Performance-based design and collapse evaluation of Buckling Restrained Knee Braced Truss Moment Frames

Abstract

A performance evaluation of a structural steel framing system called Buckling-Restrained Knee Braced Truss Moment Frame (BRKB-TMF) was conducted. This structural system combines the advantages of open-web steel truss girders and Buckling Restrained Braces (BRBs). Key advantages of open-web trusses include light weight, simple connections, and open passages for mechanical ductwork and pipes. In this system, the open-web trusses are designed to be elastic, while the BRBs are strategically placed and designed to dissipate seismic energy. The combined features of the open-web trusses and BRBs lead to a system with enhanced performance, safety, and economy. In this study, a performance based design procedure was developed for the proposed system. A four story building structure was selected as a study case. The structure designed using the presented procedure was subjected to nonlinear static (pushover) and dynamic analyses. The pushover analysis was performed to determine the overall response, the sequence of inelastic activity leading to collapse, and the failure mechanism. In the nonlinear dynamic analyses, the study frame was subjected to a suite of selected earthquake records scaled to represent various levels of earthquake ground motion intensity. An incremental dynamic analysis (IDA) approach was applied to examine the behavior of the structure at different levels of ground motion intensity including the collapse level. Using IDA results, fragility curves were created and examined. The results were used to assess the collapse margin of the structure. The analyses provided very promising results in terms of the effectiveness and robustness of the system. The example structure showed a low probability for collapse under the maximum considered earthquake (MCE) ground motions. The key design parameters were determined to be the target drift and deformation capacity of the BRBs.