Flitch beam help / feedback

[stu w]

Morning 

Any feedback regarding the flitch beam attached. 

If needs be I will get it checked by an engineer but needed some feedback first of all 

Lintel above a 2.4 m window single storey TF structure 

Cheers 

[JOE187]

Have you looked at Kerto Lvl as would think 2 x  195 x 75 bolted together would be easier than a flitch beam.

 

https://www.specifiedby.com/metsae-wood/finnjoist-i-beam/Metsa-Wood_Finnjoist-I-Beam_Brochures_Finnframe-Floor-System.pdf

[Mr Punter]

The timber will probably be 195 x 45.

 

I think it is good to centre the steel plate top-to-bottom so it doesn't bear directly on the timber above / below.

 

3 minutes ago, JOE187 said:

Have you looked at Kerto Lvl

I think this may be a struggle to source.

 

 

[stu w]

1 hour ago, JOE187 said:

Have you looked at Kerto Lvl as would think 2 x  195 x 75 bolted together would be easier than a flitch beam.

 

https://www.specifiedby.com/metsae-wood/finnjoist-i-beam/Metsa-Wood_Finnjoist-I-Beam_Brochures_Finnframe-Floor-System.pdf

Thanks for the link , but I'd rather make a flitch beam myself 

[FuerteStu]

Have you factored in the protruding nut and plate either side? 

 

 

[stu w]

3 minutes ago, FuerteStu said:

Have you factored in the protruding nut and plate either side? 

 

 

Yes I can make that work 

[Russell griffiths]

Why not just use an i beam and fill the webbs with timber to fix to and reduce the cold bridge. 

[stu w]

3 minutes ago, Russell griffiths said:

Why not just use an i beam and fill the webbs with timber to fix to and reduce the cold bridge. 

Did cross my mind , plus they would do the calcs for me 

[Russell griffiths]

1 minute ago, stu w said:

Did cross my mind , plus they would do the calcs for me 

If you went with something 120wide you could cover the outer face in ply to cover the top and bottom flange, for fixing to. 

[stu w]

1 hour ago, Russell griffiths said:

If you went with something 120wide you could cover the outer face in ply to cover the top and bottom flange, for fixing to. 

I will make some enquiries,  never really had much to do with steel

[George]

You've shown area loads but not the UDL on the beam itself. Has that been calculated?

[Gus Potter]

On 17/03/2024 at 10:22, stu w said:

Any feedback regarding the flitch beam attached. 

Good first try but I think you're out of your comfort zone here. Flitch beam design is a bit of an art and to execute this well you have to have a good understanding of how the timber, steel and bolts interact and the support conditions. To put it another way.. this sort of thing is not taught to graduate SE's doing a masters course at uni, it is a bit of a specialist subject.

 

Personally I like a flitch beam as they can be an elegant solution.. they are a bit "old school" but there is a place and a time for them and they can really suit the self builder / small Contractor, good for you having a look at this.. but it needs refinement.. well probably quite a lot! Yes you can get Kerto beams etc off the shelf but sometimes they don't have enough poke unless you make them bigger which defeats the purpose.

 

What you have drawn with the steel off the centre could introduce twisting effects not least.. to be avoided. The easy way it to centre the flitch plate and use timber packers to frame out the beam. Sometimes the makes a void that you can stuff a bit of extra insulation into.

 

At my end if I find a bog standard timber lintel isn't working I start to work my way up the timber grades. Ok we have C16 and C24 grades of timber. But a lot of Contractors I know are buying in prefabricated roof trusses and the truss folk use TR26 grade timber. Often I'll have a word with the Contractor and say... look we need 2/ 3 lengths of TR26.. get that tacked onto the order.. also a good timber merchants can rattle this up and buy well using their clout if it's part of a larger order. It may be that if push comes to shove TR26 could work rather than introducing a steel plate and the bolts.. the bolts heads clashing with other stuff etc.

 

Now if you find say TR26 is still not enough then you can go back to C16 but 63mm thick with a steel flitch plate.. this helps centre the flitch plate.. makes the twisting often go away. Your 190 deep timber is pretty standard but you're 5.0mm out on the machined size.. normally the actual size is 195 deep for the C16 and C24 grades. The TR26 sizes are a little different so watch out for that as the sizes are "bespoke" to the truss folk, not much mind but just be aware.

 

In terms of buildability... don't have the flitch plate on the outside.. bury it in the middle of the timber flitch beam and leave timber on the outside as this is much easier to fix other things to!

