Thermal Bending

[Sam Low]

HI All,

There was a thermal bending on a skid base structure, basically the both end of the skid base has a bending towards upwards which is similar to the diagram below.
I belived it is caused by expansion when hot and to shrink when cold steel.

I was wondering why the skid structure wouldn't be expand in length as per linear expansion coefficient but bending instead.

When will it be expand in length as some of the cases it will have bending deflection due to temperature variation as mention in the link below?

https://nptel.ac.in/content/storage2/courses/105101085/downloads/lec-26.pdf

Appreciate if anyone could explain in detail.
Thanks in advance!

 

[3DDave]

Not enough detail to explain in detail.

Typically unconstrained metals expand uniformly if the temperature is uniform and they bend, twist, or otherwise warp to usually small amounts when heated non-uniformly.

However, if the part is attached to a structure that is a different metal or material or the same metal at a different temperature, then the loads applied by that attachment can provide a bending moment. Example: rail road rails that warp in the summer heat when the steel expands more than the dirt they run on.

 

[Sam Low]

Hi Dave,

Thanks for the prompt reply!
The skid base structure was welded completely but only client decided to weld a covered plate on top of the skid base structure.
The thermal bending had been come into picture after all.

Anyway, do you have any idea when the thermal bending, linear expansion and volume expansion would be occurred during theraml expansion?

 

[3DDave]

Adding hot metal to cold metal with a weld is going to cause distortion, as in the bending you see.

There are entire weeks of college courses covering this subject, enough that I won't type it a little at a time.

 

[desertfox]

Hi Samlow
Here is some information on weld distortion, it’s a huge subject but this should give you some idea of what’s happening

https://www.lincolnelectric.com/en-gb/support/welding-how-to/pages/weld-distortion-detail.aspx

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Sam Low]

HI Dave,

Noted.
Thanks ya.

 

[Sam Low]

HI desertfox,

Thanks for the link! Will try to digest it. Thanks a lot!

 

[IFRs]

Bridge girders are sometimes deliberately curved by welding.

 

[onatirec]

If the heat source is at the base, it could produce a temperature gradient causing the bottom to expand more than the top - especially if there is some convection at the top wicking away energy.

 

[Tmoose]

Just to confirm, the distortion now exists with the frame at room temperature ( thermally equalized) , and the distortion was noticed AFTER welding on the "covered plate."

What is the purpose of the "covered plate." ?

If this is the case, Fairly heroic measures will be required to "un-bend" the frame.
Gently cutting the welds that secure the "covered plate" //may// improve the situation quite a bit.
A genius with an oxyacetylene torch kit may be able to true up the frame where it lies.