Investigating the Behavior of Modular Truss and Lattice Bridges with Hybrid System and Internal Redundancy

This research advances two steel modular bridge approaches, exploring the concept of modularizing nodal connectors while using standard sections as members. Modularity and redundancy are integrated, offering reduced cost and construction time as well as enhanced safety. The modular joint, a concept developed in prior research and advanced in this dissertation, is a built-up steel nodal connector that joins standard wide-flange members through moment-resisting connections to form a truss-like bridge which can tolerate the loss of a diagonal member. These flexural connections enable incremental launching, a rapid erection method that avoids heavy machinery and temporary supports. Feasibility is demonstrated through a logistics study and staged construction analyses. A hybrid redundancy approach is introduced, where the moment-resisting connections provide system redundancy (i.e., the structure can tolerate diagonal loss) and built-up chords, end diagonals, and floor beams provide internal redundancy (i.e., fracture does not propagate through bolted components). Performance is evaluated through (1) explicit dynamic analyses, evaluating the strain rates as the high-velocity stress wave from the fracture is propagated and (2) static analyses considering redundancy load combinations prescribed in the American bridge design code. The lattice joint, a built-up nodal connector comprised of welded plates inspired by the Système Eiffel, is used to from a lattice topology with WT sections as members. Hybrid redundancy is achieved through flexural connections and back-to-back bolted WT chords. Behavior numerically investigated under sudden diagonal and chord loss. A stress-based design tool was developed to guide the selection of lattice topologies for enhanced structural efficiency, reduced construction complexity, and modularity, and is demonstrated through a parametric study of 2450 geometries. Research objectives include: (1) evaluating incremental launching of truss bridges composed of modular joints, (2) introducing and investigating a hybrid approach to redundancy (i.e., internal redundancy for the chords, end diagonals, and floor beams and system redundancy for the diagonals), for truss bridges composed of modular joints and (3) investigating the behavior of modular lattice bridges and developing a stress-based design tool to select an efficient lattice topology. Ultimately, this research demonstrates that the modular and lattice joint technologies create efficient, cost-effective, and highly redundant bridges.<p></p>