Cyclic Axial Compression Mechanical Behavior Study Of GFRP-steel Composite Tube Confined RC Stub Columns

Modern buildings have complex structures and need stringent seismic performance standard; it suggests greater technical requirements for column structure as the main force structure. Confined concrete column is one of the main directions of development, and researchers gradually put forward concrete filled steel tube, steel tube confined concrete column, FRP confined concrete column, FRP-Steel composite tube confined concrete column and other forms of confined concrete column. FRP-Steel composite tube confined concrete column combines the advantages both of FRP and steel tube, and has the advantages of light weight, corrosion resistance, good binding, good ductility, strong bearing capacity and convenient construction. Therefore, this kind of column is studied in this paper, study includes:(1) Produced 10 circular GFRP-steel composite tube confined RC stub columns, of which four specimens were taken monotonic axial compression test, four were taken single circular axial compression test, and two were taken repeatedly circular axial compression test. The parameters considered are the thickness of the steel tube and the loading mode. The conclusion can be drawn from the experimental results:GFRP can effectively prevent local buckling of steel pipe, and GFRP’s destruction is the sign of damage to the specimen; the constraint of composite pipe can significantly improve the carrying capacity and ductility of the reinforced concrete; the thicker the steel, the bearing capacity slightly increased, but no significant difference in ductility; concrete’s monotonic axial compression curves are substantially coincide with the envelope curve of circular axial compression curves; multiple cycles of the specimen can reflect the effect of loading history; steel pipe’s restraint effect is very small relative to GFRP; during the cyclic axial compression, longitudinal reinforcement may reverse tension.(2) Produced 10 square GFRP-steel composite tube confined RC stub columns, of which four specimens were taken monotonic axial compression test, four were taken single circular axial compression test, and two were taken repeatedly circular axial compression test. The parameters considered are the thickness of the steel tube and the loading mode. Conclusions obtained from the experimental results are basically the same with circular specimens, but the square specimens have significant stress redistribution, bearing capacity is relatively small.(3) Based on the analysis of experimental results and the existing model, constitutive model both of the circular and the squre GFRP-steel composite tube confined reinforced concrete are derived in this paper. The model includes capacity formula, monotonic axial compression model and cyclic axial compression model, and considers the plastic strain, stress’ degradation and the effects of loading history. It can simulate the experimental curves of this article and has great practicality.