Progressive Collapse Analysis of Steel Braced Building Incorporating Buckling Restrained Brace

Abstract

Typically, lateral and gravitational loads are taken into account throughout the structural analysis and design process. For the analysis and design of typical structures, abnormal loads like vehicle impact, gas explosion, blast, etc. are often ignored. Due to that abnormal loads for which structure is not designed which result in failure of more than one load bearing structure like columns, load-bearing walls, etc. which led to failure of a large part of the structure, disproportionate to initial local failure. This failure phenomenon is referred to as “Progressive Collapse”. Many government and private agencies worked on the development of guidelines for progressive collapse analysis and design of structure, among which guidelines issued by the U. S. General Services Administration (GSA) and the Department of Defense’s (DoD) Unified Facility Criteria (UFC) are widely followed by researchers and practicing engineers. The GSA 2016 guidelines are used in this study. This study examines the potential for progressive collapse in a 9-story steel building with a braced frame and compares its performance with that of a steel Moment Resisting Frame (MRF) building. The study examines the impact of three different types of bracing, including chevron, 2-story X, and V-shaped, on the structure's progressive collapse resistance. The study considers six different arrangements of bracing in longitudinal and transverse directions throughout the building height for both types of braced frame buildings. To calculate the potential for progressive collapse, the study employs three analysis methods, namely linear static, nonlinear static, and nonlinear dynamic analysis, as recommended in GSA guidelines, using ETABS software. The analysis is performed under three different scenarios of column and/or brace removal from the ground floor of the perimeter frame. The study employs the results of linear static analysis to calculate the Demand Capacity Ratio (DCR) for critical locations in the structural element like beams, columns, and bracings of the building. The DCR results of the Inverted V Braced Frame (IVBF), 2 Story X Braced Frame (2XBF) and V Braced Frame buildings are compared to those of the MRF building. Non-linear static and dynamic analyses are then performed for the effective bracing arrangement in all types of buildings. The study develops pushdown curves and displacement-time history plots at column removal locations using non-linear static and dynamic analysis, respectively, and compares the results with those obtained for the MRF building. In addition, a 9-storey steel asymmetric building (MRF as well as Braced Building) was taken into consideration for the investigation of progressive collapse. Inverted-V Bracing is considered for the progressive collapse analysis. Three different scenarios of removing a column and/or brace from the ground level are examined using linear static, nonlinear static, and nonlinear dynamic analysis. The DCR is produced by linear static analysis, whereas pushdown curves are generated by nonlinear static analysis. The results of the nonlinear dynamic analysis are also used to create displacement-time history charts. The analysis reveals that installing bracings in the building is a viable means of enhancing its resistance to progressive collapse. The load transfer mechanism observed after the removal of columns and/or braces indicates that the bracings are functioning as an alternate path, safeguarding the beams and columns to prevent the building from collapsing. The results of the study show that all bracing configuration types investigated in the research can lessen the chance of progressive collapse. However, when subjected to various scenarios of column and/or brace removal, the Chevron (Inverted V) brace configuration in a braced frame building demonstrated more effective performance than the 2-Story X bracings and V bracing.