Can you explain this video? (An I-beam cut in half, springs apart, curved)

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Discussion Overview

The discussion revolves around the phenomenon observed when an I-beam is cut in half with a gas cutting torch, leading to the halves flying apart and curving. Participants explore the underlying reasons for this behavior, including thermal effects, residual stresses, and manufacturing processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the observed curvature is solely due to thermal expansion from the cutting torch, suggesting that most heat might dissipate with the molten iron.
  • Another participant proposes that the phenomenon could be attributed to residual stress from the manufacturing process of the beam, particularly noting the effects of cooling and setting during production.
  • A different viewpoint suggests that the I-beam's web could be placed under compression while the flanges are in tension through a specific manufacturing technique, akin to pre-stressing, which could store energy without heating the material.
  • Concerns are raised about the quality of the steel used, with one participant expressing a preference for Australian steel over Chinese steel due to differences in manufacturing practices.
  • Several participants note issues with accessing the video link, indicating a lack of consensus on its availability.

Areas of Agreement / Disagreement

Participants express differing views on the causes of the observed behavior of the I-beam, with no consensus reached on the primary explanation. The discussion includes multiple competing theories regarding thermal effects and residual stresses.

Contextual Notes

Participants mention various assumptions regarding the cutting process, the quality of materials, and the effects of manufacturing techniques, but these aspects remain unresolved within the discussion.

Flint1234
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A gas cutting-torch was used to split an I-beam lengthwise. When the last inch was cut, the two halves flew apart, with a great energy release. The halves are then seen to be curved where they were straight. The workman was unsurprised but the cameraman was thankful for a warning given seconds in advance.

Is this just a result of thermal expansion caused by the cutting torch? I thought most of the torch heat went with the molten iron blown away.
It was apparently cut by hand, slowly, I expect. The heat would have had time to conduct through the steel, diminishing the expansion.

Is there some technology that lets one build an iron I-beam with the flanges (flat sides) in tension? Something akin to automotive-window safety glass? I'm thinking one could cold-roll the center web lengthwise which would normally make it longer. Since it's locked to the flanges, that would put the web under compression and the flanges in tension.

You could put a LOT of energy into a spring that way and you wouldn't have to strike while the iron is hot.

Is that right? What's the roller machine called? Is there videos or literature?
Thanks.

My searches were all poisoned by steel cables used to pre-stress concrete or steel sheet cold-rolled into lightweight studs (or worst, steel cables used to pre-stress lightweight studs made by cold-rolling sheet steel)
 
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I would guess residual stress from when the beam was manufactured.
 
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It is simple to explain. Chinese steel is rolled to meet external dimensions at the lowest cost. No annealing or controlled cooling is done, so the stress of the last rolling and cooling remains in the beam. The web was thinnest, so it cooled and set first, then the thicker flanges cooled, contracting and compressing the web axially.
That is why I prefer to work with well-behaved Australian steel.

It is unusual to split an I-beam lengthwise, unless you are fabricating a castellated steel beam, but then you would not cut it straight, and you would not use cheap Chinese steel.
 
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A pity the link to the video seem to have been removed.
 
DaveC426913 said:
A pity the link to the video seem to have been removed.
The video is still there for me.
 
Baluncore said:
The video is still there for me.
Huh. This is what I get:

1707524695510.png


Anyway, thanks for posting the video.