Write a note on the classification of trusses.

8.A] Write a note on the classification of trusses.

Answer:-

Perfect Frame

Perfect frame is made up of a number of members just sufficient to keep it in equilibrium

m = (n * j) – r

Where m = no of members

n = 2 (for 2D-dimension frame)

n = 3 (for 3D- dimension frame)

j= no of joints

r = 3 (no of available conditions of equilibrium ie. ∑ F_x=0 ,∑Fy=0, & ∑M=0, m=3, n=2, j=3 & r=3
Therefore 3 = (2 * 3) – 3

3 = 3 therefore a perfect frame

Imperfect Frame

The frame which does not satisfies the m = nj-r is called an imperfect frame or in other words, a frame in which number of members are more or less than nj-r
m ≠ (n * j) – r
The imperfect frame are further classified into two types

• Deficient frame m < nj-r

• Redundant frame m > nj-r
m = 4, n = 2, j = 4 & r =3
Therefore 4 = (2 * 4) – 3

4 < 5 therefore a Deficient frame

m = 6, n = 2, j = 4 & r =3
Therefore 6 = (2 * 4) – 3

6 > 5 therefore a Redundant frame