Reinforced Concrete (RC) deep beams are the most encountered load distribution members in the structural system as transfer girders, foundation pile caps, bridge pier caps, shear walls, corbels, offshore structures, etc. In modern construction, deep beams with web openings are essential for the passageway of conduits, air conditioning ducts, electrical and mechanical services, etc. The discontinuity region in deep beams experience nonlinear strain distribution, where Euler-Bernoulli's theory-based design is not valid. The various international RC design codes, such as ACI 318-19, AASHTO LRFD 2020, and Euro Code - 2 (2014) adopted the Strut-and-Tie Method (STM) for deep beam design. The design guidelines for the deep beams in IS 456: 2000 need to be revised. The design procedures for deep beams with openings are still not documented. In deep beams, the diagonal shear failure is predominant. Its capacity primarily depends on the strength of diagonal strut in STM. The accurate prediction of strut capacity is essential to avoid sudden brittle failure and is a function of the compressive strength of concrete. The various uncertainties such as stress state, confinement level and inclination angle of the strut, and reinforcement distribution affect the performance of the strut. The single multiplier coefficient of uniaxial compressive strength of concrete as the strut efficiency factor accounts for strength reduction due to these uncertainties.

The significant parameters influencing strut efficiency include shear span-to-depth ratio, compressive strength of concrete, percentage tension reinforcement, and percentage horizontal and vertical web reinforcement. The above codes consider only the compressive strength in predicting strut efficiency, whereas several researchers considered the shear span-to-depth ratio also. The efficiency factor equation must include all the influencing parameters to predict the strut capacity accurately. In the past, shear behaviour, the percentage tension reinforcement is viewed only as a design parameter to avoid flexure failure. However, the dowel action of tension reinforcement significantly influences the strut capacity, which is not addressed yet adequately. The study is limited on the shear behaviour of deep beams with openings, especially the influence of web openings on strut efficiency. The aim of this study is to propose multi-parameter-based strut efficiency model to predict the accurate shear strength by analysing experimental database, performing experimental tests, and numerical parametric study on deep beams with and without openings.
Keywords: Deep beam, Strut efficiency factor, Strut capacity, Web opening, Strut inclination, Web reinforcement, Tension reinforcement.