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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