Behavior of RC two-way slabs strengthened with CFRP-steelgrid under concentrated loading

A novel composite technique of orthogonally bonding carbon fiber-reinforced polymer(CFRP)strips and steel strips is proposed to improve the performance of reinforced concrete(RC)structures based on co-working of CFRP strips and steel strips. To verify the effectiveness of the method for strengthening RC two-way slabs, seven flat slabs with the dimensions of 1 500 mm × 1 500 mm × 70 mm and an internal reinforcement ratio of 0.22% were prepared and tested until failure under concentrated loading, of which one was unstrengthened, one was strengthened with CFRP strips bonded to its soffit making a grid pattern(termed the CFRP grid), and five were strengthened with a hybrid grid of CFRP strips and steel strips in two orthogonal directions(termed the CFRP-steel grid)to the bottom with steel bolt anchorage. The investigation parameters are the strengthening method, the strip spacing(150, 200, and 250 mm)and the layers of CFRP strips(one layer, two layers, and three layers of CFRP strips are applied for CFRP-steel grid). The experimental results show that the strengthening RC two-way slabs with CFRP-steel grid are effective in delaying concrete cracking and enhancing the load-carrying capacity and deformability in comparison to the CFRP grid strengthening. The yield-line analysis model is proposed to predict the load-carrying capacity of the strengthened slabs. The prediction results are in good agreement with the experimental results.