Experimental and Analytical Investigations of Torsional Strength in Ultra-High-Performance Concrete Beams with Transverse Openings

This study investigates the torsional performance of reinforced concrete beams with transverse circular openings and examines methods to mitigate the detrimental effects of these openings using Ultra-High-Performance Concrete (UHPC) and diagonal reinforcement. The experimental component involved casting and evaluating eight beams with dimensions of 150 x 200 x 1200 mm under pure torsion. Among these, two beams were solid (without openings), one was made from normal-strength concrete (NSC), and the rest were cast with UHPC. The beams with openings were categorized into two groups based on the size of the openings-small and large. Each group comprised three beams: the first was cast from NSC and included diagonal reinforcement, the second from UHPC with diagonal reinforcement, and the third from UHPC but without diagonal reinforcement. Results indicated that all beams with openings cast from UHPC exhibited a substantial increase in ultimate torque compared to the control NSC solid beam. NSC beams with small openings showed a marginal decrease in ultimate load capacity by 1.47%, whereas those with large openings experienced a significant reduction of 17.65%. UHPC effectively compensated for the strength lost due to the absence of diagonal reinforcement in both small and large openings. Initial stiffness in NSC beams decreased by 19.4% and 70.1% for small and large openings, respectively. Conversely, UHPC beams demonstrated improved initial stiffness, with increases of approximately 64% for small and 34% for large openings. This study proposes ultimate torsional equations for UHPC beams with various opening sizes. These equations are validated by comparing them with results from previous experimental research, examining the performance of UHPC beams with and without openings.