Numerical and analytical investigations on punching shear performance of UHTCC-enhanced RC slab-column joints

Abstract

The excellent tensile strain-hardening behavior of ultra-high toughness cementitious composite (UHTCC) makes it applicable for enhancing the punching shear performance of reinforced concrete (RC) slab-column joints. However, construction of an entire slab-column structure employing UHTCC would inevitably lead to uneconomical designs. To balance the economic benefits with the punching performance, utilizing UHTCC in the core region of a slab-column joint is a promising approach. In this study, the impact of UHTCC application range (UAR) on the punching shear performance of UHTCC-enhanced RC slab-column joints (USCJs) was investigated, and an approach for determining the optimal UAR was also presented. Two USCJ specimens with different UAR were tested, and experimental results were compared with the counterpart numerical results to validate the finite element (FE) models. Twenty FE USCJ models with different UAR were established. Then the impact of UAR on development of critical cracks, ultimate resistance, and ductile behavior was examined. Analytical approaches based on the critical shear crack theory as well as on the combination of critical shear crack theory and yield line theory were adopted to predict the ultimate and flexural resistances, respectively. The failure mode was determined by comparing these two resistances and considering the ductile coefficient, based on which the effect of UAR on the failure mode was determined. The results show that the location of critical shear cracks and the appearance of flexural cracks vary with UAR. By increasing UAR, the ultimate resistance increases, but the ductile coefficient first increases and then slightly decreases. Provided that the UAR is increased to some extent, the growth rate of the ultimate resistance evidently slows down and the ductile coefficient peaks, indicating the optimal UAR considering both the economic efficiency and the punching performance. The presented approach shows promise for determining the optimal UAR in practical engineering designs.