Thermal load with thermal gradient in structural analysis

[the engineer from France]

Hello everyone , I'm conducting a static analysis of a building on pile foundations with the objective of getting the combined load at the head of all the piles. i already conducted static cases( gravity , wind ,snow,...) and now I'm conducting thermal load with thermal gradient in different locals of the structure and surprinsigly the load at the head of the piles due to thermal load is quite huge and not as expected.
Does anyone have experience with thermal load in FEM analysis ?

 

[SWComposites]

yes, in aerospace structural analysis.
thermal loads from FEA are often high because FE models tend to be over stiff (missing lots of local flexibilities).
what type of model - beam, plate, shell, solid?
how are you defining CTEs?
how are you defining boundary conditions?

 

[the engineer from France]

Thank you for anwsering.
My structural building is about 70*80 meters composed of buildings connected with expansion joints : shells and beams. My only structural material is concrete with 10^-5 K-1 for CTE and for boundary conditions , My foundation piles are blocked in translation and free to rotate.
I remarked some stress singularities in many corners in the lower parts of walls : vertical stress explodes by 4-5 times in very small area which explains the results I'm having .
I still don't have explanation for these singularities ( if it's mesh related or something else , even my mesh is quite fine with 0.5 meters elements )
Any Ideas ?

 

[SWComposites]

hmm, surely there is steel rebar in the building? you need to account for that in the analysis.

otherwise post some pictures of the areas with singularities, with stresses and boundary conditions. I suspect the boundary conditions are too rigid.

 

[ThomasH]

Impossible to answer without more information. But getting large loads or stresses due to thermal loads is not surprising in itself. The structure wants to deform in some manner due to the geometry and the thermal load. And the boundary conditions prevent that deformation.

One option is to remove the constraints and let it move freely, then you can see what your supports prevents.