Kemper Arena - Kasnas City (June 4, 1979) Jonathan R. Torch, BAE/MAE, Penn State, 2009
Introduction:
Kemper Arena in Kansas City, Missouri was opened in 1973 as the new home of the Kansas City Kings professional basketball team. This arena was known for its modern, light, and flexible structure. (Delatte 124-125) Its large roof of 324 ft x 360 ft is suspended on hangers connected to three large space frame trusses. See figure 1 below.
Below are two pictures of the Baltimore, MD Convention Center. The center also has a space frame. This space frame is similar to Kemper Arena's space trusses.
Figures 2 & 3: Space Frame Baltimore Convention Center(Images provided by M. Kevin Parfitt,P.E., Associate Professor, Penn State University)
On, June 4th, 1979 at 6:45 P.M. the roof collapsed during a storm. This storm was considerable; however over the structure's six-year lifespan it had withstood tougher winds and rains. There was no event taking place during this time, and only maintenance personnel were within the building.
The investigation of the collapse concluded the following:
1.The roof had experienced ponding during the storm. Ponding is when a roof structure deflects during a rain storm. This deflection causes more water build up, and in turn more load on the structure. The wind also caused water to pile up in vulnerable areas. 2.The hangers had been weakened by fatigue cycles over the structures lifespan of six years. 3.The roof contained no redundancy once one hanger failed. 4.The primary caused is believed to be the A490 high-strength bolts used in the hanger connections. The tension loaded hanger assemblies failed due to time-dependent fatigue . (Delatte 125)
The overall structural design, collapse, and investigative results will be explained in detail throughout this wiki report, along with unmet code requirements, and lessons learned.
Key Words:
Ponding, A490 Bolts, Space Frame, Truss, Hanger, Fatigue, Oscillations, Constructability, Flood Control Design, Prying, Tension, Flexibility
1. Ponding on the Roof:
Roofs are known to be the most vulnerable part of any structure. Roofs can leak, rot, collapse, and move. (Wearne 17) Ponding is a load effect on a roof of a structure. It occurs when there is a large amount of rain in a short period of time. This could occur during a hurricane or a strong storm. During this rain, roof drains cannot get the rainwater off the roof quick enough. Therefore, it builds up creating load on the structure. Wind can help cause ponding. Wind will blow rainwater, and cause it to concentrate in a certain area. A roof structure's flexability and limited stiffness, due to large spanning, can also cause ponding. This causes water build up, ponding, in vunerable areas where flexability leads to increased deflections. Ponding due to drain design, structure flexibility (limited stiffness), and wind all took a part in the failure of Kemper Arena's roof.
The storm was no "hundred-year flood" or "hundred-year rain", in fact it was a storm at occurred about once a year in Kansas City. Rain was heavy and wind was recorded at 70-80 MPH. (Wearne 28) In the first hour of the storm 3.5 inches of rain fell on the roof. This is about 12 hundred tons of water. (Wearne 32)
Originally, investigators thought some of the 8 roof drains had been blocked causing excessive ponding. Upon further investigation, this was not the case. All 8 roof drains were working as designed. In fact, part of the design was to allow for ponding occurring temporarily on the roof and the structure was designed to carry this additional weight. This is known as "flood control design." This design was used to prevent overloading of the city's sewer system. (Wearne 32) Calculations showed that the amount of ponding that occurred right before failure was within the limits of the design. Therefore, it can be concluded that ponding was a load concern that contributed to the failure, but it wasn't the main reason causing failure.
The Harford Civic Center is also long-span building that collasped due to weather conditions. This roof collapse relates to snow loading after a strong storm, in addition to a number of design errors. Click the following link to see the wikispace page. (Harford Civic Center)
Most recently in Citrus Heights, California (October 2009) a roof collapse of a Filco Discount Center due to water ponding occured. For a news clip of the incident visit the following url. (http://www.youtube.com/watch?v=xqvR8D6mZbw)
Kemper Arena, Harford Civic Center, and Filco Discount Center all had roof collapses. Kemper Arena and Harford Civic Center both had contributing weather loads and design errors causing failure. Filco Discount Center had extreme weather conditions causing failure. Investigation is still taking place, seeing if design errors were also present.
2. Weakened Hangers
To understand the hanger design and how they weakened, first it is important to get an overall view of the roof structural system.
