JULY 13, 1999
TABLE OF CONTENTS 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES i 
Table of Contents 
List of Figures and Tables v 
List of Acronyms ix 
Executive Summary xi 
1 Introduction 
1.1 Purpose 
1.2 Team Composition 
1.3 Methodology 
1.4 Presentation of Findings 
2 Background on Tornadoes and History of the Storm 
2.1 The Fujita Scale and Tornado Probablity 
2.2 Tornadoes and Associated Damage 
2.3 Background of the Event 
3 General Assessment and Characterization of Damage 
3.1 Property Protection 
3.1.1 Overview of Buildings Evaluated 
3.1.1.1 Residential Buildings 
3.1.1.2 Non-Resiential Buildings 
3.1.2 Load Path and Increased Loads 
3.2 Wind-Borne Debris 
3.2.1 Missile Types and Sizes 
3.2.2 Wind-Borne Missile Quantity 
3.3 Personal Protection and Sheltering 
3.4 Local, State, and Federal Regulation 
3.4.1 Oklahoma 
3.4.2 Kansas 
4 Observations on Residential Property Protection 
4.1 Single Family Conventional Construction 
4.1.1 Load Paths 
4.1.2 Roof and Wall Sheathing 
4.1.3 Connections 
4.1.4 Increased Load 
4.1.5 Roof Coverings 
4.1.6 Wall Coverings 
4.1.7 Garage Door 
4.1.8 Windows and Doors 
4.1.9 Masonry
TABLE OF CONTENTS PRELIMINARY REPORT 
ii FEDERAL EMERGENCY MANAGEMENT AGENCY 
4.2 Multi-Family Construction 
4.3 Manufactured Housing 
5 Observations on Non-Residential Property Protection 
5.1 Load Path 
5.1.1 Tilt-up with Steel Joists 
5.1.2 Load Bearing Masonry with Steel Joists 
5.1.3 Steel Frame with Masonry Infill Walls 
5.1.4 Light Steel Frame Buildings 
5.1.5 Laminated with Wood Frame 
5.1.6 Masonry with Pre-cast Floors 
5.2 Increased Load 
5.2.1 Tilt-up Precast Walls with Steel Joists 
5.2.2 Load Bearing Masonry with Steel Joists 
5.2.3 Steel Frame with Pre-cast Hollow Core 
5.3 Non-Residential Roof and Wall Coverings 
5.3.1 Roof Coverings 
5.3.2 Wall Coverings 
5.3.3 Laminated Glass 
5.3.4 Garage Doors, Exterior Doors and Windows 
6 Observations on Personal Protection and Sheltering 
6.1 Shelters 
6.1.1 Types of Shelters 
6.1.2 Use of Shelters 
6.1.3 Maintenance Issues with Shelters 
6.1.4 Shelter Accessibility 
6.1.5 Shelter Ventilation 
6.1.6 Shelter Location 
6.2 Other Places of Refuge 
6.2.1 Refuge in Residences 
6.2.2 Refuge in Non-Residential Buildings 
7 Preliminary Conclusions 
7.1 Residential Property Protection 
7.1.1 Single and Multi-family Homes 
7.1.1.1 Load Path and Structural Systems 
7.1.1.2 Increased Load Caused by Breach of Envelope 
7.1.1.3 Masonry 
7.1.2 Manufactured Housing 
7.1.2.1 Foundations 
7.1.2.2 Anchors 
7.1.2.3 Strapping 
7.1.2.4 Modules (Superstructure) 
7.2 Non-residential 
7.2.1 Load Path 
7.2.2 Increased Load Caused by Breach of Envelope 
7.2.3 Roof and Wall Coverings
PRELIMINARY REPORT TABLE OF CONTENTS 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES iii 
7.3 Personal Protection and Sheltering 
7.3.1 Residential Shelters 
7.3.2 Group Shleters 
7.3.3 Community Shelters 
7.3.4 Other Places of Refuge 
8 Preliminary Recommendations 
8.1 General Recommendations 
8.2 Property Protection 
8.2.1 Residential and Non-Residential Buildings 
8.2.2 Codes and Regulations, Adoption and Enforcement 
8.2.3 Voluntary Actions 
8.3 Personal Protection 
8.3.1 Residential Sheltering 
8.3.2 Group and Community Sheltering 
8.3.3 Places of Refuge 
9 References (Not included at this time) 
Appendixes 
Appendix A Members of the Building Performance Assessment Team 
Appendix B Acknowledgements 
Appendix C National Performance Criteria for Tornado Shelters 
Appendix D Taking Shelter from the Storm 
Appendix E List of Useful Websites
FIGURES AND TABLES PRELIMINARY REPORT 
iv FEDERAL EMERGENCY MANAGEMENT AGENCY
PRELIMINARY REPORT FIGURES AND TABLES 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES v 
List of Figures and Tables 
Figure 1-1 BPAT meeting with State of Kansas and local government officials 
Figure 1-2 BPAT meeting with Mid West City fire official 
Table 1-1 BPAT damage assessment 
Figure 2-1 Probability of tornado occurrence in the United States 
Figure 2-4 Outbreak map of May 3, 1999 tornadoes in Oklahoma 
Figure 2-5 Radar reflectivity map showing hook echo 
Figure 2-6 Radar cross-section through F5 tornado 
Figure 2-7 Outbreak map of May 3, 1999 tornadoes in Kansas 
Table 2-1 Fujita Scale 
Figure 3-1 Continuous load path for a wood frame building 
Figure 3-2 Building failure due to inward wind and uplift 
Figure 3-3 Wind uplift on residential home 
Figure 3-4 Increased loads due to breach in envelope 
Figure 3-5 Hip roof failure due to internal pressure and leeward wind forces 
Figure 3-6 Failure of gable wall due to suction forces of leeward wall 
Figure 3-7 Failure of exterior wall and roof due to increased internal pressure 
Figure 3-8 EIFA and metal component damage 
Figure 3-9 URM wall failure due to inflow winds 
Figure 3-10 Failure of steel frame structural system with masonry infill walls 
Figure 3-11 Broken window due to small missile 
Figure 3-12 Picture of moderate sized missile 
Figure 3-13 Large, high energy missile 
Figure 3-14 Examples of board missiles 
Figure 3-15 Windborne missile striking house 
Figure 3-16 Vertical striking missile 
Figure 3-17 Board missile penetrating brick veneer 
Figure 3-18 Board missile penetrating refrigerator 
Figure 3-19 Power pole missile 
Figure 3-20 Displaced large propane tank due to wind 
Figure 3-21 Steel deck missile 
Figure 3-22 Tree missile 
Figure 3-23 Quantity of flying debris 
Figure 3-24 Polyisocyanurate roof insulation on top of the school roof 
Figure 3-25 Close-up of polyisocyanurate roof insulation 
Figure 3-26 Missile striking roof 
Figure 3-27 Missiles striking exterior wall of house 
Figure 3-28 Missiles striking interior wall of house 
Figure 3-29 Underground residential shelter 
Figure 4-1 Platform construction
FIGURES AND TABLES PRELIMINARY REPORT 
vi FEDERAL EMERGENCY MANAGEMENT AGENCY 
Figure 4-2 Lateral load transfer 
Figure 4-3 Failed stapling of boards to rafters 
Figure 4-4 Staggering joints in sheathing application 
Figure 4-5 Shear load force offset by wall sheathing 
Figure 4-6 Wall failure due to inadequate lateral load resistance 
Figure 4-7 CAPTION NEEDED 
Figure 4-8 Roof-framing to wall failure 
Figure 4-9 Top plate to supporting stud connection failure 
Figure 4-10 Wall framing to sill plate failure 
Figure 4-11 Stud wall and sole plate to floor failure 
Figure 4-12 Sill plate foundation failure at wall 
Figure 4-13 Sill plate to foundation failure 
Figure 4-14 Asphalt shingles on roof 
Figure 4-15 T-lock shingles on roof 
Figure 4-16 Vinyl siding damage 
Figure 4-17 Vinyl siding damage 
Figure 4-18 Garage door failure under suction load 
Figure 4-18A Typical double-wide garage door elevation 
Figure 4-18B Plan view of typical garage door 
Figure 4-18C Reinforced horizontal latch system for garage door 
Figure 4-18D Garage door failure at track 
Figure 4-19 Partial schematic of subdivision 
Figure 4-20 Partial roof loss versus total loss under internal pressure 
Figure 4-21 ADD CAPTION 
Figure 4-22 Garage and roof failure 
Figure 4-23 Garage door failure 
Figure 4-24 Roof uplift 
Figure 4-25 Missile penetrated door 
Figure 4-26 ADD CAPTION 
Figure 4-27 Roof failure 
Figure 4-28 Interior of home with roof failure 
Figure 4-29 TEMPORARY PLACE HOLDER 
Figure 4-30 Failure of masonry construction 
Figure 4-31 Brick masonry failure 
Figure 4-32 Failure of masonry wall 
Figure 4-33 Failure of brick veneer, close-up 
Figure 4-34 Inadequate bond of mortar to galvanized brick ties 
Figure 4-35 Inadequate bonding of mortar to brick and ties 
Figure 4-36 Failure of masonry veneer wall 
Figure 4-37 Failure of masonry veneer wall 
Figure 4-38 Failure of masonry veneer wall 
Figure 4-39 Failure of masonry veneer wall 
Figure 4-40 Failure of chimney onto home 
Figure 4-41 Failure of chimney, close-up 
Figure 4-42 Failure of chimney onto home 
Figure 4-43 Failure of masonry veneer, multifamily 
Figure 4-44 Failure of masonry veneer, multifamily 
Figure 4-45 Failure of masonry veneer, multifamily
PRELIMINARY REPORT FIGURES AND TABLES 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES vii 
Figure 4-46 Failure of chimney 
Figure 4-47 Failure of chimney 
Figure 4-48 Destroyed chassis 
Figure 4-49 Failed straps 
Figure 4-50 Displaced chassis 
Figure 4-51 Pulled anchor 
Figure 4-52 Pulled and bent anchor 
Figure 4-53 Strap failure 
Figure 4-54 Roof Uplift 
Figure 4-55 ADD CAPTION 
Figure 4-56 View of displaced chassis foundation 
Figure 4-57 View of removed chassis 
Figure 4-58 Laterally shifted manufactured home 
Figure 4-59 Pulled anchors and lateral displacement 
Figure 4-60 Strap and lateral shifting 
Figure 4-61 Shifted manufactured home 
Figure 5-1 Failure of critical connections in load path 
Figure 5-2 Failure of tilt-up precast concrete walls 
Figure 5-3 Damage displaying separation of bond beams 
Figure 5-4 Broken welds and no effective vertical reinforcement 
Figure 5-5 Blown off metal roof decking 
Figure 5-6 Foundation and wall attachments 
Figure 5-7 Column anchors exhibiting ductile failure 
Figure 5-8 Column anchors withdrawn from concrete foundation 
Figure 5-9 Stroud Regional Outlet Mall 
Figure 5-10 Loss of church roof 
Figure 5-11 Motel damage from violent tornado vortex 
Figure 5-12 Out of plane buckling of the main girder 
Figure 5-13 Collapsed roof structure and exterior 
Figure 5-14 Blown off roof over school auditorium 
Figure 5-15 Exterior of an undamaged reinforced concrete wall 
Figure 5-16 Failure of tilt-up concrete wall 
Figure 5-17 Top of failed tilt up wall 
Figure 5-18 Top of failed tilt up wall 
Figure 5-19 Failed roof system with intact tilt up concrete walls 
Figure 5-20 Damage to non-reinforced masonry walls 
Figure 5-21 Hollow core plank formed on second floor 
Figure 5-22 Failure of power driven anchors 
Figure 5-23 CAPTION NEEDED 
Figure 5-24 Collapsed metal clad wall covering 
Figure 5-25 Penetration of laminated glass 
Figure 5-26 Roof and wall failure 
Figure 5-27 Structural damage due to breach in envelope 
Figure 6-1 Above ground in residence shelter 
Figure 6-2 Surrounding damage near shelter 
Figure 6-3 Entrance to ICF shelter
FIGURES AND TABLES PRELIMINARY REPORT 
viii FEDERAL EMERGENCY MANAGEMENT AGENCY 
Figure 6-4 Precast concrete storm cellar 
Figure 6-5 Storm cellar constructed of steel sheets and concrete cover 
Figure 6-6 Community shelter at manufactured home park 
Figure 6-7 Above ground in residence shelters 
Figure 6-8 Entrance to manufacturing plant group shelter 
Figure 6-9 Group shelters at manufactured home development 
Figure 6-10 Manufactured home development community shelter 
Figure 6-11 Community shelter in school gymnasium 
Figure 6-12 Unmaintained underground shelter door 
Figure 6-13 Failed wooden door of below ground shelter 
Figure 6-14 Inadequate shelter door locking device 
Figure 6-15 Ballast roof covering on community shelter 
Figure 6-16 Stairway to manufactured home community shelter 
Figure 6-17 Stairway access to group shelter 
Figure 6-18 Heavy gauge ventilation pipe for below ground shelter 
Figure 6-19 Basement windows to home vulnerable to debris 
Figure 6-20 Below ground shelter susceptible to water runoff 
Figure 6-21 Remains of interior core room 
Figure 6-22 Remaining interior core of house 
Figure 6-23 Interior bathroom of damaged home 
Figure 6-24 Missile penetrating exterior wall 
Figure 6-25 Missile piercing wall stud 
Figure 6-26 Bathroom located along exterior wall 
Figure 6-27 Second story damage 
Figure 6-28 Damaged manufactured homes 
Figure 6-29 Locker room  designated place of refuge 
Figure 6-30 School hallway 
Figure 6-31 Unsafe corridor place of refuge in school 
Figure 6-32 Unsafe corridor place of refuge in school 
Figure 6-33 Unsafe corridor place of refuge in school 
Figure 6-34 EIFS wall system torn from studs 
Figure 6-35 Collapsed non-reinforced interior CMU walls in school 
Figure 6-36 Blown off roof and ceiling over interior bathroom 
PRELIMINARY REPORT LIST OF ACRONYMS 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES ix 
List of Acronyms 
ADA Americans with Disabilities Act 
ASCE American Society of Civil Engineers 
ASTM American Society for Testing and Materials 
BOCA Building Officials and Code Administrators, International 
BPAT Building Performance Assessment Team 
CABO Council of American Building Officials 
COHBA Central Oklahoma Home Builders Association 
CMU Concrete Masonry Unit 
EIFS Exterior Insulating Finishing System 
EPDM Ethylene Propylene Diene Monomer 
EPS Expanded Polystrene System 
FEMA Federal Emergency Management Agency 
GIS Geographic Information System 
HUD Department of Urban Development 
HVAC Heating, Ventilation, and Air Conditioning 
ICBO International Conference of Building Officials 
MCHSS Manufactured Home Construction and Safety Standards 
NBC National Building Code 
NCSBCS National Conference of States on Building Codes and Standards 
NFIP National Flood Insurance Program 
NFPA National Fire Protection Association 
NOAA National Oceanic Atmospheric Administration 
NSSL National Severe Storms Laboratory 
OSB Oriented Strand Board 
SBCCI Southern Building Code Congress International 
UBC Uniform Building Code 
URM Un-reinforced Masonry
LIST OF ACRONYMS PRELIMINARY REPORT 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES x
PRELIMINARY REPORT EXECUTIVE SUMMARY 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES xi 
Executive Summary 
On the evening of May 3, 1999, an outbreak of tornadoes tore through parts of Oklahoma and Kansas, in 
areas that are considered part of "Tornado Alley", leveling entire neighborhoods and killing 49 people. 
The storms that spawned the tornadoes moved slowly, contributing to the development and 
redevelopment of individual tornadoes over an extended period of time. 
On May 10, the Federal Emergency Management Agency's (FEMAs) Mitgation Directorate deployed a 
Building Performance Assessment Team (BPAT) to Oklahoma and Kansas to assess damage caused by 
the tornadoes. The team was composed of national experts including FEMA Headquarters and Regional 
Office engineers and staff; a meteorologist; architects; planners; wind engineers; structural engineers; and 
forensic engineers. The mission of the BPAT was to assess the performance of buildings affected by the 
tornadoes, investigate losses, and describe the lessons learned. This report presents the BPATs 
observations, conclusions, and recommendations, which are intended to help communities, businesses, 
and individuals reduce future injuries and the loss of life and property resulting from tornadoes and other 
high-wind events. It is not the intent of this report to reclassify the strength of the May 3 tornadoes or the 
ratings of the damage observed, or to debate the magnitude of the wind speeds associated with those 
tornadoes. Rather, the intent is to clearly define some basic concepts associated with tornadoes and 
tornado damage that will be referred to throughout this report. 
The observations, conclusions, and recommendations in this report are grouped to address issues 
concerning (1) residential property protection, (2) non-residential property protection, and (3) personal 
protection and sheltering. The BPATs findings are correlated with the Fujita damage scale, which ranks 
tornadoes according to the damage they cause, and general tornado intensity (Table 1-1). 
Tornadoes are extremely complex wind events that cause damage ranging from minimal or minor to 
absolute devastation. For the purposes of this report, tornado intensity is simplified and referred to by 
three categories: moderate, severe, and violent. In a violent tornado, the most severe damage occurs. 
Typically, all buildings are destroyed and trees are uprooted, debarked, and splintered. In a severe 
tornado, buildings may also be destroyed, but others may suffer less severe damage, such as the loss of 
exterior walls, the roof structure, or both. Even when buildings in this area lose their exterior walls and 
roofs, interior rooms may survive. In moderate tornadoes, damage to buildings primarily affects roofs and 
windows. Roof damage ranges from loss of the entire roof structure to the loss of all or part of the roof 
sheathing or roof coverings. Typically, many of the windows in buildings will be broken by wind-borne 
debris. 
During the field investigation, the BPAT investigated buildings to identify successes and failures that 
occurred during the tornadoes. Building failures were identified as being directly struck by the vortex or 
core of the tornado, affected by winds outside the vortex of the tornado, or out on the extreme edge or 
periphery of the tornado path. Considerable damage to all types of structures throughout Oklahoma and 
Kansas was observed. Failures occurred when extreme winds produced forces on the buildings that they 
were not designed to withstand. Failures also occurred when wind-borne debris penetrated the building 
envelope, allowing wind inside the building that again produced forces on the buildings that they were not 
designed to withstand. Additional failures observed were attributed to improper construction techniques
EXECUTIVE SUMMARY PRELIMINARY REPORT 
xii BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 
and poor selection of construction materials. It was a goal of the BPAT to determine if any of the damage 
observed to both residential and non-residential buildings was preventable. 
Most residential construction in Oklahoma and Kansas is currently required to be designed per the 1995 
Council of American Building Officials (CABO) One and Two Family Dwelling Code. Although some 
amendments have been adopted by local municipalities, this code does not incorporate wind speed design 
parameters used by the newer 1997 Uniform Building Code (UBC) and 1996 National Building Code 
(NBC). Furthermore, engineering standards such as the American Society of Civil Engineers (ASCE) 7- 
95 and 7-98 design standard provide better structural and non-structural design guidance for wind loads 
than these newer codes. Although designing for tornadoes is not specifically addressed in any of these 
newer codes or standards, constructing residential homes to these codes and standards would improve the 
strength of the built environment. The BPAT concluded that building to these codes and standards would 
have led to reduced or minimized damage in areas that were affected by the inflow winds of all tornadoes 
and reduced the damage observed where moderate tornadoes impacted residential construction. 
The BPAT concluded that the best means to reduce loss of life and minimize personal injury during any 
tornadic event is to take refuge in specifically designed tornado shelters. Although improved construction 
may reduce damage to buildings and provide for safer buildings, an engineered shelter is the best means 
of providing individuals near absolute protection. 
The BPAT developed recommendations for reducing future tornado damage to property and providing 
personal protection. Broad recommendations include the following: 
 Proper construction techniques and materials must be incorporated into the construction of residential buildings to 
reduce their vulnerability to damage during extreme wind events. Existing construction techniques proven to 
minimize damage in wind-prone areas are not always being utilized in areas that are subject to tornadoes. 
 Construction should be regulated and inspected to ensure that residential buildings meet the most current building 
code requirements, including those regarding structural seismic issues. 
 For engineered buildings, the engineer should review connections to ensure adequate capacity for moderate to 
severe uplift and lateral loads that may be in excess of loads based on the building codes currently in effect. 
 Cities and appropriate local governments should adopt the 1997 UBC or 1996 NBC as the model building 
codes. 
 Cities and appropriate local governments not already using the 1995 CABO One- and Two-Family Dwelling 
Code should do so immediately. 
 The International Building Code (IBC) and the International Residential Code (IRC) should be adopted upon 
their release in 2000. 
 Shelters are the best means of providing near absolute protection for individuals who are attempting to take 
refuge during a tornado. 
 All shelters should be designed and constructed in accordance with either FEMA 320 or The National 
Performance Criteria for Tornado Shelters
DRAFT PRELIMINARY EXECUTIVE SUMMARY 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES xiii
EXECUTIVE SUMMARY 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 
Executive Summary 
On the evening of May 3, 1999, an outbreak of tornadoes tore through parts 
of Oklahoma and Kansas, in areas that are considered part of Tornado 
Alley, leveling entire neighborhoods and killing 49 people. The storms that 
spawned the tornadoes moved slowly, contributing to the development and 
redevelopment of individual tornadoes over an extended period of time. 
On May 10, 1999, the Federal Emergency Management Agencys (FEMAs) 
Mitigation Directorate deployed a Building Performance Assessment Team 
(BPAT) to Oklahoma and Kansas to assess damage caused by the tornadoes. 
The BPAT was composed of national experts including FEMA Headquarters 
and Regional Office engineers and staff; a meteorologist; architects; 
planners; wind engineers; structural engineers; and forensic engineers. 
Members of the BPAT are presented in Appendix A. The mission of the BPAT 
was to assess the performance of buildings affected by the tornadoes, investigate 
losses, and describe the lessons learned. This report presents the BPATs 
observations, conclusions, and recommendations, which are intended to help 
communities, businesses, and individuals reduce future injuries and the loss of 
life and property resulting from tornadoes and other high-wind events. The 
observations, conclusions, and recommendations in this report are grouped to 
address issues concerning residential property protection, non-residential 
property protection, and personal protection and sheltering. 
The BPATs findings are correlated with the Fujita damage scale, which 
ranks tornadoes according to the damage they cause, and general tornado 
intensity (Tables 1-1 and 2-1). It is not the intent of this report to reclassify 
the strength of the May 3 tornadoes or the ratings of the damage observed, 
or to debate the magnitude of the wind speeds associated with those tornadoes. 
Tornadoes are extremely complex wind events that cause damage ranging 
from minimal or minor to absolute devastation. For the purposes of this 
report, tornado intensity is simplified and referred to by three categories: 
violent, strong, and weak. The greatest damage occurs in a violent tornado. 
Typically, all buildings are destroyed and trees are uprooted, debarked, and 
splintered. In a strong tornado, some buildings may be destroyed, but most 
suffer less damage, such as the loss of exterior walls, the roof structure, or 
both. Even when buildings affected by a strong tornado lose their exterior 
XV 
Strong
Weak 
Violent
FEDERAL EMERGENCY MANAGEMENT AGENCY 
EXECUTIVE SUMMARY 
XVI 
walls and roofs, interior rooms may survive. In weak tornadoes, damage to 
buildings primarily affects roofs and windows. Roof damage ranges from loss 
of the entire roof structure to the loss of all or part of the roof sheathing or 
roof coverings. Typically, many of the windows in buildings will be broken by 
windborne debris. Weak tornadoes can often cause significant damage to 
manufactured housing. 
The BPAT investigated buildings to identify successes and failures that 
occurred during the tornadoes. Buildings were classified as being directly 
struck by the vortex (i.e., core) of a tornado, affected by winds outside (but 
near) the vortex of a tornado, or out on the extreme edge (i.e., periphery) of 
a tornado path. Few successes were observed by the BPAT. Successes 
consisted of the utilization of engineered shelters within a home or commercial 
building or voluntary utilization of known construction techniques that 
strengthened the structural system of a building. Considerable damage 
occurred to all types of structures throughout the areas observed in Oklahoma 
and Kansas. Failures occurred when extreme winds produced forces 
on the buildings that they were not designed to withstand. Failures also 
occurred when windborne debris penetrated the building envelope, allowing 
wind inside the building that again produced forces on the buildings that they 
were not designed to withstand. Additional failures observed were attributed 
to the construction techniques used, the selection of construction materials, 
the fasteners used, and the design of, or lack of, connections. It was a goal 
of the BPAT to determine if the damage observed to both residential and nonresidential 
buildings was preventable. 
Most residential construction in Oklahoma and Kansas is currently required to 
be designed per the 1995 Council of American Building Officials (CABO) 
One- and Two-Family Dwelling Code. Although some amendments have been 
adopted by local municipalities, this code does not incorporate wind speed 
design parameters used by the newer 1997 Uniform Building Code (UBC) 
and 1996 National Building Code (NBC). Furthermore, engineering standards 
such as the American Society of Civil Engineers (ASCE) 7-98 design 
standard provide better guidance for determining design wind loads than 
these newer codes. Although designing for tornadoes is not specifically 
addressed in any of these newer codes or standards, constructing homes to 
these codes and standards would improve the strength of the built environment. 
The BPAT concluded that buildings constructed to these newer codes 
and standards would have experienced less damage in areas that were 
affected by the inflow winds of all tornadoes and reduced the damage where 
weak tornado vortices directly affected buildings. 
The BPAT concluded that the best means to reduce loss of life and minimize 
personal injury during any tornadic event is to take refuge in specifically 
designed tornado shelters. Although improved construction may reduce 
damage to buildings and provide for safer buildings, an engineered shelter is 
the best means of providing individuals near absolute protection.
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 
Executive Summary EXECUTIVE SUMMARY 
XVII 
The BPAT developed recommendations for reducing future tornado damage 
to property and providing personal protection. Broad recommendations 
include: 
n Building Code Recommendations. Neither building codes nor 
engineering standards explicitly address design for tornadoes. 
However, designing to the wind loads in ASCE 7-98 can 
reduce damages from both weak tornadoes and in outlying 
areas damaged by strong and violent tornadoes. The model 
building codes consider these latest engineering standards, 
such as ASCE 7, when model building codes are revised, 
usually on a 3-year cycle. In order that design and construction 
practices reflect our improved understanding of high 
winds, jurisdictions having authority should consider the 
following alternatives in amending their current building code 
or in adopting new building codes: 
n Adopt the International Building Code (IBC) and the 
International Residential Code (IRC) upon their 
expected release in February 2000. 
n As an interim step to adopting the IBC and IRC, 
adopt the 1997 UBC, the 1997 Standard Building 
Code, (SBC), or the 1996 NBC as the building code 
until the IBC or IRC can be adopted. To further 
improve the wind resistance of buildings, adopt an 
amendment that requires the use of ASCE 7-98 to 
calculate wind loads. 
n As an interim step to adopting the IRC, State and 
local governments should adopt the 1995 edition of 
the CABO One- and Two-Family Dwelling Code for 
jurisdictions using previous editions of this code or 
having no residential code in place. This will provide 
some guidance for designing for wind loads. 
n Communities should consider the need for adopting ordinances 
and regulations that promote disaster-resistant 
communities by incorporating tornado shelters into new 
construction and communities. 
n The Federal Government (HUD) should review its standards 
and enforcement program in an effort to improve the performance 
of manufactured homes in moderately high wind 
events, such as in inflow areas of all tornadoes and the tracks 
of weak tornadoes. Specifically, the capacity of anchoring and 
strapping equipment and systems needs to be evaluated to 
eliminate the discontinuity between the Federal standard and 
the State and local installation and enforcement process.
FEDERAL EMERGENCY MANAGEMENT AGENCY 
EXECUTIVE SUMMARY 
XVIII 
n Consideration should be given to permanently connecting the 
manufactured home unit to its foundation. The BPAT 
observed newer double-wide manufactured houses on 
permanent foundations and did not see significant differences 
in damage between these manufactured homes on 
permanent foundations and conventionally built houses. 
Double-wide manufactured housing on permanent foundations 
performed better than both double-wide and single units 
on non-permanent foundations. 
n Construction techniques and materials to provide a continuous 
load path for wind loads should be incorporated into the 
construction of buildings, including houses. This will reduce 
their vulnerability to damages during extreme wind events. 
