THE METHOD OF SECTIONS

The method of sections is used to determine the loadings acting within a body. It is based on the

principle that if a body is in equilibrium then any part of the body is also in equilibrium. The method of

sections can also be used to “cut” or section the members of the entire truss. If the body passes through

the truss and the free-body diagram of either of its two parts is drawn, we can then apply the equations

of equilibrium to that part to determine the member forces at the “cut section.”

Example 1:

Determine the force in members GE, GC and BC of the truss shown in the figure. Indicate whether the

members are in tension or compression.

SOLUTION:

Example 2:

Determine the force in members in BF, BG and AB, and state if the members are in tension or

compression.

SOLUTION:

Reactions at A and G;

Procedure for Analysis

Either the method of joints or the method of sections can be used to determine the forces developed in

the members of a truss.

Method of Joints: Generally, if the forces in all members of the truss must be determined, the method

of joints is most suitable for the analysis.

Method of Sections: If only few member forces are to be determined, the method of sections may be

used.