Cyclic behavior and finite element modeling of wide flange steel bracing members. (February 2017) - Haddad, Madhar
Abstract: Wide-flange (WF) bracing members are being used increasingly in concentrically braced frames (CBFs). The limited number of tests WF members performed to date highlights the need for a detailed finite element model with a reliable fracture rule to understand the hysteresis behavior and to predict the fracture of WF braces subjected to cyclic loading. Building a reliable finite element model is cost effective compared to the high expense of experiments, especially when brace sizes are large and thus require a high capacity test frame with powerful actuators. Nine WF quasi-static cyclic brace tests (Fell et al., 2006; Tremblay et al., 2008; Richard, 2009) are used to validate the finite element model presented here. Material variations on the cross-sectional level are considered. Results indicate that the current model is able to simulate the overall hysteresis behavior of the WF braces accurately. Fracture in the plastic hinge that developed at the mid-length of specimens tested by Tremblay and Richard is predicted through a calibrated cyclic void growth model (CVGM) for ultra-low cycle fatigue. In addition, the current model is able to simulate the shift in the location of mid-length plastic hinge. The effects of mesh density, number of integration points, boundary conditions, initial imperfection, initial yield strength, and loading protocol on the hysteresis behavior of WF bracing members are also investigated. Highlights: A finite element model is developed to simulate the hysteresis behavior of WF braces. A calibrated fracture model is tested to predict the fracture life of WF braces. The effects of model parameters on the hysteresis behavior are addressed. A better understanding of the modes of failure for WF braces is provided. Limitations in the seismic design codes are addressed concerning WF braces.