PERFORMANCE BASED SEISMIC EVALUATION OF ECCENTRICALLY BRACED FRAMES DESIGNED USING DIFFERENT CODES

Abstract

Steel is one of the most widely used construction materials in today's world. Steel structural structures with their strength, ductile behaviour, design flexibility, easy build-ability and upgradability are regarded as the most suitable earthquake resistant construction. It is necessary to ensure proper detailing of dissipative zones in steel systems to get desired energy dissipation capacity. This Dissertation mainly focuses on eccentrically braced frame buildings. In this study, the structural aspects and behaviour of an eccentrically braced frame (EBF) are disused in detail as a function of link length relative to bay length. Provisions of different national codes, like American (ASCE 7), European (EC 3) and New Zealand (NZS 1170.5) codes, regrading limitations on width to thickness and height to depth ratios of various members, classification of ductility classes, response reduction factors, soil types, design response spectra and base shear scaling factors are compared for eccentrically braced frames. Seismic design provisions for eccentrically braced frames, their capacity design principles and various overstrength factors used in design are compared for the corresponding steel design codes. The concept of performance evaluation, criteria to select analysis procedure for performance evaluation and nonlinear modelling and their acceptance criteria for different elements in eccentrically braced frame are discussed in detail. An 8 storey eccentrically braced frame building is designed following the above mentioned three national design codes. Two types of structural systems are considered: (i) conventional eccentrically braced frames having (i.e. having pinned connections between beams and columns and 4 moment resistant connections between beams and braces) and (ii) dual system (with all connections as moment resistant). These buildings are designed with both flexure and shear links. The performance of these 12 buildings is compared by using a non linear static procedure, according to ASCE 41 and the results are compared. The study shows that the performance buildings designed with flexure links is worse than CF for DBE level of earthquake and the buildings designed with shear links have achieved a performance of LS for DBE level of earthquake and CP for MCE level of earthquake. Future scope of work is also presented.