20 Mar 2018
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United Kingdom
I’m creating an opening (Proposed 1700mm wide) in my rear external ex solid wall (it has been rebuilt using cavity with a width to match existing, 230mm, just in ground floor and half length of the wall). There is a small window and a 900mm door in that wall panel I want the opening in for the French door, the opening runs from the centre of the window opening to the centre of door opening. I ordered the RSJs (2no 178*102*19) 2800mm wide, so that its ends bear 150mm on the right and left side of window and door respectively. Long story short, the bearings will be quite long, 550mm on either side after the door and windows removed and new walls built to fill the sides of the French door. If you run the calcs, even 2.6 n/mm^2 bricks will be okay under te RSJ. However to be on the safe side, I’d like to use some sort of pad stone, and the best I can go for to match the wall outside is solid engineering bricks. However, they are only available in 65mm while the existing brick used are 73mm with thick joints to match the original 75+ bricks, so using 3 courses of 65mm e.solid bricks will be quite noticeable. Another option is using concrete padstones and then facing it with brick slips, but that means shifting them inside by ~20mm to fit the slips flush with the wall. Also bearing plate is a no no, as it will double the joint thickness between the bricks that will go inside the RSJ and the bearing bricks.

Can someone please advise on the best option above or an alternative? Only obstacle here is that it has to be an option that will match the exiting wall look outside and avoiding rendering.

So a 230mm wide wall with 30mm cavity. Factored loads are calculated as 41 kN/m, which is roughly 19 kN reaction at each bearing (4x).

One last thing, any point of rebuilding the sides of the French door using cavity walls, cause at the end, only 665mm and 1000mm long cavity wall will remain either side of the French door? One side is the corner and the rest of the other side is 30s solid wall.

See attached a rough elevation sketch using iPhone notes.



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External wall? Why are you not using a proprietary Catnic type lintel?

Surely the visual aspect of a padstone externally, is the least of your worries considering you will have a 2.8m long steel beam to disguise also. Lol.
Yeah, swap both for a single or the one for a single external lintel. No more worries.
Thank you guys for coming back to me. I agree with you too. I had a look at cantnic or similar lintel provider products, but the capacities given on their websites didn’t seem enough, unless I got for the i beam with a welded under plate lintels, that is massively expensive. I could have fabricated a similar (203UB or 178UB with a welded under late and stiffneers at certain spacings) with half the price and even cheaper than the 2 178s, but this was thought by, some of my senior engineer colleagues, not satisfactory. So I went for the 2 braced 178x102x19s, decent price (£200ish) and easy to handle. They are purchased now and I have to conceal them some how ...
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What load could you have over 1.7m that a standard lintel can't take, or can't at least be taken to the inner leaf? And how are you going to hide an ugly steel beam with something that't not at least as ugly? Brick slips? What a palaver.

Now is the time to ditch the steel and do it properly with a lintel
Your 'senior engineer colleagues' should go back to college if they come out with nonsense like that on only a 1.7m span.

PS Genuine question: why did your colleagues not think a UB with a welded plate would be OK? 1.7m is a v. small span. Having an exposed UB on an outer skin is visually, structurally and environmentally a failure.
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I would just get a lintel and forget the steels. it would cost more in all the faffing about to use the steels and you will end up with a job you aren't happy about.
I got an equivalent of a CG50, 2.1mtrs long for £65+ VAT to go over a 1.7mtr opening.

I'm not sure if they do a CG30 for you?
In my colleagues defence, I didn’t tell him about the stiffners and a told him of a wider opening then.

I have contacted the steel fabricators and they quoted me ~£100 to weld a 6mm plate to under one of the RSJs.

Catnic recommends a box lintel (BHD100) for inner leaf and an angle lintel (ANG/21D) for outer leaf.

I think the RSJ with the under plate will be the best option. But I will look it up further tonight.

CG50 won’t work for me as my cavity is only 30mm or less.

Thanks again guys.
As shown in the photo
Impressive, but an extra expense and unnecessary in a domestic context.

As the beam will be asymmetrically loaded with respect to the shear centre, there will obviously be a bending moment and therefore torsion induced in the I-beam, which needs to be allowed for on longer spans.
But those stiffeners would do little if anything to reduce the torsion-effect. Theoretically they will reduce deflection of the plate in the xx axis, but for a 6mm plate, 100mm welds every 300mm would be adequate.

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