structural element. In addition. Unless explicitly accepted by the GSA. sensitivities to assumptions for boundary conditions. as well as other possible complications due to the size of the structure. including dynamic time history nonlinear response of high-rise structures containing thousands of members and connections covering a wide range of inelastic constitutive relations for the purpose of practical design applications. However. construction that has not been hardened to resist abnormal loading). as included in Table 2. the guidance and criteria in the March 2001 document. Structural engineers. and to perform the required dynamic time-history non-linear analyses of the entire structure. Because of the inherent challenges.criteria are permitted. advancements in computer hardware and general-purpose analysis software packages over the past few years have now made it possible to employ sophisticated structural assessment techniques on large and complex structures. Table 2. Caution. The qualifications and experience of those proposed to perform the Nonlinear Procedure shall be reviewed and approved by the project manager. can now construct a global model of the whole structure to capture both material and geometric non-linearity. Guidance on Structural Requirements (Draft). reinforced by limitations in computer hardware and analysis software. Page 2-6 . complexities and costs involved. Interim Antiterrorism/Force Protection Construction Standards.e. must be exercised when using Nonlinear Procedures because of potential numerical convergence problems that may be encountered during the execution of the analysis. however. Accordingly. geometry and material models. it is imperative that only experienced structural engineering analysts with advanced structural engineering knowledge be allowed to implement these sophisticated analysis tools and judgment must be used in interpreting the results.. One such set of damage criteria that may be utilized in conjunction with a nonlinear analysis approach is outlined in an interim Department of Defense Construction Standard (Department of Defense. prior to starting the work. shall be used. recognizing the improved results that can be obtained from such procedures. with proper experience and knowledge in structural dynamics. At the time of this writing the Department of Defense was considering modifications to their guidance. March 2001) and is included in Table 2. Nonlinear Procedures have been used less frequently for progressive collapse analyses than have Linear Procedures.
5 3. Partially Restrained • Limit State governed by rivet shear or flexural yielding of plate.5 3.5 21 10.5 2 2 to 2.5 21 21 3.5 3. Acceptance criteria for nonlinear analysis1.5 21 10.5 2.5 2. or tension failure of plate.1.5 21 NOTES 1 H/25 Max sidesway 12 12 2 1. tension failure of rivet or bolt.5 1 1 1 2 2 2 1 2 2 2 2 1 3. angle or T-section One-way Unreinforced Masonry (unarched) One-way Unreinforced Masonry (compression membrane) Two-way Unreinforced Masonry (compression membrane) One-way reinforced Masonry Two-way Reinforced Masonry Masonry Pilasters (tension controls) Masonry Pilasters (compression controls) Wood Stud Walls Wood Trusses or Joist Wood Beams Wood Exterior Columns (bending) Wood Interior Columns (buckling) * Notes provided on following page.5 10. COMPONENT Reinforced Concrete (R/C) Beam5 R/C One-way Slabs w/o tension membrane5 R/C One-way Slabs w/ tension membrane5 R/C Two-way slabs w/o tension membrane5 R/C Two-way Slabs w/ tension membrane5 R/C Columns (tension controls) 5 R/C Columns (compression controls) R/C Frames Prestressed Beams Steel Beams Metal Stud Walls Open Web Steel Joist (based on flexural tensile stress in bottom chord) Metal Deck Steel Columns (tension controls) Steel Columns (compression controls) Steel Frames Steel Frame Connections. 2 20 7 6 20 20 1 DUCTILITY (µ)3 ROTATION Degrees (θ)4 6 6 12 6 12 6 2 12 ROTATION %Radians (θ)4 10.5 See Appendix D 1 1. Fully Restrained • Welded Beam Flange or Coverplated (all types) • Reduced Beam Section Steel Frame Connections. Proprietary6 Steel Frame Connections.5 3.5 3.5 H/25 Max sidesway See Appendix D See Appendix D 1. angle or T-section • Limit State governed by high strength bolt shear.Table 2.5 Page 2-7 .5 to 4.
Concrete having more than 2-degrees rotation must include shear stirrups per requirements of DAHSCWE Manual (See Reference 3. 4. Figure 2. Sidesway and member end rotations (θ) for frames.3 provided below. Ductility is defined as the ratio of ultimate deflection to elastic deflection (Xu/Xe).2. 5.3. Measurement of θ after formation of plastic hinges.2 and 2. COTR approval must be obtained for the use of updated tables.1. Rotation for members or frames can be determined using Figures 2. 2. Page 2-8 . Proprietary connections must have documented test results justifying the use of higher rotational limits. Figure 2. Page 6-1). 3.
2) Page 2-9 . (2.25LL) (2. DL = dead load LL = live load (higher of the design live load or the code live load). it is recommended that the following downward loads be applied when assessing the potential for progressive collapse as presented in this Guideline.1) Dynamic Analysis Loading For dynamic analysis purposes the following vertical load shall be applied downward to the structure under investigation: Load = DL + 0.Additionally. Static Analysis Loading For static analysis purposes the following vertical load shall be applied downward to the structure under investigation: Load = 2(DL + 0.25LL where.
To begin the automated version of the exemption process. If the type of construction is not listed in Table 3. in writing. The user will then continue to Flowchart 4 or 5 (Figures 3.4 or 3.5. or Flowchart 4 or 6 (Figures 3. Note that defended standoff is only considered as one factor in determining if a facility is exempt. If a facility is not exempt and an analysis is required.4 or 3. depicted in Figure 3.1.1. respectively) for concrete structures. to determine the potential for total exemption to the remaining methodology. The results determined in the exemption process shall be documented by the project engineer and submitted to the GSA Project Manager for review. This process does not preclude a building from being evaluated for progressive collapse potential by other well-established procedures based on rational methods of analysis that are approved. Step 4. go directly to Step 3. respectively) for steel frame structures as indicated. The user shall begin with Flowchart 3 (Figure 3. This process is documented in all STANDGARD generated progressive collapse assessment reports.6. follow the steps in Flowchart 2. Using Table 3. depicted in Figure 3.SECTION 3 – Exemption Process Section 3.1. by the GSA on a case-by-case basis. resulting from an abnormal loading situation. Otherwise. Step 3. If the facility is at an extremely low risk for progressive collapse or if the human occupancy is extremely low (as determined in this process). Begin Exemption Process Procedure: Step 1. the facility may be exempt from any further consideration of progressive collapse.2. to determine the potential for total or partial exemption to the remaining methodology. This step offers a more detailed consideration of the facility if the requirements set forth in Step 2 are not achievable or the construction type is not included in Table 3. click on the ‘Begin Exemption Process’ button (at right).1. Follow the steps in Flowchart 1. Page 3-1 .3) to determine the potential for total exemption. the analysis process is threat independent. Step 2. determine the minimum defended standoff distance consistent with the construction type and required level of protection (as determined by the GSA) of the facility under consideration. Exemption Process The following procedure provides a process for evaluating the potential for progressive collapse for reinforced concrete and steel framed buildings. The facility should be evaluated for the possibility of being exempt from further consideration of progressive collapse using the included computer program (an automated version of the exemption process) or by the following manual procedure.
For existing facilities. If the GSA Project Manager disagrees with the assessment of characteristics used in the procedure. the exemption process criteria have been designed to be conservative and therefore. Should the project characteristics change or if the GSA Project Manager disagrees with the assessment of the characteristics used in the exemption process. It should be noted that limited test data currently exists for steel frame beam-to-column connections subjected to the type of loading conditions that accompany removal of a column. there will be very few exemptions for steel frame structures. further progressive collapse consideration may be required. further progressive collapse consideration may be required. the GSA Project Manager shall review the results of this procedure documented by the project engineer. the project manager is ultimately responsible for verifying that the site and structural characteristics used in this procedure are consistent from conceptual through 100% plans (including architectural. structural and site drawings). As a result. Page 3-2 .SECTION 3 – Exemption Process In newly constructed facilities.
C3A. RM2) Masonry bearing walls with reinforced CMU pilasters (FEMA 310 Building Type: RM1. URMA) Precast Construction Precast concrete frame (FEMA 310 Building Type: PC1. W1A. S2. W1.1. PC2A) Wood Construction Wooden frame (FEMA 310 Building Type: C2A. PC1A. C2) Rigid frame structure with a frangible facade (FEMA 310 Building Type: C1. Page 3-3 . S5A) Masonry Construction Reinforced masonry wall with steel or r/c concrete frame (FEMA 310 Building Type: C3. URM. PC2.) (FEMA 310 Building Type: S1A. RM2) Shear wall structure (FEMA 310 Building Type: C2) Steel Construction Rigid frame structure with a non-frangible facade (FEMA 310 Building Type: S4) Rigid frame structure with a frangible facade (FEMA 310 Building Type: S1. S2A. Minimum Defended Standoff Distance (ft)∗ Construction Type ISC Required Level of Protection Low and Medium Higher Medium/low 25 25 25 25 25 40 35 40 35 35 130 100 130 100 100 Reinforced Concrete Construction Rigid frame structure with a non-frangible facade (FEMA 310 Building Type: C1. Butler style buildings. S3. S5. etc.SECTION 3 – Exemption Process Table 3. Minimum defended standoff distances for various types of construction. W2) 25 25 55 40 35 105 130 100 165 25 35 100 65 105 290 55 105 165 95 120 360 ∗ These distances are used in the progressive collapse exemption process only and are not directly related to general standoff distances cited in the ISC Security Criteria..e. C3. RM2) Lightweight steel framed structures (i. RM2) Flat slab structure with a non-frangible facade (FEMA 310 Building Type: C2) Flat slab structure with a frangible facade (FEMA 310 Building Type: C3.
or twofamily dwelling? No Yes Is the building a special structure (i. or adobe structure? No Has the building been designed and constructed to meet the progressive collapse requirements of either the GSA or ISC Security Criteria? No Yes The facility is a candidate for automatic exemption from further consideration of progressive collapse. bridge.5 to confirm the adequacy of the structrual design concerning progressive collapse? No Go to Flowchart 2 (Figure 3. hydraulic structure. unreinforced masonry. Proceed to Step 4 of the Exemption Procedure Yes Is there adequate documentation as defined in Section 1. intended only for incidental human occupancy or occupied by persons for a total of less than 2 hours a day? No Yes Is the building a detached one. To be used with Step 1 of the exemption process.SECTION 3 – Exemption Process Flowchart 1 Begin initial considerations Yes Is the building classifed for agricultural use. etc.. Flowchart 1. transmission tower.)? No Yes Is the building a one-story building of light steel frame or wood construction with an occupied area less than 280 m2 (3000 ft2)? No Yes Has the remaining useful life of the building been determined to be less than 5 years? No Yes Is the building a one story.e. wood.1.2) Figure 3. Page 3-4 .
3) No Is the defended standoff distance > that required for the construction type under consideration ? (Table 3. Proceed to Step 4 of the Exemption Procedure Further consideration regarding progressive collapse is required.SECTION 3 – Exemption Process Flowchart 2 Begin initial considerations Go to Flowchart 3 (Figure 3. Proceed with the analysis/design guidelines for the minimization of the potential for progressive collapse (Section 4 for Reinforced Concrete Buildings. To be used with Step 2 of the exemption process.2. Section 5 for Steel Frame Buildings) No Further consideration regarding progressive collapse is required.1) Yes No Does the structure contain single point failure mechanism(s) and/or atypical structural conditions and/or is it over ten stories? Yes Does the facility have public areas and/ or uncontrolled parking ? Yes Are these areas controlled with adequate security measures ? No Yes No Is the facility designed consistent with at least Seismic Zone 31 or Seismic Design Category D or E2 requirements ? Yes The facility is a candidate for automatic exemption from the consideration of progressive collapse. Section 5 for Steel Frame Buildings) 1 2 As defined in the 1997 Uniform Building Code As defined in the 2000 International Building Code Figure 3. Proceed with the analysis/design guidelines for the minimization of the potential for progressive collapse (Section 4 for Reinforced Concrete Buildings. Page 3-5 . Flowchart 2.
roof.6) Yes For Steel Frame Buildings: Are all perimeter bays and all affected interior bays part of continuous moment frames ? No No No Further consideration regarding progressive collapse is required. To be used with Step 3 of the exemption process.or posttensioned members ? No Yes Yes Does the facility have public areas and/or uncontrolled parking ? No Are all the perimeter bays part of a continuous moment frame designed consistent with at least Seismic Zone 31 or Seismic Design Category D or E2 requirements? Are these areas controlled with adequate security measures ? Yes No Is the facility design consistent with at least Seismic Zone 3 1 or Seismic Design Category D or E 2 requirements? Yes Yes (Concrete Only) No Yes (Steel Only) .3. Proceed with the analysis/design guidelines for the minimization of the potential for progressive collapse. walls. do the pre. Section 5 for Steel Frame Buildings) 1 2 As defined in the 1997 Uniform Building Code As defined in the 2000 International Building Code Figure 3. Flowchart 3.5) . foundation) consistent with the ISC Security criteria ? Yes Structural Considerations If applicable. Page 3-6 . For Steel Frame Buildings: Go to Flowchart 6 (Figure 3.or posttensioned members contain continuous standard symmetric steel reinforcement ? (in addition to the preor post-tensioned reinforcement) Yes Does the structural system contain any pre. For Reinforced Concrete Buildings: Go to Flowchart 5 (Figure 3. (Section 4 for Reinforced Concrete Buildings.4) No Has a blast engineer/ consultant designed the primary and secondary structural members for blast loads (frame.SECTION 3 – Exemption Process Flowchart 3 Begin additional considerations Go to Flowchart 4 (Figure 3.
do the pre. (Section 4 for Reinforced Concrete Buildings. Flowchart 4.or post-tensioned members contain continuous standard symmetric steel reinforcement (in addition to the pre. Page 3-7 . For Steel Frame Buildings: Go to Flowchart 6 (Figure 3. For Reinforced Concrete Buildings: Go To Flowchart 5 (Figure 3.5) . To be used with Step 3 of the exemption process. Proceed with the analysis/design guidelines for the minimization of the potential for progressive collapse.6) No No Further consideration of progressive collapse is required.4.SECTION 3 – Exemption Process Flowchart 4 Begin additional considerations Structural Considerations If applicable. Section 5 for Steel Frame Buildings) 1 2 As defined in the 1997 Uniform Building Code As defined in the 2000 International Building Code Figure 3.or post-tensioned members ? No Yes Yes Does the facility have public areas and/or uncontrolled parking ? No Are all the perimeter bays part of a continuous moment frame designed consistent with at least Seismic Zone 41 or Seismic Design Category F 2 requirements? No Are these areas controlled with adequate security measures ? Yes Is the facility design consistent with at least Seismic Zone 41 or Seismic Design Category F2 requirements? Yes (Concrete Only) Yes No Yes (Steel Only) No For Steel Buildings: Are all perimeter bays and all affected interior bays part of a continuous moment frame? Yes .or post-tensioned reinforcement)? Yes Does the structural system contain pre.
(Section 4) The facility is a candidate for automatic exemption from the consideration of progressive collapse. (3) Story heights <= 16 ft (20 ft for courts) Yes Yes Does the structure contain single point failure mechanism(s) and/or atypical structural conditions and/or is it over ten stories? No Yes Does the primary load bearing structure use one of the following construction types? precast concrete or gravity connections No Further consideration of progressive collapse is required.SECTION 3 – Exemption Process Flowchart 5 Final Considerations (Reinforced Concrete) No Does the facility have all of the following structural features? (1) symmetric reinforcement in all primary and secondary structural members (if applicable).5. as defined in Section 2.1. Page 3-8 . To be used with Step 3 of the exemption process. Flowchart 5. (2) structural bay widths <= 30 ft. Proceed with the analysis/design guidelines for the minimization of the potential for progressive collapse. Proceed to Step 4 of the Exemption Procedure Figure 3.
