Seismic analysis design of taller eccentrically braced frames.

摘要

The study presented in this thesis investigates the seismic behavior of taller eccentrically braced frames (EBFs) and current Canadian design procedures specified in 2005 National Building Code of Canada and steel design standard CAN/CSA S16-01(S16S1-05). Chevron-type EBFs with shear-critical links were designed for fourteen-, twenty- and twenty-five storey buildings in Montreal and Vancouver, representing typical eastern and western North-American seismic conditions. For each design location the importance of different design criteria is discussed. The demands related to the general design requirements such as strength, stiffness and the global stability were compared to the demand imposed by the capacity design. It was found that ductility requirements did not control design. Using an increase of the structural mass as indicator it was established that for Vancouver total inter-storey drift requirements governed frame design while for Montreal ensuring the global frame stability was critical. In spite of the large differences in seismic design base shears, the mass of final designs for the same frame height were almost identical. In view of these findings, the appropriate design sequence was suggested for zones with higher and moderate seismic activity. The impact of lateral force distribution (equivalent static or spectral distribution) on member selection was also investigated. It was shown that both distributions yielded similar selection of frame elements.;The seismic response of the frames was investigated using the non-linear time-history analysis to assess if the design procedures achieved desired frame response. The analyses were done for the sets of earthquake records calibrated to match design spectra at studied locations. The link response was monitored through maximum normalized link shear forces and inelastic shear rotations. The global frame behavior was observed tracing the behavior of the outer beams segment and braces, the axial forces and moments in the columns, the seismic force profile, inter-storey drift profiles and the relationship between the total inter-storey drifts and the inelastic link rotations. The seismic performance of the structures situated in west of Canada was found to be adequate, except for the top storeys where the plastic deformations exceeded the deformations predicted in the design. The extent of seismic overstrength introduced during the design phase for the structures located in the eastern Canada caused the ductility demands in the links to be reduced and lead to seismically less efficient frames.