Seismic Behavior Of Concrete Columns With High Strength Steel Bars

Experimental studies on seismic behavior of concrete columns reinforced with HRB400 grade high strength bars spread by the newly revised Code for design of concrete structures (GB50010-2002) and 400MPa grade fine grain high strength bars which are studied and developed in recent years have not been reported at home and abroad by present, which causes inconvenience in revising the item on high strength steel bars of the code GB50010 as well as in application of high strength bars in projects. As Subject of the 863 National Project and the sixth research subject group of the code GB50010, studies on seismic behavior of concrete columns with high strength bars are presented in this paper, providing theoretical and test bases for the code revising and high strength bars' application.This paper presents the experiment of 6 concrete columns with 400MPa grade high strength bars under constant axial load and cyclic lateral loads. The factors that affect their ductility and seismic behavior have been analyzed, and the influence of concrete strength, axial compression ratio and stirrups ratio have been discussed. Besides, the characters of hysteretic and skeleton curve, the reinforcement strain curve and cross-section moment-curvature curve of columns' bottom have been researched. Displacement ductility factors and energy dissipation factors has also been calculated.Based on the analysis of test results, the following conclusions can be reached: the ultimate failure modes for all properly tested columns are flexural failure. In the column load-carrying capacity design, the tensile and compressive strength of 400MPa fine grain carbon steel bar used as longitudinal reinforcement can reach its yield strength. The stirrups at the column bottom will yield if the cross section curvature at the column bottom reaches certain big value, otherwise, they will not yield. And when they begin yielding, if the corresponding displacement at the column top is greater than ultimate displacement, it is suggested that the tensile strength of high strength steel bar used as confinement stirrup with seismic design should be held below its yield strength. The test shows good ductility of all properly tested columns, and their seismic behavior is similar to normal reinforced concrete columns. In...