Flowchart 6. (5) Story heights <=16ft (20 ft for courts) Yes Yes Does the structure contain single point failure mechanism(s) and/or atypical structural conditions and/or is it over ten stories? No Yes Does the primary load bearing structure use one of the following beam to column connections? (1) Partially restrained moment. To be used with Step 3 of the exemption process. (Section 5) The facility is a candidate for automatic exemption from further consideration of progressive collapse. (See Appendix D) (2) Pre-1995'traditional" (3) Riveted (4) Post-1995 without successful AISC cyclic testing (as defined in Section 5. as defined in Section 2. Proceed to Step 4 of the Exemption Procedure Figure 3.1) No Further consideration of progressive collapse is required. Proceed with the analysis/design guidelines for the minimization of the potential for progressive collapse. (4) Structural bay width <=30 ft. Page 3-9 . (3) Connection resiliance.SECTION 3 – Exemption Process Flowchart 6 Final Considerations (Steel) No Does the facility have all of the following structural features.1? (1) Discrete beam-to-beam continuity.6. (2) Connection redundancy.1.
The potential for progressive collapse is high.1 New Construction All newly constructed facilities shall be designed with the intent of reducing the potential for progressive collapse as a result of an abnormal loading event. Page 4-1 . regardless of the required level of protection. The flowchart.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Section 4.1. the structure will not progressively collapse or be damaged to an extent disproportionate to the original cause of the damage.1.2) Redesign Structural Elements (Section 4.3) yes Does the structure meet the analysis requirements for minimizing the potential for progressive collapse? no The potential for progressive collapse is low. This method is intended to enhance the probability that if localized damage occurs as the result of an abnormal loading event. New Construction Design Guidance (Section 4. outlines this process for reducing the potential for progressive collapse in newly constructed facilities. Figure 4.1. Process for reducing the potential for progressive collapse in new construction.1) Analysis (Section 4.1. shown in Figure 4. The process presented in these Guidelines consists of an analysis/redesign approach. Reinforced Concrete Building Analysis and Design 4.1.
2.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings 4. slabs. Redundancy tends to promote an overall more robust structure and helps to ensure that alternate load paths are available in the case of a structural element(s) failure. Capacity for resisting load reversals . It is possible that many of the structural members will not be able to resist load reversals. beams and columns) such that the concrete material can behave in a ductile manner is critical.The use of redundant lateral and vertical force resisting systems are highly encouraged when considering progressive collapse.It is recommended that both the primary and secondary structural elements be designed such that these components are capable of resisting load reversals for the case of a structural element(s) failure.. girders and beams) be capable of spanning two full spans (i. dead and live loads). and to ensure connection redundancy and resilience.e. For concrete structures. Having the capability of achieving a ductile response is imperative when considering an extreme redistribution of loading such as that encountered for the case of a structural element(s) failure.e. It is recommended that the following structural characteristics be considered in the initial phases of structural design. etc.. These Guidelines should act as a supplement to the Interagency Security Committee (ISC) Security Design Criteria for New Federal Office Buildings and Major Modernization Projects. The use of detailing to provide structural continuity and ductility . the horizontal structural components (i.. Additionally.It is critical that the primary structural elements (i.1. which states that mitigation of progressive collapse be addressed in the design of new structures.. is provided for consideration during the initial structural design phase and prior to performing the progressive collapse analysis outlined in Section 4. which increases the probability that damage may be constrained. configuring connection reinforcing steel in structural elements (i. Page 4-2 . although not a requirement of these Guidelines.1 Design Guidance Structural design guidance. two full bays). This requires both beam-to-beam structural continuity across the removed column.e.e.1. beams. While the columns may contain reinforcement in all faces and be capable of exhibiting substantial capacity in all directions. Redundancy . An example illustrating the importance of having the capability to resist load reversals follows. Hence. correct detailing of connections shall be required in the design to ensure discrete beam-to-beam continuity across a column.) may only contain reinforcement needed for resisting the downward loading caused by gravity. redundancy generally provides multiple locations for yielding to occur.e. The incorporation of these features will provide for a much more robust structure and increase the probability of achieving a low potential for progressive collapse when performing the analysis procedure in Section 4.1.. girder. Consider a reinforced concrete building designed for gravity loads only (i. as well as the ability of both primary and secondary elements to deform flexurally well beyond the elastic limit without experiencing structural collapse.2 to minimize the impact on the building’s final design.
Column Negative Moment Region Beam Magnified displaced shape due to gravity loading Positive Moment Region Figure 4. the beam has very little resistance regarding the redistributed loading and will likely fail in a non-ductile manner. When the shear capacity is reached before the flexural capacity. the region of the beam designed for resisting negative moment forces is suddenly subjected to a positive moment and a substantial increase in vertical load.2 The amount of reinforcement that ACI 318 requires to be continuous may not be sufficient to prevent progressive collapse for instantaneous removal of a column. It is not likely that the structural configuration illustrated in Figure 4. Due to the reinforcement configuration.2. positive reinforcing steel (bottom steel) is provided in areas where positive moments are induced by the downward loading. Page 4-3 . Specifically. but the loss in support induces forces into the beam that were not considered in the original design. as shown in Figure 4. Likewise. non-ductile failure of the element exists which could potentially lead to a progressive collapse of the structure. negative reinforcing steel (top steel) is provided in areas where negative moments are induced by the downward loading. which could potentially lead to a propagation of additional structural failures. Along the length of the beam. ACI 318 includes a provision for structural integrity reinforcement that requires some top and bottom reinforcement to be continuous for beams such as those shown in Figure 4.3.2.2 will be capable of effectively redistributing loads when a primary support column is removed.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Consider the structural configuration shown in Figure 4. A sketch depicting the reinforcement scheme for a beam designed for gravity loads only. Capacity for resisting shear failure . the possibility of a sudden. Not only does the unsupported span length double.It is essential that the primary structural elements maintain sufficient strength and ductility under an abnormal loading event to preclude a shear failure such as in the case of a structural element(s) failure.
2 after the loss of primary column support.3. shows the inability to protect against progressive collapse.4). but the analysis considerations (Section 4. Response of the beam shown in Figure 4. However.3) and allowable extents of collapse (Section 4.1. 4. These procedures are not required by these Guidelines. such as those discussed in Section 2. must be used in the assessment of the potential for progressive collapse. Other analysis approaches may also be used.2.2 Analysis The following static linear elastic analysis approach may be used to assess the potential for progressive collapse in all newly constructed facilities. Note: A set of design procedures for preliminarily sizing structural components is included in Appendix B.1.2.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Column Ne gative Mome nt Re gion A Be am A Positive Mome nt Re gion Magnified displaced shape of beam due to the loss of column and gravity loading Loss of Primary Support Section AA Note: Providing continuous bottom reinforcing steel across the connection is essential to accommodating the double-span condition Figure 4. if desired by the project engineer. these procedures can be used to preliminarily size and detail elements prior to performing the progressive collapse analysis presented in Section 4. Page 4-4 .3.1.1.2.
The applied downward loading shall be consistent with that presented in Section 4. approach coupled with the following: • • • Criteria for assessing the analysis results A suite of analysis cases Specific loading criteria to be used in the analysis 4. 4.2 Procedure The potential for progressive collapse can be determined by the following procedure. The results from the analyses performed in Step 1 shall be evaluated by utilizing the analysis criteria defined in Section 4. Step 1. Atypical structural configurations are addressed in Section 4. 4.3. the member and/or connection capacities are greatly exceeded and it is unlikely that the structure is capable of effectively redistributing loads).1.1. Page 4-5 . the facility exhibits a low potential for progressive collapse and requires no further progressive collapse considerations. Step 2.1. However. the facility exhibits a high potential for progressive collapse and the user shall redesign the members and/or connections/joints consistent with the procedure outlined in Section 4. static analysis techniques.4 (i.2.4.2. if the analysis results show that the structural member(s) and/or connections/joints are in compliance with the analysis criteria presented in Section 4. It is recommended that 3-dimensional analytic models be used to account for potential 3-dimensional effects and avoid overly conservative solutions.2.2.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings The following procedure uses a static linear elastic. Note: If the analysis results show that the structural member(s) and/or connections/joints are not in compliance with the analysis criteria presented in Section 4.e.3.2.2.1. 2-dimensional models may be used provided that the general response and 3-dimensional effects can be adequately accounted for.1.3.1.1..4.1.2.2. The components and connections of both the primary and secondary structural elements shall be analyzed for the case of an instantaneous loss in primary vertical support.1 Analysis Techniques The following analysis procedure shall be performed using well-established linear elastic.1.2.3 Analysis Considerations and Loading Criteria The following analysis considerations shall be used in the assessment for progressive collapse for typical structural configurations. Nevertheless.
1 Typical Structural Configurations. The column considered should be interior to the perimeter column lines.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings 4.2. Plan View Page 4-6 .3.2. 1 Analyze for the instantaneous loss of 1 column that extends from the floor of the underground parking area or uncontrolled public ground floor area to the next floor (1 story). 2 Analyze for the instantaneous loss of a column for one floor above grade (1 story) located at or near the middle of the long side of the building.1.2. 1 Analyze for the instantaneous loss of a column for one floor above grade (1 story) located at or near the middle of the short side of the building.2. 3 Analyze for the instantaneous loss of a column for one floor above grade (1 story) located at the corner of the building. Facilities that have a relatively simple layout with no atypical structural configurations shall use the following analysis scenarios: Framed or Flat Plate Structures Exterior Considerations The following exterior analysis cases shall be considered in the procedure outlined in Section 4. Interior Considerations Plan View Facilities that have underground parking and/or uncontrolled public ground floor areas shall use the following interior analysis case(s) in the procedure outlined in Section 4.1.1.2.
3 Analyze for the instantaneous loss of the entire bearing wall along the perimeter at the corner structural bay or for the loss of 30 linear feet of the wall (15 ft in each major direction) (whichever is less) for one floor above grade*.1. 1 Analyze for the instantaneous loss of one structural bay or 30 linear feet of an exterior wall section (whichever is less) for one floor above grade. the wall section that would require removal consists of 30 ft of the wall beginning at the corner and extending 15 ft in each major direction. located at or near the middle of the short side of the building. For example. located at or near the middle of the long side of the building. 2 Analyze for the instantaneous loss of one structural bay or 30 linear feet of an exterior wall section (whichever is less) for one floor above grade. Plan View * The loss wall section for the corner consideration must be continuous and include the corner.2. 40 ft 15 ft 15 ft 40 ft Page 4-7 . if the structural bay of a facility is 40 ft by 40 ft.2.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Shear/Load Bearing Wall Structures Exterior Considerations The following exterior analysis cases shall be considered in the procedure outlined in Section 4.
2. in addition to the situations presented in Section 4.e.2 Atypical Structural Configurations (4.3. the user may only be required to perform one of the analysis cases.1. Thus. developing a set of analysis considerations that applies to every facility is impractical.1) All structures are generally unique and are often not typical (i.1.2. the user of these Guidelines must use engineering judgment to determine critical analysis scenarios that should be assessed. if the facility does not contain any uncontrolled parking areas and/or public areas. DL = dead load LL = live load Note: Depending on the facility characteristics and/or the outcome of the exemption process. Plan View Analysis Loading For static analysis purposes the following vertical load shall be applied downward to the structure under investigation: Load = 2(DL + 0. 4. however. The intent of these provisions should be reflected in these analysis Page 4-8 .3.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Interior Considerations Facilities that have underground parking and/or uncontrolled public ground floor areas shall use the following interior analysis cases in the procedure outlined in Section 4. The wall section considered should be interior to the perimeter bearing wall line. hence.2.2.25LL) where. For example. the user will not be required to perform the analyses for the interior considerations. 1 Analyze for the instantaneous loss of one structural bay or 30 linear feet of an interior wall section (whichever is less) at the floor level of the underground parking area and/or uncontrolled ground floor area. Additional analysis cases should be considered.. if there are significant changes in column or other load bearing member strength or configuration along any portion of the facility. buildings often contain distinguishing structural features or details).1.1.
The allowable extent of collapse for the instantaneous removal of a primary vertical support member along the exterior and within the interior of a building is defined as follows. However. Interior Considerations The allowable extents of collapse resulting from the instantaneous removal of an interior primary vertical support member in an uncontrolled ground floor area and/or an underground parking area for one floor level shall be confined to: Page 4-9 . Exterior Considerations The maximum allowable extents of collapse resulting from the instantaneous removal of an exterior primary vertical support member one floor above grade shall be confined to: 1. the allowable collapse area for a building will be based on the structural bay size. 1. Possible structural configurations that may result in an atypical structural arrangement include.a). or 2. Appendix A 4. but are not limited to.800 ft2 at the floor level directly above the instantaneously removed vertical member whichever is the smaller area (Figure 4. the following configurations: • • • • • Combination Structures Vertical Discontinuities/Transfer Girders Variations in Bay Size/Extreme Bay Sizes Plan Irregularities Closely Spaced Columns These atypical structural configurations are described in more detail in.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings scenarios.1. to account for structural configurations that have abnormally large structural bay sizes. the structural bays directly associated with the instantaneously removed vertical member in the floor level directly above the instantaneously removed vertical member. Specifically. Typically. the collapsed region will also be limited to a reasonably sized area.4 Analysis Criteria Structural collapse resulting from the instantaneous removal of a primary vertical support shall be limited. the scenarios should consider cases where loss of a vertical support (column or wall) could lead to disproportionate damage.2.4.
SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings
1. the structural bays directly associated with the instantaneously removed vertical member or 2. 3,600 ft2 at the floor level directly above the instantaneously removed vertical member whichever is the smaller area (Figure 4.4.b). If there is no uncontrolled ground floor area and/or an underground parking area present in the facility under evaluation, the internal consideration is not required.
(a) Exterior Consideration (b) Interior Consideration
Maximum allowable collapse area shall be limited to: 1 ) the structural bays directly associated with the instantaneously removed column or 2) 1,800 ft at the floor level directly above the instantaneously removed column, whichever is the smaller area.
Maximum allowable collapse area shall be limited to: 1) the structural bays directly associated with the instantaneously removed column or 2) 3,600 ft 2 at the floor level directly above the instantaneously removed column, whichever is the smaller area.
Figure 4.4. An example of maximum allowable collapse areas for a structure that uses columns for the primary vertical support system.
An examination of the linear elastic analysis results shall be performed to identify the magnitudes and distribution of potential demands on both the primary and secondary structural elements for quantifying potential collapse areas. The magnitude and distribution of these demands will be indicated by Demand-Capacity Ratios (DCR). These values and approaches are based, in part, on the methodology presented in the following references:
SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings • • • •
NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings (FEMA 274). Issued by Federal Emergency Management Agency, October 1997. Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA 356). Issued by Federal Emergency Management Agency, November 2000. Interim Antiterrorism/Force Protection Construction Standards, Guidance on Structural Requirements (Draft). Issued by Department of Defense, March 2001. Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects. U.S. General Services Administration and Applied Research Associates, Inc. November 2000.
