NISTIR 6899

RECONNAISSANCE REPORT ON DAMAGE TO 

ENGINEERED STRUCTURES DURING

THE MAY 1999 OKLAHOMA CITY TORNADO

Michael A. Riley 

Building and Fire Research Laboratory

Gaithersburg, MD 20899-8611

United States Department of Commerce

Technology Administration

National Institute of Standards and Technology

NISTIR 6899

RECONNAISSANCE REPORT ON DAMAGE TO 

ENGINEERED STRUCTURES DURING

THE MAY 1999 OKLAHOMA CITY TORNADO

Michael A. Riley 

August 2002

Building and Fire Research Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8611

United States Department of Commerce

Donald L. Evans, Secretary

Technology Administration

Phillip J. Bond, Under Secretary for Technology

National Institute of Standards and Technology

Arden L. Bement, Jr., Director
Reconnaissance Report on Damage to Engineered Structures During the May 1999 Oklahoma City Tornado

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ABSTRACT

On 3 May 1999, a major storm passed through the mid-west, spawning at least 76 tornadoes, 

and killing more than 50 people. The Oklahoma City, Oklahoma, metropolitan area was the 

hardest hit, with 43 fatalities, and 10 000 homes destroyed or severely damaged. The losses 

due to damage caused by the storm exceeded $1.1 billion. The National Weather Service rated 

the tornado that struck Oklahoma City as a F5 on the Fujita tornado intensity scale.

In the aftermath of the tornadoes, the Building and Fire Research Laboratory Structures Division sent a team to investigate the damage to engineered structures in the Oklahoma City area. 

The damage reconnaissance included an aerial survey of the largest tornado tracks in central 

Oklahoma and a two-day ground survey. The ground survey included visits to eight damage 

sites with twelve damaged engineered structures. This report provides an overview of observed damage to engineered structures, including schools, hotels, and industrial buildings, 

reports observations on debris accumulation, briefly discusses the tornado rating, and recommends actions to reduce future losses.
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ACKNOWLEDGEMENTS

This disaster reconnaissance and reporting were supported by the Structures Division, Building and Fire Research Laboratory, National Institute of Standards and Technology, U.S. Department of Commerce. The author wishes to thank the Oklahoma City emergency coordinator, Oklahoma County Sheriff's Department, and the Office of the Oklahoma State Fire Marshal, which assisted with this investigation by providing personnel, access to otherwise closed 

sites, transportation, and guidance. The author gratefully acknowledges the help of meteorologists from the National Weather Service, and the Civil Air Patrol, which provided the 

means for the aerial portion of the survey. Members of the Texas Tech University disaster investigation team provided guidance and assistance in locating many of the damage sites. Finally, the author wishes to thank Emil Simiu for his assistance with the preparation of this report. 
Reconnaissance Report on Damage to Engineered Structures During the May 1999 Oklahoma City Tornado

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CONTENTS

Abstract..............................................................................................................iii

Acknowledgements............................................................................................ v

Contents............................................................................................................ vii

List of Figures.................................................................................................... ix

List of Tables..................................................................................................... xi

1 Introduction...................................................................................................1

1.1 The Tornado Outbreak ................................................................................................. 1

1.2 NIST Reconnaissance ................................................................................................... 3

1.3 Overview of Report....................................................................................................... 6

2 Damage to Schools........................................................................................9

2.1 Overview ....................................................................................................................... 9

2.2 Kelley Elementary School ............................................................................................ 9

2.3 Westmoore High School ..............................................................................................16

3 Damage to Hotels........................................................................................21

3.1 Overview ......................................................................................................................21

3.2 Clarion Inn ...................................................................................................................21

3.3 Hampton Inn................................................................................................................22

4 Damage to Industrial and Commercial Buildings .....................................27

4.1 Overview ......................................................................................................................27

4.2 Tinker Industrial Park .................................................................................................27

4.2.1 South Building.........................................................................................................28

4.2.2 Middle and North Buildings .....................................................................................31

4.3 Peach Auto Painting.....................................................................................................31

4.4 American Freightways Depot......................................................................................34

4.5 Coors Technical Ceramics ...........................................................................................34

5 Damage to Other Engineered Structures....................................................37

6 Conclusions and Recommendations ..........................................................43

7 References ...................................................................................................47
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LIST OF FIGURES

Figure 1-1. Map of Tornado Damage Paths and F-scale Ratings in the Vacinity of Oklahoma 

City, 01 July, 1999 Revision. (Courtesy of the NWS)............................................ 1

Figure 1-2: Tornado Vortex Scars in a Field near Crescent, Oklahoma. ...................................... 3

Figure 1-3. Damage to Structures along the Tinker Diagonal, Midwest City. ............................ 4

Figure 1-4. Damaged Housing Complex South of Westmoore High School, Oklahoma City. .. 5

Figure 1-5. Damage to Westmoore High School and Surrounding Areas, Oklahoma City. ...... 6

Figure 1-6: Damage to the American Freightways Terminal and Coors Ceramics Factory, 

Oklahoma City...................................................................................................... 7

Figure 2-1: Map of Damaged Schools in South Oklahoma City and Moore................................ 9

Figure 2-2: Remains of Northern End of the Front Section of Kelly Elementary School. ...........10

Figure 2-3: Damage to Southern End of Front Section of Kelly Elementary School. ..................11

Figure 2-4: South Side of the Center Section of Kelly Elementary School. .................................12

Figure 2-5: North Side of the Center Section of Kelly Elementary School. .................................12

Figure 2-6: South Side of the East Section of Kelly Elementary School.......................................13

Figure 2-7: Collapsed Wall on West Side of the East Section of Kelly Elementary School. ........13

Figure 2-8: Collapsed Wall at North End of West Section of Kelly Elementary School. ............14

Figure 2-9: Detail of Mortar and Reinforcement in the Collapsed Wall at North End of West 

Section of Kelly Elementary School. ....................................................................14

Figure 2-10: Detail of the Cornice and Soffit on East Side of Kelly Elementary School..............15

Figure 2-11: Broken Windows on East Side of Kelly Elementary School....................................15

Figure 2-12: Aerial View of Westmoore High School. ................................................................16

