Shear resistance and structural hardening resistance models for hybrid NSC-UHPC elements

Abstract

Ultra-high performance concrete (UHPC) is being increasingly used as a thin overlay for deficient normal strength concrete (NSC) structural elements. Compared to reinforced NSC elements, hybrid NSC-UHPC elements have two stages' structural behaviour under high shear load before failure: monolithic action followed by a composite mechanical action. The composite mechanical action gives to hybrid elements a structural hardening capability after the occurrence of a diagonal shear crack and is not yet considered by most design standards. Two analytical models for hybrid elements under shear load are thus proposed to predict the shear resistance V R of the monolithic action and to predict the structural hardening resistance V Rsh of the composite mechanical action. The shear resistance model integrates the UHPC contribution in the estimation of the tensile strain at mid-height cross-section according to the general method of the Canadian code. The structural hardening behaviour is reproduced with a strut-and-tie system with plastic hinges, where the failure is controlled by the crushing of a concrete strut. Predictions of the proposed models are in very good agreement with 31 hybrid elements experimental results retrieved from the literature.