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Architecture Engineering QUESTION #2342
Question 1
In the ACI Direct Design Method for flat slabs, the total factored static moment \(M_o\) for a panel with factored load \(w_u\) per unit area, transverse span \(l_2\), and clear span \(l_n\) is:
  • \(M_o = \dfrac{w_u l_2 l_n^2}{12}\)
  • \(M_o = \dfrac{w_u l_1 l_n^2}{8}\)
  • \(M_o = \dfrac{w_u l_2 l_n^2}{8}\)✔️
  • \(M_o = \dfrac{w_u l_2^2 l_n}{8}\)
Correct Answer Explanation
Per ACI 318, \(M_o = \dfrac{w_u l_2 l_n^2}{8}\) where \(l_2\) is the panel width transverse to the analysis direction and \(l_n\) is the clear span. \(M_o\) is then split between positive and negative moments (typically 65% negative, 35% positive for interior spans) and further distributed between column and middle strips.