What is the Correct Value of Dx in Frame Analysis?

AI Thread Summary
The discussion revolves around calculating the correct value of Dx in frame analysis, focusing on equilibrium equations for forces and moments. Initial calculations for the entire frame yielded values for E and Ax, but subsequent values for By and Bx were found to be incorrect. The realization that the force at B does not necessarily act along the member led to confusion, as isolating members resulted in multiple unknowns. Ultimately, the solution was reached by summing moments about point C to find Dx, allowing for the resolution of the remaining unknowns in the system. The key takeaway is the importance of correctly applying equilibrium principles and understanding force directions in frame analysis.
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Homework Statement


pErlIgy.png



Homework Equations


ƩFx=0
ƩFy=0
ƩM=0


The Attempt at a Solution



For the entire frame:
ƩMA = 0: -360*15 -240*33 + E*12 = 0
E = 1110 lb →
ƩFx = 0: 1110 - Ax = 0
Ax = 1110 lb ←
These are the correct values so far.

Member BC:
W0a04tA.png


By = (4/3)*Bx

ƩMC=0: -240*9 + 360*9 + Bx*12 - (4/3)*Bx*18 = 0
Bx = 90 lb
By = (4/3)*90 = 120 lb

These values are incorrect.
 
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Does the force at B necessarily act along the member as you have assumed?
 
TSny said:
Does the force at B necessarily act along the member as you have assumed?

Hmm I guess it doesn't.
But I can't find another way of doing the problem. Every member seems to have 4 unknowns when isolated.
 
What can you learn from CDE?
 
TSny said:
What can you learn from CDE?

Ah, I figured it out now, thanks!

I only need the value of Dx so I summed the moments about C.
Then I solved for the three unknowns left on ABD.
 

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