There are existing proven construction practices to minimize 
damages in other wind-prone areas (hurricane areas) of the 
country. 
n Construction should be regulated and better inspected to 
ensure that buildings (including residences) meet current 
building code requirements. A lack of compliance with 
building codes was observed in many of the damaged 
buildings. 
n Garage doors are an extremely important residential building 
component. Failure of these doors led to catastrophic 
progressive failures of primary structural systems that could 
have been avoided. New garage doors should be installed 
with improved resistance to high wind loads. 
n Where new doors are not installed, retrofits should be made 
to improve the wind resistance of existing garage doors, 
particularly double-wide garage doors. These retrofits and 
new doors will better resist wind forces and should reduce 
the roof and wall damage that was observed in homes that 
experienced garage door failures. 
n Architectural features should be appropriately designed, 
manufactured, and installed to resist wind loads and to 
minimize the creation of windborne debris. To accomplish 
this, the local community may want to further regulate these 
features to ensure a reduction in potential debris materials. 
n The brick masonry industry should consider re-evaluating 
attachment criteria of masonry, specifically regarding 
product usage. Greater emphasis should be given to code 
compliance for the bond between the mortar and brick tie, 
the mortar and the brick, and the spacing of brick ties.
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 
Executive Summary EXECUTIVE SUMMARY 
n In areas subjected to high winds from either tornadoes or 
hurricanes, masonry chimneys should have continuous 
vertical reinforcing steel placed in the corners to provide 
greater resistance to wind loads. This reinforcing steel 
should be placed to the requirements set forth in the 1995 
CABO One-and Two- Family Dwelling Code (Requirements 
for Masonry Fireplaces and Chimneys for seismic zones 3 
and 4) or the masonry fireplace provisions of the IRC; 
available in February 2000. 
n Shelters are the best means of providing near absolute 
protection for individuals who are attempting to take refuge 
during a tornado. All shelters should be designed and constructed 
in accordance with either FEMA 320: Taking Shelter 
From the Storm or the National Performance Criteria For 
Tornado Shelters (Appendixes C and D). All shelters 
should provide access to persons with disabilities as necessary 
and in conformance with the Americans with Disabilities 
Act (ADA). Local officials should monitor the installation 
of shelters to ensure that the floors of all shelters are 
located at or above expected flood levels. 
n Manufactured homes typically offer little protection from 
severe wind storms and tornadoes. In the event of such 
storms, occupants of manufactured homes should exit their 
home and seek shelter in storm cellars, basements, or aboveground 
shelters. If shelters are provided in manufactured 
home parks, which is recommended, dispersed shelters, 
which can be accessed in a short time period, are recommended. 
n Prospective occupants of community shelters should be 
acutely alert to storm warnings in order to allow sufficient 
time for the travel distance to the community shelter. Custodians 
of the shelter should be similarly alert so that the 
shelter is unlocked at appropriate times. Community shelters 
should be ADA compliant and the admission rules permanently 
posted (i.e. No Pets Allowed, etc.). 
n Existing essential facilities that offer inadequate protection 
should have shelters retrofitted or a shelter added. New 
essential facilities should be designed with shelters. Interested 
states should form a committee to evaluate the need 
for tornado plans and shelters in essential facilities and other 
establishments serving the public (e.g., schools, hospitals, and 
critical facilities). All facilities for public accommodation 
should have a National Oceanic and Atmospheric Administration 
(NOAA) weather radio in continuous operation. 
XIX
FEDERAL EMERGENCY MANAGEMENT AGENCY 
EXECUTIVE SUMMARY 
XX 
n The installation of laminated glass in essential facilities 
should be considered because of the substantial protection 
that it offers from debris missiles. A recommended standard 
for determining minimum strength of openings with laminated 
glass is to conduct testing, in accordance with ASTM E 
1886, in consideration of the load criteria given in ASTM E 
1996. 
n Fire departments and emergency services agencies should 
make a list of addresses with shelters both above ground and 
below ground. This list will assist post disaster response teams 
and agencies in checking after a tornado to see if people are 
trapped inside their shelters.
CHAPTER 1 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 1-11 
1 Introduction 
1.1 PURPOSE 
The number of tornadoes that occurred on May 3, 1999, in Oklahoma and 
Kansas, their severity, and the level of devastation they caused have not been 
seen in a generation within the United States. One of the missions of the 
Federal Emergency Management Agency (FEMA) that directly supports the 
National Mitigation Strategy is: 
to significantly reduce the risk of loss of life, injuries, economic costs 
and destruction of natural and cultural resources that result from 
natural hazards. 
In response to the disasters caused by the May 3 tornadoes, FEMA deployed 
a Building Performance Assessment Team (BPAT), composed of national 
experts in engineering, architecture, meteorology, and planning, to Oklahoma 
and Kansas. The mission of the BPAT was to assess the performance of 
buildings affected by the tornadoes, investigate losses, and describe the 
lessons learned. This report presents the BPATs observations, conclusions, 
and recommendations, which are intended to help communities, businesses, 
and individuals reduce future injuries and the loss of life and property 
resulting from tornadoes and other high-wind events. 
1.2 TEAM COMPOSITION 
The BPAT included FEMA Headquarters and Regional Office engineers and 
staff; a meteorologist; planners; architects; wind engineers; structural 
engineers; and forensic engineers. The members of the BPAT are listed in the 
appendix of this report. 
1.3 METHODOLOGY 
The FEMA Mitigation Directorate deployed the BPAT to Oklahoma and 
Kansas on May 10, 1999. The team inspected both residential and nonresidential 
buildings, as discussed below. By assessing the performance of 
these buildings, the team was able to develop technical guidance concerning 
new construction and post-tornado reconstruction for state and local 
governments, building owners, architects, engineers, and contractors. 
In addition to assessing building performance, the BPAT: 
 inspected shelter areas in public buildings (e.g., schools, 
churches, day care centers, nursing homes),
CHAPTER 1 PRELIMINARY REPORT 
1-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
 investigated successes and failures of existing shelters 
during the tornadoes, and 
 evaluated existing tornado response plans within buildings 
intended for high occupancy such as schools and private industry 
facilities. 
Field investigations began on May 10 and were conducted through May 18. 
In Oklahoma, inspections were made in Bridge Creek (about 50 miles 
southwest of Oklahoma City); the Oklahoma City metroplex, including the 
suburbs of Moore, Del City, and Midwest City; the Project Impact 
community of Tulsa; and Stroud and Mulhall. In Kansas, inspections were 
made in unincorporated Sedgwick County, the City of Haysville, and 
Wichita, Kansas. 
BPATs frequently conduct aerial assessments of damage areas to gather 
general data on damage sites, acquire aerial photographs of those sites, and 
determine the focus and final composition of the BPAT. For the May 3 
tornado disasters, adequate information was provided to the team by the 
FEMA Disaster Field Offices (DFOs) and by state and local government 
agencies. Therefore, the BPAT did not conduct an aerial assessment of the 
damage areas. 
The BPAT inspected the following types of residential buildings: 
 single- and multi-family, one- to two-story wood-frame houses 
 manufactured and modular homes 
 accessory structures 
Many of the houses inspected in Kansas were constructed on basement or 
crawlspace foundations; most of the houses inspected in Oklahoma were 
constructed on slab-on-grade foundations. From its observations, the BPAT 
formed conclusions concerning the structural performance of residential 
buildings exposed to the May 3 tornadoes. The BPAT also formed 
conclusions regarding exterior architectural systems; those conclusions focus 
on roof coverings, brick veneer and other siding materials, windows, garage 
doors, and masonry chimneys. 
The non-residential building types observed included the following: 
 tilt-up pre-cast concrete walls with steel joists 
 load-bearing masonry walls with steel joists 
 load-bearing masonry with pre-cast concrete hollow-core floor 
and roof slabs 
 pre-engineered metal buildings (light steel frames) 
 buildings constructed of laminated wood arches with wood 
framing 
 buildings with masonry veneer and pre-cast concrete floors
PRELIMINARY REPORT INTRODUCTION CHAPTER 1 
PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 1-3 
 industrial plants 
 a regional shopping outlet mall 
 public use buildings inspected include a hospital, nursing homes, 
day care centers, hotels, schools 
Other important issues such as windborne debris (missiles), personal 
protection, and sheltering were investigated and are discussed in individual 
sections of this report. 
FEMA encouraged the participation of state and county government officials 
and locally based experts in the assessment process. Their involvement was 
critical because it helped to: 
 ensure that state and local building code and other requirements 
were properly interpreted, 
 increase the likelihood that local construction practices were 
fully appreciated and understood, 
 establish positive relationships among Federal, state, and local 
governments and the private sector, and 
 encourage the development of recommendations that were both 
economically and technically realistic. 
Under this premise, the BPAT met with local government officials upon 
arriving in Oklahoma and Kansas to partner in the overview and 
identification of damage areas. Team members were briefed by staff 
members of the FEMA regional DFOs and representatives of state, county, 
and local government agencies on the extent and types of damage. GIS maps 
were provided and reviewed in order to select field investigation sites and 
establish an itinerary (Figure 1-1).
CHAPTER 1 PRELIMINARY REPORT 
1-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 1-1: BPAT meeting 
with State of Kansas and 
local government officials 
in Wichita, Kansas. 
FIGURE 1-2: Meeting with 
local fire official in 
Midwest City, Oklahoma. 
Photo to be added later.
PRELIMINARY REPORT INTRODUCTION CHAPTER 1 
PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 1-5 
Collectively, the team spent over 2,000 hours in the field conducting site 
investigations and inspecting damage. Documentation of observations made 
during the site visits included field notes and photographs. The BPATs 
mission did not include recording the numbers of buildings damaged by the 
tornadoes, determining the frequency of specific types of damage, or 
collecting data that could serve as the basis of statistical analysis. 
1.4 PRESENTATION OF FINDINGS 
The observations, conclusions, and recommendations in this report are 
grouped to address issues concerning (1) residential property protection, (2) 
non-residential property protection, and (3) personal protection and 
sheltering. 
Table 1-1 correlates the BPATs findings with the Fujita damage scale 
(which ranks tornadoes according to the damage they cause) and general 
tornado intensity in terms that will be used throughout this report. For the 
purposes of this report, tornado intensity is referred to by the three categories 
listed in Table 1-1: moderate, severe, and violent. When appropriate, damage 
observations in this report are presented in terms of the Fujita scale ratings. 
Table 1-1 is intended to help the reader better understand tornadoes, the 
damage associated with them, and how mitigation efforts can be made to 
reduce the property damage and loss of life caused by tornadoes. Further 
discussions regarding the makeup of a tornado, the damage associated with 
the winds of a tornadic event and the Fujita scale are presented in Chapter 2. 
This report is intended to provide information related to mitigation efforts 
that communities, businesses, and individuals can undertake to reduce future 
injuries and the loss of life and property. It is not the intent of this report to 
re-classify the strength of the May 3 tornadoes or the ratings of the damage 
observed, or to debate the magnitude of the wind speeds associated with 
those tornadoes. The Fujita scale ratings mentioned in this report are based 
on preliminary ratings issued by the local National Weather Service (NWS) 
offices in Oklahoma and Kansas after the tornado outbreaks. The National 
Severe Storms Laboratory (NSSL) in Norman, Oklahoma, provided 
additional preliminary information regarding the tornadoes.
CHAPTER 1 PRELIMINARY REPORT 
1-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
To attain 
near 
absolute 
protection, 
a shelter 
should be 
constructed 
within or 
adjacent to a 
home, office, 
or business 
that is built 
in 
accordance 
with FEMA 
Pub. No. 320 
or the 
National 
Performance 
Criteria for 
Tornado 
Shelters. 
Must have a 
structure or 
room 
specifically 
engineered for 
extreme wind 
protection. 
Additional 
strengthening 
of building 
structure and 
envelope may 
reduce risk. 
Constructing 
building 
envelope to 
newer building 
codes and 
standards 
minimizes risk 
and injury. 
Protecting 
entire 
buildings is 
uneconomical 
and 
impractical. 
Voluntary 
retrofits 
strengthen 
homes and 
buildings 
with existing 
technology. 
Constructing 
to newer 
building 
codes and 
standards 
strengthens 
buildings. 
large, 
medium, and 
small airborne 
and 
rolling debris 
medium and 
small airborne 
and 
rolling debris 
small airborne 
and 
rolling debris 
 
	 
	 
 
 
 
 
 
 
TABLE 1-1 
The BPAT Damage Assessment Table 
 
	 
	
Chapter 2 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 2-1 
2 Background on 
Tornadoes and History 
of the Storm 
This chapter presents both a history of the May 3, 1999, tornadoes as they 
affected Oklahoma and Kansas and insight into the interaction between a 
tornado and a populated area. The Fujita scale for classifying tornado 
damage is presented in this chapter. A discussion on tornadoes and tornado 
damage is also included. 
2.1 THE FUJITA SCALE AND TORNADO PROBABILITY 
Of the 1,000 or so tornadoes reported each year in the United States, only a 
few are rated as violent events (F4 or F5 on the Fujita scale). The Fujita 
scale (Table 2-1), which was created by the late Tetsuya Theodore Fujita, 
University of Chicago, categorizes tornado severity based on damage 
observed and not on recorded wind speeds. Wind speeds have been 
associated with the damage descriptions of the Fujita scale, but the accuracy 
of these wind speeds is limited in that they are only estimates that best 
represent the observed damage and are not calibrated wind speeds. 
Although the number of violent tornadoes varies considerably from year to 
year, the average during the period from 1980 to 1989, was about 10 per 
year. On average, only one or two of these per year were rated F5. Historical 
data indicate that the number of tornado reports have been rising, in general, 
since tornado data began to be collected in the early 1900s. However, the 
data suggest that a long-term increase in the frequency of tornadoes is 
unlikely. Rather, increased reporting of tornadic events has caused the 
numbers of documented tornadoes to rise.
CHAPTER 2 PRELIMINARY REPORT 
2-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
F-0: (Light Damage) Chimneys are damaged, tree branches are broken, 
shallow-rooted trees are toppled. 
F-1: (Moderate Damage) Roof surfaces are peeled off, windows are broken, 
some tree trunks are snapped, unanchored manufacture homes are 
overturned, attached garages may be destroyed. 
F-2: (Considerable Damage) Roof structures are damaged, manufactured 
homes are destroyed, debris becomes airborne (missiles are generated), large 
trees are snapped or uprooted. 
F-3: (Severe Damage) Roofs and some walls torn from structures, some 
small buildings are destroyed, non-reinforced masonry buildings are 
destroyed, most trees in forest are uprooted. 
F-4: (Devastating Damage) Well-constructed houses are destroyed, some 
structures are lifted from foundations and blown some distance, cars are 
blown some distance, large debris becomes airborne. 
F-5: (Incredible Damage) Strong frame houses are lifted from foundations, 
reinforced concrete structures are damaged, automobile-sized debris becomes 
airborne, trees are completely debarked. 
Even today, tornadoes are unlikely to be rated as violent unless they interact 
with the built environment, so the actual numbers of violent tornadoes per 
year are probably somewhat larger than the reporting statistics suggest. 
According to calculations performed by the National Severe Storms 
Laboratory (NSSL), the most recent data (1980-1994) indicate that the within 
the regions of the United States with the highest frequency of tornado 
occurrence, an area of 2,500 square miles should expect about one tornado 
(of any intensity) per year (Figure 2-1). In other words, the chance of any 
particular square mile experiencing a tornado in a given year, within the 
designated area of Tornado Alley, is about one in 2,500. The map in Figure 
2-1 indicates by color band the probability of tornado occurrence in the 
continental United States during any given year.
PRELIMINARY REPORT BACKGROUND ON TORNADOES AND HISTORY OF THE STORM CHAPTER 2 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 2-3 
FIGURE 2-1: Annual probability of tornado occurrence in the continental United States. 
If violent tornadoes correspond to the top 2 percent of all tornadoes, an area 
of 2,500 square miles in the area of peak frequency would be expected to 
experience a violent tornado only about once every 50 years. Alternatively, a 
given square miles chances of being hit in a given year by a violent tornado 
are about one in 125,000. 
Fujita estimated that the total area within a violent tornados path that 
actually experiences damage associated with the violent wind speeds (i.e., the 
area directly impacted or struck by the tornado vortex) is only on the order of 
1 percent of the total area affected. That means that a given square mile in 
Tornado Alley has only about 1 chance in 12,500,000 of being hit by the 
winds of the vortex of a violent tornado. Given that our knowledge of actual 
tornado occurrences is not complete or perfectly accurate, the true chances of 
being hit by a violent tornado might vary from the estimates given here. 
However, the NSSL believes these numbers to be broadly representative of 
the probabilities of being affected by a violent F4/F5 tornado.
CHAPTER 2 PRELIMINARY REPORT 
2-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
2.2 TORNADOES AND ASSOCIATED DAMAGE 
Tornadoes are extremely complex wind events that cause damage ranging 
from minimal or minor to absolute devastation. Providing a complete and 
thorough explanation or definition of tornadoes and tornado damage is not 
the intent of this section. Rather, the intent is to clearly define some basic 
concepts associated with tornadoes and tornado damage that will be referred 
to throughout this report. 
In a simplified tornado model, there are three regions of wind: 
1. Near the surface, close to the core or vortex of the tornado. In 
this region, the winds are complicated and include the peak lowlevel 
wind speeds, but are dominated by the tornados strong 
rotation. It is in this region that strong upward motions occur that 
carry debris upward, as well as around the tornado. 
2. Near the surface, away from the tornados core or vortex. In this 
region, the flow is dominated by inflow to the tornado. The 
inflow can be complicated and is often concentrated into 
relatively narrow swaths of strong inflow rather than a uniform 
flow into the tornados core circulation. 
3. Above the surface, typically above the tops of most structures, 
the flow tends to become very nearly circular. 
In an actual tornado, the diameter of the core or vortex circulation can 
change with time, so it is impossible to say precisely where one region of the 
tornados flow ends and another begins. Also, the visible funnel cloud 
associated with and typically labeled the vortex of a tornado is not always the 
edge of the strong extreme winds. Rather, the visible funnel cloud boundary 
is determined by the temperature and moisture content of the tornados 
inflowing air. The highest wind speeds in a tornado occur at a radius 
measured from the tornado core that can be larger than the visible funnel 
clouds radius. It is important to remember that a tornados wind speeds 
cannot be determined just by looking at the tornado. 
Figure 2-2 shows the types of damage that can be caused by a violent tornado 
similar to the one that passed through the Oklahoma City Metroplex on May 
3, 1999. In general, as shown in the figure, the severity of the damage varies 
with distance from the vortex. Note, however, that the rotation of a tornado 
can cause winds flowing into the vortex on one side to be greater than those 
on other sides. As a result, it is not uncommon for the area of damage on one 
side of the tornado to be more extensive. Figure 2-2 reflects this situation. 
In a violent tornado, the most severe damage occurs in the area directly 
affected by the vortex (the area shaded dark red [dark gray] in Figure 2-2).
PRELIMINARY REPORT BACKGROUND ON TORNADOES AND HISTORY OF THE STORM CHAPTER 2 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 2-5 
Typically, in this area, all buildings are destroyed and trees are uprooted, 
debarked, and splintered. In the immediately adjacent area, shaded orange 
[medium gray] in the figure, buildings may also be destroyed, but others may 
suffer less severe damage, such as the loss of exterior walls, the roof 
structure, or both. Even when buildings in this area lose their exterior walls 
and roof, interior rooms may survive. In the outer portion of this area, further 
from the vortex, damage to buildings affects primarily roofs and windows. 
Roof damage ranges from loss of the entire roof structure to the loss of all or 
part of the roof sheathing or roof coverings. Typically, most or all of the 
windows in buildings in this area will be broken by windborne debris. In the 
area shaded yellow [light gray], damage is again primarily to roofs and 
windows. However, roof damage is lighter, and although windborne debris 
damage still occurs here, not all windows are broken. Damage to buildings in 
the outer fringe of this area is even lighter. Beyond this area, where the figure 
shows blue shading, buildings typically suffer no damage.
CHAPTER 2 PRELIMINARY REPORT 
2-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
2.3 
Figure 2-2: Impact of a
PRELIMINARY REPORT BACKGROUND ON TORNADOES AND HISTORY OF THE STORM CHAPTER 2 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 2-7 
violent tornado.
CHAPTER 2 PRELIMINARY REPORT 
2-8 FEDERAL EMERGENCY MANAGEMENT AGENCY 
2.3 BACKGROUND OF THE EVENT 
On May 3, 1999, a widespread outbreak of tornadoes occurred in the south 
central United States, primarily in Oklahoma and Kansas. A strong upperlevel 
storm system moved eastward towards the southern Plains from the 
Rockies during the day. Winds aloft over Kansas and Oklahoma intensified 
as the upper-level system approached. Atmospheric conditions indicated that 
rotating thunderstorms known as supercells were quite likely. The flow of 
moisture northward from the Gulf of Mexico, and daytime heating that 
pushed ambient surface temperatures up to at least 80 degrees, combined to 
produce an extremely unstable atmosphere across the southern Plains. In 
situations like this, forecasters are usually able to predict the tornado threat 
with reasonable accuracy, as opposed to more isolated tornado events, for 
which favorable conditions may not be so obvious. See the National Oceanic 
and Atmospheric Administration's (NOAAs) Service Assessment for 
details of forecasting performance in this event. The tornado outbreak was 
anticipated and, once supercells were detected by the WSR-88D radar, the 
tornado warnings from the NWS were accurate and timely, the first being 
issued at 4:47 p.m. (all times Central Daylight Time [CDT]). 
The preliminary count of tornadoes that occurred in this outbreak is 67, but 
this number may change during the analysis of all the data, which will take 
many months. Within this outbreak, there were four violent (F4 or F5) 
tornadoes according to preliminary surveys performed by the NWS. Figure 
2-4 shows the outbreaks in Oklahoma; Figure 2-7 shows the outbreaks in 
Kansas.
PRELIMINARY REPORT BACKGROUND ON TORNADOES AND HISTORY OF THE STORM CHAPTER 2 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 2-9 
FIGURE 2-4: Preliminary outbreak map of tornadoes in Oklahoma that struck on May 3, 1999. 
Courtesy of the National Weather Service. 
The tornado that caused the greatest damage and that had the greatest effect 
on residential areas was the reported F5 tornado that struck the south side of 
the Oklahoma City Metroplex. Its source was a supercell thunderstorm that 
had spawned several tornadoes earlier (Fig. 2-5). This tornado had a track 38 
miles long and lasted more than an hour, from 6:23 to 7:50 p.m. The track 
began between the towns of Chickasha and Amber, Oklahoma, southwest of 
Oklahoma City.
CHAPTER 2 PRELIMINARY REPORT 
2-10 FEDERAL EMERGENCY MANAGEMENT AGENCY 
From its touchdown point, the tornado moved northeastward, nearly parallel 
to I-44, towards Oklahoma City, hitting the rural town of Bridge Creek, 
Oklahoma, at 6:55 p.m. and crossing I-44 at about 7:05 p.m. near the South 
Canadian River. From there, it moved through several small subdivisions 
before slamming into the city of Moore, Oklahoma, and crossing I-35 near an 
overpass for Shields Boulevard. Continuing through a less densely populated 
area, the tornado crossed I-240 at about 7:35 p.m., began a wide left turn to 
travel along a north-northeast path that took it into Del City, Oklahoma, 
skirted Tinker Air Force Base, and then moved into Midwest City, 
Oklahoma, where it finally dissipated. 
Preliminary analyses by the NWS in Norman, Oklahoma, indicated that this 
single tornado damaged or destroyed more than 8,000 homes, and was 
responsible for 41 fatalities and approximately 800 injuries. Early damage 
estimates are on the order of at least $750 million. There has not been a 
tornadic event even approaching this magnitude since the F4 tornado that 
devastated Wichita Falls, Texas, on April 10, 1979. 
Figure 2-6 presents four WSR-88D images of the reported F5 tornado as it 
tracked from Moore to Midwest City. Figures 2-6a and 2-6b are actual radar 
cross-sections of the tornado taken at the location identified by the white line 
in Figure 2-6c. Figure 2-6a represents reflectivity, while Figure 2-5b 
represents storm-relative radial velocity. These images were recorded at 7:32 
p.m. on May 3, 1999. Horizontal and vertical scales are in kilometers. The 
vortex walls and the eye are delineated by different color patterns that relate 
to debris in the vortex and the wind speeds within the vortex itself. 
FIGURE 2-5: Radar 
reflectivity map at 6:56 
p.m., showing hook echo 
(circled). A hook echo is 
a structure associated 
with supercell storms. In 
many instances, the 
radar echo shows this 
type of structure when 
tornadoes are present. 
Courtesy of the National 
Severe Storms 
Laboratory.
PRELIMINARY REPORT BACKGROUND ON TORNADOES AND HISTORY OF THE STORM CHAPTER 2 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 2-11 
Figure 2-6: WSR-88D radar cross-section through the reported F5 tornado located approximately 
halfway between Moore and Midwest City, showing the debris and an apparent eye. 
Another violent tornado (rated F4) struck the small town of Mulhall, 
Oklahoma, which is located about 50 miles north of Oklahoma City. This 
tornado was produced by a different supercell storm, to the north of the 
Oklahoma City Metroplex supercell. This second supercell produced 
approximately 19 tornadoes. The F4 tornado that struck Mulhall originated in 
open country, northwest of the town of Cashion, Oklahoma, at about 9:25 
p.m. It spent the majority of its life in relatively unpopulated open country, 
hitting Mulhall around 10:15 p.m., late in its life cycle. Most of the homes 
and businesses in the Mulhall downtown area, including a public school, a 
post office, and many historic buildings, were damaged or destroyed. There 
were no fatalities recorded in Mulhall. However, the tornado was responsible 
for two fatalities; one fatality in both Logan and Payne Counties. 
Fig 2-6a Fig 2-6b 
Fig 2-6c 
Tornado 
Vortex 
Tornado 
Vortex
CHAPTER 2 PRELIMINARY REPORT 
2-12 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Dover, Oklahoma, was hit by a violent F4 tornado around 9:20 p.m. from 
another supercell that produced a family of tornadoes. This tornado was 
responsible for one fatality. The track was not investigated by the BPAT. 
The fourth violent tornado (a reported F4) struck the Town of Haysville, 
Kansas, and the southern portion of the City of Wichita, Kansas (Fig. 2-7) 
and was responsible for 5 fatalities. This tornado began around 8:13 p.m. in 
open country, west of the town of Riverdale, Kansas, in the unincorporated 
areas of Sedgwick County. Moving north-northeastward, close to the Union 
Pacific railroad tracks, the tornado hit Haysville at roughly 8:39 p.m., and 
continued into southern Wichita, crossing I-235, at about 8:44 p.m. It then 
veered to the east-northeast for a few miles, before turning northnortheastward 
again and dissipating in eastern Wichita at about 9:00 p.m. 
The track of this tornado was 24 miles long and extended east-northeastward 
through southern Wichita. The track was similar to that of the deadly tornado 
of April 26, 1991, which hit the Golden Spur Manufactured Home Park in 
Andover, Kansas. The 1991 tornado produced 5 fatalities, more than 100 
serious injuries, and $140 million in damage, according to preliminary 
estimates by the NWS in Wichita, Kansas. 
Among the less violent tornadoes of May 3, were five, including a moderate 
F3 tornado, that struck near the town of Stroud, Oklahoma, around 10:40 
p.m. There were no fatalities, but a regional outlet mall along I-44 in Stroud 
was destroyed, and the roof covering on a hospital in the town was blown 
off. 
A moderate tornado entered Tulsa, Oklahoma, in the southwest 
neighborhood of Sapulpa, where it destroyed or heavily damaged several 
manufactured homes and site built structures. The tornado moved northeast 
to the Mountain Manor neighborhood, where it damaged roofs and uprooted 
trees. The roof at Remington School was extensively damaged, and several 
industrial and commercial structures on the south side of I-44 experienced 
roof and siding damage. There were no fatalities, but the Carbondale 
Assembly of God Church, on the north side of I-44, suffered significant 
structural damage.
PRELIMINARY REPORT BACKGROUND ON TORNADOES AND HISTORY OF THE STORM CHAPTER 2 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 2-13 
FIGURE 2-7: Map of tornadoes in Kansas that struck on May 3, 1999. Courtesy of the National Oceanic 
and Atmospheric Administration.
CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-1 
3 General Assessment 
and Characterization 
of Damage 
The general types of damage the BPAT observed as a result of the May3 
tornadoes in Oklahoma and Kansas are discussed below. As a result of the 
site investigations and general field observations, important issues such 
property protection, personal protection, and sheltering were identified. A 
more detailed discussion of these issues may be found in Chapters 4,5,and 6 
of this report. 
3.1 PROPERTY PROTECTION 
During the field investigation, the BPAT investigated buildings to identify 
success and failures that occurred during the tornadoes. Building failures 
were identified as being directly struck by the tornado, affected by winds 
outside the vortex of the tornado, or out on the extreme edge of the tornado 
path. Considerable damage to all types of structures throughout Oklahoma 
and Kansas was observed. Failures occurred when extreme winds produced 
forces on the buildings that they were not designed to withstand. Failures 
also occurred when windborne debris penetrated the building envelope 
allowing wind inside the building that again produced forces on the buildings 
that they were not designed to withstand. However, other failures observed 
were attributed to poor construction, improper construction techniques, and 
poor selection of construction materials. It was a goal of the BPAT to 
determine if any of the damage observed to both residential and nonresidential 
buildings was preventable. 
