An Efficient Quadrature Beam Model to Simulate Inelastic Seismic Behavior of Steel Frames

Abstract eng:
Developing nonlinear structural models with high accuracy and affordable computing cost is a challenging issue and one of the pressing needs in earthquake engineering. The paper presents a quadrature beam model for distributed plasticity seismic analysis of steel frames. It is based on the newly developed weak-form quadrature element method, in which the variation principle and the differential quadrature analog are combined. One quadrature beam element can simulate a beam-column member with varying cross-section and nonuniformly distributed loads. The formulations of tangent stiffness matrix and consistent mass matrix are derived. The section constitutive relation of a beam-column member is directly derived using fiber model and material properties. Inelastic time history analysis of the LA 3story moment-resisting steel frame is conducted to demonstrate the accuracy and efficiency of the quadrature beam model. For verification and comparison, the frame is also analyzed using ANSYS with its BEAM188 element and OpenSEES with the force-based beam element. It is shown that: a) by increasing the number of integration points in one element, results of the quadrature beam model are in excellent agreement with those computed by the displacementbased model in ANSYS; b) degrees of the freedom and the CPU time consumption of the quadrature beam model are much lower than those of the displacement-based model; c) the convergence rate of the quadrature beam model is comparable to that of the force-based model, and the time consumption of the quadrature beam model is slightly higher. In contrast to the only available lumped mass matrix of the force-based model, it is easy to acquire consistent mass matrix in the quadrature beam model for inelastic dynamic analysis, highlighting its great potentials in seismic analysis of frames.

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