Experimental and numerical analysis of the shear performance of trapezoidal dowel connectors in steel–UHPC composite beams

This study investigates the shear performance of trapezoidal dowel connectors in steel–ultra-high-performance concrete (UHPC) composite beams through 15 push-out tests and complementary finite element simulations. The effects of dowel height, root width, and reinforcement ratio on shear resistance and failure modes were evaluated. Two distinct mechanisms were identified: steel dowel root shear failure, which dominated all experiments and most simulations, and UHPC dowel root shear-off, observed only in numerical analysis for extensive root widths. Test results showed that reducing the dowel height from 70 to 30 mm increased the ultimate shear capacity from 242 to 370 kN, while increasing the root width from 30 to 70 mm raised the capacity from 138 to 444 kN but triggered brittle UHPC failure. The reinforcement ratio (0.35%–0.75%) had a negligible influence. A simplified analytical formula for calculating shear capacity, assuming uniform load distribution, was proposed and validated against tests and simulations, with errors of less than 10%. Practical design recommendations for connector dimensions are also provided.