Bond behaviour of substandard splices in RC beams externally confined with CFRP

Bond splitting failures of substandard lap-spliced columns have led to collapse of many RC buildings during recent earthquakes in developing countries. The strengthening of lap-spliced regions with CFRP confinement can reduce the seismic vulnerability of such buildings. This paper investigates bond splitting using flexural tests on twelve RC beams with substandard lap splices (25 bar diameters) at midspan. Different confinement configurations (no confinement, internal stirrups or CFRP sheets), concrete covers and bar sizes are examined at the splice region. The results show that light CFRP confinement enhances the splice bond strength by up to 65% compared to unconfined specimens. Predictive equations from the literature are shown to yield a large scatter in results and to overestimate the strain developed in the CFRP confinement. An alternative approach to calculate the confinement strain and the additional bond strength provided by CFRP confinement is proposed and validated.

•Bond splitting is studied by testing RC beams with substandard lap spliced bars.•Steel stirrups or CFRP confinement, concrete cover and bar size were investigated.•CFRP confinement enhances the lap bond strength by up to 65% over unconfined laps.•Equations predicting the additional bond strength due to CFRP show a large scatter.•A new “strain approach” to compute the latter value is proposed and validated.