Finding FA, FB, FC, FD in 3D Static Equilibrium

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Discussion Overview

The discussion revolves around determining the reaction forces (FA, FB, FC, FD) in a 3D static equilibrium scenario, particularly in relation to a load placed on a table. Participants explore the implications of load placement, symmetry, and the complexity of 3D equilibrium equations.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the attempt made by the original poster and emphasizes the importance of knowing whether the load is centered on the table for finding reactions.
  • Another participant suggests that if the load is centered and the table legs are identical and on a level floor, the forces in the legs should be equal due to symmetry.
  • A participant expresses confusion about 3D static equilibrium and requests recommendations for relevant textbooks.
  • There is a discussion about whether a different configuration, where the center of gravity (COG) is in the middle but the supports are not in the same plane, can still be treated symmetrically.
  • One participant proposes that the loading can be represented as equivalent forces and couples at the COG, and suggests using equilibrium equations to compute reaction forces at the supports.
  • Concerns are raised about the appropriateness of posting non-homework related questions in the current forum, with a suggestion to use the General Engineering forum instead.

Areas of Agreement / Disagreement

Participants express differing views on the implications of symmetry and load placement, with no consensus reached on how to approach the problem in the case of non-centered loads or asymmetrical supports.

Contextual Notes

The discussion highlights the complexity of 3D static equilibrium problems, including the need for multiple equations of equilibrium and the potential for statically indeterminate situations when loads are not centered.

aoide
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Homework Statement



how to find FA, FB, FC, FD in 3D equiblirium static?

Homework Equations



W1 = 500kg

[URL]http://www.flickr.com/photos/djaguank/5450648168[/URL]

distance (see at image)
if you can't see the image, please follow this link

http://www.flickr.com/photos/djaguank/5450648168

The Attempt at a Solution

 
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I didn't see much of an attempt. Is the load in the center of the table? If no, forget about finding the reactions without a computer program or a copy of Roarke's 'Stress and Strain". If yes, the solution is relatively simple.
 
PhanthomJay said:
I didn't see much of an attempt. Is the load in the center of the table? If no, forget about finding the reactions without a computer program or a copy of Roarke's 'Stress and Strain". If yes, the solution is relatively simple.

yes.. its in the center.. could you tell me how to solve it?? because, i confused about 3D static..

anyway.. do you have any recomendation for 3D static equil book??

thanks
 
If it's in the center, is there any reason to believe that the force in one leg will be greater than any other, if the table sits on level floor and its legs are identical in lenght? The loading is symmetrical. Most books on statics touch on 3D, which is at a level of difficulty greater than 2D. In 3D, You are dealing with more equations of equilibrium, since there are 3 axes inolved. The particular plate problem is generally statically indeterminate if the load is not centered.
 
@phantom

thanks for your explanation, i think i start to get the idea..

anyway, how about picture in this link..

http://www.flickr.com/photos/djaguank/5452658183/

could it use symetrical?? COG for body and antenna in middle.. but the leg/support not in same plane (see picture from above)

do you have email?? i want to ask you some question, please send your email to g.ghunk.np@gmail.com

thanks again
 
aoide said:
@phantom

thanks for your explanation, i think i start to get the idea..

anyway, how about picture in this link..

http://www.flickr.com/photos/djaguank/5452658183/

could it use symetrical?? COG for body and antenna in middle.. but the leg/support not in same plane (see picture from above)

do you have email?? i want to ask you some question, please send your email to g.ghunk.np@gmail.com

thanks again
It appears that the outrigger supports are symmetrical about the axes of the plane, in which case you could represent the loading as equivalent forces and couples appied at the COG, and compute reaction forces at the 4 supports by looking at the components of the loading about each respective axis, computing the reactive forces accordingly by applying the equilibrium equations in each direction (noting due to symmetry that the loading is shared equally by the near and far supports), then add them up algebraically (a corner support may take the maximum load).
Since this does not appear to be a homework problem, you should post future questions that are not homework related in the General Engineering forum (assuming this is not homework). No private emails, please! You'll get more responses in these forums from a host of others, also.
 

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