Figure 2-13: Detail of Roof Damage to Westmoore High School. ...............................................17

Figure 2-14: Damage to Westmoore High School Classroom Roof (Inside View)......................18

Figure 2-15: Damaged, But Intact, Cladding on Westmoore High School..................................18

Figure 2-16: Damage to Cladding on East Side of Westmoore High School. .............................19

Figure 2-17: Damage to Westmoore High School and Vehicles, View From South. ..................19

Figure 2-18: Debris on North Side of Westmoore High School...................................................20

Figure 3-1: Aerial View of Damage to the Clarion Inn................................................................21

Figure 3-2: Damage to South Side of the Clarion Inn..................................................................22

Figure 3-3: Damage to North Side of the Southwest Corner of the Clarion Inn. ........................23

Figure 3-4: Damage to Western Section of the Clarion Inn. ........................................................23

Figure 3-5: Aerial View of Damage to the Hampton Inn (long rectangular building). ..............24

Figure 3-6: Damage to South Side of the Hampton Inn. .............................................................25

Figure 3-7: Damage to North Side of the Hampton Inn. .............................................................25

Figure 3-8: Detail of Damage to Masonry at the Hampton Inn...................................................26

Figure 4-1: Simplified Plan View of Tinker Industrial Park........................................................27

Figure 4-2: Damage to Western Section of the South Building at Tinker Industrial Park. .........28

Figure 4-3: Collapsed Eastern Section of the South Building at Tinker Industrial Park (View 

from Southeast)....................................................................................................29

Figure 4-4: North Side of the South Building at Joint between Sections.....................................29

Figure 4-5: Detail of Failed Column and Collapsed Roof at the Southeast Corner of the South 

Building. ..............................................................................................................30

Figure 4-6: Reinforced Masonry Wall that Failed at South Building. .........................................30

Figure 4-7: Damage to the East Side of the Middle Building at Tinker Industrial Park. ............31

Figure 4-8: Detail of Damage to the Roof of the Middle Building. .............................................32
Reconnaissance Report on Damage to Engineered Structures During the May 1999 Oklahoma City Tornado

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Figure 4-9: Detail of Damage to Western Wall of the Middle Building. .....................................32

Figure 4-10: Damage to the East Side of the North Building at Tinker Industrial Park. ............33

Figure 4-11: Roof Framing and Collapsed Walls (foreground) at Peach Auto Painting.............33

Figure 4-12: Detail of Base of Failed Wall at Peach Auto Painting. ............................................34

Figure 4-13: Damage to Coors Technical Ceramics Factory........................................................35

Figure 5-1: Aerial View of Damage to Hangars at Chickasha Airport .......................................37

Figure 5-2: Damage to the Roof of the Regency Park Baptist Church. .......................................38

Figure 5-3: Debris Damage to Building Adjacent to Regency Park Baptist Church. ..................38

Figure 5-4: Aerial View of Damage to the Tanger Outlet Center Mall. ......................................39

Figure 5-5: Destroyed Transmission Tower near Crescent, Oklahoma. .....................................40

Figure 5-6: Damage to Mulhall, Oklahoma, and United Cooperative Silos. ..............................40

Figure 5-7: Damage to Farm buildings and Silos near Crescent, Oklahoma. .............................41
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LIST OF TABLES

Table 1-1: List of Storm Supercells (Courtesy of the NWS).......................................................... 2
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1 INTRODUCTION

On 3 May 1999, a major storm passed

through the mid-west, spawning at least 76 

tornadoes, and killing 55 people. The Oklahoma City, Oklahoma metropolitan area

was the hardest hit, with 43 fatalities, and 

10 000 homes destroyed or severely damaged. Losses from the storm exceeded $1.1 

billion. The National Weather Service

(NWS) rated the tornado that struck Oklahoma City as a F5, the highest rating on the 

Fujita tornado intensity scale, with an estimated maximum associated wind speed of 

142 m/s.

In the aftermath of the tornadoes, the Structures Division, Building and Fire Research 

Laboratory, NIST, sent a structural engineer 

to investigate the damage to engineered 

structures in the Oklahoma City area. The 

damage reconnaissance included an aerial 

survey of the largest tornado tracks in central Oklahoma and a two-day ground survey. The ground survey included visits to 

eight damage sites in which nine damaged 

engineered structures were observed. This 

report presents damage observations for

schools, hotels, and industrial buildings.

1.1 The Tornado Outbreak

The Storm Prediction Center of the National 

Figure 1-1. Map of Tornado Damage Paths and F-scale Ratings in the Vacinity

of Oklahoma City, 01 July, 1999 Revision. (Courtesy of the NWS).
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Weather Service identified the threat of tornadoes in the storm developing over the

Midwestern US at 1:00 AM on 3 May 1999. 

The center issued the first tornado watch for 

the storm at 4:30 PM, and the first, weak 

tornado (A1 in Figure 1-1) was reported at 

4:51 PM. During a ten-hour period that 

afternoon and evening, the National

Weather Service Forecast Office in Norman, 

Oklahoma issued 116 warnings for

tornadoes and severe thunderstorms.

The National Weather Service investigation 

of storm and tornadoes identified 68 unique 

tornadoes caused by 11 distinct supercells 

that occurred in Oklahoma and Kansas. 

Additional tornadoes were caused by the 

storm as it moved through Texas and Tennessee.

 

1 The official death toll includes additional fatalities that are not included in this table.

Figure 1-1 shows a map of the tornado

damage paths in central Oklahoma. The 

largest of these tornadoes (A7 in Figure 1-1), 

which passed though Oklahoma City, was 

rated as an F5 by the NWS. The other tornadoes were rated from F0 to F4. Table 1-1

lists the storm supercells identified by

NWS, the number of distinct tornadoes that 

could be identified for each, the highest Fscale rating for tornadoes generated by that 

supercell, and the number of fatalities.

The vast majority of the fatalities were

caused by tornadoes generated by the first 

storm (Storm A), which passed through the 

heart of the Oklahoma City metropolitan

area. Storms B and G followed the same 

track, with storm G generating tornadoes 

that paralleled or crossed the tracks of

storm B tornadoes, about 1-1/2 hours after 

the first storm.

