Cyclic behavior of shear-critical concrete columns with unstressed steel strands as longitudinal reinforcement

Abstract

The significantly higher tensile capacity of seven-wire steel strands compared to the conventional Grade 420 (MPa) deformed bar can effectively reduce reinforcement congestion in concrete columns. As no previous studies have been reported in the literature, the realization of the above objective necessitates the critical evaluation of the flexural and shear behavior of columns. Thus, this study focused on the shear behavior of concrete columns where unstressed seven-wire Grade 1860 (MPa) steel strands were used as longitudinal reinforcement in place of conventional deformed bars. As shear behavior was under consideration, two types of transverse reinforcement layouts in rectilinear ties and multi-spiral transverse reinforcement were also considered. The experimental program consisted of the cyclic testing of six large-scale column specimens subjected to constant axial load. The tests indicated that the specimens with strands as longitudinal reinforcement failed in shear as intended in the design. Furthermore, the multi-spiral transverse reinforcement layout was more effective than the rectilinear tie layout in confining the core concrete and restraining the steel strands. Finally, both the ACI-318 simplified and detailed shear strength prediction methods were able to estimate the shear strength of the test specimens conservatively. Compared with the ACI-318 simplified method, shear strength prediction by the ACI-318 detailed method was able to produce safer estimates with less variation. In addition to the ACI method to estimate steel contribution to shear strength, modified discrete computational shear strength (mDCSS) model was also used for columns with multi-spiral transverse reinforcement. The mDCSS method provided more accurate results with less variation than the ACI method.