Study of Different Shear Kinematic Assumptions on Coupled Axial-Flexure-Shear Sectional Analysis in Shear Deformable Beam Element

Shear deformable fibre beam elements have been proposed in the recent years to account shear deformation in reinforced concrete members. These elements usually adopt a coupled axial-flexure-shear sectional model. This study aims to investigate the effect of different shear kinematic assumptions on the response of the coupled section model. Specifically, three common kinematic assumptions are compared: (1) uniform shear strain distribution, (2) parabolic shear strain distribution and (3) an inner fibre equilibrium method. In the first two cases, a fixed-pattern shear strain distribution is considred over the cross-section irrespective of the load state, while in the third case, the shear strain distribution is estimated by satisfying the inner fibre equilibrium at each load stage. A critical column section is analysed using a coupled sectional model with each of these kinematic assumptions. The concrete fibre properties is modelled using rotating smeared-crack model, and steel fibre properties is modelled using uniaxial stress–strain relation. The results from the three assumptions are compared in terms of the section shear force-shear strain response and the distribution of shear stress over the section. It is observed that the parabolic shear stain assumption closely aligns with the results of the inner fibre equilibrium method.