3.1.1 Overview Of Buildings Evaluated 
The damage assessment of buildings was divided into residential and nonresidential 
sections. Specifically, the residential buildings were categorized 
into single family housing, multi-family housing and manufactured and 
modular housing. The non-residential buildings were categorized into the 
various engineered types of construction observed. These groupings were 
made to focus on the structural performance of each type of building. In both 
cases, important observations were also made concerning exterior 
architectural systems, e.g., roof and wall coverings, windows and doors.
CHAPTER 3 PRELIMINARY REPORT 
3-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
3.1.1.1 Residential Buildings 
The residential buildings were categorized into the various types of 
construction investigated and the structural performance of each type of 
building was observed. The residential buildings investigated by the BPAT 
were: 
 single- and multi-family, one- to two-story wood-frame houses 
 manufactured and modular homes 
 accessory structures 
Residential buildings that were directly struck by the vortex of severe and 
violent tornadoes were substantially or completely destroyed. Residential 
buildings that experienced a direct strike from moderate tornadoes or 
experienced inflow winds from severe and violent tornadoes saw a wide 
range of damage. This damage range observed was broken windows and 
light building damage, partial loss of roofs and walls, separation of buildings 
from their foundations and total roof loss, and only remnants of core rooms 
surviving. 
3.1.1.2 Non-Residential Buildings 
The non-residential buildings were categorized into the various engineered 
types of construction investigated focusing on the structural performance of 
each type of building. The non-residential buildings investigated include: 
 tilt-up pre-cast concrete walls with steel joists 
 load-bearing masonry walls with steel joists 
 load-bearing masonry walls with pre-cast concrete hollow core 
floors and roof slabs 
 steel frame 
 steel frame with masonry infill walls 
The non-residential buildings investigated by the BPAT were typically 
designed by a design professional and therefore the non-residential buildings 
that were damaged by the tornadoes experienced different damage from the 
same tornadoes that damaged residential buildings. Non residential buildings 
that were directly struck by the vortex of severe and violent tornadoes were 
substantially damaged or destroyed, however, they were typically not 
reduced to rubble like the residential buildings. Non-residential buildings that 
experienced a direct strike from moderate tornadoes or experienced inflow 
winds from severe and violent tornadoes saw a wide range of damage. This 
damage range observed was broken windows and light building damage, 
partial loss of roof and wall coverings, partial loss of roof and wall systems, 
complete roof loss, and partial upper level damage with minimal lower level 
damage on multi-level buildings.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-3 
3.1.2 Load Path and Increased Loads 
Site visits in both Oklahoma and Kansas of wind-induced damage to 
residential and commercial buildings indicate that internal pressurization is a 
major contributor to poor building performance under severe wind loading 
conditions. It is recognized that maintaining the exterior envelope of a 
building has a large effect on the performance of the elements of the 
structural system. In spite of loss of a portion of the exterior envelope, the 
construction must provide a continuous load path in order to increase 
survivability of the building in events that marginally exceed the design 
winds. 
Primary structural systems are those that support the building against all 
lateral and vertical loads. Many buildings inspected had structural systems 
capable of providing a continuous load path for downward acting gravity 
loads, but were unable to provide a continuous load path for the lateral and 
vertical uplift forces generated by the tornado winds. The team looked at how 
this property damage could have been prevented or reduced in all areas of the 
windfield with the exception of directly under the vortex of violent 
tornadoes. Figure 3-1 shows a continuous load path in a wood frame (stick 
built) house.
CHAPTER 3 PRELIMINARY REPORT 
3-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
A primary effect of high winds flowing around and over a structure is the 
wind loads that act on the structure. Uplift is the force caused by the wind 
accelerating around and over buildings and other structures (Figure 3-2). An 
example of uplift strong enough to move a house off its foundation is 
presented in Figure 3-3. This house was separated from its foundation when 
it experienced winds associated severe tornado that passed through this 
neighborhood in the city of Haysville, Kansas. Although anchor bolts 
extended from the concrete foundation into the wood floor framing, nuts 
were not attached to the bolts to provide a continuous load path at this 
connection point that would have resisted the uplift forces. This deficiency 
was observed at more than just this one house. 
Figure 3-1: Diagram 
showing a continuous 
load path for a two-story 
wood frame building.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-5 
The other primary effects of wind are overturning, which is discussed in the 
Manufactured Housing sections of Chapter 4; the internal pressurization of 
a building; the lateral force acting inward or positive load created by the 
wind blowing directly on the face of the building. Most buildings are 
designed with no dominant openings, such as residential and most nonresidential 
buildings, and a breach in the building envelope due to broken 
windows, failed entry doors, or failed garage doors may cause a significant 
increase in the net wind loads acting on the building under severe wind 
conditions. In such cases the increased wind load may initiate a partial failure 
or propagate into a total failure of the primary structural system. A schematic 
FIGURE 3-2: This 
building failure is the 
result of inward wind 
forces and uplift wind 
forces acting on a 
building or structure 
during a high wind 
event. 
FIGURE 3-3: Wind uplift 
acting on this house in 
Haysville, Kansas, 
resulted in this corner 
of the building being 
lifted off its foundation.
CHAPTER 3 PRELIMINARY REPORT 
3-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
diagram illustrating the increased loads due to a breach in the building 
envelope is shown in Figure 3-4. 
Depending on the building size, number of interior rooms, number of stories, 
size of the breach, etc., laboratory tests, in wind tunnels, indicate that the net 
increase in uplift on the roof system can exceed a factor of two. The 
increased load on the roof and wall systems may cause connections between 
these systems to fail, possibly at wind speeds below the normal design speed. 
The increased load on the roof and wall systems may cause connections 
between structural members to fail, possibly at wind speeds below the 
nominal design speed. 
Examples of failures of this combination of windward/leeward/internal 
pressures are shown in Figures 3-5, 3-6, and 3-7. 
Figure 3-4: Increased 
loads on roof and walls 
due to breach in 
envelope. 
FIGURE 3-5: Failure of 
hip roof due to internal 
pressures and leeward 
wind forces acting 
together. This house, 
which was exposed to 
inflow winds of a 
violent tornado, was 
located in a suburb of 
Oklahoma City, 
Oklahoma.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-7 
Buildings that have significant openings or are mostly open structures are 
characterized as partially enclosed. Model building codes incorporate 
provisions, which take into account the effects of internal pressurization on 
partially enclosed buildings by increasing required design loads. However, 
residential buildings are typically designed as enclosed buildings and when a 
breach occurs, for example when a garage door fails, they become in effect 
FIGURE 3-6: Failure of 
this gable wall section 
was due to wind 
suction forces of the 
leeward wall. This 
house was on the outer 
edge of a violent 
tornado path. 
FIGURE 3-7 Failure of 
this exterior wall and 
roof section in Moore, 
Oklahoma, occurred 
when the windows broke 
and the front room saw 
an increase in internal 
pressure. Most of the 
debris from the roof and 
exterior wall had been 
cleaned up prior to this 
photograph. This home 
in Moore, Oklahoma, was 
located on the periphery 
of a violent tornado 
track.
CHAPTER 3 PRELIMINARY REPORT 
3-8 FEDERAL EMERGENCY MANAGEMENT AGENCY 
partially enclosed buildings and are subject to load wind increases. In many 
homes inspected, these increased loads may have exceeded the enclosed 
buildings design load specified in the applicable state or local building code, 
possibly resulting in the structural failure observed. 
A number of non-residential buildings, such as schools, factories, 
warehouses, and commercial buildings were in the direct path of the 
moderate tornado vortexes or in the inflow of severe and violent tornadoes 
and received varying degrees of damage. In a few cases, damage could be 
considered non-structural because architectural and decorative materials on 
the exterior and roofing were the only damage to the buildings. Engineering 
standards such as ASCE 7, identify these element as components and 
cladding, and provide design guidance for designing to specified regional 
wind speeds. The failure of an exterior insulating finishing system (EIFS) 
exterior wall covering and architectural roof parapet is shown in Figure 3-8 
at the Regional Mall at Stroud, Oklahoma. This was the only damage 
experienced by this particular store; however, other significant damage was 
experienced at the mall that was struck by a moderate tornado and is 
discussed later in this report. 
In other cases, structural damage occurred due to the lack of redundancy in 
the load to resist wind-induced uplift loads. Similar to the residential damage 
observed, some non-residential buildings did not have a primary structural 
system capable of providing a continuous load path capable of withstanding 
the lateral and uplift loads generated by the tornadoes. Other buildings were 
unable to withstand the wind forces once the building envelope had been 
breached. 
Figure 3-8: EIFS and metal 
component damage at the 
regional outlet mall in 
Stroud, Oklahoma.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-9 
Figure 3-9: This URM wall 
failed when inflow winds 
from a severe tornado acted 
on this building in Wichita, 
Kansas. 
Figure 3-10: The vortex of a 
violent tornado passed 
within 100 yards of this 
plastics manufacturing plant 
in the City of Haysville, 
Kansas. The wind forces 
caused the failure of its 
primary structural system: a 
steel frame with masonry 
infill walls.
CHAPTER 3 PRELIMINARY REPORT 
3-10 FEDERAL EMERGENCY MANAGEMENT AGENCY 
3.2 WINDBORNE DEBRIS 
The quantity and size of windborne debris (missiles) generated by tornadoes 
is unequaled by any other type of wind storm. The smaller missiles (e.g., 
aggregate [stone] ballast from built-up roofs, pieces of tree limbs, pieces of 
shredded wood framing members) can easily become airborne and break 
common window glass causing a rapid increase in internal air pressure within 
a building, which then results in increased load on the building (Figure 3-11). 
Moderate sized missiles (e.g., appliances, HVAC units, long wooden 
members) can also become airborne and cause considerable damage to 
buildings (Figure 3-12). Large high-energy missiles (e.g., columns, joists, 
trusses, automobiles) are often observed as rolling debris and may become 
airborne members (Figure 3-13). These large missiles can easily destroy 
framing members and structural systems of buildings. 
FIGURE 3-11: Small missiles 
commonly observed during 
the field investigations.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-11 
3.2.1 Missile Types and Sizes 
The majority of the investigated tornado tracks were through residential 
areas, which were predominantly constructed wood framing with asphalt and 
composition shingle roofs. Hence, along most of the track, wood framing 
members (e.g., roof shingles, studs, joists, trusses, sheathing and household 
FIGURE 3-13: These trusses 
and roof covering (still 
attached to the roof sheathing) 
was displaced by the winds of 
a violent tornado and are 
capable of becoming large, 
windborne missiles. 
FIGURE 3-12 These medium 
sized missiles struck and 
remained embedded within 
this manufactured home in 
Wichita, Kansas.
CHAPTER 3 PRELIMINARY REPORT 
3-12 FEDERAL EMERGENCY MANAGEMENT AGENCY 
contents) were the most common windborne missile types. Many of the 
framing members and roof shingles were broken, thereby creating an 
enormous number of small missiles that were only a few inches long. 
Although small, they had sufficient energy to break glass and injure people. 
Other framing missiles were quite large and delivered significant impact 
force. Figure 3-14 shows missile impacts on top the roof of Westmoore High 
School in Moore, Oklahoma. The missile sticking out of the roof in the 
foreground is a double 2-in by 6-in. The portion sticking out of the roof is 13 
feet long. It penetrated a ballasted ethylene propylene diene monomer 
(EPDM) membrane, approximately 3-in of polyisocyanurate roof insulation 
and the steel roof deck. The missile laying on the roof just beyond it is a 
double 2-in by 10-in that is 16 feet long. The missile in the background that 
penetrated the roof deck is a double 2-in by 6-in that had a total length of 16 
feet. The source of missiles was not determined, hence the distance to their 
origin is unknown. However, since this school building was located within 
100 yards of a violent tornado it is likely that they traveled at least a few 
hundred feet from a subdivision of the wood-frame houses that were in the 
direct path of the tornado. Figures 3-15 and 3-16 shows a board missile 
striking the roofs of residential homes that were located on the periphery of 
tornado tracks. Figure 3-17 shows a 2-in by 6-in board missile completely 
penetrating the brick veneer of a residential home. Figure 3-18 shows a 2-in 
by 6-in board missile penetrating several inches into the freezer compartment 
of a refrigerator located in a home that was on the periphery of a violent 
tornado track. The portion that is visible is 4-ft, 8-in long. 
FIGURE 3-14: In the 
foreground, a medium sized 
missile, a double 2-in by 6- 
in, 13 feet long board can be 
observed sticking out of 
Westmoore High Schools 
roof, Moore, Oklahoma. A 
larger missile, double 2-in 
by 10-in, 16 feet long board 
is lying in the background.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-13 
FIGURE 3-15: Windborne 
missile striking a house 
located in Moore, Oklahoma. 
FIGURE 3-16: A missile 
vertically striking the roof of 
a home in Mid West City, 
Oklahoma. It fell nearly 
vertical illustrating the 
importance of a strong cover 
over the top of a tornado 
shelter to protect against 
free-falling debris.
CHAPTER 3 PRELIMINARY REPORT 
3-14 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Small-sized missiles also included brick, CMU, aggregate (stone) ballast 
from built-up and single-ply membrane roofs, roof tiles, asphalt shingles, 
fences, shrubs, and tree limbs. Moderate-sized missiles included appliances 
(e.g., hot water heaters, refrigerators, dishwashers), rooftop HVAC units, 
metal roof panels, car axles and transformers from power poles. Large-sized 
missiles included automobiles, a power pole (Figure 3-19). The pole was 28- 
ft, 4-in long and had an 8 -in diameter at one end and a 7-in diameter at the 
other end. From the window, it was roughly 40 feet to the original location 
of the pole from the window. Manufactured home chassis (one of these 
penetrated a window of a home), and large propane tanks (Figure 3-20), steel 
FIGURE 3-17: A 2-in by 6- 
in can be seen completely 
penetrating the brick 
veneer of a home in 
Moore, Oklahoma. 
FIGURE 3-18: A 2-in by 6- 
in board missile 
penetrating a refrigerator 
located inside a home the 
in Country Place 
subdivision outside 
Oklahoma City, 
Oklahoma.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-15 
dumpsters, steel deck (Figure 3-21) and trees (Figure 3-22) were among 
other large missiles observed by the BPAT. Automobiles were observed to 
have been significantly displaced and destroyed in areas under the vortex of 
and in the inflow wind field near the vortex of a violent tornado. 
FIGURE 3-19: This power 
pole penetrated a 
window and extended 
several feet into the 
house after traveling 
approximately 40 feet 
from its original location. 
This home was located in 
Moore, Oklahoma, along 
the track of a violent 
tornado. 
FIGURE 3-20: Wind 
displaced this very large 
propane tank in Bridge 
Creek, Oklahoma; its original 
location could not be 
determined. This area was 
hit by the vortex of a violent 
tornado.
CHAPTER 3 PRELIMINARY REPORT 
3-16 FEDERAL EMERGENCY MANAGEMENT AGENCY 
3.2.2 Windborne Missile Quantity 
In areas where buildings were totally or nearly totally destroyed by a violent 
tornado, missiles were in such great quantity (Figure 2-23) that they often 
made a layer of rubble completely cover the ground (Figure 2-24). In many 
houses, the floors were covered with small tree branches and fragments of 
broken framing members. Figures 3-25, 3-26, 3-27, and 3-28 give some 
idea of the number of missiles that were flying during the storm. 
FIGURE 3-21: This piece 
of steel deck landed at 
the periphery of a violent 
tornado damage area in 
Moore, Oklahoma. The 
building it likely came off 
of was a few hundred feet 
away. 
FIGURE 3-22: This 
building was on the 
periphery of a violent 
tornado damage area in 
Haysville, Kansas. One 
large tree fell near the 
corner of the house and 
collapsed a large portion 
of the roof and the corner 
walls. A smaller tree 
caused minor damage on 
the other corner of the 
house.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-17 
FIGURE 3-23: Wood 
framing members and 
plywood sheathing near 
the periphery of a violent 
tornado damage area in 
Moore, Oklahoma, 
displaying quantity of 
flying debris. 
FIGURE 3-24: Debris 
generated by the vortex 
of a violent tornado in 
Moore, Oklahoma creates 
a layer of rubble across 
the ground.
CHAPTER 3 PRELIMINARY REPORT 
3-18 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 3-25: Close-up 
view of roof insulation 
boards (the boards are 4- 
ft by 8-ft) at Westmoore 
High School. This roof is 
approximately 35 feet 
above grade. Some of 
the missiles only caused 
superficial damage to the 
insulation, but several 
others had sufficient 
force to make large 
gouges in the insulation. 
FIGURE 3-26: This house 
was on the periphery of a 
violent tornado damage 
area in Moore, Oklahoma. 
Two large missiles struck 
this area of the roof.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-19 
3.3 PERSONAL PROTECTION AND SHELTERING 
The purpose of a shelter is to provide a safe refuge in the event of a tornado 
or an extreme wind storm. The BPAT observed three types of shelters as 
follows:
1. residential 
2. group 
3. community 
FIGURE 3-27: Several 
missiles struck the wall 
of this house in Del City, 
Oklahoma, including a 
medium sized piece of 
debris in the center of the 
picture. For scale, the 
square metal fastener 
plates near the board 
corners are 3-in by 3-in. 
FIGURE 3-28: Several 
missiles struck and 
perforated the interior 
wall of this house in 
Moore, Oklahoma.
CHAPTER 3 PRELIMINARY REPORT 
3-20 FEDERAL EMERGENCY MANAGEMENT AGENCY 
The residential shelters included above-ground in-resident shelters as well as 
storm cellar and basement types (Figure 3-29). The group shelter observed 
included one at a manufactured housing park and one at a plastic 
manufacturing plant. Community shelters observed included one at a 
manufactured housing park and another at a high school. Shelters are further 
discussed in Section 4.3. 
3.4 LOCAL, STATE, AND FEDERAL REGULATIONS 
Building codes and regulations for both residential and commercial/industrial 
buildings varied because of the states involved. However, regulations dealing 
with manufactured housing fall under U.S. Department of Housing and 
Urban Development (HUD) preemptive construction and safety standards. 
The design and construction of manufactured housing has been governed 
since 1976 by Federal preemptive standards which are enforced by HUD 
under Federal Regulation and through a Monitoring and Enforcement 
Contractor, the National Conference of States on Building Codes and 
Standards (NCSBCS). Recently, the HUD Standard has been placed under a 
consensus process administered by National Fire Protection Association 
(NFPA). Another tool used by HUD to regulate the manufactured home 
industry is the Federal Manufactured Home Construction and Safety 
Standards (MHCSS), 
FIGURE 3-29: 
Underground residential 
shelter, viewing door and 
stairway leading down to 
shelter. This shelter was 
located outside a 
residence.
PRELIMINARY REPORT GENERAL ASSESSMENT AND CHARACTERIZATION OF DAMAGE CHAPTER 3 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 3-21 
3.4.1 Oklahoma 
Throughout the State of Oklahoma, two of the models building codes in the 
United States are utilized on a city by city basis. In the incorporated areas 
affected by this storm, the National Building Code (NBC) promulgated by 
the Building Officials and Code Administrators International, had been 
adopted. The 1996 edition of the NBC (1996 NBC) was currently adopted by 
most communities for all construction other than detached one and two 
family buildings. The 1995 Council of America Building Officials (CABO), 
One and Two Family Dwelling Code is the currently adopted code for 
detached one and two family dwellings. 
Buildings that suffered damage during this event which were located in the 
unincorporated areas, were not covered by a model building code. 
3.4.2 Kansas 
Most communities in the State of Kansas have adopted the 1997 Edition of 
the Uniform Building Code (1997 UBC) as promulgated by the International 
Conference of Building Officials (ICBO) for commercial and industrial 
buildings. The UBC then defers to the CABO One and Two Family Dwelling 
Code for detached single family residential occupancy (Classified as R-4). 
The City of Haysville has adopted the 1994 UBC and Wichita and the 
unincorporated areas of Sedgwick County have adopted the 1997 UBC. 
Wichita has local ordinance provisions which address sheltering. These 
ordinance provisions state that as of April 15, 1994, all manufactured home 
parks of ten or more manufactured home spaces are required to have storm 
shelters (above or below grade). For parks with 20 or more manufactured 
home spaces that did not have a shelter as of April, 15, 1999, a shelter must 
be provided by April 15, 1999. The ordinance also indicates that the shelter 
must be designed by a licensed engineer or architect to applicable codes and 
laws including the UBC, ADA, and FEMAs National Flood Insurance 
Program (NFIP).
CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-1 
4 Observations on 
Residential Property 
Protection 
The damage assessment of buildings was divided into residential and nonresidential. 
This section presents the BPAT's observations on residential 
property protection. Specifically, residential properties were categorized into 
single-family housing, multi-family housing, and manufactured and modular 
housing. 
The BPAT assessed the performance of primary structural systems of 
buildings, which are those systems that support the building against lateral 
and vertical loads generated by high winds during a tornado or other high 
wind event. These systems are typically constructed of wood framing, 
sheathing, anchor bolts, and other connections. In residential applications, 
the exterior load bearing walls (i.e., walls that support roof framing) almost 
exclusively make up these primary structural systems. Non-loadbearing wall 
panels (i.e., self-supporting walls only), roof structure and diaphragm, and 
foundation are components of the building that are also part of this system or 
affect the performance of the system. The integrity of the overall building 
and structural systems depends not only on the strength of these components, 
but also on the adequacy of the connections between them. Important 
observations were also made concerning exterior architectural systems (e.g., 
roof and wall coverings, windows and doors). 
4.1 SINGLE FAMILY CONVENTIONAL CONSTRUCTION 
The BPAT observed damage to a large number of wood frame single-family 
houses, which are commonly referred to as "conventional" or stick-built 
construction. These houses were mostly one- or two-story buildings, many 
with pre-engineered wood trusses with metal truss plate connectors. Several 
homes had hip roofs with site-built rafter construction and board roof 
sheathing. Platform construction was observed in all cases (Figure 4-1). The 
structures observed in Oklahoma were predominately slab-on-grade with 
some crawl-space foundation construction. In Kansas, the structures were 
predominately wood frame construction placed on a basement or "crawl 
space" foundation.
CHAPTER 4 PRELIMINARY REPORT 
4-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
4.1.1 Load Paths 
The preparation of quality construction plans and the assurance of the 
construction of a continuous load path  from the roof sheathing to the 
ground  are key to maintaining structural integrity, regardless of the 
magnitude of the wind loads. Several different building materials and 
systems are usually involved in constructing and completing this continuous 
load path, and like a chain, the system is only as good as its weakest link. 
Primary structural systems are those that support the building against all 
lateral and vertical loads. Due to the wind damage observed, the team 
FIGURE 4-1: Platform 
construction typically 
observed during the field 
investigation.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-3 
focused on how this damage could have been prevented or reduced in all 
areas of the tornado windfield, with the exception of directly under the vortex 
of violent tornadoes. 
Damage or failure was observed in essentially all building elements that 
constitute the lateral and vertical force resisting systems. Those elements are 
the roof sheathing, roof framing, load bearing and non load bearing wall 
framing, diaphragms, diaphragm chords, attachments and connections, and 
foundation systems. If the elements are not adequately tied together or 
connected, the system will fail. As discussed in the following sections, the 
damage ranged from considerable to total, depending on the type of framing, 
construction methods, and wind load experienced at the building. 
4.1.2 Roof and Wall Sheathing 
Sheathing in light-frame construction serves many purposes. One is to 
receive the wind and load and distribute or carry the load to its supporting 
members such as the roof rafters or wall studs. The second purpose is to 
provide resistance to loads in the direction of the sheathing. This second 
purpose is illustrated in Figure 4-2, the roof sheathing acts as a horizontal 
diaphragm and transfers lateral loads to the supporting walls. 
Roof sheathing observed in Oklahoma consisted primarily of rough sawn 1- 
in by 8-in planks placed side by side or 4-ft by 8-ft plywood sheets. The 
fasteners observed connecting the sheathing to the supporting rafters or truss 
top cords were nails and staples. Figure 4-3 shows a typical situation where 
the stapling of the boards to the rafters or trusses was not adequate. In the 
application of both sheathing materials, it appeared there was a concerted 
effort to stagger the joints as required by code as shown in Figure 4-4. 
FIGURE 4-2: Lateral load 
transfer to supporting 
walls by roof and wall 
sheathing.
CHAPTER 4 PRELIMINARY REPORT 
4-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
As that load reaches the top of the walls, the shear has to be transferred to the 
top plate by some method of fastening. After the fastener transfers its load, 
there will be a force at the top of the supporting wall that is intended to be 
resisted by the shear wall. The wall sheathing (Figure 4-5) typically 
establishes the capacity of a shear wall. 
FIGURE 4-3: Failed 
stapling of boards to 
rafters viewed from 
home in Moore, 
Oklahoma. 
FIGURE 4-4: Although 
roof sheathing was lost 
at this Wichita, Kansas, 
home code 
requirements of 
staggering joints in 
sheathing applications 
was observed. This 
house experienced 
inflow winds from a 
severe tornado.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-5 
The force in the wall then must be transferred to the floor below, which in 
turn must transfer it in a similar manner to the foundation. It is this load 
transfer mechanism that the BPAT attempted to observe. 
Wall sheathing observed consisted primarily of insulated fiber board or 
combination siding/sheathing. With the exception of garage end walls, it was 
difficult to ascertain any consistent failure of wall sheathing because it 
appeared the entire wall was either lifted or blown inward or outward as the 
result of windward or a combination windward/leeward pressure (Figures 4-3 
and 4-4). 
One example of an inadequate lateral load-resisting element that was 
observed was the garage end walls or returns that act as the frame for the 
garage door. A normal code minimum width for the return is four feet. This 
one measures 22-in which is clearly inadequate to resist code-required loads. 
At least one of the model building codes has a minimum width of such panel 
as 32-in with a special web and special hold anchors. Also, there were a 
number of cases where the garage bearing walls failed and the garage roof 
fell to the ground essentially intact. An example of this failure is presented in 
Figure 4-6 from a house that experienced inflow winds from a severe tornado 
in Wichita, Kansas. 
FIGURE 4-5: Shear 
load force carried by 
wall sheathing.
CHAPTER 4 PRELIMINARY REPORT 
4-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
4.1.3 Connections 
Post disaster assessments continue to support the fact that improved 
connections could have resulted in better performance of building structural 
systems, attributing to a reduction in loss of life, injuries, and property 
damage. The BPAT observed a wide range of connection deficiencies or 
failures in areas subjected to moderate winds. It is important to keep in mind 
that the loads seen by these connections were not known, but were believed 
to be with design requirements and safety factors of model building codes. 
The wind forces that act on the roof of a building make the roof sheathing to 
roof framing connection the important first line of defense. Unfortunately, 
these connections are often overlooked during construction. When the roof 
envelope is breached (i.e., roof sheathing is blown off), additional damage is 
likely to occur as wind forces enter the building and act on interior walls not 
designed for lateral loads. Figure 4-7 shows a typical example of inadequate 
fastening. 
FIGURE 4-6: Wall failure 
due to inadequate lateral 
load resistance in 
Wichita, Kansas. The 
return wall at the garage 
inadequate to carry 
loads may have led to 
this failure.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-7 
Working from the roof system down toward the foundation, the next critical 
connection is the connection between the roof framing and the wall system. 
The result of failure of this connection is shown in Figure 4-8. If the roofframing-
to-wall-connection was adequate to withstand forces of uplift, lateral 
load, and shear transfer, the ability of the structure to withstand the loads 
generated by moderate winds is increased. Forces would now include the 
dead load of the wall and its coverings and its shear wall capacity; however, 
this was not the case in this location and the roof was separated from the rest 
of the house. 
FIGURE 4-7: Roof truss 
failure. A single nail 
(circled) was used to 
connect each truss to 
the top plate. This house 
was in Midwest City, 
Oklahoma and 
experienced inflow 
winds from a violent 
tornado.
CHAPTER 4 PRELIMINARY REPORT 
4-8 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Figure 4-8 shows a seldom seen type of failure that may have been caused by 
a combination of uplift, diaphragm chord forces, and horizontal bending of 
the double 2-in by 4-in members commonly used as a top-plate. There were 
few observed failures of the connection of the double-top-plate to the 
supporting studs below, although one example is shown in Figure 4-9. With 
platform construction, the walls are typically framed while lying flat on the 
floor of the house. 
FIGURE 4-8: Failure of a 
double top-plate. The 
uplift of the roof truss 
previously attached to 
this double top-plate 
caused separation of the 
two members that 
comprise this top-plate.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-9 
Once the wall is erected, the sill plate should be connected to the foundation. 
In Oklahoma, the foundation was typically a slab-on-grade foundation. In 
Kansas, basement and crawl space foundations were more common than 
slab-on-grade construction. Figure 4-10 represents one of many observed 
failures of the wall-to-sill-plate connection. In this instance, the sill plate 
remained anchored to the foundation but the toe-nailed or face-nailed 
connection of the studs to sill plate were inadequate to resist uplift loads from 
a severe tornado that struck this Oklahoma home. 
