PERFORMANCE BASED DESIGN OF STEEL FRAMES

Abstract

Steel structures have been known to perform well during earthquakes and are considered mostly earthquake resistant. Even though steel is a ductile material by virtue of its inherent material properties, it is necessary to ensure the proper detailing of dissipative zones in a steel frame to ensure high energy dissipating capacity. In this dissertation, different aspects related to steel buildings, ranging from the structural typologies and their seismic behaviour, to the damage analysis during past earthquakes and consequent lessons learnt are discussed. The concept of Performance Based Design (PBD) of steel frames, and the modelling parameters and acceptance criteria of steel structures as per ASCE 41-06 are discussed in detail. The recently developed method of Performance Based Plastic Design of steel structures, which is recognized as an ideal method for future practice is also discussed in this Dissertation. A comparative study of building ductility classifications, response reduction factors, normalised base shear coefficients and seismic design provisions for Moment Resisting Frames (MRF), Concentrically Braced Frames (CBF) and Eccentrically Braced Frames (EBF) as per American (ASCE 7), European (EC 8), New Zealand (NZS 1170.5) and Indian Standard (IS 1893:2002) is also performed. Since the Indian Code does not give any recommendations for the design of EBF, Model Code guidelines have been proposed in this study, based on the comparative study of codes and available literature. The dissertation also presents a comparative study of seismic performance of different structural systems for steel buildings, designed as per Indian codes. This involves modelling, analysis and design of eight storey Steel Special Moment Resisting Frame (SMRF) building, Special Concentric Braced Frame building (SCBF), Dual Frame building and an Eccentrically Braced Frame (EBF) building in SAP 2000 software. The performance of the four buildings is evaluated using. Non Linear Static Pushover Analysis as per the provisions of ASCE 41-06 and the adequacy of force based design philosophy adopted by IS 800: 2007 is examined. In the final stage of this work, the methodology of PBD based on the concept of Direct Displacement Based Design (DDBD), as developed by Priestley et al. (2007) has been illustrated and a Comprehensive *Performance Based Design (CPBD) methodology incorporating the concept of DDBD, and acceptance criteria of ASCE 41-06 has been developed. The proposed methodology has been demonstrated and validated using a design example of an eight storey Steel Moment Resisting Frame building.