Timber Beam Design Calcs 1

[ectm]

Hello,
Can anyone recommend where I can get free timber beam design software to design a simply supported timber purlin for a pitched roof? The load is 7kN/m and the span is 4m. I am proposing to use a 300mmx75mm timber purlin.

Thanks.
E.

 

[FSS]

Sounds like a simple calculation. Why not just do by hand?

 

[COEngineeer]

Just design it as if it were #2 rectangular (that will fit the circle).

 

[richardm]

I am always slightly worried when I see this sort of question, because if you can't do it by hand, perhaps you should be speaking to somebody who can.

That said ... as your question is posed in metric you might find it instructive to visit

http://www.trada.co.uk,

where you will have to register, and then visit Technical Information / Software Toolbox.

 

[xxpegasus11]

I agree with FSS and richardm. Is this a theory/student question or a real design? If you clarify perhaps we can help. Either way its a simple matter of calculating forces, no software is required. I assume you are asking about complying with code requirements/building regulation calculation? BS5268 Structural Use of Timber sets out the relevant clauses if you have a copy. Theres a number of textbooks with examples - Structural Timber Design by Kermani is one. All outline permissible stresses and factors. Building Regulations Approved Document A (freely available from

http://www.direct.gov.uk)

used to include tables for sizing purlins, now withdrawn from latest version but you may still be able to get 1992 edition and are now only available on Trada for members.

Are you loadings/span correctly calculated? Your purlin would fail code requirements on bending,shear and deflection.

 

[COEngineeer]

Oh, i thought it was a log beam. Yeah, simple calc. I know there is load reduction for sloped roof but I always design it if it were flat. You always check Live load deflection and total load deflection. This question does sound like a do it your self project question.

 

[RARWOOD]

Use a span table in the IRC.

 

[Lutfi]

Why are structural engineers asking for free software? I am really perplexed by this often appearing questions in this forum. Few questions and I really do not want to step on any ones toe in my feedback:

1. Even if one finds free software, how do you ensure its accuracy and methodology?
2. What is wrong with doing things long hand?
3. Are new and young engineers are out of touch with reality when it comes to performing hand calculations?
4. Does anyone in this forum want to use a structure designed by an engineer who performed his calculations on free software he found on the Internet and he had no clue how the software functions and what codes it uses?

Young engineers should motivate themselves to do calculations manually and then may be graduate to writing their own programs or buying a bona-fide and tested preprograms. Even at that, they must be trained on how to utilize the software.

I often wonder how many young structural engineers can perform moment distribution manually!

Just to prove my point, I came across an engineer who was using STAAD to design a concrete beam using lateral loads. Well, guess what? STAAD does not design beams for weak axis bending. If you do not believe me, check their technical manuals!!

I hope I got my point across.


Regards,
Lutfi

 

[brinkley]

From my understanding, a purlin is a architectural accent that protrudes from the roof structure like a cantilever. So how can a so called purlin be simply supported???

 

[dik]

Purlins are often simply supported secondary beams and may or may not have cantilevered ends, more likely not. If you can imagine a floor plate with the main beams (often called girders) supporting a series of secondary beams (often called purlins).

In bridge work, the main girders or trusses are those that support the span of the bridge. These can support secondary beams that span from edge to edge. These are sometimes called purlins. Alternatively, the secondary beams can support yet another series of beams that are sometimes called purlins.

With pre-engineered metal buildings, the main 'rigid' frames support smaller roof beams, these are often called purlins. The beams supporting the cladding for the walls are generally called girts.

Dik

 

[xxpegasus11]

I think the purlin he meant was in reference to a UK pitched rafter (US stick roof?). A purlin would be placed underside and as support to rafters to reduce rafter span. This purlin would then itself be supported usually by diagonal struts onto a bearing wall. The purlin could be simply supported, or if struts located away from free ends then cantilever ends. ( as would normally apply to a hip roof for instance)

All the same, a fairly simple timber beam calculation