Collapse risk assessment of steel moment resisting frames designed with deep wide-flange columns in seismic regions

Elkady, Ahmed (2016) Collapse risk assessment of steel moment resisting frames designed with deep wide-flange columns in seismic regions. McGill University, Doctoral Thesis, 481pp.

Record type: Thesis (Doctoral)

Abstract

In the context of Performance-Based Earthquake Engineering, there is an increasing need to quantify the collapse resistance of frame buildings under severe ground-motion shaking. The primary objective of this thesis is to advance, through experimental and analytical research, knowledge on the collapse risk assessment of steel frame buildings with steel moment-resisting frames (MRFs) designed in highly seismic regions in North America. Emphasis is placed on the characterization of the steel column hysteretic behaviour as well as the composite floor action and the destabilizing effects of the gravity framing system of steel frame buildings with steel MRFs. The dynamic stability of beam-columns that utilize deep and slender wide-flange cross sections is investigated through full-scale experimental testing. Some of the unique features of the experimental program involve realistic boundary conditions, unidirectional and bidirectional lateral loading and the use of various types of lateral loading protocols. The experimental data provide insight on the damage progression and deteriorating mechanisms observed in wide-flange beam-columns. The hysteretic behaviour of a wide range of cross-sections is further evaluated through a corroborating finite element (FE) parametric study. The findings of the coordinated experimental and analytical research are used to proposed recommendations for the seismic design of steel beam-columns in steel MRFs. A comprehensive system-level analytical study is then conducted in order to evaluate the collapse risk of steel frame buildings with special moment-resisting frames (SMFs) as per ASCE (2010) and Type D Ductile steel MRFs per NBCC (2010). The contributions of the composite floor slab and the gravity framing system are included in the analytical model representations of the steel frame buildings. These contributions have been historically ignored in prior analytical studies. In that respect, a practical approach is developed for modeling (a) the non-symmetric hysteretic behaviour of composite steel beams and panel zones as part of fully-restrained beam-to-column connections; and (b) the hysteretic behaviour of steel beams as part of conventional single-plate shear-tab beam-to-column connections. The collapse risk of typical steel frame buildings with steel MRFs is evaluated based on advanced collapse metrics such as the mean annual frequency of collapse. Based on the findings of the comprehensive system-level analytical study, the strong-column/weak-beam ratio that is typically used in the seismic design of steel MRFs is re-assessed such that a uniform probability of collapse can be achieved over the life expectancy of the steel frame buildings. A new definition of system overstrength (i.e., dynamic overstrength factor) is also proposed.

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