Setting bar-bending requirements for high-strength steel bars

The reinforcing steel industry is currently developing high-strength reinforcing bars with specified yield strengths of 80 and 100 ksi, due to increased demand for such grades in concrete construction. However, none of the higher steel grades are able to match the benchmark mechanical properties of grade 60 steel; with each high-strength variant diverging from benchmark behavior in different ways. There is concern that the less ductile higher grade reinforcing bars may fracture at the bends and may require larger bend diameters. Limited tests are available that investigate the relation between bend diameter and the ductility, or conversely the brittleness, of reinforcing bars at bends. No such tests exist for the newly developed high-strength reinforcement having yield strengths of 80 and 100 ksi. Bend/re-bend (or re-straightening) tests were conducted on grade 60 and higher grade reinforcing bars to investigate relations between bend diameters and bend performance. The tests were monitored using digital image correlation technology from which never-before recorded comparative measures were obtained. Test results indicated significant differences in bend performance between bars of varying grades, such that wider bend diameters may be necessary for certain higher grade bars.