Sway or Non Sway Frame

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The designer needs to determine if the column is in a sway or non-sway frame. A frame is non-sway if it is sufficiently supported by lateral bracing, such as structural walls. Structural walls used for elevator shafts, stairwells, partial building enclosures, or interior stiffening elements provide substantial drift control and lateral bracing. In many cases, even a few structural walls can brace a multi-story, multi-bay building. Sway must be checked for each direction and floors. ACI 318-19 provides three methods to determine if the lateral stiffness is sufficient to designate the frame as non-sway.

  1. Section 6.2.5.1, ACI 318-19: Columns are non-sway if the gross lateral stiffness of the walls (bracing elements) in a story is at least 12 times the gross lateral stiffness of the columns in that story. This is a simple, conservative hand calculation.
  2. Section 6.6.4.3(a), ACI 318-19: Columns are non-sway if the increase in column end moments due to second-order effects does not exceed 5 percent of the first-order end moments.
  3. Section 6.6.4.3(b), ACI 318-19: Columns are non-sway if the stability index “Q” does not exceed 0.05 as shown in Eq. (6.6.4.4.1)

Sway or Non Sway frame

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