Engineering Statics

D-3


Determine all forces exerted on member AI if the frame is loaded by a 48 lb. force directed horizontally to the right and applied (a) at point D, (b) at point E.

The reactions are usually solved first.  Note that only 
a vertical force can be resisted by a roller.
For force equation yields the reaction at H.
The moment equation gives the vertical reaction at I.
The force equation in the H direction yields the final 
unknown.  Note how each equation only contained one unknown.
The FBD of member AI is drawn as loaded for part A. 
Since all members are truss components all forces must 
lie along the members.
Forces in the y direction yields BA<sub>y</sub> and by 
geometry also the other members.
A moment equation is written about F.
The moment equation about F yields the force BC.

The diagram shows all the forces acting on member AI with 
the loading for part a.
The diagram shows all the forces acting on member AI with 
the loading for part b.

The force equation in the y direction yields the for in BA.
The moment equation yields for the force in BC
The x direction force equation gives the force FG.
The FBD with all calculated forces is shown for loading b.