On 14 Aug, 08:39, Simon wrote:
On 14 Aug, 07:38, Tony Bryer wrote:



On Thu, 13 Aug 2009 23:10:02 GMT BigWallop wrote :

If these timber joists are hanging on only one side of the RSJ, then you
have a twisting action as the loads increase and begin pulling on that side.
Is this something you are allowing for?

Timber is at least fifteen time weaker than steel, so any infill of the web
of the RSJ will mean nothing to actual load bearing properties of the steel.
Drilling into or through the steel can change its loading character
dramatically. *Holes under stress can allow cracking to take place through
the rolled grain of the RSJ in certain circumstances. *600mm spacing sounds
like one of these circumstances.

I agree about considering the effects of torsion, but can't see that drilling
holes in the beam will have an effect on the steel that's left. I am though a
little puzzled at the OP saying he wants to drill holes in the flange rather
than the web. Running the same calc through our ProSteel program shows that
even a 50mm hole through the web is quite OK - smaller ones for through bolts
will have a negligible effect.

I still think spending a little time talking to, not hiring, a proper
engineer will help out on your project and let you do the works without any
faffing about. *Even if you give the engineer a retainer for their
consultation, it's better than trying and failing with this type of job.

Whoops, drilling through the web of course - I "mis-wrote" !
The torsion thing I mentioned in an earlier post - yes it is a
concern.
I'm not sure how you talk to astructengwithout hiring one (unless
you have a mate)
- please let me know !
As far as 10mm holes at stated intervals - I cannot see a problem with
that. However,
I would probably drill them just either side of an exact central line.
The timber infill is not adding strength to the RSJ - it just gives a
connection method
and stabilises the hanger. If hanger is wrapped over, the top of the
RSJ takes up some
strain. Method I mentioned is standard for loft joists - at least it
has been mentioned several
times in web searches. Not always with joists hanging from both sides.
If hanger is up close, leverage is only over half the RSJ width = 2.5
inches.
Only question is added point load on RSJ, and torsion. I believe I
will have to hire astructeng
for this - unless I meet one round the shops to talk to !
I guess the weight above the RSJ and side restraint will need to be a
factor in counteracting
the twisting forces. However, torsion would be an issue on any beam
supported off the side
of another.

I've drawn some plans for thestructeng, and he will need to do a
site visit (look at bearings).
The bearing on one end of the RSJ is quite a lot, and new support can
be offered 1/3 along the
RSJ via aircrete wall and padstone if required.

I'll let you know what thestructengsays. And if I have to pay
him ;-)

Cheers,
Simon.

Well, I've had a local struct eng round. I'd told him the rough
details on the phone, and he was umming and ahhing about the double
RSJ I mentioned before. When he found out the floor load was on the
side walls and not the RSJs had said it "oh, its fine then".

He OK'd my plans for hanging one purlin off the RSJ with timber bolted
to the web and jiffy hangers, and said the existing weight on the RSJ
from the wall above was sufficient to overcome torsional forces.
He made a lot of fuss telling me how to fit masonry joist hangers for
some reason, but said to dry pack above the joist hanger flange and
leave it a week before the main roof tile load goes on.

He had done some calcs after I phoned him, but only charged me for
verbal advice (100 quid + VAT), and will write me a letter detailing
his general advice but without calcs. If the BCO was calcs at any
point, he'll get the info from his file and do the calcs for me (for
another 100 quid !)

Now I need to work out how to drill 10mm holes in the web of the RSJ.
10mm thick. Best drill bit, cutting paste etc ?

Simon.