Behavior of incrementally launched modular steel truss bridges

This paper presents a numerical investigation of the behavior of steel bridges composed of modular joints during erection by incremental launching. The modular joint is a nodal connector made up of flat and cold bent steel plates that are joined to standard wide-flange members to form a truss-type bridge. Members and modular joints have flanges and webs that are connected independently by bolted splices, resulting in moment-resisting connections. This capability of the nodal connectors to transmit flexure enables a truss-type system to be incrementally launched and provides enhanced resiliency through system redundancy (i.e., the structure can tolerate the loss of a diagonal member). This paper specifically investigates logistics related to this kit-of-parts approach, focusing on transportation to site, “shaking out” of the steel components for erection, and erecting components while minimizing the need for high-capacity cranes. A high-fidelity, three-dimensional Finite Element (FE) model using shell elements that incorporates staged construction is used to understand the behavior of a 119-m (390-ft) two-lane vehicular bridge during incremental launching and in service. The focus is on evaluating the global behavior of the system and local behavior of the modular joints and the members. Results demonstrate the erection advantages of this novel modular approach. The detailed FE modeling approach is compared with a design-level model using frame elements, culminating in guidelines for design and analysis. • Incremental launching of a modular truss bridge is investigated by staged analyses. • Assembly using inexpensive RT 65 cranes ensures feasibility in remote locations. • Global stability and high shear capacity were found during launching. • Uplift was prevented by additional backspan and counterweight. • Guidelines for design and analysis are developed.