minimizing beam sagging by adding more supports

[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..

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 ...

 

[rb1957]

is this a beam ? with a simple load you can use math to solve the double redundancy you get from adding additional supports. the advantage of doing it this way is you can run many simulations very quickly. a strategy I might suggest is place one support at the peak, analyze the single redundancy then place your 2nd support at the peak. see how that works, move the extra supports a little to see the changes/sensitivity.

read up on "three moment equation" and "unit force method"

another day in paradise, or is paradise one day closer ?

 

[trish129]

is this a beam ? with a simple load you can use math to solve the double redundancy you get from adding additional supports. the advantage of doing it this way is you can run many simulations very quickly. a strategy I might suggest is place one support at the peak, analyze the single redundancy then place your 2nd support at the peak. see how that works, move the extra supports a little to see the changes/sensitivity.

read up on "three moment equation" and "unit force method"

thank you rb..

yes its a beam...

can you please outline the steps i need to take according to your suggestion.....

what do you mean by peak? at the point of maximum deflection?

where can i find three moment equation and unit forc method and what is the relevance of both to my problem?

 

[rb1957]

when you add additional supports to a beam you make the problem statically indeterminate and need additional equations to solve. hence "three moment equation" and "unit force method" ...

"where can i find ... ?" ... they have this new fangled thingimy called an "internet" and I've heard people can do "google searches" about damn near anything; sounds like a place to start.

another day in paradise, or is paradise one day closer ?