Variable Stiffness Reduction Factor for Stability Design of Steel-concrete Composite Columns

In United States practice, the strength of composite columns is assessed with available strengths that are computed considering member length effects. This approach has advantages; however, developing axial compression‐bending moment interaction diagrams that account for member length effects is not a straightforward task. Current methods result in unconservative error for highly slender members with large bending moments. While it is theoretically possible to develop more accurate interaction diagrams, a simpler approach, and one which more directly addresses the cause of the unconservative error, is to improve the accuracy of the stiffness used in the elastic analyses to determine required strengths. In this work, new recommendations are developed for this stiffness for steel‐concrete composite columns. The recommended stiffness is a function of required axial compression and bending moment, which increases accuracy and enables improved available strength calculations, resulting in more efficient designs.