Stiffness reduction factor requirements for the stability analysis of frames with rotary straightened W-shapes

Rotary straightened wide-flange cross-sections are becoming more common in the structural steel industry. The rotary straightening process results in a different residual stress distribution compared to those produced without rotary straightening. Previous research has indicated that the current stiffness reduction factor specified in Chapter C of AISC 360 for stability design which accounts for partial yielding is not appropriate for rotary straightened W-shapes. The beam element stiffness reduction (tau) material model for rotary straightened hot-rolled sections was previously validated and preliminary studies indicated that a different stiffness reduction model is warranted. This paper presents the results of a parametric study of the current and proposed stiffness reduction models on hot-rolled steel W-shapes. Beam finite element models were created in MASTAN2 and second-order inelastic analyses were conducted. A range of different cross-section geometries typically used for beam-columns were investigated, which includes various flange and web slendernesses and aspect ratios. Columns and beam-columns were investigated with uniaxial bending about the major and minor axes and multiple axial load ratios. Additionally, several common planar steel frames were investigated to assess the model's influence on system stability. For columns, beam-columns, and frames, the effects of the assumed residual stress pattern on the stability limit state are discussed. The results of this sensitivity study are presented along with comparisons and recommendations for further study of the tau stiffness reduction values for hot-rolled steel rotary straightened members.

Learning Objectives:
Identify the geometric and load conditions which are the most sensitive to stiffness reduction modeling for hot-rolled steel rotary straightened W-shapes.

View content