Lattice modelling of substandard RC beam-column joints considering localization issues

Abstract

The strain adjustment for quasi-brittle materials to minimize the mesh size effect and localization issues are investigated by the nonlinear lattice modelling approach for substandard reinforced concrete (RC) beam-column joints (BCJs). The lattice model is generated by implementing the truss analogy for the concrete and reinforcement steel members in RC BCJs. The relevant uniaxial material properties in OpenSees are assigned to the truss members. The reinforcement bond-slip relationship is modelled by zero-length springs attached to steel and concrete elements. The modelling approach is validated by comparing the simulated responses to the experimental behaviour of inadequately detailed RC test specimens. A 3-story 3-bay frame tested with a pseudo-dynamic testing procedure and two substandard RC BCJs tested under quasi-static cyclic loading, one of which contains a slab and an out-of-plane beam, are simulated. To avoid the mesh size effect and localization issues, the strain-based softening function in the uniaxial material property of concrete is adjusted by adopting the crack band approach. Analysis results of the rigid joint model assumption, which does not account for the joint deformation, are also compared with the outcomes of the lattice model. By minimizing the mesh size effect, more realistic results are obtained using the lattice modelling technique with high computational efficiency and less analysis efforts. The model accuracy in reproducing the experimental behaviour and response quantities of prime interest is at a reasonable level for the investigated test specimens.