Ideas on how to span a 10m opening

[Pigsfoot]

Hi,

 

I after some ideas please before i go to a structural engineer for guidance.

 

I am looking to build a pergola in my garden which will be 10mtrs X 6mtrs. The 10 Mtr span needs to be completely open so as to not obstruct a view. Initially i was thinking of a steel structure using a 152 x 152 I beam's forming a ring all around the outside sat on legs with another beam in the middle and infill with 3mtrs long timbers... basically a large flat roof design on legs.

 

I'm not 100% sure if the steels are big enough to span 10mtrs hence why i will get advice from a structural engineer but i started to wonder if there is another way to do this hence why i'm after idea's.

 

So far i have thought of maybe using Pozi Joists, Ladder frames, the steel structure.. i'm open to any idea really as long as it is capable of the open span i need. When built the whole structure will be clad so doesn't really matter what the frame actually looks like. Loading wise i guess i need to consider snow and also myself climbing up to sweep off the roof maybe.

 

The drawing shows my initial idea, ignore the 10.5 mtr span, its actually only 10Mtrs.

 

Thanks

ning the 10mtr width

[Temp]

Google says you can get green oak beams upto 12m but I'm not sure what size you would need.

 

You may also need wind braces.

 

"Instant Oak Beam Online Quotes - up to 12.5 metre sawn to size"

UK Timber Ltd

https://www.uk-timber.co.uk

 

https://www.uk-timber.co.uk/custom-cut-fresh-sawn-oak-beams

 

 

 

Edited August 15, 2023 by Temp

[George]

Is the roof going to be open or covered?

 

This is bread and butter stuff for an engineer. The main issue you'll have isn't the beam, which is trivial to calculate, but how to achieve lateral stability. If you need a completely open vista then steel moment frame is pretty much the only viable option.

 

Oak timber would not work at that span - it would need to be trussed to work and knee braces would be unlikely to provide adequate lateral stability.

[Iceverge]

 

Something like this I'm guessing but larger? 

 

That 10m span is going to be tricky with a flat roof. You're lightly to end up with a very thick roof section.

 

You could put a hollow core concrete plank up there at 250mm thick if you like the brutalist look. It would require crane access and substantial support and foundations however but it'd probably be cheap. 

 

More elegant perhaps might be a tensioned fabric sun sail. 

 

 

 

 

[Bonner]

There are steel or aluminium prefabbed trusses used for stages which will span 10m, can’t imagine they will be cheap though. If you don’t find a cost effective single span, a 100mm post in the middle would be a game changer

[Pigsfoot]

Hi All, Thank you for all the idea's

 

@George, yes the roof will be covered as it needs to offer shade. I'm fully expecting the roof to be something like 300mm deep but to be fair i'm looking for that type of look.. substantial.. the legs will be min 150mm box and i'm only stopping there as larger box section gets very expensive due to increasing the wall thickness also so i may pack it out with timbers as its being clad and just make them look bigger.. possibly match the roof thickness

 

@Iceverge, yes the first picture is what i'm looking to achieve but on a much bigger scale. I did speak to a manufacturer of those type of Pergolas but nearly had a heart attack when they told me a estimated price of around £72,000 ! The sail is a nice idea and we have had one before. The downside is you have to have at least one side which is very high to get the correct fall and still have the lowest side around 2.5 mtrs to be able to walk underneath. The other issue is no matter what you do to make sure you never get water sitting on it they always seem to go green and dirty.

 

@Bonner. I'l try to find some, are they the square type frames with the diagonal cross joints? I agree ( and pretty much everyone i spoke to also ) re the centre post but that would just ruin the whole look unfortunately... and although this is certainly a challenge i know it must be possible.. i guess if steel is the only way it comes down to how big ?

 

Thinking allowed... although the 10 mtrs span must to totally clear i could have 45 degree angle beams from the roof to the legs on the 6 mtrs sides i guess.. maybe that woudl help with stability ?

[Bonner]

https://www.lighthouseaudiovisual.co.uk/alustage--decotruss-quad-truss-straight-sections-128670-p.asp?_=&variantid=128860&gclid=CjwKCAjw5_GmBhBIEiwA5QSMxKV6vL-sDFllRQ4ihhcRtq3Tq_vdAa_dQFscuii-7RgTTHgZvapFohoCc2cQAvD_BwE
Something like these? Search for lattice beam 

[Mr Punter]

Steel frame will probably be the best option.  It could be erected with a lorry mounted hiab.  Is there decent access?