Investigating modular truss bridges with hybrid system and internal redundancy

This paper introduces a hybrid approach for the redundancy of modular steel truss bridges, where system redundancy of the diagonal members is achieved through flexural connections at nodes and internal (member) redundancy is provided for the chords, end diagonals, and floor beams. To achieve flexural connections for system redundancy and to serve as the module, the “modular joint” – a built-up section of cold-bent and flat plates – is used to connect standard wide flange members. The strong axis orientation of the members coupled with moment connections between modular joints and members enables the bridge to survive the loss of a diagonal member through load redistribution by flexure. Internal redundancy, where fracture of one component of a cross-section does not propagate to other components, for the chords, end diagonals, and floor beams is achieved by stacking and bolted members. As prior work has investigated system redundancy, this research focused on numerically understanding the instantaneous dynamic behavior of a 119-m (390-ft) two-lane vehicular bridge when subjected to sudden loss of one component of the internally redundant chords and end diagonals through explicit dynamic finite element analyses. These analyses are important for characterizing the strain rates as the high velocity stress wave from the fracture propagates. Static analyses were performed using the redundancy load combinations provided by the American bridge design code, considering both instantaneous (Redundancy I load case) and long-term (Redundancy II load case) behavior. The paper concludes with recommendations for the implementation of this hybrid redundancy approach.