Solving Truss Homework: Finding All Forces in Members

[ajd-brown]

Homework Statement

I need to find all the forces acting in the members of this truss.

Homework Equations

Sum x = 0
Sum y = 0
Sum Mom. at any point = 0

The Attempt at a Solution

i have tried using the method of sections and method of joints to solve this truss, but i cannot get any more values than the AF and AB, which = 25.9 and 12.99 respectively.

I don't want anybody to do it for me, i just need some help with the correct method, i think the fact that it is not statically determinate may have an impact, also does anybody have any idea as to how to improve this design/make it easier to solve? from experimenting in the program force effects, the addtion of the extra members on top of the truss decreased compressive forces dramatically. i will be making this truss out of 3mm square balsa wood, so compressive forces need to be minimised.

Thanks,

Anthony

 

[SteamKing]

Why do you think this truss is statically indeterminate?
You will need to know the dimensions of the truss in order to help you resolve the internal forces.

Hint: it appears that your truss is symmetric about point C in terms of geometry and loading. If you have found AF and AB, what forces will you find in the other end of the truss at ED and EH?

 

[ajd-brown]

Hint: it appears that your truss is symmetric about point C in terms of geometry and loading.

so this mean i can cut the truss in half, but what should i do with the central 25n load, should i half it or keep if the same?

as far as indeterminacy goes, i thought that because it does not satisfy m+3=2j (where m is number of members and j is number of joints,) that it is indeterminate, i take it that i am wrong.

thank you for your time and reply,

Anthony