On 18/03/2024 at 09:52, George said:

You've shown area loads but not the UDL on the beam itself. Has that been calculated?

Yes, can't say much more at my end either until we have an idea of the load the beam is carrying.

 

On 17/03/2024 at 18:39, Mr Punter said:

I think it is good to centre the steel plate top-to-bottom so it doesn't bear directly on the timber above / below.

Mr Punter has highlighted an intrinsic and key point that is in the design code. The timber shrinks, the steel plate doesn't so that is why we make the steel a bit less deep (aim for 8 -10mm) than the timber. So it is the timber that bears on the support rather than the knife edge of the steel plate.

 

I mentioned earlier that flitch beam design is a bit of an art! Now buried in the design codes and design guidance is a tiny bit that says you need to check the grain of the timbers each side of the plate for the grain direction / orientation. If you have a timber joist often they way they are cut leaves timber on one side that is younger so it shrinks more than the older timber on the opposite side of the vertical face.. this causes the timber to "cup". For a flich beam with the plate in the centre you put the inside bit of the tree on the outside away from the plate so it cups away from the middle. The bolts on a flitch beam are staggered away from the horizontal centre line so that when the timber cups it doesn't split along the midline. Takes a bit of getting your head round all of that!

 

Ok to sum up.. Don't be put off by my technical comment.. rather.. think about it from a buildability point first, material cost / time, who is going to do the work and how you are going to fit insulation / plasterboard to what you have.. I kind of hope you're going to do this yourself as you have taken the time to think it through.. and you'll probably take more care and end up with a better job than a Contractor would do.. the result is you'll get do something that is supposed to do what you intended for the money yiu have spent.

 

Hope this helps.

 

 

 

 

 

 

 

[stu w]

9 hours ago, Gus Potter said:

Good first try but I think you're out of your comfort zone here. Flitch beam design is a bit of an art and to execute this well you have to have a good understanding of how the timber, steel and bolts interact and the support conditions. To put it another way.. this sort of thing is not taught to graduate SE's doing a masters course at uni, it is a bit of a specialist subject.

 

Personally I like a flitch beam as they can be an elegant solution.. they are a bit "old school" but there is a place and a time for them and they can really suit the self builder / small Contractor, good for you having a look at this.. but it needs refinement.. well probably quite a lot! Yes you can get Kerto beams etc off the shelf but sometimes they don't have enough poke unless you make them bigger which defeats the purpose.

 

What you have drawn with the steel off the centre could introduce twisting effects not least.. to be avoided. The easy way it to centre the flitch plate and use timber packers to frame out the beam. Sometimes the makes a void that you can stuff a bit of extra insulation into.

 

At my end if I find a bog standard timber lintel isn't working I start to work my way up the timber grades. Ok we have C16 and C24 grades of timber. But a lot of Contractors I know are buying in prefabricated roof trusses and the truss folk use TR26 grade timber. Often I'll have a word with the Contractor and say... look we need 2/ 3 lengths of TR26.. get that tacked onto the order.. also a good timber merchants can rattle this up and buy well using their clout if it's part of a larger order. It may be that if push comes to shove TR26 could work rather than introducing a steel plate and the bolts.. the bolts heads clashing with other stuff etc.

 

Now if you find say TR26 is still not enough then you can go back to C16 but 63mm thick with a steel flitch plate.. this helps centre the flitch plate.. makes the twisting often go away. Your 190 deep timber is pretty standard but you're 5.0mm out on the machined size.. normally the actual size is 195 deep for the C16 and C24 grades. The TR26 sizes are a little different so watch out for that as the sizes are "bespoke" to the truss folk, not much mind but just be aware.

 

In terms of buildability... don't have the flitch plate on the outside.. bury it in the middle of the timber flitch beam and leave timber on the outside as this is much easier to fix other things to!

Yes, can't say much more at my end either until we have an idea of the load the beam is carrying.

 

Mr Punter has highlighted an intrinsic and key point that is in the design code. The timber shrinks, the steel plate doesn't so that is why we make the steel a bit less deep (aim for 8 -10mm) than the timber. So it is the timber that bears on the support rather than the knife edge of the steel plate.

