On 12 Aug, 04:20, John Rumm wrote:
BigWallop wrote:
"John Rumm" wrote in message
news:QrSdnTLLy_Ecmx_XnZ2dnUVZ8sqdnZ2d@brightview. co.uk...
sm_jamieson wrote:
I have just exposed the existing RSJs to which new load is to be
applied to support my roof.
We would need more detail of the roof construction...

Clay tiles are about 0.77 kN/m^2 for example.

The BCO said the bearings may need to be exposed but has said nothing
more. For peace of mind I
probably need a structural engineer to check things, but can anyone
give a rough feel for the loadings here ?

Old fashioned RSJ, width 125mm, height 150mm, flange thickness 10mm at
the edges, 15mm at the web,
web thickness 10mm. Span is 2800mm. Can anyone tell me what type of
loads this beam can take (assuming bearings are OK). Also, what type
of point load could it take near the middle of the span ?
Quite substantial!

I had a little play in SB4, and assuming I selected the appropriate beam
(i.e. please don't take my word for it - try it yourself!), it looks
like it would cope with a point load of just over 57kN in the middle of
the span!

Cheers,

John.

Also taking in snow weight and high wind loading, in both pull and push
directions, your calculations would drop that figure to around 49 - 50 kN in
the centre. *But it isn't so much the RSJ itself that needs calculating.
The RSJ is only as strong as the platforms it rests on. *If the existing
wall pads are crumbling and dried out, then they may cause slip or sag to
the ends of the beam. *This is not a good thing to have, under any loading
circumstances.

The loading it can take is what it can take - that obviously needs to
include static, live, and wind etc. loads. The thrust of what I was
saying however is that there is a fair chance this steel is more than
"adequate"!

Also, *Fire regulation now say that the steel must have a minimum of three
hour protection from direct heat along the full length of any structural
works. *So allow for the BCO to add that equation once the works have begun.
Each Building Control Person seems to have their own particular way to
create an adequate heat barrier on these things, so ask them first about
this, before getting pads and other things done.

Three hours seems like quite a lot in a domestic situation. Do you have
a reference to the relevant section of the ADs?

--
Thanks guys. The roof dead load is 1 tonne (very close to), including
snow load is 3 tonnes (roof is quite shallow). Roof is bearing on
several purlins such that each purlin end is carrying just over 200kg,
including snow load.
I can add an extra support under the RSJ, reducing span to about 1.8
metres (aircrete loadbearing wall passes under, whereI could easily
add a padstone - replace an aircrete block with 7N block). The bearing
I can see on one end looks like the RSJ is dry on a thick quarry tile
bedded on strong cement mortar (most of house is lime mortar), and I
assume all bearing are around 4" (t'other end must be, its in a 9"
wall).
To check the bearings properly you'd need to remove a brick next to it
and have a look.

Other issue is how to support the purlin on the RSJ. RSJ is inset
against 9" wall above it by 2". FIrst row of bricks on RSJ are dry
laid headers (2" overhang off RSJ), don't think it would be wise to
bear a masonry hanger direct on one of these.
I could drill the RSJ and bolt timber bearer and use a jiffy hanger,
but I'm not sure how drilling some 10mm holes through the RSJ affects
it, or how hanging weight off only one side could unbalance it.
When I say I'm not sure about all this, I could make a educated guess,
but a struct eng could insure it !
Simon.