Residual stress – strain relations inversely derived from experimental moment – curvature response of RC beams with fibres compared to the recommendations of design codes

Abstract

The layer approach is a simple tool to predict the moment–curvature behaviour of steel fibre reinforced concrete (SFRC) beams. The material stress–strain response of compressive concrete and tensile reinforcement is simple, as for ordinary RC structures, whereas the residual stress–strain relation for SFRC in tension determines the accuracy of the deformation analysis and is difficult to establish. The common practice is to construct a residual stress–strain relation based on standard bending tests. While the residual stresses obtained from such tests represent the softening behaviour of SFRC, the response of the tensile zone of structural members with longitudinal reinforcement is more complex due to the interaction between the residual softening stresses and tension stiffening stresses. This study aims to investigate the adequacy of the RILEM residual stress modelling approach. The residual stress–strain relations are derived from the results of standard notched beams and are compared to the stress–strain diagrams inversely obtained from the experimental moment–curvature response of SFRC beams. An experimental study of 8 full-scale SFRC beams with longitudinal reinforcement including the tests of standard notched beams was carried out. The variables were the volume levels of fibres and reinforcement ratio. To produce accurate moment–curvature diagrams, beams were tested in four-point bending with strains measured at four levels throughout the constant bending zone. The predicted curvatures of SFRC beams following the RILEM recommendations were compared to the tests. A limited curvature analysis was also performed using Model Code 2010 and the Australian Bridge Code. Similarly, the residual stress - strain relations inversely derived from the structural tests were compared to the specifications of the codes mentioned above.