Table 1-1: List of Storm Supercells (Courtesy of the NWS).

Supercell

Number of 

Tornadoes

Highest

F-Scale 

Rating Fatalities Storm Name Notes

Storm A 12 F5 38

Elgin – Chickasha – Bridge 

Creek – Moore – Choctaw 

Storm

Storm that damaged Oklahoma 

City.

Storm B 21 F4 2

Anadarko – Minco – Union 

City – Piedmont – Mulhall –

Perry Storm

Storm C 2 F0 0 Okarche Storm

Storm D 8 F3 1

Pink – Shawnee – Stroud –

Tulsa Storm

Storm E 8 F4 1 Geary – Dover Storm

Storm G 6 F3 0

El Reno – Cashion – Crescent 

– Mulhall 2 Storm

Storm H 3 F1 0

Omega – Hennessey – Marshall Storm

Storm I 1 F1 0 Fairview Storm

Storm J 3 F1 0 Boynton – Peggs – Chewey 

Storm

Storm K 3 F4 5 Conway Springs – Wichita –

Augusta Storm

Storm L 1 F0 0 Henryetta Storm

Total 68 471
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1.2 NIST Reconnaissance

On 4 May 1999, the morning after the tornado outbreak, the initial damage reports 

indicated that the damage was unusually

severe and that some significant structures 

had been damaged; however, the full magnitude of the damage was not apparent. The 

damage investigation reported herein began 

on the morning of 5 May 1999.

The first phase of the reconnaissance consisted of an aerial survey conducted with 

meteorologists from the National Weather 

Service. The Norman, Oklahoma squadron 

of the Civil Air Patrol (CAP) provided a 

plane and pilot. The survey consisted of 

two flights between 8:00 AM and 2:00 PM 

CDT on 5 May 1999. During the first flight 

the team surveyed the damage caused by 

two storm cells (storms A and D), between 

Chickasha and Stroud, and including 

Southern Oklahoma City, Moore, Del City, 

Midwest City, and Choctaw. (In Figure 1-1

Chickasha is located near the bottom center 

of the map; Stroud is located near the mid 

right side of the map.) During the second 

flight, the team surveyed the damage

caused by two additional storm cells

(storms B and G), between Perry (near the 

top center of the map) and Union City (near 

the center of the map), including Mulhall, 

Crescent, and Piedmont. The observations 

from this survey were used to determine 

where the damage was heaviest and to locate significant structural damage that

should be investigated more thoroughly.

The tornadoes caused a wide range of damFigure 1-2: Tornado Vortex Scars in a Field near Crescent, Oklahoma.
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age and destruction in addition to the structural damage described in detail in this report. Figure 1-1 shows the distinct scars left 

by one of the tornadoes as it passed through 

a field near Crescent, Oklahoma.

The second phase of the reconnaissance

consisted of a two-day (6-7 May 1999)

ground survey by the author. On the morning of 6 May 1999, the Oklahoma County 

Sheriffs Department assisted the investigation by making a deputy available to act as 

a guide. The most heavily damaged areas 

of Midwest City were toured, including the 

heavily damaged area along the Tinker Diagonal, shown in Figure 1-3. In particular, 

damage to the Clarion Inn and Hampton 

Inn, both on the north-east side of the

Tinker Diagonal, and the Peach Auto Painting garage, on the south west side of the 

Tinker Diagonal, was investigated. The

survey also included a tour of the residential area of Midwest City, north of SE 15th

Street, which was heavily damaged.

The ground survey was continued on the 

afternoon of 6 May 1999 with the assistance 

of a State Fire Marshall. Efforts were focused on surveying the damage to South

Oklahoma City, particularly the area

around Westmoore High School. The high 

school had suffered roof damage, while the 

surrounding residential areas were devastated. Figure 1-4 and Figure 1-5 show the 

damage to the housing development south 

of the school, the apartment complex to the 

Figure 1-3. Damage to Structures along the Tinker Diagonal, Midwest City.
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east of the school, and the school itself. For 

safety reasons access to the high school was 

limited. Access was allowed to the classroom portions of the building, which had 

moderate damage and only small sections 

of roof covering missing. However, access 

was not permitted to the auditorium, which 

had lost a large portion of its roof.

The last day of the reconnaissance, Friday, 7 

May 1999, concluded the ground survey. 

By this time, much of the emergency phase 

of the clean-up operation was complete. All 

streets were open, which reduced traffic

congestion and eased travel between sites. 

One damaged structure of interest had already been bulldozed, and some rubble had 

already been removed at other sites.

The morning of 7 May 1999 was spent investigating the damage to the Tinker Industrial Park in Midwest City. The three buildings at this site had all been damaged, and 

one building had partially collapsed. Although, the partially collapsed building

could not be entered, extensive information 

on the damage could be obtained by observing the building from the outside, and there 

was access to the other two buildings.

Next, the damage investigation was conducted in an industrial section of Oklahoma 

City. The American Freightways terminal, 

shown in Figure 1-6, could not be investigated because the cleanup of the debris was 

already at an advanced stage, and most of 

the wreckage had been moved. Of the remaining buildings damaged in that industrial section it was possible to investigate 

only the Coors Ceramics factory (Figure 

Figure 1-4. Damaged Housing Complex South of Westmoore High School, Oklahoma City.
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1-6).

The investigation was concluded in Moore 

and was focused on Kelley Elementary

School. Many surrounding buildings were 

damaged or destroyed, and a most of the 

school was leveled. The damage to the remaining portion of the school was so severe 

that no one was allowed access within ten 

meters of the building.

The Regency Park Baptist Church, located a 

few blocks from the school, also suffered

significant damage, although it was not in 

the direct path of the tornado.

1.3 Overview of Report

The purpose of this report is to detail findings from the NIST damage reconnaissance. 

Information on the tornadoes based on information issued by NOAA is shown in Fig. 

1-1. Section 2 describes observations of

damage suffered by schools: the Kelly Elementary School and the Westmoore High

School. Section 3 describes observations of 

damage to hotels: the Clarion Inn and the 

Hampton Inn. Section 4 is concerned with 

damage to: three buildings in Tinker Industrial Park; the Peach Auto Painting building; 

and the Coors Technical Ceramics building. 

