Experimental investigation of time-dependent shear deformation in RC beams strengthened with CFRP straps

Abstract

Understanding the long-term shear performance of un-strengthened and FRP-strengthened reinforced concrete (RC) beams is important. The shear behaviour under sustained loads impacts the load-sharing between the concrete, internal and external reinforcement. This in turn influences the reliability of a strengthening system over the longer-term. The current work considers RC beams strengthened in shear with transverse pre-stressed unbonded carbon-fibre-reinforced polymer (CFRP) straps. CFRP-strap strengthened beams have previously been shown to exhibit substantial increases in shear capacity when subjected to short-term monotonic loading. However, after diagonal shear cracks occur, shear deformations can start to become significant. To investigate the time-dependent shear behaviour, an un-strengthened control beam and a series of RC beams strengthened with pre-stressed CFRP straps were subjected to sustained loads. Using a detailed measurement scheme, the time-dependent deformations of the experimental beams were recorded over a duration of up to 523 days. The primary objective was to extract the shear components of deflection and to thereby assess the longer-term interactions. The measured shear deformations were found to increase with time and depended on the sustained load level.