Symmetric and Asymmetric Strengthening of Two-Span RC Beams Using FRCM Systems

Abstract

This paper reports on the feasibility of using fabric-reinforced cementitious matrix (FRCM) systems to strengthen two-span reinforced concrete (RC) beams that are structurally deficient in their sagging regions. In addition to one unstrengthened control beam, nine beams strengthened either symmetrically or asymmetrically with polyparaphenylene benzobisoxazole (PBOFRCM), carbon (CFRCM), and carbon fiber–reinforced polymer (CFRP) sheets were tested under a five-point load configuration. Test results showed that increasing the strengthening ratio resulted in significant increases in the yielding and load-carrying capacity of the beams. Beams symmetrically strengthened with PBOFRCM showed high ductility indices ranging between 100% and 121% of that of the control beam, whereas those strengthened with CFRCM and CFRP showed ductility indices of 45% and 34% of that of the control beam, respectively. Moreover, beams symmetrically strengthened with PBOFRCM systems encountered moment redistribution ratios between 42% and 82% of that of the control beam compared with 10% and 9% only for those strengthened with CFRCM and CFRP systems, respectively. The asymmetric strengthening configuration in which FRCM systems were used along with CFRP sheets proved to be an efficient method to enhance the ductility and moment redistribution capacity of the strengthened beams. Analytically, the rigid-body-rotation approach was modified to predict the moments and curvatures at the plastic hinges of the strengthened sections. The predicted moments and curvatures showed a notable agreement with the experimental values.