On 24/10/2012 16:55, John Rumm wrote:
On 24/10/2012 09:55, GMM wrote:
On 23/10/2012 01:43, John Rumm wrote:


Probably not as "industry standard" or trustworthy, but there
are a number of smart phone apps about that will do calcs at least on a
single beam.
Might be worth trying one of those if you have platform for that.


It's interesting that there seem to be more apps available than
web-based calculators. Unfortunately most of these seem to be in
American and I'm not sure how C16 compares with their specs but, putting
a trial dimension of 4m in, using Redwood or Southern Pine (which seem
to come out the same and probably equate broadly) gives a deflection of
69mm for a 6x2 for a light floor loading, which seems an awful lot. For
some reason, the one I was using seems not to accept 2" beams after the
first use so I can't go back and check but the deflection for 8x2 was
about 20-something mm so about a 2" difference.

Give me the specs of a beam if you like and I will see what numbers I
get...


Thanks John, that would be very useful. All lengths are 4m (a little
variation but no more than 100mm) and the TRADA tables say a 47 x 195
joist is good for that at 400 centres but of course give no further
information. (A number of apps etc simply give the same data in their
calculators - you put in the size and it tells you the max span.)

Clearly very small ones would be inadequate at this length, but it would
be interesting to know what the performance of 7" (ie 47 x 170) and 6"
(47 x 145) would be at 4m for C16 timber. From what the tables
indicate, the advantage of C24 is pretty minimal, so hardly worth the
trouble of sourcing etc except in very marginal situations).

I'll most likely cover with chipboard (8x2 t/g sheets), which comes in
18 or 22mm. I'm assuming that there's little difference here for 400mm
joist centres (and would go for 18 as it's lighter) and the more
important factor is to screw it down to every joist but I could easily
be corrected on this (!)

It's also pretty clear that a span of 4m will benefit from strutting at
mid span, so that's on the agenda too.

Friday night - must be time for a cold one (!)

Cheers!