Good point! We can lower the ceiling slightly to accommodate a few more cm.
Steel beam sizing
- Thread starter twillmo
- Start date
Good point! We can lower the ceiling slightly to accommodate a few more cm.
interesting read which lead this anorak to a thread dated Aug 2013 which some of you contributed to which was also interesting. Are you converted to the folding wedge philosophy yet Woody?
Aug 2013 ref a bit open ended, long time ago so probably forgot so here is actual thread Some movement during extension work-ok? | Page 2 | DIYnot Forums
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Thanks for sharing, interesting comments and concept - but in reality would you specify a beam and effectively ignore the dead load deflection in your design based on the presumption that the builder can properly preload the beam?
Would you expect the average builder to be familiar with the concept of preloading with wedges, and if not, to read and follow a method statement rather than just banging the beam in how he always does it? I wouldn't!...
@jks7492
Fair points; for a small span of -say- 3m in an internal wall, the way most builders approach it by just banging the beam in works most of the time.
But when you start looking at longer spans, you know that deflection increases rapidly for a given section and it's then that problems arise, usually resolved by bigger and heavier sections - then cranes or splices come into the mix.
In the LABC publication I referred to, one of the contributors claimed that, in domestic work, you only need to consider bending and live load. I would question that because you could theoretically put in a 152UC on a 6m span, pre-loaded with wedges and when it ends up looking like a banana, tell the client its ok for bending and live load.
On long spans, we do need to advise builders of the need to pre-load the beam to reduce the risk of cracking upstairs. I recently did a 7.5m span with a 254 x 254. But the builder used the bang-it-in approach (despite being advised what to do beforehand) and of course the back wall and bedroom/bathroom floor followed the beam south. Cue solicitors............
Fair points; for a small span of -say- 3m in an internal wall, the way most builders approach it by just banging the beam in works most of the time.
But when you start looking at longer spans, you know that deflection increases rapidly for a given section and it's then that problems arise, usually resolved by bigger and heavier sections - then cranes or splices come into the mix.
In the LABC publication I referred to, one of the contributors claimed that, in domestic work, you only need to consider bending and live load. I would question that because you could theoretically put in a 152UC on a 6m span, pre-loaded with wedges and when it ends up looking like a banana, tell the client its ok for bending and live load.
On long spans, we do need to advise builders of the need to pre-load the beam to reduce the risk of cracking upstairs. I recently did a 7.5m span with a 254 x 254. But the builder used the bang-it-in approach (despite being advised what to do beforehand) and of course the back wall and bedroom/bathroom floor followed the beam south. Cue solicitors............
As in the beam that I checked that I mentioned earlier in the thread. The span was around 8m and the live load deflection was within the limits of span / 360 (22mm). Dead and live load deflection was over 50mm whereas span / 250 would limit deflection to 32mm.
Even allowing to take up 50% of the deflection with the preload, this would still leave another potential 25mm of deflection, which still has the potential to lead to significant cracking in the wall above.
Plus, as you say, you will have a very noticeable sag that will have to be carefully hidden in the finishes.
Another concern is the potential springiness of the beam under live loads. Hopefully not too much of an issue considering the usually small proportion of live load (in domestic situations anyway), but in certain situations that too has potential to cause problems.
I didn’t design this one - I only checked it. I can’t remember what section size was used but I think it was a smaller 203 UC, pretty sure it wasn’t any bigger than a 60.
Anyway, they ended up with a post somewhere near the middle at the end of their kitchen island.
I’ve done a couple of similar ones recently. One was even longer and they insisted on a single beam - it ended up being a 305 UC something…
I don’t know if that one is in yet - going to be a fun job for the builder and will also need a splice which could have its own issues.
The other one the client was happy to have a frame in the middle splitting the span and ended up with 203 UCs for the beams and frames.