Engineering Question - Slings & eyebolts

danza

danza

danza

Soldato
Joined
28 Mar 2005
Posts
13,679
Location
Drunken badger punching
Is there a reliable general calculation I can use to work out the effective reduction in SWL of an eye bolt, when loads are acting at any angle other than 90 deg. to the bolts axis? Got 4 off M36 eyebolts with an SWL of 6.3T each being used for the lifting of a 10T load. The sling angles are pretty hellish-looking, and I've a feeling that M36 isn't enough.

Also, am I right in saying that one bolt must be omitted from the loading calcs, as effectively only 3 do the work (with the 4th only balancing the load)? This is obviously assuming a 4 point lifting system.

Cheers!
 
We always refer to the manufacturers information in work. I remember us being asked to re-machine a die bed which was 30 tons. We lifted it on static eye bolts rated at something like 10 tons each. But when we looked at 90degrees they were only rated to 3 tons each. I will see if I can find any data.
 
It's hard using manufacturers data, if you don't know who they are.
In my case I assumed the eyebolts were made to DIN580 standard & base my calculations on that, & allowed a bit extra for safety.
 
Those charts are a little higher than my book here. It says in my book with a sling angle of 60 to 90 degrees a pair can lift 3.2 tonnes.

Eye bolts with a link are a little stronger. They are 63% swl at 90 degrees. A m36 one will hold 3.2 tonnes vertically.
 
I given a eyebolt slide rule calculator 20 years ago.

Brilliant thing,German made I think, you entry sling angle, weight, etc & it gave you the eyebolt size.
 
KaHn said:
You mean out of plane? You don't.

Check here for more information on eyebolts.

http://www.thecrosbygroup.com/html/default.htm

KaHn
Click to expand...

I don't mean out of plane, sorry. the slings will be angled, but in line with the plane of the bolt. The bolts will be collared.

Anyway, for the info guys. I'll need to look at the actual sling angles tomorrow and see what I come up with.
 
danza said:
I don't mean out of plane, sorry. the slings will be angled, but in line with the plane of the bolt. The bolts will be collared.

Anyway, for the info guys. I'll need to look at the actual sling angles tomorrow and see what I come up with.
Click to expand...

Then for Crosby eye bolts over 45degrees its 30% at 45deg and 25% at 90deg.

KaHn
 
danza said:
Also, am I right in saying that one bolt must be omitted from the loading calcs, as effectively only 3 do the work (with the 4th only balancing the load)? This is obviously assuming a 4 point lifting system.

Cheers!
Click to expand...

Yes in a four bolt arrangement, only allow for the SWl of three bolts. Think of a three legged stool, all legs take ~equal load. A four legged stool can wobble if just one leg is slightly longer. Using slings I would always calculate on just three.

Personally I would avoid horizontal loads by having a cruciform lifting beam with vertical slings down to your eyebolts
 
nkata said:
Yes in a four bolt arrangement, only allow for the SWl of three bolts. Think of a three legged stool, all legs take ~equal load. A four legged stool can wobble if just one leg is slightly longer. Using slings I would always calculate on just three.

Personally I would avoid horizontal loads by having a cruciform lifting beam with vertical slings down to your eyebolts
Click to expand...

No thats incorrect, you generally take a skew factor for 4 point lifts, you take a 66/33 (or 75/25 in some codes) split between the slings. Also they are other things to take into account and not just skew.

i.e. 2 slings see 66% of the load and the other two take 33% of the load, this is based on the standard lifting guidlines from BS ISO and Offshore lifting guidelines.

You will also have to take into account the load paths if your structure isn't symmetric as the skew could affect on load path but not another.

And the fact you want to fabricate a lifting beam over just using eye bolts is slightly absurd unless it is a really akward lift or very delicate, or if you are having trouble with the reduction factors look at using swivel eyes (again crosby).

If you want some more guidelines I'll post engineering codes for lifting but it will probably confuse you if you haven't seen things like skew factors, dynamic amplification factors etc etc.

