Question

The structure shown below is

• A. determinate
• B. internally indeterminate
• C. mechanism
• D. externally indeterminate

Answer 1

The correct option is C mechanism


As all the joints are hinged the structure can be treated as a truss.

$\therefore \text{Degree of static indeterminacy}$
$\left(D_S\right)=m+r-2j$

m $\to$ No. of member = 10
r $\to$ No. of reactions = 3
j $\to$ No. of joints = 8

$\therefore D_S=m+r-2j=-3$

$D_S<0,$
structure is unstable hence forming a mechanism.