Innovative connection schemes for longitudinal ribbed UHPC bridge deck at steel diaphragm

The numerous transverse wet joints required in long-span steel-UHPC composite bridge decks increase on-site workload and introduce new-old UHPC interfaces that are susceptible to cracking. This study proposed three connection schemes for the UHPC ribbed deck at steel diaphragms (T-shaped wet joints, high-strength bolted connections, and welded connections) and optimized the structural configurations through finite element analysis to satisfy the anti-cracking, slip and fatigue requirements based on the codes T/CECS G D60–21–2025 and JTG D64–2015. A negative bending test on the welded connection scheme showed that the load–displacement response comprised the constant-stiffness stage, crack-development stage, and reinforcement-yield stage. Due to the stiffening effect of the diaphragm’s upper flange, cracks first occurred at the weld sections between the rib-bottom steel plate and the flange, whereas UHPC above the diaphragm web did not crack until the maximum width of other cracks reached 0.05 mm, which explained the unchanged stiffness during this period. After reinforcement yielding, crack widths increased rapidly, and the main crack developed at the diaphragm-web section. Compared with the wet-joint scheme, the welded connection exhibited significantly improved crack resistance, post-cracking stiffness, flexural capacity and ductility. Overall, the proposed methods offer new connection solutions for UHPC bridge decks, reducing the number of transverse wet joints and improving anti-cracking performance in long-span composite bridges.