A Reassessment of the Analysis Provisions for Bond and Anchorage Length of Deformed Reinforcing Bars in Tension

Abstract

Analysis and design provisions for the bond and anchorage length of deformed reinforcing bars in reinforced concrete elements are typically developed based on the assumption that the strain variations along the bar becomes approximately linear at or near the ultimate state of bond failure. Hence the assumption of the development of uniform bond stress along the anchorage length is used to calculate anchorage lengths of bars regardless of the variations in anchorage lengths or bar diameter. This paper describes an ongoing experimental research program in the Centre for Infrastructure Engineering and Safety (CIES) at the University of New South Wales, Sydney aimed at assessing the effects of different structural factors on the anchorage requirements of modern high strength steel reinforcing bars, including the cases of end development and lapped splices of deformed bars in tension. While the fundamental assumption of uniform bond stress development could be justified for relatively shorter anchorage length, the study found that an increase in anchorage length and bar diameter leads to a reduction of average ultimate bond stress which might be due to the non-uniformity in the development of bond stress along the anchorage zone. It is shown in this paper that the variability in the development of bond stress due to variable anchorage lengths is associated with the variable degree of plastic deformation in the concrete's tensile zone. This paper outlines the importance of these effects on the development of analysis and design guidelines for anchorage of reinforcement.