2. Slenderness Effects and Sway or Nonsway Frame Designation
Columns and stories in structures are considered as non-sway frames if the increase in column end moments due to second-order effects does not exceed 5% of the first-order end moments, or the stability index for the story (Q) does not exceed 0.05. ACI 318-19 (6.6.4.3)
∑Pu is the total vertical load in the first story corresponding to the lateral loading case for which ∑Pu is greatest (without the wind loads, which would cause compression in some columns and tension in others and thus would cancel out). ACI 318-19 (6.6.4.4.1 and R6.6.4.3)
Vus is the factored horizontal story shear in the first story corresponding to the wind loads, and Δo is the first-order relative deflection between the top and bottom of the first story due to Vus. ACI 318-19 (6.6.4.4.1 and R6.6.4.3)
From Table 1, load combination (2.3.2-2 No. 2) provides the greatest value of ∑Pu.
Since there is no lateral load in this load combination, the reference applied an arbitrary lateral load representing (Vus) at the top of the first story and calculated the resulting story lateral deflection (Δo).
Thus, the frame at the first story level is considered sway.