RSJ wider than blocks

selfbuildextension · 6 Sep 2020

I have a 146mm inner beam and a 133mm outer beam supporting a new cavity wall to be built on top

Can I set these so that they are 300mm edge to edge and sit the blocks flush with the front edge or do the blocks need to be centred on each beam? The beams are not going to be bolted together.

tony1851 · 6 Sep 2020

Your SE should have advised you.
If you set the blocks level with the edge of the flanges they will be off-centre from the web and there will be a slight torsional force on the beams; but if the span/loads are not too great, probably no big deal.

selfbuildextension · 6 Sep 2020

I've just laid my first two courses on the inner beam and then thought it wasn't right, looks like the drawings show blocks to edge on outer skin but centre on inner skin

It's holding 2.5m of cavity wall inner skin, first floor joists and vaulted ceiling/roof.

I guess I'm going to either have to redo or ask if i can get away with it.

23vc · 6 Sep 2020

Might be because inner skin is carrying the roof load, so that’s the one that gets centred on the (bigger) beam. I guess the outer skin beam could move to the right on the pic a bit but would push the hung rafters across too unless they got birdsmouthed over it a bit

tony1851 · 6 Sep 2020

For a 2.5m span, both those beams are Massive!

Your SE obviously studied at the Belt-and-Braces-Railway-Bridge-Girder-School-of-Engineering. Building the skins off centre for either of those beams will not be a problem!

Sleep easy

.

selfbuildextension · 6 Sep 2020

@tony1851 Span is 5130mm, I was referring to the height of wall on top sorry

tony1851 · 6 Sep 2020

selfbuildextension said:
@tony1851 Span is 5130mm, I was referring to the height of wall on top sorry

Ah, that explains the size of the beams.
Torsional forces will be bigger on that span, but in all probability you'll still be OK, as the factors of safety the SE has to use allow for some discrepancy and variations in workmanship.
Why not have a word with the SE just to check as he will be aware of the loads involved, and it's only a simple check.

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RSJ wider than blocks

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