Determination of strut efficiency factor for concrete deep beams with and without fibre

Based on the variation of strain along the cross section, any region in a structural member can be classified into two regions namely, Bernoulli´s region (B-region) and Disturbed region (D-region). Since the variation of strain along the cross section for a B-region is linear, well-developed theories are available for their analysis and design. On the other hand, the design of D-region is carried out based on thumb rules and past experience due to the presence of nonlinear strain distribution. Strut-and-Tie method is a novel approach that can be used for the analysis and design of both B-region as well as D-region with equal importance. The strut efficiency factor (βs) is needed for the design and analysis of concrete members using Strut and Tie method. In this paper, equations for finding βs for bottle shaped struts in concrete deep beams (a D-region) with and without steel fibres are developed. The effects of transverse reinforcement on βs are also considered. Numerical studies using commercially available finite element software along with limited amount of experimental studies were used to find βs.