Acrows and needles, and installing goal post steelwork.

[Ron-ski]

I'm soon going to be fitting goal post steelword to the rear of our house, whilst I've fitted steel beams before it's never been to this scale, except when I helped the builders over 10 years ago take out the wall in our kitchen which was of similar size.

The opening is going to be 3500mm wide, but due to the columns requiring bolting to the foundations the actual brickwork removed will be wider at foundation level, which is 750mm below DPC.

I plan on using 5 pairs of acrows, spaced at about 810mm centres along the opening, using 47 x 125 x 1200 C16 timbers in pairs as the needles. The outer acrows would be 300mm away from the building, with the inner acrows 400mm away from the wall. Acrows will be screwed to the sole plates and head plate, and needles.

The internal floor is concrete, externally I need to dig down 750mm to the foundation, so the soil at this depth should be pretty well compacted, but sole boards will be used inside and out.

The house is a two storey house with gable end above, 60mm cavity, total wall thickness 265mm, built in the 70's.

Would the above be sufficient to hold the house up whilst the wall is removed to allow fitment of the steelwork?

Would the side return wall require any bracing?



I presume it would be better to install the crossbeam and hold it in place with a couple of acrows. Then remove remove enough wall to hang the columns from the beam, drill the base plate fixing into the foundation and install the studs, then grout under the columns, and once set tighten the nuts?

Edit: Beam will be placed by the wall internally prior to putting the acrows in - best I not forget or it could get rather difficult!

 

[tony1851]

Why on earth do you need a goal post if the opening is only 3500??

 

[Ron-ski]

@tony1851 Because the external return to the corner is only 480mm, so the brickwork is tied into the post, otherwise the corner could flex in strong winds, and potentially be blown out.

 

[^woody^]

the corner could flex in strong winds, and potentially

Have you been listening to engineers?

Perhaps the beam and roof hold it. Or perhaps the wall does not get blown out just like every single wall without buttressing had not been moved by any wind before about 15 years ago when this nonsense was bought in. And just like garages which seem to be exempt from this rule and from high winds.

Anyway, one acro per side per m is normally enough.

 

[tony1851]

Clearly the SE has explained this to you in simple, lay terms.
So why not go back to the SE and tell him/her in equally lay terms;

"the overturning force of the wind on the pier will be countered by the 'pre-compression' on the pier caused by the weight of brickwork above. There will also be other walls in the house parallel to the wind, which together will provide sufficient lateral stiffness to the house as a whole."

Frankly, your SE is lazy. It is easier for him/her to pull up a spread sheet, input a few numbers, and give you a print-out showing masses of useless figures
and symbols, and charge you for the privilage. The problem is that you - the client - has to pay well over the odds for a frame which is - frankly - unnecessary.

A suitably-designed beam - such as an I-beam with a welded plate, or even an off-the-peg lintel, would suffice for the load from above; and appropriate figures to prove stability of the side wall under wind load, should be all that is necessary.

 

[Ron-ski]

the corner could flex in strong winds, and potentially

Have you been listening to engineers?

Perhaps the beam and roof hold it. Or perhaps the wall does not get blown out just like every single wall without buttressing had not been moved by any wind before about 15 years ago when this nonsense was bought in. And just like garages which seem to be exempt from this rule and from high winds.

I've been listening to my own common sense, it may not get particularly windy here in the south east, but I've lived through two very bad storms, one in the late 70's and the other in 1987, and there's been others since. Surely you remember seeing picture on the TV of houses with wall's missing, and gable ends, only recently a school was closed because a wall fall down (probably due to shoddy workmanship), I suggest you open your eyes! I'd rather not assume the wall will be strong enough, also being an mechanical engineer myself I can understand how the wall will be weakened. I'd rather not take the chance with my home (or anyone else's for that matter), which has my family in it thank you!

@tony1851 Perhaps my SE is lazy, I've gone back and asked if there is any alternative and they've said no.

Besides that wasn't the question, I was hoping for some people with experience to answer my questions about the acrows and needles, which @^woody^ did partially answer.

 

[tony1851]

Perhaps my SE is lazy, I've gone back and asked if there is any alternative and they've said no.

Well, they would, wouldn't they, because they would look foolish if they turned round and said "Oh, we've just realized there is a cheaper, easier option which is just as good".
Don't get me wrong - I'm not suggesting anyone should compromise on structural stability. But the diagrams and dimensions given in Approved Doc. A are really just 'rules of thumb'. They can make many SEs lazy, when they should really be creative to see if other approaches work.
Anyway - that aside - good luck with your project!

 

[Ron-ski]

@tony1851 Appreciate what you are saying, but without going to another SE with another fee I doubt I'll ever really know if there is another viable option.

What's you're opinon on the the needles, two x 5" x 2" C16 adequate enough, with 5 pairs of acrows?

 

[tony1851]

I think those would be fine. But have you considered using Strongboys - with these, you have more space to work.
(the inner row of props here are just supporting the floor joists, which run onto the wall).

 

[Ron-ski]

Thanks, I have considered Strongboys, but from what I've read they can't take as much weight and are not ideal for cavity walls, and I thought they had to go closer to the wall so gave less space.

 

[tony1851]

They can be used for cavity walls - the house in the pic is a 1920s house with brick/cavity/brick; yours looks like a modern house which will have lightweight block internally?
But it's down to whatever you feel comfortable with.

 

[tomfe]

View attachment 102263

Wow you need your beard cutting, that reminds me of a dog next door used to have

 

[^woody^]

(the inner row of props here are just supporting the floor joists, which run onto the wall)

... which are in turn holding the wall up?

 

[tony1851]

In practice the floor joists will of course be supporting the inner skin - builder was just using the Stongboys as overkill (presumably).

 

[Ron-ski]

They can be used for cavity walls - the house in the pic is a 1920s house with brick/cavity/brick; yours looks like a modern house which will have lightweight block internally?
But it's down to whatever you feel comfortable with.

Inner wall is light weight block, not Thermalite though. I'll feel most comfortable using needles and acrows, I know everything is well supported then.