A sign for an automobile service station is supported by two aluminum poles of hollow circular cross section, as shown in the figure. The poles are being designed to resist a wind pressure of 70 lb/ft^2 against the full area of the sign. The dimensions of the poles and sign are h1 = 16 ft, h2 = 7 ft, and b = 13 ft. To prevent buckling of the walls of the poles, the thickness t is specified as one tenth the outside diameter d. (a) Determine the minimum required diameter of the poles based upon an allowable bending stress of 7100 psi in the aluminum. Round your answer to two decimal places.   d = ___ in. (b) Determine the minimum required diameter based upon an allowable shear stress of 2100 psi. Round your answer to two decimal places.  d = ___ in.

A sign for an automobile service station is supported by two aluminum poles of hollow circular cross section, as shown in the figure. The poles are being designed to resist a wind pressure of 70 lb/ft^2 against the full area of the sign. The dimensions of the poles and sign are h1 = 16 ft, h2 = 7 ft, and b = 13 ft. To prevent buckling of the walls of the poles, the thickness t is specified as one tenth the outside diameter d.

(a) Determine the minimum required diameter of the poles based upon an allowable bending stress of 7100 psi in the aluminum. Round your answer to two decimal places.

  d = ___ in.

(b) Determine the minimum required diameter based upon an allowable shear stress of 2100 psi. Round your answer to two decimal places.

 d = ___ in.