Method of Sections

1
Method of Sections

• The method of sections enables the calculation of
  force in one truss member. It does not require
  balancing forces at each joint but requires
  ensuring equilibrium over finite portions of the
  truss.

2
Example

• Compute force in member BD.

3
Compute Force BD

• Compute Force BD.
• BD ?Mc 0
• BD 1000 lbs C

4
Compute Force CD

• Compute Force CD.
• CD ?Fy 0
• CD 0 lbs

5
Compute Force CE

• Compute Force CE.
• CE ?MD 0
• CE 1000 lbs T

6
Partial, Improper and Complete Constraint

• Partial constraint 2n gt mr (more equations
  then unknowns)
• Over rigid 2n lt mr (less equations then
  unknowns statically indeterminate)
• Complete or improper constraint 2n mr (
  equations equals unknowns)