Behavior of Composite CFT Beam-Columns Based on Nonlinear Fiber Element Analysis

The results obtained from nonlinear fiber element analyses for concrete filled tubes (CFT) are discussed. The studies were aimed at assessing primarily the overall behavior and stability effects on these structural elements as a prelude to a large full-scale testing program. The study focuses on ultimate strength analyses for CFT composite columns with different stress-strain models for both concrete and steel. Fiber analyses using OpenSees are used to assess the impact on the ultimate strength based on the assumed stress-strain material curves, member slenderness, initial imperfections, and both material and geometric nonlinearities. Fiber analysis results are also compared with those obtained from AISC (2005). Fiber-based results show a compatible correlation with the expected element behavior, which is also captured in the current AISC (2005) Specifications.