Welcome to our community

Be a part of something great, join today!

Statics truss problem.

bergausstein

Active member
Jul 30, 2013
191
can you help me continue this problem. I'm stuck @ joint C. please use joint method.
please click the image to fully view it. thanks!
mech 1.png
 

BAdhi

Member
May 27, 2012
47
Re: statics truss problem.

When trying to solve these kind of problems try to find the stress of the nodes where there are only two unknown forces (since you can only get two equations per node). You've chosen the node A first, which is fine since $F_{AX}$ is zero thus leaving with only two unknown stresses.

But if you chose node C next you will find there are three unknowns. So my advice is analyse the Node B (which has only two unknown stresses) before going for node C. From there you can find the stress of the joint $F_{BC}$.

Now you'll only have two unknowns in node C since $F_{AC}$ and $F_{BC}$ is known.
 

bergausstein

Active member
Jul 30, 2013
191
Re: statics truss problem.

can you help me create the free body diagram at joint B. thanks!
 

BAdhi

Member
May 27, 2012
47
MHB.png

$$\begin{align}
\rightarrow \displaystyle \Sigma \vec F &= 0\\
F_{AB} \sin \alpha - F_{BD}\sin{\beta} &= 0
\end{align}$$

$$\begin{align}
\uparrow \displaystyle \Sigma \vec F &= 0\\
F_{AB} \cos \alpha + F_{BD}\cos{\beta} +F_{BC} -400&= 0
\end{align}$$

I think you can find the appropriate values for $\alpha$ and $\beta$. $F_{AB}$ is known from node A (please consider that I've taken stress of the arm AB as a compression while you've taken it as a tension).
 

bergausstein

Active member
Jul 30, 2013
191
I did find the angle $\alpha$ but I don't know how to find angle $\beta$. can you help me find it.
 

BAdhi

Member
May 27, 2012
47
MHB.png

Use the right angle triangle.
 

bergausstein

Active member
Jul 30, 2013
191
$\beta=$63.4 degrees am I correct?
 

BAdhi

Member
May 27, 2012
47
Yes that's correct. I hope you can manage to find the other stresses.
 

paulmdrdo

Active member
May 13, 2013
386
how can we solve this using method of sections?