FIGURE 4-9: Failures of 
the connection of the 
double-top-plate to the 
supporting studs below 
by home located in 
Moore, Oklahoma. This 
home was located 
along the periphery of 
a violent tornado.
CHAPTER 4 PRELIMINARY REPORT 
4-10 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Failures between the sill plate and the foundation or floor below were 
observed. Some of these failures occurred when the sill plate itself failed due 
to extreme winds associated with the vortex of a violent tornado, as seen in 
Figure 4-11. In this figure, anchored bolts were used to secure the sill plate 
to the foundation. In both Oklahoma and Kansas, bolts, nails, and epoxy 
anchors were observed securing sill plates to foundations. In one instance in 
Oklahoma, straps from the foundation were observed securing the sill plate 
to the foundation. Another factor observed that contributed to failures of 
wall systems was that the bottom-plate (sole- or sill-plate) was not integral 
with the siding or other means of transferring the force. The connection was 
weak as seen in Figure 4-12. 
FIGURE 4-10: Wall 
framing to sill plate 
failure. This house in 
Del City, Oklahoma, 
experienced a direct hit 
from the vortex of a 
violent tornado.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-11 
In the event adequate connections and structural elements are provided above 
the sill-plate to foundation connection is almost the last link in the chain. The 
BPAT saw many examples of failures at the connection to the foundation. 
Figures 4-11, 4-12 and 4-13 highlight these weaknesses. Uplift, racking and 
moderate windward forces combined to cause separation of this connection. 
FIGURE 4-11: Stud-wall 
and sole-plate-to-floor 
failure on a second story 
wall. This multi-family 
residence in Wichita, 
Kansas, was located 
approximately a few 
hundred feet from the 
vortex of a violent 
tornado and was 
exposed to inflow winds. 
FIGURE 4-12: Failure at 
base of wall between 
wall studs and sill-plate. 
The sill-plate, which 
was connected to the 
foundation slab with 
anchor bolts and nails, 
has splintered.
CHAPTER 4 PRELIMINARY REPORT 
4-12 FEDERAL EMERGENCY MANAGEMENT AGENCY 
4.1.4 Increased Load 
For buildings that are designed with no dominant openings, such as 
residential buildings, a breach in the building exterior envelope due to broken 
windows, failed entry door, or failed garage door may cause a significant 
increase in the net loads acting on the building under severe wind conditions. 
In such cases, the increased load may initiate a partial failure or propagate 
into a total failure of primary structural systems. A schematic diagram 
illustrating the increased loads due to a breach in the building envelope is 
shown in Figure 3-4. Depending on the building size, number of interior 
rooms, number of stories, size of the breach, etc., wind tunnel tests indicate 
that the net increase in uplift on the roof system can exceed a factor of two. 
The increased load on the roof and wall systems may cause connections 
between these systems to fail, possibly at wind speeds below the normal 
design speed. 
FIGURE 4-13: Failure of 
this sill-plate to 
foundation connection 
occurred at this home 
outside Oklahoma City, 
Oklahoma. The vortex of 
a violent tornado passed 
very close to this home.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-13 
4.1.5 Roof Coverings 
Virtually all of the residential roof coverings in the areas the BPAT 
investigated in Oklahoma and Kansas were asphalt or composition shingles 
(Figure 4-14). Almost all of the shingles were three-tab or laminated, but a 
small number of T-lock shingles were also observed (Figure 4-15). Shingle 
age ranged from relatively new to quite old (more than 15 years). It was 
observed that for homes located near the far periphery of the tornado, 
damage was typically limited to intermittent shingle damage only. Shingle 
damage increased dramatically as the distance from the vortex decreased. 
FIGURE 4-14: Asphalt 
shingles covering roof of 
residential home. 
FIGURE 4-15: Several Tlock 
shingles on this 
house were lifted and 
torn. This house was on 
the periphery of the 
damage track left from a 
moderate tornado in 
Wichita, Kansas.
CHAPTER 4 PRELIMINARY REPORT 
4-14 FEDERAL EMERGENCY MANAGEMENT AGENCY 
4.1.6 Wall Coverings 
Brick veneer over wood framing was a predominate wall covering in the 
investigate areas of Oklahoma. A detailed discussion of masonry used for 
load bearing walls and wall coverings is presented later in this section. Vinyl 
siding was another common wall covering. A large number of houses on the 
periphery of the tornado tracks lost siding. In many cases (Figure 4-16), the 
vinyl had been installed over wood or hardboard siding. In all of the 
investigated cases, although the vinyl was blown off, the underlying wood or 
hardboard siding was undamaged (except for missile impacts). The siding of 
the home in Figure 4-16 was attached with roofing nails. In one area, the 
nails were 30-in and 21-in apart. The failure of the siding occurred when the 
vinyl pulled over the nailheads. Additionally, the home in Figure 4-16 
suffered some asphalt shingle damage. Houses with vinyl siding that were 
closer to the vortex commonly had extensive missile damage (Figure 4-17). 
Pieces of vinyl siding of this home were blown off by wind or torn away by 
missiles. The siding on this home was also fastened with roofing nails. The 
roofing nails were placed at 13.5-in, 10-in, 20-in, and 13.5-in along one 
length of siding. The vinyl siding also pulled over the nailheads. Homes with 
other siding materials exhibited limited missile damage even though the 
missile loading was likely similar. 
FIGURE 4-16: The vinyl 
(white) that was 
installed over wood 
siding experienced 
damage; however, the 
wood siding was 
undamaged. The home 
was located along the 
periphery of a violent 
tornado in Wichita, 
Kansas.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-15 
Wood siding and hardboard siding and panels were also observed. In a few 
instances along the periphery of the tornado tracks, blow-off of these 
materials was observed. However, it appeared that these materials typically 
exhibited good resistance to wind speeds that were in the range of current 
design conditions (e.g.,70 mph, fastest mile sustained or 90 mph 3 second 
peak gust) of the 1997 UBC, 1996 NBC and 1995 CABO codes. 
4.1.7 Garage Doors 
Along the track periphery, it was common to see residential garage door 
failures (Figure 4-18). The door in this figure likely had a tested load 
resistance of 12.5 psf; a common test pressure for doors of similar 
construction. The design load on this door would be 13 psf using UBC 1997 
and 18 psf using ASCE 7-98. Hence the load derived from ASCE 7-98 is 44 
percent higher than the tested resistance of the door. Had this door met the 
wind loading derived from ASCE 7-98, this failure may have been avoided. 
Most of the investigated doors were made of thin metal. Failures were 
typically caused by wind pressure, rather than by missiles. The most common 
failure mode observed was the door rollers disengaging from the door tracks. 
This was likely caused by excessive door deformation (see Figures 18A- 
18D). Door failure resulted in increased load on the building. 
FIGURE 4-17: Some 
pieces of vinyl siding 
were blown off and in 
other areas the siding 
was torn away by 
missiles. The home was 
located along the 
periphery of a violent 
tornado in Mullhall, 
Oklahoma.
CHAPTER 4 PRELIMINARY REPORT 
4-16 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-18: This 
double-width garage 
door failed under a 
suction load in Moore, 
Oklahoma. 
FIGURE 4-18A:Typical 
double-wide garage door 
elevation
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-17 
FIGURE 4-18B: Plan view of typical garage door shown in Figure 4-18A. 
FIGURE 4-18C: Detail A 
from Figures 4-18 A and 
B. Recommend 
reinforced horizontal 
latch system for garage 
door.
CHAPTER 4 PRELIMINARY REPORT 
4-18 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Detail B from Figures 18 
e door failure at 
track and recommend 
assembly improvements.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-19 
The BPAT conducted an extensive assessment of garage door performance at 
Greenbriar Eastlake Estates in Oklahoma City. A violent tornado directly 
struck this subdivision and destroyed many homes. The house in Figure 4-18 
was located approximately 200-300 feet away from the vortex of the tornado 
as it moved from the southwest to the northest of this neighborhood. A 
partial schematic map of the Greenbriar Eastlake Estates is shown in Figure 
4-19. The rectangles represent the average dimensions of homes surveyed 
with house labels appearing within the rectangles. The homes surveyed in 
this subdivision are constructed of wood framing with brick veneer. The 
roofs on these homes were hip, gable, or a combination of the two. The 
majority of the homes were single-story, some with cathedral ceilings. Most 
house floor plan configurations are simple L, T, or rectangle shapes. Roof 
decking was observed to be mostly dimensional lumber with some Oriented 
Strand Board (OSB) and plywood sheathing. Roof rafter and wall top-plate 
connections were typically toe nailed with two 16d nails with no added straps 
or clips. Overall, material quality was observed to be typical for the 
Oklahoma City area. Windows were observed to be of average quality, as 
were front, back, and side entry doors. The large majority of the homes 
observed had single skin aluminum, non-insulated, and non-reinforced 
double width garage doors. 
Homes located at H and A are shown in Figure 4-20. The damage states of 
the two homes are significantly different even though they are located 
directly across the street from one another, approximately 95 feet, and may 
have experienced relatively similar wind conditions based on the 
approximate track location (Figure 4-19). The home located at H had seven 
broken windows, primarily at the back of the home as a result of debris 
generated from a failed wooden fence. It also had one breached glass entry 
door, and lost approximately 60% of its roof covering. The home located at 
A lost its entire roof and several exterior walls. For the remaining structures, 
similar across-the-street damage gradients were observed between the 
homes, A through G and H through N, with the exceptions of the home at 
location F, which did not lose its entire roof, and the home at location G, 
which did not lose any roof, but did sustain severe roof framing damage due 
to uplift. Table 4-1 (not included at this time) lists observed damage states 
for all homes shown in Figure 4-19, illustrating the expected decreasing 
damage gradient as the distance between home and storm track increases.
CHAPTER 4 PRELIMINARY REPORT 
4-20 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Several failed garage doors were observed lying at the back of the garage for 
many homes A through G, indicating that the garage doors failed due to 
positive (inward) pressure. These failures of the garage doors are believed to 
have initiated or contributed to the catastrophic roof and exterior wall failures 
for homes A through G, a direct consequence of load increase due to a large 
breach in the building envelope. Examples of this may be seen in Figures 4- 
20 and 4-22. Note that the failed garage door in Figure 4-20 is crumpled up 
against the car, suggesting a door failure under positive pressure. A partial 
roof failure (house F) is depicted in Figure 4-22. In this case the garage door 
was also found within the garage as shown in the picture inset. The observed 
location of the failed garage door and the localized roof damage suggests that 
the failed garage door may have initiated or played an important role in the 
roof failure. Many of the moderately to severely damaged homes observed 
had a significant amount of structural damage to the garage area and to the 
immediate surrounding area, but did not necessarily have the same 
magnitude of structural damage at the opposite side of the building where no 
garage was located. 
A final example of observed internal pressurization and roof uplift is shown 
in Figures 4-23 and 4-24 for the house located at G. The garage door failed 
by positive pressure and was found inside the garage. Figure 4-24 shows 
strong evidence of the early stages of roof uplift between the garage roof and 
exterior wall. The ceiling was observed to have pulled away from the exterior 
wall perimeter, indicating that the whole roof frame was lifted up. The space 
shown in Figure 4-24 was apparent along most of the perimeter of the garage 
ceiling. Figure 4-21 shows an exterior view of the roof and wall interface 
where the initiation of roof uplift was observed. Tension cracks in the brick 
FIGURE 4-19: Partial 
schematic map of an 
Oklahoma City 
subdivision that was 
affected by inflow winds 
from a violent tornado.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-21 
veneer and a large gap along the length of the right exterior wall between the 
roof and top plate were also observed. 
FIGURE 4-20: Home in 
Moore, Oklahoma, with 
partial roof loss (H) vs. 
home with total roof loss 
due to garage door 
failure (A) under positive 
pressure.
CHAPTER 4 PRELIMINARY REPORT 
4-22 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-21: A 2x4 
member extends out of 
the gap that runs the 
length of this garage 
wall between the top of 
the wall and the roof 
framing 
FIGURE 4-22: Garage 
door failure possibly 
resulting in the localized 
partial roof failure on the 
left side of this home 
located in Moore, 
Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-23 
For several of the homes, H through N, it was observed that the garage doors 
had sustained permanent deformation due to negative (outward) pressure 
loads. This observation supports the assumption that the garage doors for 
homes A through H located across the street failed in positive pressure, as 
shown in Figure 4-18 for the home located at H. This door failed under a 
suction load. This door likely had a tested positive load resistance of 12.5 
psf. The design load on this door would be 13 psf negative and 11 psf 
positive using UBC 1997, and 18 psf negative and 14 psf positive using 
ASCE 7-98. Hence, using a 1.5 safety factor in calculating design loads, the 
FIGURE 4-23: A view of 
home G with a garage 
door that failed due to 
positive or inward acting 
wind loads. 
FIGURE 4-24: Roof uplift 
between garage roof and 
exterior wall at home G.
CHAPTER 4 PRELIMINARY REPORT 
4-24 FEDERAL EMERGENCY MANAGEMENT AGENCY 
positive load derived from ASCE 7-98 is 68% higher than the design 
resistance of the door. Had this door met the wind loading derived from 
ASCE 7-98, this failure may have been avoided. Full scale pressure tests on 
garage doors have also demonstrated that a typical garage door is 
significantly stronger in negative (outward) loading than in positive (inward) 
loading, which may explain why no garage doors completely failed on the 
homes, H through N (assuming comparable winds). 
4.1.8 Windows and Doors 
Glass in exterior windows and doors, glass storm doors, and glass sliding 
doors in buildings in or along the tornado vortex track rarely survived. It was 
common for virtually every pane of glass to be broken on all sides of a 
house. Further from the vortex track, where winds were either inflow or 
outflow winds, it was common to see several broken panes on only one or 
two sides of the house. As the distance from the track vortex increased, the 
incidence of glass breakage decreased. Glazing failure often resulted in 
increased wind load on the building from internal pressurization. 
Exterior doors typically performed better than windows; however, many 
were blown out of their frames and others were breached (Figure 4-25). 
Depending on room size, the existence of interior doors, and the ability of 
internal pressures to propagate through multiple rooms within the building, 
the breach of windows or a failed entry door may cause pressurization of 
only a portion of the building interior and may be often limited to the room 
where the breach occurred. In order for the breach to increase the overall 
uplift loads acting on the roof, the internal pressures must be able to 
FIGURE 4-25: A missile 
penetrated this exterior 
door in Del City, 
Oklahoma. Interior 
hollow-core doors 
typically offer even less 
missile protection than 
common exterior doors.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-25 
propagate through to the attic space. For this to occur, the initial breach and 
subsequent internal pressurization must also breach through to the attic, 
typically through the attic entryway. If the attic entry door consists of a set of 
pull down stairs, the likelihood of attic pressurization is minimal. When the 
attic opening is a scuttle access, covered with a simple unattached push-toopen 
panel, the BPAT observed the risk of attic pressurization is dramatically 
increased. Another way in which the attic can become pressurized is by 
failure of the ceiling drywall, thus providing an opening to the attic space. 
Also, depending upon the location of attic vent openings, the attic could be 
pressurized through the vents. 
Thus, a window breach or entry door failure may be unlike a garage door 
failure where the internal pressure is directly transferred to most of the roof 
system via the ceiling rafters or to the bottom roof truss chords. When a 
window or door fails, interior doors may slam closed and contain the effects 
of internal pressurization to a single room. If the room is isolated from roof 
framing (e.g., a first story window on a two-story home, very little increase 
in roof uplift can be expected. If the interior doors or walls attached to the 
room fail, then the pressurization process will be repeated for adjoining 
rooms. 
Several window failures at the back of the home located in Country Place, a 
subdivision of Oklahoma City, are shown in Figure 4-26. These homes were 
located along the periphery of a violent tornado. Other than a small piece of 
sheathing missing from the roof edge, the roof damage is limited to the loss 
of roof covering material only. In contrast, several pieces of roof deck 
sheathing failed on the front portion of the roof as depicted in Figure 4-27. 
Note that no breaches to the front exterior wall were observed. Figure 4-28 
shows a view of the interior of the same dwelling taken from outside the left 
hand window breach seen in Figure 4-26. The photograph of the interior 
suggests the possibility that internal pressurization may have contributed to 
the roof deck sheathing loss. This is suggested by the holes in the ceiling, in 
particular the right hand hole above the interior doorway. There is evidence 
to suggest that internal pressure may have pushed the ceiling away from the 
top of the interior wall where the ceiling drywall failed. Note that there is no 
evidence of drywall debris on the floor directly below the drywall failure 
suggesting the drywall was ejected into the attic. This suggests that internal 
pressurization may have caused the drywall to fail leading to pressurization 
of the attic space and contributing to the sheathing failure of Figure 4-27. 
The drywall debris on the floor in front of the entry door belongs to the 
collapsed ceiling drywall to the left and was likely the result of rain water 
damage entering through the roof.
CHAPTER 4 PRELIMINARY REPORT 
4-26 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-26: Damage to 
back of home in the 
Country Place 
Subdivision in Oklahoma 
City, was limited to 
several window failures 
and minor roof damage. 
The home was located 
along the periphery of a 
violent tornado. 
FIGURE 4-27: Front of 
home in Figure 4-26 
where several pieces of 
roof decking failed.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-27 
A more serious effect of a failed or breached window or door is when the 
pressurization results in the partial or total loss of an adjoining exterior wall. 
When this failure mode occurs, the breach is often located near a corner 
where high suction (negative) loads occur on the adjacent wall. The 
consequence of losing an exterior wall may initiate the partial or total loss of 
the roof if the wind speed and direction are favorable. Figure 4-29 shows the 
failure of a portion of exterior wall (leeward side) due to internal 
pressurization following the breach of a window (windward side). 
FIGURE 4-28: View of 
interior of home in 
Figures 4-26 and 4-27. 
Figure 4-29: Box temp. 
being used as place 
holder
CHAPTER 4 PRELIMINARY REPORT 
4-28 FEDERAL EMERGENCY MANAGEMENT AGENCY 
4.1.9 Masonry 
The BPAT observed brick masonry veneer construction and its failure from 
moderate wind loads was at numerous locations throughout the inspected 
subdivisions of the Oklahoma City metroplex and the Willow Lake Estates in 
Bridge Creek, Oklahoma. In Figure 4-30, the north wall of a house had been 
framed with 2-in by 6-in studs with 1-in by 4-in let-in corner bracing, 
covered with 1-in thick plastic foam insulation boards and brick veneer. 
Several studs remained upright, but the brick veneer lay on the ground. 
Corrugated metal brick ties remained fastened to the studs, and had pulled 
out of mortar joints. Onsite evaluation indicated that much of the damage had 
been caused by straight inflow winds near ground level associated with a 
nearly severe tornado, similar to that experienced from severe thunderstorms 
or other typical design events and not from a tornado vortex (Figures 4-30 
and 4-31). 
FIGURE 4-30: Failure of 
brick masonry veneer 
construction. The vortex 
of the severe tornado 
that caused the winds at 
this site passed 
approximately 30 feet 
from this building in 
Bridge Creek, Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-29 
Preliminary discussions with Central Oklahoma Home Builders Association 
(COHBA) in Oklahoma City indicated that almost all residences constructed 
in the last several years in the Bridge Creek area had framed walls and brick 
veneer on all four sides. COHBA also indicated that this construction 
complied with the 1995 CABO One and Two Family Dwelling Code. 
At Country Place and Eastlake Estates in the southwest suburbs of Oklahoma 
City, the BPAT observed an increasing number of 1- to 5-year-old homes 
with brick veneer failures. The wind speeds at these locations could not be 
determined. However, based on the team's observation of the damage and 
debris, plus wood framed walls remaining standing, it would appear that 
many homes with brick veneer failure were subjected to moderate tornadoes 
or straight inflow wind forces and were outside the vortex of a violent 
tornado (Figures 4-32 and 4-33). 
FIGURE 4-31: Brick 
veneer failure at the 
house shown in Figure 4- 
30.
CHAPTER 4 PRELIMINARY REPORT 
4-30 FEDERAL EMERGENCY MANAGEMENT AGENCY 
The BPAT also observed several problems that led to premature failure of 
the brick veneer, such as inadequate bonding of mortar to galvanized brick 
ties, inadequate bonding of mortar to brick, and nail pull-out at brick ties. 
The BPAT observed that brick veneer was generally constructed using 3-in 
brick, which appeared to be a dense brick of low porosity. Location and 
number of brick ties varied considerably, from 16-in on center vertically and 
horizontally, to ties at top, midheight, and near bottom of walls. There were 
several walls with up to 1.5-in to 2.0-in gaps behind brick and with brick ties 
only inserted -in to 1.0-in into mortar joints. Most ties were fastened 
through foamboard sheathing into studs with one 6d common nail per tie. 
FIGURE 4-32: Failure of 
masonry veneer wall of a 
home located along the 
periphery of a violent 
tornado, Moore, 
Oklahoma. 
FIGURE 4-33: Failure of 
masonry veneer wall, 
close-up view, Moore, 
Oklahoma. This home 
was located along the 
periphery of a violent 
tornado.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-31 
In many cases, sections of brick veneer wall panels could be easily pulled 
loose by hand, and where brick veneer was left standing, it could easily be 
pushed in with hand pressure (Figures 4-34, 4-35 and 4-36). 
FIGURE 4-34: Inadequate 
bonding of mortar to 
galvanized brick ties, 
Bridge Creek, Oklahoma.
CHAPTER 4 PRELIMINARY REPORT 
4-32 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-35: Inadequate 
bonding of mortar to 
galvanized brick ties, 
Bridge Creek, Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-33 
In Del City and Mid West City, in the southeast suburbs of Oklahoma City, 
the BPAT observed several more examples of brick veneer (both clay and 
concrete brick) failure. Most of the failure appeared to have been caused by 
negative wind pressure (suction) on leeward and side walls (Figures 4-36, 4- 
37, 4-38, and 4-39). These walls were also in an area that was in the inflow 
wind area of a violent tornado, but outside the vortex. 
FIGURE 4-36: Failure of 
masonry veneer wall, 
Del City, Oklahoma.
CHAPTER 4 PRELIMINARY REPORT 
4-34 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-37: Failure of 
masonry veneer wall, 
viewed collapsed on the 
ground. This home, 
located in Oklahoma 
City was in the vortex of 
a violent tornado. 
FIGURE 4-38: Failure of 
masonry veneer wall of 
home located along the 
periphery of a violent 
tornado in Oklahoma 
City. Masonry ties are 
circled.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-35 
In Moore, Oklahoma, at a subdivision south of Westmoore High School that 
was in the direct path of a violent tornado, newer homes located in the 
periphery of the damaged areas approximately a few hundred feet from the 
vortex had failures of brick chimneys and brick veneer walls. Brick chimneys 
snapped off near the eave and crashed through the house roof, breaching the 
building envelope and placing occupants at risk of injury or death from 
falling masonry and other debris. Masonry veneer walls appeared to fail from 
suction (negative) loads pulling the veneer away from the stud framing. 
Again, the majority of masonry veneer was single width, 3-in brick. 
Chimneys were 28-in wide by 24-in deep and made of 3-in brick, with a 10- 
in by 10-in clay tile flue in the center, leaving a large gap between flue and 
exterior brick. The height of chimney was about 8-ft above eave height. No 
vertical or horizontal reinforcement was present. Ages of houses did not 
appear to make any difference on bonding of mortar to brick ties or bonding 
of mortar to brick., as some were 30 years old and others only one year old. 
This type of chimney construction should perhaps be limited in its maximum 
unsupported height, even when considering nominal (non-tornadic) design 
wind loads(see Figures 4-40 through 4-42). 
FIGURE 4-39: Failure of 
masonry veneer wall of 
home located along the 
periphery of a violent 
tornado, Del City, 
Oklahoma.
CHAPTER 4 PRELIMINARY REPORT 
4-36 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-40: Failure of 
brick chimney onto roof 
of home located along 
the periphery of a violent 
tornado, Moore, 
Oklahoma. 
FIGURE 4-41: Close-up 
view brick chimney 
failure in Figure 4-40.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-37 
4.2 MULTI-FAMILY CONSTRUCTION 
The majority of single-family housing construction in areas of Kansas 
devastated by the May 3 tornadoes was of older construction with exterior 
cladding other than brick masonry. However there were a few homes and 
several two-story apartments with brick veneer that had extensive damage 
(Figures 4-43 through 4-47). 
Most of the observations for single family structures are applicable to multifamily 
(low rise, condo and garden apartment) construction with the addition 
of an example of a large overhang. 
FIGURE 4-43: Failure of 
masonry veneer. 
FIGURE 4-42: Failure of 
brick chimney onto top 
of home located along 
the periphery of a 
violent tornado, Moore, 
Oklahoma.
CHAPTER 4 PRELIMINARY REPORT 
4-38 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-44: Failure of 
masonry veneer at a 
multi-family housing 
unit in Wichita, Kansas. 
This building 
experienced inflow 
winds from a severe 
tornado.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-39 
FIGURE 4-46: Chimney 
failure onto roof of single 
family attached housing, 
Wichita, Kansas. This 
building was located 
along the periphery of a 
severe tornado. 
FIGURE 4-45: Failure of 
masonry veneer in 
multifamily housing 
located along the 
periphery of a severe 
tornado, Wichita, 
Kansas.
CHAPTER 4 PRELIMINARY REPORT 
4-40 FEDERAL EMERGENCY MANAGEMENT AGENCY 
4.3 MANUFACTURED HOUSING 
Damage to manufactured homes was observed in Oklahoma and Kansas. 
Performance of units on temporary foundations utilizing anchors and straps 
were assessed as well as the performance of units on permanent foundations. 
In Bridge Creek, Oklahoma, approximately 50 miles west of Oklahoma City, 
11 deaths were reported from a violent tornado; most of these deaths were 
individuals taking refuge in manufactured housing. While some 
manufactured homes were directly hit by the vortex, estimates of wind speed 
based on observed damage to buildings and trees during the site visit 
indicated that most buildings were impacted by straight inflow winds and not 
by the vortex of a tornado. 
There were several sites in the area that were observed to have the 
manufactured house wood framing completely destroyed and separated from 
the twisted remains of the steel chassis, and the chassis and debris at a 
distance from the original anchorage site. Ages of homes could not be 
determined; no data plates or labels could be found. Most of the 
manufactured homes in this location were single-wide, 14-ft by 60- or 70-ft 
units, originally connected to the ground by helical ground anchors and 
galvanized steel straps fastened to the steel chassis beams. 
Foundation support was typically provided by ungrouted (dry stacked) 
concrete masonry unit (CMU) piers at six to eight feet on center under each 
chassis beam. The total number of anchors per home varied considerably, 
from four to eight per home. The most spectacular failure observed was a 14- 
ft by 60-ft manufactured home chassis found about 200 yards to the northeast 
FIGURE 4-47: Chimney 
failure onto roof of single 
family attached housing 
located along the 
periphery of a severe 
tornado, Wichita, 
Kansas.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-41 
of its original anchorage site (Figure 4-48). This home was not affected by 
the vortex of a tornado, rather, it was affected by the inflow winds whose 
violent tornado vortex was approximately 300-400 ft away from this home. 
At the original site, vertical and diagonal straps remained attached to the 
ground anchor, but had failed about two to three feet from the anchors 
(Figure 4-49). The first anchors had been fastened about 12-feet from the east 
end. Both the number of anchor straps and tensile capacity of the straps were 
inadequate to resist wind uplift forces (Figure 4-50). 
FIGURE 4-49: Failed 
straps at the anchorage 
of a manufactured home 
in Bridge Creek, 
Oklahoma. This site was 
300-400 feet from a 
violent tornado vortex. 
FIGURE 4-48: This 
14-ft x 60-ft 
manufactured home 
chassis in the 
background of this 
picture moved about 
200 yards from its 
original anchoring 
site in Figure 4-49, 
Bridge Creek, 
Oklahoma.
CHAPTER 4 PRELIMINARY REPORT 
4-42 FEDERAL EMERGENCY MANAGEMENT AGENCY 
After completing several site visits in the Oklahoma City metroplex, the 
BPAT visited Mulhall, Oklahoma, about 50 miles north of Oklahoma City. 
There were several double-wide manufactured houses damaged by a severe 
tornado. One 28-ft by 60-ft home had rotated on its piers, 2-ft to the east at 
the north end and 1-ft to the west at the south end. Three helical anchors 
were pulled out that had been installed about one-foot into the ground on the 
northwest end of the home (Figure 4-51). Anchor straps that were still 
attached to ground anchors and chassis beams were loose, which allowed 
lateral movement of the unit. Anchor depth into the loose sandy soil did not 
appear to be adequate to resist wind uplift and overturning forces (Figures 4- 
52 and 4-53) generated by a severe tornado whose vortex passed nearby, but 
did not directly strike the homes. 
FIGURE 4-50: Strap 
anchoring failure most 
likely led to the 
displacement of this 
chassis, Bridge Creek, 
Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-43 
Figure 4-51: Ground 
anchor of manufactured 
home pulled from soil. 
This home in Wichita, 
Kansas, was located 
within the inflow area of 
a severe tornado. 
