THE METHOD OF SECTIONSThe method of sections is used to determine the loadings acting within a body. It is based on theprinciple that if a body is in equilibrium then any part of the body is also in equilibrium. The method ofsections can also be used to “cut” or section the members of the entire truss. If the body passes throughthe truss and the free-body diagram of either of its two parts is drawn, we can then apply the equationsof 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 themembers 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 orcompression.
Procedure for AnalysisEither the method of joints or the method of sections can be used to determine the forces developed inthe members of a truss.Method of Joints: Generally, if the forces in all members of the truss must be determined, the methodof joints is most suitable for the analysis.Method of Sections: If only few member forces are to be determined, the method of sections may beused.