Section 5 describes observations of damage 

to a limited number of other engineered

Figure 1-5. Damage to Westmoore High School and Surrounding Areas, Oklahoma City.
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structures. A large number of other buildings and structures suffered damage, but 

were not inspected or assessed in detail.

Figure 1-6: Damage to the American Freightways Terminal and Coors Ceramics Factory, 

Oklahoma City.
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2 DAMAGE TO SCHOOLS

2.1 Overview

Three schools were heavily damaged or destroyed by tornadoes, two in the Moore

school district and one in Mulhall.

The Kelley Elementary School in Moore was 

destroyed, while the nearby Westmoore

High School lost part of its roof and had 

significant interior damage. The locations 

of these schools are shown in Figure 2-1, 

along with the approximate tornado path. 

This tornado (A7 in Figure 1-1) was rated F5 

by NWS, and was near its peak strength

when it passed through South Oklahoma 

City and Moore.

The Mulhall-Orlando Elementary School in 

Mulhall was destroyed by a tornado rated 

F4 by NWS (B20 in Figure 1-1) that touched 

down south of Crescent and continued

through Mulhall. News reports indicated 

that the brick building was partially leveled. 

The section that housed most of the classroom space was destroyed. A single classroom and the school library were the only 

rooms that survived. Owing to time constraints NIST was unable to investigate the

damage to this school.

2.2 Kelley Elementary School

The Kelley Elementary School was located 

at 1900 N Janeway Ave. in Moore. According to school district personnel at the site, 

this steel and masonry building was conFigure 2-1: Map of Damaged Schools in South Oklahoma City and Moore
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structed around 1960. The building was

struck directly by the tornado, which leveled part of the building and severely damaged the rest. Almost the entire roof was 

torn away, and no safe spaces remained.

The site was visited on May 7 PM. At that 

time, close access to the building was restricted due to the possibility of falling debris. Reconnaissance was performed from 

the site perimeter, and close inspection to 

determine member sizes was not possible.

The building was constructed with steel

frames and masonry walls. Many of the 

exterior walls were load bearing, with reinforced concrete cap beams. The roof was

constructed with corrugated steel panels

supported by steel trusses. An overhanging 

cornice, constructed from timber and plywood, surrounded it.

The school building had three distinct sections, roughly forming an “H” in plan. The 

front section was at the western end of the 

building. This section housed the cafeteria, 

offices, and classrooms. The center section 

consisted of classrooms along a hall that ran 

east-west, and connected the front and back 

sections. The back section, at the western 

end of the building, consisted of additional 

classroom space on either side of a hall that 

ran north south.

The damage to the building ranged from 

complete destruction of some areas to the 

loss of roof panels and broken windows.

The front section of the building suffered 

varying damage. The main entrance was 

near the center of this section, and most of 

the structure north of the entrance was severely damaged or destroyed. As shown in 

Figure 2-2, most of the walls and the roof in 

this part of the building collapsed. The

damage was less severe near and south of 

the entrance. Here some walls and some 

parts of the roof survived. Figure 2-3 shows 

the damage to the southern end of the front 

section. The front wall of the cafeteria had 

collapsed inward and a portion of the roof 

has collapsed, but much of the roof surFigure 2-2: Remains of Northern End of the Front Section of Kelly Elementary School.
Reconnaissance Report on Damage to Engineered Structures During the May 1999 Oklahoma City Tornado

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vived. South of the cafeteria, the roof was 

severely damaged, but most of the walls 

had survived.

The center section of the building was the 

most severely damaged. Here the roof

trusses ran north-south, with the southern 

ends supported by a steel beam on steel

columns. The northern ends of the centermost trusses were supported by a reinforced concrete cap beam on a concrete

block wall with brick facing, while the eastern and western trusses were supported on 

steel beams supported by the cap beam and 

the end walls. Both the southern and

northern walls were destroyed and nearly 

all roof covering was removed. The steel 

columns along the south wall, visible in

Figure 2-4, bent, but did not fail. The loss of 

the north wall, however, removed all support for the north side of the roof leading to 

its collapse, as shown in Figure 2-5.

The eastern section of the building lost

nearly its entire roof and a section of the 

western wall collapsed. Many of the roof 

trusses were lifted off and every window 

was broken. Although most of the walls 

survived, this section of the building could 

not have provided a safe space for the occupants. Figure 2-6 shows the south entrance to the central hallway in this section. 

Figure 2-7 shows the western side of the

northern end of this section, where the wall 

and part of the roof collapsed.

This school had numerous structural weaknesses, which contributed to the destruction. The most significant weakness that 

was observed was the inadequate reinforcement in the masonry walls. The walls 

had only minimal horizontal reinforcement 

and no vertical reinforcement. Inspection of 

one collapsed wall, shown in Figure 2-8, 

revealed that only every third course of the 

concrete block was reinforced. Moreover, 

the mortar was poorly bonded to both the 

reinforcing bars and the blocks (Figure 2-9). 

Figure 2-3: Damage to Southern End of Front Section of Kelly Elementary School.
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Additional horizontal reinforcement, vertical reinforcement, and a better bond with 

the mortar would all have significantly increased the strength of the walls.

Another significant weakness was the

wooden soffit beneath the cornice, shown in 

Figure 2-10. The failure of the soffit allowed 

the wind to penetrate under the roofing, 

thereby increasing the total wind load on

the roof. The wood studs used to support 

the soffit were simply toe-nailed to the supporting member. These connections could 

not withstand extreme loads, and failure of 

sections of the soffit contributed to the roof 

failures.

A third major weakness was the glazing. 

The glazing appeared to be standard

weight, monolithic annealed glass, which

was shattered by the wind and flying debris 

as shown in Figure 2-11. The glazing fragments would have posed a severe hazard to 

the building occupants.

Figure 2-4: South Side of the Center Section of Kelly Elementary School.

Figure 2-5: North Side of the Center Section of Kelly Elementary School.
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Given the age of this building and its unsatisfactory construction, its failure is not surprising. This is not to say that the school 

did not meet building codes, or that its design and construction were deficient as

compared to conventional practice, but the 

design and construction of this school were 

not nearly sufficient to withstand the tornado wind loads. Better built structures 

would have suffered lesser damage and

Figure 2-6: South Side of the East Section of Kelly Elementary School.

