Do structural changes need to match plans exactly?

[runk40]

Hi, I am looking to get one and half internal walls removed to open up my kitchen and dinning room which requires 2 beams and extra support for the half landing above.

I have had plans drawn up by a structural engineer and he has used a wooden beam strengthen with a steal plate and joist hangers to attach to the wall for one beam and a steal RSJ for the other.

However since getting builders round to quote the job and look at the plans they seemed to prefer and feel more safe to construct everything from steal and use pad stones, as this is a stronger construction and it's easier to work with one main material - steal

now obviously this proposal would be "over kill" in relation to the suggested plans using timber, so my question is would BC still sign this off? or would I need to get the plans changed first to show the new design in steal rather than timber?

my guess was that if we are using stronger materials than proposed then it should be OK, but someone said that BC would only sign it off if it matched the plans.

thanks in advance

 

[Nakajo]

I think you should have a chat with Building Control. My guess is that they would want to see revised calcs. You should want this too!

 

[tony1851]

if we are using stronger materials than proposed

In terms of structural design, that means nothing.

As above speak with BC, though the inspector will probably say something like 'yes that's OK as long as you can give us calcs to justify it'

Which to me begs the question: why did the SE design a flitched beam instead of using steel in the first place?

 

[freddiemercurystwin]

If you use steel then unless the builder uses obviously oversized steels then new calculations are likely to be required.

What 'timber beam' has the SE specified? Normally when they opt for timber its just some normal joist bolted together which I have found most builders prefer over steel. Or is this a glulam or something?

 

[runk40]

Hi Thanks for your reply

he has suggested two standard 6 inch joists with a steal plate sandwiched in between (think its called a flex beam) this will then be on a joist hanger at one end and at the other end run into a C section RSJ to create a T junction where the 2 beams meet.

I guess builders feel the joint would be easier in steal either bolted or welded on site, rather messing about with a timber beam into steal.

 

[freddiemercurystwin]

It’s called a flitch beam and is pretty standard and in fact most builders prefer it as it avoids a heavy steel so fair play to the SE tbh. Can’t see what’s difficult with regards to the connections. Strange.

 

[tony1851]

I guess builders feel the joint would be easier in steal either bolted or welded on site, rather messing about with a timber beam into steal.

It makes little difference, really, as long as the 'C' shape (actually a Parallel-Flange Channel?) has a reasonable depth of flange. Still think it would be easier in 152 deep steel, though.

 

[runk40]

I guess builders feel the joint would be easier in steal either bolted or welded on site, rather messing about with a timber beam into steal.

Still think it would be easier in 152 deep steel, though.

Hi thanks for your reply, are you saying you think it would be easier to use all steal construction?

 

[tony1851]

What size of main steel beam has the SE specified?