Experimental study of tension stiffening in GFRP RC tensile members under sustained load

Abstract

Sustained load effects on steel reinforced concrete structures due to creep and shrinkage in the concrete have been widely studied. However, knowledge of behaviour under sustained loads needs extending to the more recently developed fibre reinforced polymer (FRP) reinforced concrete structures. In this experimental study, the effect of tension stiffening on tensile glass fibre reinforced polymer (GFRP) reinforced concrete elements under sustained load is investigated. A total of six specimens with three different concrete strengths were tested for a period of between 35 and 40days, when it was seen that deformations stabilized. Some of the specimens included internal instrumentation of the reinforcing bar to capture the reinforcement strain profile and analyse long-term effects. Results confirm bond deterioration due to sustained load, with a reduction in the mean bond stress and concrete tensile stress, and showed how deterioration stabilized at approximately 28days. The influence of concrete strength on the loss of tension stiffening is also confirmed, with higher concrete compressive strength showing the smallest loss of concrete tensile stresses. The results are compared to predictions using Eurocode 2 approach, in which the effects of sustained load are incorporated by applying the effective modulus method (EMM). Predictions using this methodology compare well with experimental results.