Numerical modelling of slab-column joint of RC flat plates

Abstract

In the design of reinforced concrete flat plates, the region around the column always pose a critical analysis problem where punching shear failure occurs due to brittle nature of this failure mode. Column tends to punch through the slab because of the shear stresses that act around the perimeter of the column and develop a failure surface in the form of a truncated cone or pyramid shape. This punching shear failure is one of the topics of intensive research work in the recent years. The slabcolumn connection behaviour is also critical as it transfers combined gravity and lateral loads. The performance of slab-column connection has often been less than satisfactory under seismic action. This has prompted the design community to establish rather restrictive rules for flat plate system in earthquake prone region. Before carrying out numerical model of slab-column connection, some existing literatures on the relevant field based on experimental investigation, analytical methods, numerical models and various codes of practice are thoroughly reviewed. A numerical model of slab-column joint of RC flat plate have been generated by using ‘ABAQUS’ software based on nonlinear finite element method. For nonlinear finite element analysis, material nonlinearity is modeled by considering the nonlinear effects due to cracking and crushing of concrete and yielding of steel reinforcement. A complete model requires the elastic properties, inelastic stressstrain relations and failure criteria of concrete. Regarding the concrete material behaviour, a nonlinear user-defined material approach based on the concrete damage plasticity model is used. On the other hand, reinforcing steel behaves as an elasticperfectly plastic material. A sensitivity analysis has been performed for mesh density to obtain a reliable solution. The numerical results of present finite element model have been verified with the experimental results and other numerical results. A satisfactory result has come in between the present numerical results and the experimental results or other numerical results which indicates the suitability and accuracy of present finite element model. All loads are applied in terms of displacement control criteria. A systematic parametric study of material and geometric parameters like concrete compressive strength, the amount of longitudinal reinforcement, yield stress of steel, effect of compression reinforcement, slab thickness, column dimensions and boundary conditions is carried out to identify the effects of different parameters on punching shear strength of flat plates. ACI 318-08/BNBC 2006 code provision is found to be more conservative in case of punching shear design of flat plates. It underestimates the influence of maximum material and geometric parameters to predict the actual punching capacity. Hence, a modification to the ACI 318- 08/BNBC 2006 code equation has been discussed and verified against the results of present finite element results. Four different slab-column joint of RC flat plates have been modeled numerically under different design specifications and analyzed to study the effects of different load combinations and loading sequence. The design and performance of these slabs have been discussed considering ACI 318-08/BNBC 2006 code provisions. It has been found that strength of slab-column connection improves if seismic design is performed. The performance of flat plate high-rise building structure with shear-wall has been checked under combined gravity and lateral loads considering different seismic zone. The percentage of moment transfer through different strip of slab is also analyzed under gravity and lateral loads.