Figure 2-7: Collapsed Wall on West Side of the East Section of Kelly Elementary School.
Reconnaissance Report on Damage to Engineered Structures During the May 1999 Oklahoma City Tornado

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posed a lesser hazard to their occupants,

particularly since the true intensity of the 

tornado may have been less than F5 (see, 

e.g., Phan and Simiu, 1998a).

We note the lack of a safe space in this

school. If the tornado had struck while

Figure 2-8: Collapsed Wall at North End of West Section of Kelly Elementary School.

Figure 2-9: Detail of Mortar and Reinforcement in the Collapsed Wall at North End of West 

Section of Kelly Elementary School.
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classes were in session, many of the students might have been seriously injured or 

lost their lives. In our opinion there is a 

definite need to identify and upgrade 

schools and other public buildings that are 

inadequately built and do not provide safe 

spaces for their occupants.

Figure 2-10: Detail of the Cornice and Soffit on East Side of Kelly Elementary School.

Figure 2-11: Broken Windows on East Side of Kelly Elementary School.
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2.3 Westmoore High School

The Westmoore High School is located at 

12613 S Western Ave, Oklahoma City. The 

zone of largest wind speeds of the tornado 

passed less than 90 meters south of this

school. Numerous homes in the housing

development south of the school (See Figure 

1-4) were destroyed, as were most of the 

buildings in the apartment complex to the 

east (See Figure 1-5). The school itself escaped destruction, sustaining primarily roof 

damage and loss of architectural cladding.

At the time the tornado struck, there were 

approximately 100 occupants inside the

school. Eyewitnesses indicated that many 

of these people had been in the school auditorium at the time the NWS tornado warning was received. By the time the tornado 

struck, the auditorium had been evacuated, 

and everyone had moved to interior corridors. A large section of the auditorium roof 

was blown off and smaller areas of the roof 

over corner classrooms were also lifted off. 

Fortunately, the school's structure remained 

intact, preventing any loss of life.

The damage to the school included the loss 

of some roof sections, significant damage to 

the roofing material over large portions the 

building, loss of architectural cladding, and 

significant wind and water damage to the 

contents of rooms that lost portions of their 

roofs or windows.

The school’s roof had a wide variety of

types of damage, as shown in Figure 2-12. 

As mentioned above and shown in Figure 

2-13, a large section of the auditorium roof 

was destroyed. A smaller section of the 

northwest corner of the roof was also lost. 

The roof covering was heavily damaged in 

many locations, with the worst damage occurring in the southeast corner above the 

gymnasium and the auditorium. Many

other sections of the roofing were damaged, 

including large sections near the center of 

Figure 2-12: Aerial View of Westmoore High School.
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NIST 17

the school and near the northwest corner.

Figure 2-14 shows the section of roof that 

was lost from one classroom. This classroom was located near the northwest corner 

of the building, and had much of its contents damaged by the water and wind that 

entered through the damaged roof. 

Steel architectural cladding, which appeared to be lightly attached, was also

damaged. Figure 2-15 shows some of the 

damaged cladding on a North face of the 

building. This cladding appeared to be

lightly connected only by nails and small 

diameter screws to the buildings' masonry. 

The tornado winds removed most of the 

cladding from the south and east faces of 

the building’s southeast corner. This damage can be seen in Figure 2-16 and Figure 

2-17. 

Of particular interest was the large quantity 

of debris in the vicinity of the school. 

Figure 2-18 shows some of the debris that 

had collected on the north side of the building. Much of this debris was likely from the 

large number of homes south of the highschool that were destroyed by the tornado, 

as shown in Figure 1-4.

Figure 2-13: Detail of Roof Damage to Westmoore High School.
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Figure 2-14: Damage to Westmoore High School Classroom Roof (Inside View).

Figure 2-15: Damaged, But Intact, Cladding on Westmoore High School.
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Figure 2-16: Damage to Cladding on East Side of Westmoore High School.

Figure 2-17: Damage to Westmoore High School and Vehicles, View From South.
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Figure 2-18: Debris on North Side of Westmoore High School.
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3 DAMAGE TO HOTELS

3.1 Overview

At least three hotels were severely damaged 

or destroyed by the tornadoes. Two of

these hotels, the Clarion Inn and the Hampton Inn, were located adjacent to each other 

on the north side of the Tinker Diagonal in 

Midwest City. The tornado appears to have 

crossed the highway moving primarily 

northward at this point. It appears to have 

passed over the southwest corner of the

Clarion Inn, and directly over the Hampton 

Inn and an adjacent building.

The damage to these two hotels was surveyed on Thursday, May 6th. At this point 

some debris have already been cleared to 

allow for search and rescue operations;

however, demolition of what remained of 

the hotels had not yet begun. The Clarion 

was heavily damaged, while the Hampton 

was demolished by the tornado.

3.2 Clarion Inn

The Clarion Inn had sections that used distinctly different construction. The lobby

and some of the central portions of the

building were constructed with steel framing, lightweight cladding, and a sheet metal 

roof. The two-story high accommodation 

areas were constructed with masonry walls 

between the rooms on the first floor, and 

wood and masonry walls on the second

Figure 3-1: Aerial View of Damage to the Clarion Inn.
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floor. The second floor slab and roof were 

precast concrete slabs. The exterior walls 

consisted of floor to ceiling glass windows.

This hotel had varied damage, as shown in 

Figure 1-3 and Figure 3-1. The southwest 

corner was destroyed, while the northeast 

corner had little damage. Some of the central areas of the hotel were also destroyed. 

Figure 3-2 shows the variation in damage 

along the southern side of the hotel’s accommodation area. In the southwest corner, the roof slab had been lifted off and 

nearly every window broken on both floors. 

In addition, many of the interior walls on 

the second floor near the end of the building were destroyed as shown in Figure 3-3.

Much of the western and central section of 

the hotel was severely damaged. As can be 

seen in Figure 3-4, much of the cladding

was removed from this steel framed section, 

and some two story high portions collapsed. 

In addition, a large volume of debris, from 

both the hotel and the nearby buildings, collected in the opened western and central

sections of the hotel.

