On Softening Behaviour of Force-Based Shear-Flexible Concrete Frame Element

The seismic analysis of concrete frames to study their collapse behaviour poses a major difficulty in modelling their softening response. A reliable determination of post-peak response under the combined loading of axial, flexure and shear forces requires advanced numerical models and constitutive formulation. While force-based frame elements are commonly used for analysis by researchers, they are known to have numerical issues of strain localisation and associated mesh dependence in the presence of softening material. Several techniques have been developed to address this problem, but they are mostly limited to the frame elements based on the Euler–Bernoulli beam theory. This paper aims to evaluate some of these techniques to obtain objective results for a shear-flexible frame element. The study element is based on the Timoshenko beam theory. The stress–strain relationship of the concrete material is defined using a smeared crack model, which takes into consideration the normal-shear interaction. The numerical results demonstrate that the available techniques, together with proper consideration of characteristic length in the numerical integration, can provide mesh-independent results for shear-flexible elements.