Research Spotlight: Major and Minor Axis Stiffness Reduction of Steel Beam-Columns Under Axial Compression and Tension Conditions

2017 Annual Stability Conference Presentation

Session S4 – Stability of Beam-Columns
Wednesday, March 22, 2017
4:30 pm

Major and Minor Axis Stiffness Reduction of Steel Beam-Columns Under Axial Compression and Tension Conditions

This research focused on developing a deeper understanding of the stiffness reduction that occurs in W-Shapes due to yielding of the cross-section under uniaxial bending and axial loading conditions. A detailed fiber element model was used to develop three-dimensional m-p-t surface plots: (a) minor axis bending under axial compression; (b) major axis bending under axial compression; (c) minor axis bending under axial tension; and (d) major axis bending under axial tension. The m and p conditions around the perimeter of the 3D surfaces were studied in detail and analytical expressions are provided for each of the loading conditions at the initial yield and fully plastic conditions. The m-p-t surface plots were used as a basis to develop a nonlinear material model for practical use. The material model was used as normalized tangent modulus expressions in MASTAN2, and it was found to provide results that were in close agreement with published benchmark frame results. The material model is based on reasoning that is consistent with what is known about the effects of the residual stresses in W-shapes. It provides a straightforward approach for modeling the distributed plasticity when conducting a nonlinear analysis of planar steel frames with compact W-shapes. The material model can accommodate any W-shape and assumed maximum value of residual stress.

Barry T. Rosson, Florida Atlantic University, Boca Raton, FL