Flexural strength recovery of RC one-way slabs having cut-outs using NSM-SHCC plates

Abstract

Creating a cut-out in an existing Reinforced Concrete (RC) slab became a common practice to allow passing facility services. This cut-out interrupts the loading trajectories resulting in the existence of weak points. Thus, the ultimate capacity of such slab including cut-out decreases with the increase of the size of the opening. In this paper, a new technique based on near-surface mounted has been employed using precast plates made of Strain-Hardening Cementitious Composites (SHCC). These SHCC plates were designed to compensate the cut reinforcement due to cut-out. The used plates had three different widths; 100, 200 and 300 mm, while their thickness was kept constant at 20 mm. One reference slab without cut-out, in addition to, nine damaged slabs with central cut-outs, were prepared and tested under incremental static loading. The tested slabs have the same dimensions; thickness = 140, effective depth = 120 mm, width = 1200 mm and span = 2200 mm. For the cut-out, a rectangular shape with constant width of 200 mm has been used, while the length parallel to the supporting line was varied considering three values; 200, 400, and 600 mm. All slabs were reinforced with a single bottom steel mesh with a longitudinal reinforcement ratio of 0.65%. The slabs having cut-outs were divided into three groups (I, II and III); each one included three different cut-outs. The slabs of group I were tested without strengthening. On the other hand, group II was strengthened at the tension side only, whereas, group III was strengthened at both tension and compression sides. Based on the experimental findings, the load-carrying capacities of group II raised by 15–57% compared to group I; however, this increase was accompanied by a significant decrease in the developed ductility where the displacement-based ductility index could be dropped by 58% for the slab having cut-out length of 600 mm. For group III, the application of SHCC plates at both tension and compression sides enabled the strengthened slabs to restore nearly the lost capacity resulting from providing the cut-out with a good ductility performance.