Lintel/RSJ calculations
lewis
support a load bearing wall/floor above?
Is there an online source of information for this or a supplier with costs/
beam size info etc ?
TIA
Lewis
Peter Crosland
professionally? If the job requires building regulations approval, which it
probably does, then they are going to want proper calculations done. In any
case it is false economy to bodge such a potentially dangerous, not to
mention costly, job.
Tony Bryer
I'm not sure whether there is any exact rule of thumb, but someone with
long experience usually has a pretty good idea of what is required.
Beam depth = 1/12 of clear span is a good place to start, though the
exact size may be more or less: which is why people buy our SuperBeam
software - though as the disclaimer used to say (before a lawyer made
us remove it) "if you don't know what you're doing this program will
help you design dangerous structures even more quickly"!
More generally I agree with Peter's comments.
--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
stuart
if its an alteration you will need a building warrent...if you are doing
plans yourself stick anything in the plan....building control will tell you
if its too small
If you are replacing wooden lintels (such as in a dry rot attack)
prestressed concrete is the same strength as wood for the same
thickness.......again, if in doub't phone building control
i always work on the rule "if it looks strong enough it probably is!"
remember a lintel only holds the weight of an equalatral trinagle drwan
above it, no matter how tall the wall.......(provided its a bonded wall)
lewis <le...@noemail.co.uk> wrote in message
news:utq83jd...@corp.supernews.com...
dg
There is no rule of thumb.
There are only equations to calculate the load that the section will
take before it either bends, deflects, buckles, or shears.
You need to determine the loads - dead loads (permanent) and live
loads(temporary), and if these are uniformily distributed, act only on
part of the beam or just a single point.
You then check the maximum force acting on the beam, and if this will
cause failure in any of the categories (bending, shear etc).
Lintel manufactures will have done the calcs for you, so that you know
that one of their products will take a load of "x" newtons - so you
just have to work out the loads present.
Also don't forget the lintel/beam supports as some walls will need a
padstone bearing to spread the load
dg
dg
> In article <utq83jd...@corp.supernews.com>, Lewis wrote:
> > What`s the rule of thumb for calculating beam size for a RSJ/lintel
> > to support a load bearing wall/floor above?
> > Is there an online source of information for this or a supplier with
> > costs/ beam size info etc ?
>
> I'm not sure whether there is any exact rule of thumb, but someone with
> long experience usually has a pretty good idea of what is required.
> Beam depth = 1/12 of clear span is a good place to start, though the
> exact size may be more or less: which is why people buy our SuperBeam
> software - though as the disclaimer used to say (before a lawyer made
> us remove it) "if you don't know what you're doing this program will
> help you design dangerous structures even more quickly"!
>
> More generally I agree with Peter's comments.
I have tried most programs and found that they tend to over-specify
section sizes and padstones.
I have had scenarios where the programs have suggested unfeasibly deep
sections for normal domestic supports. This is especially true when
point loads are applied.
I have previously found that by doing calcs to BS 5950 I have arrived
at a 178 deep section, and software has suggested a 406 deep beam
(which nobody wants in their kitchen!). And this was attained by using
exactly the same values.
I concluded that the programs are too cautious - perhaps to protect
against legal action?
BTW, 1/12 span may be OK for deflection, but not necessarily for any
other possible reactions.
Having said that, for a normal house (ie traditional 3 bed semi) and
for a typical kitchen or lounge knock-through, then a 178 or 203 deep
section is normally suffifient.
But this work normally requires Building Regs, and therefore proper
calcs.
You should not rely on rules of thumb, the bloke down the steel yard
or a software program. You should get the beam properly designed by
someone who is sufficiently competant.
dg
dg
> if its an alteration you will need a building warrent...if you are doing
> plans yourself stick anything in the plan....building control will tell you
> if its too small
>
> If you are replacing wooden lintels (such as in a dry rot attack)
> prestressed concrete is the same strength as wood for the same
> thickness.......again, if in doub't phone building control
>
> i always work on the rule "if it looks strong enough it probably is!"
>
> remember a lintel only holds the weight of an equalatral trinagle drwan
> above it, no matter how tall the wall.......(provided its a bonded wall)
>
(and possible some wind load as well)
dg
Paula
floor room in a two-story house without having a several-inch lintel
hanging down from the ceiling and several-inch bits of wall extending
into the room on either side? (And, yes, preferably without having
the house fall down!) I have recently moved into a small house which
has an entry porch sticking out about 5 feet from half of the front of
the house (not an add-on porch, but built as part of the original
house). I was pondering extending the lounge out along the other half
of the house so the front of the house was even all the way across and
I had a bit larger lounge. But obviously that would be alot better
option if the whole room still looked like one room instead of lintels
etc. Is there a way to do this but it's very expensive? Or can it
not be done at all? What if the extension was for both floors rather
then just the ground floor - does that make a difference? Bit of an
ignorant question, I know, but this is my first-ever house and first
time even considering this sort of thing!
Thank you -
Paula
BJ
Paula wrote:
Suggest you look up Structural Engineers in Yellow pages, describe your
requirements as above, speak to them, if they are interested ask for a
detailed quote for their services.
Regards
BJ
Tony Bryer
> I have previously found that by doing calcs to BS 5950 I have arrived
> at a 178 deep section, and software has suggested a 406 deep beam
> (which nobody wants in their kitchen!). And this was attained by using
> exactly the same values.
>
> I concluded that the programs are too cautious - perhaps to protect
> against legal action?
I can't comment on what anyone else's programs do, but ours (subject to
any constraints you enter) will tell you the lightest or shallowest
(where headroom is a factor) section you need. We don't second guess
what the user wants to do - if the actual stress is 99.9% of that
allowed by the BS it is OK. If you want to go up a size to have
something in reserve, that is up to you.
If you only need a 178 deep beam and a program comes up with a 406 then
I would carefully look at the data entry: in our apps you enter
distributed loads as load per metre run: occasionally someone enters the
total load instead of this figure so (say) for a 3.6m beam they have put
3.6x the correct load on it, with the result you describe. As I say to
the users of our software: "if it looks wrong, it probably is"
dg
Yes is could be done - a beam or lintel could be built into the wall
at first floor joist level, thus avoiding it being seen below the
ceiling line. The support may be able to bear on the existing walls at
the side of the opening and so avoid the projecting nibs.
However, the work you describe would involve building regs approval,
so you should let a suitably qualified person worry about it for you
and draw some plans up.
dg