Acceptance criteria for the primary and secondary structural components shall be determined as:
QUD QCE
QUD = QCE =
Acting force (demand) determined in component or connection/joint (moment, axial force, shear, and possible combined forces) Expected ultimate, un-factored capacity of the component and/or connection/joint (moment, axial force, shear and possible combined forces)
Using the DCR criteria of the linear elastic approach, structural elements and connections that have DCR values that exceed the following allowable values are considered to be severely damaged or collapsed. The allowable DCR values for primary and secondary structural elements are:
DCR < 2.0 for typical structural configurations (Section 4.1.2.3.1) DCR < 1.5 for atypical structural configurations (Section 4.1.2.3.2)
The criteria for atypical structural configurations (i.e., DCR < 1.5) may be limited to the ‘atypical’ region if this is localized. For example, consider a structure that uses transfer girders along one face of the perimeter and a typical structural configuration for the remainder of the structure. The perimeter structural bays along the side of the building that utilizes transfer girders shall use a DCR that is less than or equal to 1.5,
SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings but the remainder of the building shall use a DCR that is less than or equal to 2.0 for the assessment of the potential for progressive collapse. The approach used in estimating the magnitude and distribution of the potential inelastic demands and displacements used in these Guidelines is similar to the ‘mfactor’ approaches currently employed in FEMA 273 and 356 for linear elastic analysis methods.
The step-by-step procedure for conducting the linear elastic, static analysis follows.
Step 1. Remove a vertical support from the location being considered and conduct a linear-static analysis of the structure as indicated in Section 4.1.2.2. Load the model with 2(DL + 0.25LL). Step 2. Determine which members and connections have DCR values that exceed the acceptance criteria. If the DCR for any member end connection is exceeded based upon shear force, the member is to be considered a failed member. In addition, if the flexural DCR values for both ends of a member or its connections, as well as the span itself, are exceeded (creating a three hinged failure mechanism – Figure 2.2), the member is to be considered a failed member. Failed members should be removed from the model, and all dead and live loads associated with failed members should be redistributed to other members in adjacent bays. Step 3. For a member or connection whose QUD/QCE ratio exceeds the applicable flexural DCR values, place a hinge at the member end or connection to release the moment. This hinge should be located at the center of flexural yielding for the member or connection. Use rigid offsets and/or stub members from the connecting member as needed to model the hinge in the proper location. For yielding at the end of a member the center of flexural yielding should not be taken to be more than ½ the depth of the member from the face of the intersecting member, which is usually a column (Figure 4.5). Step 4. At each inserted hinge, apply equal-but-opposite moments to the stub/offset and member end to each side of the hinge. The magnitude of the moments should equal the expected flexural strength of the moment or connection, and the direction of the moments should be consistent with direction of the moments in the analysis performed in Step 1. Step 5. Re-run the analysis and repeat Steps 1 through 4. Continue this process until no DCR values are exceeded. If moments have been re-distributed throughout the entire building and DCR values are still exceeded in areas outside of the allowable collapse region, the structure will be considered to have a high potential for progressive collapse.
Construction Material Strength Increase Factor Reinforced Concrete Concrete Compressive Strength Reinforcing Steel (tensile and yield strength) Concrete Unit Masonry Compressive Strength Flexural Tensile Strength Shear Strength Wood and Light Metal Framing All Components 1. Table 4.0 1.5 Material Properties For these Guidelines the design material strengths may be increased by a strengthincrease factor to determine the expected material strength (for determining capacities.25 1.0 1.2. These values are given in Table 4.1. These should be used only in cases where the designer or analyst is confident in the actual state of the facility’s materials.2.0 1.2. 4. Strength-increase factors for various construction materials. etc.25 1.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Rigid Offset Hinge Location Before After Figure 4.5. Rigid offset placement.).0 Page 4-13 .
it is recommended for the case where a dynamic analysis is performed. design details. bearing wall..g. Because of this. etc. the analyst shall realistically approximate the type of boundary conditions (e. This includes all material properties. An example sketch illustrating the correct and incorrect way to remove a column is shown in Figure 4.2. fixed.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings 4.e.6.) that is removed should be removed instantaneously. and should be aware of any limitations or anomalies of the software package(s) being used to perform the analysis. Also the vertical element removal shall consist of the removal of the vertical element only.. etc. the speed at which an element is removed in a dynamic analysis may have a significant impact on the response of the structure.3 for discussion of member removal approach).).1. Vertical Element Removal The vertical element (i. In addition. While the speed at which an element is removed has no impact on a static analysis. the vertical supporting element should be removed over a time period that is no more than 1/10 of the period associated with the structural response mode for the vertical element removal. This removal should not impede into the connection/joint or horizontal elements that are attached to the vertical element at the floor levels. It is critical that the user understand that the sketch is not representative of damage due to any specific threat (see Section 1. Page 4-14 . the column. simple.6 Modeling Guidance General The analytic model(s) used in assessing the potential for progressive collapse should be modeled as accurately as possible to the anticipated or existing conditions. etc.
Page 4-15 . Sketch of the correct and incorrect approach for removing a column.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Correct approach to removing a column Original Structural Configuration Incorrect approach to removing a column Figure 4.6.
the redesigned structure shall be reanalyzed consistent with analysis procedure outlined in Section 4.2). Page 4-16 .0 or less for primary and secondary structural members in the design of deficient components and connections.2 should be redesigned consistent with the redistributed loading determined in this process in conjunction with the standard design requirements of the project specific building code(s) using well-established design techniques.1. achieve the allowable values associated with that criteria for the redistributed loading.1. the deficient components should be designed to. Step 2. the deficient components should be designed to.1 Procedure The following steps shall be followed when redesigning the deficient structural elements identified in the analysis procedure (Section 4. The redesign criteria for typical and atypical structural configurations follow: Typical Structural Configurations Structural elements and beam-to-column connections must have a DCR value of 2. Upon the completion of Step 1.2 and determined to have a high potential for progressive collapse shall be redesigned to a level that is consistent with a low potential for progressive collapse.1. as a minimum.5 or less for both primary and secondary elements in the design of deficient components and connections.3. 4. the structural elements and/or connections identified as deficient in Section 4. as a minimum. If an approved alternate analysis criteria is used. Atypical Structural Configurations Structural elements and beam-to-column connections must have a DCR value of 1. As a minimum. Step 1.2. If an approved alternate analysis criteria is used.1.3 Redesign of Structural Elements Structural configurations that are analyzed consistent with Section 4. achieve the allowable values associated with that criteria for the redistributed loading.1.1.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings 4.
It should be noted that to achieve a low potential for progressive collapse more than one iteration of the redesign/analysis process may be required. For example. Page 4-17 . material properties. assess the potential for progressive collapse as the result of an abnormal loading event.0 for primary and secondary structural elements. However.2 Existing Construction Existing facilities undergoing modernization should be upgraded to new construction requirements when required by the project specific facility security risk assessment and where feasible. etc. a change in the size of structural members may alter the magnitude and distribution of the redistributed load.2 indicates the spandrel beams from the 2nd floor level to the roof level for a given rigid frame structure are not adequate in regards to the analysis criteria presented in Section 4.1. analysis criteria. the addition of symmetric reinforcement (for reinforced concrete elements). The designer has the freedom to evenly distribute an improved redesign along the total height of the facility or concentrate them over a few floor levels (Figure 4. but the remainder of the building may be designed to have maximum DCR values of 2.8. as defined in Section 4. assume the results of Section 4. and modeling guidance.2. shown in Figure 4. as long as the overall intent of minimizing the potential for progressive collapse. moment resisting connections.1. shall also apply to existing construction. is accomplished.1. the design criteria for atypical structures may be limited to the ‘atypical’ region if this is localized. The designer is not limited to a particular method for improving the original design with respect to the minimization of the potential for progressive collapse.2.2 concerning analysis techniques.4.7. consider a building that uses transfer girders along one face of the perimeter and a typical structural configuration for the remainder of the structure. For the example illustrated in Figure 4. 4. such as greatly increasing member sizes. For example. procedure. outlines the process for assessing the potential for progressive collapse in existing facilities. The perimeter structural bays shall be designed to have a DCR value of 1.5. The flowchart.1. The ‘analysis’ provisions contained in Section 4. analysis considerations and loading criteria.4.SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Note: In order to achieve the necessary design requirements. as a minimum. facilities undergoing modernization should. significant structural changes may be required.5 or less. In addition. and shall be documented in accordance with the provisions in Section 1.7). Findings of this analysis should be incorporated into the project-specific risk assessment.
Page 4-18 .SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Original Design Spandrel beams size and capacities moderately increased Redesign (improvements distributed evenly over the entire height) Spandrel beams size and capacities significantly increased Redesign (improvements concentrated on the 2nd and 3rd floor level) Figure 4.7. Possible approaches for the redesign of a structure that has been determined to have high potential for progressive collapse.
2) Yes Does the structure meet the analysis requirements for minimizing the potential for progressive collapse? No The potential for progressive collapse is low.8.1. Report Figure 4. Page 4-19 .SECTION 4 – Progressive Collapse Guidelines for Reinforced Concrete Buildings Existing Construction Analysis (Section 4. The potential for progressive collapse is high. Process for assessing the potential for progressive collapse in existing Construction.
Report The potential for progressive collapse is high. This method is intended to enhance the probability that if localized damage occurs as the result of an abnormal loading event.3) Yes Does the structure meet the analysis requirements for minimizing the potential for progressive collapse? No The potential for progressive collapse is low.1.1. the structure will not progressively collapse or be damaged to an extent disproportionate to the original cause of the damage. The process presented in these Guidelines consists of an analysis/redesign approach. Figure 5. Steel Frame Building Analysis and Design 5. shown in Figure 5.1.1. regardless of the required level of protection.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Section 5. Process for reducing the potential for progressive collapse in new construction. New Construction Design Guidance (Section 5. Page 5-1 .1) Analysis (Section 5.1 New Construction All newly constructed facilities shall be designed with the intent of reducing the potential for progressive collapse as a result of an abnormal loading event. outlines this process for reducing the potential for progressive collapse in newly constructed facilities.1.2) Redesign Structural Elements (Section 5. The flowchart.
1.e.1. as well as the global configuration of primary and secondary structural steel girders. Accordingly. which states that mitigation of progressive collapse be addressed in the design of new structures.1 Local Considerations Discrete beam-to-beam continuity – Providing discrete beam-to-beam continuity (as defined in Section 2. Connection resilience – Providing connection resilience (as defined in Section 2. It is therefore imperative that the following local beamto-column connection characteristics be ascertained and/or implemented during the initial phases of structural design. as well as the ability of girders and beams to deform flexurally well beyond their elastic limit without experiencing structural collapse.1.2. This structural design guidance.. 5. Examples of good detailing practice that ensures ductile behavior in steel frame connections include: 1. although not a requirement of these Guidelines. as well as the global frame recommendations made herein. The configuration of weld line geometries such that a given line of weld metal is loaded primarily along its length in shear. It is critical that floor girders and beams be capable of spanning two full spans (i. beams and columns.1) in the design of steel frame connections is considered essential to mitigating progressive collapse in newly constructed steel frame structures. a double span condition consisting of two full bays) as a minimum.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings 5. and minimizes the potential for highly Page 5-2 .1 Design Guidance Structural design guidance is provided in these Guidelines for addressing the mitigation of progressive collapse.1. not in tension across its throat. as it may affect the detailing of local beam-to-column-to-beam connections. This requires both beam-to-beam structural continuity across the removed column. to minimize the impact on the building’s final design. a structural engineer should be able to demonstrate that a proposed beam-to-column connection system for a given project provides a connection geometry that exhibits the physical attributes needed to mitigate the effects of instantaneous column loss. Accordingly.2. The incorporation of these features will provide for a much more robust steel frame structure and increase the probability of achieving a low potential for progressive collapse when performing the analysis procedure in Section 5. a structural engineer should be able to demonstrate that a proposed beamto-column connection system for a given project provides a structurally-redundant clearly defined beam-to-beam continuity link across a column that is capable of independently redistributing gravity loads for a multiple-span condition.1.1) in the design of steel frame connections is considered fundamental to mitigating progressive collapse in newly constructed steel frame structures. These Guidelines should act as a supplement to the Interagency Security Committee (ISC) Security Design Criteria for New Federal Office Buildings and Major Modernization Projects. is provided for consideration during the initial structural design phase and prior to performing the progressive collapse analysis outlined in Section 5. inherently results in robust performance.
a structural engineer must select a beam-to-column-to-beam connection configuration that provides positive.. and structural plates) such that the applied loading is resisted nearly uniformly across a beam flange. because of their proven ductility. Connection Rotational Capacity . while demonstrating the connection’s ability to force the formation of plastic hinges in the girder or beam outside the beam-to-column connection.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings restrained condition due to the expected shrinkage of newly deposited welds during the cooling process. or a beam flange cover plate. both public domain and proprietary. The configuration of the connection’s base metal elements (i. which highlight the important attributes and differences in their connection geometries.3. created by a “missing column” scenario. It is questionable whether the structural configuration illustrated in Figure 5. structural continuity may be compromised under such events.2 will be capable of effectively redistributing loads when a primary support column is removed.2. columns.e. and while maintaining sufficient axial load carrying capacity in both the beam and the connection that joins beam to beam across the removed column. in order to successfully achieve a double span condition. is considered fundamental in mitigating progressive collapse. such configurations may be vulnerable to progressive collapse. dead and live loads). Connection redundancy – Providing connection redundancy (as defined in Section 2. column flange. multiple and clearly defined beam-to-beam load paths. when the beam-to-columnto-beam connection is subjected to column removal. Accordingly. a double span condition is created for the beam.e. 2. as shown in Figure 5. inherently results in ductile performance. The ability of a girder or beam in a steel frame system to structurally accommodate a double span condition. Appendix D identifies both preNorthridge and post-Northridge moment connection types. Research has shown that in many cases..Only steel frame beam-to-column connection types that have been qualified by full-scale testing to verify that they provide the required level of connection rotational capacity should be used in the design of new buildings to mitigate progressive collapse. Accordingly. beams. Appendix D provides a listing of various connection types. in a direction parallel to its rolled direction. the beam-to-column connection. As shown in Figure 5. Depending upon the type of beam-to-column-to-beam connections used. and provides descriptions and isometric sketches.1) in the design of steel frame connections is considered essential to mitigating progressive collapse in newly constructed steel frame structures. including a depiction of its anticipated flexural deformation under the influence of gravity loads only (i. girder. An example illustrating the physical characteristics of a typical steel frame beam-tocolumn-to-beam ‘traditional’ moment connection scheme is shown in Figure 5.3. Page 5-3 .
SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Figure 5. after the loss of primary column support.3. shows the inability to protect against progressive collapse. Page 5-4 . Response of the framing scheme shown in Figure 5.2. Figure 5.2. A sketch depicting a steel frame beam-to-column-to-beam ‘traditional’ moment connection scheme prior to removal of primary column support.
