Overly conservative design?

bsr · 11 Nov 2019

Hello

My SE has specified a 178x102 UB 19 for a one-wall knock through. Span is 203cm. I asked him about increasing the span slightly; he came back and said this beam was good for 250cm.

He also said that it made no difference whether the beam was flushed or butted to the joists as he had assumed the compression flange was unrestrained.

I'm wondering if this means the beam is over-specified and I might be able to get him to try something smaller? What's your view? I ask because I have 6" ceiling joists so a 152x89 UB 16 could be set flush in the ceiling.

Would you also expect to have to pay extra for him having "another go", so to speak?

Finally, can you give a rough idea of the extra cost to flushing in the beam? I was thinking about £350: an extra days' labour for cutting and fixing timbers (£200), extra costs for a drilled beam (£50), timber ledgers, bolts and 10 joist hangars (£80), extra props since you would have to prop both sides (£20).

Thanks

bsr

^woody^ · 11 Nov 2019

When you do steel calcs, you start at the lowest section and see if it works. So he should have started with a 6x3 in any case, and if you ask him, if he did his job properly he should say "no a 6" wont work so I designed it with a 7" beam". If he says "I'll check but it will cost you", then he did not do his job prperly so you should not pay for the first one!

I don't know what you mean by "flushing the beam", unless it refers to the calcs and the toilet. But all beams should be loaded on the top flange reagrdless of the joist position. I'll just wait for Isambard to come along shortly ......

bsr · 11 Nov 2019

Thanks. "Flushing" was the term he used. I meant having the UB in the ceiling void so that the ceiling is continuous - cutting the joists either side and then hanging them from the beam. What's the correct term to use?

^woody^ · 11 Nov 2019

There is no term for it. The beam goes in the floor/ceiling or under it, and that's what it's called.

I hope your engineer is not one to make things up. LOL

tony1851 · 11 Nov 2019

The beam-size depends not just on the opening width, but also what area of floor the beam is supporting; and presumably there will be a wall upstairs, either directly over the breakthrough, or offset slightly?
But unless the rooms are unusually wide, a 152 x 89 would almost certainly be OK, and as Woods noted, the SE should have started there.
Quite frankly, it would take him no more than 93 seconds to check the smaller size (he's already worked out the loads and other factors) so to charge you any more would be a little unreasonable (imo anyway).

bsr · 12 Nov 2019

Thanks, I've gone back to him and asked him to confirm it wasn't OK. It might be because there is some roof load on the wall due to a full length dormer conversion.

tony1851 · 13 Nov 2019

bsr said:
Thanks, I've gone back to him and asked him to confirm it wasn't OK. It "might" be because there is some roof load on the wall due to a full length dormer conversion.

"might" !!??

There either is, or is not, some roof load on the wall.

If he's an SE, he's probably graduated from the Notquitesure School of Engineering in Nowheresville.

bsr · 13 Nov 2019

There is roof load on the wall. The SE hasn't replied. I'm saying the beam MIGHT be bigger than normal because of the roof load on it.

Leofric · 14 Nov 2019

^woody^ said:
There is no term for it. The beam goes in the floor/ceiling or under it, and that's what it's called.

If it isn't fully within the floor space it is a downstand beam. Just saying.

Dereekoo · 14 Nov 2019

Perhaps when the SE states flush he means the floor joists are resting on top of the beam and when he says butted they are supported within the web of the beam. This would perhaps clarify his statement of the beam being designed with the compression flange unrestrained (worst case) i.e the floor joists on top of the beam. Perhaps as the floor joist are 6" deep a 7" beam is required so the joists can be fitted in the web. What is the OPs intentions re the joist/beam interface.

bsr · 15 Nov 2019

Nah, I checked, by flush he meant butted up to them. My preference is to hide the beam in the ceiling depending on the cost. Joists are existing on both sides so couldn't be built into the web.

Any thoughts on my second question as to the cost increase for hiding the beam?

^woody^ · 17 Nov 2019

Tbh, the only price you should be interested in is for putting the beam in the ceiling, as other wise it's a crap job.

Dereekoo · 20 Nov 2019

bsr said:
Nah, I checked, by flush he meant butted up to them. My preference is to hide the beam in the ceiling depending on the cost. Joists are existing on both sides so couldn't be built into the web.

So in your original post - He also said that it made no difference whether the beam was flushed or butted to the joists as he had assumed the compression flange was unrestrained. - he actually said whether the beam was butted or butted? quite a bizzare SE you have there.

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Overly conservative design?

Leofric

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