Modeling the Nominal Flexural Strength of W-Shape Beams Using a New Inelastic Model

The stiffness reduction of compact W-Shapes with an ECCS residual stress pattern was studied in detail using a fiber element model with over 2,000 elements. For given major-axis and minor-axis bending moment conditions, the distribution of stresses throughout the cross-section and associated reduced stiffness were evaluated and used to develop an inelastic material model for use as normalized tangent modulus expressions in MASTAN2. For W-Shape beams with varying unbraced length and loading conditions, limit load analyses were conducted using the new material model with 14-DOF line elements in MASTAN2 and were compared with published results and with those obtained using shell elements in ABAQUS. The ABAQUS models include nonlinear material properties, geometric imperfections and residual stresses. Also studied was the material model’s ability to develop realistic nominal flexural strength curves over a range of W-Shape dimensions and to validate the suggested constants used in the model. Discussion and recommendations are provided regarding the material model and its use with line elements when following the design provisions of Appendix 1.3 in the AISC Specification for Structural Steel Buildings.

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