Local strain of reinforcement and tension stiffening in reinforced concrete walls

This paper presents the development of a mathematical model for determining the ratio between the global strain of an RC wall and the local tensile strain in the vertical reinforcement. It was found that the parameters affecting the ratio of local to global strain are the ultimate tensile strength of the concrete and percentage of vertical reinforcement. A comparison of the different tensile strength models in various concrete codes (i.e. AS 3600, NZS 3101, EN 1992-1-1 and ACI 318) was undertaken and a recommendation for the mean ultimate tensile strength of concrete is presented. Elastic and inelastic bond stress values for D500N reinforcement is included, however it was found that while the level of bond stress between the reinforcement and concrete affects crack widths, it does not affect the ratio of local to global strain. The mathematical model developed was validated against recent experimental testing performed in the Smart Structures laboratory, with very good correlation observed. Charts have been produced for determining the local strain in the reinforcement from the global strain and vice versa. The paper concludes with a brief discussion on how the developed model could be used to account for tension stiffening effects in RC walls.