Effects of U-wrap anchored doubly FRP strengthened reinforced concrete beams on ductility and serviceability improvements

Abstract

This paper presents a paradigm shift from the classical thinking that CFRP strengthening increases ultimate capacity only. It addresses a new strengthening technique change that yields significant improvements in ductility and serviceability. A series of eight reinforced concrete beams were cast and tested under four-point bending until failure. The beams were divided into two groups: the control group comprising two beams without any strengthening, and one beam reinforced with one tension layer only. The examined group consisting of four beams having double FRP layers in compression and a single layer in tension, with different anchorage configurations. Additionally, one beam in the examined group had a lower concrete strength. The results demonstrated that the doubly strengthened beams exhibited larger post-cracking stiffness and load capacity compared to the control beams. The anchoring of tension layers and incorporation of compression FRP layers significantly increased ductility of the beams. The utilization of U-wrap anchors successfully shifted the failure mode from sheet debonding to FRP rupture and FRP buckling in the compression zone, effectively maximizing the benefits of the FRP reinforcement. Moreover, the addition of compression FRP layers improved the load distribution and reduced the critical compressive stresses.