High shear forces, Vxx for positive temperature gradient load case

Question:

Good day. The shear forces, Vxx at the edge/corner of the portal frame structure is very high under positive temperature gradient load case. I only applied a temperature difference of 11 C, but the shear force is up to around 1400 kN, compared to that due to live load HA & HB45 which is only around 190 kN. Shear due to temperature is almost 8 times higher than HB45 vehicle.

I would like to ask if this is normal? Should it be considered in design? and why does this occur, or how is it calculated by the software?

Thanks.

Answer:

Hello, 

Thanks for getting in touch.
Basically, this is the issue with FEA modeling. As we know in FEA models results mainly depend upon the nodes. Now in plate elements, as extreme plates, there are no other elements that share the loads that come onto the extreme nodes (in our case per node only  1 element). That is the reason for high results on extreme nodes as compared to the internal nodes which are shared between 4 plate elements. 



If you see the extreme plate in detail, forces are high only at the corner line, at the internal line results are approximately equal to the inner element. By default, the program shows only the maximum value of the plate that why it seems like extreme plates are taking very high forces. 



Same concept for element having 676 KN/m VXX. Here, the node is shared by only 2 element.
So we would suggest to check the results at the center of the plates for corner elements :-



Hope this helps. 

Regards,
Rohan Agarwal
Structural Engineer

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Creation date: 4/27/2022 6:04 PM (Rohan)      Updated: 5/10/2022 6:30 AM (dklee@midasit.com)
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