DEBONDING FAILURE OF REINFORCED CONCRETE BEAMS STRENGTHENED WITH EXTERNAL CFRP FABRIC

摘要

Debonding failure of the concrete cover in reinforced concrete beams retrofitted with FRP composites is a brittle phenomenon that in most cases occurs in an abrupt manner. A thorough understanding of the peeling mechanism is required for characterization of failure and for realistic estimation of the ultimate loads. The research reported here examines the mechanism of cover failure of precracked reinforced concrete beams retrofitted with unidirectional carbon fiber reinforced polymer (CFRP) fabric. The experimental portion of the program pertains to the determination of cover debonding sequence by way of distributed optical fiber sensors embedded at the interface between concrete and the CFRP fabric. The experimental evidence indicated the influence of transverse flexural and bond cracks in controlling the cover delamination phenomenon. Based on the experimental observations, a simple model is proposed through which it is possible to estimate the critical force in the fabric at the time of debonding failure and therefore the ultimate load. Experimental results from the present study as well as those of other investigators were employed in the evaluation of the model. The critical force in the fabric depends on the spacing of transverse cracking in the concrete cover. Due to wide scatter, i.e. a factor of 2, in crack spacings, wide scatter was observed in the computation of ultimate loads. Therefore, an upper and lower bound approach was developed for estimation of the ultimate loads.