Zero Force Members and Method of Joints!
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- čas přidán 28. 03. 2022
- Question 6-7: Determine the force in each member of the Pratt truss , and state if the members are in tension or compression.
If you have any recommendations for future problems, or have suggestion for tutorials in the future, feel free to leave a comment!
could you do a step by step procedure on Fkj and Fkd??
Sure. If you need to this on paper, you can solve for an unknown variable in terms of the other variable in one equation, and plug this into your other equation. Here is what it would look like:
Looking at equation 1, if we solve for Fkj in terms of Fkd, we have the following:
Fkj = -1.26Fkd + 14.14
Now, plug this into equation 2 for Fkj, and solve for Fkd:
0 = 28.28cos45 + Fkdcos63.43 - (- 1.26Fkd + 14.14)cos45
0 = 1.34Fkd + 10
Fkd = - 7.45 (Negative, therefore compression)
Hope this helps.
@@simple_civil I get it now, thanks man
@@jimzbyrelbistoer9546 Glad I could help!
Thanks man! Really needed this :)
No problem, glad it could help!
Summing the forces in the Y direction for K. Would Fkd be positive in your first equation instead of negative because the direction of the force is pointed upward?
Hey! I did this video a while ago, but Ill see if I can help.
From the FBD (free body diagram) I have, Fkd is drawn in the positive x (pointed to the right with respect to the joint) and the negative y (pointed downward with respect to the joint). So the signs in the equations seem to be right based on what is drawn.
Then when Fkd is solved, we end up with a negative value, meaning the Fkd drawing needs to be flipped and pointed towards the joint.
Then, based on our convention, we are pushing the joint. Thus, Fkd is a compressive force.
Hope this helps!
hi i have a question if we have forces on L and H. would LC and HE be zero force members too?
thank you so much for this video.
Hey! thanks for the support by the way.
Like I said in the video, it is best to break down a four member joint into a FBD to imagine the reactions taken by each. I believe in the case you are asking for, we would have four y components and three x components in the members cumulatively. So in this case, it is hard to say without analyzing other joints to determine some unknowns in that joint first.
Hope this helps!
If you are using the 45, 45, 90-degree triangle, how can you have two legs that are equal to length 2, and a hypotenuse that also has a length of 2 while maintaining a 90-degree angle? It simply goes against the trig ratios of the unit triangle.
Bit confused by this. The hypotenuse length is not really relevant to the problem and the dimension of the hypotenuse is not mentioned explicitly. Sorry!
this video is amazing and to the point ! would like to get calculating deflection of truss by virtual work method.
which notepad do you use for this video ?
Thanks for the support! I have a structural analysis course that will eventually cover the virtual work method. For now though, I am more focused on completing a full strengths of materials playlist.
As for the notepad, I am using a 'Wacom One'. Super affordable and user friendly.