A joint assembly is a bridge element at which many different pieces of steel are attached. This type of joint assembly, allowing little or no flexibility for movement, was a typical design practice when the bridge was built 30 years ago. Les Fafard, director of WisDOT's Waukesha district office, said that starting at the joint assembly, the initial crack in the girder developed suddenly. This caused two of the three horizontal steel girders supporting the bridge to buckle. Cold weather contributed to the sudden failure of the steel girder.
Steel becomes more brittle in low temperatures.
The stresses of vehicular traffic were also a factor. Dr. John Fisher, of Lehigh University, said the failure is unlike any on record. The Hoan Bridge failure was the first of its kind ever observed in the United States and is likely to have a national and potentially worldwide impact on bridge design and repair practices. They concluded that the cracks or rips in the girders were NOT related to fatigue, but were caused by the sudden, catastrophic failure of the structure. FHWA engineers performed extensive tests on the quality of the bridge materials, and used a computer model to study the connection joints where the failure occurred.