Deformation Capacity of Columns with 700 MPa Longitudinal Reinforcement and Hoops

Abstract

To study the effect of Grade 700 MPa longitudinal rebars and hoops on the deformation capacity of RC and composite columns, eight rectangular columns were tested under cyclic lateral loading and uniform axial compression. The test parameters were the hoop type (rectangular or spiral hoops), hoop spacing, the use of composite steel section, and the shape of cross section (square column or rectangular wall-column section). All columns exhibited ductile behavior after flexural yielding. Compared to rectangular hoops and crossties, spiral hoops significantly enhanced the deformation capacity of RC and composite columns by providing lateral confinement and by restraining local buckling and tensile fractures of longitudinal rebars. On the other hand, the use of embedded steel section had limited effect on the deformation capacity because of the relatively low yield strength of the steel section. In the case of wall-column section, as the section depth increased, the deformation capacity decreased due to the increased shear demand. Existing nonlinear analysis modeling methods were applied to the test specimens. The prediction results underestimated the tested deformation capacity, particularly for columns with spiral hoops.