Beam-column behavior and design equations for high-strength composite filled tube (CFT) members: Investigating the interaction between section and member slenderness ratio

Abstract

This paper investigates the influence of the section and member slenderness ratio on the axial-moment interaction behavior for high-strength concrete-filled tube (CFT) members. An extensive parametric study is conducted with the aim of extending the material strength limitations in the AISC 360-22 for composite members and investigating the reduction of strength as the member slenderness increases. A 2D fiber-based model using OpenSees software was developed and calibrated based on experimental studies to conduct an extensive parametric study, which includes; (1) member (global) slenderness; (2) section slenderness; (3) section's aspect ratio; (4) material strength; (5) level of axial loading. The study demonstrates that the unconservative error in the current design equations can be as high as 25 % for high member slenderness, while the conservatism in the high section slenderness can be more than 200 %. The proposed interaction curve and the design equations demonstrate high accuracy in predicting the maximum strength of the CFT members under combined loading conditions for a wide range of parameters, including the conventional strength CFT members. A fundamental insight into behavior is presented along with the results. This paper discusses the potential simplification of these findings into design equations that can be used in everyday practice.