Simulation of Steel Brace Hysteretic Response Using the Force Analogy Method

Steel concentrically braced frame (CBF) systems are widely used in buildings to resist lateral loads, because they possess high lateral strength and stiffness. For seismic applications, braces dissipate energy through tension yielding and compression buckling, and the lateral response of the CBFs is dominated by the complex cyclic inelastic behavior of the braces. Significant effort has gone toward developing accurate and efficient brace models, and these models fall into three broad categories: finite element, phenomenological, and physical theory. Finite-element models are accurate but computationally expensive, and phenomenological models are computationally efficient but depend on experimental results for calibration. Physical theory models, which are based on fundamental structural behavior, provide a balance of efficiency and accuracy. The present research implements an existing brace physical theory model for use in the force analogy method, which is an accurate, efficient, and stable algorithm for conducting dynamic analysis when coupled with the state space formulation. The brace model, which uses two sliding plastic mechanisms to capture axial and lateral brace deflections and to relate these to the brace force, is validated against prior experimental results. The brace model is also implemented in a frame, where inelastic response occurs in both the frame and the braces, to demonstrate application of the model and the potential for simulating complex inelastic dynamic CBF behavior with the force analogy method.