Improved proposed panel zone Model for seismic design of steel moment-resisting frames

Abstract

In capacity-designed steel moment resisting frames (MRFs), the column-web panel zones are designed to experience limited inelasticity. One of the main obstacles in letting the panel zone attain large inelastic distortion angles is the associated increase in the beam flange-to-column face weld fracture potential. Subassembly experiments indicate that properly detailed beam-to-column connections utilizing weak panel zones may possess a satisfactory seismic performance. However, a steppingstone in embracing a balanced design philosophy in steel MRFs is to have a robust panel zone model to accurately predict the panel zone joint shear resistance.

Available panel zone models are typically idealized with multi-linear models. These include; (a) an elastic branch up to uniform column web yielding; (b) an inelastic branch accounting for the contributions of the column flanges and continuity plates; and (c) a third branch to acknowledge the steel material’s strain hardening, assuming that above a certain shear distortion the column flange contribution is negligible. With regard to the elastic branch, past studies demonstrated that the shear strain distribution is non-uniform at the onset of yielding, often leading to panel zone shear resistance overestimation. The second branch is defined based on calibrations with limited experimental data of scaled specimens (i.e., the column flange thicknesses are less than 25mm). This typically leads to a panel zone shear resistance overestimation by up to 40%.

This paper proposes an improved mechanics-based panel zone model that could be potentially used for the seismic design of steel MRFs. This model is based on rigorous continuum finite element (CFE) simulations validated with available
experimental data. To investigate the current panel zone model discrepancies, the CFE models employ varying panel zone aspect ratios and column flange thicknesses. We propose an updated elastic stiffness that captures bending as well as shear deformations within the panel zone. We also propose expressions to predict the panel zone shear strength at three levels of shear distortions. These expressions account for the realistic stress distributions within the web panel and column flanges. Comparisons between the proposed model and available experimental data are presented. The proposed panel zone model demonstrates superior performance in predicting a panel zone’s behavior compared to prior formulations.

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Identifiers

ORCID for Ahmed Elkady: orcid.org/0000-0002-1214-6379

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