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Civil Engineering QUESTION #6606
Question 1
A wide-flange section is used as a beam-column. If the axial load ratio $P_u / (\phi P_n)$ is greater than 0.2, which interaction equation form is required by AISC?
  • $\frac{P_u}{\phi P_n} + \frac{M_u}{\phi M_n} \le 1.0$
  • $\frac{P_u}{2\phi P_n} + \frac{M_u}{\phi M_n} \le 1.0$
  • $\frac{P_u}{\phi P_n} + \frac{8}{9}(\frac{M_{ux}}{\phi_b M_{nx}} + \frac{M_{uy}}{\phi_b M_{ny}}) \le 1.0$✔️
  • $\frac{P_u}{\phi P_n} + \frac{1}{2}(\frac{M_u}{\phi M_n}) \le 1.0$
Correct Answer Explanation
For $P_u / \phi P_n \ge 0.2$, the AISC interaction formula weights the axial component fully and reduces the moment component slightly (multiplied by 8/9). For ratios < 0.2, the axial component is halved.