Strength of laps and anchorages of plain surface bars

Abstract

Although plain round or square section reinforcement is no longer used in new construction, there are many older structures still in service built with such bars. As a consequence of the increasing need for assessment of existing construction, there is a continuing need for information on their performance. Research into plain surface bars essentially ceased when ribbed bars became the norm, and plain bars have consequently been bypassed in the developments in the understanding of bond since 1960. An analysis of test data on bond of plain surface bars is presented, and an empirical expression for bond resistance is derived, which parallels that for ribbed bars in the fib Model Code 2010. The analysis finds various parameters that show marked differences in their influence on the bond resistance of ribbed and plain bars. In particular, the strong influence of cover ratio for plain bars observed in the test data was unexpected. A comparison with the provisions of the fib Model Code 90 demonstrates that, in some situations, the margin of safety against failure of straight plain bar anchorages may be too low.