Experimental results of sustained load (creep) tests on FRP reinforcing bars for concrete structures

Unlike steel reinforcement, the creep failure of FRP reinforcing bars may occur at tensile stress levels considerably lower than their static failure stress. Thus, the creep strength of a particular FRP bar type plays a role in determining its allowable service stress level. Under constant service load levels, creep strain accumulates within FRP reinforcing bars at a rate that decreases asymptotically with time. This phenomenon contributes to the overall long-term deformation of FRP reinforced concrete elements. The effort at hand provides a series of creep evolution results for two types of glass FRP bars. Creep tests have been conducted under different constant sustained stress levels (15%, 30% 45%, 60% and 75% of the guaranteed tensile strength f ^z.ast; _fu) at the University of Sherbrooke. Out of the prospective 10000 hour test duration, periods ranging from 2000 to 8000 hours have elapsed on the erected samples. The testing method applied was in accordance with the available guidelines (CSA-S806-02 and ACI 440.3R-04) as well as the ISIS Canada Product Certification of FRP Materials (ISIS Canada 2006). The obtained results show that the accumulated creep strain is insignificant at/under sustained tensile load levels equivalent to 45% of their guaranteed tensile strength f ^z.ast; _fu. Over a time frame of 6000 hours there is no evident sign of creep rupture, at the latter load magnitude, for both bar types.