Pr. Walker et al., Measured and design bond strengths of deformed bars, including the effect of lateral compression, MAG CONCR R, 51(1), 1999, pp. 13-26
This paper deals with research undertaken at Oxford Brookes University into
the bond strength of deformed bars set in normal-weight concrete. It brief
ly 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 resu
lts 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 undere
stimate the bond strength. However, when the bars have low cover-to-diamete
r ratios or where the bars are spaced in pairs vertically, the code appears
to give unsafe values. The European codes provide better predictions of th
e bond strength because they take account of the majority of the influencin
g factors. However, they do not adequately account for the variables over t
he full range and are conservative in many circumstances, particularly when
lateral pressure is applied. An alternative design procedure is proposed w
hich is based on the experimental evidence and takes account of the main fa
ctors influencing the bond.