Figure 4-52: Anchor of 
manufactured home bent 
and pulled up from soil. 
This home in Wichita, 
Kansas, was located 
within the inflow area of 
a severe tornado.
CHAPTER 4 PRELIMINARY REPORT 
4-44 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Several manufactured homes had lost plywood roof sheathing and roof 
trusses, and some only lost asphalt roof shingles. Fastening of the roof 
sheathing and roofing materials was inadequate to resist wind uplift (Figures 
4-54 and 4-55) from inflow winds of a severe tornado. 
Figure 4-53: Strap torn 
off from chassis of 
manufactured home. 
This home in Wichita, 
Kansas, was located 
within the inflow area of 
a severe tornado. 
Figure 4-54: Roof and 
wall damage 
experienced due to 
inadequate resistance to 
lateral and uplift wind 
forces associated with 
straight inflow winds of 
a moderate tornado, 
Wichita, Kansas.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-45 
In Haysville, Kansas, the BPAT visited the Sunset Field Addition on South 
65th Street near the historic district, where several double-wide manufactured 
housing units were constructed on permanent concrete crawl space 
foundations. It was reported that roofs and several walls of the units had been 
destroyed, but that the floors had remained on the foundation walls. Later, 
during demolition, the floor system and steel chassis beams with steel 
outriggers and steel angle bracing had been lifted off the foundation. 
Although the floors had remained on the concrete walls, there were no bolts 
or positive connections between the chassis or perimeter wood joist and the 
sill-plate, pockets in the concrete walls, or center piers (Figure 4-56). Straps 
that had been stapled to wall studs and to perimeter joists did not appear 
adequate to resist wind uplift or lateral loads (Figure 4-57), and fastening of 
the roof system to walls had been inadequate. 
Figure 4-55: Damage to a 
manufactured home 
located on the periphery 
of a severe tornado, 
Wichita, Kansas.
CHAPTER 4 PRELIMINARY REPORT 
4-46 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Several double-wide manufactured housing units partially survived high 
wind forces. However, ground anchors were pulled out of the soil, or they 
were bent over, loosening up tie-down straps. Homes shifted laterally from 
wind forces and fell off unreinforced and ungrouted CMU block piers. In 
some cases, tie-down straps with metal clips for attachment to chassis beams 
were loose and lying on the ground (Figures 4-58 through 4-61).(location 
and wind?) 
FIGURE 4-56: Lack of 
bolts or positive 
connections present 
between the chassis 
and foundation, 
Haysville, Kansas. 
FIGURE 4-57: A close 
up of the manufactured 
home floor and chassis 
after it was removed 
from the permanent 
foundation in Figure 4- 
56.
PRELIMINARY REPORT OBSERVATIONS ON RESIDENTIAL PROPERTY PROTECTION CHAPTER 4 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 4-47 
FIGURE 4-58: This 
manufactured home 
laterally shifted from 
wind force generated 
along the periphery of a 
violent tornado, 
Haysville, Kansas. 
FIGURE 4-59: View of 
anchor strap and 
attachment indicating 
lateral shifting of a 
manufactured home, 
Haysville, Kansas. This 
home was located along 
the periphery of a violent 
tornado.
CHAPTER 4 PRELIMINARY REPORT 
4-48 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 4-60: View of 
anchor strap and 
attachment indicating 
some lateral shifting of a 
manufactured home 
located along the 
periphery of a violent 
tornado, Wichita, 
Kansas. 
FIGURE 4-61: 
Manufactured home 
laterally shifted from 
wind force generated 
along the periphery of a 
violent tornado, Wichita, 
Kansas.
CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-1 
5 Observations on 
Non-residential 
Property Protection 
This section presents the BPAT's observations on non-residential property 
protection. The non-residential buildings were categorized into the various 
engineered types of construction focusing on the structural performance of 
each type of building. Important observations were also made concerning 
exterior architectural systems (e.g., roof and wall coverings, windows and 
doors). 
A number of non-residential buildings, such as schools, factories, 
warehouses, and commercial buildings were in the direct path of the tornado 
vortexes or in the inflow/outflow and received damage. In a few cases, 
damage could be considered non-structural because architectural and 
decorative materials on the exterior and roofing were the only damage to the 
buildings; in engineering standards such as ASCE 7, these materials are often 
referred to as components and cladding. In other cases, structural damage 
occurred due to the lack of redundancy in the structural system in the form of 
a continuous load path to resist wind-induced uplift loads. 
5.1 CONTINUOUS LOAD PATH 
A continuous load path from the roof structure to a building foundation is 
essential for a building. This load path, the members and connections 
between members, is capable of withstanding gravity or downward design 
loads. However, during high wind events such as tornadoes, lateral loads and 
uplift loads will act on the building and test the capacity of the continuous 
load paths. Figure 5-1 shows critical connections in the continuous load paths 
for representative types of non-residential buildings that sustained structural 
damage. In addition to the lateral wind forces that are often considered in 
design, significant uplift loads generated by the high wind velocity associated 
with tornadoes act on the roofs. To resist these loads, adequate connections 
must be provided between the roof decking and roof structural support, bar 
joists or other structural roofing members and walls, and foundation and 
walls or structural columns. Each of these connections must be capable of 
resisting uplift and lateral loads as well as gravity loads.
CHAPTER 5 PRELIMINARY REPORT 
5-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
5.1.1 Tilt-up Precast Concrete Walls with Steel Joists 
Inspection of a damaged tilt-up precast concrete wall building in Moore, 
Oklahoma, found no deficiencies with connections between the tilt-up walls 
and the foundation. However, connections between the roof systems and the 
tilt-up walls failed in some buildings. In a commercial building along 
Interstate I-35 outside Del City, Oklahoma, failure of these connections 
caused a loss of diaphragm action, which then led to collapse of the endwalls 
of this building and will be discussed further in Section 5.2.1. Figure 5-2 is a 
photograph of this building. The vortex of a violent tornado passed 
approximately 200 yards from this building, generating inflow winds that 
removed the roof of this structure. Once the roof of the building was 
removed and diaphragm action was lost, the endwall that was already being 
acted upon by outward (suction) wind forces failed. 
FIGURE 5-1: Critical 
connections that failed 
in the load path 
resulting in structural 
damage or collapse.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-3 
5.1.2 Load Bearing Masonry with Steel Joists 
The BPAT inspected Kelly Elementary School in Moore, Oklahoma, which 
was in the direct path of the vortex of the violent tornado. The school 
included a steel frame building in the main section, and a section that was 
constructed with load bearing masonry walls with steel joists. 
This section discusses the damage associated with the masonry wall section 
of the building; Section 5.1.3 will discuss the steel frame section of the 
school. Figure 5-3 shows damage to the Kelly Elementary School. Arrows 
show separation between the bond beam and its supporting wall and 
separation between the bond beam and roof bar joists. At both locations, 
connections between the bond beam, joists, and walls were adequate for 
gravity load, but could not carry the high uplift loads that were caused by 
winds associated with the violent tornado. 
FIGURE 5-2: Tilt-up 
precast concrete walls 
at a storage building 
located outside Del 
City, Oklahoma. After 
the roof joists 
separated from the 
walls, this end wall 
became unable to 
withstand suction 
forces and failed.
CHAPTER 5 PRELIMINARY REPORT 
5-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Figure 5-4 shows a close-up of a joist end over the old cafeteria. The arrow 
shows a location where the roof deck was supported for gravity load, but not 
welded for uplift. Below the arrow, broken welds can be seen. Also visible 
in Figure 5-4 is the lower portion of the external wall. As illustrated in the 
photograph, no effective vertical reinforcement was found in the wall. 
Consequently, the wall had low resistance to uplift in combination with high 
lateral wind loads. 
FIGURE 5-3: Kelly 
Elementary School, in 
Moore, Oklahoma, hit by 
vortex of violent tornado. 
Damage to school 
displaying separation 
between the bond beam 
and supporting wall and 
separation between bond 
beam and roof bar joists.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-5 
5.1.3 Steel Frame with Masonry Infill Walls 
The BPAT visited a regional outlet mall in Stroud, Oklahoma, where the 
entire roof was blown away and significant damage to the building was 
evident. This mall was struck by a moderate tornado that collapsed the 
central portion of the buildings steel frame and damaged many of its 
masonry and steel frame walls. Figure 5-5 shows standing seam roof 
attachments of the decking to the purlins in one area of the mall that failed 
under the uplift loading. It was observed that threaded fasteners used to 
attach portions of the exterior cladding to the frame performed better than the 
standing seam roof attachments. 
FIGURE 5-4: Failed 
structure showing 
broken deck welds, and 
no effective vertical 
reinforcement. Kelly 
Elementary School, 
Moore, Oklahoma, hit by 
vortex of violent 
tornado. 
FIGURE 5-5: Metal roof 
deck of regional outlet 
mall, Stroud, 
Oklahoma, blown off 
when hit by moderate 
tornado vortex.
CHAPTER 5 PRELIMINARY REPORT 
5-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Figure 5-6 shows the attachment of columns to the foundation and 
attachment of the wall bottom plates to slab concrete. At the arrow on the 
right in Figure 5-6, anchor bolts were provided but the apparent lack of nuts 
on the anchor bolts permitted the column to lift off of the foundation. At the 
center arrow, anchor bolts with properly attached nuts provided a high level 
of restraint to column lift off. The arrow at the left of Figure 5-6 shows a wall 
bottom plate that was attached to the concrete slab by power driven nails. 
Although the plate held at this location, lack of penetration by the nails into 
the concrete permitted the plate to pull out at many other locations. 
Additional nail penetration would be needed to assure consistent attachment 
of wall bottom plates to the slab. 
Most bolts with nuts exhibited a ductile steel failure as shown in figure 5-7. 
This was the failure mode observed in most cases. This was also the failure 
mode for the anchorages at the steel water tower in Mulhall, Oklahoma. 
However, some of the bolts observed at the mall did pull out of the concrete 
foundation, indicating a failure in the concrete bond (see Figure 5-8). 
FIGURE 5-6: Attachment 
of columns to foundation 
and attachment of wall 
bottom plates to concrete 
slab. Regional outlet 
mall, Stroud, Oklahoma, 
hit by moderate tornado 
vortex.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-7 
5.1.4 Light Steel Frame Buildings 
The BPAT investigated the regional outlet mall that was destroyed in Stroud, 
Oklahoma. Figure 5-9 shows damage to the outlet mall. In this structure, 
most of the metal roof deck was blown off by the tornado. In addition, much 
of the metal curtainwalls used above lower, exterior masonry walls were 
destroyed. 
FIGURE 5-7: Column 
anchors that 
exhibited ductile 
failure at the regional 
outlet mall in Stroud, 
Oklahoma, hit by 
moderate tornado 
vortex. 
FIGURE 5-8: Column 
anchors that withdrew 
from concrete 
foundation at the 
regional outlet mall in 
Stroud, Oklahoma, hit 
by moderate tornado 
vortex.
CHAPTER 5 PRELIMINARY REPORT 
5-8 FEDERAL EMERGENCY MANAGEMENT AGENCY 
5.1.5 Laminated Wood Arches with Wood Frame Roof 
Lack of load path also resulted in severe damage to the Regency Park Baptist 
Church in Moore, Oklahoma. This building was approximately one block 
north and across the street from Kelly Elementary School. The vortex of a 
violent tornado passed approximately a few hundred yards to the south. 
Figure 5-10 shows the rigid frames remaining after the roof had been 
removed by the tornado. Loss of load path between the rigid frames and the 
roofing resulted in severe damage to the facility. 
FIGURE 5-9: Stroud 
Regional Outlet Mall, 
Stroud, Oklahoma was 
struck by the vortex of a 
moderate tornado. 
FIGURE 5-10: This 
church suffered loss 
of roof due to lack of 
load path between the 
rigid laminated wood 
arches and the roof 
purlins which 
supported roof 
sheathing. Inflow 
area of a violent 
tornado, Moore, 
Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-9 
5.1.6 Masonry Walls with Pre-cast Hollow Core Floors 
In several locations, combined effects of upward suction wind loads with 
horizontal wind loads caused unexpected damage to structures. When a 
continuous load path for uplift and lateral loads did not exist, roof failures 
and upper level floor failures were observed. Figure 5-11 shows the remains 
of a motel in Mid West City, Oklahoma, hit by a violent tornado vortex. The 
arrows show a steel beam that had been deflected inward significantly when 
the floor slab was lifted during the tornado. There was no positive 
connection between the steel beam and the floor above. 
5.2 INCREASED LOAD 
At a plastics manufacturing plant in Haysville, Kansas, a combination of 
upward and horizontal wind loads when the plant site was hit by a violent 
tornado caused out-of-plane buckling of the bottom flange of a main girder 
supporting the roof (Figure 5-12). One arrow shows the column that 
supports the girder, while the other arrow shows the bottom flange of the 
girder. It can be seen that the bottom flange has displaced significantly 
sideways in relation to the top flange of the girder. Inspection along the 
length of the girder indicated that the bottom flange was braced along its 
length at every purlin except at the location of the supporting column. This 
lack of bracing permitted buckling and out-of-plane displacement of the 
bottom flange. However, due to the light gravity loads left on the roof after 
the wind forces diminished, collapse did not occur. 
FIGURE 5-11: Motel in 
Mid West City, 
Oklahoma that 
experienced major 
damage when struck by 
the vortex of a violent 
tornado.
CHAPTER 5 PRELIMINARY REPORT 
5-10 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Another example of the effects of uplift and horizontal wind forces is seen in 
Figure 5-13 at Kelly Elementary School in Moore, Oklahoma. The exterior 
wall collapsed inward indicating that the roof had lifted up as the wind loads 
acted inward on the wall. Failure to have a continuous load path from the 
joists supports into the masonry wall to resist uplift forces contributed to 
collapse of the wall. The exterior masonry wall is seen lying on the floor 
beneath the collapsed roof structure. 
FIGURE 5-12: Out-ofplane 
buckling of the 
main girder supporting 
the roof created by a 
combination of uplift and 
horizontal wind loads. 
Plastics plant, Haysville, 
KS hit by violent tornado. 
This building was in the 
inflow area of a severe 
tornado. 
FIGURE 5-13: Collapsed 
roof structure and exterior 
at Kelly Elementary 
School in Moore, 
Oklahoma struck by the 
vortex of a violent 
tornado.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-11 
The Westmoore High School in Moore, Oklahoma, was a relatively new 
structure that was within 100 yards of the vortex of a violent tornado. 
Although most of the roofs stayed on this building, the roof over the 
auditorium stage was blown off. Figure 5-14 shows the walls where the bar 
joists had been attached prior to the tornado. In all cases, welds failed 
between bar joist ends and embedments in the walls in the auditorium stage 
roof. This loss of load path permitted the roof to be lifted up off of the 
reinforced concrete walls. 
Figure 5-15 shows the exterior of the reinforced concrete wall at Westmoore 
High School following the tornado. This 12-in thick by approximately 35-fttall 
wall remained essentially undamaged, even though the diaphragm action 
of the roof was lost. The construction of the stage area integrated an I-beam 
horizontal frame, shown in Figure 5-14, with the reinforced concrete walls. 
This frame provided diaphragm action that helped stabilize the walls. Prior 
to the tornado, the bare concrete had been covered with a decorative metal 
curtainwall. The entire curtainwall blew off during the tornado while brick 
masonry veneer on the lower wall remained, with virtually no damage. 
FIGURE 5-14: Roof 
blown off over top of 
auditorium at 
Westmoore High 
School, Moore, 
Oklahoma hit by inflow 
winds of violent 
tornado.
CHAPTER 5 PRELIMINARY REPORT 
5-12 FEDERAL EMERGENCY MANAGEMENT AGENCY 
5.2.1 Tilt-up Precast Concrete Walls with Steel Joists 
Diaphragm action is needed to supply lateral support at the tops of external 
walls for commercial buildings with open architecture, such as warehouses 
and open office buildings. When the support is lost, wind load resistance is 
greatly reduced and structural failure often follows. 
Figure 5-16 shows a tilt-up concrete wall that failed after loss of an interior 
diaphragm made up of steel joists and metal deck. This building was located 
approximately 200 yards from a violent tornado vortex near Del City, 
Oklahoma. As can be seen in Figure 5-16, the wall was well attached at the 
foundation level. However, loss of diaphragm at the top of the wall 
permitted the wall to blow outward and collapse. 
FIGURE 5-15: Exterior 
view of an undamaged 
reinforced concrete 
wall, Westmoore High 
School, Moore, 
Oklahoma, hit by inflow 
winds of a violent 
tornado. Note: 
decorative metal wall 
covering was peeled 
from this wall. 
FIGURE 5-16: Failure 
of tilt-up concrete 
wall in Del City, 
Oklahoma, hit by 
inflow winds of a 
violent tornado.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-13 
A factor contributing to collapse of the tilt-up wall was the placement of the 
vertical reinforcement. Close inspection of the broken surface indicated that 
reinforcing bars were placed near the exterior face of the wall. In tilt-up 
construction, the bars commonly are placed at mid-thickness of the wall. 
Placement of the reinforcement, as indicated by the arrow in Figure 5-16, 
significantly reduced the resistance of the wall to outward deflection or 
movement. 
Figures 5-17 and 5-18 show the top of the tilt-up precast concrete wall that 
failed. Figure 5-17 shows that diaphragm action provided by a beam 
supported by the wall was lost when the beam pulled out of the wall pocket. 
Failed welds tying the roof into the top of the tilt-up wall can also be seen in 
Figure 5-18. Visual inspection showed that only one of the four walls of the 
building collapsed. The other walls had part of the diaphragm action 
provided by remaining portions of the roof. 
FIGURE 5-17: Top of 
failed tilt-up wall.
CHAPTER 5 PRELIMINARY REPORT 
5-14 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Tilt-up walls at a facility that was located under the vortex of a moderate 
tornado in Wichita, Kansas, survived virtually undamaged, despite loss of 
metal deck roofing. As can be seen in Figure 5-19, trusses spanning the open 
area maintained diaphragm action. 
5.2.2 Load Bearing Masonry with Steel Joists 
In Figure 5-19, damage to a portion of the building having a steel joist roof 
supported on masonry walls can be seen at the left. Walls in this portion of 
the building collapsed when subjected to the vortex winds of a moderate 
tornado. Even though some diaphragm action was maintained, the masonry 
FIGURE 5-18: Top of 
failed tilt-up wall. 
FIGURE 5-19: The tiltup 
precast concrete 
walls in this building 
did not fail when the 
roof system failed. 
Note: many roof joists 
are still in place. 
Building was located 
in Wichita, KS and 
was hit by moderate 
tornado vortex.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-15 
walls did not have enough lateral load resistance under the combined uplift 
and horizontal load of the tornado. 
Figure 5-20 shows damage to both interior and exterior unreinforced 
masonry walls (URM) at Kelly Elementary in Moore, Oklahoma. Wind 
loads due to the vortex of a violent tornado lifted the roof system until the 
bond beam atop the URM wall failed. When this bond beam failed, the roof 
separated from the building and some interior walls failed. 
5.2.3 Masonry Walls with Pre-cast Hollow Core Floors 
At a motel in Mid West City, Oklahoma, which was hit directly the vortex of 
a moderate tornado, failures occurred between the second floor precast 
hollow core panels and their supporting walls. 
Figure 5-21 shows the location where hollow core plank had formed the 
second floor. The arrow at the right shows a dowel from the masonry wall 
into grout between the ends of two hollow core panels. One of the panels 
that had been at the edge of the building was found up on the second level 
and across on the far side of the building as shown by the arrow on the left of 
Figure 5-21. Apparently the uplift wind forces from the tornado were large 
enough to overcome the tie-down force provided by the very short dowels. 
The hollow core plank appears to have been lifted and blown across the 
width of the building. 
Figure 5-20: Damage to 
interior and exterior 
unreinforced masonry 
walls when bond beam 
failed at Kelly 
Elementary School in 
Moore, Oklahoma. The 
school was struck by 
the vortex of a violent 
tornado.
CHAPTER 5 PRELIMINARY REPORT 
5-16 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Elsewhere along the edge of the second floor of the motel, failure occurred 
between the hollow core planks and exterior walls of the building. As shown 
in Figure 5-22, lower plates for the walls had been attached to the hollow 
core planks using power driven anchors. As indicated by the arrows, the 
powder driven anchors pulled out during the tornado. 
FIGURE 5-21: Hollowcore 
plank formed on 
second floor of a 
Midwest City, 
Oklahoma, hotel that 
was struck by the 
vortex of a moderate 
tornado. 
FIGURE 5-22: 
Attachments of lower 
plates for wall to 
hollow core plank 
using power driven 
anchors failed when 
required to carry loads 
generated by the winds 
of a moderate tornado 
vortex. This motel was 
located in Midwest 
City, Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-17 
5.3 NON-RESIDENTIAL BUILDING ENVELOPES 
In many cases, tornado damage patterns observed demonstrated that 
additional collapse of buildings was caused by breach of the building 
envelope. Openings in the envelope caused by loss of garage doors or broken 
windows frequently contributed to local loss of roofs or walls of the building. 
The following is based on a limited number of non-residential building site 
visits by the BPAT. 
5.3.1 Roof Coverings 
The following roof types were observed: 
 Ethylene propylene diene monomer (EPDM) with 
aggregate (stone) ballast 
 built-up (aggregate ballast over cap sheet) 
 metal panel (architectural and structural) including standing 
seam 
 tile 
All of the roofs observed experienced blow-off problems, except for a builtup 
cap sheet roof that was at the periphery of the tornado damage area. 
Windborne missiles, wind driven and free-falling, punctured some of the 
roofs. In the case of metal panels on pre-engineered frames, it was not 
determined whether the panels blew off before or after failure of the 
supporting frames. 
Site visits revealed poor connections between wood nailers and the structure 
at roof perimeters. In one case, roofing nails were used to attach perlite 
insulation. This type of attachment offered very little uplift resistance. 
In one case, loss of a large portion of a built-up roof with aggregate ballast 
resulted in significant rainfall water infiltration into a hospital in Stroud, 
Oklahoma. After the storm, the hospital was closed and the patients moved to 
a facility about 30 miles away, which significantly reduced the availability of 
emergency medical services over this area of rural Oklahoma. The 
characteristics of the damage to the hospital were not indicative of tornado 
winds due to its distance from the tornado vortex. Rather, it is likely that the 
damage was caused by thunderstorm winds. The failure initiated when the 
coping lifted or with lifting of the nailer the to which the coping was attached 
(Figure 5-22). The nailer was poorly attached to a 4-in CMU that formed the 
parapet wall. In some areas, the CMU block parapet lifted slightly.
CHAPTER 5 PRELIMINARY REPORT 
5-18 FEDERAL EMERGENCY MANAGEMENT AGENCY 
5.3.2 Wall Coverings 
Brick veneer is discussed in Section 4.1.3.2. Some metal wall coverings over 
steel studs collapsed (Figure 5-24). Some Exterior Insulating Finishing 
System (EIFS) failures were observed. 
Figure 5.23: Nailer at the 
roof of the hospital in 
Stroud, Oklahoma. The 
roof surface in this photo 
was replaced prior to this 
photo, but the same 
nailer was used again. 
FIGURE 5-24: This metalclad 
wall covering 
collapsed and in other 
areas it was blown 
completely away.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-19 
5.3.3 Laminated Glass 
In a few instances, examples of laminated glass performance were observed. 
In some cases the glass remained in the frame after windborne missile impact 
(Figure 5-25). In another case, the glass was punched out of its frame. The 
school in Figure 5-25 is located adjacent to Regency Park Baptist Church in 
Moore, OKLAHOMA in Figure 5-10. The vortex of a violent tornado 
passed a few hundred yards south of this building. 
5.3.4 Garage Doors, Exterior Doors and Windows 
The breach of overhead commercial doors caused internal pressurization of 
the structure leading to significant load increases. Not unlike the residential 
case, a breach in the building envelope was observed, in some cases, to 
initiate a partial or total failure of primary structural systems. This was 
particularly true for pre-engineered buildings, which typically had little 
redundancy in load transfer of their structural systems. Figure 5-26 shows a 
breached commercial overhead door belonging to a bread manufacturing and 
FIGURE 5-25: The corner 
of a table penetrated this 
laminated glass, but the 
glass remained in its 
frame. This school 
suffered major damage 
from inflow winds of a 
violent tornado in Moore, 
Oklahoma.
CHAPTER 5 PRELIMINARY REPORT 
5-20 FEDERAL EMERGENCY MANAGEMENT AGENCY 
distribution center in Wichita, KS. The building exterior walls were 
constructed using both concrete masonry block and tilt-up concrete panels. 
The roof deck was standing seam metal on a Z purlin system. The door 
failure appears to be a result of positive (inward) pressure. The breach may 
have caused a sufficient enough rapid increase in load to produce failure of 
the URM block wall. It is worth noting the location of the failed door is near 
a corner where high negative suction or (outward) pressure is likely to occur 
on the adjacent wall. As a result of the exterior wall collapse, severe damage 
to the roof system occurred due to the loss of the load bearing exterior 
support wall. However, notice that the roof collapsed to the interior of the 
building, which may indicate that uplift loads acting on the roof were 
insufficient to cause progressive peeling failure of the roof system. 
Figure 5-27 illustrates another condition in Wichita, KS where breach of the 
building envelope contributed to additional structural damage. In this case, 
loss of showroom windows and an overhead door greatly increased loads in 
the showroom and on the wall at the left of the photograph. These increased 
loads caused the walls to fail and the roof to partially collapse, thereby 
greatly increasing structural damage in the building. 
FIGURE 5-26: Failure of 
roof and walls on 
structure due to 
increased loads caused 
by initial failure of garage 
door, Wichita, Kansas.
PRELIMINARY REPORT OBSERVATIONS ON NON-RESIDENTIAL PROPERTY CHAPTER 5 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 5-21 
Figure 5-28 shows a steel door that appears to have been opened by impact 
of a heavy object. This door at Kelly Elementary School in Moore, 
Oklahoma, led into an area where the roof was completely missing. The 
breached door may have caused an increase in load that propagated damage 
to that part of the building envelope. A nearby door, which was also heavily 
impacted, but did not open, was located in an area of the school that saw less 
damage to the wall and roof of the building. 
FIGURE 5-27: Additional 
structural damage caused 
by breach of envelope in 
Wichita, Kansas.
CHAPTER 5 PRELIMINARY REPORT 
5-22 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 5-28: Damaged 
door most likely opened 
by impact with heavy 
object. Kelly Elementary 
School, Moore, Oklahoma.
CHAPTER 6 
Building Performance Assessment: Oklahoma and Kansas Tornadoes 6-1 
6 Observations on 
Personal Protection 
and Sheltering 
Existing and new construction can be strengthened to better resist wind 
forces associated with inflow and outflow winds and moderate tornadoes; 
however, sometimes more protection is required. To survive a violent 
tornado directly beneath the vortex or to minimize potential loss of life for 
any tornadic event, a hardened above ground or below ground shelter, 
specifically designed and constructed to provide near absolute protection, is 
the best alternative. 
6.1 SHELTERS 
Engineered shelters not only provide the best protection against loss of life 
for individuals subjected to a tornado, but also furnish the only protection 
reliably capable of providing survival. This section presents observations on 
the types of shelters observed by the BPAT. 
6.1.1 Types of Shelters 
Both above ground in-resident shelters and below ground shelters were 
successfully utilized in the May 3 storms in Oklahoma and Kansas, and were 
responsible for saving many lives. The above ground in-residence shelters 
observed were constructed of cast-in-place concrete. Figure 6-1 shows an 
above ground in-residence shelter located in Del City, Oklahoma, that 
consists of a reinforced concrete room (including a roof slab) located behind 
the brick veneer which was hit by inflow winds and was about 50 feet from 
the vortex of a violent tornado. Figure 6-2 shows the extent of damage the 
tornado caused on the homes surrounding the shelter. Homes in the 
foreground were hit by the tornado vortex. Homes adjacent to the home in 
Figure 6-1 were hit by inflow winds and are in the background. The other 
type of personal above ground shelter observed is an insulated concrete 
formed (ICF) shelter shown in Figure 6-3 which was hit by inflow winds of 
violent tornado in Bridge Creek, Oklahoma.
CHAPTER 6 PRELIMINARY REPORT 
6-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 6-1 Above ground 
in-residence shelter hit by 
strong inflow winds near 
the vortex of a violent 
tornado in Del City, 
Oklahoma. Arrows 
indicate the extent of this 
reinforced concrete 
shelter that cannot be 
seen due to the exterior 
brick masonry veneer. 
