Lattice modelling of sub-standard reinforced concrete beam-column joints

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 sub-standard beam-column joints. The lattice model is generated by the implementation of truss analogy. In the lattice modelling approach, the concrete and reinforcement members in an RC joint are modelled as truss elements with their own material properties. The reduction in compressive strength due to transverse tensile strain was taken into account in the diagonal concrete members. The reinforcement bar slip relationship was captured by zero-length springs attached to steel and concrete elements. The modelling approach was validated by comparing the simulated responses to the experimentally obtained responses of an inadequately detailed RC 3-story 3-bay frame tested with pseudo dynamic testing procedure and two sub-standard RC beam-column joints tested under quasi-static cyclic loading, one of which contains a slab and an out-of-plane beam. To avoid the mesh size effect and localization issues, the compressive strain at complete stress release in the linear softening branch is adjusted following the crack band approach. A rigid joint model assumption is compared with the lattice model which accounts for the joint deformation. More realistic results are obtained using the lattice modelling technique with high computational efficiency and less demanding in computation time by minimizing the mesh size effect. The model accuracy in reproducing the experimental response is at a reasonable level.