Development of Nonlinear Hysteresis Model for Concrete Filled Steel Tube Column

Abstract eng:
Concrete filled steel tube(CFT) is a round or rectangular steel pipe structure filled up with concrete. The confinement effect of concrete due to surrounding steel tube causes triaxial stress state which improves strength and ductility of concrete. Therefore this type of structure has many benefits over steel or reinforced concrete columns such as improved performance of stiffness, load capacity and energy absorption. Moreover outer steel tube can be used for casting of concrete. Considering those advantages, applications of CFT are increasing and a number of studies have been conducted. As a result, various methods to analytically evaluate the performance of CFT are developed. The main purpose of this study is developing the nonlinear model for CFT which can estimate not static strength but hysteresis behavior. As CFT columns may fail due to not only material failure in a section but also instability of the structure, more rigorous numerical are required in order to secure their strength and serviceability. To this end, nonlinear analysis model which take into account both material and geometric nonlinearity is developed. For a reinforced concrete, cracking of concrete and yielding of surrounding steel tube are main causes of material nonlinearity. But in the case of the CFT, material behavior is significantly changes along stress level due to confinement effect. Considering its frequent applicability to high-rise buildings, geometric nonlinearity due to the P-∆ effect must be considered. The fiber section approach was adopted for section analysis because it requires only uniaxial stress strain relation which was frequently developed and improved through former researchers. An incremental-iterative numerical scheme based on arc-length method is adopted to ensure displacement controlled nonlinearity. Material property for both concrete and steel can consider loading/unloading path. Therefore hysteresis behavior of structure can be examined. Through comparison of the obtained numerical results with experimental data, the introduced numerical model is validated. Developed numerical model can be used for evaluating both ultimate strength and force-displacement relation of CFT. Unlike RC columns, force-displacement relation to calculate absorbed energy is more important for CFT. Because improved energy absorption capacity is advantageous for resisting earthquake loading. References [1] Susantha Kas, Ge H, Usami, T, Uniaxial stress-strain relationship of concrete confined by various shaped steel tubes. Engineering Structures. 23,1331-47, 2001. [2] Lakshmi B, Shanmugam N E, Nonlinear Analysis of In-Filled Steel-Concrete Composite Columns, Journal of Structural Engineering. ASCE, 128, 7, 922-933. 2002. [3] H.G. Kwak, J.K. Kim, P-∆ effect of slender RC columns under seismic load. Engineering Structures, 29, 11, 3121-3133, 2007.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket