Experimental characterisation of load responses to failure of a RC frame and a NSM CFRP RC frame

Abstract

This paper presents results from loading to failure of two reinforced concrete (RC) frames. The control frame was under-reinforced with 0.94% tension steel in the beams. The second frame was as the control, with the additional use of up to 0.35% near-surface mounted tension CFRP reinforcement in the positive moment zone and one negative moment zone of the beams. Each frame was indeterminate to the degree four and comprised a rectangular bay with tip-restrained cantilever extensions to represent beam lengths to contraflexure in adjacent bays. The FRPRC frame was found to carry 37% more load than the control. Using the recorded beam reinforcement strains in nonlinear constitutive RC models, the peak moments along the frame were quantified and shown to satisfy equilibrium. Accordingly, the control frame, but not the FRPRC frame, was found to exhibit significant beneficial moment redistribution at higher loads which offset the adverse moment redistribution due to cracking at lower loads. The control frame exhibited ductile failure. Surprisingly, the brittle separation of the FRP which defined failure of the FRPRC frame started in the beam’s midspan zone without evidence of local yield. This non-yield midspan separation mode, normally associated with extensive steel yield, should be studied further.