Although I agree that use of such a beam is a bad idea, it is interesting to note the many houses built up to the mid 60's with first floor walls built off a single or doubled timber joist.
Walls built off timber from new would settle naturally, but its a different matter when retrospectively fitting a timber support in situations like this.
dg
I had some advice from the group recently on getting a beam. The structural engineers I contacted wouldn't get out of bed for less than =A3250!
I downloaded the SDA product. which worked a treat to calculate the beam I needed.
Tim
dg wrote:
interesting to
Use lime mortar (as Grand Designs did tonight) and such problems go away.
Yes, but double joists nailed together have a lot of lateral stiffness when compared with one of IMM's TJI beams which are basically 50x50 top and bottom with a ply web.
Quite so: on site you'd put the beam in and build the wall up - probably in lime mortar - and as the beam deflected under the weight the mortar would accommodate this. If you put a beam under an existing wall you need to properly preload it or there is a risk that over a period the weight will gradually shift to the beam causing cracking. This would be far more likely with timber which (a) deflects more - deflection is usually what governs timber member sizing; and (b) creeps: put x tons on a steel beam and it deflects by y .. and never moves any further; put x on a timber and next week/month you'll find that the deflection is more than it is now.
Ahhh no ... there is no ply web, it is akin to 14mm OSB, but not ply.
They are also 90mm wide for typical domestic beams not 50mm, and 300mm deep.
It is unfair to compare the stiffness of one TJI beam against a joist, TJI beams are designed with a complete homogenous floor system ... i.e. Silent Floor Where the Intralam ring beam and the glued & fixed deck all contribute to the finished performance not one individual beam.
Rick
And I have absolutely no problem with them being used for such. I am totally unconvinced that a single TJI is a suitable substitute for a steel beam supporting a masonry wall over.
Given that they are likely to be deeper than a standard joist (let alone SHS steel), have less lateral stability, and no doubt cost more, it seems hard to see the advantage in most domestic house construction projects. Which does make you wonder why some fool keeps sugesting them!
On Wed, 15 Sep 2004 08:10:59 +0100, a particular chimpanzee named "Andrew Barnes" randomly hit the keyboard and produced:
Are you sure? Has he asked you for calculations, or just to let him know what beam you intend to put in? IME, for a 2m opening, if you were to specify a reasonably-sized beam (i.e., a 178 x 102 UB) then it's unlikely that the BCO wouldn't accept this without calculations.
If necessary you could try a box lintel from Catnic, who I understand will provide calculations for you.
On Sun, 19 Sep 2004 00:13:45 +0100, a particular chimpanzee named Tony Bryer randomly hit the keyboard and produced:
IMM's managed to do what he does best; come up with an unworkable, stupid idea, and get the rest of us to argue amongst ourselves as to exactly why it's unworkable and stupid.
Mine wanted calculations for a 80 cm opening over a doorway (2 standard
100*65 lintels)On Fri, 24 Sep 2004 21:24:59 +0100, a particular chimpanzee named "G&M" randomly hit the keyboard and produced:
With point loads on them or less than three courses of masonry over them, perhaps? Pre-stressed lintels require the composite effect of the masonry over them to work satisfactorily. Perhaps asking for calcs was a way of proving to someone who argues every point that they won't work.
Or maybe you've just pissed him off something rotten.
There were two courses then the upstairs floor joists. I phoned the lintel manufacturer up for their figures and they offered to do the calcs for me for free. Which they did and it passed easily.
If refusing to submit full plans counts then yes I've pissed him off something rotten. I always use a building notice as it allows more flexibility as you take apart an old building and need to modify things.
Just thought about this again. You are talking crap of IMM proportions. All pre-stressed lintels have a point loading specification so no brick courses are mandatory. Indeed it is quite common to place joists directly on them.
Also if you have more than three courses of brick above a 80cm opening all loads above and outside the triangle are taken by the side walls so the only loading on the lintel is a few bricks.
I have been presuming you were a real live BCO but if that is the case I would have expected you to have a much better understanding of loading calculations.
I think that's crap of IMM proportions from yourself, actually. I've got in front of me the BRE's 'Good Building Guide' no. 10 (dated November '91 - so probably not the latest version). This gives simplified methods for estimating loadings where temporary openings are to be made.
The BRE publication defines two triangles, both with a base 10% wider than the clear span of the opening - 880 mm in this case. The load triangle has base angles of 45 deg. and the weight of the masonry plus any point loads supported within this triangle are considered to be supported 100% by the lintel. The height of this triangle is clearly equal to half its base, so extends up to 440 mm above the opening - that's nearly 6 courses of brick, not 3.
Then there is the interaction triangle, which has 60 deg. base angles and the apex at half the base times sqrt(3) - 762 mm. 50% of any loads placed within the interaction zone, being the area that's inside the interaction triangle but not the load triangle, are considered to be supported by the lintel.
Thus only loads higher than 10-and-a-bit courses above the lintel can be safely ignored without resorting to more precise calculation methods. That's not quite what you said above.
Hmmm...
Sorry - I accept I made a typo there as I was thinking about blocks which I was using that day but typed bricks. However the original point still stands that good lintels don't need these layers for strength purposes.
Checked and can confirm all Naylor lintels are non-composite and do not need three layers of brick or any other method to give them their quoted strength. Joists or other point loads can be lain directly on them within the loads given in the tables on their website.
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