4. Page 5-5 . published by the American Institute of Steel Construction (AISC). which must comply with the most current provisions of Appendix S. By demonstrating the ability of a given beam-to-column moment connection to achieve the level of inelastic rotational capacity stipulated by the cited AISC standard. The location of the plastic hinge will normally be identified in the full-scale cyclic test report being used to qualify the connection for the required rotational capacity. including full-scale monotonic testing of double span conditions subjected to instantaneous column removal under sustained gravity loads.e. as illustrated in Figure 5. for example. Each connection type may have different critical sections for which the connection strength demand must be calculated. can be readily determined for addressing the increased connection strength demand on all critical sections to be designed or investigated. and joining welds that make up the connection. in accordance with the provisions of Section 1. bolts.In order to complete the design or investigation of a given beam-to-column connection type. Mp = FyeZx). 2002. Note that Mp includes the use of the expected yield strength Fye which accounts for over strength in the nominal yield strength of the beam.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Accordingly. the ramping up effects. which is numerically equal to the plastic moment capacity of the beam (i. starting from the known location of Mp and continuing to the centerline of column. as those already tested. using a nationally recognized fully-developed procedure. The next step requires the drawing of the beam’s moment diagram for a double span condition. By superimposing the location of the known plastic hinge on the moment diagram. column sizes. the ability of a beam to accommodate the anticipated rotational demand on the connection created by a double span condition can be ascertained. for establishing a proposed connection’s rotational capacity qualification by testing.5. it is essential to determine the shears and flexural strength demands at each critical section. beam sizes. the structural engineer should provide compliance documentation to the GSA. the sizing (or investigation of design adequacy) of the various plates. plus strain hardening of the beam (see FEMA 356). albeit conservative for certain connection types. and level of anticipated column web panel zone participation. Seismic Provisions for Structural Steel Buildings. Until additional research has been conducted. The proposed connection type should use similar beam spans. This location determines the magnitude of the moment at this point on the moment diagram. the use of the AISC standard is considered to be both practical and prudent. dated May 21. depending on its particular connection geometry and the kinds of connection elements employed. column orientation (major axis versus weak axis).. The connection strength demand for each critical section may be calculated by first determining the location of the plastic hinge for a particular connection type being considered for the steel frame design. Determination of Connection Strength Demands .
Additionally. Page 5-6 . However.1. Global frame redundancy tends to promote an overall more robust structure and helps to ensure that alternate load paths are available in the case of a structural element(s) failure.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Figure 5.4. Note: bending moment can increase significantly from beam’s plastic hinge location to centerline of column.2.1. Note: A set of design procedures for preliminarily sizing structural components is included in Appendix B. 5.The use of redundant lateral and vertical force resisting steel frame systems are highly encouraged when considering progressive collapse. these procedures can be used to preliminarily size and detail elements prior to performing the progressive collapse analysis presented in Section 5. which increases the probability that damage may be constrained. These procedures are not required by these Guidelines.1. Moment gradient for ‘missing column’ scenario to determine connection strength demand at each critical connection element.2 Global Considerations Global Frame Redundancy . global frame redundancy generally provides multiple locations for yielding to occur.
5.2. Step 1.1. Step 2. Other analysis approaches may also be used. the facility exhibits a high potential for progressive collapse and the user shall redesign the members and/or connections/joints consistent with the procedure outlined in Section 5.1.2. Page 5-7 .1. 2-dimensional models may be used provided that the general response and 3-dimensional effects can be adequately idealized.3) and allowable extents of collapse (Section 5.1.4 (i.3.4).3.3. such as those discussed in Section 2.1. However.1.1 Analysis Techniques The following analysis procedure shall be performed using well-established linear elastic. must be used in the assessment of the potential for progressive collapse. the member and/or connection capacities are greatly exceeded and it is unlikely that the structure is capable of effectively redistributing loads). The following procedure uses a linear elastic.2.4. The results from the analyses performed in Step 1 shall be evaluated by utilizing the analysis criteria defined in Section 5. Note: If the analysis results show that the structural member(s) and/or connections/joints are not in compliance with the analysis criteria presented in Section 5. static analysis approach may be used to assess the potential for progressive collapse in all new and upgraded construction.e.2 Analysis The following linear elastic.1.2.1.1. The components and connections of both the primary and secondary structural elements shall be analyzed for the case of an instantaneous loss in primary vertical support.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings 5. Nevertheless.1.2.2 Procedure The potential for progressive collapse can be determined by the following procedure. static approach coupled with the following: • • • Criteria for assessing the analysis results A suite of analysis cases Specific loading criteria to be used in the analysis 5.2.. the facility exhibits a low potential for progressive collapse and requires no further progressive collapse considerations.1. It is recommended that 3-dimensional analytic models be used to account for potential 3-dimensional effects and avoid overly conservative solutions. if the analysis results show that the structural member(s) and/or connections/joints are in compliance with the analysis criteria presented in Section 5.4. but the analysis considerations (Section 5.2. The applied downward loading shall be consistent with that presented in Section 5.2. static analysis techniques.
significant changes in beam span and/or size. Such unique structural differences shall include.3.1. uniform.2.2. and significant changes in column orientation or strength (weak vs. Plan View Page 5-8 .1. Additional analysis scenarios may be required for such cases. differences in beam-to-beam connection type (simple vs.1 Typical Structural Configurations The analysis scenarios selected for investigation shall be sufficient in number to include all unique structural differences that could affect the outcome of predicting either the low or high potential for progressive collapse. major axis).2. For facilities that have a relatively simple.2. the following analysis scenarios may be used: Framed Structures Exterior Considerations The following exterior analysis cases shall be considered in the procedure outlined in Section 5.2. moment connection). 2 Analyze for the instantaneous loss of a column for one floor above grade (1 story) located at or near the middle of the long side of the building.1.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings 5. Several atypical structural configurations are addressed in Section 5.2. 1 Analyze for the instantaneous loss of a column for one floor above grade (1 story) located at or near the middle of the short side of the building. and repetitive layout (for both global and local connection attributes). but are not limited to. 5.1.3 Analysis Considerations and Loading Criteria The following analysis considerations shall be used in the assessment for progressive collapse for typical structural configurations.3. with no atypical structural configurations. 3 Analyze for the instantaneous loss of a column for one floor above grade (1 story) located at the corner of the building.
The column considered should be interior to the perimeter column lines. Plan View Page 5-9 .2.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Interior Considerations Facilities that have underground parking and/or uncontrolled public ground floor areas shall use the following interior analysis case(s) in the procedure outlined in Section 5.2. 1 Analyze for the instantaneous loss of 1 column that extends from the floor of the underground parking area or uncontrolled public ground floor area to the next floor (1 story).1.
located at or near the middle of the long side of the building. In this case.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Shear/Load Bearing Wall Structures Exterior Considerations There may be combination structures that use steel framing combined with load bearing wall sections. 40 ft 15 ft 15 ft 40 ft Page 5-10 .2. 3 Analyze for the instantaneous loss of the entire bearing wall along the perimeter at the corner structural bay or for the loss of 30 linear feet of the wall (15 ft in each major direction) (whichever is less) for one floor above grade*. 2 Analyze for the instantaneous loss of one structural bay or 30 linear feet of an exterior wall section (whichever is less) for one floor above grade.1. if the structural bay of a facility is 40 ft by 40 ft. 1 Analyze for the instantaneous loss of one structural bay or 30 linear feet of an exterior wall section (whichever is less) for one floor above grade.2. the following exterior analysis cases shall be considered in the procedure outlined in Section 5. the wall section that would require removal consists of 30 ft of the wall beginning at the corner and extending 15 ft in each major direction. Plan View * The loss wall section for the corner consideration must be continuous and include the corner. For example. located at or near the middle of the short side of the building.
1) Depending on the facility characteristics and/or the outcome of the exemption process.. DL = dead load LL = live load Note: (5.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Interior Considerations Facilities that have underground parking and/or uncontrolled public ground floor areas shall use the following interior analysis cases in the procedure outlined in Section 5.25LL) where.3. All structures are generally unique and are often not typical (i.e.3.1. The intent of these provisions should be reflected in these analysis scenarios. the user of this guideline must use engineering judgment to determine critical analysis scenarios that should be assessed. the scenarios should consider cases where loss of a vertical support (column or wall) could lead to Page 5-11 .1. the user will not be required to perform the analyses for the interior considerations.2. in addition to the situations presented in Section 5. buildings often contain distinguishing structural features or details).2.2.1. Plan View Analysis Loading For static analysis purposes the following vertical load shall be applied downward to the structure under investigation: Load = 2(DL + 0. hence. The wall section considered should be interior to the perimeter bearing wall line. 5. the user may only be required to perform one of the analysis cases. 1 Analyze for the instantaneous loss of one structural bay or 30 linear feet of an interior wall section (whichever is less) at the floor level of the underground parking area and/or uncontrolled ground floor area. Specifically.2 Atypical Structural Configurations.2. developing a set of analysis considerations that applies to every facility is impractical. Thus.1. if the facility does not contain any uncontrolled parking areas and/or public areas. For example.
However. the allowable collapse area for a building will be based on the structural bay size.2. Interior Considerations The allowable extents of collapse resulting from the instantaneous removal of an interior primary vertical support member in an uncontrolled ground floor area and/or an underground parking area for one floor level shall be confined to: Page 5-12 . but are not limited to.4 Analysis Criteria Structural collapse resulting from the instantaneous removal of a primary vertical support shall be limited.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings disproportionate damage.5. the following configurations: • • • • • Combination Structures Vertical Discontinuities/Transfer Girders Variations in Bay Size/Extreme Bay Sizes Plan Irregularities Closely Spaced Columns These atypical structural configurations are described in more detail in Appendix A.800 ft2 at the floor level directly above the instantaneously removed vertical member whichever is the smaller area (Figure 5. Possible structural configurations that may result in an atypical structural arrangement include. 1.a). the structural bays directly associated with the instantaneously removed vertical member in the floor level directly above the instantaneously removed vertical member or 2.1. 5. Typically. The allowable extent of collapse for the instantaneous removal of a primary vertical support member along the exterior and within the interior of a building is defined as follows. the collapsed region will also be limited to a reasonably sized area. to account for structural configurations that have abnormally large structural bay sizes. Exterior Considerations The maximum allowable extents of collapse resulting from the instantaneous removal of an exterior primary vertical support member one floor above grade shall be confined to: 1.
Acceptance Criteria An examination of the linear elastic analysis results shall be performed to identify the magnitudes and distribution of potential demands on both the primary and secondary structural elements for quantifying potential collapse areas. girders. If there is no uncontrolled ground floor area and/or an underground parking area present in the facility under evaluation.600 ft2 at the floor level directly above the instantaneously removed vertical member whichever is the smaller area (Figure 5. the structural bays directly associated with the instantaneously removed vertical member or 2. Upon removing the selected column from the structure. 3. columns. whichever is the smaller area.5. have exceeded their respective maximum allowable demands. joints or connections. an assessment is made as to which beams.b). whichever is the smaller area. ft 2 Removed column Maximum allowable collapse area shall be limited to: 1) the structural bays directly associated with the instantaneously removed column or 2) 3.800 at the floor level directly above the instantaneously removed column.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings 1. the internal consideration is not required.600 ft 2 at the floor level directly above the instantaneously removed column. An example of maximum allowable collapse areas for a structure that uses columns for the primary vertical support system. Figure 5. The magnitude and distribution of demands will be Page 5-13 .5. (a) Exterior Consideration (b) Interior Consideration Plan Plan Elevation Elevation Removed column Maximum allowable collapse area shall be limited to: 1 ) the structural bays directly associated with the instantaneously removed column or 2) 1.
a value of (3/4)*DCR should be used (factor of 3/4 for uncertainties). For atypical structural configurations.2) where..SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings indicated by Demand-Capacity Ratios (DCR).e. November 2000. on the methodology presented in the following references: • • • • NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings (FEMA 274). and possible combined forces) QC E = Expected ultimate. structural elements and connections with DCR values exceeding those given in Table 5. The perimeter structural bays along the side of the building that utilizes transfer girders shall use a DCR that is multiplied by a reduction factor of 3/4. Page 5-14 . March 2001. These values and approaches are based. For example. U. un-factored capacity of the component and/or connection/joint (moment. but the remainder of the building shall use a DCR per Table 5. in part. Under no conditions is a DCR less than 1.S. axial force. Issued by Federal Emergency Management Agency. Acceptance criteria for primary and secondary structural components shall be determined as: DCR = QUD QCE (5. DCR = (3/4)*DCR) may be limited to the ‘atypical’ region if this is localized. Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA 356). Note: The criteria for atypical structural configurations (i. shear. axial force. Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects.0 required. Member ends exceeding their respective DCR values will then be released and their end moments re-distributed. consider a structure that uses transfer girders along one face of the perimeter and a typical structural configuration for the remainder of the structure. Guidance on Structural Requirements (Draft).1 for the assessment of the potential for progressive collapse.1 are considered to be severely damaged or collapsed. Issued by Federal Emergency Management Agency. shear and possible combined forces) Using the DCR criteria for the linear elastic approach. November 2000. October 1997. Inc. General Services Administration and Applied Research Associates. Issued by Department of Defense. QUD = Acting force (demand) determined in component or connection/joint (moment. Interim Antiterrorism/Force Protection Construction Standards.
25LL). These illustrations should aid the engineer in selecting the appropriate connection DCR values from Table 5. For a member or connection whose QUD/QCE ratio exceeds the applicable flexural DCR values. Failed members should be removed from the model. Load the model with 2(DL + 0. Step 2. as well as the span itself. the structure will be considered to have a high potential for progressive collapse. Step 1.2. In addition. are exceeded (creating a three hinged failure mechanism – Figure 2. static analysis follows. The magnitude of the moments should equal the expected flexural strength of the moment or connection. Re-run the analysis and repeat Steps 1 through 4.2). if the flexural DCR values for both ends of a member or its connections. and all dead and live loads associated with failed members should be redistributed to other members in adjacent bays. If moments have been re-distributed throughout the entire building and DCR values are still exceeded in areas outside of the allowable collapse region. Step 3. If the DCR for any member end or connection is exceeded based upon shear force. Determine which members and connections have DCR values that exceed the acceptance criteria provided in Table 5. This hinge should be located at the center of flexural yielding for the member or connection. At each inserted hinge. Remove a vertical support from the location being considered and conduct a linear-static analysis of the structure as indicated in Section 5.1. the member is to be considered a failed member. Continue this process until no DCR values are exceeded. Use rigid offsets and/or stub members from the connecting member as needed to model the hinge in the proper location. the member is to be considered a failed member.6).2. For yielding at the end of a member the center of flexural yielding should not be taken to be more than ½ the depth of the member from the face of the intersecting member. The step-by-step procedure for conducting the linear elastic. Step 5.1. apply equal-but-opposite moments to the stub/offset and member end to each side of the hinge. Page 5-15 . A variety of connection illustrations are provided in Appendix D. and the direction of the moments should be consistent with direction of the moments in the analysis performed in Step 1. place a hinge at the member end or connection to release the moment. Step 4.1. which is usually a column (Figure 5.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings The approach used in estimating the magnitude and distribution of the potential inelastic demands and displacements used in these Guidelines is similar to the ‘m-factor’ approaches currently employed in FEMA 273 and 356 for linear elastic analysis methods.
Rigid offset placement.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Rigid Offset Hinge Location Before After Figure 5. Page 5-16 .6.
bf 2t f ≥ or 65 Fye 2 h 640 ≥ tw Fye c. Acceptance criteria for linear procedures— steel frame components.1. Linear interpolation between the values on lines a and b for both flange slenderness (first term) and web slenderness (second term) shall be performed. c.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Table 5. Values for Linear Procedures Component/Action Beams – flexure a. and the lowest resulting value shall be used.5 a. Other Page 5-17 . Other Columns – flexure For 0 < P/PCL < 0. DCR bf 2t f ≤ 52 Fye 3 and h 418 ≤ tw Fye b. and the lowest resulting value shall be used. bf 2t f ≥ or 65 Fye 1.25 h 460 ≥ tw Fye Linear interpolation between the values on lines a and b for both flange slenderness (first term) and web slenderness (second term) shall be performed. bf 2t f ≤ and 52 Fye 2 h 300 ≤ tw Fye b.
