Abstract
Six specimens of high strength concrete columns with butt-welded closed composite stirrups were tested under cyclic lateral loads, to study the structural performance (deformation) and hysteretic characteristics of the columns. The influences of the axial compression ratio and the volume-stirrup ratio were considered. According to the regression analysis of the test results, it was determined that the unloading stiffness and strength degradation rate under repeated loading conditions are mainly dependent on the two parameters of the “displacement ductility factor” and “axial compression ratio”. According to the test results, the skeleton curves were determined by the section layer and the statistical regression analysis methods. By considering the influence of axial compression ratio and the volume-stirrup ratio to the hysteretic characteristics of high strength concrete columns confined by butt-welded closed composite stirrups, the shear force-lateral displacement restoring force model was established. The results show that the axial compression ratio has a great influence on the strength degradation of the columns. As the axial compression ratio increases, the strength degradation of the columns occurs faster. On the other hand, the volume-stirrup ratio has a reverse effect on the strength degradation of the columns, with the increase of the volume-stirrup, the strength degradation of the column is observed gradually and slowly. The stiffness degradation of the columns increases as the axial compression ratio increases while the volume-stirrup ratio decreases.
Highlights
The restoring force models are a practical mathematical models derived from the restoring force characteristics and deformation relation curves obtained by the test results, which concretely reflects the structural performance and seismic performance of components in the elastic-plastic seismic response analysis of structures [1, 2]
1) The axial compression ratio had a great influence on the strength degradation of the columns
The volume-stirrup ratio had a reverse effect on the strength degradation of the columns, as the volume-stirrup ratio increased a gradual and slower strength degradation of the columns was observed
Summary
The restoring force models are a practical mathematical models derived from the restoring force characteristics and deformation relation curves obtained by the test results, which concretely reflects the structural performance and seismic performance of components in the elastic-plastic seismic response analysis of structures [1, 2]. Many scholars at home and abroad have done extensive experimental studies on the restoring force characteristics about concrete frame columns, steel reinforced concrete columns and concrete filled steel tubular columns [3, 4], and offered a series of calculation model for calculating the restoring force characteristics [5]. The under-mentioned research materials for the restoring force models were reviewed [6]. The restoring force model still has the following problems: 1) It does not consider the effect of the axial compression ratio to the skeleton curve and the post-yield unloading rigidity. It is necessary to execute further experimental studies focused on these problems
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