FIGURE 6-2: Damage to 
houses near the home in 
Figure 6-1.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-3 
Below ground shelters included shelters constructed in basements as well as 
self-contained shelters located out of the building footprint, sometimes 
known as storm cellars. Basements were typically constructed of cast-in 
place concrete or CMU walls, and ceilings were normally wood framed 
structures constituting the structure for the floor above. Basements intended 
for occupancy and normal use contained windows, some of which were 
planned for egress from sleeping spaces. A basement may function as a place 
of refuge, but can not be considered an engineered shelter unless it has been 
designed to perform as a shelter. Refer to Section 6.2.1 for use of typical 
basements for refuge. The storm cellars observed by the BPAT were 
constructed of cast-in-place or precast concrete (Figure 6-4), and 
prefabricated steel with a concrete cover (Figure 6-5). Figure 6-6 shows a 
community shelter observed by the BPAT. The BPAT did not observe 
fiberglass or steel tank storm cellars, though numerous proprietary storm 
cellar systems are available that are constructed of these materials. 
FIGURE 6-3: Entrance to 
the ICF shelter in Bridge 
Creek, Oklahoma. This 
residence and shelter 
were on periphery of the 
inflow winds of a violent 
tornado, and damage was 
limited to light missile 
impacts.
CHAPTER 6 PRELIMINARY REPORT 
6-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 6-4: This precast 
concrete storm cellar was 
located immediately 
behind a residence in 
Sedgwick County, 
Kansas. This residence 
and shelter were on the 
periphery of a violent 
tornado path. 
FIGURE 6-5: Del City 
storm cellar constructed 
of steel sheets with a 
concrete cover. This area 
was directly struck by the 
vortex of a violent 
tornado.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-5 
6.1.2 Use of Shelters 
Shelters observed by the BPAT appeared to be constructed and located by 
occupant type. 
Family-size shelters situated near or in the residence for immediate use in the 
case of danger were evident throughout Oklahoma and Kansas. In 
Oklahoma, the BPAT observed a few above ground in-residence shelters that 
had been added to their existing homes or incorporated into the construction 
of their new homes. In Kansas, no above ground in-residence shelters 
damaged by the tornadoes were inspected by the BPAT. However, the 
BPAT did inspect new reinforced concrete above ground in-residence 
shelters that were being constructed in Wichita, Kansas (Figure 6-7). 
FIGURE 6-6: Community 
Shelter at a Wichita, 
Kansas, manufactured 
home park. While the 
park was directly hit by a 
severe tornado, the 
shelter was not within the 
damaged area.
CHAPTER 6 PRELIMINARY REPORT 
6-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Group-sized shelters were the second type of shelter observed. A groupsized 
shelter was located within a plastics manufacturing plant in Haysville, 
Kansas, and is intended to accommodate factory workers (Figure 6-8). The 
plant's shelter functioned daily as a conference and lunch room for 
employees. Although a violent tornado damaged other buildings on the plant 
site, the building containing this shelter received damage only in one isolated 
area, where a partial roof collapse occurred. Other smaller group-sized 
shelters were observed at a new manufactured home rental development, 
which provided precast concrete shelters (1 per 4 homes) (Figure 6-9). None 
of the group-size shelters observed by the BPAT were directly impacted by a 
tornado on May 3, 1999. 
FIGURE 6-7: Above 
ground in-residence 
shelters under 
construction in Wichita, 
Kansas.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-7 
Community-sized or mass shelters were also inspected by the BPAT. A 
manufactured home community shelter in Wichita, Kansas, was constructed 
partially underground, located at one end of the large development, and was 
intended to house all residents of the development (Figure 6-10). 
Approximately 200 people reportedly sought shelter in this building during 
the May 3, 1999, tornadoes. Another community-sized shelter was located 
underground and under the concrete bleachers in the Mid West High School 
gymnasium in Mid West City, Oklahoma (Figure 6-11). Approximately 500 
people sought shelter here during the May 3, 1999 tornado (the shelter has a 
FIGURE 6-8: Entrance to 
the plastics 
manufacturing plant 
group shelter in Haysville, 
Kansas. 
FIGURE 6-9: Group 
shelters at a 
manufactured home 
development in Wichita, 
Kansas.
CHAPTER 6 PRELIMINARY REPORT 
6-8 FEDERAL EMERGENCY MANAGEMENT AGENCY 
capacity of 3,500). A similar shelter is located at Del City, Oklahoma, High 
School. Members of the community are generally aware of the location of 
these shelters. Interviews with residents of the manufactured home 
community indicated that parking was a problem at the community shelter. 
In contrast, ample parking is available near the gymnasiums for those 
seeking shelter. 
FIGURE 6-10: 
Manufactured home 
development community 
shelter in Wichita, 
Kansas. 
FIGURE 6-11: Community 
shelter, Mid West High 
School gymnasium in Mid 
West City, Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-9 
6.1.3 Maintenance Issues of Shelters 
The BPAT observed deficiencies in some shelters inspected during the field 
investigation. Underground, partially underground shelters, or shelters 
located exterior to buildings were subject to moisture and the associated 
deterioration. Insufficient attention often was paid to these shelters with 
regard to waterproofing of walls and roofs and resulted in musty and damp 
environments. These conditions were perhaps merely an inconvenience for 
the family-size or small group shelter, but were potentially environmentally 
hazardous to occupants with allergies or respiratory ailments in the large 
group and community shelters. 
In numerous cases, the BPAT observed that poor selection of building 
materials and maintenance of painted items such as hinges and latches led to 
failures or poor performance (Figure 6-12). Storm cellar doors observed by 
the BPAT were often covered with thin gauge sheet-metal and exhibited 
deterioration of the zinc galvanization resulting from corrosion. The sheetmetal 
storm cellar doors were often backed with untreated plywood that was 
usually found to be rotted, delaminated, or otherwise deteriorated to the point 
where it was no longer useful in providing protection to the shelter opening. 
Numerous other deficiencies were observed regarding shelter doors and 
hardware. Most of the storm cellar doors were of insufficient thickness to 
withstand tornadic wind forces and windborne missiles. Most shelter door 
latching devices were also insufficient to withstand wind forces and missiles 
FIGURE 6-12: Door to 
underground shelter with 
rotting wood and 
corroded hinges.
CHAPTER 6 PRELIMINARY REPORT 
6-10 FEDERAL EMERGENCY MANAGEMENT AGENCY 
and one observed failure resulted in the door destruction and the partial 
filling of the storm cellar with debris (Figure 6-13). Widespread door failures 
were observed on the below-ground shelters; this included both metal and 
wooden doors. The above ground in-resident shelters observed had hollow 
metal doors and three hinges on one side and an insufficient single deadbolt 
locking device (Figure 6-14). The door metal skin thickness and the single 
lock would have probably been insufficient to secure the door had they 
experienced a direct missile strike from a violent tornado vortex or near 
vortex inflow area. 
FIGURE 6-13: Failed 
wooden door at a below 
ground shelter in 
Oklahoma.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-11 
Other shortcomings of shelters were observed by the BPAT. The community 
shelter in Figure 6-15 produced a potential safety hazard to nearby buildings 
resulting from missile generation from a fence and a ballasted roof covering. 
Figure 6-15 shows the aggregate ballast roof covering on the community 
shelter in Wichita, Kansas. A security fence that surrounded this roof area 
was damaged and removed by the winds of the violent tornado that impacted 
the opposite side of this community. Aggregate ballast shown in the photo 
may become airborne during high wind events and cause damage to other 
properties and injure individuals attempting to access the shelter. 
FIGURE 6-14: Shelter door 
of home in Del City, 
Oklahoma, showing an 
insufficient deadbolt 
locking device. The 
circled area on the door 
frame is the catch for the 
only latching mechanism 
on the door.
CHAPTER 6 PRELIMINARY REPORT 
6-12 FEDERAL EMERGENCY MANAGEMENT AGENCY 
6.1.4 Shelter Accessibility 
The observed above ground in-residence shelters were easily accessible by 
the home occupants. Observed door widths would have allowed access by 
wheelchair or otherwise disabled occupant. The group or community shelters 
observed by the BPAT had restrictive entrances that may have hampered 
access to the shelters by persons with disabilities. Figure 6-16 shows stairs 
leading to the entrance of a community shelter in Kansas. Additionally, 
several of the community shelters were locked and required authorized 
admission. Access to the community shelter in Figures 6-10 and 6-16 was 
restricted to community members without pets and the travel distance from 
the far end of the development to the shelter was approximately several city 
blocks. The group shelters observed also require access via stairs at both the 
plastics manufacturing plant and the manufactured home rental development. 
Figure 6-17 shows the stairs required to access the group shelter and the 
manufactured home rental development. 
FIGURE 6-15: Ballast roof 
covering on a community 
shelter in Wichita, Kansas 
was a potential source of 
deadly windborne 
missiles to those seeking 
to access the shelter.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-13 
FIGURE 6-16: Stairway 
leading to entrance of 
manufactured home 
community shelter, 
Wichita, Kansas. The only 
means of accessing this 
structure were this 
stairway and an identical 
on at the other side of the 
shelter.
CHAPTER 6 PRELIMINARY REPORT 
6-14 FEDERAL EMERGENCY MANAGEMENT AGENCY 
The gymnasium community shelters required suitable storm warnings 
because of travel time, distance, and time required to open the facility. In 
unincorporated Sedgwick County, Kansas, a wheelchair bound individual, 
who resided in a manufactured home was unable traverse the stairs into a 
neighbor's home and down into the basement. The individual attempted to 
take shelter back in his manufactured home and was killed by a violent 
tornado that destroyed the manufactured home. 
6.1.5 Shelter Ventilation 
The observed above ground in-residence shelters did have outlets for forced 
air ventilation from the home HVAC system; however no other method of 
natural ventilation was included. All observed underground or partially 
underground shelters outside the building footprint had some means of 
natural passive ventilation. The most common types of ventilation 
FIGURE 6-17: Stairway 
access to group shelter at 
manufactured home 
rental development, 
Wichita, Kansas. This 
development was not 
affected by any of the 
tornadoes that struck on 
May 3, 1999.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-15 
mechanism observed were vent pipes (Figure 6-18) or turbine ventilators 
(Figure 6-9). The vent pipe in Figure 6-18 was sufficiently thick enough to 
not be broken by windborne debris and was capped to prevent the intrusion 
of debris. The turbine ventilator observed in Figure 6-9 was 8-inches in 
diameter and made of light gauge metal. It would have been easily destroyed 
by flying debris if impacted by even a moderate tornado, thereby allowing 
free-falling debris to enter the shelter through the 8-in diameter opening in 
the roof of the shelter, placing the safety of the occupants at risk. 
6.1.6 Shelter Location 
Most above ground in-resident shelters observed were easily accessible by 
the occupants. Their location within the house allowed access with minimal 
threat to wind and windborne debris. Basements and basement shelters 
offered the same advantages, but posed an access problem to occupants with 
disabilities. Basement windows and wells, however, were poorly protected 
and vulnerable to windborne debris (Figure 6-19). In addition, basement 
shelters only offered minimal protection when the house was blown off the 
foundation, leaving those seeking shelter in the basement subject to 
windborne missiles. 
FIGURE 6-18: Heavy gauge 
ventilation pipe for a 
below ground shelter in 
Oklahoma withstood 
considerable debris 
impact.
CHAPTER 6 PRELIMINARY REPORT 
6-16 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Storm cellars (underground cellars) were located either in the front, side, or 
rear yards of the homes. Front yard locations were vulnerable to vehicular 
traffic and water runoff. The side and rear yard cellars were also vulnerable 
to water runoff (Figure 6-20). In many cases, the cellar entrance was 
insufficiently raised above grade and would have allowed for easy entrance 
of water. 
FIGURE 6-19: Basement 
windows of residential 
home, showing 
vulnerability to debris.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-17 
6.2 OTHER PLACES OF REFUGE 
If a specially designed tornado shelter is not available for refuge, people are 
forced to seek shelter in areas not intended to be places of refuge. Although 
some areas typically offer a relatively greater level of protection than others, 
when people take refuge in a portion of a building that was not specifically 
designed and built as a tornado shelter, they are at significant risk of being 
injured or killed if a tornado of any intensity directly strikes the building or 
passes nearby. The following sections discuss areas where occupants often 
seek shelter protection areas within residential and non-residential buildings 
that do not have specifically designed tornado shelters. 
FIGURE 6-20: This below 
ground shelter is 
susceptible to water 
runoff.
CHAPTER 6 PRELIMINARY REPORT 
6-18 FEDERAL EMERGENCY MANAGEMENT AGENCY 
6.2.1 Refuge in Residences 
For conventionally-constructed residences without basements or specially 
designed tornado shelters, observations following the Oklahoma and Kansas 
tornadoes, as well as previous post-tornado damage investigations, 
consistently revealed that interior bathrooms and closets offer the greatest 
occupant protection. Interior bathrooms and closets are small rooms that do 
not have an exterior wall (Figure 6-21). 
In many instances, only the interior core of the residence was left standing 
while the exterior walls and other interior walls and the roof structure and 
ceiling were blown away. The surviving core typically was composed of a 
bathroom, a closet or two, and perhaps a kitchen wall that was stiffened by 
cabinets (Figure 4-22). While interior bathrooms and closets typically offer 
the greatest protection, people taking refuge in them are at great risk during a 
tornado, as illustrated by Figures 6-23, 6-24, 6-25, and 6-26. While some 
minimal protection from missiles is provided by the core walls and cabinets, 
in many cases the rooms were left open to the sky when the buildings roof 
was blown away and occupants were therefore totally unprotected from free 
falling missiles (see Section 3.3). 
FIGURE 6-21: Remains of 
an interior room or core 
of a home in a Moore, 
Oklahoma, subdivision 
that was hit by a violent 
tornado.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-19 
FIGURE 6-22: Interior 
core of house remains, 
consisting of a bathroom, 
closets and a wall with 
kitchen cabinets after 
being struck by a severe 
tornado. 
FIGURE 6-23: This house 
outside of Moore, 
Oklahoma, was affected 
by inflow winds 
associated with a severe 
tornado. The roof and 
ceiling were blown off of 
the interior bathroom of 
this house, the door was 
blown into the bathroom, 
and the tub was full of 
debris. This bathroom 
was not a safe refuge.
CHAPTER 6 PRELIMINARY REPORT 
6-20 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 6-24: A 10-ft long 2- 
in by 6-in missile penetrated 
the exterior wall of this 
house in Wichita, Kansas, 
which was sheathed with 
hardboard panels. The 
missile, which was 
generated from the vortex of 
a severe tornado, then 
penetrated the gypsum 
board and tile tub enclosure, 
the tempered glass shower 
door, and the interior 
partition near the door 
frame. At the interior 
partition, it pierced through 
a wall stud and projected a 
few inches into the hallway 
(Figure 6-25). 
FIGURE 6-25: The missile in 
Figure 6-24 impacted and 
broke a 2-in by 4-in wall 
stud after traveling through 
the bathroom.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-21 
If the residence was more than one floor above grade, the first floor 
consistently was found to suffer less structural damage than the second floor 
(Figure 6-27). Therefore, greater protection was afforded when refuge was 
taken in interior bathrooms or closets on the first floor rather than the second. 
FIGURE 6-26: This 
bathroom was on an 
exterior wall and had a 
window. It was not a safe 
refuge.
CHAPTER 6 PRELIMINARY REPORT 
6-22 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Basements were uncommon in the areas investigated in Oklahoma; however, 
many of the houses investigated in Kansas did have basements. Basements 
typically provided greater occupant protection than first floor bathrooms or 
closets; however, as with first floor bathrooms and closets, basements were 
not immune to tornado damage. In one instance, a vehicle was blown into a 
house, penetrated the first floor, and hit or nearly hit the basement slab and 
then was sucked back out of the house. In other instances, missiles traveled 
down the stairway to the basement and flew into rooms at the bottom of the 
stairway. Basements, that were partially above grade and had windows, were 
observed to be susceptible to missile penetration (Figure 6-19). 
Below-grade crawl spaces were also observed in Kansas. These spaces 
provided protection from missiles traveling horizontally, but as with 
basements, minimal protection was provided from free falling missiles when 
the house above was blown off its foundation. In one case, a person in a 
below-grade crawl space was seriously injured even though the floor 
sheathing remained in place. There was reportedly sufficient high-speed 
wind flow within the crawl space to blow the person around, causing 
numerous injuries that required hospitalization. 
Based on the BPAT observations, persons taking refuge in bathrooms or 
closets in manufactured houses not attached to properly constructed 
permanent foundations appear to be at significantly greater risk of injury or 
death than persons taking similar refuge in conventionally constructed 
housing (Figure 6-28). The bathrooms and closets of manufactured houses 
typically provide very little protection. The BPAT observed a possible 
exception in some of the newer manufactured homes placed on proper 
FIGURE 6-27: The second 
story of single and multifamily 
houses typically 
experienced far greater 
damage than the first 
story. This multi-family 
home in Wichita, Kansas, 
was affected by inflow 
winds of a severe 
tornado.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-23 
foundations, built to the Department of Urban Development's (HUD's) newer 
wind requirements, and designed to resist increased wind loads. 
6.2.2 Refuge in Non-residential Buildings 
The BPAT also investigated a selected number of public use buildings in 
order to determine the existence of formalized emergency plans for tornado 
refuge. These buildings included public schools, nursing homes, and a daycare 
center. In all cases, each had a formal tornado refuge plan. 
The nursing home tornado refuge plan, which was successfully exercised 
during the storm, consisted of evacuating staff and residents to the central 
core of the building and evacuating the long, exposed corridors of the 
building. The day-care centers plan similarly utilized a central corridor; 
however, the building was not occupied during the storm. Neither building 
was directly hit by a tornado or suffered major damage. 
The emergency plans of five public schools were reviewed by the BPAT. 
Westmoore High School, located in the City of Moore, was within 100 yards 
of the vortex of a violent tornado and received building envelope and roof 
structure damage. Just prior to the storm, several hundred students and 
parents occupied the auditorium. In accordance with the emergency plan, 
most of the students and parents were moved to a predetermined area in a 
central core of the building where they successfully took refuge (Figure 6- 
29). Other individuals reportedly took refuge in a reinforced concrete 
stairwell adjacent to the auditorium. 
FIGURE 6-28: Damaged 
and destroyed 
manufactured homes in 
Wichita, Kansas, that 
were in the direct path 
of a severe tornado.
CHAPTER 6 PRELIMINARY REPORT 
6-24 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Eastlake Elementary in Moore, Oklahoma, was on the outer periphery of a 
violent tornado and received minor building envelope and cladding damage. 
The building construction consists of CMU walls with brick veneer and builtup 
roof over steel decking and steel bar joists. Interior classroom walls were 
also built of CMU. The tornado plan for the school indicated that the places 
of refuge consisted of each classroom within the building, even though each 
classroom entrance door (from the interior hallway) was flanked by a large 
glass sidelight (Figure 6-30). There were no exterior windows in the exterior 
wall of the classrooms. Centrally located offices were also identified as 
places of refuge with the building. None of the identified areas appeared 
sufficiently constructed to withstand a direct hit by a violent tornado. 
FIGURE 6-29: Westmoore 
High School, Moore, 
Oklahoma, central locker 
core - a designated place 
of refuge.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-25 
Tornado refuge plans for Northmoor Elementary and Kelly Elementary in 
Moore and Sooner Rose Elementary in MidWest City were reviewed by the 
BPAT. None of the schools were occupied during the storm. Northmoor and 
Kelly were of a similar design and construction and had similar emergency 
plans of taking refuge in the double loaded corridors. Figure 6-31 shows a 
double loaded corridor of Northmoor that illustrates the corridor masonry 
walls topped with windows. Sooner Rose Elementary was a different 
construction type from the above, but contained similar windowed corridors 
(see Figure 6-33). Figure 6-32 shows a similar corridor in Kelly Elementary, 
which was destroyed by the storm. Obviously, had these corridors been used 
for shelter during the impact of a violent tornado, numerous injuries or deaths 
would have occurred. 
FIGURE 6-30: Eastlake 
Elementary, Moore, 
Oklahoma, glazed 
sidelight at classroom 
entrance.
CHAPTER 6 PRELIMINARY REPORT 
6-26 FEDERAL EMERGENCY MANAGEMENT AGENCY 
FIGURE 6-31: Northmoor 
Elementary place of 
refuge, Moore, Oklahoma 
- double loaded corridor 
with clerestory windows. 
This corridor offers little 
protection from a violent 
tornado as shown in a 
school of similar design 
in Figure 6-32. 
FIGURE 6-32: Kelly 
Elementary School, 
Moore, Oklahoma, place 
of refuge - double loaded 
corridor with clerestory 
windows. These interior 
corridor walls had brick 
masonry up to a height of 
approximately 7 feet. 
Glass extended from the 
top of the masonry to the 
top of the wall.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-27 
If a tornado is approaching an occupied non-residential building that does not 
have a specifically designed tornado shelter, or a tornado plan indicating 
places of refuge, it is difficult for building occupants to quickly determine 
where persons should be directed to take refuge. Some walls appear to offer 
substantial resistance to wind and windborne missile loads, but in fact have 
very little resistance. For example, an exterior insulation finish system 
(EIFS) can be mistaken for a concrete wall. However, most EIFS wall 
assemblies consist only of a thin layer of synthetic stucco over expanded 
polystyrene (EPS) insulation and gypsum board that is supported by studs, 
and a layer of gypsum board on the interior side of the studs (Figure 6-34). 
Brick and CMU walls can also be deceiving. If they are adequately 
reinforced and braced, they can offer a significant level of protection. But if 
they are inadequately reinforced or braced, they can collapse, thereby 
trapping and crushing people (Figure 6-35). 
FIGURE 6-33: Sooner 
Rose Elementary School, 
Mid West City, 
Oklahoma. According to 
the tornado plan for this 
school, this hallway is 
designated as a place of 
refuge  double loaded 
corridor.
CHAPTER 6 PRELIMINARY REPORT 
6-28 FEDERAL EMERGENCY MANAGEMENT AGENCY 
Basement areas without windows and concrete stair towers in multistory 
buildings generally provide a reasonable level of protection for occupants. 
Interior corridors and smaller rooms that do not have glass openings in doors 
or walls, and are inward as far as possible from exterior walls, may provide 
protection or a false sense of security, depending on the severity of the 
tornado and the proximity to the tornado vortex (Figure 6-36). Rooms with 
large ceiling spans such as auditoriums and gymnasiums should be avoided 
at all costs, unless specifically designed as shelters (e.g., more than 40 ft 
between walls or columns) often provide a lower level of occupant protection 
FIGURE 6-34: EIFS wall 
system torn from metal 
wall studs. 
FIGURE 6-35: The nonreinforced 
interior CMU 
walls in this area of Kelly 
Elementary collapsed 
after the roof system was 
removed by vortex winds 
of a violent tornado.
PRELIMINARY REPORT OBSERVATIONS ON PERSONAL PROTECTION AND SHELTERING CHAPTER 6 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 6-29 
than rooms with smaller spans. Again, these areas of refuge have been shown 
to provide little protection from the effects of a direct hit by a violent tornado 
vortex. 
FIGURE 6-36: The roof 
and ceiling over this 
interior bathroom blew 
off. CMU from a firewall 
a few feet away blew 
into the bathroom, 
which was located on a 
motel's second floor in 
Mid West City, 
Oklahoma. This 
bathroom was not a 
safe refuge when 
impacted by the vortex 
of a severe tornado.
CHAPTER 7 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 7-1 
7 Preliminary 
Conclusions 
The preliminary conclusions presented in this report are based on the BPAT's 
observations, an evaluation of relevant codes and regulations, meetings with 
State and local officials, and other interested parties such as organizations 
representing builders and contractors. The conclusions of this report are 
intended to assist communities, businesses, and individuals and to provide 
technical guidance for personal and property protection. 
7.1 RESIDENTIAL PROPERTY PROTECTION 
The BPAT observed considerable damage to single-family housing, multifamily 
housing, and manufactured and modular housing. Failures observed 
resulted from windborne debris and high winds that often produced forces on 
buildings not designed to withstand such forces. Failures, in some cases, also 
were observed that were due to improper construction techniques and poor 
selection of construction materials. Damage, in some situations, could have 
been reduced or avoided if newer building codes and engineering standards 
that provided better guidance for high wind events had been adopted, 
followed, and enforced. 
The majority of residential construction in Oklahoma and Kansas is currently 
required to be designed per the 1995 CABO One and Two Family Dwelling 
Code. Although local municipalities have adopted some amendments to this 
code, it does not incorporate wind speed design parameters used by the 
newer 1997 UBC and 1996 NBC codes. Furthermore, engineering standards 
such as ASCE 7-95 and 7-98 provide better structural and non-structural 
design guidance for wind loads than these newer codes. Although designing 
for tornadic wind events is not specifically addressed in any of these newer 
codes or standards, constructing residential homes to these codes and 
standards would improve the strength of the built environment. Building to 
these codes and standards would have led to reduced or minimized damage 
in areas that were affected by the inflow winds of all tornadoes and reduced 
the damage to residential construction impacted by the vortices of moderate 
tornadoes. 
7.1.1 Single- and Multi-family Homes 
The BPAT observed many single-family residential buildings that were in 
the direct path of tornado vortices or in the inflow areas that received
CHAPTER 7 PRELIMINARY REPORT 
7-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
structural damage. This damage was typically a result of the lack of 
redundancy in the structural system to resist wind-induced uplift loads, windinduced 
lateral loads, or increased loads on the building due to internal 
pressurization and a breach of the building envelope. It is crucial to establish 
a continuous load path in order to provide improved resistance to wind forces 
and windborne debris. 
In residential areas affected by the vortices of violent and severe tornadoes, it 
is difficult to economically construct a home that is tornado-resistant. 
However, improved construction and implementation of construction 
techniques that are used in other high wind-prone regions of the country may 
have significantly reduced the property damage caused by moderate tornado 
vortices and inflow winds of severe and violent tornadoes. 
7.1.1.1 Load Path and Structural Systems 
Foundations in the single- and multi-family homes performed adequately 
during the tornadoes in both Oklahoma and Kansas. The deficiency or failure 
mode of the load path at this point was the connection of the structural 
systems to the foundation. Wood framing relied on the connection of the sill 
plate or floor framing to the foundation wall or slab to maintain the load path. 
Straps, anchor bolts, epoxy set anchors, and nails were the most common 
fasteners. When properly used, the straps, anchor bolts, and epoxy set bolts 
maintained the connection of sill plate and floor framing to the foundations 
for most wind conditions. However, numerous instances of anchor bolts 
without nuts or misaligned anchor bolts at the sill plate and floor framing 
resulted in the house lifting off the foundation. Nailing of the sill plate to the 
foundation was adequate only in the areas that incurred minimal damage 
from inflow winds along the periphery of the tornado paths. 
Wall framing in single-and multi-family houses failed at the sill plate (sole 
plate) to stud connection under all wind conditions. This was the most 
common failure observed by the BPAT in wall framing. Revisions in the 
normal way of constructing wall framing are necessary if these weak links 
are to be addressed. A positive method of connecting the studs to the sill 
plate that can resist reasonable uplift forces is a necessity for providing a 
continuous load path. 
Wood framed walls also saw failures at the double top plate connection with 
the wall and the roof systems. Attention must be given to ensure a positive 
connection is provided for the uplift load transfer from the double top plate to 
the wall below. Straps or other connectors that would ensure a continuous 
load path to resist uplift loads were not observed at this location. Nails were 
the primary fasteners at this connection. Failures were observed between the 
studs and the top plate and between the two top plates. Typically, when this 
connection failed, no continuous structural sheathing was observed to help 
with this load transfer. Full length wood structural panels, from the top plates 
to the sill plate or floor framing, could act well as the uplift load transferring
PRELIMINARY REPORT PRELIMINARY CONCLUSIONS CHAPTER 7 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 7-3 
mechanism. The sheathing or other means of transferring the force must be 
connected to the double top plate by sufficient fasteners such as those 
required to attach sheathing as contained in the model building codes. 
The primary shear wall failure observed was that of garage return end walls 
that frame the garage door. The narrow walls where failure was observed 
possessed an aspect ratio (height to width ratio) that generally was less than 
recommended by industry or allowed by model building codes. The current 
building codes, which contain industry recommendations that are intended to 
provide a narrower shear wall, but yet be capable of resisting the design wind 
loads, should be followed. 
Although most of the roof framing configurations observed did not include a 
sufficient connection of the rafter to the ceiling joist, at least one of the 
model building codes does require such connection. In those cases where the 
ceiling joists existed and were parallel and adjacent to the roof rafters, 
additional resistance would have been provided if roof framing was 
connected to the ceiling joists. For the cases where the roof framing and 
ceiling joists were not parallel or adjacent, an insufficient number of 
observations were made to be able to draw any conclusions. 
Roof geometry was observed to affect building performance in two 
significant ways. First, the roof geometry affected both the local and overall 
wind loads acting on the roof. Second, the roof geometry affected the overall 
strength of the roof system based on its framing configuration (e.g., hip 
versus gable framing). In general, for residential (low rise) structures, the 
more complex shaped roofs experienced lower local loads (e.g., component 
and cladding loads such as individual roof deck sheathing loads) than did 
more simple roof geometry. The lower localized loads usually are the result 
of interference between the complex roof shape and the wind flow, which 
hinders the development of large negative pressure regions on the roof 
surfaces. 
