Resolving forces on Hydraulic Parallelogram frame

[Mech King]

Hi guys,

I want to check that I am going about this problem in the right way:

The attached image shows a parallelogram type frame with a hydraulic ram located from corner to corner as shown (E to C). There is a load applied to a platform in the far bottom right hand side of the drawing. This load is -4635N. The frame is pin supported and fixed at the base E.

I have worked out that the force on the ram must be 16141N. I have taken moments about the Pivot D. Since the ram is the only thing stopping the frame from collapsing once the load is applied, then the ram and the applied load are the only factors to take into account to determine the ram force:

Ram force = [(640+450)X (-4635)]/313 = -16141N.

Note that the 313 mm above is the perpendicular distance from the ram centreline to the pivot D.

I have then gone on to use the method of sections to resolve the forces in the beams.

The platform creates a normal reaction “Fr” just below A and also an X and Y force at A.
Fr= (-4635x450)/150 = 13905N

Summing forces in the X and Y direction will give the force components at A, these are:
FAx = -13905N, FAy = 4635N.

It is at this point where I get a bit confused. I could use the method of sections to resolve the forces along member ABC. I presume I am right in assuming that given that members EB, CD and the ram (EC) are all two force members. I am torn between this method or could I simply treat the parallelogram BCDE with the Ram EC as two triangles and resolve the forces and then apply these forces the member ABC.

I have got my self into a bit of a pickle, on what seemed like a straight forward problem. Could somebody please advise me on how to proceed and whether my current approach is correct?
This has been bugging me for days.
Any advice will be a life saver,

Many thanks

Amir

 

[Achy47]

Hello Amir,

It seems like you have a good understanding of the problem and have taken the appropriate steps to solve it. Your method of using the method of sections to resolve the forces in the beams is a valid approach. However, as you mentioned, you could also treat the parallelogram BCDE and the ram EC as two separate triangles and resolve the forces in each of them. This would also give you the correct solution. Ultimately, it depends on which method you feel more comfortable with and which one you think will give you the most accurate results.

In terms of your current approach, I would suggest double checking your calculations and making sure you have taken all the necessary factors into account. It can be easy to make a mistake, especially when dealing with complex structures like this one. Also, make sure to consider the direction of the forces and whether they are compressive or tensile.

Overall, it seems like you are on the right track and have a good understanding of the problem. Keep up the good work and don't hesitate to reach out for further clarification or assistance. Good luck!


(Scientist)