Avoiding Disproportionate Collapse of Major Bridges

Avoiding disproportionate collapse following some small triggering event is an important aspect in the design of major bridges. A general approach for designing structures against disproportionate collapse is outlined and applied to bridges. Compared with buildings, bridges are primarily horizontally aligned structures with one main axis of extension. The provision of alternative load paths, therefore, is often not only more difficult but also less important. It is found that continuous girder bridges are preferably made collapse resistant by segmentation—which can require the insertion of joints or hinges—or by reducing the probability of key element failure. In cable-stayed or suspension bridges, the stay cables or hangers are the key elements that are particularly vulnerable. A collapse triggered by the loss of a cable is prevented by designing the bridge for loss-of-cable load cases; corresponding nonlinear dynamic analyses are presented. This measure should be complemented by protecting the cables against vehicle impact and malicious action. The robustness of suspension bridges can be raised by the methods of segmentation and alternative paths. The protection of the components of the suspension cables against malicious action deserves particular attention. Arch bridges have similarities with suspension bridges and much of the respective statements apply.