Rsj – u-beam sizes in full renovation

[chippy 70]

Hi all, im new to this site so bare with me.. im about to renovate a 1920/30’s semi-detached property, its a big job for me alone, it needs everything, from new concrete ground floors, new joists to 1st & 2nd floor, also partially new roof for a loft conversion.. ive already done the house next door which is an identical house (as & opposite) and had the help of an architect & also SE for u-beam sizes.. this time round i'm changing a couple of things, i:E its having a single storey kitchen extension instead of a double extension with bedroom above, reducing the extended kitchen size by adding a downstairs bathroom & also splitting the kitchen to have a utility room, other than this and the entrance hallway, the whole ground floor will be open plan. there were 9 beams involved with next doors renovation, & 7 in this one.

The questions I have are.. the main existing building is W6.66m x L6.6m, the ground floor beam used to go through the centre of the building was 6.9m (150mm bearing on 600mm pad stones) so 6.6m span with a 100x100mm structural post built into the hallway stud wall at the 1.9m point, so remaining span is 4.6m (15ft), post built on a 1mx1mx0.6m concrete pad.. what size u-beam could I use for this? I was hoping to keep a flush ceiling, so to hide rsj between plasterboard and floorboard on a 225x47mm timber joist floor. will a 203 x 133 x 30kg do this span?

For those who need to know, 1st floor has 3 bedrooms & bathroom (typical 3 bedroom home).

Next question – instead of the hallway stud with structural post built in, would it be a better option to build a 100mm concrete block 7.30N wall, onto the 100-120mm RC35 concrete Slab, and Simpson tie this into existing building, then sit the u-beam on this, doing away with the post?

Any advice is appreciated.

 

[^woody^]

You need to ask that engineer for help again for the beams.

A concrete wall should not be built off an un-thickened floor slab, nor the floor loaded from a post.

 

[chippy 70]

Hi woody.. ok so il forget the block wall.. back to the stud with SS post.. the SE stated this for the house next door.. concrete pad stone 1mx1mx.6m under slab.. just incase I've not been explaining correctly.. the beam would be spanning the whole width of room.. 6.6m and built into the party wall and also the pine end side of house.. the post is there at the 4.5 point to break up the span.. this is what's on the drawing for 1st house.. what I wanted to know is what size u-beam I could use to fit between plasterboard and floorboards.. hidden.

 

[jake7462]

If this house is identical to the previous house, and the beam spans and loads are the same then why would the beam size be different to the one previously specified by your SE?

 

[chippy 70]

Hi jake.. both these houses are mine.. on the previous house, the beam seems a bit over the top for the span.. 254x146x46.. I've seen smaller beams in other properties ive worked on with wider spans.. 5m+.. similar 3 bed houses. It seems different SE's have got different ideas.. last time I used 11x2 joists when the required joist for the span was a 8x2.. this time I'm using 9x2s.. (should be 8×2's) hoping I could hide beam this time using a 203x133x30.. just wanted to know if this is sufficient for a 15ft span in a typical 3 bed property..

 

[jake7462]

Ok makes a bit more sense now.

Yes a 254x146x43ub sounds like overkill for a 6.6m span with an internal post. Have you got your SE’s calcs from the job to look at what he’s done?

I suspect a 203x133 ub would be fine at that span as you’ve described with the post, but you won’t know for definite without doing a proper calculation based on the actual loads on the beam.

As for joists, you should be able to get a good idea of whether or not your SE is overdesigning - have a look for the TRADA timber joist span tables and you’ll be able to estimate what size you’d need. An 11” joist in a domestic job sounds pretty crazy to me...

 

[tony1851]

If it's spanning two gaps 1.9/post/4.6, there's a good chance a 152 x 152 x 37 UC section would work - it depends on the area of floor supported and the position and construction of walls upstairs.

A 203 x 133 x 30 would certainly work; a 254 x 146 x 46 is just bonkers rookie 'engineering'.

With a 152 beam you could get down to 8" joists or maybe 7". What you have to be careful of is joist shrinkage once they are in the house and the heating is on. If the joist tops are only just above the top of the steel, any shrinkage will eventually show as a hump in the floor following the line of the steel beam.

 

[chippy 70]

hi again Jake7462 & tony1851.. the actual calcs for the beam in question i cant find.. sods law.. it was a 32page booklet and that and a couple others are missing.. ive included a drawing below of the ground floor, and also the S.S. POST calcs.. but hopefully you can see where we're at with the drawing.. i also seen a calculation done on BEAMCALCS.uk with an example of the 203x133x30 beam being used over a 5m span.. i could include the link if it helps..
thank you both for any advice.. much appreciated

 

[jake7462]

Both of the opinion that a 203x133x30ub would be more than enough do the job, but your building control inspector isn’t going to take the word of someone on a forum for it. He’ll want to see proper calculations done by a structural engineer - not much more advice to give really!

 

[jeds]

You've got to wonder? A 100x100x10 SHS column is so far over the top. I'd bet money a 4mm would be plenty - and a smaller 3.6mm would probably be plenty.

 

[tony1851]

You've got to wonder? A 100x100x10 SHS column is so far over the top. I'd bet money a 4mm would be plenty - and a smaller 3.6mm would probably be plenty.

Agreed.
Furthermore, OP mentioned that the post was being built into a stud wall, so a 90 x 90 SHS might be more appropriate, allowing for the inevitable shrinkage of 4" x 2" studs

 

[chippy 70]

hi again all.. with regards to the structural post, i agree with the post being a 90x90 to fit comfortably in a stud.. so im going to change that.. also ive come across this table on one of the inspector websites..
https://www.newbuildinspections.com/wp-content/uploads/2016/07/Chapter6_5_2013.pdf

it does mention the 203x133x30kg UB, but also the 152x152x37kg.. the floor AREA its supporting is just under 40sqm at 39.95sqm, so am i right by saying the 152x152x37kg UC is more suitable or stronger should i say than the 203x133x30kg UB??

 

[chippy 70]

also any advice for drilling holes for services in this beam.. any restrictions on size and positions? thanks again all

 

[tony1851]

hi again all.. with regards to the structural post, i agree with the post being a 90x90 to fit comfortably in a stud.. so im going to change that.. also ive come across this table on one of the inspector websites..
https://www.newbuildinspections.com/wp-content/uploads/2016/07/Chapter6_5_2013.pdf

it does mention the 203x133x30kg UB, but also the 152x152x37kg.. the floor AREA its supporting is just under 40sqm at 39.95sqm, so am i right by saying the 152x152x37kg UC is more suitable or stronger should i say than the 203x133x30kg UB??

That table is OK so far as it goes, though it doesn't seem to allow for the load from any partitions which might be supported by the floor joists.

And your situation is different because your beam is 'continuous' in that it spans across two gaps. In fact, that makes for a lighter beam because the inevitable reverse bend over the support post helps to negate the downward bend mid-span. Because the spans are so different, there will actually be a slight uplift force at the outer end of the 1.9m span (assuming the load was uniformly spread along the whole length of the beam) but that would be countered by being built into the wall.

On those spans (assuming the beams are just carrying floor load) you could safely use either a 152 x 152 x 23 or a 203 x 102; both would be OK for stress and deflection.

 

[chippy 70]

good morning tony, there will be partitions on the floor, 3 bedrooms and a bathroom, a stairwell of approx 2mx2m is in the 6.6 x 6.6m square, taking away approx 4sqm of the floor area.. the stairs is supported freely on doubled up joists built in to the pine end wall and sitting on the ground floor partition, so this weight of stairs shouldn't come into the overall loads. do you think the 152x152x23 is still ok?
thanks again for the help