Measured and design bond strengths of deformed bars, including the effect of lateral compression

Abstract

This paper deals with research undertaken at Oxford Brookes University into the bond strength of deformed bars set in normal-weight concrete. It briefly describes pull-out tests on some 150 specimens (providing 300 results), in which the variables were the position of the bar during casting, lateral pressure, cover, bar diameter, concrete strength and bar spacing. The results of the tests are compared with the values predicted by the British and European Codes of Practice BS 8110, Eurocode 2 and CEB-FIP Model Code 1990. Generally, the British code is shown to be very conservative and to underestimate the bond strength. However, when the bars have low cover-to-diameter ratios or where the bars are spaced in pairs vertically, the code appears to give unsafe values. The European codes provide better predictions of the bond strength because they take account of the majority of the influencing factors. However, they do not adequately account for the variables over the full range and are conservative in many circumstances, particularly when lateral pressure is applied. An alternative design procedure is proposed which is based on the experimental evidence and takes account of the main factors influencing the bond.