what size rsj

[johnad]

How would I calculate what size rsj to use ?
I live in a bunger low and wish to take the wall down between the kitchen and lounge the wall is 3m long including an existing door all that is resting on top of the wall is the ceiling timbers in the loft.
The kitchen ceiling rests on this wall as do the lounge ceiling timbers so it’s just a case of supporting the two ceilings.
There is no binders coming down onto this wall but there would be one sitting above the very end of the new rsj.
This is over to the side of the loft so it is almost impossible to walk above it.
Also
I’m taking one end of the rsj into the cavity wall would this be ok or would it need extra support ? The other end will be onto the existing hallway wall running in the same line.
Also the top of the wall has a timber running on the top to witch the ceiling timbers are fixed would I leave this in place with the rsj under or should I remove it 1st. ?
Any advice would be appreciated

 

[RonnyRaygun]

If you want to calculate what size rsj to use, you need to do the following:

Work out what loads the RSJ will be taking.
Work out is bending moment.
Work out its deflection.
Work out its effective length.
Find a steel section and work out its capacity, ensuring that the moment capacity of the section (at its effective length, not its actual length) is greater than the calculated bending moment in the beam.
You will also want to limit deflection to span / 360 for imposed loads and span / 250 for dead and imposed loads.

Of course, even if you do this, building control might want the calcs done by a structural engineer...

If you do want to have a go at doing it yourself, download a copy of the Steel Designers' Manual, and see if you can get hold of a copy of the Blue Book for section capacities.

Doesn't really matter if people can walk above or not. Standard domestic imposed attic load is 0.25kN/m^2 uniformly distributed.

The cavity wall will be fine. A single engineering brick or a 330x100x140 deep mass concrete padstone will be plenty to spread the load at the bearings.

A 203 x 102 section will eat a 3 metre span, but you have to prove that to building control.

 

[jeds]

Tell you what. Assuming it is only ceiling load only you need a 127x76x13UB. But if you need calcs for building regs it'll cost you £125.

 

[RonnyRaygun]

Was I being a bit too literal??

 

[theoldun]

Thank you John for replying to the OPs question with a sensible answer.
oldun.

 

[RonnyRaygun]

Hang on Old Un. Was that a dig at my response

The OP's opening gambit was

How would I calculate what size rsj to use ?

I gave him all the info he needed to be able to do that - he may actually be interested in the theory behind beam design.

I also gave him a beam size and info on what to use as bearings. I was conservative with my size as price difference between a 203x102 and a 127x76 wouldn't make much difference to the price over the whole project. Also, I wouldn't want to underdesign a beam working on very limited information and then feel responsible when something went wrong.

As Jeds said, a 127x76 will do the job too, but BC might still want calcs to prove it.

 

[RonnyRaygun]

I think you've got it in for me ya old bugger