Factors of Safety

I am looking for a bit of advice, hopefully someone on t'web can help.

I am an engineer who is new to the scaffolding game and I am learning the idiosyncrasies associated with scaffolding.
I am starting to carry out some design now and I have a few example calcs from previous scaffold designs to refer to as a "startet for 10".

I have a few questions regarding loads used in design calculations.;

Is scaffolding structural design carried out to "Serviceability Limit State" (unfactored loads) or to Ultimate Limite State" (factored loads)?

If design is to "Ultimate Limit State", What factors of safety are applied / used in scaffolding design?

I have not seen any being applied in the examples I have, they all appear to be designed to "Serviceability Limit States". However I note that in EN12811-1:2003: Clause 10.1.1 & 10.1.3 that they refer to Ultimate Limit State.

my concern is that I follow the reference examples that I have, which incorrectly use unfactored loads and produce an incorrect design.

Scaffold design is traditionally designed in the UK using the permissible stress approach. All of the values for compression, shear, slip of couplers etc. in TG20:08 use SWL values with the factor of safety already applied.
I wouldn't recommend teaching yourself however as there are many factors which you will not be able to consider or learn without the help of an experienced engineer and without input from experienced scaffolders.

biffo0911 said:

I wouldn't recommend teaching yourself however as there are many factors which you will not be able to consider or learn without the help of an experienced engineer and without input from experienced scaffolders.

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Thanks Biffo, you're right I wouldn't dream of trying to learn this on my own, I am fortunate that I am working for a scaffolding company with some very experienced scaffolders who are teaching me the dark arts of scaffolding, i.e. how they will actually build it, so got some good support there. I am basically putting the numbers to justify their proposed scaffold arrangement.
I joined the scaffolding company from an engineering consultancy background so I am fairly comfortable in the use of the British Standards / Eurocodes.
My main concern (resulting in original post) was that I could not see in the example calcs, that I have, any factors of safety being applied, I had not appreciated that SWL table in TG20 already included factors of safety.

Thanks again.

Permissible.

See SWL tables in TG20.

Roarz said:

I am looking for a bit of advice, hopefully someone on t'web can help.



If design is to "Ultimate Limit State", What factors of safety are applied / used in scaffolding design?

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I have a copy of BS EN 12811-1 in which, for the ultimate limit state, the gamma f is given as 1.5 for all permanent and variable loads and 1.0 for accidental loads. The gamma m for steel & aluminium is given as 1.1. You will see in the first post in the thread on ultimate limit state design referred to by Swifty that there is an error in the way that these are described.

Complying with BS EN 12811-1 is a nightmare if you try to include the effect of imperfections and secondary effects due to deflections etc. Add to that the lack of data about the materials, most of which are not manufactured to European standards and I cannot believe that anyone can properly apply this code to the design of scaffolding.