Consider a 4-member structure as shown in Fig. 3.2. This type of structure is called non-rigid. Under the application of loads, the structure can adopt various configurations. Degree of freedom of this structure is one. This because, each member has 3 degrees of freedom. So total degree of freedom is 12. Four pin joints arrest 2 degrees of freedom. In addition, left and right supports arrest 2 and 1 degrees of freedom, respectively. Hence, total degrees of freedom: 12-8-3=1. This is called mechanism