3D Statics problem
3D Statics problem
(OP)
I need a little help on this 3D statics problem. Any takers?
Heckler ![[americanflag] americanflag](https://www.tipmaster.com/images/americanflag.gif)
Sr. Mechanical Engineer
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This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.





RE: 3D Statics problem
Tara
http://tinyurl.com/4ydjg7m
RE: 3D Statics problem
You can go farther only by introducing a structural link between the loads and the reactions.
prex
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RE: 3D Statics problem
one solution would be FE, determining the reactions from the stiffness of the internal structure.
another solution would be to assume effectively an equal stiffness for all the reactions, and mathematically solve the overdefined matrix (google "least squares solution for overdefined set of equations").
another approach, assume your 4 reaction points are pinned (rather than fixed), though that still leaves 6 redundancies. a solution is to solve for each pair of reaction points (6 reactions = 6 equations of equilibrium). this'll give 6 different sets of reactions, assume the average is a reasonable solution.
RE: 3D Statics problem
react the applied load so that A and B react 31.46/45.25*1175 = 817 lbf and C and D react 358 lbs. Then A reacts 20.25/17.12 = 990 lbs and B reacts -173 lbs; C reacts 13.25/11.25*358 = 422 lbs and D reacts -64 lbs. check ... 990-173+422-64 = 1175 lbs.
another approach ... each reaction point reacts load along a vector between the point and the load ... now only 4 unknowns ...
RE: 3D Statics problem
Mike McCann
MMC Engineering
RE: 3D Statics problem
RB can you expand on your method. I'm having trouble following your path. Thanks
Heckler![[americanflag] americanflag](https://www.tipmaster.com/images/americanflag.gif)
Sr. Mechanical Engineer
o
_`\(,_
(_)/ (_)
This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.
RE: 3D Statics problem
if your 4 pts are truly fixed then the problem is quite intractable for a hand calc.
if you run your FE with pinned pts then you'll get something to compare with hand calc and something to show you how critical are the reaction moments.
for a hand calc to compare with this, try ...
1) assume the reaction at each point is along a vector between the point and the load, so the three compenents at each point are direction cosines of the resultant reaction ... 4 unknowns reasonable to solve; or
2) assume only two reaction points are effective (say A and B). solve the equations of equilibrium. again for a different pair (A and C) and so on ... 6 combinations, 6 different results, the average is probably a reasonable compromise.
RE: 3D Statics problem
RE: 3D Statics problem