Steel beams for cavity wall

mfarrow · 15 Mar 2014

Hi

We're currently thinking about an extension, and I'm starting with the drawings to see what we can do with the space we've got.

Certain plans I've seen online state beams for cavity walls to be drilled and bolted 'at 1/3 span centres'.

What does this mean? Are the beams simply bolted together with say M12 bolts at 1/3 span? If so what does this serve? I would not think this enough to allow simultaneous deflection of both beams, if that's what it's for.

tony1851 · 15 Mar 2014

The beams are usually bolted together through the webs, with spacer tubes.

And you're right - for larger spans and loading, they won't allow simultaneous deflection of the beams, so any calculations for the beams cannot be done on the basis that they work together.

It's something that engineers sometimes specify, so building inspectors usually ask for them, so architects usually note them on the plans, but I doubt anyone could actually justify them technically. Complete waste of time if you ask me.

RonnyRaygun · 15 Mar 2014

It is possible to join the beams in such a way that they work as one. One way is to weld a piece of channel to the web of the one beam, and bolt through the channel to the web of the other beam with two bolts.

More common to design the beams separately, designing the one for the more heavily loaded inner leaf and the other for the less heavily loaded outer skin.

It's still simpler if the same depth beam is used in both leaves, although the beam weight can be decreased in the outer leaf.

tony1851 · 15 Mar 2014

RonnyRaygun said:
It is possible to join the beams in such a way that they work as one. One way is to weld a piece of channel to the web of the one beam, and bolt through the channel to the web of the other beam with two bolts.

.

Yes, that would work as one, though at the end of the day it might be cheaper to put an 8x8 column section up with a wider plate on top (if they could lift it, that is!).

RonnyRaygun · 15 Mar 2014

tony1851 said:
RonnyRaygun said:

It is possible to join the beams in such a way that they work as one. One way is to weld a piece of channel to the web of the one beam, and bolt through the channel to the web of the other beam with two bolts.

.

Click to expand...

Yes, that would work as one, though at the end of the day it might be cheaper to put an 8x8 column section up with a wider plate on top (if they could lift it, that is!).

I agree, I've never done it myself, but someone told me that they were requested to do it by a BCO once...
Not unreasonable if one beam is not sufficient to carry the inner leaf alone.

mfarrow · 15 Mar 2014

OK thanks chaps, looks like my thinking was correct.

I've downloaded SuperBeam to play around with (don't worry I'll get them done properly approaching the time) and have been looking at different steels types.

Would I be right in thinking that PFC, UC and UB are most commonly available in the UK? What about SHS and RSJ?

tony1851 · 15 Mar 2014

mfarrow said:
Would I be right in thinking that PFC, UC and UB are most commonly available in the UK? What about SHS and RSJ?

Can't see any advantage in using PFCs over UBs.

SHS would be expensive; nobody uses RSJs any more (don't think they're rolled now).

mfarrow · 22 Mar 2014

In America, at least, it appears to be a bit of both: http://www.aisc.org/content.aspx?id=3786

Any ideas of order of magnitude for hollow sections before I start calling round?

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Steel beams for cavity wall

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