5 a.5 Fully Restrained Moment Connections Pre-Northridge (Pre 1995) Welded unreinforced flange (WUF) Welded flange plate (WFP) Welded cover plated flanges Bolted flange plate (BFP) Post-Northridge (FEMA 350) Public Domain Improved WUF-bolted web Improved WUF-welded web Free flange Welded top and bottom haunches Reduced beam section Post-Northridge (FEMA 350) Proprietary Proprietary System 3 2 2 2 2 2 2 2 2 2 ≤3 (See Footnote 3) Page 5-18 . bf tw ≥ or 65 Fye 1 h 400 ≥ tw Fye Columns Panel Zone – Shear Column Core – Concentrated Forces 2 2 1. Values for Linear Procedures Component/Action Columns – flexure For P/PCL > 0.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Table 5.1. DCR bf 2t f ≤ 52 Fye 1 and h 260 ≤ tw Fye b. Acceptance criteria for linear procedures— steel frame components (continued).
5 (high strength bolts) 1. b.5 3 DCR Double split tee Bolted flange plate Failure in net section of flange plate or shear failure of rivets or bolts b. 1 (high strength bolts) 2 2 Composite top and clip angle bottom Shear connection with or without slab 1. c. b. b. a. a. Shear failure of rivets or bolts Tension failure of horizontal leg of angle Tension failure of rivets or bolts Flexural Failure of angle Shear failure of rivets or bolts Tension failure of rivets or bolts Tension failure of split tee stem Flexural Failure of split tee 3 (rivets).5 3 2 (rivets). d. c. b. 1. e.5 (rivets). Acceptance criteria for linear procedures— steel frame components (continued).5 1. d.5 2 3 3 1. Notation for Table 5.5 (high strength bolts) 1. 1.5 (high strength bolts) 1.5 3 3 (rivets). d.5 (high strength bolts) 1.5 1. Values for Linear Procedures Component/Action Partially Restrained Moment Connection Top and bottom clip angle a.1: bf Fye h tw PCL P tf d dbg = = = = = = = = = Width of the compression flange Expected yield strength Distance from inside of compression flange to inside of tension flange Web thickness Lower bound compression strength of the column Axial force in member taken as Quf Flange thickness Beam depth Depth of the bolt group Page 5-19 . a.1.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Table 5. Yield of end plate Yield of rivets or bolts Failure of weld Failure of deck reinforcement Local flange yielding and web crippling of column Yield of bottom flange angle Tensile yield of rivets or bolts at column flange Shear yield of beam flange connections 3 (rivets). c. 1. c. Weld failure or tension failure on gross section of plate Bolted end plate a. 1.
0 are required.5 Material Properties For these Guidelines the design material strengths may be increased by a strengthincrease factor to determine the expected material strength.2. K1-2.75). 3. For connections to weak axis of column (Figure D 3 Appendix D) treat as atypical (DCR*0.2 and Table 5. These should be used only in cases where the designer or analyst is confident in the actual state of the facility’s materials. DCR values are for connection to strong axis of column. Page 5-20 . K1-4 and K1-8. Tested proprietary connections must have documented test results that justify using DCR values greater than these. 5. 4.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings 2. A DCR of 1 will be used for all other untested proprietary connections.1. 5. No DCR values less than 1. A DCR of 2 will be used for all untested proprietary fully restrained moment connections. These values are provided in Table 5. Under no circumstances should a DCR value exceeding 3 be used for any proprietary connection. Column core concentrated force capacity shall be determined from AISC (1993) LRFD Specifications equations K1-1. even for atypical conditions.3.
A9 ASTM. ksi 50 60 50 60 55 46 55 46 55 46 60 67 55 Yield Strength2. Grade 50 Group 1 Group 2 Group 3 Group 4 Group 5 A36/36M-00 & Dual Grade Group 1 Group 2 Group 3 Group 4 Remarks Rivet Steel Medium Steel Rivet Steel Medium Steel Structural Steel Rivet Steel Structural Steel Rivet Steel Structural Steel Rivet Steel Plates. A141 ASTM.2. Page 5-21 . A9 (Buildings) revised Oct. 2. A36/A36M-00 Group 1 Group 2 Group 3 Group 4 Group 5 ASTM. Properties based on ASTM and AISC Structural Steel Specification Stresses Date 1900 1901-1908 1909-1923 1924-1931 Specification ASTM. 1933 ASTM. The indicated values are representative of material extracted from the flanges of wide flange shapes. A9 Buildings ASTM. A140-32T issued as a tentative revision to ASTM. ksi 30 20 25 30 28 23 30 25 30 25 33 36 30 1932 1933 Structural Steel 52 28 Rivet Steel Structural Steel Rivet Steel Structural Steel 52 60 52 62 59 60 62 70 28 33 28 44 41 39 37 41 50 50 51 50 50 49 50 52 49 1934 on 1961 . A9 (Buildings) ASTM. Lower-bound values for material after 1960 are near minus one standard deviation values from statistical data. A140-32T discontinued and ASTM. Shapes.30. A7 Buildings ASTM. Default lower-bound material strengths1 — steel frame components. Bars Eyebar flats unannealed Structural Steel Tensile Strength2. A9 Buildings ASTM. A9 Buildings ASTM.30. A9-33T (Buildings) revised Oct. A9 tentatively revised to ASTM.1990 1961 on Structural Steel 65 66 68 72 77 Structural Steel 66 67 70 70 1990 on 1. Lower-bound values for material prior to 1960 are based on minimum specified values. A140-32T adopted as a standard ASTM.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Table 5. A9 ASTM. A572. 1933 ASTM.
g.05 1. Group 4 ASTM A572/A572M-89. Property Tensile Strength Yield Strength Year Prior to 1961 Prior to 1961 1961 .05 1.present Tensile Strength Yield Strength All All 1.10 1.05 1.10 1.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Table 5.1990 ASTM A36/A36M-00l ASTM A572/A572M-89.10 1.3.05 1. For materials not conforming to one of the listed specifications. the analyst shall realistically approximate the type of boundary conditions (e.05 1.2. Group 2 ASTM A572/A572M-89. Group 5 ASTM A36/A36M-00l & Dual Grade Group 1 ASTM A36/A36M-00l & Dual Grade Group 2 ASTM A36/A36M-00l & Dual Grade Group 3 ASTM A36/A36M-00l & Dual Grade Group 4 ASTM A36/A36M-00l ASTM A572/A572M-89. simple.. In addition. and should be aware of any limitations or anomalies of the software package(s) being used to perform the analysis.10 1.1990 1961 .05 1.present Yield Strength 1990 .10 1.05 1. Group 3 ASTM A36/A36M-00l Dual Grade. design details. etc.10 1.10 1.10 1. etc. fixed. Group 5 ASTM A36/A36M-00l Plates ASTM A36/A36M-00l Dual Grade. Group 3 ASTM A572/A572M-89. Factors to translate lower-bound properties to expected-strength steel properties. Group 4 ASTM A572/A572M-89.05 1.05 1. This includes all material properties.1. 5. Group 2 ASTM A36/A36M-00l Dual Grade.10 1.05 1.10 1. Group 1 ASTM A572/A572M-89. Group 2 ASTM A572/A572M-89. Page 5-22 .6 Modeling Guidance General The analytic model(s) used in assessing the potential for progressive collapse should be modeled as accurately as possible to the anticipated or existing conditions.05 1.05 1. Group 1 ASTM A36/A36M-00l Dual Grade.10 1961 .10 1.10 1. Group 4 Not Listed1 Not Listed1 Specification Factor 1.present 1961 .present Tensile Strength 1990 .). Group 1 ASTM A572/A572M-89. Group 3 ASTM A572/A572M-89.
SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings
Vertical Element Removal
The vertical element (i.e., the column, bearing wall, etc.) that is removed should be removed instantaneously. While the speed at which an element is removed has no impact on a static analysis, the speed at which an element is removed in a dynamic analysis may have a significant impact on the response of the structure. Because of this, it is recommended for the case where a dynamic analysis is performed, the vertical supporting element should be removed over a time period that is no more than 1/10 of the period associated with the structural response mode for the vertical element removal. Also the vertical element removal shall consist of the removal of the vertical element only. This removal should not impede into the connection/joint or horizontal elements that are attached to the vertical element at the floor levels. An example sketch illustrating the correct and incorrect way to remove a column is shown in Figure 5.7. It is critical that the user understand that the sketch is not representative of damage due to any specific threat (see Section 1.3 for discussion of member removal approach).
Correct approach to removing a column
Original Structural Configuration
Incorrect approach to removing a column
Figure 5.7. Sketch of the correct and incorrect approach for removing a column.
5.1.3 Redesign of Structural Elements
Structural configurations that are analyzed consistent with Section 5.1.2 and determined to have a high potential for progressive collapse shall be redesigned to a level that is consistent with a low potential for progressive collapse.
5.1.3.1 Procedure
The following steps shall be followed when redesigning the deficient structural elements identified in the analysis procedure (Section 5.1.2).
As a minimum, the structural elements and/or connections identified as deficient in Section 5.1.2 should be redesigned consistent with the redistributed loading determined in this process in conjunction with the standard design requirements of the project specific building code(s) using well-established design techniques. The redesign criteria for typical and atypical structural configurations follow: Typical Structural Configurations Structural elements and beam-to-column connections must meet the DCR acceptance criteria in the design of deficient components and connections. If an approved alternate analysis criteria is used, the deficient components should be designed to, as a minimum, achieve the allowable values associated with that criteria for the redistributed loading. Atypical Structural Configurations Structural elements and beam-to-column connections must meet the DCR acceptance criteria in the design of deficient components and connections. Note that a reduction factor of 3/4 must be multiplied to the DCR value for atypical structures. If an approved alternate analysis criteria is used the deficient components should be designed to, as a minimum, achieve the allowable values associated with that criteria for the redistributed loading.
Step 2. Upon the completion of Step 1, the redesigned structure shall be reanalyzed consistent with analysis procedure outlined in Section 5.1.2. Note:
In order to achieve the necessary design requirements, significant structural changes may be required, such as increasing member sizes, providing beam to beam continuity across the column (for steel frame connections), strengthening of moment resisting connections, etc. However, the design criteria for atypical structures may be limited to the ‘atypical’ region if this is localized. For example, consider a building that uses transfer girders along one face of the perimeter and a typical structural configuration for
SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings the remainder of the structure. The perimeter structural bays shall be designed to meet DCR acceptance criteria with a reduction factor of 3/4 applied to the DCR value, but the remainder of the building may be designed with no reduction factors applied to the DCR value. It should be noted that to achieve a low potential for progressive collapse more than one iteration of the redesign/analysis process may be required. For example, a change in the size of structural members may alter the magnitude and distribution of the redistributed load. The designer/analyst is not limited to a particular method for improving the original design with respect to the minimization of the potential for progressive collapse. For the example, in Figure 5.8, assume the results of Section 5.1.2 indicate the perimeter girders from the 2nd floor level to the 13th floor level for a given moment frame structure are not adequate in regards to the analysis criteria presented in Section 5.1.2.4. The designer has the freedom to evenly distribute an improved redesign from the 2nd floor level to the 6th floor level by introducing a Vierendeel truss to support the remaining floors from the 7th floor level to the 13th floor level (Figure 5.9), as long as the overall intent of minimizing the potential for progressive collapse, as defined in Section 5.1.2.4, is accomplished.
Page 5-26 . Extent of Vierendeel truss upgrade application using moment connections on exterior frames. Extent of upgrade application using moment connections on exterior frames.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings Figure 5.8. Figure 5.9.
material properties. Process for assessing the potential for progressive collapse in existing construction.10. and shall be documented in accordance with the provisions in Section 1. shown in Figure 5.2 concerning analysis techniques. and modeling guidance. assess the potential for progressive collapse as the result of an abnormal loading event.10. as a minimum.2) yes Does the structure meet the analysis requirements for minimizing the potential for progressive collapse? No The potential for progressive collapse is low. In addition. Findings of this analysis should be incorporated into the project-specific risk assessment. facilities undergoing modernization should.1.SECTION 5 – Progressive Collapse Guidelines for Steel Frame Buildings 5. analysis considerations and loading criteria.1. Existing Construction Analysis (Section 5. The ‘analysis’ provisions contained in Section 5. analysis criteria.2 Existing Construction Existing facilities undergoing modernization should be upgraded to new construction requirements when required by the project specific facility security risk assessment and when feasible. Report Figure 5. procedure. The potential for progressive collapse is high.5. Page 5-27 . shall also apply to existing construction. The flowchart. outlines the process for assessing the potential for progressive collapse in existing facilities.
F. Air Force AFPAM 32-1147 (I).” Paper from The Structural Engineers World Congress. Navy NAVFAC P-1080. J. Dunn. Department of State. Crawford.G. September 1979. England. D. 11.. October 1975. and DSWA DAHSCWEMAN-97. Department of Defense. 10. Washington. 2. and Siess. Held at the University of Texas at Austin.E. Karagozian & Case Structural Engineers. “Progressive Collapse-Symposium Summary. CA. C. March 1990. March 5. 9.. 8. 7. Office of Foreign Building Operations. J.” Journal. American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures. 2001. R. 5.. and Colwell. Department of Defense Interim Antiterrorism/Force Protection Construction Standards – Guidance on Structural Requirements (Draft). 12. Corley. 3. and Schriever. P. Washington. and Building Codes. Resources 1. and Karns..C. “Economics of Protection Against Progressive Collapse. Burbank. Washington. W. National Bureau of Standards. ACI 6. Breen. National Research Council. D. 1975. 1972. “Research Workshop on Progressive Collapse of Building Structures. D.. “The Avoidance of Progressive Collapse: Regulatory Approaches to the Problem.” Research Report TR-01-10. 4. D.SECTION 6 – Resources Section 6.” Division of Building Research.P.” NBSIR 74-542. The Building Regulations. 1992. W. B.R.C.E. Published by the Stationery Office. November 1975.” National Bureau of Standards. November 18-20. D. Houghton. J.C. 2001. Page 6-1 . Published by the American Society of Civil Engineers.1. New York. Abnormal Loads. Army TM5-855-1. Breen. September 1974. pp.E. “Design Studies to the Vulnerability of Office Buildings to Progressive Collapse due to Terrorist Attack. D. August 1998. Architectural and Engineering Design Guidelines and Criteria for New Embassy Buildings. Chapman. “Reducing Collateral Damage From Malevolent Explosions: Things Learned from the Oklahoma City Bombing. Washington.C. Burnett. ASCE 7-95. 997-1004. Design and Analysis of Hardened Structures for Conventional Weapons Effects. Allen. July 1998. J.F. P.” National Bureau of Standards. “Progressive Collapse. E.
