Comparative evaluation of concrete constitutive models in non-linear finite element simulations of slabs with different flexural reinforcement ratios

Abstract

Two types of failures can be observed in reinforced concrete slabs supported on columns: flexural and punching. Flexural failure occurs due to the formation of a yield-line mechanism, while punching failure occurs when a punching shear crack with a truncated cone shape develops around the connection. However, flexure-driven punching shear failures due to the yielding of the slab’s flexural reinforcement can occur in the immediate vicinity of the column. These failures appear in a similar manner to “pure” punching shear failures with an additional ductility resulting from the flexural reinforcement yielding. Since these flexure-driven punching failures occur in reinforced concrete slabs with low reinforcement ratio, the paper investigates the punching shear response of reinforced concrete slab-column connections with various flexural reinforcement ratios to distinguish the different failure modes that can be observed: punching and flexural-punching. First, the study presents the calibration procedure needed in three-dimensional non-linear finite element analyses (FEA) to simulate the punching shear failure of reinforced concrete two-way flat slabs without transverse reinforcement under static concentric loading. The calibration approaches are developed with reference to two advanced constitutive concrete models available in two different FEA software. Two series of experimental tests are selected from literature: plain concrete specimens under uniaxial and biaxial loadings and slab-column connections under concentric punching. It is shown that the numerical solutions using both concrete models can capture the cracking and failure mode accurately. It is emphasized that the numerical models provide a valuable tool to characterise failure processes and behavioural mechanisms for the simulation of slabs with varied reinforcement ratios. Numerical simulations showed that the failure mode transition within low and high reinforced concrete slabs can be highlighted by flexural-punching and punching shear mechanisms. In addition, the new code predictions of ACI 318-19 for punching shear of slabs with low reinforcement ratios are presented and discussed in comparison to EC2-2004 predictions and the experimental results. Finally, a numerical assessment of slab-column connections with reinforcement ratios varying between 0.2 and 2.2% is conducted to thoroughly investigate the effect of the flexural reinforcement ratio on the punching behaviour.