In general, for flat, gable, and hip roof geometry, the largest localized loads 
occurred near the corners, the gable ends, and the edges of the roof ridge, 
respectively. However, the largest localized loads for gable roofs are 
noticeably higher than those for hip roofs. The net uplift forces acting on 
roofs are less dependent on roof geometry than are the localized component 
and cladding loads that are often the governing design loads when 
engineering standards such as ASCE 7-95 are used. As the total roof area 
increases, the contribution of intense localized loads to a total roof failure is 
reduced significantly. Although a localized load may fail a single piece of 
roof sheathing, it certainly will not cause the entire roof to fail. Such 
localized roof failures often allow rainfall to enter the structure causing 
significant collateral damage to the building interior and furnishings. When 
the roof fails as a single entity, it is the overall combination of all wind loads 
that will cause this failure.
CHAPTER 7 PRELIMINARY REPORT 
7-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
The effect of roof shape on the performance of residential structures in high 
winds varies with the size of the component being considered (e.g., roof 
covering, roof sheathing, single truss, entire roof, etc.), the wind directions 
producing the high winds, and the method and quality of construction. 
However, hip roof systems are a stronger system because of the method by 
which they are constructed. 
7.1.1.2 Increased Load Caused by Breach of Envelope 
BPAT inspections of wind-induced damage to residential buildings indicate 
that internal pressurization is a major contributor to poor building 
performance under moderate to severe wind loading conditions. Field 
observations provide strong evidence of partial and total roof and exterior 
wall failures that may have been initiated due to breaches in the building 
envelope leading to internal pressurization and significant load increases. 
Roof and wall coverings, garage doors, entry doors, and windows that are 
exposed to severe or violent tornado vortex winds are not expected to 
survive. However, on the periphery of severe and violent tornado tracks and 
in moderate tornadoes where the wind speeds may be near or below design 
wind speed conditions, the performance of these elements was less than 
expected. If non-structural envelope elements are suitably designed and 
tested to meet the wind loads derived newer standards, such as ASCE 7-95 
and ASCE 7-98, and are appropriately installed, much of the damage on the 
periphery of severe and violent tornado tracks and in the track of the vortex 
of moderate tornadoes would be significantly reduced. An exception to this 
would be missile-induced damage. 
For residential buildings, a significant contributor to catastrophic failures due 
to internal pressurization appeared to be the failure of single skin, noninsulated, 
and non-reinforced double width garage doors. Breaches of 
windows and entry doors might also cause significant damage to the 
residential building through internal pressurization. However, if wind speed 
and direction do not produce high local loads elsewhere on the building, the 
effect might not be as dramatic as that associated with a larger breach such as 
a residential garage door. Preliminary investigations determined that most 
garage doors are not rated or tested for wind pressures that may be calculated 
from the design wind speeds indicated in the currently enforced 1995 CABO 
Dwelling Code. Although this code does not address designing garage doors 
and other architectural finishes for the wind speeds prescribed in the code, if 
these doors had been designed for the design wind speed and associated wind 
pressures, damage in the inflow areas of the moderate and severe tornadoes 
might have been significantly reduced. 
The observed wind performance of T-lock asphalt shingles was not 
significantly better than that of three-tab or laminated strip asphalt and 
composition shingles. Wind-induced damage to T-lock shingles was 
observed on roofs that were likely exposed to wind speeds that were in the
PRELIMINARY REPORT PRELIMINARY CONCLUSIONS CHAPTER 7 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 7-5 
range of current code prescribed design conditions (i.e., 70 mph, fastest mile 
or 90 mph 3 second peak gust). 
Vinyl siding offers very limited resistance to low-energy missiles. The vinyl 
siding investigated also offered limited wind load resistance. Although the 
nailing patterns were erratic and the distance between nails was relatively 
large, it is difficult to envision that the investigated products had sufficient 
strength to meet the wind loads derived from new codes and standards such 
as ASCE 7-95 and ASCE 7-98. 
7.1.1.3 Masonry 
The BPAT observed extensive brick veneer loss in homes of all ages, 
indicating inadequate composite action caused by a failure of the brick ties. 
Masonry veneer and framed walls are generally assumed to provide some 
level of composite action to resist dynamic high wind forces, even though 
this is not considered explicitly in design. However, to act as a composite 
section, the connection between the veneer and backup wall (normally 
galvanized steel brick ties) needs to be maintained. Extensive degree of brick 
veneer loss in homes of all ages indicates inadequate composite action 
caused by a failure of the brick ties or due to the flexibility (relative to 
stiffness of the wall) of brick ties as installed. Some walls appeared 
undamaged, but could be deflected with hand pressure. 
Many of the failures observed stemmed from brick tie bond failure. In a 
majority of cases of masonry veneer loss, either corrugated or scalloped-edge 
galvanized steel brick ties remained attached to wall studs with one 6d 
common nail (withdrawal load = +/- 30 lb times a safety factor of 4 or 5), 
when a non-structural foam sheathing was used. The bond between mortar 
and brick tie was not sufficient to even exceed the withdrawal capacity of the 
tie nail. Therefore, there was inadequate bond between mortar and brick tie 
to resist the high wind forces experienced. The 1995 CABO One and Two 
Family Dwelling Code specifies that the maximum horizontal spacing of 
brick ties is 24-in on center, and each tie shall support not more than 3.25 sq. 
ft of wall area. At the code-required spacing to support 3.25 sq. ft, the 
maximum wind suction pressure on the veneer prior to failure could not have 
exceeded 37 psf, unless the rigid brick facing failed prior to the deflection 
required to allow the brick tie to develop its full capacity. 
There were a few instances of nail pull-out at brick ties fastened to wall 
studs. Therefore, in these cases the wind suction pressure exceeded the 
withdrawal strength of the one nail holding the brick tie. Causes of failure 
could be insufficient nail length or diameter, low withdrawal resistance, or 
ties having too high a tributary area. 
The 1995 CABO One and Two Family Dwelling Code also requires that if 
sheet metal is used, it shall not be less than No. 22 U.S. gauge by 7/8-in 
corrugated. There were many instances of brick ties spaced at greater
CHAPTER 7 PRELIMINARY REPORT 
7-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
distances. The most common form of tie was a 7/8-in wide galvanized steel 
strip with a -in deep scalloped edge on each side (center strip was 3/8-in 
wide), with very minor corrugation (less than 0.5 mm). There was notable 
absence of code compliance in what could be considered a random sample of 
homes impacted by the tornadoes. 
Because failures of masonry veneer were found at homes from less than 1 
year old to over 20 years old, mortar bonding strength did not seem to vary 
with age. Most brick used in the Oklahoma City area seemed to be of high 
density and low porosity, which could have affected bonding of mortar. 
There were several instances of loose brick on the ground with no mortar 
attached or only attached to one side. Mortar bond strength was inadequate to 
bond bricks together and to bond mortar to brick ties to resist negative 
(suction) wind pressures experienced. Some possible causes could be from a 
weak mortar mix, a too dry mortar, or use of low porosity brick. 
There were several instances where an air space between veneer and plastic 
foam insulation sheathing was 1.5-in or more, which reduced embedment 
length of brick ties in mortar joints to 1-in or less. Some model building 
codes specify 1-in maximum air space or grouted space, and 1.5-in minimum 
embedment of brick tie into mortar. 
7.1.2 Manufactured Housing 
The design and construction of manufactured housing has been governed 
since 1976 by Federal preemptive standards that are enforced by the U.S 
Department of Housing and Urban Development (HUD) under Federal 
Regulation and through a Monitoring and Enforcement Contractor, the 
National Conference of States on Building Codes and Standards (NCSBCS). 
Recently, the HUD Standard has been placed under a consensus process 
administered by National Fire Protection Association (NFPA). 
Wind resistance standards for manufactured housing differ from and are less 
than model building code provisions and standards for conventional site-built 
and modular or panelized construction. Minimum wind pressures for design 
of all homes located outside of the hurricane coastline are 15 psf for 
horizontal wind loads and 9 psf for net uplift load (equivalent to about a 65 
mph fastest mile wind speed, less than the 70 mph fastest mile wind speed 
specified in the CABO One and Two Family Dwelling Code, and lass than 
the 80 mph fastest mile wind speed specified in the 1997 UBC for this area 
of the country). Explicit engineering or test-based performance provisions 
require a minimum safety factor of 1.5 relative to these nominal design loads. 
However, simplified nominal design wind loads and the required safety 
factors do not consider the rare but significant overload that may occur due to 
inflow winds of violent and severe tornadoes or direct strike by the vortex of 
any tornado. Nominal loads are primarily associated with the level or risk 
that is associated with extreme thunderstorm winds. Also, the affects of
PRELIMINARY REPORT PRELIMINARY CONCLUSIONS CHAPTER 7 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 7-7 
exposure (not necessarily a factor for tornadic events) are not considered in 
nominal design wind loads. 
Installation and setup of manufactured housing, including foundations, 
ground anchors, and strapping or cables, are enforced by State and local 
officials. The Federal Standards only address the design of the overall 
anchoring and tie-down systems and require that they be designed by a 
qualified professional. 
In general, manufactured housing did not resist wind forces as well as 
conventional site-built detached single-family dwellings for inflow winds of 
violent and severe tornadoes and vortex winds from all tornadoes. This was 
primarily because of inadequate fastening of roof systems to wall systems 
and inadequate resistance to uplift and overturning provided by anchorage 
and tie-downs. An exception to this was the observed improved performance 
of newer manufactured homes that had been installed on permanent 
foundations. 
7.1.2.1 Foundations 
Permanent foundations performed better in resisting lateral wind loads than 
did ungrouted and unreinforced CMU piers having wood leveling shims 
under the chassis beams. However, the BPAT observed that connections of 
chassis and perimeter joists to permanent foundations were inadequate to 
resist the moderate wind uplift and overturning forces generated at the 
periphery of most tornado track investigated. It is difficult to make positive 
connections and then to inspect once the units are erected. In addition, local 
building officials the BPAT interviewed did not seem to be aware of 
manufacturers installation or set-up instructions with specific connection 
requirements for permanent foundations. 
7.1.2.2 Anchors 
Depths and locations of helical ground anchors and soil conditions varied 
considerably from site to site. Ground anchors pulled out of the soil because 
of inadequate depth, or steel anchor shafts bent over from lateral wind forces, 
thus leading to failure of the superstructure. Some ground anchors were 
installed at an angle with the base under the home, leading to bending of the 
shaft from lateral wind forces. Thus, deformation of the anchor and strapping 
arrangement could allow significant movement (vertically and horizontally) 
prior to developing substantial resistance to wind loads. Most ground anchors 
did not appear to comply with requirements of the Federal Manufactured 
Home Construction and Safety Standards (MHCSS), which states the 
following: 
Sec. 3280.306(f) Anchoring equipment shall be capable of resisting 
an allowable working load equal to or exceeding 3,150 pounds and 
shall be capable of withstanding a 50 percent overload (4,725 pounds
CHAPTER 7 PRELIMINARY REPORT 
7-8 FEDERAL EMERGENCY MANAGEMENT AGENCY 
total) without failure of either the anchoring equipment or the 
attachment point on the manufactured home. 
In 1994, the standard was revised to add Sec. 3280.306(b)(2) For anchoring 
systems, the instructions (provided by the manufacturer) shall indicate: 
(ii) That anchors should be certified by a professional 
engineer, architect, . . . as to their resistance, based on the maximum 
angle of diagonal tie and/or vertical tie loading . . . and angle of 
anchor installation, and type of soil in which the anchor is to be 
installed; (iv) That ground anchors should be installed to their full 
depth, and stabilizer plates should be installed to provide added 
resistance to overturning or sliding forces. 
7.1.2.3 Strapping 
Galvanized steel strapping in several instances failed in tension from wind 
uplift and overturning forces, or became loose when the home moved 
laterally from wind forces. In addition, connections of strapping to chassis 
beams often came loose and were on the ground, and there was no positive 
bolted or welded connection. The apparently premature failure of these ties 
was related to the number of ties, location of first ties from end of chassis, 
and tensile strength or ductility of steel. Several of the following provisions 
of the Federal MHCSS appeared to not be consistently complied with, 
possibly leading to failure: 
Sec. 3280.306(c)(1) The minimum number of ties required per side 
shall be as required to resist the design loads . . . 
(2) Ties shall be evenly spaced as practicable along the length of the 
manufactured home with not more than 8 feet open-end spacing on 
each end. (This provision was revised in 1994 to require not more 
than 2 feet open-end spacing on each end). 
The Material Specification for Strapping, Steel, and Seals, with 
Notice #1 and Amendment #2, only Type 1, Finish B, Grade 1 of the 
plating/coating sections are applicable, was Federal Spec. FS QQS-
781H-1974 with 1977 amendments. (This was revised in 1994 to 
Standard Specification for Strapping, Flat Steel and Seals  ASTM 
D3953-91). 
7.1.2.4 Superstructure 
Generally, newer manufactured housing units, particularly multi-wide units 
on permanent foundations, resisted straight-line inflow wind forces better 
than older single-wide units. Newer units are generally constructed of more 
conventional wall and roof framing, and connections between roof systems 
and walls, and walls to floors, provide load paths to transmit wind uplift, 
lateral, and overturning forces to the foundations. Internal shear walls, and
PRELIMINARY REPORT PRELIMINARY CONCLUSIONS CHAPTER 7 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 7-9 
bolted or steel strapped floors and roofs of multiple units at marriage walls 
provide a stiffer three-dimensional structure. However, attention does need to 
be paid to uplift straps from roofs to walls and walls to floors, and to bolting 
of units to permanent foundations, similar to conventional site-built home 
construction in tornado-prone areas. 
7.2 NON-RESIDENTIAL PROPERTY PROTECTION 
Visual observations indicated that non-residential structures were, with few 
exceptions, as vulnerable to damage as conventionally built residential 
construction. Many non-residential buildings received structural damage as a 
result of lack of redundancy in the load path to resist wind-induced uplift 
loads. Observed damage, however, was not as complete or devastating for 
non-residential buildings that were exposed to similar vortex winds of violent 
and severe tornadoes as that observed in residential construction. This was 
primarily due to the engineering that is required by model building codes for 
non-residential buildings and that is not required for residential buildings. 
Non-residential construction in Oklahoma is currently required to be 
designed per 1996 NBC and non-residential construction in Kansas is 
designed per the 1994 and 1997 UBC, depending upon local jurisdiction. 
Although local municipalities have adopted some amendments, these 
amendments were not significant relative to the structural issues discussed in 
this report. For current construction, these model building codes provide 
guidance for loads other than gravity loads. However, engineering standards 
such as ASCE 7-95 and 7-98 provide better structural and non-structural 
design guidance for wind loads than these newer codes. Although designing 
for tornadic wind events is not specifically addressed in any of these newer 
model building codes or standards, constructing non-residential buildings to 
these codes and standards would improve the strength of the built 
environment. Building to ASCE 7-95 or 7-98 would have led to reduced or 
minimized damage in areas that were affected by the inflow winds of all 
tornadoes and reduced the damage observed where moderate tornadoes 
impacted non-residential construction. 
7.2.1 Load Path 
Although non-residential construction is currently designed to specifically 
consider some wind load resistance, a lack of attention to uplift and lateral 
loads resulted in failure to provide a continuous load path and greatly 
increased damage to the buildings. In many cases, structural damage would 
have been negligible if adequate uplift resistance had been provided to steel 
roof joists and metal roof deck systems. Additional resistance to uplift could 
have significantly reduced damage to engineered construction on the 
periphery of severe and violent tornadoes or a moderate tornado track. 
Construction with materials such as URM block and brick that is capable of 
carrying gravity loads, but unable to carry uplift loads, will continue to lead
CHAPTER 7 PRELIMINARY REPORT 
7-10 FEDERAL EMERGENCY MANAGEMENT AGENCY 
to wall and roof failures during moderately high wind events. Better attention 
to the design of and selection of materials for connections throughout the 
structural system will also minimize and reduce the number of failures that 
are currently observed in non-residential construction after moderately high 
wind events such as along the periphery of severe and violent tornadoes or in 
the tracks of moderate tornadoes. 
After roof decking and other parts of the structure were blown loose by the 
wind, these pieces became windborne missiles that created additional 
damage to nearby structures. Greater attention to attachment of perimeter 
wood nailers, copings and metal edge flashings, and perimeter attachment of 
metal roofing panels will enhance performance of roof coverings and reduce 
the debris on the periphery of severe and violent tornadoes and in the tracks 
of moderate tornadoes. 
7.2.2 Increased Load Caused by Breach of Envelope 
The BPAT observed that the failure of commercial overhead doors, 
depending on their location, may initiate or contribute to major failures of 
primary structural systems. Observations suggest that overhead doors failing 
near building corners may significantly contribute to catastrophic failures of 
exterior walls and roof systems. This is particularly true for pre-engineered 
metal (light-steel frame) buildings that typically have little redundancy in 
their load transfer paths. For buildings that have several interior rooms or 
partitions, the propagation of internal pressures may be hindered and 
collateral damage to exterior walls minimized. 
Breach of the building envelope was observed to result in extensive collateral 
damage to non-residential buildings. Garage doors and large windows were 
particularly vulnerable. All garage and overhead doors should have adequate 
strength to resist wind loads derived from the latest engineering standards, 
such as ASCE 7-95 or 7-98, that provide design guidance for non-structural 
elements such as garage doors and windows. Also, owners of buildings that 
use EIFS for exterior walls should be advised by the building designer that, 
although the wall has the appearance of concrete, it offers insignificant 
resistance to high wind pressures and windborne missiles unless the EIFS is 
over concrete or reinforced CMU. 
A large number of missiles, which had been generated from roofs on 
essential facilities (e.g., hospitals), and buildings such as schools were 
observed. Aggregate and paver surfacing should not be used for roofs 
because they can be picked up by winds and cause significant damage to 
architectural finishes, windows, and doors. 
Protection of windows from wind pressures and windborne debris was not 
extensively investigated by the BPAT. However, it is important to consider 
protecting glass in essential facilities. Laminated glass, like shutter protection 
systems, can offer substantial protection from modest-energy windborne
PRELIMINARY REPORT PRELIMINARY CONCLUSIONS CHAPTER 7 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 7-11 
missiles. Laminated glass has the potential to offer significant occupant 
protection along the periphery of severe tornado tracks and in the tracks of 
moderate tornadoes and is a permanent protection device that does not need 
warning time to be installed, which can be a problem with many storm 
shutter systems. 
7.3 PERSONAL PROTECTION AND SHELTERING 
The best way to reduce loss of life and minimize personal injury during any 
tornadic event is to take refuge in a specifically designed tornado shelter. 
Although improved overall construction may reduce damage to buildings and 
contribute to safer buildings, an engineered shelter is the only means of 
providing individuals near absolute protection from severe and violent 
tornadoes. 
7.3.1 Residential Shelters 
The residential shelters observed by the BPAT included above-ground inresidence 
shelters and storm cellars. Although the above-ground in-residence 
shelters provided safety for the occupants, no direct missile strikes were 
recorded on the shelter doors that the BPAT was able to locate and visit. The 
doors observed were light gauge hollow metal with a single deadbolt locking 
device, which is less than the 14 gauge hollow metal door held by three 
hinges and three deadbolts, as required in FEMA 320: Taking Shelter From 
the Storm: Building a Safe Room Inside Your House. 
Assuming proper construction and location outside flood-prone areas, storm 
cellars offered safety during severe wind events. Observed problems with 
storm cellars included lightweight doors and hardware, poor maintenance, 
and unprotected ventilators. Storm cellars are typically not fully 
waterproofed and therefore can be damp, musty environments with poor 
ventilation. Ventilators were not constructed of heavy gauge steel or 
protected by heavy gauge shrouds or saddles that would have prevented their 
removal by debris or extreme winds during a tornado, allowing the 
subsequent entrance of free falling missiles and debris through the remaining 
openings in the shelter roof. 
7.3.2 Group Shelters 
The BPAT observed group shelters at a manufactured housing rental 
development and at a plastics manufacturing plant in Haysville, Kansas. A 
rental development of manufactured homes provided shelters at a rate of one 
shelter per four homes. Shelters were located in close proximity to the homes 
and were quickly accessible by the occupants, but none of these shelters were 
easily accessible to persons with disabilities. All group shelters were below 
or partially below ground and required access by stairs.
CHAPTER 7 PRELIMINARY REPORT 
7-12 FEDERAL EMERGENCY MANAGEMENT AGENCY 
The group shelter at the plastics manufacturing plant functions daily as a 
conference room and lunchroom. On May 3, 1999, it performed its third 
function as a tornado shelter. Although the building housing the shelter was 
not significantly damaged (one area suffered roof damage), other buildings 
that are part of the plant complex suffered substantial damage. The workers 
at the plant when the tornadoes struck and who were able to utilize the 
shelter were uninjured. 
7.3.3 Community Shelters 
The BPAT observed two community shelters that were utilized during the 
May 3 storm. One shelter was located in a manufactured housing park in 
Wichita, Kansas. The second shelter was located in Mid West City at the Mid 
West City High School gymnasium. Both were partially below-ground 
shelters and suffered from problems of moisture infiltration, mustiness, poor 
ventilation, and poor exterior doors and hardware. Other concerns common 
to community shelters include travel time required to access the shelter, 
accessing the shelter when the shelter is locked, accessibility for persons with 
disabilities (ADA compliance), and rules for gaining admittance. 
7.3.4 Other Places of Refuge 
Not all buildings, residential or non-residential, have designated tornado 
shelters or staffs with tornado plans for implementation during an event. 
Subsequently, in buildings without designated shelters or places of refuge, 
occupants are left on their own to identify places of refuge appropriate in a 
tornado event. The observations of the Oklahoma City and Kansas tornadoes, 
as well as other tornado events, indicate that small interior rooms within 
buildings often survive when the other portions of the building are destroyed. 
Rooms such as closets beneath staircases, small bathrooms, or other small 
rooms are the preferred place of refuge when no hardened shelter is provided 
in the building. 
Basements can also offer another alternative place of refuge. However, the 
observed basements demonstrated vulnerability from windborne missiles 
through windows, window wells, and through the above wood floor/ceiling 
structure. Although not observed in this storm event, previous observations 
have shown unreinforced basement walls collapsed as the result of the 
floor/ceiling diaphragm displacement by the winds of the tornadoes. 
The BPAT visited public use facilities during the field investigations to 
determine how these facilities addressed tornado threats that affect the users 
of the facilities. The team interviewed staff at schools, day-care centers, 
nursing homes, and churches, and found that not all public use facilities had a 
formalized tornado emergency refuge plan. Additionally, not all public 
facilities had a NOAA weather radio in continuous operation to monitor 
storm events that may lead to a tornado. When tornado plans were 
implemented by a facility, these plans were often not conspicuously posted
PRELIMINARY REPORT PRELIMINARY CONCLUSIONS CHAPTER 7 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 7-13 
and the plans were not always exercised as drills so building occupants could 
become familiar with the plan. It is unclear whether all plans allow sufficient 
time for the building occupant type (e.g., children, elderly, etc.) and if the 
shelter had adequate capacity for the quantity of building occupants and 
others who may attempt to seek shelter in the planned place of refuge.
Chapter 8 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 8-1 
8 Preliminary 
Recommendations 
The recommendations contained in this report are based solely on the 
BPAT's observations and conclusions. When these recommendations are 
implemented, they will facilitate future personal and property protection 
from extreme wind events. 
8.1 GENERAL RECOMMENDATIONS 
The May 3, 1999 tornadoes were disastrous in terms of lives lost and 
property destroyed, but out of this disaster comes the opportunity to reflect 
on the things that are important in peoples lives. Out of these reflections, 
Oklahoma and Kansas communities can commit to planning for future 
tornadoes through promoting sustainable construction and tornado-resistant 
communities. 
As the people of Oklahoma and Kansas rebuild their lives, homes, and 
businesses and plan for future economic development, there are several ways 
they can reduce the effects of future tornadoes, including: 
 Design buildings to the most current building codes and standards 
that provide greater protection against moderate tornado-generated 
winds. 
 Provide safe refuge in the event of a severe or violent wind storm or 
tornado in the form of engineered shelters. 
More specific recommendations are included in the following subsections. 
Mitigating future losses, however, will not be accomplished by simply 
reading this report; mitigation is achieved when a community actively seeks 
and applies methods and approaches that lessen the degree of damage, 
injuries, and loss of life that may be sustained from future tornadoes. 
8.2 PROPERTY PROTECTION 
Property protection recommendations have been divided into subsections on 
residential and non-residential building considerations, codes and 
regulations, and voluntary actions.
CHAPTER 8 PRELIMINARY REPORT 
8-2 FEDERAL EMERGENCY MANAGEMENT AGENCY 
8.2.1 Residential and Non-residential Buildings 
Proper construction techniques and materials must be incorporated into the 
construction of residential buildings to reduce their vulnerability to damage 
during moderately high wind events. Existing construction techniques proven 
to minimize damage in wind-prone areas are not always being utilized areas 
that are subject to tornadoes. Construction must be regulated and inspected to 
ensure that residential buildings meet the most current model building code 
requirements. 
It is recommended that, for engineered buildings, the engineer review 
structural connections to ensure adequate capacity for moderate to severe 
uplift and lateral loads that may be in excess of loads based on the building 
codes currently in effect. To address the issues of construction that may be 
mitigated to improve building performance, the following recommendations 
are provided: 
 Sheathing at areas of discontinuity should be fastened in a manner that 
will resist uplift forces with a factor of safety over the design wind 
pressure stipulated in applicable building codes and standards. Some 
current building codes reflect an increased fastener size intended to 
address high wind areas. 
 The masonry industry should consider re-evaluating attachment criteria 
of masonry, specifically regarding product usage. Greater emphasis 
should be given to code compliance for the bond between the mortar and 
brick tie, the mortar and the brick, and to the spacing of brick ties. 
 Garage doors are an extremely important residential building component. 
Failure of these doors led to catastrophic progressive failures of primary 
structural systems that could have been avoided. New garage doors 
should be installed with improved resistance to moderately high wind 
loads. Retrofits should be made to improve the wind resistance of 
existing garage doors, specifically double-wide garage doors. These 
retrofits and new doors may reduce the roof and wall damage that was 
observed in homes that experienced garage door failures. 
 The Federal Government (HUD) should review its standards and 
enforcement program in an effort to improve the performance of 
manufactured homes in moderately high wind events, such as in inflow 
areas of severe to violent tornadoes and the tracks of moderate tornadoes. 
Specifically, the capacity of anchoring and strapping equipment and 
systems needs to be evaluated to eliminate the discontinuity between the 
Federal standard and the State and local installation and enforcement 
process. 
 Consideration should be given to permanently connecting the 
manufactured home unit to its foundation. The BPAT concluded
PRELIMINARY REPORT PRELIMINARY RECOMMENDATIONS CHAPTER 8 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 8-3 
that newer manufactured homes on permanent foundations 
performed as well as conventional stick built homes in resisting 
lateral wind loads, as long as there was an adequate connection 
of the chassis and perimeter joists to the permanent foundation. 
 For non-residential buildings, the BPAT recommends using threaded 
fasteners to attach joists and metal decking to supporting frames and 
walls. In many of the roof system failures observed by the BPAT, current 
welding practices were insufficient in carrying loads and weld failures 
were common. 
 To reduce the number of missiles generated from roofs on essential 
facilities (e.g., hospitals) and buildings such as schools, aggregate ballast 
and paver surfacing should not be used. Enhanced wind design for the 
roof covering on essential facilities should be considered for those 
facilities located in tornado-prone areas. 
 When wood construction is not utilized, reinforced concrete and partially 
reinforced masonry with adequate ties to foundations and roofs should be 
used in areas with a high probability of being hit by a tornado. Ties 
between concrete and other materials should be made with drilled-in 
fasteners or cast-in-place fasteners. 
 Diaphragm action to resist shear forces must be maintained and 
reinforcement must be properly placed in concrete and masonry walls to 
reduce the possibility of collapse. Masonry walls should be engineered 
and constructed to support the specific architecture of the building. 
 Precast concrete buildings should have anchors to prevent the uplift of 
hollow core planks and other precast elements. Better performance 
would have been obtained if drilled-in expansion anchors or throughbolts 
had been used to attach the walls to the floors. Use of powderdriven 
anchors to attach bottom plates of walls to concrete should be 
avoided unless they are very closely spaced to achieve sufficient pull-out 
resistance. 
 Undamaged sections of brick veneer walls should be inspected, and 
where they can be deflected or pulled off, the air space behind the veneer 
should be grouted and reinforced, or be replaced. 
 A brick veneer wall system should be designed as a "stand alone" 
system. Current construction practices for brick veneer need to be 
improved so that a flexible connection between the framed wall and the 
veneer does not result. 
 It may be necessary to fasten brick ties with ring or screw-shank nails to 
prevent nail pull-out at brick ties.
