Using nonlinear finite element modeling for punching shear design of concrete slabs

Nonlinear Finite Element Analysis (NLFEA) is currently available in many commercial programs. At the same time computing power has increased to the level that routine use of NLFEA for structural analysis became feasible. Structural concrete shows distinctly nonlinear behaviour and thus the available constitutive models, within FEA packages, include considerations for nonlinear material constitutive behaviour, damage, plasticity and concrete-reinforcement interactions. However, the results of FEA of concrete structures, depend on the choice of numerous modelling parameters making them susceptible to errors in assumptions, and dependent on decisions of the modeler regarding meshing, boundary conditions, and constitutive models for concrete. This paper presents a discussion of how to rationally approach NLFEA of structural concrete with the example of concrete slabs susceptible to punching shear failure. The analyses are done using the concrete damaged plasticity (CDP) model available in ABAQUS. The importance of rational choices of modelling parameters and the calibration of the FEA models based on experimental results is discussed. The paper shows specific examples where NLFEA was used to expand the existing experimental databases, perform detailed parametric studies and propose improvements in the design formulas available in the codes.