Incorporating Erection Tolerances

[Comach]

When preparing fabrication drawings of structural steelwork there is a requirement to allow a clearance dimension for the end connections to facilitate steelwork erection. This is normally 1 or 2mm depending on the connection and building design.

Can anyone tell me how this is accommodated in the Autocad Structural Package?

Update: What I am referring to; for clarification; is the 'end clearance' as defined for example in the Corus Bluebook and previously the BSC publications on Structural Steelwork. Sometimes this is also referred to as an 'erection tolerance or clearance'.

[kathy71046]

I'm not sure I understand the question.

The model is your "ideal" and any slackness you need for erection should be part of the connection design.

[Comach]

I'm not sure I understand the question.

The model is your "ideal" and any slackness you need for erection should be part of the connection design.

That's correct it should be part of the connection design, but its not simply a case of 'any slackness you need' it is mandatory requirement when dimensioning steel fabrication drawings.

Fabrication detailing in accordance with BS EN 1993-1-2 & BS5950 sets out specific detailing clearances and I simply wondered if this information was integral to the Autocad Structural product or otherwise facilitated.

[kathy71046]

It dimensions whatever you model. (if it's not skewed or diagonal)

It automatically has a 2mm bolt clearance when creating bolted connections, or 1mm for M12 and under.

Other clearances such as distance from a member to cleat or edge distances need to be input to the options when creating the connections.

Weld size and type, as well as bolt and material grades are specified as project parameters, but can be changed when creating connections or inserting members.

Will it automatically create everything to your specific countries' codes? No.
Can you create a setup where most things will comply? Yes, but it will take some work.

[Comach]

It dimensions whatever you model. (if it's not skewed or diagonal)

That's interesting - what are the limitations if skewed or diagonal?


Other clearances such as distance from a member to cleat or edge distances need to be input to the options when creating the connections.

If I understand this correctly, the software provides an option to specify the offset distance from the centre of the connecting beam to my end cleat or end-plate when creating my connections?


Will it automatically create everything to your specific countries' codes? No.
Can you create a setup where most things will comply? Yes, but it will take some work.

I don't believe that clearance allowance when detailing an end connection is country specific, its just good practice to facilitate erection but also to permit some allowance for member sizing, rolling exactness, straightness over length and cross section and also paint thickness.

Which is why as a standard practice that I would have thought this would have been integral to the product.

The reason why I mentioned this is because a local fabricator just received a bunch of 'fabrication drawings' from a consultant created in Autocad Structural without clearance allowance on the dimensions...so they wanted to send the drawings back but the Consultant said he had no knowledge of clearance requirements for fabrication and was not sure how to do this in Autocad Structural....so they asked me to help as structural fabrication is my area of expertise but as I had no prior knowledge of Acad Structural I am not able to advise accordingly.

[kathy71046]

That's interesting - what are the limitations if skewed or diagonal?

Skewed it won't dimension (or label holes), and it only does orthagonal, so any dims along a diagonal have to be done manually



If I understand this correctly, the software provides an option to specify the offset distance from the centre of the connecting beam to my end cleat or end-plate when creating my connections? see pic for a dialogue screenshot

Not quite, you specify pretty much everything, plates, bolts, chamfers, welds, there are a lot of connections, and each has normally 4 tabs of info that can be adjusted as required.




its just good practice to facilitate erection but also to permit some allowance for member sizing, rolling exactness, straightness over length and cross section and also paint thickness.

Then this would be up to the detailer to do, as far as I can see.

I have never come across this as a requirement, but I am probably doing projects that are nothing like yours.

The only place I see this as a requirement is if your steel is jammed between existing walls, which isn't something I encounter very often.

[Comach]

Then this would be up to the detailer to do, as far as I can see.

Yes I can see that a lot of fabricators may need to spend time sorting out drawings from third parties. That to me is counter productive because one of the key aspects of the Revit/Acad Structural combo is that the data should be capable of direct input into the fabrication stream thereby negating a lot of interim work to convey design intent.


I have never come across this as a requirement, but I am probably doing projects that are nothing like yours.

That surprises me and concerns me!


The only place I see this as a requirement is if your steel is jammed between existing walls, which isn't something I encounter very often.

Its nothing to do with steel jammed between walls, that is a separate consideration - it is simply a standard fabrication draughting requirement for all steelwork regardless of the steel project.

But you did clarify one point for me in that the option is not directly facilitated in this software.

This is a major concern because if people are submitting fabrication drawings without consideration for clearances then they are simply not doing it right, which brings me back to the reason why I asked the question in the first place.

The end clearance for connections into an adjoining web is defined as t/2 + 2mm, end cleat projection from the end of the web is normally 3mm, but some European countries use 5mm, beam connections butted to the face of column usually allow 1mm nominal clearance..

I think what may be prudent is to do some detail drawing samples on my blog - I may just scan some examples!

[kathy71046]

I suspect that your "end clearance" is something that is used by me, but not "labelled" as such. I am still not entirely clear as to what you mean by the term, however there are tolerances that are modelled in as part of my drawings.

[krlee_399]

I've also noticed there is no allowance for this on ASD, although we have a good fabby and he has no problems reading the drawings and makes the allowances himself, although I'd prefer it if clearances were incorporated as standard.....I've thought whether it could be country specific but surely all fabbys cut all their steel the same way nd would surely make allowances for welds etc

Be interesting to know if this can be taken into account on asd

[Comach]

......... I'd prefer it if clearances were incorporated as standard....

I don't think it would be too difficult to build in optional parameters when preparing the dimensional information for an end connection in ASD. I have not actually used ASD yet! but as the question has highlighted some issues I will try and get hold of an evaluation copy and check it out.

This to me though is a serious omission, I do have concerns about Autodesk and their practices with steelwork...you know for many years the steel section sizes for at least the BS portion in Autocad Inventor were wrongly sized...in fact right up until version 2010, I am not sure if they have fixed that yet. The variations were marginal but nevertheless wrong.


......I've thought whether it could be country specific but surely all fabbys cut all their steel the same way and would surely make allowances for welds etc


I would think that they do.

For Katika: see attached from the Corus Handbook, under the 'Dimensions for Detailing' section.