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 $\alpha=50^{\circ}$ . Tank diameter is 1.6 m, thickness is
20 mm, and internal pressure is 2.75 MPa. Modulus $E=210 \mathrm{GPa}$ and
Poisson's ratio $v=0.28$ . The longitudinal strain in the the wall of the
Tank is approximately: (A) $1.2 \times 10^{-4}$
(B) $2.4 \times 10^{-4}$
(C) $3.1 \times 10^{-4}$
(D) $4.3 \times 10^{-4}$