I have Incorrect results in modal analysis of an arch bridge, what's wrong with the modeling?
Hello dear researchers
I modeled a concrete arch bridge in Abaqus, model has many parts that are assembled, because of complications in its geometry I merged meshes of all parts instead of merge geometry to mesh the structure of bridge simply, is it a correct method?
I test this method for a simple beam that it was consists of 2 parts. I compared the result of this model with the result of the continues beam, the results were same.
But in the main bridge model the modal analysis result was incorrect. What is wrong do you think? The inp file of the model has been attached.
The picture of the modeled bridge and some pictures of modal shape of the bridge which are incorrect have been attached.
Any help is appreciated
Hi Elham,
It is OK if you model the bridge's components individually and then assemble them together. However, you need to use additional links (i.e. tie, coupling) to combine these parts together instead of merging them as one piece, which is shown in your inp file. Because your each structural component won't share same nodes with others, it will give you unreasonable results.
Additionally, my comment is always try to consider what kind of problem you would like to solve in your FE analysis, and what results you expect from the analysis. Your model is so delicate that it will take longer time during calculation, especially for nonlinear analysis of concrete behaviors. I will bring up the idea of beam element to model the bridge if I was in your position.
Hope these could help.
Xiangxiong
Hi Elham
I guess re-considering your boundary conditions and/or revising the connection in assembly of components may resolve the problem. Merging meshes, actually puts the structure in a "Welded" shape. All parts are welded together.
Please check the following:
a) try to re-consider the boundary conditions (some BCs may be missing or not correctly set)
b) Make sure the material props are set correctly
c) Make sure the mesh is fine enough (check the independency from mesh test with first natural frequency as your criterion)
Hope it helps.
I am reasonably sure that your support conditions (restraints) are incorrect.. Please, revise your support conditions. regards, john
I am almost sure that your restraints (boundary conditions) are incorrect. Please revise. regards, john
Hello,
Do sanity check and ensure the connectivity.
If you find abnormality in results check the following
1.check the connectivity b/w the assy.(obviously the contacts are to be linear-bonded contact)
2.apply appropriate material/boundary condition which is realistic.
Regards,
Velu A
Hello,
it is just a suggestion but maybe it will help.
Build your bridge in CAD as a whole. Export it via step or stl and use Z88 for modal analysis. Here you can also define your boundary conditions. Have a look at FEM-Helden it is in german but there are also figures to understand.
Regards
Frank
www.z88.de
www.fem-helden.de
how did you model damping? proportional or non proportional? Also check out that you are ploting the same dofs.
You obtain zero eigenmodes. The reason is that your elements are not connected with each other and the parts can translate or rotate. This can happen, if you mesh the parts seperately.If this is the case, the separate parts have no boundary condition and therefore they can move freely. You can merge the nodes and the problem should be solved.
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