KaHn
 
KaHn said:
No thats incorrect, you generally take a skew factor for 4 point lifts, you take a 66/33 (or 75/25 in some codes) split between the slings. Also they are other things to take into account and not just skew.

i.e. 2 slings see 66% of the load and the other two take 33% of the load, this is based on the standard lifting guidlines from BS ISO and Offshore lifting guidelines.

You will also have to take into account the load paths if your structure isn't symmetric as the skew could affect on load path but not another.

And the fact you want to fabricate a lifting beam over just using eye bolts is slightly absurd unless it is a really akward lift or very delicate, or if you are having trouble with the reduction factors look at using swivel eyes (again crosby).

If you want some more guidelines I'll post engineering codes for lifting but it will probably confuse you if you haven't seen things like skew factors, dynamic amplification factors etc etc.

KaHn
Click to expand...

Talking as an appointed person for lifting, mainly large crane lifts, I can see what you are saying but, eyebolts are notorious with four point angled lifts. The chances of all four being oriented right when correctly tightened are small, this is to do with thread starts, tolerances etc. Personally I would keep the angles as small as possible or negligeable.

Whether pairs of slings can be said to act together depends on whether they terminate as a two leg brother or a four leg to a common head link.

Using 33% (3 legs) of the load as the eyebolt load is not dissimilar to your 66%/33% split in any case, 66% / 2.

Modular lifting beams with certification are available for hire, if a single lift, or if a common lift, could be fabricated and tested, but that was not my first thought.
 
nkata said:
The chances of all four being oriented right when correctly tightened are small, this is to do with thread starts, tolerances etc. Personally I would keep the angles as small as possible or negligeable.
Click to expand...

This is why the lifting guidlines are used to determine these effects on the lift, the orientation of eyebolts etc falls into good L.O.L.E.R. practice, eyebolts aren't great but can be used if the correct guidelines are followed, if the OP wants something more rebust I suggest using swivel eyes.

http://www.liftingsafety.co.uk/product/crosby-swivel-hoist-ring-2435.html

I've used these for offshore lifts many times.

Whether pairs of slings can be said to act together depends on whether they terminate as a two leg brother or a four leg to a common head link.
Click to expand...

I'd assume if it was a dedicated piece of rigging he would be using a controlled sling set, i.e. using a materlink assembly, hard eyes each end and correct terminations. The fabricated slings should be within tollerances based on BS EN 13414.


Using 33% (3 legs) of the load as the eyebolt load is not dissimilar to your 66%/33% split in any case, 66% / 2.
Click to expand...

That wasn't my point about the 4 point lift, it was due to load paths on a lift. How the structure reacts to a 3 point lift vs 4 point lift.

Also if you want to discuss qualifications I've done offshore and subsea lifting analysis for things ranging from 1Te to 1000+ Te and a maximum of 3500Te for a project in gulf of mexico using the saipem s7000.

But just saying :).

KaHn
 
KaHn said:
Also if you want to discuss qualifications I've done offshore and subsea lifting analysis for things ranging from 1Te to 1000+ Te and a maximum of 3500Te for a project in gulf of mexico using the saipem s7000.

But just saying :).

KaHn
Click to expand...

Not too into trading experience, my background is in civils so have not generally exceeded large crawler capacity with tandem lifts and bridge lifts with jacks but I am sure that we would agree on a specific lifting scheme or have similar views on how to attach to and perform the lift.

We do not have enough info from the OP to be definitive. Size and centroid of object, available plant, headroom, nearby obstructions, services,......the list goes on. Eyebolts with raking slings would not be my initial preference but it may be the preferred scheme for this operation.

regards, andy.
 
KaHn said:
Also if you want to discuss qualifications I've done offshore and subsea lifting analysis for things ranging from 1Te to 1000+ Te and a maximum of 3500Te for a project in gulf of mexico using the saipem s7000.

But just saying :).

KaHn
Click to expand...

Sounds interesting, care to discuss it over a pint sometime..?:o
 
You must log in or register to reply here.
Back
Top Bottom