3.3 Hampton Inn

The Hampton Inn had a steel frame at the 

southwestern corner, where the hotel lobby 

was located. The two-story accommodation 

area of the hotel was constructed with heavily reinforced concrete block walls at both 

ends, and concrete block walls between the 

rooms on the lower floor. The partitions of 

the upper floor, and outside walls of both 

floors, were constructed of cold rolled steel 

studs, with gypsum board cladding on the 

inside and stucco cladding on the outside. 

The floors and roof were pre-cast concrete 

slabs.

Figure 3-2: Damage to South Side of the Clarion Inn.
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Figure 3-3: Damage to North Side of the Southwest Corner of the Clarion Inn.

Figure 3-4: Damage to Western Section of the Clarion Inn.
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This hotel was completely destroyed as

shown in Figure 1-3 and Figure 3-5. The 

precast concrete roof was lifted off and carried some distance. Much of the remainder 

of the second story collapsed and was

swept off the floor slab. The outside walls 

of the south side of the lower floor were 

demolished, leaving only the masonry walls 

and the precast concrete floor slab of the 

second floor standing.

As shown in Figure 3-6 little of the structure 

remained intact and the rooms provided

little protection from the wind and flying 

debris. Figure 3-7 shows the damage to the 

north side of the hotel. Here the exterior 

cladding was stripped away, but some of 

the interior wall cladding remained in

place.

Figure 3-8 shows a detail of the damage to 

the masonry wall, including reinforcing

bars that were exposed when the concrete 

block was demolished.

Figure 3-5: Aerial View of Damage to the Hampton Inn (long rectangular building).
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Figure 3-6: Damage to South Side of the Hampton Inn.

Figure 3-7: Damage to North Side of the Hampton Inn.
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Figure 3-8: Detail of Damage to Masonry at the Hampton Inn.
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4 DAMAGE TO INDUSTRIAL AND COMMERCIAL BUILDINGS

4.1 Overview

A large number of industrial and commercial buildings were damaged or destroyed 

by the tornadoes. Time constraints limited 

the number of damaged industrial buildings that could be surveyed. Damaged industrial buildings that were visited include 

Peach Auto Painting, three buildings at

Tinker Industrial Park, Coors Ceramics, and 

the American Freightways Depot.

4.2 Tinker Industrial Park

This industrial park consisted of three

buildings, all recently constructed. The two 

northern buildings are rectangular in plan, 

running east to west. The southernmost 

building was “U” shaped. A simplified

plan view of the industrial park site is

shown in Figure 4-1.

All three buildings were single story; constructed with steel frames, steel truss roofs, 

and some reinforced concrete block walls. 

Portions of the buildings had either window 

walls or brick facing on steel stud walls.

The tornado passed just south of the industrial park, causing the most severe damage 

to the south building, while the north building was the least damaged.

By the time Tinker Industrial Park was visited on Friday morning, much of the exterior debris had been cleared away, particularly around the south building. Clean up 

and removal of salvageable items from the 

interiors of the middle and north buildings 

was underway, and construction crews

Collapsed

Portion of

Building

Roof

Damaged or

Destroyed

Areas of Wall

or Cladding

Damage

North Building

Middle Building

South Building

Figure 4-1: Simplified Plan View of Tinker Industrial Park
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were preparing to demolish what was left of 

the south building.

4.2.1 South Building

The south building was the newest of the 

three buildings. The main section had been 

completed less than one month before the 

tornado, and the foundation for an enlarged 

central section was under construction. The 

C-shaped portion, shown in Figure 4-1, was 

completed and the central and eastern portions were occupied. The structure and exterior of the western portion were complete, 

but the interior was still being finished.

The front, western, end of the building had 

a glass window wall around three sides. 

This wall did not have any vertical structural supports, and it was blown inward by 

the tornado, as shown in Figure 4-2. While 

the interior of this portion of the building 

was destroyed, the structure suffered only 

minor damage.

The central portion of the building suffered 

broken windows and roof damage, as well 

as severe damage to the interior and contents.

The eastern portion of this building collapsed, as shown in Figure 4-3. This part of 

the structure consisted of tubular steel columns, supporting heavy steel beams and 

roof trusses. The western wall of this section was constructed of heavily reinforced 

concrete blocks, while the other walls were 

constructed of lightweight steel studs and 

brick cladding.

The tornado appears to have pushed this 

portion of the building towards the northeast, rotating it counterclockwise. The largest deformations occurred along the southern edge, while the northeast corner moved 

only a bit, as can be seen in Figure 4-4.

Figure 4-2: Damage to Western Section of the South Building at Tinker Industrial Park.
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The columns on the eastern and southern 

sides of this portion failed, as shown in

Figure 4-5, and the entire section collapsed 

with the roof largely intact. The relatively 

well-reinforced masonry wall on the western side of this section of the building, 

shown in Figure 4-6, collapsed to the east, 

and reinforcing bars that were anchored

into the foundation pulled out or failed.

Figure 4-3: Collapsed Eastern Section of the South Building at Tinker Industrial Park 

(View from Southeast).

Figure 4-4: North Side of the South Building at Joint between Sections.
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Figure 4-5: Detail of Failed Column and Collapsed Roof at the Southeast Corner of the 

South Building.

Figure 4-6: Reinforced Masonry Wall that Failed at South Building.
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4.2.2 Middle and North Buildings

The north and middle buildings were both 

severely damaged. They suffered broken 

windows, damaged window walls, loss of 

roof covering, masonry damage, and some 

structural damage. Air conditioning units 

and other mechanical equipment were

blown off the roofs. Enough of the buildings' envelope was damaged that the interior partitions and building contents were 

severely damaged.

Figure 4-7 shows damage to the east face of 

the middle building. This building contained a mixture of office and warehouse 

space. In addition to losing a significant 

portion of its roof, as shown in Figure 4-8, 

the glazing and masonry cladding, of both 

the west and east ends of the building, were 

damaged. Damage to the exterior wall on 

the west side can be seen in Figure 4-9. 

Wind entering the damaged areas swept

through the building, almost completely

demolishing the interior space and contents.

