Seismic retrofit of shear-critical reinforced concrete beams using CFRP

Ageing infrastructure and improvements to design code shear provisions has led to a situation in which many older structures are now considered structurally deficient and are in need of rehabilitation or retrofit. Many of these structures may be at risk of catastrophic failure if their shear-critical components fail in a brittle manner, which could be induced during an earthquake or due to overloading. An effective method for upgrading these shear-critical components is by applying externally bonded fibre reinforced polymers (FRP), which have been shown to significantly enhance shear strength. However, current design codes (ACI 440.2R-08, CSA S6-06) fail to accurately predict strength improvements and have yet to be verified with large-scale beams or those subjected to cyclic loading. As such, large-scale (400 × 650 × 3600 mm) shear-critical reinforced concrete beams were tested under reversed cyclic loading to simulate a seismic event. The beams contained less than design code recommended transverse steel reinforcement for shear and were retrofitted with various FRP wrap configurations. It was found that the FRP retrofits greatly improved shear strength under reversed cyclic loading, attributed to the relatively elastic-like behaviour of the retrofitted specimens. In addition, retrofits with sufficient FRP strengthening to promote flexural yielding were found to improve ductility by reducing post-yield shear strength deterioration.

► Shear-critical reinforced concrete beams were strengthened with carbon FRP wraps.
► Shear strength and ductility enhancement was observed under reversed cyclic loading.
► FRP retrofits reduced shear crack growth and limited crack spacing.
► Closed wrap FRP retrofits reduced concrete shear strength degradation.
► Design code FRP strain limits were found to be overly conservative.