E.” The Journal of Structural Engineering. 22. D. 19. 15. “FEMA 273 – NEHRP Guidelines for the Seismic Rehabilitation of Buildings.” Federal Emergency Management Agency. November 2000. 17. Volume 109. “FEMA 274 – NEHRP Commentary on Guidelines for the Seismic Rehabilitation of Buildings. “Provision in Building Against Disproportionate Collapse. V. A. P. July 1998. Number 4. April 1977.V.” Journal of the Structural Division. Leyendecker.. Gumpertz & Heger. 1973. 23. Ellingwood. 14. "Progressive Collapse Analysis of the Moorhead Building Using GSA Guidelines.. D. Ettouney. March 1997. “FEMA 356 – Prestandard and Commentary for the Seismic Rehabilitation of Buildings. 104(3). ASCE. 2003. Ellingwood.Recommended Seismic Evaluation and Upgrade Criteria for Existing Welded Steel Frame Buildings. 63. R. B. “FEMA 350 . 2000. 2000. B. Page 6-2 . W. E. Waltham. and Leyendecker.” Paper from The Structural Engineers World Congress.Recommended Seismic Design Criteria for New Steel Moment-Frame Buildings.” National Bureau of Standards.. Mudlock.." Simpson. 25. 24.” Federal Emergency Management Agency. July 1. March 12. Massachusetts.” Federal Emergency Management Agency. 2000. and Yao. April 1983. D. “Fortskridanda Ras (Design to Avoid Progressive Collapse).” Federal Emergency Management Agency. and DiMaggio. July 1998. M. and Longinow. Washington. 1997. pp. 16. Aquino.. “Approaches for Design Against Progressive Collapse. 18.” Paper from The Institution of Civil Engineers and the Institution of Structural Engineers Half Day Meeting. Ellingwood. Publication No.SECTION 6 – Resources 13. E. Desai. “Probability of Failure from Abnormal Load. Bruce and Leyendecker. Ellingwood.. “Design Methods for Reducing the Risk of Progressive Collapse in Buildings. Dusenberry. 20." Paper from Structural Engineers World Congress. 26.C.. “FEMA 351 . 1978. M. 21.” Federal Emergency Management Agency. Inc. October 1997. “FEMA 355D – State of the Art Report on Connection Performance.” Federal Emergency Management Agency. T. Kelly. B. “Integrated Study of Progressive Collapse of Buildings. S. “The Impact of the Ronan Point Collapse 25 Years After. 413-423.” The National Swedish Board of Urban Planning.
October 8. and Leyendecker.R. Myers. R. Hinman. G. The Interagency Security Committee. National Bureau of Standards..76. E. 775-808. Building Technologies Division Office of Property Development Public Building Service General Services Administration. 1997. 38. D... November 1974. D. “Lessons From The Oklahoma City Bombing. February 1977 37. “The Implications of the Report of the Inquiry into the Collapse of Flats at Ronan Point. Breen. Volume 47. 1978. Ferahian. D. Number 7. Inc. Bryson. pp. N. 32. J. July 1969. 30. “Buildings: Design for Prevention of Progressive Collapse.C. and Swatta. Moorhead Federal Building Progressive Collapse Investigation and Upgrade Design Report. 29. V. D. Page 6-3 . “Analysis of Non-reinforced Masonry Building Response to Abnormal Loading and Resistance to Progressive Collapse... Fuller.F.” The Structural Engineer. Somes. No. Civil 28. E. California. 1997).E.” Research Report MHP 0232800-1.C. “Progressive Collapse Analysis and Design Guidelines Case Study: William S. Berkeley. McGuire. January 13. Leyendecker. Volume 3: technical papers. W.r01.. “Robustness – Appraisal of existing large panel systems (LPS) buildings. 7. Virginia.J. 31. 34. E.” National Bureau of Standards. January 1976. 33. Number 2. Berkeley. M. Proceedings V. ISC Security Criteria for New Federal Office Buildings and Major Modernization Projects.. Washington. J. Houghton. Canning Town. Karns. “Investigation of the Skyline Plaza Collapse in Fairfax County.C. Defensive Design Techniques..” Paper from The Institution of Civil Engineers and the Institution of Structural Engineers Half Day Meeting. “Seismic Resistance vs Progressive Collapse of Precast Concrete Panel Buildings. 1977.” NBSIR 74526. S. M. “Progressive Collapse of Flat Plate Structures. Washington.” ACI Journal. GSA Security Criteria (Draft Revision. D. J. February 1972. “Abnormal Loading on Buildings and Progressive Collapse. Kim. March 1997. July 11-15. D. 36. Leyendecker. May 28.” Proceedings of the Workshop on Earthquake-Resistant Reinforced Concrete Building Construction.” National Bureau of Standards.. Volume 42. 35. Matthews.V.V. Long Beach. 2001. Houghton & Partners. 2003. and Hammond. Hawkins. July 1979.” ASCE Press. and Mitchell.. E. N.SECTION 6 – Resources 27.” Engineering.E. Washington... University of California.
U.” Paper from The Institution of Civil Engineers and the Institution of Structural Engineers Half Day Meeting. Springfield. May 2003. November 2000. E. “Robustness – the SCOSS Report.” Paper from The Institution of Civil Engineers and the Institution of Structural Engineers Half Day Meeting.” Federal Emergency Management Agency Mitigation Directorate. “Progressive Collapse-Preventative Measures in the United Kingdom.. Canada. 44. National Research Council of Canada 1995. and Nethercot. J. Structural Engineers Association of California (2001).. “Explosions in Domestic Structures. J. D and Stretch. Vicksburg. D. 51. Smith.B. “Progressive Collapse Analysis of the Las Vegas Federal Building and U. R. 48. Inc.dwellings and small buildings. February 1994. 43. K.. J. Gaithersburg. J. Applied Research Associates.A. Menzies. MD. Commentary and Recommendations on FEMA 350. Standards of Seismic Safety of Existing Federally Owned or Leased Buildings and Commentary (ICSSC RP4/NISTIR 5382). June 1995. FEMA 350 Task Group. Brokaw. March 2003.” The Structural Engineer. March 1997. Menzies. Number 19. Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects. STANDGARD User’s Guide. Courthouse. K. 49. “Robustness – trends in practice.” Paper from Structural Engineers World Congress.” Journal of Structural Engineering. 41. Rasbash. 45. “The Oklahoma City Bombing-Improving Building Performance Through MultiHazard Mitigation.” National Research Council. Inc. General Services Administration and Applied Research Associates. “Protecting Buildings from Bomb Damage.S. 42.SECTION 6 – Resources 39. Page 6-4 .” Applied Research Associates. MS. Narayanan. “Resistance to Progressive Collapse Requirements in Ontario. March 1997. “Progressive Collapse Loads for Flat-Roof Structures. Building and Fire Research Laboratory. National Building Code of Canada. October 1969. Herrle. July 1998. 50. 40. Volume 47. 47. August 1996.. 46. Executive Summary only.S. National Institute of Standards and Technology. July 1998. J. Murtha-Smith. Issued by the Canadian Commission of Building and Fire Codes. Inc.. 52. prepared by SEAOC Seismology Committee.” Paper from the Structural Engineers World Congress.
54.C. Yokel. R. 2002. Department of Defense. and Schwab. National Bureau of Standards.Y. 20234.. F. D.SECTION 6 – Resources 53. Unified Facilities Criteria (UFC) DoD Minimum Antiterrorism Standards for Buildings (UFC4-010. H. J. A. August 1975.01). Washington.” NBSIR 75-715. Page 6-5 . Pielert. “The Implementation of a Provision Against Progressive Collapse.
for determining the critical scenarios that should be assessed. The user may consider. If vertical discontinuities are present in the primary structural configuration. buildings often contain distinguishing features or details). The user shall use engineering judgment to determine the critical situations that should be assessed for the potential for progressive collapse. but not be limited to the other atypical arrangements that follow. Thus. The considerations may be similar to those utilized in typical building configurations. Page A-1 . the user of this guideline must use engineering judgment to determine critical analysis scenarios that should be assessed in order to meet the intent of this guideline.. but additional configurations may be necessary depending on the structural makeup.e. Examples of vertical discontinuities.1). Vertical Discontinuities Structures that have vertical discontinuities may warrant additional consideration for progressive collapse. analyses of the response of the building for a loss of primary vertical support in these areas shall be considered. Possible structural configurations that may result in an atypical structural arrangement include but are not limited to the following items. developing a set of analysis considerations that works for every facility is impractical. Atypical Structural Configurations Because all structures are unique and are often not typical (i. Combination Structures For facilities that utilize a combination of frame and wall systems for the primary supporting structure the analyst shall apply considerations similar to that presented for typical building configurations.APPENDIX A – Atypical Structural Configurations Appendix A. Discontinuous column line Potential areas for considering a loss in primary vertical support Discontinuous shear wall Potential areas for considering a loss in primary vertical support Figure A.1. Examples of vertical discontinuities include discontinuous shear walls or columns such as the use of transfer girders (Figure A.
Structural bays that are greater than 30 ft in any direction are considered extreme.2). The removal of a primary support along the exterior of this structure could potentially collapse three structural bays from the ground floor level to the roof. Page A-2 .2.3. Plan Irregularities Plan irregularities such as re-entrant corners could present vulnerable areas in regards to the potential for progressive collapse.APPENDIX A – Atypical Structural Configurations Variations in Bay Size/Extreme Bay Sizes A building configuration that contains structural bay(s) that have a large variance in size (compared to what may be considered a typical bay size of the facility) or extremely large bay sizes should be considered vulnerable and an assessment of the potential for progressive collapse shall be performed in these areas (Figure A. This type of structural configuration should be investigated regarding potential for progressive collapse. For example consider the hypothetical structure shown in Figure A. Examples of buildings with substantial variation in bay size and extreme bay sizes. Variation (increase) in structural bay size Potential areas for considering a loss in primary vertical support Extreme structural bay size (greater than 30 ft in any direction) Potential areas for considering a loss in primary vertical support Figure A.
4) may present uncertainty to the analyst when deciding on what primary vertical support to remove in the analysis process. In the situation where structural columns are closely spaced.APPENDIX A – Atypical Structural Configurations Plan View Re-entrant corner (a) (b) Re-entrant corner Loss of primary vertical support Figure A. Typically. some of the columns are likely to be architectural in nature as opposed to a true structural column. (a) Example of a structure with a re-entrant corner. Closely Spaced Columns Structures that have closely spaced columns (Figure A. Structures that have this type of structural configuration shall be analyzed for a loss in support from both the architectural column as well as the structural column to assess the potential for progressive collapse.3. the structure should be analyzed for the loss of both columns if the distance between the columns is less than or equal to 30% of the longest dimension of the associated bay. Page A-3 . only the loss of one column shall be required in the analysis. Otherwise. (b) The probable response of the structure for the case of a loss in primary vertical support in the re-entrant corner.
Page A-4 .4. Example of a building that has closely spaced columns.APPENDIX A – Atypical Structural Configurations Figure A.
B.. etc. seismic. Unfactored. ultimate capacities of the foundation elements may be used for this design provision. a column. but may be used to develop preliminary sizes and possibly enhance the initial structural design prior to assessing the potential for progressive collapse as outlined in Section 4. click on the ‘Begin Minimum Design Base Shear Determination’ button (at right).1 Foundation The building foundation and foundation/structure connection should be designed such that for the case of an instantaneous removal of a primary vertical component (i.e. Design Guidance The design provisions outlined in this section are not required by this Guideline.1. specific blast design.g. To begin the automated version of the Design Base Shear process. Minimum Design Base Shear The minimum design base shear values may be determined using the included program (an automated version of the Design Base Shear procedure) or by following the ensuing procedure.) additional foundation design consideration based on the provisions outlined in this section are not necessary. the design should be capable of meeting the greater of the requirements of this section as well as all other required building codes or specific blast design requirements. etc.1. Hence. wall section.). Begin Minimum Design Base Shear Determination Page B-1 .) these elements are capable of resisting the potential redistribution of forces. etc. seismic. additional foundation design considerations are recommended based on the magnitude(s) determined in this section in conjunction with using unfactored.APPENDIX B – Design Guidance Appendix B. In order to enhance that possibility the following minimum design base shear procedure is presented for use in the design of the building foundation and foundation/structure connection. ultimate load capacities in the design of the foundation elements. Note: If the base shear magnitude(s) determined in this section is less than the base shear value(s) determined for other load requirements (e.g. if the base shear load(s) determined in this section is larger than the base shear value(s) determined for other load requirements (e.2.2 and Section 5... The procedures outlined in this Appendix shall be used to supplement the requirements of the project specific building code(s) in the design of both primary and secondary structural elements. However.
Determine the required base shear value for resisting abnormal loads using equation B.APPENDIX B – Design Guidance Procedure The following procedure shall be used to determine the specific minimum base shear requirements for each major direction of the building (Figure B. πγ 2.000T (lb) (B.030 for reinforced concrete moment-resisting frames and eccentric frames Ct = 0. determine Ln. using equation B. Using Figure B.3.020 for all other construction types An example of this process is shown in Appendix C.035 for steel moment-resisting frames Ct = 0. 25 (B. Λave.3) (ft) SD = minimum defended standoff distance (ft) H = total height of building (ft) W = width of considered face (ft) *Ln should be rounded down to the nearest foot Step 2.3) T = Ct ( H ) 0.2) Step 5. select the Λn values consistent with the ranges (Ln) determined in Step 1.1.1.1) γ = 144Λ aveWH (B. Using Table B. Step 1. Ln* = the ranges from point X to points n (1 through 25 as depicted in Figure B. where. Step 3.75 and Ct = 0. using equation B.3.2. Page B-2 . Calculate the average Λ value. Vb = where.2). Λ ave = ∑Λ n =1 25 n Step 4. Calculate γ.
APPENDIX B – Design Guidance Figure B.3. Geometry parameters needed for calculating the design base shear value for Face A (similar for Face B). Consideration of this process should be performed for both Face A and B. Page B-3 .2. Illustration depicting the two primary faces. H SD Figure B.
42 34.44 48.74 33.68 99.01 192.69 50.73 43.15 280.78 34.88 37.1.06 36.86 55.65 39.51 35.63 42.22 182.74 48.99 81.52 303.48 173.36 397.84 58.17 77.65 109.93 55.76 32.30 43.49 51.09 40.31 37.56 329.92 50.29 124.49 260.48 44.81 89.31 91.54 31.38 46.41 116.69 74.73 96.18 42.64 165.00 69.56 68.12 39.15 62. Range Ln (feet) 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 Λ 566.26 35.41 33.43 87. Λn values for ranges 10 through 300 feet.01 60.58 360.04 79.84 243.02 54.49 145.15 53.84 31.10 45.39 75.60 40.88 35.14 34.11 41.87 497.05 47.03 82.17 49.19 38.31 52.08 32.46 37.85 65.70 120.45 32.22 129.75 38.88 44.12 105.06 72.59 41.91 Range Ln (feet) 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 Λ 59.50 71.59 158.40 112.48 215.81 57.27 139.24 151.52 442.73 46.81 102.APPENDIX B – Design Guidance Table B.54 134.95 94.34 63.18 85.82 56.08 33.57 64.64 228.18 66.03 203.66 36.25 Page B-4 .14 31.
43 16.84 18.28 23.08 19.27 16.29 17.68 16.APPENDIX B – Design Guidance Table B.60 16. Λn values for ranges 10 through 300 feet (continued).52 16.23 21.83 20.66 22.85 16.41 30.45 27.46 24.81 22.33 18.23 27.35 22.35 29.77 16.70 20.96 30.06 21.74 18.96 19.61 23.94 23.85 28.20 25.11 23.90 27.20 Page B-5 .02 16.61 29.50 22.65 17.68 30.58 25.29 24.63 18.35 16.1.84 17.20 20.28 19.67 27.39 19.94 16.50 21.36 21.13 27.82 24.37 28.64 24.53 18.78 21.96 22.44 23.92 21.38 26.12 22.09 20.56 17.45 20.85 19.23 18.21 22.47 17.58 20.93 17.13 18.01 24.06 18.33 20.87 29.17 25.97 25.01 26.38 25.38 17.10 28.61 19.77 23.11 17.95 18.79 26.58 26.03 17.43 18.50 19.74 17.77 25.64 21.61 28.14 29.17 19.73 19. Range Ln (feet) 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 Λ Range Ln (feet) 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 Λ 30.96 20.20 17.
