Q$.$ A crane$-$runway bracket is fastened to the roof truss by means of two identical bolts as

shown in Fig. below. Determine the size of the bolts, if the permissible tensile stress in the

bolts is limited to $75\frac{N}{m}{m}^2.$

Sol.

Given $P=20kN,e=550mm,({}_t{)}_{\text{m}\text{a}\text{x}}=75\frac{N}{m}{m}^2$

The bolts are subjected to tensile stress on account of the following

two factors:

$($i$)$ direct tensile stress because the force $P$ is parallel to the axis of

the bolts; and

$($ii$)$ tensile stress due to the tendency of the bracket to tilt about

the edge C due to eccentricity of the force P$.$

Direct tensile force

$P_1=P_2=\frac{P}{(No.of\text{b}\text{o}\text{l}\text{t}\text{s})}=\frac{20{10}^3}{2}=10000N$