Figure 4-10 shows damage to the East face 

of the North building. Most of the damage 

to this building occurred at the eastern end, 

with the worst damage occurring in the

northeast corner.

4.3 Peach Auto Painting

This garage-type structure was constructed 

of pre-cast concrete with steel columns,

heavy steel roof beams, cold rolled steel

roof purlins, and sheet metal roof covering. 

This facility appeared to be reasonably well 

constructed, but it had been pushed over to 

the east and destroyed by a nearly direct hit 

from the tornado. The garage doors, located on the west side of the building appeared to have failed inward before the

structure collapsed, which may have contributed to the failure. Figure 4-11 shows 

what remained of the facility as viewed

from the south. Here the walls had collapsed outward, and the roof, which had 

lost its covering, collapsed towards the east. 

Figure 4-12 shows how part of the western 

wall failed. The section shown in this photo 

was located between two garage doors.

Figure 4-7: Damage to the East Side of the Middle Building at Tinker Industrial Park.
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Figure 4-8: Detail of Damage to the Roof of the Middle Building.

Figure 4-9: Detail of Damage to Western Wall of the Middle Building.
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Figure 4-10: Damage to the East Side of the North Building at Tinker Industrial Park.

Figure 4-11: Roof Framing and Collapsed Walls (foreground) at Peach Auto Painting.
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4.4 American Freightways Depot

This facility, shown in the center of Figure 

1-6, was hit by the brunt of the tornado 

when it was near its strongest, and the facility was destroyed. Semi-tractors and trailers had been tossed on their sides and much 

of the structure was reduced to rubble. Unfortunately, by the time the site was visited 

on Friday morning, demolition of the remains of the building was nearly complete 

and it was not possible to gain any meaningful data about the structural damage.

4.5 Coors Technical Ceramics

The Coors Technical Ceramics factory,

shown in the upper left of Figure 1-6, had 

two distinct types of construction. The

main section of the factory was constructed 

of heavy structural steel bents, with cold 

rolled girts and purlins, and steel cladding. 

An office area on the southern side of the 

building had masonry walls, and the structural system could not be identified. The 

tornado passed to the south and east of the 

factory, but nearly all of the damage was 

located in the northwest corner of the building. As shown in Figure 4-13, in this area of 

the structure the cladding, girts, and purlins 

failed, and the wind caused extensive internal damage. The heavy steel structural

bents; however, were mostly undamaged.

Figure 4-12: Detail of Base of Failed Wall at Peach Auto Painting.
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Figure 4-13: Damage to Coors Technical Ceramics Factory.
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5 DAMAGE TO OTHER ENGINEERED STRUCTURES

The tornadoes that struck central Oklahoma 

damaged or destroyed a wide range of

other types of structures. 

Some of the first buildings to be damaged 

by the tornadoes were hangars at the

Chickasha airport. As shown in Figure 5-1, 

a number of these hangars lost large portions of their roof covering. However, the 

tornado that struck the airport was relatively weak, and the structural systems appeared to have survived. 

The Regency Park Baptist Church, which is 

located in Moore, about three blocks from 

the Kelly Elementary School, lost its roof, 

most of its windows, and suffered extensive 

damage from flying debris. The church was 

constructed of masonry walls, with glulam 

timbers supporting a wooden roof. The

tornado, which passed some distance southeast of the church, lifted off the roof, but left 

the timber supports intact, as shown in

Figure 5-2. The masonry walls appeared to 

suffer only minor damage near where the 

roof was connected. An attached building, 

located to the east of the church itself, suffered much more severe damage due to

heavy debris loading. The large tire, shown 

in Figure 5-3, was one of the largest single 

pieces of debris observed. 

Figure 5-1: Aerial View of Damage to Hangars at Chickasha Airport
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Figure 5-2: Damage to the Roof of the Regency Park Baptist Church.

Figure 5-3: Debris Damage to Building Adjacent to Regency Park Baptist Church.
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At the other extreme, the Tanger Outlet

Center mall in Stroud was destroyed by

tornado similar in size to the tornado that 

damaged the hangars at Chickasha airport. 

This tornado appeared to have passed directly over the mall. As shown in Figure 

5-4, nearly the entire mall was destroyed. 

At least 53 stores demolished, and most of 

the roof was lost. 

Throughout the area struck by the tornadoes large numbers of telephone poles and 

power lines were brought down by the

winds. In many places, large power

transmission towers had collapsed from the 

wind loads on the towers and the power 

lines, as shown in Figure 5-5.

Finally, a wide variety of other infrastructure was damaged by the tornadoes. Extensive damage was observed to farm buildings and other agricultural related structures. Figure 5-6 shows some of the damage 

that occurred to the United Cooperative in 

Mulhall. A storage building and numerous 

grain silos (located in the lower left of the 

photo) were destroyed. The town of Mulhall (located in the center of the photo) was 

extensively damaged. Figure 5-7 shows the 

damage that occurred at one farm near

Crescent. Here storage silos were overturned and destroyed, one farm building 

was leveled, and other buildings were damaged.

Figure 5-4: Aerial View of Damage to the Tanger Outlet Center Mall.
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Figure 5-5: Destroyed Transmission Tower near Crescent, Oklahoma.

Figure 5-6: Damage to Mulhall, Oklahoma, and United Cooperative Silos.
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Figure 5-7: Damage to Farm buildings and Silos near Crescent, Oklahoma.
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6 CONCLUSIONS AND RECOMMENDATIONS

The destruction and losses caused by the 3 

May 1999 tornadoes were the result of an 

unusually large and powerful storm. The 

tornado that passed through Oklahoma

City certainly was extremely strong. The F5 

rating that was given to this tornado by the 

NWS appears to be reasonable when the 

destruction caused by this tornado is compared to that of other large tornados. However, the vast majority of the damage could 

have been caused by wind loads associated 

with much smaller tornados, and only a few 

of the strongest buildings would have required F4 or larger wind speeds to be damaged as they were. It is entirely possible 

that the most destructive wind speeds that 

occurred in the May 3 tornadoes corresponded to the F4 tornado scale rating,

rather than to an F5 scale.