23 13.12 13.09 15.03 14.56 14.74 15.1.82 12.87 12.34 12.92 12.13 14.63 14.29 12.31 14. Range Ln (feet) 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 Λ Range Ln (feet) 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 Λ 16.38 14.66 15.44 13.66 13.89 14.16 15.07 13.01 13.52 15.25 14.77 12.15 12.44 Page B-6 .04 15. Λn values for ranges 10 through 300 feet (continued).67 12.68 11.89 13.61 13.44 15.12 16.95 13.23 15.28 13.52 12.17 13.60 11.30 15.89 15.81 11.93 11.33 13.11 12.59 15.52 11.APPENDIX B – Design Guidance Table B.96 14.76 11.39 13.72 12.07 12.20 12.62 12.50 14.43 12.38 12.84 13.44 14.72 13.07 14.96 15.48 12.98 11.76 14.85 11.72 11.37 15.02 11.48 11.57 12.69 14.81 15.82 14.19 14.64 11.89 11.02 12.50 13.78 13.55 13.97 12.56 11.25 12.
The typical. From Figure B.1. Column parameters determined in this procedure should be used only if they exceed the sizes required by other load requirements. Using Table B. Ln. n Ln* SD = = = story level the ranges from point “X” to the mid-height of each story level Figure B.4. required column size for each floor level may be determined using the included program (an automated version of the Column Sizing procedure) or by following the ensuing procedure.5 (ft) minimum defended standoff distance along the building face under consideration (ft) *Ln should be rounded down to the nearest foot Step 2. where. click on the ‘Begin Column Sizing Determination’ button (at right). To begin the automated version of the Column Sizing process. Step 3. Step 1.APPENDIX B – Design Guidance B. Procedure Begin Column Sizing Determination The following procedure shall be performed in the directions of both major axes as shown in Figure B. Calculate Λsn using equation B. determine values of Ln. The remaining steps should be performed independently for each story level (n).5.4 Λ sn = wb Λn 25 (B. select the Λn values consistent with the ranges. determined in Step 1.4) Page B-7 . Column Sizing The following procedure may be used for developing preliminary column sizes in structures that utilize columns as the primary lateral force resisting system.2 Lateral Force Resisting System The following procedures are design provisions for ensuring that the lateral force resisting system contains at least moderate resistance regarding laterally applied abnormal loads.
5.250 (psf) Page B-8 . K1n = 15. w1 w2 n K 1n (B. w2 n = wa n where.6.4. wb = typical bay width (ft) Step 4.5. TA 1.6) w1 = Unit weight assumed for equation B.a) K1n = 16. Calculate the adjusted bent story stiffness (K2n) using equation B. Determine the required bent story stiffness (K1n) using equation B.n0 (lb/in) for steel frames (B.5. wan = actual unit weight for the bent and story under consideration (psf) TA = Tributary plan area of bent (ft2) as shown in Figure B.5595Λ2s.APPENDIX B – Design Guidance where. K 2n = where.952 Λ2s.n2 (lb/in) for r/c frames or flat slab structures (B.b) Step 5.5 derivation = 100 psf w2n = Adjusted unit weight for the bent and story under consideration (psf) where.
Distance parameters needed for determining Λn. SD X Figure B.5.4.APPENDIX B – Design Guidance Bent Tributary Area of Bent (shaded area) Tributary Area of Bent (shaded area) X Bent SD=Minimum Defended Standoff Distance X Defended Perimeter Column SD=Minimum Defended Standoff Distance Figure B. The bent story stiffness shall be evaluated for both major axes. Page B-9 . Illustration of a facility being considered for column sizing.
The required moment of inertia for each column can then be calculated using equation B. 3 K H (B.5ρ + 0. the following equation can be used for sizing reinforced concrete columns. wc = concrete unit weight (pcf) f’c = concrete strength (psi) Using the moment of inertia value calculated in equation B.8. Hn = Story height (inches) E = modulus of elasticity (psi) For reinforced concrete.g. Icoln calculated in equation B.7. I col n = where. K coln = K 2 n / N where.9) b = column width (in) d = column effective depth (in) ρ = positive (and negative) reinforcing ratio An example of this process is shown in Appendix C.8.APPENDIX B – Design Guidance Step 6. a steel manual (e.5 ' E = w1 c 33 f c where.083] (in4) 2 (B.8. Once the adjusted bent story stiffness has been calculated. E can be determined as: . Page B-10 . the required column stiffness can be determined by using equation B. AISC) can be referenced to select an appropriately sized steel column. N = number of columns in bent (B.8) I coln = col n n (in4) 12 E where. bd 3 [5.. Using the moment of inertia value.7) Step 7.
Specifically.1 shall be applied to the lateral force resisting system using a well-established ‘Equivalent Lateral Force Procedure’ such as the approaches outlined in the following references: • • NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures. In addition.10. Lateral force resisting system parameters determined in this procedure shall be used only if they exceed the parameters required by other load requirements.1.6) when subjected to the vertical load requirement defined in equation B. The lateral force resisting system is capable of resisting the transverse loading associated with the seismic base shear value(s) to within allowable limits as defined by the utilized procedure. Note: Performance of this design provision is not necessary if all of the following items have been satisfied: • • • An Equivalent Lateral Force Procedure has been previously performed for the project specific seismic base shear value(s). Volume 2 Structural Engineering Design Provisions. The lateral force resisting system must be capable of resisting the applied transverse loading to allowable limits as defined by the utilized procedure. 1997 Uniform Building Code. Design to Resist Column Buckling The columns along the perimeter of the facility. Page B-11 . 1997 Edition (FEMA 302).10. facilities having uncontrolled parking areas or public areas require column designs to resist potential buckling. between the 1st floor above grade and 3rd floor above grade should be designed using acceptable design techniques to resist buckling for an additional story of unsupported length (Figure B.APPENDIX B – Design Guidance Equivalent Lateral Force Procedure The base shear value(s) determined in B. The seismic base shear value(s) are larger than the base shear value(s) determined in B.7) when subjected to the vertical load requirement defined in equation B. all columns in uncontrolled parking areas or public areas should be designed using acceptable design techniques to resist buckling for an additional story of unsupported length (Figure B. Issued by Federal Emergency Management Agency. 1997.
Load = 2(DL + 0. DL = dead load LL = live load Unfactored. ultimate load capacities of the columns may be used for this design consideration.APPENDIX B – Design Guidance The load requirement for this design provision consists of the vertical loading presented in equation 4.25LL) where. Roof (B.6.10 applied at each floor level. Perimeter consideration for column buckling. Page B-12 .10) 4th Floor 3rd Floor 2nd Floor 1st Floor Loss of lateral support Figure B.
7.APPENDIX B – Design Guidance Underground Parking Loss of lateral support Underground Parking Loss of lateral support Public ground floor area Loss of lateral support Figure B. Page B-13 . Uncontrolled parking areas or public area considerations for column buckling.
10 for determining the applied load requirements that shall be used in the design of the girder to resist load reversals. The load determination for designing this component includes the dead load associated with (1) the weight of the girder and (2) the load associated with the weight of the slab that the girder supports and the project specific live load requirements. Note: An example of designing horizontally oriented elements for load reversals would include the consideration of a primary girder. For example.1 – B.2. in order to achieve this design requirement. primary structural elements shall be designed to resist loading reversals associated with a reverse in the transverse loadings determined in B. ultimate capacities of the structural elements may be used for this design provision. The structural components should be designed to resist this loading when applied in a downward direction and also when applied in an upward direction. These loads shall be utilized in conjunction with Equation B.10 applied in the (1) downward direction and (2) upward direction.APPENDIX B – Design Guidance B. symmetric reinforcement (which will increase the ultimate load capacity of the element) for reinforced concrete construction or moment resisting connections may be necessary. Page B-14 . etc.3 Design to Resist Load Reversals The primary and secondary structural elements should be designed with acceptable design techniques to effectively resist load reversals in the following locations: Facilities that have uncontrolled parking areas or public areas: At least one structural bay deep around the perimeter of the structure from the ground floor to the roof level and for all interior structural bays for at least three floors above grade or Facilities that do not have uncontrolled parking areas or public areas: At least one structural bay deep around the perimeter of the structure from the ground floor to the roof level. Horizontally oriented (i. girders. Unfactored.. Vertically oriented.e. roof beams.) primary structural elements shall be designed to resist the vertical load requirement given in equation B.
Page B-15 .4 Design to Resist Shear Failure For the applied loading given in equation B. When the shear capacity is reached before the flexural capacity. Note: It is essential that the primary structural elements maintain sufficient strength and ductility under an abnormal loading event to preclude a shear failure.APPENDIX B – Design Guidance B. ultimate load capacities of the primary structural elements may be used for this design provision. primary and secondary structural elements should be designed to resist shear failure in the following locations: Facilities that have uncontrolled parking areas or public areas: At least one structural bay deep around the perimeter of the structure from the ground floor to the roof level and for all interior structural bays for at least three floors above grade or Facilities that do not have uncontrolled parking areas or public areas: At least one structural bay deep around the perimeter of the structure from the ground floor to the roof level. the possibility of a sudden. Unfactored.10. non-ductile failure of the element exists which may lead to a progressive collapse of the structure.
the façade system should be considered ‘non-frangible’. Example Calculations C.e. 7 f c ⎝ ⎠ and b = 1 (considering a unit width of the wall) Hence.APPENDIX C – Example Calculations Appendix C. Page C-1 .0025 Treat as a simply supported. The r/c wall does not contain windows and has the following properties: f c' = 4.15 psi > 1. lb .1 Nonfrangible/Frangible Façade Examples Example 1 Consider a reinforced concrete (r/c) wall that spans 12 feet between floor levels and acts as a one-way slab system (i.5 in (6 in slab with 1. ρf y ⎞ ⎛ ⎟ = (ultimate bending moment) − 1 M u = ρbd 2 f y ⎜ ' ⎟ ⎜ 1 .000 psi ρ = 0.5 in cover) L = 12 ft or 144 in The flexural capacity of a simply supported beam or one way slab can be determined as: Capacity = 8M u L2 (psi) where. the wall imparts transverse load to the floor levels). one-way slab subjected to a uniformly distributed load where: 12 ft d = 4.0 psi M u = 2970 Hence.in in Capacity = 1.000 psi f y = 60..
Structural Bay Metal Panel (CMU backing) Wall 8 ft 8 ft 8 ft Floor Level b 12 ft Glass Glass Glass a 10 ft Floor Level 25 ft Figure C. This façade consists of a window system and a metal panel/CMU infill wall system. The flexural capacity of a simply supported two-way slab can be determined as: Page C-2 . Structural Bay Area = 12 ft x 25 ft) Window = 3(8’x10’) Metal Panel/CMU Wall = 300 ft2 . The glass consists of a 3/8 inch thick monolithic annealed pane with the following maximum yield strength: f y = 12. determine the percent of wall occupied by each façade system.APPENDIX C – Example Calculations Example 2 Consider a combination façade system such as that shown in Figure C.1.240 ft2 = 300 ft2 = 240 ft2 = 60 ft2 (80%) (20%) Only consideration of the window capacity for determining whether the façade system is frangible or non-frangible is required since the Metal Panel/CMU Wall consists of less than 25% of the wall area per structural bay. First.1. Combination façade system. The window openings are 8 ft (b) by 10 ft (a) and are capable of achieving two-way action.750 psi The glass will be analyzed as simply supported on all four edges and subjected to a uniformly distributed load.
2. Structural Bay Precast Concrete Panel 8 ft 8 ft Floor Level b 12 ft Glass Glass a 10 ft Floor Level 25 ft Figure C. lb .6 Hence.65 psi < 1.in in Capacity = 0.0 psi M u = 299. This façade consists of a window system and a metal panel/CMU infill wall system.375 Hence. Combination façade system.2. the façade system should be considered ‘frangible’.3M u 22. Page C-3 . M u = f y S = (ultimate bending moment) and S = I/c = 0.3M u ⎞ + ⎟ ⎜ ab ⎠ 2 ⎝ a2 (psi) where.APPENDIX C – Example Calculations Capacity = 1 ⎛ 22. Example 3 Consider a combination façade system such as that shown in Figure C.0044 (in4/in and b = 1 (assuming unit width) t = glass thickness = 0.0235 (in3/in) and I = bt3/12 = 0.
3%) (46.7%) Consideration of both the window capacity and wall capacity is required for determining whether the façade system is frangible or non-frangible. The window openings are 8 ft (b) by 10 ft (a) and are capable of achieving two-way action. Now consider the precast concrete panel portion of the façade. Recall that the largest of the capacities determined dictate whether the façade system is considered frangible or non-frangible.240 ft2 = 300 ft2 = 160 ft2 = 140 ft2 (53.750 psi Thus the capacity of the windows are: Capacity = 0. the façade system assessed in this example should be considered ‘non-frangible’.APPENDIX C – Example Calculations First. Thus.0 psi (See Example 1 for precast concrete wall capacity determination) This part of the façade system should be considered ‘non-frangible’. determine the percent of wall occupied by each façade system.15 psi > 1. The glass consists of a 3/8 inch thick monolithic annealed pane with the following maximum yield strength: f y = 12. Structural Bay Area = 12 ft x 25 ft Window = 2(8’x10’) Metal Panel/CMU Wall = 300 ft2 . Page C-4 . Hence. the capacity of the precast concrete wall is: Capacity = 1. Assume this façade system has properties similar to the properties given in Example 1.65 psi < 1.0 psi (See Example 2 for window capacity determination) This part of the façade system should be considered ‘frangible’.
Using Table B.4) (rounded to the nearest foot) = minimum defended standoff distance (ft) = total height of building (ft) = width of considered face (ft) Step 2.1. resulting in a total Λ value ΣΛ = 956.67 Step 3.1. Calculate γ. Face B minimum standoff distance. γ = 144Λ aveWH = 41. using equation B.600 Page C-5 .331. where. H Face A width (see Figure C.4. Calculate the average Λ value. Wa Face B width (see Figure C. determine Ln. Wb Face A minimum standoff distance. Λave.APPENDIX C – Example Calculations C. The base shear for Face A is calculated as: Step 1. 150 ft. 75 ft.2. using equation B.3). 80 ft. = = = = SDa = SDb = reinforced concrete or steel frame 50 ft.3).27 Step 4.1. The calculated Ln and Λn values are summarized in Table C. 100 ft. Λ ave = ∑Λ n =1 25 n 25 = 38.2 Design Base Shear The procedure to determine base shear requirements as described in Appendix B is illustrated by the following example: Building parameters: Construction Type Total building height. select the Λn values consistent with the ranges (Ln) determined in the Step 1. Ln SD H W = the ranges from point X to points n (1 through 25 as depicted in Figure C. Using Figure C.
Determine the required base shear value for resisting abnormal loads using equation B.APPENDIX C – Example Calculations Table C. Calculated Λ values for Face A.3.000T (lb) T = Ct ( H ) 0. Vb = where.030 for reinforced concrete moment-resisting frames and eccentric frames Ct = 0.75 and Ct = 0. πγ 2.035 for steel moment-resisting frames Ct = 0.020 for all other construction types Page C-6 . Step 5.1.
