Mechanical performance of steel-concrete double composite continuous beams with constrained shear connectors

To enhance the material utilization efficiency in the negative moment regions of steel-concrete composite beams, a double composite beam with constrained shear connectors was proposed. Flexural tests were carried out on one simply supported beam and one continuous beam. Analysis was performed on the failure mode, load-bearing capacity, interface slip, and strain distribution characteristics of the steel-concrete composite beam with constrained shear connectors. Based on finite element simulation, the interfacial mechanical mechanism and plastic hinge formation mechanism of the steel-concrete double composite beam were revealed. The stiffness degradation law was further explored for the steel-concrete double composite beam by establishing a characteristic-point-based mid-span load-deflection curve model. The research results show that the failure mode of the steel-concrete double composite beam is tensile-shear failure with inclined cracks at the inflection point. Cracks in the concrete at the bottom of the slab in the negative moment region are fine and few in number. Compared with conventional steel-concrete continuous composite beams, the double composite beam exhibits increases of 49% in load-bearing capacity and 67% in stiffness. Stiffness degradation of the double composite beam exhibits a three-stage characteristic: stable stiffness in the elastic stage, moderate stiffness degradation in the elastoplastic stage, and significant stiffness degradation in the ultimate plastic stage. The theoretical model is suitable for evaluating the deformation capacity and overall stiffness degradation law of the double composite beam. Numerical results indicate that the flexural stiffness of the intermediate support section of the double composite beam is 1.66 times that of the mid-span section. During loading, the plastic hinge forms earlier in the mid-span than at the support. The shear connectors on the additional steel plate bear 34% of the interfacial shear force in the negative moment region, thereby enhancing the interfacial shear stiffness. Under a large deformation, the working state coefficient of the additional steel plate interface reaches 0.49, indicating significantly improved utilization efficiency. The double composite structure fully leverages the complementary characteristics of high tensile strength of steel and high compressive strength of concrete, improves the crack resistance of the bridge deck in the negative moment region of the steel-concrete composite beam, and fundamentally resolves the engineering challenge of concrete slab cracking and low material utilization efficiency in the negative moment region of steel-concrete composite beams.