Ductility Capacity Models for Buckling-Restrained Braces

Abstract eng:
Buckling-restrained braces (BRBs) have recently become popular for use in the primary lateral-force-resisting systems of structures located in high seismic regions of the United States. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. While testing has shown that BRBs possess high ductility capacity, no generally accepted method yet exists to predict the cumulative plastic ductility (CPD) capacity of BRBs, where capacity is defined as deformation undergone before fatigue fracture of the brace. To address this lack of knowledge, this study investigated ductility capacity modeling of BRBs. A database of 76 BRB tests was compiled, and parameters from the test database were considered as potential predictive parameters in a CPD capacity model for BRBs. Two types of capacity models were considered in this research: end-capacity models, which predict a static total CPD capacity and remaining capacity models, which predict available (or remaining) CPD capacity after a given deformation history is imposed. The maximum likelihood estimation method was used to calibrate the capacity model parameters to maximize the probabilities that predicted values match test results, providing an unbiased model that relates predictive parameters to CPD capacity. Results show that the end-capacity formulation has limitations and may lead to results that contradict behavior, whereas the remaining capacity formulation is more intuitive and moderately precise.

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