help on using BS13155:2020 for design a simple lift beam

[jedstress]

Hi all,

I am currently working on a lifting beam which has to be designed/analysed in accordance with BS13155:2020.
In the past, I have designed lifting beams which were based upon the clients own safety factor requirements and manuals, therefore BS13155 wasnt used as such.

The following is an extract from bs13155:2020 Annex A:
"A.1 Verification of mechanical strength by calculation
The mechanical strength shall be proven for the specific working load limit in accordance with
EN 13001-3-1.
The maximum permissible tilting angle specified for the attachment shall be taken into account in
calculations.
The design load used in calculations shall be derived using coefficients as given in 5.1.2 and 5.2 for both
yielded and elastic conditions.
The mechanical strength shall be calculated in accordance with EN 13001-1 and the limit design stress
shall be in accordance with:
— for the elastic condition, the allowable stress method;
— for the yielded condition, the limit state method."

§5.1.2 states that:
"5.1.2.1 Load lifting attachments designed for a maximum of 16 000 load cycles
— Elastic condition: the mechanical load bearing parts shall be designed to withstand a static load of
two times the load they are required to sustain under the intended operating conditions without
permanent deformation.
— Yielded condition: the mechanical load bearing parts shall be designed to withstand a static load of
three times the load they are required to sustain under the intended operating conditions without
releasing the load even if permanent deformation occurs.
The coefficients mentioned above cover the uncertainties of the value of the actual load and the impact
factor for hoisting a grounded load (dynamic effect) in general applications. The proof of fatigue strength
is not necessary, it is covered by the global safety of the proof of static strength."

As stated above, and referring to BS 13001-1, the limit state method for the yielded condition mentions dynamic factors, partial safety factors and risk coefficients to be applied to the applied loads.

So, based upon §5.1.2 (above), is BS13155 suggesting that these individual load factors/risk coefficients etc (from BS 13001-1) be replaced by a single load factor of 3 for the yielded condition? And the limit design stress (allowable stress) is material Ftu/1.10?

Regarding the allowable stress method for the elastic condition, where is the load factor of 2 (BS13155) applied? The admissible stress for this method equals the material Fty/(overall safety factor x risk coefficient).

I have attached snippets of the two stated methods.

Apologies if the answers are obvious but I want to make sure that I don't misinterpret the two methods and usage of load factors.

Thanks in advance

 

[desertfox]

Hi jedstress

I'm no expert but to my way of thinking from what you have posted is that there are two design criteria and you choose either the elastic design or the state limit design. I will have a scout around and see what else I can find.

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

 

[desertfox]

Hi jedstress

Here is a link that might explain it better

https://www.linkedin.com/pulse/differences-between-working-stress-method-limit-state-cedric

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

 

[rb1957]

which approach gives the lower margin ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[jedstress]

The lifting beam shall be designed for a maximum of 16 000 load cycles.

Going off the below link, it seems as though, for <16000 load cycles, the requirement is basically 2x load for elastic and 3x load for ultimate. The resulting stresses are then compared against the material allowable. All the partial safety factors and risk coefficients etc seem to matter only for >16000 cycles.

[URL unfurl="true"]www.diva-portal.org/smash/get/diva2:1672178/FULLTEXT02
[/url]
However, correct me if I am wrong, the extract from BS13155 §5.1.2.21 doesn't quiet read out like that for <16000 cycles.


FYI BS13155 §5.1.2.2. states:
"5.1.2.2 Load lifting attachments designed for more than 16 000 load cycles
The proof of the static strength and fatigue strength shall be based in accordance with EN 13001-1,
EN 13001-2 and EN°13001-3-1.
For static strength, the value of the risk coefficient (γn) defined in EN 13001-2, shall be 1,4."

Reading through the document in the above link, it seems to make sense. However, as it reads, BS13155 §5.1.2.1 seems abit more involved than just applying 2x/3x the load and checking against material aloowabel without any additional knock downs.

