Stresses when lifting a beam 2

[maatjie_mike]

Hi,

The attached picture shows a scenario where a beam with 2 lifting points is lifted by a crane by a chain with 2 legs. My question is:

- When considering the beam, is the way I have added the three stresses together correct (Stress_tot)?

Kind regards
Michael

 

[desertfox]

The beam in this case is being lifted by a crane and positioned in some construction or other, so it’s only on the crane a short while, the only concern is while it’s being lifted, or put it another way, I doubt a beam that fails by lateral buckling under its own weight would be much good for anything.



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

 

[1503-44]

Then why the lugs? Beams are lifted all the time without welded lugs attached to them.
I could say the same for doing a stress analysis for a beam under self weight load. A beam that didn't meet combined stresses allowable for self weight also wouldn't be good for much either. Why all the calcs? You're going to do all that, then close the page because its only 5% F-total,

I'm telling you that was a waste of time. We knew max combined stress wouldnt even be close before we started that exercise and now we poo poo the criteria that actually might have some impact on final results???

 

[desertfox]

If you look at the OPs post on the 06/05/2021 He clearly states the lug design is not considered here and the sketch is not accurate, in fact I certainly wouldn’t put lifting lugs in the position that’s shown on his sketch, however he was asking about stresses during the lift. Now if the lifting cables were vertical, then the small additional moment due to the 45 degree angle of the cables would disappear and the beam under self weight would sag and give tensile and compressive stresses in the normal way. My attempt to show how to calculate lifting stresses of the beam in a similar manner to that of the OP’s sketch showed that the additional bending moment was about 25% extra when compared with lifting cables being vertical for the lift. I have seen lugs welded on beams ,frames etc and then burnt off once they are in position, alternatively I have seen ropes/straps wrapped around beams and also lifted in place and so long as this is
Done in a safe manner it’s not a problem. Given that we don’t know the shape or size of the beam or it’s intended use we are both second guessing but reading between the lines of the original post I believe that the poster just wanted to know how stress the beams while it’s positioned but I could be wrong.

If the beam was going to buckle under its own weight when placed horizontal in a structure, I would of thought that it would have been considered long before it was going to be lifted by a crane.

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

 

[1503-44]

I was just suggesting he also think about alternate criteria for his design other than max combined stress, mostly because that is seldom if ever used in AISC for the same kind of problems structural engineers have every day. I'm happy to let the OP decide if that is relevant to his situation or not. Especially if all we can do is out suppose one another.

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I take no responsibility for any damages or injuries of any kind that may result.

 

[desertfox]

Hi 1503-44

Yes agreed unless we get more information then I guess we could go round in circles

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

 

[1503-44]

happens all the time.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

 

[WARose]

I doubt lateral buckling would be a problem in this case because it’s only self weight of the beam that’s involved....

I've seen members buckle under self-weight in lifting. The rules that govern buckling are built around support conditions that are not present in lifting (i.e. it could be much weaker). Also lateral restraint at various points that also may not be present during lifting. We kick this around quite a bit on the structural board.....here is a thread I started:

https://www.eng-tips.com/viewthread.cfm?qid=446703

ASME's BTH-1-2017 has a equation for the buckling load.

 

[1503-44]

Well I definitely agree. I've designed a spreader bars for a large offshore lift once and I did consider the full length as unbraced.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.