Flexural Strengthening of Reinforced Concrete Beams with Externally Bonded Hybrid Systems

Abstract

Carbon fiber reinforced polymers (FRP) have been used widely as Externally Bonded Reinforcing (EBR) materials for strengthening and retrofitting of RC structural members, both in flexure and shear. The use of high strength Galvanized Steel Mesh (GSM) strengthening material has recently gained wide acceptance as well. Both CFRP and GSM have many advantages and some shortcomings. One of their major shortcoming is the lack of ductility. Recently developed Aluminum Alloys (AA) has high ductility and some desirable features that may overcome some of the shortcomings of GSM and CFRP laminates. The major aim of this research is to develop a hybrid ductile strengthening system by combining AA plates with GSM and CFRP laminates to strengthen RC beams in flexure. An experimental program that includes tensile test of six coupon specimens and five flexure tests of beam specimens were conducted. The test results showed the effect of hybrid combination on both strength and ductility of the tested beams and that the newly proposed hybrid systems are promising in improving the flexural behaviour in terms of strength and ductility. The tested hybrid coupons of AA with high density steel mesh (SMH) and AA with CFRP showed an increase in the strain capacity by 6.52 and 4.55 times, respectively compared to that of GSM and CFRP alone. The flexural capacity of the beams strengthened with hybrid laminate increased by around 28% over the control beam, while the beam strengthened with hybrid GSM and AA (SMH+AA) laminate showed an ultimate deflection equivalent to 98.5% of the un-strengthened control beam. The failure modes of the tested beams included debonding and delamination and they were influenced by the type of hybrid system used.