Question

If m is number of members; r is reactions; and j is number of joints then in case of a planar structure, 3m + r < 3j leads to
1. stable structure
2. determinate structure
3. unstable structure
4. indeterminate structure

Answer 1

Correct Answer - Option 3 : unstable structure

Explanation:

for a planar structure static indeterminancy is given by,

D_s = 3m + r - 3j

if D_s > 0, It will be indeterminate and stable

if D_s < 0, it will be geometrically unstable

In question it is given that 3m + r < 3j, it implies that D_s < 0, so structure is unstable.