Alternate Load Paths Redundancy Analysis of Steel Truss Bridges

An analysis method to quantify the alternate load paths (ALPs), inspired by the concept of ALP for progressive analysis of buildings, is proposed for steel truss bridges subject to the loss of a critical member. Quantification of ALP in bridges is defined as the spectra of the surrounding members undergoing load redistribution to prevent collapse following the sudden damage to member(s) of a bridge. Two indicators - demand to capacity ratio for linear elastic analysis and strain ratio for nonlinear dynamic analysis - were incorporated into the analysis method and applied to a representative long-span truss bridge. The results of the ALP analysis showed that the three-dimensionality of truss bridges, stemming from the upper and lower braces, sides trusses, floor beam trusses, and the reinforced-concrete deck, played a primary role in protecting the bridge from collapse following the sudden removal of a member(s).