Load-bearing performance of curved-pultruded GFRP square tube-metal hybrid emergency bridge: Experimental and numerical investigations

Extreme events often disrupt transportation networks and create an urgent need for lightweight, rapidly deployable emergency bridges. To overcome the high self-weight, corrosion susceptibility, and limited deployment efficiency of conventional steel systems, and to resolve the stiffness-assembly efficiency trade-off in existing fiber-reinforced polymer (FRP) emergency bridges, this study proposes and experimentally evaluates a curved-pultruded glass fiber-reinforced polymer (GFRP) square-tube-metal hybrid emergency bridge. In the proposed system, arch-shaped curved-pultruded GFRP square tubes enhance structural stiffness through geometric arch action, whereas modular joints using pre-tightened tooth connections (PTTCs) and single-lug-and-yoke-plate (SLYP) joints enable rapid assembly. Three-point bending tests were performed under four representative SLYP pin configurations within the elastic stage, followed by an ultimate failure test on the symmetric 3-pin configuration, with pins installed in Girders 1, 3, and 5. The results demonstrate that pin configuration governs the global stiffness and transverse load-sharing behavior of the bridge. Specifically, increasing the number of pins improves stiffness by enhancing tensile-force transfer and rotational restraint between adjacent girders, whereas a more uniform pin layout promotes better transverse force coordination. Ultimate failure was governed by local buckling and matrix compression damage near the GFRP arch-foot region, with no evident damage in the PTTCs or bolt-hole areas. A validated finite element (FE) model agreed well with the experimental results in terms of ultimate bearing capacity, and parametric analyses further confirmed that uniform pin arrangements delay the onset of local buckling and improve global structural stability. The proposed system therefore offers a promising solution for short-span composite emergency bridges.