The safety of bridges

This article uses the 2007 bridge collapse of Interstate Highway I35W over the Mississippi River in Minneapolis as a case example for the author's essage on the question of why bridges collapse and what engineers should do, beyond what is already being done. The collapse of the Minneapolis bridge was sudden, unexpected, and complete as the structure disintegrated within seconds. Rescue response was almost immediate, and many heroic acts were performed by the surviving passengers, police, and rescue workers, demonstrating that the community was well-prepared for an emergency. However, questions immediately arose about how something like this could happen, whether it is safe to drive over any bridge, and who was responsible. The author provides an historical perspective to begin to address these questions, using the 1967 Point Pleasant Bridge (Point Pleasant, West Virginia) collapse as a case example. The Point Pleasant bridge collapse resulted in changes in the design, construction, inspection, and maintenance of bridges throughout the country. The author notes that the most important change instituted after the Point Pleasant bridge collapse was the need for redundancy so that when a local joint or member collapses, the entire bridge does not experience progressive collapse. The author then describes a few of the many possible causes of bridge collapse, including previously unimagined effects of natural forces, deliberate destruction in war, carelessness or accidents, fatigue and brittle fracture of structural members and connections, decay from cracking or corrosion, unfamiliarity with new materials, details and structural systems at the time of construction, and unseen or unknown hazards. The remainder of the article reviews the Minneapolis bridge collapse, describing lessons gleaned from this event, which emphasize observation and monitoring of already-constructed bridges. The author concludes that it will require sustained discipline to store and evaluate monitoring information for the life of most bridges, as the majority of them will never have a noteworthy event observed.