SEISMIC PERFORMANCE ASSESSMENT OF MEGA-BRACED FRAME

Abstract

Mega-braced frame is mainly preferred in designing of super-tall buildings, but to check the adequacy of mega-braced frame for low-rise, mid-rise, and high-rise buildings, seismic assessment of these buildings is necessary to performed. In this thesis, two types of bracing is adopted in designing, i.e., multistorey X-bracing and stacked bracing. A sample building is analysed by using software SAP2000 and design procedure is validated with the help of International building code (IBC). By following the same design procedure, all braced frame is analysed by linear method and nonlinear dynamic method. To investigate the collapse behavior of buildings, hinges are assigned in all structural members. In bracing members hinges are assigned manually by considering optimum ranges of slenderness ratio and width to thickness ratio of respective member. The mode of failure is important in comparing the performance of building for low and high seismic events. By comparing the results of nonlinear time history analysis performed on buildings, the braced frame which is more appropriate to execute good performance is selected in designing. The failure mechanism and plastic hinge formation explains details of the behavior of building, by comparing their results for all buildings, best performed bracing is determined for low-rise, mid-rise and high-rise braced frame. Interstorey drift ratio (IDR) has direct relation with behavior of structure component and ductility of structure. So this thesis explains the pattern of IDR at each storey level for all the structures analysed. On other hand the pattern and magnitude of forces coming on foundation level is compared for low-rise, mid-rise and high-rise structure. The column members which are deforming significantly during time history analysis, are compared with respect to the designed axial force