steel beams for thick wall. 1

[Wilko78]

Hi there,

I'm based in uk and have done some calculations to size beams to replace a load bearing stone wall

Wall thickness is 530mm so approx 500mm stone/mortar wall excluding render.

I have sized 2 off 203x203x 46 uc beams. This only comes to 406mm total width.

I'm not sure whether I should specify 250mm wide top plates for each beam (totalling 500mm) to ensure full contact between wall and beams. Or whether the 100mm overhang (spread over 33mm either side of each beam) is acceptable. I can find no guidance in specifications for this.

Would I be able to use a top plate if I could get away with 2 times smaller 153uc beams, as these would be much narrower.....

Any thoughts? apologies if this is a simple one, but I cant find the solution in any of my books or online.

Thanks in advance.

 

[jayrod12]

The canadian codes limit masonry supporting elements to L/480 vertically with a 20mm max. It further goes on to limit glass block walls to L/600. I would expect solid stone to be as brittle as glass therefore I'm with everyone else, you should strive to halve (or almost) your current deflection.

 

[Wilko78]

Hi guys,

OK, I must apologies, I hadnt linked the L/688 to the 8mm for my particular span. I was looking within the document for the actual ration L/688. I do appreciate the support (pardoning pun) you guys have provided.

Well the 8mm is certainly something new to me, with my 15mm deflection I'll take a look through and see what can be done as i'm about double the guidance in that document. Both the British Standards and the Eurocodes dont mention a specific value for deflection. However I am always learning and certainly am not going to ignore good technical guidance. particular where safety is involved.

406x178x74 meets the deflection requirements of 8mm (7mm deflection).

sequence of construction I would leave to the builder, however as an engineer I should "design it to be built".

my preference and my guidance on the drawing would be to lift one beam in at a time. resin anchoring first beam to a padstone and allowing to cure. padstone will be set on the existing 530mm thick wall or possibly new engineer brick column if builders find loose masonry.

repeating for next beam. I was going to use CHS spaced at 600 centres along the length of beam to maintain uniform installation. however the stiffeners would negate the need for these. I do like that detail and would probably suggest it.

I have a suspicion that a deeper beam will be too much for the client (head room) and that the compromise will be a shorter opening....

I've been extremely conservative in the load assumptions, but with old stone walls, I'd rather not assume a nice simple loading scenario and two beams supporting weight provide the bearing capacity which will allow me to sleep at night.

I want to minimise site welding, so perhaps have the top plate tack welded to the top of one beam prior to installation. then other beam sit underneath that plate....

 

[KootK]

Will sequence be:

1) Install one beam.

2) Remove stone below opening.

3) Install other beam?

I'm trying to establish whether or not there will be a case where only one beam will be supporting the stone for a while.

I guess that I'm also not clear on how the top plate would be installed if the beams went in one at a time.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Wilko78]

I was thinking that Acroprops and "strong boys" would be used to support load, while enough of wall is demolished (and piers built) for the new beams. Beams would be installed one at a time. Once ready, the strong boys would be removed one at a time, and the gap packed out in sequence.

The two beams offer support across the mean of the wall thickness. I dont feel comfortable assuming that the load will be directly beneath the centre line of wall, so full wall thickness support is needed.

By assuming this I suppose I could have halved the loads, and looked at reducing the beam depth, however as has been pointed out by those that responded (thanks again) I needed to pay extra care to the deflection in masonry. Plus I am a Civil Engineer by training and we always like to include alot of redundancy

I will need to speak with client and ask if the reduction in head room is acceptable. The architects drawings show no elevation in their plans.....SO its either reduce head room or reduce opening width. Even if he was accepting of the reduction in headroom, I dont think there will be enough masonry left above the supports (due to roof line) to be acceptable regardless.

Do you think a top plate would be acceptable or just a little too much overkill?

 

[tony1851]

Hi Wilko,

I know this is an old thread but just wondered how you went on with this, as I did a very similar job a couple of years ago; also UK-based.
House was an old Yorkshire farmhouse, walls were a little less than 500 thick - ashlar/rubblecore/rough stone internally. I used two 203x203x52 with a few separate plates above - the 203s because of limited headroom. Span was 5m. The plates were to stop all the rubbish from the core falling through. There was slight cracking in the external wall, but of little consequence because the place was completely gutted and it was easily pointed up.
In your case, I suspect you may have excessive deflection - consider 203x203x60s - 47s are a bit weedy.

 

[Wilko78]

Hi Tony1851,

after taking some guidance from the responses I received, particularly with respect to the deflection limits, I ended up with the following:

limiting the opening to 4.8m. this was more to do with the available clearance above the beam (conflict between roof line and the new beams).

2 off 356x171x67 UBs
with 3 off 203x133x25 UB stiffeners

10mm plate welded to top of beams 500mm wide, to provide full support accross the cross section of the opening.

padstone was also selected.

Interesting to hear that I'm not the only one working on these large stone wall projects. I've had a similar one come in, with a 600mm wide opening. I've had to spec 3 beams to provide continuous support across the wall on that project.