CE 201 Statics

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CE 201 - Statics

• Chapter 6 Lecture 21

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THE METHOD OF SECTIONS

• The method of sections is based on the fact that
  if a body is in equilibrium, then any part of the
  body is in equilibrium. This method can be
  applied by cutting the body into two parts and
  including all loadings acting on the body in the
  free-body diagrams.

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The method of sections can also be applied to cut
several members of an entire truss.
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• After isolating both parts, the equilibrium
  equations (?Fx0 ?Fy0 ?Mo0) can be applied to
  both sections. Since we have only three
  equilibrium equations, one should choose a
  section that has at most three unknowns.

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• Notes
• The line of action of each member can be
  identified from the geometry of the truss
• the member forces acting on one part of the truss
  are equal but opposite to those on the other part.

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• The unknown member forces (FBE, FBC, and FFE) can
  be determined by applying the three equilibrium
  equations to the free-body diagram of one part.
• Support reactive forces can be found by applying
  equilibrium equation on the entire truss.
• One of the main advantages of the method of
  section is the ability to determine directly the
  force in a particular member.
• The direction of member forces can either be
  assumed or found by inspection.

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Procedure for Analysis

• Make decision on where to section or cut the
  truss
• Draw the free-body diagram of the part to be
  considered in analysis
• Before isolating the two parts, determine the
  support reactive forces
• Decide about the direction of the forces
• Apply equilibrium equations

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