Experimental and analytical study on the bending performance of UHPC-NC narrow steel box composite beams under negative moments

A novel UHPC-NC composite structure was proposed to enhance the load-bearing capacity of concrete beam bridges under negative bending moments. Parameters including steel fiber content in UHPC, reinforcement ratio, and steel box filling height were varied across 8 UHPC-NC narrow steel box composite beam specimens. The study involved testing, and measurement of failure modes, crack distribution, deformation characteristics, and crack widths. Additionally, a method for calculating maximum crack widths was developed based on crack distribution patterns. Furthermore, a computational model for predicting the ultimate bearing capacity of UHPC-NC narrow steel box composite beams was constructed. The computed results aligned closely with experimental findings, validating the accuracy of the proposed computational model.