Punching Shear Responses of Flat-Plate Assemblages Strengthened with Engineered Cementitious Composites

Abstract Flat plate flooring systems are susceptible to punching shear failures at slab-column joints, which is pointed out as one of critical obstacles in its application to high-rise buildings in strong wind or seismic regions. Therefore, it is crucial to develop effective strengthening methods for the flat plate structure against the punching shear failure. To enhance punching shear strength, engineered cementitious composites (ECC) exhibiting strain-hardening behavior under tension and shear have been experimentally investigated in recent studies as thin-layer strengthening materials for slab-column connections. Although those studies demonstrated potential benefits of ECC to improve the punching shear capacity, testing parameters were somehow limited due to economic constraints of physical experiments, and also there are inconsistent results from different studies. Therefore, this paper presents a numerical parametric study on punching shear responses of typical flat plate interior joint assemblages strengthened in punching-critical regions by ECC layers. The flat-plate assemblages were selected and designed according to a prototype flat plate building in Kazakhstan, where various flat plate slab systems have been dominantly adopted in practices. Nonlinear finite element models were developed for the assemblages with and without strengthening and then verified via existing experimental results from the literature. A large set of parameters of ECC materials were investigated, including its strengths, thickness, widths, and locations, through nonlinear finite element analyses. The effects of the parameters on the punching shear strength were analyzed and discussed in detail. On this basis, it has been found that ECC layers can increase the punching shear strength up to 40% with an optimal retrofitting design by applying the ECC with 30 mm thickness and 30 MPa strength on both tension and compression sides of the slab. In addition, this study presents an analytical procedure for estimating the punching shear strength of the flat-plate assemblage strengthened with ECC layers.