4A6[1] Disaster Case Study
Kemper Arena Roof Collapse
Group 4
Byrne, Amy
Kelly, Sam
Shine, Niamh
Introduction
The Kemper Arena was built in 1973 as the new home for the local Kansas City King
basketball team with a capacity of 17,600 seats at a cost of $23.2million. The Kemper Arena
was built on the site of the old Royals Horse and Cattle Fair and was named after R. Cosby
Kemper, one of the city’s founding fathers. The arena was built primarily for the basketball
team but was also used to host other sports and events such as rodeos, ice shows, football
(association) games and large conventions, including the 1976 National Republican
Convention. The design of the arena won an American Institute of Architects award in 1976.
Design
The arena was designed by Helmuth Jahn of
C.F. Murphy and was located on an elevated,
isolated site on the outskirts of the city. The
design of the roof was such that it was
suspended from above, as is illustrated in
Figure 1. This was done so that the arena could
Figure 2
feature uninterrupted sightlines. The roof measured 97x108m and was suspended on
hangers from three large space frame cantilever trusses. Each truss was 16.5m wide and
space 30m apart. The pipe sections making up these trusses were as large as 1.2m in
diameter. The roof structure consisted of reinforced concrete supported on a light steel
open web joists with steel angle chords. The weight of the roof itself was 1.3kN/m 2 and the
additional load it was designed to carry was 1.25kN/m2 (rain, mechanical systems and other
hanging loads). Each, of the 42, hangers
was designed to carry 622kN in tension
whilst supporting the roof. They had to
resist the horizontal wind force which
tended to move the roof horizontally like a
gigantic inverted pendulum. Between the
bottom of the hangers and the top chords
of the steel trusses, the connection
consisted of a steel base plate and a thin
Figure 1
plate of plastic composite, Micarta, to
ensure a good contact and to ensure the connection is not entirely rigid. The connection for
the hangers used ASTM A490 high-strength bolts.
Storms frequent the region and as part of an effort to reduce the storm water run-off into
the city’s sewers, the roof was designed to hold water as a temporary reservoir. The roof
had eight 120mm diameter drains and once the water depth exceeded 50mm, water could
pour out over scuppers. The stiffness of a flat roof, such as the one used in the design of the
Kemper Arena, is important in order to prevent ‘ponding’. ‘Ponding’ is the term given to a
flat roof collecting rainwater and deflecting under the weight, which in turn holds
progressively more water.
Certain problems in the design arise immediately, before disaster struck. The bolts used in
the hangers, ASTM A490, are not recommended for use with fatigue or variable loads as the
design codes warn against this. This is something that may not have been taken account for
in the design of the arena. This could have been possibly due to the factor of safety being
adequately high under design loads. The frequency of storms and the location of the site
would mean many varying loads would be acting on the structure over its lifetime. The
number of drains on the roof, 13, was not enough as the local legal code required 8 times as
many drains. The feature of having the roof as a temporary reservoir could only aggravate
‘ponding’ and be cause for largely variable loads depending on the amount of rainfall in a
given storm.
Disaster
On June 14th, 1979 at approximately 6.45 p.m. the roof of the Kemper Arena collapsed. It
was during a storm, which resulted in downpours of 108 mm/hr and winds of 112 km/hr. A
single employee was the only person in the arena at the time of the collapse. He described
the sound of the roof collapsing as explosive.
A large 60x65m section of the roof suddenly collapsed onto the arena floor underneath. This
in turn caused a massive air pressure surge which blew out some of the walls. The overall
result was a stadium full of broken and twisted chunks of steel.
Throughout the arenas 6 year lifespan it had experienced and withstood greater storms
than the one that had caused the dramatic collapse. Kansas is situated in an area which is
known to regularly encounter severe storms and rainfall. Therefore this particular storm
should not have been a major concern. But due to several factors, including ‘ponding’,
fatigue and lack of redundant members, the storm managed to cause the roof of the arena
to fail.
Investigation
All parties involved appointed their own investigators in order to establish the cause as soon
as possible to avoid lengthy and costly litigation. It became apparent early in the
investigation that there was no single cause.
James L. Stratta, a civil engineer and failure analyst appointed by the city authorities,
believed that the A490 bolts, connecting the suspended roof and space frame, were to
blame. “The bolts broke at the root of the thread. It appears to be a direct tension failure,”
he observed. He added, “They may have failed because of something else”. However, bolts
taken from the disaster site were sent for stress testing and met their design specifications,
which applied to dead loading.
Some experts believed that the cause of the roof collapse
was due to ‘ponding’. The approx. 10,500m2 roof contained
eight 120mm diameter drains, placed towards the centre
because the roof’s inverted pitch, each of which could
discharge water at a rate of 0.0015m3/s. Investigators
found that the drains were not blocked, however, Kansas
City code required one such drain for every 186m2 of roof,
which meant that the arena should have had a minimum of
65 drains. Substantial ‘ponding’ had taken place and
although it had not exceeded the design load-bearing
capacity of the roof, it had in fact contributed to failure.
Figure 3
The main issue with the design of the arena was its flexibility. It is well
known that tornadoes are a common occurrence in Kansas so wind
would have been a big factor in the design of the building. According to
Roger McCarthy from Failure Analysis Associates (FaAA), “It was open,
more airy, and much [lighter] – inevitably there was greater flexibility in
this structure.” Because the roof was so flexible, the water which had
accumulated was able to move around, this along with the high windspeeds meant that the roof was subjected to a cycle of increasing loads
causing increased deflection and the roof became unstable. The A490
Figure 4
bolts, although passing design specification, are not designed for dynamic
loading. The movement of the roof fatigued and loosen the bolts causing them to fail.
Stratta reported “They [the bolts] apparently failed at between one-fourth and one-fifth of
what they should have been able to carry”. The University of Missouri tested the bolts and
concluded that the bolts would loosen if subjected to a torque of between 540kNm and
1020kNm. The bolts should have been designed to withstand 3,800kNm of torque.
Lack of redundancy was another major factor that led to its collapse. After one hanger failed
due to bolt fatigue, the remaining hangers could not withstand the additional loading.
Conclusions
The cause of the collapse of the Kemper Arena roof contributed to the expansion of the
knowledge base of the international Engineering community. The collapse highlighted the
importance of paying attention to stiffness as well as strength of a structure. Analysis of
fatigue, stiffness and strength is required for good design. Roger McCarthy of the FaAA sums
up the main lesson to be learnt from this disaster: “Sometimes we get too close to the
margin between strength and load and we forget that there are really two things you have
to worry about in a structure. One is strength and the other is the stiffness. Sometimes the
stiffness will govern the design. Even though you don’t need the extra material for strength
you may need the extra material for rigidity.
The key lessons learnt were evident when the arena roof was rebuilt. The steel bolts and
plates were replaced by much more ductile single steel part for each hanger. The roof was
raised and fourteen drains were added. An electronic monitoring device was installed to
give advanced warnings of any motion problems in the roof.
References
Why Buildings Fall Down: How Structures Fail - Matthys Levy and Mario Salvadori - W.W. Norton, 2002.
Collapse : Why Buildings Fall Down - Philip Wearne - Channel 4 Books, 1999.
Beyond Failure: Forensic Case Studies for Civil Engineers - Norbert J. Delatte Jr. Ph.D., P.E. ASCE Press.