Response of FRP-retrofitted reinforced concrete panels to blast loading

This study deals with the structural response and ultimate resistance of reinforced concrete panels retrofitted with externally bonded fibre reinforced polymer (FRP) sheets and laminates. Eighteen 1000 x 1000 x 70 mm reinforced concrete panels were made of 40 MPa concrete. Each panel was reinforced with two orthogonal layers of top and bottom steel mesh reinforcement, with an average reinforcement ration of 0.003 and yield strength of 400 MPa. Five of the panels were used as control and were not retrofitted with any FRP. Four panels were identically retrofitted with four 500 mm wide unidirectional glass FRP (GFRP) sheets, with two sheets applied in a cross shape to the top surface and the other two sheets similarly applied to the bottom surface. The sheets were bonded to the concrete by means of epoxy. The FRP sheets covered the middle half of the panels. Five other panels were similarly retrofitted with uni-directional carbon (CFRP) sheets. The remaining four panels were retrofitted with CFRP laminate strips. The strips were 80 mm wide and were applied diagonally, akin to X-brace, to the bottom and top surfaces of each panel. Four of the control panels and twelve of the FRP retrofitted panels were subjected to various blast pressures, emanating from 13.4, 22.4 or 33.4-kg of ANFO explosive at a standoff distance of 3 m. The blast wave characteristics, including incident and reflected pressures and impulses were measured and recorded. The central deflection and strains in the reinforcing steel and the concrete/FRP surfaces were also measured and recorded. The post-blast damage and mode of failure of each panel were observed, and panels that were not completely damaged were subsequently statically tested to find their residual strength.; The test data and observations revealed that the panels retrofitted with either the GFRP or the CFRP sheets had higher blast resistance and they generally performed better than the control panels, but the panels with the CFRP laminates did not perform better than the control panels. The relative performance of the GFRP and CFRP sheet retrofitted panels was the same, despite the fact that the CFRP has both higher strength and modulus.; Theoretical analysis of the test data showed that the software CONWEP can predict the blast wave parameters relatively accurately and is a useful tool for estimating blast loads on structures. The dynamic analysis of the panels was performed using a closed-form solution. When the flexural rigidity of reinforced concrete at different load levels was properly considered, the closed-form solution was able to predict the observed response of the panels reasonably well. However, using elastic properties of the panels and assuming uncracked sections, grossly over-estimated the blast moments acting on the panels. Overall, the analytical solution was found adequate for the purpose of the current study.