The roof structure was designed as concrete, reinforced by a corrugated steel deck. This deck was supported on light trusses spanning 54 feet long and spaced 9 feet apart. These light trusses were then supported by heavier trusses (drop trusses), spanning 99 feet in the opposite direction. This system was then hung from the lower chords of 3 large space frame trusses. (Levy & Galvadori 61)
Now, it is known that the hangers (42 in total) transfer the entire roof load to the 3 large space frames. Design calculations showed that each hanger was to support a tension force of 129 kips. This load included dead, rain, mechanical, and live loads. The hangers also had to withstand horizontal wind forces. (Levy & Galvadori 61-62)
The hangers experienced many oscillations caused by wind loads throughout the 6 year life of the structure. These oscillations directly affected the bolt connections of the hangers. It had been estimated that the connections were subjected to 24,000 oscillation cycles. (Levy & Galvadori 63) An extreme amount of oscillations, over time, can cause fatigue in steel elements. This is what happened to the hanger connections. The bolts involved experienced fatigue, and over time the tension loads they were designed to take, were no longer met.
3. Lack of Redundancy in Roof Design
The first hanger failed due to prying action in the hanger caused by the static loads. The bolts of the hanger connection could not withstand this prying force and therefore failed. Once, one hanger connection failed, the load was distributed to adjacent hangers. These hangers could not take the additional load, and a chain effect started causing a large section of the roof to fall in.
An additional failure dealing with lack of redundancy in design can be found on wikispace page Ronan Point.
4. A490 High Strength Bolts
A490 High Strength Bolts are warned against using under variable loads by several reliable steel codes. Table 1 below, provided by the Research Council on Structural Connections (RCSC) represents design value considerations for A490 Bolts when considering oscillations.
(Table 1, RCSC 39)
The connections were estimated to see 24,000 cycles as discussed previously. Therefore, the maximum bolt stress design could have been interpreted as 49 ksi. This was not the case; a value of 58 ksi was used in the initial design. Please note; this research was not available during the time the structure was designed.
Unmet Code Requirements:
Unmet code requirements of Kemper Arena took place from design all the way through construction.
One design flaw dealt with a blind reliance on computer-model outcome analysis. (Wearne 22) During construction bowing occurred in some chord members of placed trusses. This bowing was early evidence showing the trusses were too flexible. The owner and contractor notified the engineers of this concern. The engineers concluded that the computer analysis was correct and the bowing was not an important concern. This was not a design error because the trusses had appropriate strength requirements. However, this design did not meet servicability requirements due to the flexibility of the truss members creating noticeable deflections.
Another design concern dealt with the number of drains on the roof. The roof was originally designed with only 8 drains, when code requirements called for more. This design allowed water to build up on the roof, so the city's sewer city wouldn't be overloaded. However, the flexibility of the roof structure was overlooked. The roof's flexibility allowed additional water to build up.
Finally, construction errors also took place. One major error dealt with roofing materials used. The contractor made a roofing material change, due to the complexity of construction, with no discussion with the structural engineer. This change increased the roof systems constructability, however, it also added 5 pounds per square foot more weight. This additional weight may not seem like a lot, however, with a large roof area it is something the structural engineer should have been aware of.
All of these design and construction flaws most likely made some contribution to the increased fatigue in the hanger connection bolts and ultimately the roof collapse.
Lessons Learned:
Human error is something that will never go away in engineering design, even with all the advances in computer technology. It is up to the engineer to choose the proper input parameters when using the computer analysis software, and to make sure the analysis makes sense and meets code requirements. As an engineer it is important to acknowledge that computer analysis programs are just helpful design tools and nothing more. (Modern Marvels)
Another lesson learned deals with effective communication. The construction errors on this project could have been eliminated if proper communication was implemented. On any design and construction project, it is important that all members feel comfortable asking questions and seeking help when decisions are made.
Conclusions:
Kemper Arena's roof collapse was a very costly and unforeseen failure. Thankfully, no one was killed during this catastrophic event. If the arena was occupied during the collapse it could have been extremely devastating.
This failure will be a teaching tool for present and future engineers. Firstly, it gives great insight into A490 bolt usage and concerns. A structural engineer will now be aware of fatigue failure of A490 bolt connections. Secondly, it teaches that effective communication between construction and design team members is very important throughout the project. Finally, it shows that an engineer should not rely solely on computer analysis programs for member and connection design. These programs are just helpful tools to speed up the design process. It is up to the engineer to verify the calculations, member sizes, and connection design.
Bibliography:
Delatte, Norbert. Beyond Failure - Forensic Case Studies for Civil Engineers. Reston, VA: ASCE, 2009.
Levy, Matthys and Galvadori, Mario. Why Buildings Fall Down - How Structures Fail. New York, NY: W.W. Norton & Company, 1992.
Wearne , Phillip. Collapse - When Buildings Fall Down. Channel 4 Books, 1999.
Modern Marvels - More Engineering Disasters. History Channel: 2005, DVD.
RCSC, Committee, "Specification for Structural Joints Using ASTM A325 or A490 Bolts." RCSC. (2004).
