[10] 1. Design a spiral column cross section to support Pu 500 kips and Mu= 200 ft-kip. The column is in a braced frame and has an unsupported length of

9 ft. f'c= 4,000 psi and f y = 60 ksi. Assume that the column is pin-fixed and M1 / M2 = +0.7. The column is not exposed to the environment. The maximum nd, f,0.45D f (A, / A.)–center-to-center spacing of the spirals is s < \frac{\pi d^2spfy}{0.45DCFc\mleft\lbrack\mleft(\frac{Ag}{ac}\mright)-1\mright\rbrack} where dsp = diameter of spiral, Dc = diameter of core (outside to outside of spirals), Ag= gross area, and Ac =area of core. Hint: for a spiral column, based on Cl. 10.3.6.1 of ACI-318. A_{g(\text {trial})}=\frac{P_{u}}{0.55\left(f_{c}^{\prime}+f_{y} \rho_{t}\right.}