Knock out / steels / acrows

[23vc]

Having spent nearly 2 years building my 2 storey extension myself, it's finally time to do a knock out inside. It's the pretty common scenario of an existing cavity wall being knocked out to form an open plan kitchen diner. 2 pairs of steels each side of a 600mm ish pillar of existing wall kept in the middle.
Never done this before (I've put steels in but only on a new build where there's nothing above to prop up) so I'm after some tips or a sanity check of what I'm planning
- prop up inside with acrows and scaffold planks up against the joists which run into the wall, about 2 foot back from the wall
- prop up outside with strongboys above where the steel's going in
- use a stihl saw to cut the outside brickwork out
- knock the inside brickwork out level with the bottom of the joists
- push the new steel on the inner leaf up against the bottom of the joists with more acrows
- put the padstones in, let it go off
- pack with slate or shims on the outside to make sure no gaps and point up, let it go off
- take out all the props
- can you do inside leaf completely before starting outside, to save on the number of acrows you need?
Sorry, that's a bit of a ramble, but any critique of it very welcome as always!
Cheers
John

 

[catlad]

Accro's make sure you put some screws in the top
of the scaffold plank to stop them falling out when you
are winding them up.
Especially if your working alone.

 

[23vc]

Thanks will do

 

[noseall]

- can you do inside leaf completely before starting outside, to save on the number of acrows you need?

I wouldn't say so, no. Less wriggle room whilst inserting the inner fella and they need matching up to bolt together.

Get an extra couple of Acro's to put under the steels so that you can do the padstones.

 

[23vc]

Cheers. I’ll assume the rest of the plan is vaguely ok if I don’t hear otherwise.

 

[noseall]

Cheers. I’ll assume the rest of the plan is vaguely ok if I don’t hear otherwise.

 

[Notch7]

Accro's make sure you put some screws in the top
of the scaffold plank to stop them falling out when you
are winding them up.
Especially if your working alone.

That cant be emphasised enough - winding up one acrow can loosen another and a falling acrow can kill.

You need to do the work in correct order, or you will get stuck. Usually you need to get the steels on the genie first up tight to the wall, then the strongboys in place.

If you are using a genie lift you might need fork extensions. Sometime you need to knock out a few bricks a floor level so the lift can be pushed forward far enough.

 

[23vc]

Cheers notch, not using a lift. Using ‘volunteers’

 

[23vc]

Done half of it today, cheers for the advice. Just need to let the padstones go off, not sure if I can take the props out tomorrow or if it needs a couple of days?
Edit: minimum seems to be 48 hours, so they ain’t coming out tomorrow. Glad I checked.

 

[tony1851]

I wouldn't say so, no. Less wriggle room whilst inserting the inner fella and they need matching up to bolt together.

Get an extra couple of Acro's to put under the steels so that you can do the padstones.

Why bolt them together?

 

[noseall]

Why bolt them together?

Because welding them in situ is a pain in the erse.

 

[tony1851]

I would agree that site welding once the beams are in position would be impractical at best and probably unreliable and a fire risk.

By bolting, the aim is obviously to make the beams work together and so increase "strength" and reduce the tendency of slender beams to buckle sideways.
But connecting the beams by bolting with spacer tubes achieves nothing. I know that SEs specify it, Building Inspectors ask for it, good builders do it, but it's a case of "we've always done it that way" and nobody can explain why it should work.

The old steel design code (BS 5950 : 1990) specifically does not allow for fixing two beams together if the aim is to reduce buckling and/or enable load transfer between them. Also, google "LABC: Don't just bolt your beams together!" - an interesting read if ever your local bco demands bolting.

 

[noseall]

I've often asked what it achieves in terms of where you would be if the beams just rested along side each other. I've argued that the walls are already linked together with tie wires etc.
We haven't always done it that way either. My old gaffer didn't used to (or wasn't asked to) bolt them together. I do find it hilarious the differing requests of bolting arrangements from varying SE's for similar situations.