Additional Reading:
Goldberger, Paul. "Storm Causes Roof to Fall At an Arena in Kansas City." New York Times 04 Jun 1979, A18.
Goldberger, Paul. "Kansas City Arena Loses Roof In Storm." New York Times 06 Jun 1979, A1.
Hadipriono, Fabian. "Investigative Studies of Ceiling Collapses." ASCE Journal of the Performance of Constructed Facilities. Vol 2. 1988.
Kerley, James. "Time-Dependent Failure Mechanisms and Assessment Methodologies." Cambridge University Press. 1982
Table of Contents
Kemper Arena - Kasnas City (June 4, 1979)
Jonathan R. Torch, BAE/MAE, Penn State, 2009
Introduction:
Kemper Arena in Kansas City, Missouri was opened in 1973 as the new home of the Kansas City Kings professional basketball team. This arena was known for its modern, light, and flexible structure. (Delatte 124-125) Its large roof of 324 ft x 360 ft is suspended on hangers connected to three large space frame trusses. See figure 1 below.
Below are two pictures of the Baltimore, MD Convention Center. The center also has a space frame. This space frame is similar to Kemper Arena's space trusses.
Figures 2 & 3: Space Frame Baltimore Convention Center(Images provided by M. Kevin Parfitt,P.E., Associate Professor, Penn State University)
On, June 4th, 1979 at 6:45 P.M. the roof collapsed during a storm. This storm was considerable; however over the structure's six-year lifespan it had withstood tougher winds and rains. There was no event taking place during this time, and only maintenance personnel were within the building.
The investigation of the collapse concluded the following:
1. The roof had experienced ponding during the storm. Ponding is when a roof structure deflects during a rain storm. This deflection causes more water build up, and in turn more load on the structure. The wind also caused water to pile up in vulnerable areas.
2. The hangers had been weakened by fatigue cycles over the structures lifespan of six years.
3. The roof contained no redundancy once one hanger failed.
4. The primary caused is believed to be the A490 high-strength bolts used in the hanger connections. The tension loaded hanger assemblies failed due to time-dependent fatigue . (Delatte 125)
The overall structural design, collapse, and investigative results will be explained in detail throughout this wiki report, along with unmet code requirements, and lessons learned.
Key Words:
Ponding, A490 Bolts, Space Frame, Truss, Hanger, Fatigue, Oscillations, Constructability, Flood Control Design, Prying, Tension, Flexibility1. Ponding on the Roof:
Roofs are known to be the most vulnerable part of any structure. Roofs can leak, rot, collapse, and move. (Wearne 17) Ponding is a load effect on a roof of a structure. It occurs when there is a large amount of rain in a short period of time. This could occur during a hurricane or a strong storm. During this rain, roof drains cannot get the rainwater off the roof quick enough. Therefore, it builds up creating load on the structure. Wind can help cause ponding. Wind will blow rainwater, and cause it to concentrate in a certain area. A roof structure's flexability and limited stiffness, due to large spanning, can also cause ponding. This causes water build up, ponding, in vunerable areas where flexability leads to increased deflections. Ponding due to drain design, structure flexibility (limited stiffness), and wind all took a part in the failure of Kemper Arena's roof.
The storm was no "hundred-year flood" or "hundred-year rain", in fact it was a storm at occurred about once a year in Kansas City. Rain was heavy and wind was recorded at 70-80 MPH. (Wearne 28) In the first hour of the storm 3.5 inches of rain fell on the roof. This is about 12 hundred tons of water. (Wearne 32)
Originally, investigators thought some of the 8 roof drains had been blocked causing excessive ponding. Upon further investigation, this was not the case. All 8 roof drains were working as designed. In fact, part of the design was to allow for ponding occurring temporarily on the roof and the structure was designed to carry this additional weight. This is known as "flood control design." This design was used to prevent overloading of the city's sewer system. (Wearne 32) Calculations showed that the amount of ponding that occurred right before failure was within the limits of the design. Therefore, it can be concluded that ponding was a load concern that contributed to the failure, but it wasn't the main reason causing failure.
The Harford Civic Center is also long-span building that collasped due to weather conditions. This roof collapse relates to snow loading after a strong storm, in addition to a number of design errors. Click the following link to see the wikispace page. (Harford Civic Center)
Most recently in Citrus Heights, California (October 2009) a roof collapse of a Filco Discount Center due to water ponding occured. For a news clip of the incident visit the following url. (http://www.youtube.com/watch?v=xqvR8D6mZbw)
Kemper Arena, Harford Civic Center, and Filco Discount Center all had roof collapses. Kemper Arena and Harford Civic Center both had contributing weather loads and design errors causing failure. Filco Discount Center had extreme weather conditions causing failure. Investigation is still taking place, seeing if design errors were also present.
