BCs for a stool

[hiyer]

I have to analyze an assembly very similar to a stool (4 legs welded to a flat plate) and was wondering what is the best way to apply restraints without using symmetry. The legs can spread out but cannot move vertically. I can restrain UZ but what about UX & UY? I'm using 2nd order tets for meshing. Any ideas??

 

[johnhors]

I assume your loading is in Z only and all legs are already restrained in Z, then fix one leg in X and Y as well Z, then select another leg, if your second leg is at an X offset from the first then fix this in Y and Z only, else if it is at a Y offset from the first then it must be fixed in only X and Z.

Follow this, and the stool legs are free to spread outwards under vertical load without any restriction.

 

[crisb]

If the area at the base of the legs is significant and you fix that whole area in the z direction you will probably inadvertantly apply a rotational fixity at that point, is that what you want?
Alternatively you could calculate the reactions at the base of the legs, apply these as pressures, and apply the fixity elsewhere (at the flat plate?).

 

[hiyer]

Thanks for your replies. The area at the base is not large, the legs are made of tubular steel. I will apply the BCs as described by John and see how the model behaves. Appreciate your inputs!

 

[GregLocock]

And you will get answers anywhere within -100 to +100% of the real situation. That's why stools have three legs.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[hiyer]

Greg,

I'm not sure I understand your post fully.......would you elaborate on it a bit more?

 

[GregLocock]

Imagine a simple 4 legged stool standing on a rigid floor. Apply a vertical load to the seat, somehwere between the 4 legs.

Wha is the load taken by each leg?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ThomasH]

Why do you model a stool with tets?

Why not use four beams and a plate, something tells me that might remove some of the confusion.

Good Luck

Thomas