What are the force components for each member in the loaded truss?

[SteelDirigibl]

Homework Statement

I need help with trusses.

Determine the force in members: (a)AD, (b)CD, (c)AB, (d)BC, (e)BD of the loaded truss. (Note: compression forces must be negative.)

Homework Equations

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The Attempt at a Solution

I found the components of AB and BC since upward components at A and C are 900 lb upward and cotan(30.3)*900 is 1540. But how do I get the components of the others? (and why/how do I know that BC is zero?

 

[SteelDirigibl]

well i got it figured out, but I am finding I am having trouble determining if it is compression or tension. how can I figure this out? my numbers are generally right but the opposite sign.

 

[PhanthomJay]

Tension forces always pull away from the joint or member on which they act, and compression forces always push toward the joint or member on which they act. Whether you use the method of joints or sections, your free body diagram will give you the direction of the force using the equilibrium equations at those joints or sections.