Numerical bond analysis using experimentally derived local bond laws: A powerful method for evaluating the bond strength of steel bars

The transfer of forces across the interface between steel bars and concrete through bond is one of the most important aspects that control the behavior of reinforced concrete members. This paper summarizes the results of a series of experimental and analytical studies undertaken by the writer at the American University of Beirut for evaluating the bond characteristics of developed or spliced bars in tension under different design and strength variables. Particular emphasis is placed on the evaluation of the average bond strength that develops in steel bars at bond failure by integrating experimentally based local bond law(s) into a numerical analysis technique of the bond problem. A general experimentally derived local bond stress-slip relationship corresponding to the splitting mode of bond failure is presented. With simple modification of the characteristic parameters, the relationship is applicable for plain normal-strength concrete, high-strength concrete, concrete confined with transverse steel ties, fiber-reinforced concrete (FRC), and concrete confined externally with fiber-reinforced polymer (FRP) laminates. The accuracy of the numerical analysis results and the local bond law(s) was verified by comparing them to a large body of test data. The mechanism by which the concrete compressive strength and concrete confinement influence the bond strength is discussed, and generalized expressions of the bond strength of steel bars embedded in FRC- or FRP-confined concrete are presented.