The primary reason for most of the building 

losses caused by these tornadoes is simply 

that the buildings — like most ordinary

buildings — were not designed to withstand the wind loads associated with even 

weak tornadoes. The basic design wind

speed for the Oklahoma City area specified 

in “Minimum Design Loads for Buildings 

and Other Structures” [ANSI/ASCE-7/95, 

1996], the current standard at the time of the 

tornados, is 40 m/s (90 mph). This wind 

speed corresponds to just an F1 tornado. In 

fact, a building design to resist the code 

wind loads with a safety factor of 2.0 will 

have reached its design limit in winds of 

just 57 m/s (127 mph), which corresponds 

to a weak F2 tornado. There are strong reasons to believe that the wind speeds typically ascribed to tornadoes are significantly 

larger than the actual speeds [Phan and

Simiu, 1998a; 1998b]. On the other hand, 

there is little doubt that the wind loads that 

occurred during the Oklahoma City tornado 

were much greater than the loads the buildings were designed for. Still, in many cases 

weaknesses in the design and construction 

of the buildings had a significant contribution to building failures.

The large amount of debris that was created 

by the tornadoes likely played a major role 

in damaging other buildings and structures. 

It certainly contributed to breaching the envelope of many buildings, and may have 

been the primary cause of broken windows 

and other cladding damage. It appears that, 

for some buildings in Tinker Industrial

Park, and the building attached to the Regency Park Baptist Church, the debris,

rather than the wind itself, was the major 

cause of damage.

Breaching of a building’s envelope, including breaking windows, failing doors, or destruction of the roof covering, can lead to 

significantly increased pressures inside the 

buildings. This increased pressure can

cause the loads on the roof and leeward 

walls to increase significantly, thereby causing the failure of structures that might otherwise have survived the tornado.

Three weaknesses that were commonly observed were un-reinforced or lightly reinforced masonry walls, poor connection details, and low strength glazing.

 Since buildings in the Oklahoma City area 

are primarily designed for gravity loads,

typical masonry walls are either unreinforced or have a minimal amount of lateral reinforcement. This level of reinforcement is more than sufficient for most loading cases; however, the extreme lateral

loads caused by the tornado winds far exceeded the resistance that such walls can

provide. The collapsed masonry walls at 

Kelley Elementary School (Figure 2-9) provide the best example of masonry that provided little lateral resistance to the wind
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loads. However, the relatively well reinforced concrete block wall that collapsed at 

the south building in Tinker Industrial Park 

shows that even strongly constructed masonry can fail in these extreme winds, particularly when there are other weaknesses 

in the structure. 

One case of a poor detail that may have contributed to structural failure was the nailed 

wooden soffit on the over-hanging cornice 

at Kelley Elementary School (Figure 2-10). 

At first glance, the soffit was only architectural, not structural in nature, and should 

not have contributed to the strength of the 

building. However, the cornice and soffit 

may have contributed to the building failure in two ways. By extending the roof a 

few feet beyond the walls of the building, 

this overhang increased the roof area and, 

therefore, the total load on the roof and its 

support structures. The soffit itself had

simple nailed connections, and although 

there is no way to determine if the soffit or 

the roof first failed, it is quite likely that the 

relatively lightly constructed soffit failed at 

low wind speeds. Once the soffit failed, the 

wind loads would have increased significantly on the overhanging portion of the 

roof. The increased wind load could have 

caused the covering to fail near the roof

edges and peel from the entire roof.

Many of the buildings that were investigated had lost many or all of their windows. 

In most cases the glazing was simply a single layer of annealed glass, which has two 

properties that make it dangerous during

large tornadoes. It has relatively low

strength, which increases the probability 

that it will be broken by the wind pressure, 

flying debris, or a combination of the two. 

When it breaks, it tends to shatter and the 

shards become dangerous missiles that can 

cause serious harm. Tempered and laminated glass both provide better strength,

reducing the chance of the building envelope being breached, especially by wind. 

Laminated glass will not fragment when

broken, thereby reducing the risk of injury 

to building occupants.

The extent of the damage in Oklahoma City 

to homes, schools, commercial, and industrial buildings highlights the need for protected safe spaces. In homes, small underground or in-home shelters can provide the 

necessary safe haven. Schools and other 

public buildings need large shelters or other 

heavily reinforced areas that will remain

intact even in the event of a powerful tornado. While underground shelters will

provide the highest level of safety, adequate 

safety can be provided in well-reinforced 

corridors, which do not have windows,

have reinforced roofs, and have doors capable of withstanding the wind pressures and 

debris loads. 

Even with readily accessible shelters, adequate warning of approaching tornado is 

essential. In the case of the Oklahoma City 

tornadoes, NOAA, with the help of local TV 

stations, was able to provide warnings well 

in advance. 

The destruction that occurred in Oklahoma 

City shows that changes and improvements 

to building codes are necessary to minimize 

the loss of life and property. Increasing the 

wind resistance of buildings can be

achieved through a variety of methods. 

Improved anchorage between the roof and 

the rest of the building, and between the 

building and its foundation will provide a 

better load path. Reinforced masonry walls 

and cladding, reinforced doors, and laminated or other high strength glazing will all 

help to keep the building envelope intact 

during strong winds. Better attention to 

connection details can maximize the structural strength of a building for little additional cost.
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Unfortunately, much is unknown about the 

nature of large tornadoes and the loads that 

they generate on structures. A better understanding of the tornadoes, the wind

speeds, and the wind loads they generate is 

necessary for engineers to be able to design 

safer and more risk-consistent structures. It 

will also help to speed the acceptance of

better building codes, and will allow better 

estimation of the true risk of losses due to 

large tornadoes. Achieving this understanding will require considerably more

data, as well as better methods of classifying tornadoes.
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7 REFERENCES

“Minimum Design Loads for Buildings and 

Other Structures,” (1996) ANSI/ASCE7/95, Revision of ANSI/ASCE 7-93, ASCE, 

New York.

Phan, L., and Simiu, E. (1998a). “Tornado 

Aftermath: Questioning the Tools,” Civil 

Engineering, ASCE, December 1998.

Phan, L., and Simiu, E. (1998b). “The Fujita 

Tornado Intensity Scale: A Critique Based 

on Observations of the Jarrell Tornado of 

May 27, 1997,” NIST Technical Note (TN 

1426), July 01, 1998.