A Semi-Empirical Equation based on the Strut-and-Tie Model for the Shear Strength Prediction of Deep Beams with Multiple Large Web Openings

Abstract

The behavior and shear strength of full-scale (T-section) reinforced concrete deep beams, designed according to the strut-and-tie approach of ACI Code-19 specifications, with various large web openings were investigated in this paper. A total of 7 deep beam specimens with identical shear span-to-depth ratios have been tested under mid-span concentrated load applied monotonically until beam failure. The main variables studied were the effects of width and depth of the web openings on deep beam performance. Experimental data results were calibrated with the strut-and-tie approach, adopted by ACI 318-19 code for the design of deep beams. The provided strut-and-tie design model in ACI 318-19 code provision was assessed and found to be unsatisfactory for deep beams with large web openings. A simplified empirical equation to estimate the shear strength for deep T-beams with large web openings based on the strut-and-tie model was proposed and verified with numerical analysis. The numerical study considered three-dimensional finite element models, in ABAQUS software, that have been developed to simulate and predict the performance of deep beams. The results of numerical simulations were in good agreement and exhibited close correlation with the experimental data. The test results showed that the enlargement in the size of web openings substantially reduces the elements' shear capacity. The experiments revealed that increasing the width of the openings has more effect than the depth at reducing the load-carrying capacity.

Simplified shear equation of deep concrete beam considering orientation effect of opening and mechanical properties of fibre-concrete interface

“…[ 25 ] earlier reported the over-conservative design results when the [ 24 ] model was used in the design, as it underestimates the shear strength of beams with openings. This was confirmed in the present study which showed mean absolute errors of 19.7, 18.5, 13.9 and 9.3% for the [ 24 , 25 , 28 ] and the current proposed shear model, respectively. This indicates that using the model by Ref.…”

“…The model by Ref. [ 28 ] has a high prediction of shear capacity. This is because the model used the measured shear capacity in modelling instead of the factors such as the compressive strength of concrete, among others that contribute to the overall shear capacity of the beam.…”

“…Stuy by Ref. [ 28 ] captured the orientation effect of opening; however, no consideration was taken on the effect of fibres and the model did not consider various factors affecting shear capacity, rather it considered the maximum measured/experimental shear capacity in the model formulation. The model by Ref.…”