RSJ above bi-folds to support roof joists

3 Jul 2017
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United Kingdom
Hi, I'm looking for advice on installing an RSJ to support some joists above bi-fold doors in a garage. The building has 6x2 joists running 5.5m front to back on hangers on an 8x3 joist which runs above the bi-folds which are 4.2m wide. I'm looking to add some additional "insurance" support just inside the bi-folds by way of a 4.5m steel underneath the joists and wondered what uprights I should use. I was thinking of using 8x3 C24 timber stood vertically at each end (or even two 8x3's bolted together at each end), but have read conflicting opinions on standing a steel on timber uprights.... Any thoughts....?
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Well if its brick built I would knock holes in the wall and site it there.
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Thanks for the input Catlad. I did consider a flitch plate and having spoken to the steel place today, I'm going with a 152x89 rsj. The rsj is actually a little cheaper and less involved to install than the flitch plate.
Unless there's somone here that's not only conversant with timber buildings, but also your particular design, then I suspect you need to go back to the original builders/designers. You don't seem to mention as to why you're doing the job (insurance doesn't adequately cover it), are the bifold doors already there - in which case why do you feel the need to reinforce what would be an existing 8x3 beam.

You would need to at least use oak to support a steel beam, and certainly larger than an 8x3, more likley 6x6, but wood shrinks (minimally along it length though) as it dries, so steel uprights would be better, but will the foundations support them, or would you need to add additional reinforcement for the uprights; and the reinforcement would very likely be needed for any upright to take the additional loading and support.
Thanks Doggit, It's a fairly basic timber structure on top of a single course of dense concrete blocks. The bi-folds are now in place and the reason I'm doing it is paranoia - I'm simply looking to back up the 8x3 beam - there's some valuable cars in there! The steel will be supported on steel uprights - acrow props initially (although they may just stay there...).
Acrow props will not do the job whatsoever. As it's an insurance job (so to speak), I'd be inclined to add a support in the middle of the 6x2's (which is possible where you were going to anyway) and this would just need to be another 8x3, or even an 8x2 C24; but can you knock a hole into one of the walls, with enough of a gap in the cavity, to then slide the beam back into the other wall. Taking into account Catlads idea of a flitch beam, you might be able to use a pair of 6x2's with a plywood or steel centre.
I'm curious- why wouldn't the acrow props work? Surely they're not going anywhere...? Sadly it's not possible to put the support in the middle of the 6x2's.
The acrows are effectively just holding the beam up by tension, but you're also trusting yours to support not only the beam, but the floor above it; and that makes them pretty poor insurance. Not so good when you take the whole scenario into account. And heaven forbid someone knocks them by accident; then you've got a lawsuit on your hands. But is it possible to provide additional support anywhere along the length of the ceiling.
The props would be supporting the rsj at the same points at which it would be supported if it were in / on the wall ie at each end. There is no floor above. It's "just" a garage so I would secure the props in place- one will be in the corner and the other at the other end of the bifolds (pretty much against the wall either side of the bifolds). There would be no chance of them being knocked. There is no opportunity to support the beams elsewhere and that's not the area of concern. It's the 8x3 above the bifolds that is the "weakest link" so I'm just looking to put a steel in place behind it to "assist" and prevent any sag above the bifolds.
Okay, it's a garage, and so I can assume that there's no room above it, so that would be why you've got 6x2's over 5mt, only supported on a 8x3 beam at the front. If you're looking to reinforce the 8x3, then I'd be inclined to look to provide the support on the back of it, and support the additional beam from inside the garage, so time to post a picture of the front, and the ceiling inside the garage, and the rear of the bifold doors if you can.
If you are happy to leave the props in place then there is not a problem
with that, just make sure the rsj is fixed to the timber beams and fix through
the top of the acro's into rsj with the holes provided.
I would just back up the existing 8x3 with either another or an 8x 2 bolted and dog tooth washered together. What is the roof covering

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