BIG MAC Posted July 13, 2011 Share Posted July 13, 2011 I have cast a couple of small lintels (say 1.5 wide However I want to form a large opening in a gable wall for patio doors and have noticed the French guys round our way tend to use scaffold boards and clamps to create their form work I am interested how they get their reinforcement into the centre if the lintel and how they get the things looking so perfect. I thought of lining the shutter with plastic (I intend to face the lintel with brick slips if I can get them then 'point in the gap between brick and stone. Any suggestions or links to diagrams would be helpful. Link to comment Share on other sites More sharing options...
Pierre ZFP Posted July 13, 2011 Share Posted July 13, 2011 I came across this which has no end of rural building descriptions complete with many diagrams.It seems that the reinforcing used is a cage placed a certain distance from the shuttering. Easy to see from the diagramshttp://www.scribd.com/doc/52208237/146/Casting-reinforced-concrete-lintels Link to comment Share on other sites More sharing options...
BIG MAC Posted July 13, 2011 Author Share Posted July 13, 2011 Hi Pierre That is kind of what I am looking for I think ....thank you. I am going to have a read and let you know.. Link to comment Share on other sites More sharing options...
pachapapa Posted July 13, 2011 Share Posted July 13, 2011 Just google armature linteau.An armature is a welded up deformed steel section ready for placing in the coffrage.Most bricos will have it.A Point P publication I dont use them too expensive.http://www.scribd.com/doc/22255141/Armatures Link to comment Share on other sites More sharing options...
Chancer Posted July 13, 2011 Share Posted July 13, 2011 I just used plain fer à beton and made my own spacers, they showed but I knew that it would all be covered anyway. You could hang the fer à bêtons or the armature from the top of the coffrage.If the finish is important then the pros use a special mould release plywood, it looks just like the kind of stuff that is used for the beds of trailers without the dimpled finish, it is the best plywood that I have ever seen outside of a patternmaking shop, needless to say it is stratospherically priced, I would use conti-board!!A good chance to buy yourself loads of serre joint à maçons, a tip for the coffrage, if you are casting it into an opening with brickwork above, i.e. cutting an opening in a wall then it pays to create a sort of funnel/hopper to pour the concrete into, this needs to extend above the finished linteau to create a hydro-static head so that the concrete fills the void completely and flows into the corners, the excess left protruding can be chipped away while it is still green and buttered up.Sorry if this is teaching you to suck eggs BigMac, you know far more about building than I. Link to comment Share on other sites More sharing options...
BIG MAC Posted July 13, 2011 Author Share Posted July 13, 2011 It's never too late to learn new things mon ami. I have lots of experience but not a great deal of it in French farmhouses. I am a great proponent of doing things the complicated way to discover there was an easier or more economic way hence why I put it to the forum to see what you guys came up with ...I hadnt cosidered creatting a 'chute' to allow me to vibrate in the mix and replenish at the same time. It makes sense. Back in Uk its down to Travis's and pick up a precast lol Link to comment Share on other sites More sharing options...
BIG MAC Posted July 13, 2011 Author Share Posted July 13, 2011 Cheers Pachapapa I was under the impression what we call cages were semmeles de - foundation etc. so once again I am enlightened. Link to comment Share on other sites More sharing options...
Chancer Posted July 13, 2011 Share Posted July 13, 2011 You can get the pre-cast ones here, at least you can hand over a fortune and wait..................... and wait.........................and wait for them to actually order them for you and for la rentrée to come.I actually enjoy casting them in situ, its one of the things that I have taken to heart from French construction, it fills the void completely and saves being pi55ed around by the grossistes, I even made the moulds to make my own cast in situ period window cills. Link to comment Share on other sites More sharing options...
pachapapa Posted July 13, 2011 Share Posted July 13, 2011 Semelle same word as sole of a shoe.Because all french houses must be built to withstand earthquakes "chainage" is used to achieve this factor of safety.As a result armatures are widely available fabricated in diameters depending on the probability of earth tremors for the area of construction.Even in an old farm house it is cheaper to cast a reinforced lintel rather than put in a secondary oak poutre above the stone lintel. Link to comment Share on other sites More sharing options...
BIG MAC Posted July 13, 2011 Author Share Posted July 13, 2011 I intend to set some of the lintels back and face them out with Oak planks. Thanks all for some good info Link to comment Share on other sites More sharing options...
Chippiepat Posted July 14, 2011 Share Posted July 14, 2011 If your going to face the lintels with oak planks why not use oak for the lintel?I've done many of these & I don't feel the price of oak is over expensive if compared to the time fa**ing about with concrete & shuttering,if you fix planks to the face & underside of the lintel, in my opinion the corner joint of the two is going to look ugly & amateurish,better of just plastering it.Good luck whichever way you go. Link to comment Share on other sites More sharing options...
fisherman Posted July 14, 2011 Share Posted July 14, 2011 I expect that there is a really good reason why not. But if you are facing the lintel why not use an RSJ. Link to comment Share on other sites More sharing options...
BIG MAC Posted July 15, 2011 Author Share Posted July 15, 2011 I can get green oak easy enough however what I am talking about is to set the lintels back enough to allow a reasonable sized oak plank (say 175 x100) to be set in as a dummy lintel but have the structural one cast behind this should allow a reasonable sized opening to be formed in a gable I would think.........maybe wants some more thinking about Link to comment Share on other sites More sharing options...
