Concrete compressive stress distribution of RC members subjected to flexure

Abstract

In flexural capacity design, the concrete compressive stress-strain curve of reinforced concrete (RC) members is scaled down from the uni-axial concrete stress-strain curve so that the maximum concrete compressive stress adopted in design is less than the uni-axial strength to incorporate the strain gradient effect due to bending. While, the use of the scaled down concrete stress is often found to underestimate the flexural strength of RC members even the material safety factors are taken as unity. In order to investigate the effect of strain gradient on the maximum concrete compressive stress that can be developed in flexural RC members, as well as on the flexural capacity of those members, one pair of plain concrete (PC) and three pairs of RC inverted T-shaped specimens were fabricated and tested under concentric and eccentric loads. Based on the axial force and moment equilibriums, the maximum concrete compressive stress developed in the eccentrically loaded specimens under strain gradient is determined by modifying the concrete stress-strain curve obtained from the counterpart concentrically loaded specimens. Furthermore, a pair of equivalent rectangular concrete stress block parameters for the purpose of flexural strength design of RC members is determined based on the obtained maximum concrete compressive stress. Comparisons of flexural strengths between the tested results of some RC members conducted by other researchers and the predicted results of those members by the proposal from this study, as well as the theoretical values based on the provisions from some current design codes were made to validate the applicability of those obtained concrete stress block parameters.