Experimental investigation of RC deep beams with web reinforcement and improvement of ACI 318–19 strut coefficient

Abstract

This paper presents an experimental investigation of ten deep beams with a shear span-to-depth ratio of 1.0. Nine of the ten deep beams were provided with web reinforcement, which improves the load carrying capacity of deep beams to a maximum of 15%. Diagonal crack width of 0.3 mm was observed at beam's service load with a web reinforcement ratio of more than 0.46% in both vertical and horizontal directions. Addition of web reinforcement in both directions controls diagonal crack width effectively. ACI 318–19 strut-and-tie model provisions for deep beams with web reinforcement were analysed using experimental investigations of the present study and extensive deep beam data points from literature. It is observed that ACI 318–19 predicts shear capacity of deep beams with a better mean strength ratio of 0.67 compared to AASHTO, EC2, fib MC 2010. Shear strength limits of ACI 318–19 are found to be highly conservative. ACI 318–19 strut coefficient has been evaluated from database of beams that are failed other than yielding of tie. It has been found that the strut coefficient strongly depends on concrete strength, and use of a single strut factor may produce an unsafe estimation of deep beam capacity. Strut coefficient is proposed in this study for strut-node interface with adequate transverse reinforcement as a function of concrete strength. Proposed strut coefficient improves the capacity estimation of deep beam compare to ACI 318–19, AASHTO, EC2, and fib MC 2010. Proposed method has the lowest coefficient of variation for shear strength estimation, and overestimation percentage is within 5%.