Engineering Statics

D-20


Determine the force in members DG and EG of the truss shown.

A FBD of the truss is drawn in order to solve for external 
forces.
The moment equation allows to solve for G<sub>y</sub>.
The force equation allows us to solve for the horizontal 
reaction At F.  G, being a roller, cannot have a horizontal 
reaction.
The truss is cut through DG and EG, the two required members 
as well as DF, which is not required. Only the FBD of the 
top of the truss is drawn.
Taking moments about point D allows EG to the only 
unknown and hence can be solved for.  Note how the right 
side of the truss behaves somewhat like the truss on 
problem 19, but rotated 90 degrees.  We expect the members 
on the right side to be in compression, the members on left 
to be in tension.
Taking forces in the x-direction allows us to solve for DG.