Abnormal deformation in DY direction in Steel Composite sections

Question:


Hello,

Client has a problem with the results of calculation for the composite structure.
He tried to modeling an object with three spans in a horizontal arch (arch + easement curves)

In the case of using the composite cross-section and considering the construction stages, we see the strange horizontal displacements (in the XY plane) which are certainly not real.



1. File 1 - including full geometry, sections, phases.
In the results of the displacement there are strange "teeth" in the points between the crossbars. The construction is loaded with vertical load evenly spread over the entire length of the girders, so such displacement can not occur.

2. File 2 - simplified model, without all crossbars. The same cross section for all components was defined ans the same constructions stages were introduced.
Again, in phase 1, strange vertical displacement results in curved spans in the plan has occur.

3. File 3 - the control file - the same as File 2 but instead of composite sections, the steel cross sections with the same parameters were defined. In this file the horizontal displacements are okay.

From the above, there is some error in modeling the cross section?

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Answer:Dear User,

This teething is basically because of the divisions in the elements.
When you select all the elements , go to Node/ Elements > Merge to just have a single element between the cross beams, you will notice this teething would be avoided.

This is nothing but the deformation in DY direction, due to twisting of the member about X axis. When the elements have no. of divisions, this deformations in DY direction would be present because there is no lateral restrain offered by the cross beams. This is more pronounced in a composite girder than steel alone girder, because of the additional twisting offered by load on the slab.

Alternatively, you may check on the Warping degree of freedom in the section properties, to introduce the stiffness property concerned with twisting, and now you may not, the teething would be avoided

Hope this clarifies your concern. Do let me know if further clarification if required.