New Structural Robustness and Structural Redundancy Indices for Bridges: Practical Application of In-Service Bridge Evaluation

Evaluations and rehabilitations of existing bridges are becoming more frequent given the increase in aging infrastructure across North America. Although numerous design strategies have been proposed to reduce the probability of progressive collapse of in-service bridges, the Canadian Highway Bridge Design Code (CSA S6:19) does not prescribe quantitative procedures or measures to assess the structural robustness of bridges. Robustness-based evaluations are therefore needed to help optimize resources for assessing and repairing the significant number of existing bridges across Canada. To address this research gap, a new structural robustness index is presented along with a separate index for structural redundancy. Both indices are bounded between zero and one and consider the structural response holistically by accounting for the performance of all elements in a quantifiable manner. A user-friendly framework of analysis is presented for both indices to facilitate application in engineering practice. The framework of analysis is first demonstrated on a simple two-dimensional truss structure subjected to lateral load, and the results are compared with five existing robustness measures published elsewhere. Lastly, to showcase the utility of the indices through practical application, the framework of analysis is utilized on an existing truss bridge in Nova Scotia subjected to various levels of corrosion.