Calculation Method of Ultimate Bearing Capacity of UHPC Composite Beam with Narrow Steel Box

To improve the cracking problem in the negative bending moment zone of composite beams, a new structure of UHPC narrow steel box composite beams was proposed. Ultra high performance concrete material (UHPC) was used to partially replace ordinary concrete (NC) in the wing plate, and its mechanical performance was studied. Two UHPC narrow steel box composite beams with different reinforcement ratios and one NC narrow steel box composite beam specimen were designed, and the full process static loading test was conducted using reverse loading method. Research had shown that as the reinforcement ratio of the experimental beam increased, the cracking load, yield load, and stiffness of the composite beam all significantly increased; the relative slip between NC interfaces in the wing plate of ordinary concrete composite beams was more significant compared to the interface slip between NC UHPC layers in the wing plate of UHPC composite beams; the use of UHPC material in the wing plate could significantly increase the cracking load of the beam and effectively improve the cracking problem in the negative bending moment zone of the composite beam. A calculation method for bending moment and ultimate bearing capacity in the elastic stage was proposed, which was in good agreement with the experimental values; nonlinear simulation analysis was conducted on three experimental beams using ABAQUS software, and the simulated values were found to be in good agreement with the experimental values.