2. Weakened Hangers
To understand the hanger design and how they weakened, first it is important to get an overall view of the roof structural system.
The roof structure was designed as concrete, reinforced by a corrugated steel deck. This deck was supported on light trusses spanning 54 feet long and spaced 9 feet apart. These light trusses were then supported by heavier trusses (drop trusses), spanning 99 feet in the opposite direction. This system was then hung from the lower chords of 3 large space frame trusses. (Levy & Galvadori 61)
Now, it is known that the hangers (42 in total) transfer the entire roof load to the 3 large space frames. Design calculations showed that each hanger was to support a tension force of 129 kips. This load included dead, rain, mechanical, and live loads. The hangers also had to withstand horizontal wind forces. (Levy & Galvadori 61-62)
The hangers experienced many oscillations caused by wind loads throughout the 6 year life of the structure. These oscillations directly affected the bolt connections of the hangers. It had been estimated that the connections were subjected to 24,000 oscillation cycles. (Levy & Galvadori 63) An extreme amount of oscillations, over time, can cause fatigue in steel elements. This is what happened to the hanger connections. The bolts involved experienced fatigue, and over time the tension loads they were designed to take, were no longer met.
3. Lack of Redundancy in Roof Design
The first hanger failed due to prying action in the hanger caused by the static loads. The bolts of the hanger connection could not withstand this prying force and therefore failed. Once, one hanger connection failed, the load was distributed to adjacent hangers. These hangers could not take the additional load, and a chain effect started causing a large section of the roof to fall in.
An additional failure dealing with lack of redundancy in design can be found on wikispace page Ronan Point.
4. A490 High Strength Bolts
A490 High Strength Bolts are warned against using under variable loads by several reliable steel codes. Table 1 below, provided by the Research Council on Structural Connections (RCSC) represents design value considerations for A490 Bolts when considering oscillations.
The connections were estimated to see 24,000 cycles as discussed previously. Therefore, the maximum bolt stress design could have been interpreted as 49 ksi. This was not the case; a value of 58 ksi was used in the initial design. Please note; this research was not available during the time the structure was designed.
Unmet Code Requirements:
Unmet code requirements of Kemper Arena took place from design all the way through construction.
One design flaw dealt with a blind reliance on computer-model outcome analysis. (Wearne 22) During construction bowing occurred in some chord members of placed trusses. This bowing was early evidence showing the trusses were too flexible. The owner and contractor notified the engineers of this concern. The engineers concluded that the computer analysis was correct and the bowing was not an important concern. This was not a design error because the trusses had appropriate strength requirements. However, this design did not meet servicability requirements due to the flexibility of the truss members creating noticeable deflections.
Another design concern dealt with the number of drains on the roof. The roof was originally designed with only 8 drains, when code requirements called for more. This design allowed water to build up on the roof, so the city's sewer city wouldn't be overloaded. However, the flexibility of the roof structure was overlooked. The roof's flexibility allowed additional water to build up.
Finally, construction errors also took place. One major error dealt with roofing materials used. The contractor made a roofing material change, due to the complexity of construction, with no discussion with the structural engineer. This change increased the roof systems constructability, however, it also added 5 pounds per square foot more weight. This additional weight may not seem like a lot, however, with a large roof area it is something the structural engineer should have been aware of.
All of these design and construction flaws most likely made some contribution to the increased fatigue in the hanger connection bolts and ultimately the roof collapse.
Lessons Learned:
Human error is something that will never go away in engineering design, even with all the advances in computer technology. It is up to the engineer to choose the proper input parameters when using the computer analysis software, and to make sure the analysis makes sense and meets code requirements. As an engineer it is important to acknowledge that computer analysis programs are just helpful design tools and nothing more. (Modern Marvels)
Another lesson learned deals with effective communication. The construction errors on this project could have been eliminated if proper communication was implemented. On any design and construction project, it is important that all members feel comfortable asking questions and seeking help when decisions are made.
Conclusions:
Kemper Arena's roof collapse was a very costly and unforeseen failure. Thankfully, no one was killed during this catastrophic event. If the arena was occupied during the collapse it could have been extremely devastating.
This failure will be a teaching tool for present and future engineers. Firstly, it gives great insight into A490 bolt usage and concerns. A structural engineer will now be aware of fatigue failure of A490 bolt connections. Secondly, it teaches that effective communication between construction and design team members is very important throughout the project. Finally, it shows that an engineer should not rely solely on computer analysis programs for member and connection design. These programs are just helpful tools to speed up the design process. It is up to the engineer to verify the calculations, member sizes, and connection design.
Bibliography:
Additional Reading: