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The three unknown member forces F , F and F can be
BC
GC
GF
obtained by applying the three equilibrium equations to the free-body
diagram in Fig. 1-76,b. If, however, the free-body diagram in Fig. 1-
76,c is considered, the three support reactions D , D and E will
x
y
x
have to be known, because only three equations of equilibrium are
available. (This, of course, is done in the usual manner by considering
a free-body diagram of the entire truss.)
a
b c
Fig. 1-76.
When applying the equilibrium equations, we should carefully
consider ways of writing the equations so as to yield a direct solution
for each of the unknowns, rather than having to solve simultaneous
equations. For example, using the truss segment in Fig. 1-76,b and
summing moments about C would yield a direct solution for F since
GF
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