Solving a Statics Problem: Where Do I Start?

[tufftrav]

Statics problem

i have been working on this problem now for 2 hours and haven't gotten anywhere,
taking the moment around joint a or b still leaves you with 2 unsolved equations. and suming the forces leaves with 2 also can anyone point me in the right direction, i just need to determine the reactions at a, and b i have drawn a Free body diagram. thanks

http://img255.imageshack.us/my.php?image=staticsum4.png"

 

[tufftrav]

the length from a to b is 8' and 6' from b-e I am sorry i didn't put that in my drawing

 

[tiny-tim]

Welcome to PF!

the length from a to b is 8' and 6' from b-e I am sorry i didn't put that in my drawing

Hi tufftrav! Welcome to PF!

(This is the same question as in thread https://www.physicsforums.com/showthread.php?t=224637, isn't it?)

Can you please clarify:

Is the whole thing on a fixed pivot at the centre, E?

What is the force at C (also called E)?

Are A and B resting on the ground (you've called them "joints"), or what?

 

[tufftrav]

yea i double posted, the only pivot is at c, the is a force at e 100#, and force at d 100#, points a, and b were pin joints.

 

[PhanthomJay]

I've always found these frame problems difficult. You have to use more than the equilibrium equationss when you have more unknowns than the number of those equations. The equilibrium equations will give you the y values of the reactions at a and b, but not the x values, which must exist at both these supports for stability. I think I would look at the recations due to each applied force separately, then combine them in the end to get the total reactions. When you look at them separately this way, you can identify which of the 2 members is a so called '2 force' member for that load, that is, it is not subject to shear, and has axial load only (internal bending moments in a member at pins cannot transfer at those pins to other members).