Experimental and Theoretical Research on Bending Performances of a New UHPC–Steel–Concrete Composite Section

This study centers on the Binzhou no. 4 Bridge and proposes an innovative steel-ultrahigh-performance concrete (UHPC) composite joint, serving as a pivotal component of multilong-span continuous hybrid girder bridges comprising integrated prestressed concrete (PC) and steel–UHPC girders. The structural response was systematically analyzed and interpreted through negative bending tests on a 3:1 scaled-down model coupled with finite-element analysis, with particular emphasis on flexural performance, cracking load, failure modes, and force transfer mechanism. Finite-element analysis incorporating varying UHPC parameters was performed. The ultimate bearing capacity of the composite beam reaches 580.3 t. Attributable to shear-induced failure of the PC beam, the most unfavorable position of the steel–concrete composite beam transitions from the pure bending section to the shear span section. The bearing plate and shear studs dominate the force transmission. The incorporation of the UHPC layer substantially mitigates the loads borne by each structural component, while the extension length of the UHPC layer on the concrete beam exhibits negligible influence on the forces acting upon these components. Furthermore, the ultimate bearing capacity of the steel–concrete composite beams was computed, demonstrating excellent consistency with finite-element simulation outcomes. The disparity between the calculated and the simulated values remains below 10%.