Numerical investigations on the influence of transverse beams and slab on the seismic behavior of substandard beam-column joints

The paper investigates the seismic performance of non-seismically designed reinforced concrete exterior and interior beam-column joints. The study focuses on the influence of transverse beams and slab on the sub-assemblies which are failing due to a joint shear failure. In the case of exterior joints, top and bottom longitudinal deformed bars of the loaded beam are anchored with a 90 degrees bend in the joint, where no transverse reinforcement is available. The work is carried out in the framework of a 3D finite element analysis, where the microplane model with relaxed kinematic constraint is used for the constitutive law of concrete. First, the numerical approach is validated against an experiment from the literature carried out on an exterior edge joint with transverse beams and monolithically cast slab. The verification of the modeling approach is done in terms of cyclic load-displacement behavior and crack pattern. The validated modeling approach is then used to further analyze various configurations of exterior and interior joints without and with transverse beams and slab. The results of the numerical study show that the presence of transverse beams leads to an increased joint shear strength due to the confining action, whereas the slab substantially affects the flexural behavior of the loaded beam as well as the overall load transfer in the sub-assembly. It is found that the presence of slab leads to an unsymmetric load-displacement behavior under positive and negative moments, particularly when a relatively high effective slab width is contributing under negative moments. The results are evaluated to obtain the values of critical principal tensile stresses for joint shear strength that might be appropriate for the analysis of joints of different configurations considering the presence of transverse beams and slabs.