 

[desertfox]

Hi Jedstress

The 16000 cycles seem to me to be restricted to lifting attachments ie to me that means slings, shackles etc and not the main mechanical bearing parts.



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

 

[jedstress]

Desertfox, I have read BS13155 and it seems to cover various types of lifters includimg lifting beams, clamps, C hooks etc. And it has also been specified by the client. Therefore, I'm confident that it applies to the main lifter fabrication too.

Rb1957, I wasn't sure what you meant by your question. My question was about trying to understand what bs13155 requirements are and how it expects to implement it via bs13001. The method description in bs13155, especially for <16000 cycles, seems confusing. But reading through the worked example in the link I mentioned earlier, it seems too simple. So I was trying to figure out if the worked example is actually bs13155 compliant or have they overlooked partial safety factors etc.

 

[desertfox]

Hi Jedstress

From the link you sent in your last but one post I found this:-

Conclusion from SS-EN 13155- 2021
For under 16 000 the proof of fatigue strength is not needed, it is covered by global safety factor. According to SS-EN 13155:2021 (Clause 5.1.2.1)
For over 16 000 the proof of fatigue strength and the proof of static strength according to SS-EN 13001 series is to be done.
So, for the lifting beams and forks that are intended for under 16 000 load cycles there is no requirement for proof of fatigue strength as it is covered by the global safety of the proof of static strength. For the ones intended for over 16 000 load cycles it should be in accordance with EN 13001-1, EN 13001-2 and EN 13001-3-

So my question to you is :- is the lifting beam you are designing required to operate more than 16000 cycles? If not then you only need to consider the global safety of the proof of static strength. If more than 16000 then fatigue must be considered

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

 

[jedstress]

Hi desertfox,

I can confirm that the lifter will operate <16000 cycles.

I recall reading that extract but what confused me was "only need to consider the global safety of the proof of static strength". The author from the link ignored all partial safety factors etc for <16000 cycles for static checks. But he included these factors for >16000 cycles.

However, the extract from BS13155 doesn't mention anything about ignoring these additional safety factors for static checks; it only mentions exclusion of fatigue checks for <16000 cycles.

Maybe I am overthinking it, and maybe the author from the link has used the earlier BS versions thus fully understanding their requirements. But at the same time I wanted to ensure that I haven't overlooked BS13155 requirements especially for <16000 cycles.

 

[desertfox]

Hi Jedstress

This table is from BS13155 and it says for less than 16000 cycles to use the 2x static load criteria and so that’s what I would follow, not sure what you mean with all the other partial safety factors

Relevant info and proposed solution for standard SS-EN 13155-2021
Equipment
Requirement
Descriptor Clause Measure number
Solution proposal
Lifting forks
Mechanical load bearing parts
<16 000 load bearing cycles
5.1.2.1
Elastic condition: 2 x Static load, yielded condition: 3 x Static load
See simulation execution in report
Mechanical load bearing parts
>16 000 load bearing cycles
5.1.2.2
Given in SS-EN 13001 series
See 13001 excel sheet
Lifting beams
Mechanical load bearing parts
<16 000 load bearing cycles
5.1.2.1
Elastic condition: 2 x Static load, yielded condition: 3 x Static load
See simulation execution in report
Mechanical load bearing parts
>16 000 load bearing cycles
5.1.2.2
Given in SS-EN 13001 series
See 13001 excel sheet

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

 

[rb1957]

Interesting how different approaches to fatigue analysis there are.

If we (in aerospace) wanted a fatigue life of 16000 cycles we'd describe that as a safe life, and in order to have a safe life of 16000 cycles, we'd need an analytical life of 16000*N cycles, where "N: is (predictably enough) the "safe life factor" ... anything from 3 (for landing gear to 5 for typical structures, to 10.

Whereas "you guys" seem to factor the load. No criticism, just an observation.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.