FEA of a beam sagging under its own weight

[trish129]

i am trying to determine the maximum deflection of a beam on account of its sagging due to its own weight.
I have the CAD MODEL of the beam and i import its IGS into ANSYS WB14.static structural.

I performed analytical calculations considering uniformly distributed loading and simply supported beam to find the maximum deflection..need to verify it with FEA in ANSYS WB 14


1.is it a uniformly distributed loading case ?

2.i need to simply support the beam at both ends..but when i select the lower edge of the beam and goto SUPPORTS i find that the simply supported option is there but DISABLED(greyed out)..what to do now?

3.i need to apply the loading..how to go about this?

help needed..

 

[Drej]

1.is it a uniformly distributed loading case ?

Why aren't you just applying a 1g gravitational load in the model? For the hand calcs you can assume a UDL but it is easy to apply gravity to the FE model.

2.i need to simply support the beam at both ends..but when i select the lower edge of the beam and goto SUPPORTS i find that the simply supported option is there but DISABLED(greyed out)..what to do now?

Apply your boundary conditions manually rather than choosing a pre-assigned condition and assume that it's done what you want. Remember also that a strict mathematical simply supported beam isn't always what people think it is i.e. it is not both ends "pinned".

3.i need to apply the loading..how to go about this?

Assume you mean self-weight, therefore see response to (1) above.



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[trish129]

Dear Drej,

thank you for your reply..

you said "Apply your boundary conditions manually rather than choosing a pre-assigned condition and assume that it's done what you want. Remember also that a strict mathematical simply supported beam isn't always what people think it is i.e. it is not both ends "pinned"."
--> what supports do i apply then,given the fact that simply supported option is greyed out.i.e.there but disabled..?

secondly,I would need to add a support in the mid of the base of the beam(between the two extreme edges)..only edges,vertices,complete faces get highlighted ...but i want to select the middle of the base..how do i do that?

 

[inline6]

is this a line, surface or solid element model?

 

[trish129]

I am performing an FEA of a beam that is to be analyszed for maximum sagging under own weight...the purpose is to minimise the sagging by adding more supports...

analytical calculations considering two extreme end supports,i.e simply supported beam case revealed a maximum deflection of 17.5 mm in the mid..

so to verify this result..i needed to perform FEA of this beam..i had the CAD model and imported its IGS file into ansys workbench 14 and applied gravity load to it ..but the problem was that the simply supported option in SUPPORTS was found greyed out..so i overcomed this problem by fixing one end of the beam and applying a displacement support at the other extreme end...this worked and gave 17.341 mm deflection(had to run the mesh with medium revelance,else it was giving errors).

i found this tutorial more useful

https://confluence.cornell.edu/display/SIMULATION/ANSYS+12+-+Beam

and followed it and instead of fixed and displacement supports,this time i used remote displacement supports at each ends by selecting two extreme VERTICES of a single edge of the beam base( and selecting rigid rather than deformable in the the selection details of remote displacement).....it did work...but with error "unconstrained,,rigid body motion)....

now..i wanted to apply two more supports so as to see how much the sagging dies out..so for this i had to make vertices to locate the supports underneath so first i edited the geometry in design modeler and SPLIT both parallel edges of the beam base into 3.so it gave me 4 equally spaced vertices..(two extreme ends and two at the split lines intersections)..

now I attached 1 remote displacement support at the 1st(extreme edge of the beam base) by inputting 0 for all three translations..and for the rest of the three remote displacement supports along this same edge.....and solved it for directional deformation only..it did give results but yet again with that same error...still i think it should work..

was there a simple and a more easy way for what i already did ?

screen shots of my work atached..

i want to know if there can be a DOE with a defined deflection limit to be met so that i can perform this analysis with other sets of support spans without having to edit the geometry everytime ...

 

[IDS]

Checking a non-FEA calculation with a simple FEA run is a reasonable thing to do, but why not keep things as simple as possible? If you are interested in beam deflections why not use beam elements, which will be much easier to set up and be sure that support conditions are appropriate?

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/