Experimental study on flexural behavior of strengthening timber beams with near surface mounted CFRP bars and strips

To learn the effectiveness of flexural strengthening of timber beams with near surface mounted CFRP, 17 timber beams were experimentally studied. There were three unstrengthened reference beams and 14 beams strengthened with near surface mounted (NSM) CFRP bars or strips. The test parameters included the type of CFRP, the position of NSM (tension face or the bottom of the sides), the number of CFRP bars and strips (1 or 2), additional anchoring of NSM CFRP bars and strips (U iron nail or CFRP U stirrup), and additional CFRP sheet bonded to the tension face. The test results show that the ultimate flexural strength of the timber beams are increased by 14%~85% with an average of 39% due to NSM CFRP bar or strip strengthening. Their ultimate deflections are increased by an average of 32%. The initial flexural stiffness of the timber beams is also enhanced by NSM CFRP bar strengthening, while this increase is not significant by NSM CFRP strip strengthening. The strain distribution along the height of the NSM CFRP bars strengthened beams at middle-span is nearly linear during the whole loading process, while there is some different by NSM CFRP strip strengthening. This preliminary study shows that neither an increase of the number of CFRP bars/strips nor the addition of extra anchoring can significantly enhance the bending capacity of strengthened beams, but bonding an additional CFRP sheet to the tension face of the NSM strengthened beams can.