Analytical calculation of the in-plane shear strength of fibre-reinforced concrete

Existing code prescriptions for determining the shear strength of fibre-reinforced concrete (FRC) elements are either empirical or rely on important assumptions that require further clarification. A mechanically based method is here proposed to determine the fibres and the shear reinforcement contributions to the in-plane shear strength of membrane elements. The method is derived from the comprehensive Cracked Membrane Model for FRC to determine in-plane shear strength of FRC panels and is suitably adapted to determine the shear strength of beam elements. The proposed methodology is compared to existing code formulations and validated against experimental results from 14 panels subjected to in-plane shear stresses and from 34 beams failing in shear. The average ratio between experimental and calculated shear strength is 1.00 for the panels and 1.11 for the beams, with coefficients of variation 11 % and 24 %, respectively. The proposed analytical methodology enables the determination of shear strength and failure modes in FRC elements, with or without shear reinforcement. Equations providing the fibre contribution and the compression field inclination are derived from mechanical considerations, emphasizing the key influencing variables. The proposed method can serve as a basis for codelike formulations for shear strength linked to the involved mechanics, but for which further levels of simplification are still required.