Experimental and numerical investigation of the flexural behavior of one-way RC slabs strengthened with near-surface mounted and externally bonded systems

Abstract

This study investigated the flexural performance of one-way reinforced concrete (RC) slabs strengthened with two distinct strengthening systems: near-surface mounted (NSM) bars and externally bonded (EB) carbon fiber-reinforced polymer (FRP) strips. The NSM bars comprised four types: carbon FRP (CFRP), basalt FRP (BFRP), glass FRP (GFRP), and stainless-steel (SS) bars. The NSM-strengthened slabs showcased substantial enhancements in yield and ultimate load capacity, ranging from 20 % to 55 % and 59-123 %, respectively. In comparison, those strengthened with EB-CFRP strips displayed increases from 46 % to 107 % and 45-177 %, respectively, depending on the axial stiffness ratio of the strengthening system provided. Furthermore, the slabs reinforced with NSM-BFRP bars showed an 11-25 % improvement in their ductility indices. In contrast, the slabs reinforced with EB experienced a decrease in ductility ranging from 38 % to 50 %. This reduction was attributed to the differences in the modes of failure observed in both strengthening systems. The rupture of the NSM-FRP bars and the strain readings associated at the end of testing confirmed that the tensile strength of the NSM-FRP bars was fully exploited whereas the EB-CFRP strips utilized only 29-36 % of their ultimate tensile strain due to debonding. A finite element (FE) model was formulated to anticipate the behavior of the strengthened slabs. A strong correlation between the numerical predictions and the experimental outcomes was observed. The experimental-to-numerical ratios of the ultimate load ranged between 1.0 and 1.08 for the NSM-strengthened slabs and between 0.98 and 1.38 for the EB-strengthened slabs. This validated the FE models' ability to capture the nonlinear performance of the strengthened slabs.