Define Under rigid, just rigid and over rigid trusses

Before we start, we all know that trusses classification is based on their rigidity.

A under rigid truss is one in which number of members are not sufficient to maintain the stability of structure under external loading. Here if number of members (n) is less than (2j-3), the truss is known as under rigid.

A just rigid truss is, in which number of members are just sufficient to maintain the structure stable under external loading. If any of its member is removed its rigidity gets destroyed. Here if number of members (n) is equal to (2j-3), the truss is known as just rigid.

A relation between number of joints (j) and number of members (n) for a just rigid is given as n= 2j-3

Over rigid truss is, in which number of members are full sufficient to maintain the structure stable under external loading. If the number of members (n) are more than (2j-3), the truss is said to be over rigid.

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