Behaviour of RC slabs strengthened against punching shear using L CFRP laminates

Punching shear failure is a typical failure mode for flat reinforced concrete (RC) slabs and develops in a brittle manner and with little warning. To avoid this type of failure, the punching shear capacity of slabs needs to be carefully considered in the design process and adequate punching shear reinforcement provided. Many existing slabs are required to take increased loading which exceeds their original load ratings due to changes of use. These require strengthening in punching shear to safely carry the increased loading requirements. In this paper, L CFRP laminates are explored for shear strengthening of RC flat slabs. FRP laminates were inserted vertically through predrilled holes in the slabs to act as shear reinforcement. Four tests were carried out on large scale specimens representing internal slab-column connections. All the slabs had the same dimensions of 2300mmx2300mmx200mm. One slab, without strengthening, served as a control slab while the other three slabs were each strengthened with a different shear strengthening configuration. The behavior of the strengthened slabs was assessed in terms of failure load, FRP strain and failure mode. The experimental results confirm that using L CFRP laminates approximately doubles the shear capacity of a strengthened slab compared to the control slab. The dominant failure for the strengthened slabs was punching shear outside the shear reinforced zone. The maximum strain of FRP laminates achieved from the strengthening method was more than 5000 microstrain prior to the failure.