Mechanics of materials; determine normal stress?

Question

Here is the link to the diagram and following that is all of the question details, good luck and thank you for helping:

http://i434.photobucket.com/albums/qq65/chris15012/P1-11.jpg

The rigid bar EFG is supported by the truss system shown. Knowing that the member CG is a solid circular rod of 0.75-in. diameter, determine the normal stress in CG.

Answer 1

Hi chris,

Actually i think the question asks about another member other than CG, Because CG is a zero memeber (for sure!),The first thing to do while solving a truss problem is to find the zero members.

The rule says the joint ( as joint G) which is not loaded and joins only two members is a has members.i.e. they carry no force.

Now you make sure that the question asks for member CG, If it really asking for the member CG then write down that this member is a zero member.

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Anyway, here i have calculated another members, and i hope they are helpful to you.

Cutting a section with vertical line at mid of BCdown through EF. We then will have three forces, and the load :

Fbc, Fbf, and Fef. and the 3600lb

Summing the moment about point B and equalize to zero (static)

then Fef * 3 = 3,600 * 4  

  Fef = 4,800 lb

Summing the moment about point F and equalize to zero (static) :

Then Fbc = 0

Summing forces in y direction and equalize to zero :

Then 3,600 = Fbf (3/4), where 3/4 is sin the angle.

Then Fbf  = 6,000 lb

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Would you please inform me about the title and author of the book that you work from .. if  you're busy forget about it.

Good Luck, Hope you high grades :)