Description
Progressive collapse is defined as the propagation of failure from a local damage that results in structural collapse. Throughout history there have been many tragic building and bridge collapses that have increased the amount of interest and research in the field of progressive collapse within the structural engineering community. Notable cases include the collapse of the two World Trade Center towers in New York City in 2001, and the collapse of the I-35W truss bridge in Minneapolis in 2007. Even though there is no universally accepted definition, structural robustness can be described as the ability of a system to absorb an initial damage and not collapse. Although often used interchangeably with robustness, redundancy is defined as the ability of a system to carry additional load after the first member has failed, an attribute that has been advocated as beneficial for robustness.
A critical review of the definitions of robustness versus redundancy from a structural engineering perspective will be presented, accompanied by a review of the existing robustness and redundancy measures published in peer-reviewed journals and technical documents. Furthermore, this paper will showcase a new structural robustness and structural redundancy index that were formulated to account for all relevant aspects of each characteristic identified in literature. Following the critical review, the new indices will be utilized to assess an existing truss bridge subjected to various damages as a real-life case study. Nonlinear static finite element analyses of the truss bridge in intact and damaged states will be performed to obtain the necessary index parameters. Lastly, a retrofit will be proposed for the bridge to increase its robustness and redundancy and illustrate the application of the structural robustness and structural redundancy indices when improving the safety of existing structures.
