Learning Goal: Learning Goal:

To apply the method of sections to a truss and determine the unknown forces in

specified members.

If a truss is in equilibrium then every member in the truss must also be in equilibrium.

This principle is used in analyzing a truss using the method of sections. To apply the

method of sections, we use an imaginary cut through members of the truss to

expose the forces in those members as external forces.

$($Figure $1)$

If the free$-$body diagram of the joint on either side of the cut is known, we can apply

the equations of equilibrium to that part of the member to determine the forces at the

cut section. Since only three equilibrium equations $,$ and

${\displaystyle \underset{?}{\overset{?}{}}}{M}_O=0)$ can be applied to the free$-$body diagram of any segment, we should

try to select a cut that passes through no more than three members of the truss in

which the forces are unknown.

For the Howe bridge truss shown, $d=2\mathrm{.}75m,F_1=2950N,F_2=2150N,$

$F_3=2350N,$ and $F_4=4450N.$

$($Figure $2)$

Figure

To apply the method of sections to a truss and determine the unknown forces in

specified members.

If a truss is in equilibrium then every member in the truss must also be in equilibrium.

This principle is used in analyzing a truss using the method of sections. To apply the

method of sections, we use an imaginary cut through members of the truss to

expose the forces in those members as external forces.

$($Figure $1)$

If the free$-$body diagram of the joint on either side of the cut is known, we can apply

the equations of equilibrium to that part of the member to determine the forces at the

cut section. Since only three equilibrium equations $,$ and

${\displaystyle \underset{?}{\overset{?}{}}}{M}_O=0)$ can be applied to the free$-$body diagram of any segment, we should

try to select a cut that passes through no more than three members of the truss in

which the forces are unknown.

For the Howe bridge truss shown, $d=2\mathrm{.}75m,F_1=2950N,F_2=2150N,$

$F_3=2350N,$ and $F_4=4450N.$

$($Figure $2)$

Figure