A Cylindrical Tank Is Assembled by Welding Steel Sections in a Heli-

A cylindrical tank is assembled by welding steel sections in a heli- cal pattern with angle $\alpha=50^{\circ} \text {. Tank diameter is } 1.6 \mathrm{~m}$ 20 mm, and internal pressure is 2.75 MPa. Modulus E = 210 GPa and
Tank is approximately:
Poisson's ratio $v=0.28$ . The circumferential strain in the wall of the (A) $1.9 \times 10^{-4}$
(B) $3.2 \times 10^{-4}$
(C) $3.9 \times 10^{-4}$
(D) $4.5 \times 10^{-4}$