Question

Consider the statements below the truss shown:

P. The truss is externally determinate.
Q. The truss is internally stable.
R. The static indeterminacy of truss is 1.
S. The truss is internally unstable.
T. The truss is statically determinate.
Out of above statements, correct statements are:

• A. S and T
• B. P, S and T
• C. P, Q and R
• D. R and S

Answer 1

The correct option is B P, S and T

$M=13,j=8,r=3$
$D_S=m+r-2j$
$=13+3-2\times 8=0$
$\Rightarrow$ The truss is statically determinate.
$\Rightarrow$ The middle portion of truss is unbraced, thus the truss is internally unstable.
$\Rightarrow$ External indeterminacy = r - 3 = 3 - 3 = 0