SEISMIC DESIGN PROCEDURE FOR STEEL MULTI-TIERED CONCENTRICALLY BRACED FRAMES BEYOND CSA S16 LIMIT

摘要

Steel Multi-Tiered Braced Frames (MT-BFs) generally represents a more practical and cost-effective solution in tall single storey steel buildings such as airplane hangars, recreational buildings or convention centers. Special seismic design requirements including column design for in-plane and out-of-plane flexural demands have been introduced for MT-BFs in the Canadian steel design standard CSA S16. In the current CSA S16, MT-BFs are also limited to three and five tiers, respectively, for Type MD (moderately ductile) and Type LD (limited ductility) braced frame categories. In this paper, a 4-tiered Type MD braced frame, exceeding the 3-tier height limit, is designed with explicit consideration of the propagation of brace tension yielding along the frame height. The design is also performed neglecting the flexural demands in the columns. The seismic response of both frames is investigated though nonlinear dynamic analysis. In-plane flexural bending demands on MT-BF columns can be properly predicted by the proposed design and inelastic deformations can properly distribute along the frame height when yielding is triggered in more than one tier. Column buckling occurred when bending moments were omitted in design.