Bearing Capacity Research On FRP Confined Filled Steel Tube Columns

In the recent several years, the material of fiber reinforced polyer (FRP) is applied for kinds of industry and the civil construction, the bridge, the seacoast and the underground project as well as the special structure. The concrete filled steel tubular (CFT) column is wrapd by the material of FRP, so it is named as FRP confined concrete filled steel tubular column (CCFT). By using the CCFT, not only the bearing capacity of the CFT is enhanced , but also the FRP tube insufficient plasticity and the steel pipe corrosion problem in the certain degree are solved, while the component weight is reduced, which make the CCFT be used widely in the world. The text mainly focused on the research to the ultimate supporting capacity of the CCFT. The solution obtained in this paper met well with the test results.On the one hand , the ultimate load calculation formula for the above CCFT under axial compressive was derived based on the fourth strength theorem and the failure parameter equation of concrete compressived in the three directions and relative factors were analysed. The formulas can provide the reference to theoretical research and engineering design. (1) The theoretical results calculated with the fourth strength theorem and the failure parameter equation of concrete compressived in the three directions are in good agreement with the literature data and it shows that the fourth strength theorem and the failure parameter equation of concrete supported three directions compression is feasible for the CCFT. (2) Through contrasting the ultimate supporting capacity of the CCFT and the CFT, we can educe that the concrete intensity, steel intensity as well as fiber layer and type are the primary influence factors of the ultimate bearing capacity. The ultimate bearing capacity of the CCFT is enhanced as the enhancement of concrete intensity rank; Comparing with the CFT, the concrete intensity rank is higher, the ultimate bearing capacity of the CCFT enhancement rate actually reduces; The ultimate bearing capacity of the CCFT is also enhanced as the enhancement of steel intensity; Comparing with the CFT, the steel intensity is higher, the ultimate bearing capacity of the CCFT enhancement rate reduces; For the CCFT with the identical type of steel, although the steel tube wall is thicker, its ultimate bearing capacity enhancement rate reduces yet; Comparing the CCFT with the CFT, the fiber layer is more, its ultimate bearing capacity enhancement rate is enhanced correspondently; For the FRP with the same layer, the ultimate bearing capacity enhancement rate also obtains the enhancement along with the FRP material tensile strength enhancement; Comparing with the CFT, the enhancement rate of the ultimate bearing capacity of the CCFT increases along with the ratio of restraint coefficient of fiber and steel tube. When the fiber layer and the type are the same, the enhancement rate of the ultimate bearing capacity reduces along with the increment of the restraint effect of steel tube. (3) The theory results calculated with the ultimate equilibrium theory are in good agreement with the literature data and it shows that the ultimate equilibrium theory is feasible for the CCFT.On the other hand, based on the achievements in theoretical research, the line elasticity stress-strain relationships were used for fiber, the Von Mises failure criterion and isotropic hardening stress-strain relationships were used for steel, as well as the William-Warnke failure criterion and elastic-plastic stress-strain relationships used for concrete in term of ANSYS 9.0. The CCFT were carried on the 3D simulation , the capacity behavior and ultimate load of CCFT were analyzed under axial compression. It can be conduded as follows by ANSYS analysis. (1) When the CCFT are loaded under the ultimate bearing capacity, the concrete is crushed, the steel tube is yielded completely, the partial fibers have achieved the tensile strength, this part of fibers are pulled; (2) When the CCFT is loaded under the ultimate bearing capacity,the load-displacement curve has manifested the ultimate bearing capacity and the displacement also increased, and it also has displayed the function of restricting the concrete by comparimg the CCFT with the CFT. After the CFT achieves the ultimate bearing capacity, the capacity changement is not big, still has a certain of plasticity, but the bearing capacity of CCFT rapidly reduces when the CCFT achieved the ultimate bearing capacity, its decrement speeds up along with the increment of fiber layer, and the plastic performance of the component obviously reduces by comparimg with the CFT. When the more fiber layers are used, brittle destruction of CCFT is much obviously.