RSJ's, cavity trays and spacer bars.

[bmb4cjt]

Hey guys,

Think I know the answer but having 2 RSJs placed for extension and just wanted to check stuff before everything is set and the strong boys are taken out.

They've not been finished but double checking; cavity tray above needed? and spacer bars needed or just bolting together with threaded rod sufficient.

Also as it is 2 RSJs bolted together so they're on the same level, rather than welded bottom plate leaving a step down to the external leaf on cavity. Will fixing the DPC sheet to inside of the internal leaf suffice or really need to take out the block above and bed it in?

Cheers

 

[^woody^]

Whether a cavity tray is required depends on what it's above the beam.

Whether spacers are required depends on how wide the beam and cavity wall is.

I don't understand the reference to DPC

 

[tony1851]

Spacer tubes and threaded bars used to join webs together are as much use as a chocolate teapot. They do not enable the beams to work together as one - infact the Code of Practice for steelwork design prohibits this practice.
Yet architects and SEs specify them, building inspectors ask for them, builders put them in, but none of them can offer any explanation as to why?
Anyway, try this for some bedtime reading........
https://www.labc.co.uk/news/beware-don’t-just-bolt-your-beams

 

[bmb4cjt]

Cheers guys, @tony1851 I read that and made me think it wasn't that vital but just they'd been bricked in without spacer bars and didn't want to get them pulled up later on if BCO comes round. So although not really needed or necessary best put them in to prevent knock back later on?

Would you chaps think it would be wise to put a cavity tray in mid wall in this scenario? We've an external wall which ends up internal lower down (quick sketch picture lower attached)

 

[bmb4cjt]

@^woody^ quick sketched the scenario we have above the bifold with 2 rsjs rather than the usual I beam welded to bottom plate. SE initially wanted a RHS welded to resist torque from wall but was crazy expensive so compromised this as we're rendering the outside anyway so will concrete board the beam.

Is it enough to cavity tray and pin the internal skin of existing wall above (b) or ideally sat in bed of brickwork (c).

 

[^woody^]

C

 

[bmb4cjt]

Cheers @^woody^

What are your thought on the other wall cavity tray? Needed or am I going OTT

Would you chaps think it would be wise to put a cavity tray in mid wall in this scenario? We've an external wall which ends up internal lower down (quick sketch picture lower attached

 

[tony1851]

So although not really needed or necessary best put them in to prevent knock back later on?

Why put them in if they are not necessary? aka as jumping through hoops - bonkers!

See this from BS 5950 for steelwork design:

 

[^woody^]

Why put them in if they are not necessary? aka as jumping through hoops - bonkers!

See this from BS 5950 for steelwork design:View attachment 240040

Are you selectively quoting there, Isambard?

That quote seems to relate to lateral restraint, but the purpose of bolting independent beams together is so they act as one single beam in a load sharing arrangement.

 

[tony1851]

It two beams are to be fixed together so that they act as one in terms of preventing lateral torsional buckling or deflection, it will not be achieved by a few lengths of spacer tube and some threaded bar from B&Q. That is why the design Code advises against that assumption.

For two beams to work as one, they need to be connected rigidly by welding (difficult on site) or by a combination of shop-welding and site-bolting with correctly designed slip-resistant bolts. Although not impossible, this is difficut to achieve with two 'I' beams, but easier with two channels back-to-back.

 

[^woody^]

Bolts join beams and columns quite well without welding. The same principle plus a suitable tube spacer to pull the beams together, works on the same principle for two beams in this situation.

 

[tony1851]

Bolting beams to columns is nothing like bolting two parallel beams together with spacer tubes and threaded bar and expecting them to work as one. It's been likened to two drunks trying to prop each other up.

(Where's jeds when you need him.....?)

 

[^woody^]

(Where's jeds when you need him.....?)

You've sent him to sleep

 

[Notch7]

Spacer tubes and threaded bars used to join webs together are as much use as a chocolate teapot. They do not enable the beams to work together as one - infact the Code of Practice for steelwork design prohibits this practice.
Yet architects and SEs specify them, building inspectors ask for them, builders put them in, but none of them can offer any explanation as to why?
Anyway, try this for some bedtime reading........
https://www.labc.co.uk/news/beware-don’t-just-bolt-your-beams

thats interesting, Ive certainly had SE specs with spacers on it....and followed it many times, I cant say ever questioned it either.

 

[bmb4cjt]

Hey @^woody^ and @tony1851

Got the builders to put the dpc in over the steels (although advised I'd read too much on google and some houses don't have them and they don't have damp problems) they have but not quite as neat as I'd liked.

The steel continues out the side of the wall resting on padstones outside to create the opening for the bifold. I'd have thought they'd have run the stepped 450mm the full length but looks like it's been ripped where the current wall terminates. Should I be bothered by this gap or am I being OTT (above the steel is the first floor bedroom so the cavity wall continues up and the house is rendered).

Also should the cavity be being opened to continue the wall looks like it's been bricked up and they're using wall starters on the return of the outerskin? Imagine this'll cause a cold bridge?