Experimental and numerical study on the effect of web openings on the torsional behavior of pre-compressed hollow UHPC beams

Hollow ultra-high-performance concrete (UHPC) members subjected to axial pre-compression and torsion represent realistic loading scenarios commonly observed in modern engineering structures, including bridge box girders, prestressed members, and high-rise tubular columns. The inclusion of web openings further reflects practical design requirements. However, the combined effect of pre-compression, torsion, and openings on UHPC members remains insufficiently addressed in literature. To address this gap, the present study integrates experimental work with numerical simulation to provide novel insights into the structural behavior of UHPC beams under complex loading scenarios. The experimental study involves testing five UHPC pre-compressed reinforced hollow beams with central openings under torsion. Their results are presented in terms of cracking and ultimate torque, failure modes, cracking pattern, elastic and cracked torsional stiffness, post-cracking load-carrying capacity, torsional ductility, strain in lower steel bars and torque-angle of twist curve. In the numerical study, 23 UHPC beams (including the 5 tested beams) are modeled using the finite element method with Abaqus software. The presentation of numerical results includes some measurements that could not be experimentally reported. Based on the findings, key recommendations are also proposed to guide future design and implementation of UHPC members under combined loading.