Strut efficiency on shear strength, and ductility of RC deep beams with large rectangular openings in shear span

This study reports experimental investigations on reinforced concrete (RC) deep beams with web opening in the shear span to evaluate the effect of large rectangular openings on strut efficiency, shear strength, and ductility.The tested beams had dimensions of 1300 x 200 x 500 mm, with rectangular openings varying in size from 200 100 mm to 300 150 mm.The shear span-todepth ratio (a/d) was maintained at 0.75.The beams were reinforced with 0.30% web reinforcement in each direction and 1.80% flexural tension reinforcement.The ultimate load capacities of beams with openings of 200 x 100 mm and 300 x 150 mm were 61 and 76% lower, respectively, than that of the reference beam.The ultimate load of the beam with the larger opening was 38% lower than that of the beam with the smaller opening.Horizontal web reinforcement, detailed at the upper and lower corners of the large openings, effectively mitigated the reduction in initial stiffness and ductility.The inclination of the critical strut varied with the opening size, affecting the ultimate load capacity and failure mode.An accurate prediction of the shear capacity is essential to prevent sudden failures.The strut-and-tie model for deep beams with openings located at the centre of the shear span has been simplified.Additionally, a strut efficiency factor was formulated as a function of concrete strength, considering the influence of the critical strut angle.