Bridge structures are unique for a number of reasons. Bridges are subjected to repetitive moving traffic. They often have long spans supported by slender columns. Bridges are usually exposed to the environment subjecting them to temperature changes and moisture. Bridges are also exposed to the forces of wind, flowing water, and other environmental forces. All of these factors, and many more, are considered in the design of a bridge. Bridges must be designed to be flexible to adjust to environmental conditions but be stable enough to support the weight of the traffic and provide a sense of security to those using the bridges.
There are many reasons that a bridge might fail. Factors that could lead to failure might include exceeding design capacity, unexpected environmental forces, fatigue and lack of maintenance. Usually, it is a combination of factors that result in failed structures.
Bridges are designed by licensed professional engineers in accordance with design codes. Codes, based on experience and research, have proven reliable for many years. Many engineers and agencies participate during the construction of bridges to verify compliance with the construction documents. After construction, agencies perform periodic inspections and maintenance to insure that the bridges remain safe and serviceable.
Experts will investigate the Interstate 35 bridge collapse near Minneapolis. It is too early to speculate on the factors that might have been involved in the collapse. The investigators will use the information available to them which might include traffic studies, original design documents, maintenance and inspection records, weather and other environmental records, video recordings, and work that has been completed or is scheduled to be completed on the bridge. Stream and river flow records may also be considered. They will also study the wreckage to better determine where the bridge initially collapsed and how other segments of the bridge collapsed afterwards. Samples of bridge components materials will probably be taken for analysis and cataloged for future reference.
The National Council of Structural Engineers Associations offers its sincere condolences to the families of those affected by this tragedy. We offer our support to the various agencies that will undertake the arduous task of determining what went wrong and what can be done to prevent similar events from occurring in the future.