 

I mentioned earlier that flitch beam design is a bit of an art! Now buried in the design codes and design guidance is a tiny bit that says you need to check the grain of the timbers each side of the plate for the grain direction / orientation. If you have a timber joist often they way they are cut leaves timber on one side that is younger so it shrinks more than the older timber on the opposite side of the vertical face.. this causes the timber to "cup". For a flich beam with the plate in the centre you put the inside bit of the tree on the outside away from the plate so it cups away from the middle. The bolts on a flitch beam are staggered away from the horizontal centre line so that when the timber cups it doesn't split along the midline. Takes a bit of getting your head round all of that!

 

Ok to sum up.. Don't be put off by my technical comment.. rather.. think about it from a buildability point first, material cost / time, who is going to do the work and how you are going to fit insulation / plasterboard to what you have.. I kind of hope you're going to do this yourself as you have taken the time to think it through.. and you'll probably take more care and end up with a better job than a Contractor would do.. the result is you'll get do something that is supposed to do what you intended for the money yiu have spent.

 

Hope this helps.

 

 

 

 

 

 

 

Yes thank you very much for your feedback.  I am going to construct it myself as I have made a fair few flitch beams in the past from SE drawings, but many years ago 

I have forwarded all the relevant information and drawings to an SE who regularly designs flitch beams so will await his calculations/alterations I need to make , i will be interesting to see how far out I am from the initial drawings.

The 190 I use in the drawing is just purely because a stock item in c24 at my merchants , I did think about using thicker section either side with a steel in the middle 

Edited March 20 by stu w

[Gus Potter]

On 20/03/2024 at 10:29, stu w said:

will be interesting to see how far out I am from the initial drawings.

Probably not much.. depends on the loading.

 

Good to see you have made a few in the past, they are elegant in their own way and are one of the solutions in my toolkit.

 

For all.. in principle how they work is great for teaching material behaviour. We know that steel is stiffer and stronger than timber. But how do you how much load the steel plate carries and how much the timber? What we do is to recognise that as the timber and steel is bolted together then they must both bend by the same amount and thus we can work out how much load the timber and steel is carrying respectively.

 

The detailed design is quite complex, especially if using the Eurocodes. There is bolt slip, bolt bearing, timber creep and list of other bits to consider in all the calculation. The timber creep adds complexity. Over time the timber creeps.. like a ceiling in an old pub and this "relaxation" needs a bit of thought as the apportioning of the loading changes as time goes by.

 

Post a photo of the finished article!

 

All the best.

[stu w]

44 minutes ago, Gus Potter said:

Probably not much.. depends on the loading.

 

Good to see you have made a few in the past, they are elegant in their own way and are one of the solutions in my toolkit.

 

For all.. in principle how they work is great for teaching material behaviour. We know that steel is stiffer and stronger than timber. But how do you how much load the steel plate carries and how much the timber? What we do is to recognise that as the timber and steel is bolted together then they must both bend by the same amount and thus we can work out how much load the timber and steel is carrying respectively.

 

The detailed design is quite complex, especially if using the Eurocodes. There is bolt slip, bolt bearing, timber creep and list of other bits to consider in all the calculation. The timber creep adds complexity. Over time the timber creeps.. like a ceiling in an old pub and this "relaxation" needs a bit of thought as the apportioning of the loading changes as time goes by.

 

Post a photo of the finished article!

 

All the best.

Thank you I certainly will , I will get the calculations/design confirmation back Monday/Tuesday. 

20 years ago at university when studying the institute of wood science and technology course,  I went on to do a short 18 month sister course, structural design in timber ( yes very basic but gave me some insight ) . I have done the loading calculations with snow etc and hands up used some previous designs what I have made on site from structural drawings with similar spans

Very interested to see how mine compares with a structural engineers when he returns it next weeks .

Still lots to learn with so many variables as you say combining timber and steel 

 

 

Edited March 23 by stu w

[stu w]

On 18/03/2024 at 09:52, George said:

You've shown area loads but not the UDL on the beam itself. Has that been calculated?

I have calculated this myself but want to get it checked so it can used 

[Gus Potter]

1 hour ago, stu w said:

Very interested to see how mine compares with a structural engineers when he returns it next weeks .

Still lots to learn with so many variables as you say combining timber and steel 

Me too, not a day goes by where I don't learn something.. problem I have is that older I get the more I realise how much I don't know! I went to University at forty, best thing I did as it gave me the tools to teach myself.

 

Interesting background you seem to have. You're among kindred spirits here on BH, mind you be careful what you wish for.

 

Seriously though, if you've done a few of these before post some photos on how you did it, the tools you needed, what is going on at the supports etc.. that practical stuff.. so new folk can see how it's done properly.