Experimental and analytical studies on bond behaviour of tensile lap spliced FRP reinforcing bars in concrete

Abstract

There are very limited studies on the bond of spliced fibre reinforced polymer (FRP) reinforcing bars. Spliced bars are necessary for the limitation of the available bar lengths (standard manufactured length of reinforcing bar). In addition, this type of splice is required at the construction joints. Furthermore, bundled bars are required instead of spaced bars in case of heavily reinforced concrete structures. By using bundled bars, the congestion of reinforcement can be avoided.The current standards for steel reinforcement (such as CSA A23.3 and ACI 318) cannot be used for the FRP bars due to the inherent differences in their mechanical properties and surface configurations. There are no design recommendations available regarding the use of spliced bundled FRP bars.The results of this research project will fill this gap. In this context, 33 large-scale concrete beams reinforced with single or bundled tensile spliced FRP bars were subjected to a four-point flexural test until failure. Two types of FRP bars were used, namely glass FRP and carbon FRP bars.The effects of the bar diameter, splice length, number of bundled bars, confinement by stirrups, and thickness of the concrete cover on the bond strength, bond stress distribution, cracking behaviour and mode of failure of the spliced FRP bars in concrete were investigated. Furthermore, the research presented herein evaluates the existing recommendations for the spliced FRP bars (CAN/CSA-S6-00, ISIS-M03-01, CAN/CSA-S806-02, and ACI 440.1R-03). In addition, the average bond stresses and the critical splice lengths for the FRP bars with different diameters were investigated.The flexural test results indicated that the FRP stress limit is directly proportional to the splice length. Moreover, the ultimate strength analysis method can be used to predict the maximum stress in the spliced FRP bars.The results of these experiments show that the transverse reinforcement (steel stirrups in this case) is effective at increasing the bond strength. An objective of this research work was to develop an equation to predict the maximum average bond stress of the tensile lap-splice of FRP bars embedded in concrete.The proposed equation, which relates the average bond stress to the thickness of the concrete cover, the FRP bar diameter, the splice length, the concrete compressive strength, and the transverse reinforcement ratio, agrees well with the test data.--Résumé abrégé par UMI.