Tests investigating the punching shear of a column-slab connection strengthened with non-prestressed or prestressed FRP plates

This paper investigates the effectiveness of bonding non-prestressed and prestressed carbon fibre reinforced polymer (CFRP) plates to the tension surface of concrete column-slab connections in both the serviceability and ultimate limit state. For the prestressed plates different prestressing forces were applied to the CFRP as part of the strengthening technique. The structural response of the strengthened specimens was compared with a non-strengthened reference specimen in terms of punching shear strength, deflection profile, strain, crack opening displacement and failure modes. It was found that using prestressed CFRP plates improved the serviceability; in terms of deflection and cracking, but did not enhance the ultimate behaviour as much as the non-prestressed CFRP plates. The development of the critical diagonal crack (CDC) was the main reason for the reduction in the ultimate capacity of the strengthened slabs.