Concentric tubular steel braces subjected to seismic loading: Finite element modeling

Steel buildings are susceptible to damage during earthquakes if an unreliable bracing system is used. A well-designed and detailed concentric bracing system is needed for steel buildings in a seismically active area. Failure of a concentric bracing member occurs at the mid-length plastic hinge. A refined finite element model has been developed to simulate the hysteresis behavior of bracing members under cyclic loading including fracture. The model provides similar hysteresis behavior to previous (Shaback and Brown [1]) and two new experiments (Tremblay et al. [2]). The specimens were subjected to different loading protocols. It was found that an initial imperfection affects the pre-buckling and first buckling cycles but has no effect on the following cycles. The greater the initial yield stress of the HSS, the earlier is the occurrence of local buckling. The cumulative plastic strain is greater at the outer surface than at the inner surface of the compressive corners/web of the mid-length plastic hinge where fracture initiates. Significant local rotation follows the same trend as the significant plastic strain of the same element where fracture initiates.