Axial load tests of concrete compression members with high strength spiral reinforcement

Axial load tests were performed to evaluate the confinement effectiveness of high strength spiral reinforcement in concrete compression members. The tests included 24 and 14 in. (610 and 356 mm) diameter circular cross section compression members with spiral nominal yield strengths that ranged from 78 to 140 ksi (538 to 965 MPa). It was found that while spiral steel stresses in excess of GO ksi (414 MPa) are achieved the nominal yield strength of the spiral may not be achieved. The stress reached in the spiral depends in part upon the compression member diameter, with smaller diameter members able to reach a greater fraction of the nominal yield strength as compared to the larger diameter members. For a given concrete cover thickness, these smaller diameter members have a greater volume fraction of spiral reinforcement as compared to larger diameter members. Compression members made with, high strength spirals exhibit the same ductile axial load-axial shortening behavior expected from members made with mild steel spirals.