Module 5 : Force Method - Introduction and applications
Lecture
2 : The Force Method
Example 5.9 Find the force in various members of the pin-jointed frame shown in Figure 5.12(a). AE is constant for all members.
Solution: The static indeterminacy of the pin-jointed frame = 1. The vertical reaction at C is taken as unknown force R . The computation of deflection of point C due to applied loading and R are shown in Tables 5.2 and 5.3, respectively.
Table 5.2
Member
Length
AB
AC
L
0
1
0
AD
The vertical displacement of joint C due to applied loading =
(
)
Table 5.3
Member
Length
AB
AC
L
R
1
R
AD
The vertical displacement of joint C due to R = (
)
Adding the displacement of point C due to applied loading and R and equating it to zero i.e.
kN
The force in various members of the frame are as follows
(
) 
(
)
kN
kN (Tensile) 
kN (Compressive) 
kN (Compressive) 
