The redundancy (Indeterminacy) of Trusses is determined using formula 'M+R=2J'. Where 'M' is thenumber of members in structure, 'R' is the number of support reactions and 'J' is number of joints. There arecertain Truss configurations, which satisfy this equation, but still they are 'Unstable'. For such trusses amethod was devised to check the Instability, which is called as 'Zero Load Test'.
In this test Engineer do not apply any load on any joint of the truss;hence theoretically the member forcesshould remain to be 'Zero'. But the Engineer assumes a fictitious value in any one of the members of truss.Then he analyses entire truss 'Joint' by 'Joint'. At the end he approaches to the initial joint, but still is findthat the Equilibrium Equation can be satisfied. Such trusses are to be considered as 'Unstable'.
This submission was not accepted into the wiseGEEK Writing Contest because it does not meet the 400 word minimum requirement.