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Old 9th July 2010, 09:53 PM   #1
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Default steel purlins, what do i enter?

I'm a bit confused on what to enter and where. also what beam i should select.

I need calcs for steel purlins (girders/beam that is an I shape?) to span a maximum span is 3.4M

the roof is to be slate, 150x47 wooden rafters at 600 centers.

ridge to wall plate is 5M

id like to know what to enter in these boxes? can anyone help me or does anyone have a calc for this type of span

many thanks
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Old 10th July 2010, 10:07 PM   #2
Tony Bryer
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 829
Default Re: steel purlins, what do i enter?

Generally we don't like to answer this sort of question except to say that taking off loads is such a crucial part of the calculation process that you do need to be able to do this accurately if you're using our software.

In this case, assuming I have visualised the situation correctly, you need to calculate the roof load per square metre. The required load on the purlin needs to be entered in kn/m run - this will be your load per square metre x rafter length eaves-ridge/2.
Tony Bryer, Greentram Software Pty Ltd
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Old 6th October 2010, 11:09 PM   #3
Nick Jackson
Join Date: Dec 2008
Posts: 22
Default Re: steel purlins, what do i enter?

In addition to Tony's comments I would also add that as you are building in the UK you will need to add an imposed load for wind/snow in accordance with BS6399 - normally this would be 0.75kN/m2 or 1.00kN/m2, corrected for pitch (the imposed load is applied on plan) depending on site altitude. Also, don't forget plasterboard and insulation, watertanks etc.

A further complication you may face is that Local Authority Building Control Officers will probably not accept your calcs unless prepared (or checked/approved) by a structural engineer with professional idemnity cover.

I am based in South Wales and, as a practising structural engineer, I could help. Google Greystone Technical Ltd if you need assistance.


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Old 14th October 2010, 08:40 AM   #4
Tom Dawson
Join Date: Jan 2010
Posts: 13
Default Re: steel purlins, what do i enter?

Hi Nick

I don't believe that local authorities have the authority to refuse to accept calculations from a person who is not an SE, or from a SE without PI cover.

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