Λave. using equation B. Ct = 0.035).658 πγ 2.4. Λ ave = ∑Λ n =1 25 n 25 = 33. Using Table B.APPENDIX C – Example Calculations For a reinforced concrete frame.668 (lb) ≅ 99 kip on Face A.2. select the Λn values consistent with the ranges (Ln) determined in the Step 1.8 Step 4.1.564 πγ 2.75 and Vb = = 0.000 Page C-7 . Calculate the average Λ value.75 and Vb = = 0.1. Using Figure C.000T = 98. Ln SD H W = = = = the ranges from point X to points n (1 through 25 as depicted in Figure C. using equation B.39 Step 3. Calculate γ.4) (rounded to the nearest foot) minimum defended standoff distance (ft) total height of building (ft) width of considered face (ft) Step 2. thus T = Ct ( H ) 0.252.000T = 115. determine Ln.03.113 (lb) ≅ 115 kip on Face A. If the frame had been steel (Ct = 0. then T = Ct ( H ) 0. The base shear for Face B is calculated as: Step 1. where. γ = 144Λ aveWH = 18. The calculated Ln and Λn values are summarized in Table C.2. resulting in a total Λ value ΣΛ = 845.
APPENDIX C – Example Calculations Table C. Determine the required base shear value for resisting abnormal loads using equation B.564 (as previously calculated) πγ πγ 2.000T = 50. then Vb = πγ 2.000T = 43.572 (lb) ≅ 44 kip on Face A.035 and T = 0.834 (lb) ≅ 51 kip on Face B. Step 5.000T = 0. For a steel frame (Ct = 0. Page C-8 .3.2.75 and Vb = (lb) 2. Calculated Λ values for Face B.658). Vb = T = Ct ( H ) 0.
Page C-9 .APPENDIX C – Example Calculations Figure C. Generalized geometry parameters for base shear calculation. H SD Figure C.4.3. Perform base shear calculation for both faces (A & B) of the building.
n Ln SD = = = story level the ranges from point “X” to the mid-height of each story level (Figure C.3. From Figure C. Table C. L (ft) 80 82 86 91 Λ 46.APPENDIX C – Example Calculations C. Face B Actual unit weight. all floors Face A minimum standoff distance.63 40.Column Sizing The procedure to determine preliminary column sizes as described in Appendix B is illustrated by the following example: Building parameters : Construction Type Total four-story building height. Face B width.3. Using Table B. select the Λn values consistent with the ranges. 12 ft. The calculated Ln and Λn values for Face A are summarized in Table C. 75 ft. Typical bay width. where. Face B minimum standoff distance. = = = = = = = = = = = = = reinforced concrete. 150 ft. 12 ft. f’c = 4000 psi 50 ft. Ln.6) (rounded to the nearest foot) minimum defended standoff distance along the building face under consideration (ft) Step 2. H H1 H2 H3 H4 Wa Wb bwa bwb wan SDa SDb The procedure will be demonstrated for Load Level 2 in both major directions as shown in Figure C.1. 14 ft. determine values of Ln.88 42. 12 ft.1 44. 15 ft. Calculated Ln and Λn values for Face A. Story Level 1 2 3 4 Story Height (ft) 14 12 12 12 Total Height (ft) 14 26 38 50 Range. Face A Typical bay width.5.12 Page C-10 . Face A width.3 Lateral Force Resisting System . 70 psf 80 ft.6. determined in Step 1. 30 ft. 100 ft. For Face A: Step 1.
Story Level 1: Step 3. Determine the required bent story stiffness (K1n) using equation B.6.1 / 25 = 55. K 2n = where w1 w2 n K 1n = 86. The example will demonstrate the steps for story level one.5b for reinforced concrete frames or flat slab structures: K1n = 16.157 (lb/in) Step 5.5 derivation = 100 psf w2n = Adjusted unit weight for story 1 = 126 psf and w2 n = wa n where. wan = actual unit weight = 70 psf TA = Tributary plan area of bent = 30 ft x 75 ft = 2250 ft2 TA 1.n2 = 109. Step 4.32 25 bwa = typical bay width (ft) = 30 ft.5595Λ2s.APPENDIX C – Example Calculations The remaining steps should be performed independently for each story level (n). Calculate the adjusted bent story stiffness (K2n) using equation B. Calculate Λsn using equation B.250 = 126 psf Page C-11 .633 (lb/in) w1 = Unit weight assumed for equation B.4 (adjust for actual bay width) Λ sn = where. wb Λ n = 30 * 46.
Illustration of a facility being considered for column sizing. Page C-12 .5.APPENDIX C – Example Calculations Bent Tributary Area of Bent (shaded area) Tributary Area of Bent (shaded area) X Bent SD=Minimum Defended Standoff Distance X Defended Perimeter Column SD=Minimum Defended Standoff Distance Figure C.6. The bent story stiffness shall be evaluated for both major axes. SD X Figure C. Distance parameters needed for determining Λn.
7.8.439 where. b = d = 12 inches.APPENDIX C – Example Calculations Step 6. Once the adjusted bent story stiffness has been calculated.254 psi where. the required column stiffness can be determined by using equation B. E can be determined as: . Hn = Story height = 168 inches E = modulus of elasticity (psi) For reinforced concrete.01) and a square column. K coln = K 2 n / N = 14. 3 K H I coln = col n n (in4) 12 E where.083] (in4) 2 Page C-13 . I coln K H = col n n 12 E 3 = 1488 in4 Using this moment of inertia value. wc = concrete unit weight = 150 pcf f’c = concrete compressive strength = 4000 psi Therefore. b = column width (in) d = column effective depth (in) ρ = positive (and negative) reinforcing ratio For one percent steel (ρ = 0. The required moment of inertia for each column can then be calculated using equation B. the following equation can be used for sizing reinforced concrete columns: I col n = where. bd 3 [5.5ρ + 0.5 ' E = w1 c 33 f c = 3. N = number of columns in bent = 6 (75/15 + 1) Step 7.834.
Determine the required bent story stiffness (K1n) using equation B. Step 3.n2 = 11. Step 4.APPENDIX C – Example Calculations For Face B: Step 1. From Figure C.08 The remaining steps should be performed independently for each story level (n).167 (lb/in) Page C-14 .6) (rounded to the nearest foot) = minimum defended standoff distance along the building face under consideration (ft) Step 2. Ln. K 2n = w1 w2 n K 1n = 9. Using Table B.5b for reinforced concrete frames or flat slab structures: K1n = 16. The calculated Ln and Λn values are summarized in Table C.51 34. wb Λ n = 15 * 33. Calculate the adjusted bent story stiffness (K2n) using equation B.1.6. Calculate Λsn using equation B. determined in Step 1.08 / 25 = 19. n Ln SD = story level = the ranges from point “X” to the mid-height of each story level (Figure C.3. where. Table C.3.5595Λ2s.551 (lb/in) Step 5. The example will demonstrate the steps for story level four.78 33. Calculated Ln and Λ values for Face A. determine values of Ln.85 25 bwb = typical bay width (ft) = 15 ft.4 (adjust for actual bay width) Λ sn = where. Story Level 1 2 3 4 Story Height (ft) 14 12 12 12 Total Height (ft) range. select the Λn values consistent with the ranges. L (ft) 14 100 26 102 38 104 50 109 Λ 36.5.26 35.
3 K H I coln = col n n (in4) 12 E where.2 in4 Using this moment of inertia value.01) and a square column.083] (in4) = 2 For one percent steel (ρ = 0.250 = 126 psf K coln = K 2 n / N = 1.5 derivation = 100 psf w2n = Adjusted unit weight for story 4 = 126 psf where. w1 = Unit weight assumed for equation B. b = d = 7 inches. wan= actual unit weight = 70 psf (psf) TA = Tributary plan area of bent = 15 ft x 150 ft = 2250 ft2 Step 6.254 psi Therefore.7.834. I coln K H = col n n 12 E 3 = 99.8. Hn =Story height = 144 inches E = modulus of elasticity = 3. The required moment of inertia for each column can then be calculated using equation 4. the dimensions can be determined from: I col n bd 3 [5. Page C-15 . the required column stiffness can be determined by using equation B. w2 n = wa n where. Once the adjusted bent story stiffness has been calculated. TA 1.APPENDIX C – Example Calculations where.528 where.5ρ + 0. N = number of columns in bent = 6 (75/15 + 1) Step 7.
APPENDIX D –Structural Steel Connections Appendix D. developed following the Northridge earthquake. developed after Northridge Earthquake Full-penetration welds between beam and column flanges.573) SlottedWeb™ (US Patent Nos.738 and 6.680. 6.1. 6. Connection Description Public Sector (Public Domain) Type Figure Welded Unreinforced Flange (WUF) Welded Flange Plates (WFP) Welded Cover-Plated Flanges Bolted Flange Plates (BFP) Improved WUF-Bolted Web Improved WUF-Welded Web Full-penetration welds between beams and columns. PR = Partially Rigid Moment Connection FR = Fully Rigid Moment Connection FR D-5 Page D-1 .303) Note: Patented moment connection with full-depth side plates and fillet welds. Structural Steel Connections Table D.017. welded web developed after Northridge Earthquake Web is coped at ends of beam to separate flanges.583 and 6.427. Flange plate with full-penetration weld at column and fillet welded to beam flange Beam flange and cover-plate are welded to column flange Flange plate with full-penetration weld at column and field bolted to beam flange Full-penetration welds between beam and column flanges. FR D-4 SImilar to WUF moment connections with extended slots at weld access holes to separate the beam flanges from the beam web in the region of the connection. may have composite slab FR D-1(a) FR FR FR or PR FR D-1(b) D-1(c) D-1(d) D-1(a) FR D-1(a) Free Flange Welded Top and Bottom Haunches Reduced Beam Section Top and Bottom Clip Angles Double Split Tee Composite Top and Clip Angle Bottom Bolted Flange Plates Bolted End Plate Shear Connection with or without Slab FR D-1(e) FR FR PR PR PR PR PR PR D-1(f) D-1(g) D-2(a) D-2(b) D-2(a) similar D-1(d) D-2(c) D-2(d) Proprietary SidePlate™ System (US Patent Nos.138. flanges. 5.660. bolted web. 5. bolted or welded web. Steel moment frame connection types.237.516. designed prior to code changes following the Northridge earthquake.591. welded web tab resists shear and bending moment due to eccentricity due to coped web developed after Northridge Earthquake Haunched connection at top and bottom flanges developed after Northridge Earthquake Connection in which net area of beam flange is reduced to force plastic hinging away from column face developed after Northridge Earthquake Clip angle bolted or riveted to beam flange and column flange Split tees bolted or riveted to beam flange and column flange Clip angle bolted or riveted to column flange and beam bottom flange with composite slab Flange plate with full-penetration weld at column and bolted to beam flange Stiffened or unstiffened end plate welded to beam and bolted to column flange Simple connection with shear tab.
Fully rigid moment connections. Page D-2 .APPENDIX D –Structural Steel Connections (a) WUF Fully Rigid Connection (b) Welded Flange Plate (c) Welded Cover Plated Flanges (d) Bolted Flange Plate (e) Free Flange (f) Top and Bottom Haunch Figure D.1.
1. (a) Bolted or Riveted Angle (b) Double Split Tee (c) End Plate (Unstiffened) (d) Typical Shear Connection (without slab) Figure D.2.APPENDIX D –Structural Steel Connections (g) Reduced Beam Section Figure D. Partially rigid moment connections. Page D-3 . Fully rigid moment connections (continued).
which inherently eliminates the highly-restrained condition and the high-order tri-axial strain concentrations that are intrinsic to the basic geometry of ‘traditional’ moment connection systems.591. 6. The proprietary SidePlate™ connection system (US Patent Nos.516.3 Weak axis connections. and is shown schematically in Figure D.660. under the patent laws of the United States and other countries. SidePlate™ Connection System – SidePlate Systems. Inclusion of these proprietary systems herein does not constitute an endorsement by GSA on their fitness for any specific purpose. 5. A discussion of several types of proprietary connections is included herein. Designers wishing to consider specific proprietary connections for use in their structures should consult both the licensor of the connection and the applicable enforcement agency to determine the applicability and acceptability of the individual connection type for the specific design application. Proprietary Moment Frame Connections General This section presents information on patented fully-restrained steel frame moment connections that have been privately developed.138. Its connection geometry centers around a physical separation (commonly referred to as a ‘gap’) between the face of the column flange and the end of the beam. Instead. Inc.017. and 6.APPENDIX D –Structural Steel Connections (a) Fully Rigid Connection (b) Typical Shear Only Connection Figure D.573) is used in both new and retrofit construction. Use of these technologies without the express written permission of the licensor is in violation of intellectual property rights. Other proprietary connections not included in this listing also exist.583. These proprietary connections have been evaluated by recognized enforcement agencies and found to be acceptable for specific projects and/or for general application within the jurisdiction’s authority. by means of parallel full-depth side plates.4. all moment load transfer from the beam to the column reverts back to Page D-4 .427 6.
. insures the formation of plastic hinges at beam ends. SidePlate™ moment connection system. the continuous full-depth side plates replicate the continuous top and bottom main reinforcement steel through the column(s).sideplate. across the column. Page D-5 .. San Diego. The top and bottom beam flange cover plates are used to bridge the difference between flange widths of the beam(s) and the column. the two side plates plus the column’s own web]. Inc. configured with simple unrestrained fillet welds principally loaded longitudinally in shear for increased reliability and robustness. SidePlate™ steel frame connection technology replicates the torsional and lateral bending stiffness and strength properties of reinforced concrete beams and girders. In addition. and are designed with adequate strength and stiffness to force all significant plastic behavior of the connection system into the beam.4. which. using predictable equivalent force couples and basic engineering principles.APPENDIX D –Structural Steel Connections simple statics. by creating steel box sections with continuous. robust structural steel plates. typically provided in modern reinforced concrete structures to insure discrete beam-to-beam continuity across the column. ICBO ER-5366. This also improves the dynamic performance properties when subjected to blast loading. The parallel full-depth side plates act as robust continuity elements to sandwich and connect beam-to-beam. All full-scale cyclic tests have been conducted at the Charles Lee Powell Structural Research Laboratories. University of California. The construction of the SidePlate™ connection system uses all fillet-welded fabrication. full scale testing and performance can be obtained directly from SidePlate Systems.com. as well as the City and County of Los Angeles (COLA RR 25393 and LACO-TAP Bulletin 3). in a worst-case “missing column” scenario. (800) 475-2077 or www. Additional information on the SidePlate™ connection including use. Reliance on panel zone deformation of the column’s web is eliminated by providing three panel zones [i. The connection has been evaluated and accepted for use as a moment connection in Special Moment Frames (SMF) by the International Conference of Building Officials.e. in the vicinity of the beam-tocolumn joint. outside the beam-to-column joint itself. Figure D. Cypress. California. The SidePlate™ connection’s tested cyclic rotational capacity exceeds all current Connection Qualification Criteria [AISC (2002) Seismic Provisions Structural Steel Buildings and FEMA 350] for large inter-story drift angle demands from earthquakes. modeling characteristics.
680. Missouri. Separating the beam web from the beam flanges reduces the large stress and strain gradients across and through the beam flanges by permitting the flanges to flex out of plane. the slots in the beam web adjacent to the beam flanges allow the beam web and flange to buckle independently. ICBO ER5861. It is similar to the Welded Unreinforced Flange (WUF) moment connection with the addition of slots in the column and/or beam webs to separate the flanges from the web. Additional information on the connection and its performance can be obtained directly from Seismic Structural Design Associates.5.5. Moreover. Inc. The proprietary SlottedWeb™ connection (US Patent Nos. Camdenton. SlottedWeb™ moment connection. (866) 750-SSDA or www. 5.303) is shown schematically in Figure D.net. The connection has been evaluated and accepted for use as a moment connection in Special Moment Frames (SMF) by the International Conference of Building Officials. Inc.738 and 6. thereby eliminating the degrading of the beam strength caused by lateral torsional buckling.ssda.237.APPENDIX D –Structural Steel Connections SlottedWeb™ Connection – Seismic Structural Design Associates. Figure D.. Page D-6 .
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