Anyone able to advise on using an inverted bowstring truss for mezzanine floor supports

[Chris HB]

OK, I’m wondering if this is even possible there, so please bear with me on this… not a huge span (4.500mm), the max depth in the centre is around 360mm, and the max depth at the ends of 115mm. Would this be possible? 

Edited May 2 by Chris HB

[George]

If you mean can you hang a mezzanine from roof trusses then almost certainly not.

 

If you mean can you use an inverted bowstring truss as a mezzanine beam then yes, so long as it is designed (or is adequate if it is recycled) properly for the span and loading.

Edited May 2 by George

[Chris HB]

6 minutes ago, George said:

If you mean can you hang a mezzanine from roof trusses then almost certainly not.

 

If you mean can you use an inverted bowstring truss as a mezzanine beam then yes, so long as it is designed (or is adequate if it is recycled) properly for the span and loading.

sorry, yes, I meant as in supporting a small mezzanine floor! 

[Chris HB]

don't suppose anyone knows of a bowstring truss calculator or anything? 🤣

[George]

Best off contacting a local structural engineer. 

[Gus Potter]

On 02/05/2024 at 20:34, Chris HB said:

don't suppose anyone knows of a bowstring truss calculator or anything? 

Hi Chris. Had a look at the link to your blog... looks a great project... keep posting!

 

I'm wondering if what you have is really a true bow string truss in the Misson hall, it looks more like it could be what we would call a traditional raised tie truss. Once the amount of "raising of the tie" gets beyond a certain point they often rely a bit on thick walls to prevent some of the spread. What's the wall construction?

 

Below is a diagram of common prefabricated trussed rafter shapes which can be handy when trying to describe roughly what you think you have. There are many different types and variations of roof. Traditional roofs often work in a similar way but common ones are the King / Queen and raised tie.

 

I think I can see where you might be wanting to do re hanging a part Mez floor from the roof assembly. I take it the floor would fly past the windows so you have part of the window below the floor and part above?

 

You've got me thinking. There are a few things worth having a look at..but all this needs to take account of the location and material delivery. My Sister lives on one of the Islands.. some folk buy a camper van and use that to transport materials to the Islands. Be careful as if your van is sitting on the axle stops and you're all dressed up in you building gear Calmac (ferry operator) et al may ask to look inside and make you pay for a commercial vehicle.

 

Anyway within reason you could have a look at forming a ridge beam to run gable to gable with a bit of intermediate support to support the mez  floor. It would be a long beam thus not practicable to get to the Hall in one length. You could use short steels (that fit in your van)  and bolt them together.. messy. Another option is to turn this into a joinery excercise and see if you could form a parallel timber truss (see diagram below) on site to run gable to gable. You would form the connections with plywood gusset plates and a structural glue (Cascamite or similar). This is much more flexible as if you make a mistake it's easily rectified as you're using off the shelf timber and ply. 

 

The mez floor could be hung from this.. Your in the middle of the ocean so Architecturally a Nautical approach is a good approach? I don't know if you going for a traditional look or would consider a mix of old and contemporary?  Anyway say contemporary. I'm thinking tension wires may be a good option for hanging the mez floor. I've got a job on at the moment and I'm using wire assemblies to strengthen a roof truss that come as a kit as it's a small domestic project. The loads I have on this job are pretty small so I was looking for the thinnest wire I could get away with architecturally.

 

Have screenshotted a bit out my CAD file below and the web address is:

 

https://www.s3i.co.uk/fork_fork_tensioner_wire_rope_assembly.php#

 

Caveat.. I'm not affiliated to the supplier, don't warranty their performance etc. However a big plus point is they provide declared loads for their assemblies which we as SE's need to have and as the come pre assembled we don't then need to test them on site etc. Surprisingly the prices are pretty reasonable for small quantities and they deliver.. well hopefully they will when the Client buys them..

 

At some point is does look like you'll need an SE to guide you and make sure what you are doing is safe. As your on the Islands you'll need to stick to the book regulation wise or the locals will shop you if a newcomer, until you settle in an become resident.

 

That's it for now.. hope some of this helps.