General Equilibrium Problems  (example continued)

 

The FBD of truss ABCDE is as follows:

Note that the unknown forces at the pin and roller supports have been identified.

 

 

Next, apply the equations of equilibrium:    ΣFx = 0,  ΣFy = 0,  ΣMconvenient point = 0

 

          ΣFx = 0  gives    Ax  +  800  =  0

 

       ΣFy = 0  gives   Ay  - 1200  +  Ey  =  0

 

Pick the convenient point to sum moments to be point A.

 

Counterclockwise  Σ MA= 0  gives   Ey (2)  - 1200 (2)  -  800 (4) = 0

 

 

The result is three equations in the three unknown support reactions  Ax, Ay, and Ey.

 

 

From the first equation of equilibrium   Ax  = - 800 N.  (opposite direction as shown).

 

 

From the third equation of equilibrium  Ey  =  2800 N (in direction shown).

 

 

Then from the second equation of equilibrium  Ay =  - 1600 N (in opposite direction).

 

 

 

Click here to continue with another example.

 

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