Perfect Truss & Imperfect Truss

Analysis of frames:

  • A frame is a structure made of several bars/ rods welded / rivetted together
  • The bars are angle irons/ channels of “i” or “t” sections. These are called members
  • On application of load on to the structure, the members remain loaded with tensile/ compressive load
  • Members under tension are called “tie”
  • Members under compression are called “strut”
  • The structure formed by the members (tie/ strut) is called “truss”
  • Extensively used in roof, bridge, sheds etc.

Perfect Truss:

  • Structure is made of members just sufficient to keep it in equilibrium, when loaded without any change of shape
  • N = 2j – 3 where ‘n’ is the number of members and ‘j’ no of joints
  • It is efficient and optimized structure.

Imperfect Truss:

  • Structure is made of members more or lesser than the minimum numbers necessary to keep it in equilibrium, when loaded
  • N ≠ 2j – 3
  • N > 2j – 3 redundant
  • N < 2j – 3 deficient
  • Inefficient structure



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