steel purlins, what do i enter?

[gehngus]

Hi.
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

[Tony Bryer]

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.

[Nick Jackson]

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.

Regards

Nick

[Tom Dawson]

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.

Tom