Size Effects in Reinforced Concrete Beams Strengthened with CFRP Straps

Abstract

A carbon fibre reinforced polymer (CFRP) strap system has been identified as a promising method for retrofitting existing reinforced concrete (RC) structures. The CFRP straps, which can be prestressed, act as additional transverse reinforcement and have been shown to increase the shear capacity of RC beams. Since the straps are unbonded, the strap strain consists of any initial prestrain plus an additional strain due to crack opening. Hence, in a retrofitted beam, there are two potential sources of size effects: within the base RC structure; and that inherent in the unbonded strap system. RC beams with low transverse reinforcement ratios have been found to exhibit a reduction in capacity with increasing depth. In strengthened beams, the crack opening strap strain decreases with increasing beam depth and the initial prestrain becomes of increasing importance. The potential interaction between the two sources of size effects presents difficulties when assessing the overall beam behaviour.