Experimental Investigation On Eccentric-Loaded Behavior Of Spiral Stirrup Concrete Filled Square Steel Tubular Columns

Concrete filled square steel tubular(CFST) members as a kind of steel-concrete composite structure, contains the characteristics of steel structure and reinforced concrete structure, and has the advantages of high bearing capacity, relatively simple connection details, connection convenience and good flexural performance. Thus it has been widely used in engineering practice. Nevertheless, the constraint effect of square steel tube is inferior compared to circular steel tube, the constraint effect is mainly concentrated in the four corners of square steel tube and the core concrete.In order to solve the problem of non uniformity constraint effect of square steel tube on core concrete, the spiral stirrups is configured in CFST, which is called spiral stirrup concrete filled square steel tubular(SSCFST) columns in this thesis. Then seventeen SSCFST columns and one CFST column were tested under eccentric compression load to improve the bearing capacity and deformation performance by strengthening the constraint effect of square steel tube on the core concrete.In this thesis, the mechanical performance of SSCFST columns under eccentric compression are studied by the method of combining the experimental research, numerical simulation and theoretical analysis. On the basis of the experiment, the methods of calculating the ultimate strength of SSCFST columns under eccentric loading are presented. The main contents are:1. Taking the spiral stirrup space distance along the longitudinal axis of the column, ration of outer diameter of spiral stirrup to side length of square steel tubular, height-width ratio, eccentricity ratio, longitudinal reinforcement ratio and steel tubular thickness as change parameter, seventeen SSCFST specimens and one CFST specimen were tested under the monotonic static loading. The failure modes, load-displacement curves, load-strain curves and feature point parameters are obtained by the test. The influence of above vary parameters on the failure mechanism, bearing capacity and ductility of the specimens were analyzed.2. Basing fiber model method, the non-linear program about the bearing capacity calculation of SSCFST column was compiled, and the whole process of specimens were simulated. The calculation method of ultimate bearing capacity of SSCFST columns under eccentric compression is proposed based on the analysis of numerical calculation. The results show that the two calculation methods proposed in this thesis are reliable.3. Based on numerical method, thirty two orthogonal numerical experiments including nine factors and four levels were carried out. Combining range analysis and variance analysis, the primary and secondary relationships and influence level of different parameters on SSCFST columns were determined. The contribution of the steel tube and spiral stirrup were analyzed on the base of the bearing capacity of unit steel, and reasonable values of different parameters were proposed.