On June 4, 1979, in the same facility that once had hosted the Republican National Convention, nearly a third of Kemper Arena’s roof collapsed during a rainstorm. A supervisor had observed water pouring in and the scoreboard falling. Finally, a large area of the roof collapsed onto an unoccupied seating area.
Designed by architect Helmut Jahn, the 17,600-seat Crosby Kemper Memorial Arena was regarded as innovative for its design simplicity with no interior columns to obstruct spectator views. Three exterior space frames supported the roof: three acres of concrete and steel weighing over 1,500 tons.
The roof was designed to release rainwater gradually through intentionally undersized drains, each servicing individual tributary areas. But the June 4 storm was intense, raining over 4 inches per hour with winds gusting to 70 mph. Overloads at the roof drains were exacerbated by winds that pushed water unevenly and by deflection of the space frame and roof trusses, which caused ponding.
Exponent inspected the debris and zeroed in on steel truss connections in the flat portion of the roof between the famed Space Frames, which had held the roof up. The collapse was triggered by fracture of the high strength bolts, part of the hanger that suspended the roof from the space frames. Analysis demonstrated that failure of just one of four bolts per hanger resulted in a large prying load on the three remaining bolts. Once they failed, the hanger shed its load, overloading adjacent hangers. Lack of proper estimation of rainwater loads under high wind conditions, and lack of redundancy in the roof support system (ability to transfer loads after partial system failure) were principal shortcomings of the design, which was based on commonly accepted but sometimes erroneous understanding of uniform rainwater loading and even distribution of connection load to individual bolts. The issues were corrected, and the arena re-opened within a year.