Investigation of direct shear behavior at UHPC interfaces incorporating high-strength steel lap joints
Shujun Hu, Xiaopeng Yin, Wen Liu, Sizhi Zeng, Qing Zhi
Abstract
In prefabricated concrete structures, interfacial slip induced by shear at connection zones can critically undermine structural integrity, particularly when load transfer relies on reinforcing bar lap splices. To address this issue, this study investigates the direct shear performance of high-strength reinforcing bar lap joints embedded in ultra-high-performance concrete (UHPC), with a focus on both monolithic UHPC interfaces and UHPC-to-normal concrete (NC) composite joints. A total of 18 Z-shaped push-out specimens were fabricated and tested, comprising 10 monolithic UHPC specimens and 8 UHPC-NC composite specimens. Four key variables were systematically studied: the grade of reinforcing steel (400 MPa vs. 500 MPa), lap splice length (4 d to 10 d ), presence of welded anchor plates, and application of 1 MPa lateral confinement. Experimental results demonstrate that increasing the lap length markedly improves the shear capacity of UHPC-NC composite specimens, with a maximum gain of 27.6 %, whereas the improvement for monolithic UHPC specimens is more limited (3.8 %–5.2 %). Upgrading the rebar strength from 400 MPa to 500 MPa led to increases in shear resistance ranging from 6.4 % to 20 %, while the application of 1 MPa lateral confinement further enhanced the interface’s load-bearing capacity by 6.9 %–7.5 %. Although the installation of anchor plates did not significantly affect peak shear strength, it effectively delayed slip failure and promoted a more ductile response. These findings clarify the shear transfer mechanism at UHPC interfaces with lap-spliced high-strength reinforcement and provide quantitative insights into the influence of key design parameters. The study offers practical guidance for optimizing lap joint configurations and contributes to the development of more reliable design methodologies for UHPC-NC connections in prefabricated structural systems subjected to high shear demands.