Influence of weak-axis flexural yielding on strong-axis buckling strength of wide flange columns

In multitier braced frames, the columns are typically wide flange sections with the weak axis oriented in the plane of the frame. Weak-axis buckling strength is commonly computed using an effective length equal to the tier height and the strong-axis buckling strength is based on an effective length equal to the total height of the braced frame. During a large seismic event, inelasticity in the braces can result in differential tier drifts that induce weak-axis flexural yielding of the columns. This inelasticity is not considered in current column strength curves. As a first step toward quantifying the influence of weak-axis flexural yielding on strong-axis buckling strength of wide flange columns, several representative isolated columns were subjected to compressive loads in combination with varying levels of weak-axis flexural yielding using three-dimensional finite element analysis. The results from the computational studies suggest that strong-axis buckling strength can be significantly degraded due to the presence of weak-axis flexure if the weak-axis rotation is large and torsional restraint is not provided at the tier levels.