CHAPTER 8 PRELIMINARY REPORT 
8-4 FEDERAL EMERGENCY MANAGEMENT AGENCY 
 Architectural features should be appropriately designed, manufactured, 
and installed to minimize the creation of windborne debris. To 
accomplish this, the local community may want to further regulate these 
features to ensure code compliance. 
 The installation of laminated glass in essential facilities should be 
considered because of the substantial protection that it offers from 
modest-energy missiles. Testing should be conducted in accordance with 
ASTME 1886, based on load criteria given in SBCCI STD 12. 
8.2.2 Codes and Regulations, Adoption, and Enforcement 
To better address structural and architectural issues related to moderately 
high wind events, State and local governments should consider adopting the 
most current edition of their model building code. Other recommendations 
related to building codes and enforcement are provided below: 
 Cities and appropriate local governments should adopt the 1997 UBC or 
the 1996 NBC as the model building codes. Amendments that require 
calculation of wind loads via ASCE 7-95 or the new ASCE 7-98 should 
also be adopted. Currently, the 1997 UBC & 1996 NBC reference ACSE 
7-95, but allow their own UBC/NBC methods to be used; it is important 
to note that wind calculations from these methods will result in lower 
loads than calculations from ASCE 7-95 or 7-98. For buildings other 
than one or two family dwellings, state and local governments should 
adopt the latest codes that specify the most current engineering standards 
for wind loads for the design of structural components and cladding. 
 Governments using a previous version of the 1995 CABO One- and 
Two-Family Dwelling Code should update to the 1995 version 
immediately. This will provide some guidance for designing for 
moderate wind loads. 
 The International Building Code (IBC) and the International Residential 
Code (IRC) should be adopted upon their release in 2000. Although these 
codes do not directly address the threat of tornadoes, they address wind 
load issues using ASCE 7-98 for both non-residential and residential 
construction, respectively. Use of codes based on ASCE 7-98 will reduce 
future losses from moderately high wind loads. 
 Greater emphasis should be given to code compliance, particularly for 
wall and roof covering wind loads and resistance. Homebuilders and 
code enforcement agencies should consider developing an active 
education and outreach program with contractors to emphasize the 
importance of code compliance for wind resistance. 
 State and local governments should consider creating a task force with 
the different building code groups and construction industry groups to
PRELIMINARY REPORT PRELIMINARY RECOMMENDATIONS CHAPTER 8 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 8-5 
determine if basic wind speed classifications should be reconsidered for 
tornado-prone areas. 
8.2.3 Voluntary Actions 
There are a number of voluntary actions that can be undertaken to reduce the 
risk of property damage in inflow areas of severe and violent tornadoes and 
in moderate tornado tracks. Some of these are included in the following 
recommendations. 
 To improve tornado resistance, individuals, builders, communities should 
use existing hurricane-resistant technologies (straps, clips, etc.) to protect 
themselves, their property, and their homes. 
 The design of wood frame structures should utilize connection devices 
such as anchors, clips, and straps to provide a continuous load path for 
all loads; gravity, uplift, and lateral. 
 Communities should consider the need for adopting ordinances and 
regulations that promote disaster-resistant communities by incorporating 
tornado shelters into new construction and communities. 
 Fire departments and Emergency Services Agencies should make a list of 
addresses with shelters, to assist in checking after a tornado to see if 
people are trapped inside shelters. 
8.3 PERSONAL PROTECTION 
Shelters are the best means of providing near absolute protection for 
individuals who are attempting to take refuge during a tornado. Whether a 
shelter is constructed by a homeowner for protection of his family or is 
constructed as a group or community shelter, all shelters should be designed 
and constructed in accordance with either FEMA 320 or The National 
Performance Criteria For Tornado Shelters. At a minimum, shelter doors 
should be constructed of 14 gauge hollow metal and be held by 3 hinges and 
3 deadbolts with three points of contact. Ventilators should be constructed of 
heavy gauge steel or protected by heavy gauge shrouds or saddles to prevent 
their removal by the storm and the entrance of debris through the remaining 
openings. Below grade portions of the shelter should be waterproof. All 
shelters should provide access to persons with disabilities as necessary and in 
conformance with the ADA. Local officials must monitor the installation of 
shelters to ensure that the floor of all shelters is located at or above expected 
flood levels.
CHAPTER 8 PRELIMINARY REPORT 
8-6 FEDERAL EMERGENCY MANAGEMENT AGENCY 
8.3.1 Residential Sheltering 
People should be encouraged to have in-residence or nearby shelters. 
Although this report advocates that buildings may be strengthened to better 
resist high wind events, a shelter is still considered the only means of 
providing near absolute personal protection. 
8.3.2 Group and Community Sheltering 
The following recommendations are given regarding group and community 
shelters, and also address the reason people have congregated (i.e., 
residential, public areas, etc.): 
 Many manufactured homes offer only minimal protection from severe 
wind storms and tornadoes. In the event of such storms, occupants of 
manufactured homes should exit their home and seek shelter in storm 
cellars, basements, or above-ground shelters. If shelters are provided in 
manufactured home parks, which is recommended, dispersed shelters, 
which can be accessed in a short time period are recommended. 
 Prospective occupants of community shelters should be acutely alert to 
storm warnings in order to allow sufficient time for the travel distance to 
the community shelter. Custodians of the shelter should be similarly alert 
so that the shelter is unlocked at appropriate times. Community shelters 
should be ADA compliant and the admission rules permanently posted 
(i.e. No Pets Allowed, etc.). 
 Essential facilities are critical to government response following a severe 
wind event or tornado. Site-specific evaluations should be made at 
essential facilities and other important facilities such as schools and 
daycare centers to determine the best locations for occupants during a 
storm. An assessment should be conducted to identify and provide 
signage to the designated refuge within or at the facility and evaluate the 
adequacy of the identified refuge to ensure people have a safe place to go 
and time to get there. All public use facilities must have a NOAA 
weather radio in continuous operation. Communities should consider 
enforcing this requirement by adopting as appropriate law or ordinance. 
 Existing essential facilities that offer inadequate protection should have 
shelters retrofitted or a shelter added. New essential facilities should be 
designed with shelters. Interested states should form a committee to 
evaluate the need for tornado plans and shelters in essential facilities and 
other establishments serving the public (e.g., schools, hospitals, and 
critical facilities).
PRELIMINARY REPORT PRELIMINARY RECOMMENDATIONS CHAPTER 8 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 8-7 
8.3.3 Place of Refuge 
If a specifically designed tornado shelter is not available and refuge has to be 
taken in a residential or non-residential building, the following are 
recommended: 
 State and local governments should develop education programs to assist 
homeowners and other property owners in developing a tornado safety 
plan similar to a fire safety plan. The plan should include the 
identification of a place of refuge and essential supplies. A tornado safety 
plan should include: 
 Seek refuge in a basement or below-grade crawl space, in an area 
away from the entry to the basement or crawl space. If the 
basement is partially above grade and has windows, seek shelter 
in a room within the basement that does not have windows. 
 If a residence does not have a basement or below-grade crawl 
space, seek refuge on the first floor in an interior bathroom or 
closet. If refuge is taken in a bathroom, lay in the tub. 
 In a non-residential building that does not have a basement, seek 
refuge on the first floor in a concrete stair tower, interior 
corridor, or a small room that does not have glass openings in 
doors or walls and is as far inward as possible from exterior 
walls. Avoid rooms that are more than 40 feet between walls or 
columns. 
 Wherever refuge is taken, lay on the floor if space permits, or 
kneel down. Cover up with pillows or heavy blankets for added 
protection.
CHAPTER 9 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES 9-1 
9 References 
Bledsoe, Bob, May 10, 1999, Interoffice Memo, Public Works/Community 
Affairs, Tulsa, Oklahoma. 
Doswell, C.A. III, and D.W. Burgess, 1988: Some issues of United States 
tornado climatology. Monthly Weather Review, Vol. 116, pp. 495-501. 
Grazulis, T.P., 1993: Significant Tornadoes, 1680-1991. Environmental Films, 
St. Johnsbury, VT, 1326 pp. 
Kelly, D.L., J.T. Schaefer, R.P. McNulty, C.A. Doswell III, and R.F. Abbey, 
Jr., 1978: An augmented tornado climatology. Monthly Weather Review, Vol. 
106, pp. 1172-1183. 
FEMA 320: Taking Shelter from the Storm 
National PerformanceCriteria for Tornado Shelters (see Appendix C) 
Note: See Appendix E for related worldwide websites 
1994 and 1997 Uniform Building Code 
1996 National Building Code 
1997 Standard Building Code 
1995 CABO One and Two Family Dwelling Code 
ASCE 7-98: Minimum Design Loads for Buildings and Other Structures
APPENDIX A 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES A-i 
Appendix A 
MEMBERS OF THE BUILDING PERFORMANCE ASSESSMENT TEAM FOR THE OKLAHOMA AND 
KANSAS TORNADOES 
TEAM MANAGEMENT 
CLIFFORD OLIVER, CEM 
Co-Team Leader 
Mitigation Directorate, Headquarters 
Federal Emergency Management Agency 
Washington, DC 
PAUL TERTELL, P.E. 
Project Officer and Co-Team Leader 
Mitigation Directorate, Headquarters 
Federal Emergency Management Agency 
Washington, DC 
E. SCOTT TEZAK, P.E. 
Team Manager 
Structural Engineer 
Greenhorne & O'Mara, Inc. 
Greenbelt, Maryland 
TEAM MEMBERS 
W.GENE CORLEY 
Structural Engineer 
Vice President 
Construction Technology Laboratories, Inc. 
Skokie, Illinois 
CHARLES A. DOSWELL III, Ph.D. 
Research Meteorologist 
National Severe Storms Laboratory 
National Oceanic Atmospheric Administration 
Norman, Oklahoma
APPENDIX A PRELIMINARY REPORT 
FEDERAL EMERGENCY MANAGEMENT AGENCY I A-ii 
G. ROBERT FULLER, P.E. 
Research Structural Engineer 
National Association of Home Builders Research Center 
Upper Marlboro, Maryland 
JERRY MALLORY 
Kansas State Emergency Management Agency Representative 
Johnson County Office of Planning, Development and Codes 
Olathe, Kansas 
PETER R. MONTPELLIER, M.E.Sc., B.Eng. 
Scientist 
Applied Research Associates, Inc. 
Raleigh, North Carolina 
ROBIN P. MUNNIKHUYSEN 
Environmental Scientist 
Greenhorne & O'Mara, Inc. 
Greenbelt, Maryland 
ROBERT NAUMANN 
Environmental Scientist 
Greenhorne & O'Mara, Inc. 
Greenbelt, Maryland 
PAUL ROHNE, JR., P.E. 
Region VI Liaison 
Disaster Field Office 
Federal Emergency Management Agency 
Oklahoma City, Oklahoma 
LIZ SINTAY 
Public Affairs Officer 
Disaster Field Office 
Federal Emergency Management Agency 
Oklahoma City, Oklahoma 
PAM SOPER 
Region VII Liaison 
Disaster Field Office 
Federal Emergency Management Agency 
Wichita, Kansas 
THOMAS L. SMITH, A.I.A 
Architect 
TLSmith Consulting, Inc. 
Rockton, Illinois
PRELIMINARY REPORT APPENDIX A 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES A-iii 
LARRY J. TANNER, P.E. 
Research Associate 
Wind Engineering Research Center 
Texas Tech University 
Lubbock, Texas 
WILLIAM D. WALL, P.E. 
Conference Services Manager 
International Conference of Building Officials 
Kansas City Conference Services Office 
Gladstone, Missouri
APPENDIX B 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES B-i 
APPENDIX B 
ACKNOWLEDGEMENTS 
The BPAT would like to thank the following people for their assistance with the site visits or review of 
the BPAT report: 
Mike Abedini, Norland Plastics Company, Haysville, Kansas 
Kenny Heitzman, Fire Marshall, Midwest City, Oklahoma 
Keith Eaton, Project Superintendent, Tanger Outlet Centers, Stroud Oklahoma 
Jim Cranford, Code Administrator, City of Wichita, Kansas 
Randal Dorner, Public Works Director, City of Haysville, Kansas 
Chad Bettles, Building Inspector, City of Haysville, Kansas 
Glen Wiltsee, Department of Code Enforcement, Sedgwick County, Kansas 
Laurie Bestgen, FEMA, Region VII, Kansas City, MS 
Samuel Winningham, FEMA, Region VII, Kansas City, MS 
Bob Bissell, FEMA, Deputy Federal Coordinating Officer-Mitigation (DFCO-M), Region VII, Kansas 
City, MS 
Jim Gilliam, FEMA Mitigation Division Director, Region VII, Kansas City, MS 
Dennis Lee, FEMA Deputy Federal Coordinating Officer-Mitigation (DFCO-M), Region VI, Oklahoma 
Frank Pagano, FEMA Mitigation Division Director, Region VI, Denton, TX 
John Pangburn, Mayor, Mulhall, Oklahoma 
Edwin Murabito, Architect, Edw.Murabito and Associates, Wichita, Kansas 
Kevin Daves, The Core, Wichita, Kansas 
Bruce Wedel, Principal, Bridge Creek High School, Oklahoma 
A.D. Lewis, Bridge Creek, Oklahoma
APPENDIX B PRELIMINARY REPORT 
FEDERAL EMERGENCY MANAGEMENT AGENCY I B-ii
APPENDIX C 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES C-i 
Appendix C 
NATIONAL PERFORMANCE CRITERIA FOR TORNADO SHELTERS
National Performance 
Criteria for Tornado Shelters 
Tornado shelters under construction in the Country Club Courts subdivision by The Core Inc., Wichita, Kansas 
Federal Emergency Management Agency 
Mitigation Directorate 
Washington, D.C 
First Edition 
May 28, 1999
National Performance Criteria for Tornado Shelters 
Page 2 of 8 
National Performance Criteria for Tornado Shelters 
Federal Emergency Management Agency 
Mitigation Directorate 
Washington, D.C. 
Comments and Questions 
The Federal Emergency Management Agency, in cooperation with the Wind Engineering Research Center 
at Texas Tech University, has developed these performance criteria for tornado shelters. Comments on 
these criteria should be directed to: 
Program Policy and Assessment Branch 
Mitigation Directorate 
Federal Emergency Management Agency 
500 C Street, S.W. 
Washington, D.C. 20472 
e-mail: building.science@fema.gov 
Technical questions on these performance criteria should be directed to: 
Wind Engineering Research Center 
Texas Tech University 
Box 41023 
Lubbock, TX, 79409-1023 
(888) 946-3287 ext. 336 
e-mail: ltanner@coe.ttu.edu 
Limit of Liability 
These performance criteria are based on extensive research of the causes and effects of windstorm damage 
to buildings. Shelters designed and built to these performance criteria should provide a high degree of 
occupant protection during severe windstorms. Any variation from these design or construction 
performance criteria, or deterioration of the structure, may decrease the level of occupant protection during 
a severe wind event. 
Because it is not possible to predict or test for all potential conditions that may occur during severe wind 
storms or control the quality of the design and construction, the Federal Emergency Management Agency, 
Texas Tech University and others involved in the development of this performance criteria do not warrant 
these performance criteria. 
The Federal Emergency Management Agency, Texas Tech University and others involved in the 
development of these performance criteria neither manufacture nor sell shelters based on these performance 
criteria. The Federal Emergency Management Agency, Texas Tech University and others involved in the 
development of these performance criteria do not make any representation, warranty, or covenant, 
expressed or implied, with respect to these performance criteria, or the condition, quality, durability, 
operation, fitness for use, or suitability of the shelter in any respect what so ever. The Federal Emergency 
Management Agency, Texas Tech University and others involved in the development of these performance 
criteria shall not be obligated or liable for actual, incidental, consequential, or other damages of or to users 
of shelters or any other person or entity arising out of or in connection with the use, condition, and other 
performance of shelters built from these performance criteria or from the maintenance thereof.
National Performance Criteria for Tornado Shelters 
Page 3 of 8 
Introduction 
Shelters constructed to these performance criteria are expected to withstand the effects of 
the high winds and debris generated by tornadoes such that all occupants of the shelter 
during a tornado will be protected without injury. These performance criteria are to be 
used by design professionals, shelter manufacturers, building officials, and emergency 
management officials to ensure that shelters constructed in accordance with these criteria 
provide a consistently high level of protection. The following describes the performance 
criteria. 
Performance Criteria 
1. Resistance to Loads from Wind Pressure for Shelters 
a) Wind pressures are to be determined using ASCE 7-95 Minimum Design Loads 
for Buildings and Other Structures (or revisions to this standard). Pressures for 
the Main Wind Force Resisting System (MWFRS) are to be used for the walls, 
ceiling, structural attachments and foundation system. Pressures for Components 
and Cladding are to be used for the door(s) and other attachments to the exterior 
of the shelter. For computing wind pressures to be used as a service load, the wind 
velocity (V) shall be 250 mph (3-second peak gust). 
b) The shelter walls, ceiling and floor will withstand design pressures such that no 
element shall separate from another (such as walls to floor, ceiling to walls). Such 
separation shall constitute a failure of the shelter. 
c) The entire shelter structure must resist failure from overturning, shear (sliding), 
and uplift from design pressures. Note: For the in-residence shelter designs 
described in FEMA 320, ceiling spans and wall lengths were less than 8 feet and 
the design of the wall and ceiling was governed by the need for missile protection. 
For larger shelters, the capacity of structural elements to withstand the forces 
described in above in 1. (a) shall be determined by engineering analysis. For 
larger shelters, the plans in FEMA 320 can be used only for missile (airborne 
debris) resistance. 
d) The Allowable Stress Design (ASD) method shall be used for the shelter design 
for any of the construction materials selected (concrete, concrete masonry, wood, 
etc.). Unfactored load combinations shall be used in accordance with ASCE 7-95 
for allowable stress design. Because of the extreme nature of this design wind 
speed, other environmental loads, such as flood or earthquake loads, should not be 
added. An alternative design method for materials with accepted Load and 
Resistance Force Design (LRFD) standards may be used in lieu of ASD.
National Performance Criteria for Tornado Shelters 
Page 4 of 8 
e) No importance factor shall be added to the pressure calculations because the 
extreme nature of the design event already accounts for critical nature of the 
shelter. Therefore, the importance factor (I) used in the design computations shall 
equal one. The internal gust coefficient (GCpi) shall be for buildings with no 
openings. 
f) In the event that the roof of the shelter is exposed at grade, the roof of the shelter 
shall be able to resist wind pressures as determined in sections 1(a) through (e). 
2. Windborne Missile Impact Resistance On Shelter Walls and Ceiling 
a) Loads from windborne missile impacts must be considered. For design purposes, 
it is assumed that the design wind speed of 250 mph propels a 15-lb. missile 
horizontally at 100 mph. The design missile is a nominal 2x4 wood board, 
weighing 15 lbs., striking the shelter enclosure on end 900 to the surface. The 
vertical missile design speed is 2/3 of the horizontal speed or 67 mph. For Below- 
Grade Shelters, only the impact from vertical missiles on the shelter roof must be 
considered. Note: From testing, it has been shown that the primary failure of 
enclosure materials from missile impact has been shearing of the material due to 
the high velocity and that missile perforation resistance is provided by a material 
(or combination of materials) that provide energy dissipation of the missile 
impact. 
b) The walls and ceiling of a shelter must resist perforation by the design missile 
such that the missile does not perforate the inside most surface of the shelter. 
Only shelter wall openings used for access are permitted. Windows, skylights, or 
other similar openings shall not be used unless they have been laboratory tested to 
meet the missile impact criteria of section 2(a). Note: The Wind Engineering 
Research Center at Texas Tech University has tested numerous materials and 
material combinations and should be contacted regarding performance of those 
materials. For in-residence shelters, the designs of FEMA Publication No. 320 
Taking Shelter From the Storm: Building a Safe Home in Your Home should be 
used. For other than in-residence shelters, it is recommended that materials 
proven to provide the required stiffness and missile impact resistance such as 
reinforced concrete or reinforced concrete masonry should be used. 
c) Alternative materials and material combinations for both shelter walls and 
ceilings shall be permitted after testing has proven the alternative materials will 
meet the missile impact criteria contained herein. Note: Existing missile impact 
standards in the Standard Building Code, the South Florida Building Code, the 
Texas Department of Insurance Code, and ASCE 7 do not include missiles of the 
size, weight or speed of those discussed in these performance criteria. Therefore, 
those standards may not be used to determine applicability of alternative 
materials and material combinations for tornado-generated missiles.
National Performance Criteria for Tornado Shelters 
Page 5 of 8 
3. Other Loads 
 The designer should assess whether an adjacent structure is a liability to the shelter, 
that is, if it poses a threat to the shelter from collapse. If the adjacent structure is 
deemed a liability, the loads imposed upon the shelter due to the collapse of this 
adjacent structure shall be considered as an additional impact load on the shelter. 
4. Shelter Access Doors and Door Frames 
a) Shelter entry doors and their frames shall resist the design wind pressures for 
components and cladding in section 1 of this criteria and the missile impact 
loads of section 2 of this criteria. Only doors and their frames that can resist 
calculated design wind pressures and laboratory tested missile impacts are 
acceptable. All doors shall have sufficient points of connection to their frame 
to resist design wind pressure and impact loads. Unless specifically designed 
for, each door shall be attached to their frame with a minimum six points of 
connection. Note: See the design specifications and details for shelter doors in 
FEMA publication 320 for additional guidance. Door designs and materials 
of construction included in FEMA publication 320 were developed through 
calculations and laboratory testing at Texas Tech University. 
b) A protective missile resistant barrier is permitted to protect the door opening. 
The door should then be designed to resist wind pressures. 
c) The size and number of shelter doors shall be determined in accordance with 
applicable fire safety and building codes. In the event the community where 
the shelter is to be located has not adopted current fire safety and building 
codes, the requirements of the most recent editions of a model fire safety and 
a building code shall be used. Note: The design specifications and details for 
shelter doors in FEMA publication 320 are for single swinging doors not 
exceeding 3 feet in width. No laboratory missile impact testing has been 
performed on double swinging doors or other door configurations other than 
3 feet wide single swinging doors. 
5. Shelter Ventilation 
a) Ventilation for shelters shall be provided through either the floor or the ceiling 
of the enclosure. A protective shroud or cowling, meeting the missile impact 
requirements of section 2 of these criteria, must protect any ventilation 
openings in the shelter ceiling. The ventilation system must be capable of 
providing the minimum number of air changes for the shelters occupancy 
rating. In the event the community where the shelter is to be located has not 
adopted a current building and/or mechanical code, the requirements of the 
most recent edition of a model building code shall be used. Note: Ventilation 
may be provided with ducts to an outside air supply.
National Performance Criteria for Tornado Shelters 
Page 6 of 8 
b) If ventilation to the shelter is provided by other than passive means, then all 
mechanical, electrical and other equipment providing this ventilation must be 
protected to the same standard as the shelter. In addition, appropriate design, 
maintenance and operational plans must ensure operation of this equipment 
following a tornado. 
6. Emergency Lighting 
 Emergency lighting shall be provided to all shelters serving over 15 persons. 
7. Shelter Sizing 
 The following are minimum floor areas for calculating the size of shelters: 
 Adults 5 square feet per person standing 
 Adults 6 square feet per person seated 
 children (under the age of 10) 5 square feet per person 
 Wheelchair bound persons 10 square feet per person 
 Bed-ridden persons 30 square feet per person 
8. Shelter Accessibility 
a) The needs of persons with disabilities requiring shelter space must be 
considered, and the appropriate access for such persons must be provided in 
accordance with the Americans with Disabilities Act (ADA). 
b) In designing shelter(s), the designer shall consider the time required for all 
occupants of a building and facility to reach refuge in the shelter(s). Note: 
While the National Weather Service has made great strides in providing 
warnings, to provide greater protection, it is recommended that in locating 
shelters or multiple shelters, all occupants of a building or facility should be 
able to reach a shelter within 5 minutes, and that all occupants should be in a 
shelter with doors secured within 10 minutes. 
9. Emergency Management Considerations for Shelters 
a) Each shelter shall have a tornado emergency refuge plan; this plan is to be 
exercised at least twice per year.
National Performance Criteria for Tornado Shelters 
Page 7 of 8 
b) Shelter space shall contain, at a minimum, the following safety equipment: 
 Fire extinguisher surface mounted on the shelter wall. In no case shall a 
fire extinguisher cabinet or enclosure be recessed into interior face of the 
exterior wall of the shelter. 
 Flashlights with continuously charging batteries 
 First aid kit rated for the shelter occupancy 
 Potable water in sufficient quantity to meet the drinking needs of the 
shelter rated occupancy for 8 hours 
 A NOAA weather radio with continuously charging batteries 
c) The following placards and identification shall be installed in each building 
with a shelter other than shelters within single family residences: 
 The location of each shelter shall be clearly and distinctly identified with 
permanently mounted wall placards located throughout the building that 
direct the building occupants to the shelter. 
 The outside of all doors providing access to a shelter shall be clearly 
identified as a location to seek refuge during a tornado. 
 Placards shall be installed on the inside of each shelter access door or 
immediately adjacent that instructs shelter occupants on how to properly 
secure the shelter door(s). 
10. Additional Requirements for Below Grade Shelters: 
 The shelter must be watertight and resist flotation due to buoyancy from 
saturated soil. 
 The shelter must contain either battery-powered radio transmitters or a signalemitting 
device to signal the location of the shelter to local emergency 
personnel should occupants in the shelter become trapped due to debris 
blocking the shelter access door. 
11. Multihazard Mitigation Issues 
a) Flooding 
 No below grade shelter shall be constructed in a Special Flood Hazard 
Area or other area known as being flood prone. 
 In the event that an above ground shelter is located in a Special Flood 
Hazard Area (SFHA) or other known flood prone area, the floor of the 
shelter shall be elevated to or above the Base Flood Elevation or other 
expected level of flooding. 
 All shelters constructed in a SFHA and/or other regulatory floodplain 
areas shall conform to state and local floodplain management 
requirements.
National Performance Criteria for Tornado Shelters 
Page 8 of 8 
b) Earthquake 
 Shelters located in earthquake prone areas shall be designed and 
constructed in accordance with seismic safety provisions contained in 
local building codes. In the event the community where the shelter is to be 
located has not adopted a current building code, the requirements of the 
most recent edition of a model building code and/or the National 
Earthquake Hazard Reduction Program Recommended Provisions shall be 
used. 
12. Construction Plans and Specifications 
 Complete detailed plans and specifications shall be provided for each shelter 
design. Sufficient information to ensure that the shelter is built in accordance 
with both the specific requirements and intent of these performance criteria 
shall be provided. Note: The plans and specifications found in FEMA 
publication 320 are a good basis for developing plans (including standardized 
details) and specifications. 
13. Quality Control 
 The quality of both construction materials and methods shall be ensured 
through the development of a quality control program. This quality control 
program shall identify roles and responsibilities of the contractor, design 
professional, and local permit official in ensuring that the shelter is 
constructed with materials and methods that meet the requirements stipulated 
in the plans and specifications developed from these performance criteria. 
14. Obtaining Necessary Permits 
 Prior to beginning construction, all necessary state and local building and 
other permits shall be obtained and clearly posted on the job site. Note: 
Model building codes do not address the design of a tornado shelter. 
Therefore the owner and the design professional should ensure that the 
shelter is properly designed and constructed. 
Sources of Additional Information 
FEMA has developed two publications that may be of assistance in developing tornado 
shelter designs: 
 FEMA TR-83B Tornado Protection: Selecting and Designing Safe Areas in Buildings 
 FEMA 320 Taking Shelter From the Storm: Building a Safe Room Inside Your House 
A copy of FEMA 320 can be ordered by calling 1-888-565-3896. FEMA TR-83B, and all 
other FEMA publications, may be ordered by calling 1-800-480-2520.
APPENDIX D 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES D-I 
Appendix D 
TAKING SHELTER FROM THE STORM BROCHURE
APPENDIX D PRELIMINARY REPORT 
FEDERAL EMERGENCY MANAGEMENT AGENCY I D-II
PRELIMINARY REPORT APPENDIX D 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES D-III
PRELIMINARY REPORT APPENDIX E 
BUILDING PERFORMANCE ASSESSMENT: OKLAHOMA AND KANSAS TORNADOES E-i 
Appendix E 
LIST OF WEBSITES 
FEMA: National Performance Criteria for Tornado Shelters 
http://www.fema.gov/library/npc_ts.htm 
FEMA: Taking Shelter From the Storm: Building a Safe Room Inside Your House 
http://www.fema.gove/mit/tsfs01.htm 
FEMA: Taking Shelter From the Storm Plans 
http://www.fema.gov/mit/shplans/index.htm 
The Blast Shelter Links Page 
http://members.aol.com/rafleet/links1.htm 
Wind Engineering Research Center, Texas Tech University 
Tornado Safe Room 
http://www.wind.ttu.edu 
Tornado Project Online 
Storm Shelters 
http://www.tornadoproject.com
APPENDIX E PRELIMINARY REPORT 
FEDERAL EMERGENCY MANAGEMENT AGENCY I E-ii