- 【标题】Effect of gravity columns on mitigation of story drift concentration for concentrically braced steel
frames
- 【摘要】In strong earthquake events, multi-story concentrically braced steel frames (CBFs) are prone to
form a story-collapse mechanism after buckling and yielding of the braces in a story. With the addition
of continuous gravity columns and the increased lateral stiffness and strength they provide, however, it
becomes possible to reduce the concentration of story drift and prevent the story collapse. Nonlinear
dynamic analysis is implemented for a three-story CBF, and it is demonstrated that a drift concentration
is inevitable, particularly in the first story, when the CBF is subjected to a set of large ground
motions with a probability of exceedance of 2% in 50 years. A simplified theoretical formulation is
presented to characterize the effect of gravity columns. Two cases are considered: gravity columns
perfectly fixed, and gravity columns pinned at the base. It is noted that significant mitigation of
drift concentration can be achieved, particularly when gravity columns are fixed at the base. Nonlinear
time-history analysis is further performed to validate the theoretical observations and quantify the
stiffness/strength demands of gravity columns to avoid drift concentration. The analysis results support
the trends and observations obtained from the theoretical formulation. Finally, numerical simulations
are implemented with the seismic force reduction factor Ds, slenderness ratio of braces λ, and number of
stories, as major analysis variables. The results demonstrate that a few (e.g. four) fixed-base gravity
columns can lead to collapse prevention for reasonably designed low-rise CFBs under the set of large
ground motions.
- 【关键词】Concentrically braced steel frames (CBFs); Gravity columns; Drift concentration factor (DCF);
Story collapse Column base
- 【索引】SCI: 504MV, EI: 093412266536, Citation: 10
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