Example $19\mathrm{.}1$

A partially prestressed pretensioned mast is to be designed to suit the following data:

Spacing of poles $=100m$

Free$-$standing height of the pole above the ground $=10m$

The pole is to carry twin$-$conductor high$-$voltage lines $(60$ cm apart$)$ on a cross tree at $9$ m above$-$ground level.

Conductor size: effective over all diameter $=10mm$

Tension in each conductor $=5kN$

Poles are to be located in Mangalore;

Wind pressure for this zone $($IS: $875-1964)=10\frac{N}{m}{m}^2$

$28-$day cube strength of concrete $=50\frac{N}{m}{m}^2$

Modulus of elasticity of concrete $=40\mathrm{.}5k\frac{N}{m}{m}^2$

Modulus of rupture of concrete $=5\frac{N}{m}{m}^2$

High$-$tensile wires of $5$ mm diameter available.

Ultimate tensile strength $=1600\frac{N}{m}{m}^2$

Loss ratio $=0\mathrm{.}7$

Permissible stress in concrete under service loads:

Compressive stress in concrete, $f_{cw}=18\frac{N}{m}{m}^2$

Tensile stress in concrete, $f_{tw}=5\frac{N}{m}{m}^2$