Chancer Posted July 15, 2011 Share Posted July 15, 2011 [quote user="fisherman"]I expect that there is a really good reason why not. But if you are facing the lintel why not use an RSJ.[/quote]Answering for myself, cost.The steel stockholder here will only sell a 6 metre lengthof whatever section you want, the builders merchants will sell it by the cut length but the price was astronomical and guess where they get it from!!! Basically they pay for the 6m length + the cutting charge + delivery to them then add their traditional (a nice way of putting it!) margin and delivery to the builder.I did a load of structural work inside and by a lot of jiggling managed to do my beams and columbs with one 6m length, a real compromise as it fell short by 400mm and I had to extend the columbs with stubs of the same section from the scrapyard and also plate across the webs of the IPH with 6mm guillotined sheet, in the UK I would have just ordered and paid or what I wanted. It was however the one and only time in 6 years that my polite and reasoned refusal to pay the extortioante price demanded and subsequent negotiations actually resulted in a sale being made rather than me being thrown out with my ears ringing with Picard gros mots, he listened and critically understood my situation, i explained the price I would pay at my UK supplier and that it would be cheaper to have them sent over by a dedicated transport than what he was asking, he matched the price without haggling or offering something derisory like 5%, he dropped 55%.For that particular job I had to use steelwork as I had cut an 2 meter opening for a stairwell right through the middle of a 9 meter RSJ supporting the upper floor and roof, for anything else cast in concrete is far cheaper and quicker. Link to comment Share on other sites More sharing options...
pachapapa Posted July 15, 2011 Share Posted July 15, 2011 A couple of photos taken at a vide grenier at St Chartre in La Vienne; unfortunately the gate was locked so I am still wondering about it. Unfortunately to date I have not been close enough in my travels to satisfy my curiosity.[IMG]http://i282.photobucket.com/albums/kk244/pachapapa/PICT0146.jpg[/IMG][IMG]http://i282.photobucket.com/albums/kk244/pachapapa/PICT0145.jpg[/IMG][8-)] Link to comment Share on other sites More sharing options...
Chancer Posted July 15, 2011 Share Posted July 15, 2011 Great photo PP.Looks like it was cast in situ using parpaing de chainage and then the etau's removed, no sign of the armature projecting though so either it wasnt long enough or no re-inforcing is fitted, I am hoping that it will only be the soleplate of a flat roof sitting on it.Above my head as we speak is a similar lintel but the ceinture de bêton continues all the war around and is tied into another one that I cast on top of the old rear brick wall (just like the photo) to stabilise it and to make one contiguous ring beam.I have seen artisans around here do thngs like the photo, when I have warned the owners and they have taken it up with the maçons they just say they are the pro's and know what they are doing, indeed they do..................... Link to comment Share on other sites More sharing options...
fisherman Posted July 15, 2011 Share Posted July 15, 2011 OK an RSJ is expensive. What about a fitched beam (Steel plate sandwiched between two wood beams.) The steel gives the strength and the wood stops the steel twisting. Quite an old fashioned solution but perhaps flat stock is easier to get from a local fabricators.Just exploring possibilities. Link to comment Share on other sites More sharing options...
Chancer Posted July 15, 2011 Share Posted July 15, 2011 Great idea Fisherman and easy to do the calcs for and hence "prove" if necessary, my cut n shut composite columb is a bit of a stretch to "prove".I will try to memorise that for the future. Link to comment Share on other sites More sharing options...
BIG MAC Posted July 15, 2011 Author Share Posted July 15, 2011 That cast in situ looks as though its bending under its own weight. Main advantage to me with RC is that I can put a large beam up on my own. Link to comment Share on other sites More sharing options...
Chancer Posted July 15, 2011 Share Posted July 15, 2011 Everything deflects under its own weight, as long as it is within the elastic limit of the material all should be well.Well if its not an aircraft or other structure subject to repeated cyclic loadings that is.Still looks pretty iffy to me though, i wonder if the builder was that nice Mr O Leary, you know, him who was last seen hiding from Basil Fawlty who was carrying a garden gnome with a look of intent on his face [:D][:D][:D] Link to comment Share on other sites More sharing options...
pachapapa Posted July 16, 2011 Share Posted July 16, 2011 At parpaing length of 50 cms there is a free span of about 4 metres, looked iffy when I took the photo, plus there is no anchorage to the vertical chainage of the jambs.However very strong beams can be fabricated if the concrete is carefully cured slowly with the toroidal steel members under controlled tension. When the tension is released the whole of the beam is under a compressive stress of a magnitude commensurate with the static and dynamic loads anticipated in a rock hoisting shaft. These beams are called buntons and are placed horizontally encastré in vertical circular concrete lined shafts; RSJs are also used but are more expensive.Tried googling for info but all I get is someone called Emma Bunton![:D] Link to comment Share on other sites More sharing options...
Chancer Posted July 16, 2011 Share Posted July 16, 2011 I think that the re-inforcing rods in normal off the shelf concrete lintels are also prestressed. It puts the concrete in (pre)compression allowing greater bending moments to be achieved before the flexion causes one face to go into tension, in which concrete has little strengthOOPS, silly me to use the words normal and off the shelf in France [:D] Link to comment Share on other sites More sharing options...
Rabbie Posted July 16, 2011 Share Posted July 16, 2011 [quote user="pachapapa"]However very strong beams can be fabricated if the concrete is carefully cured slowly with the toroidal steel members under controlled tension. When the tension is released the whole of the beam is under a compressive stress of a magnitude commensurate with the static and dynamic loads anticipated in a rock hoisting shaft. [/quote] Your vocabulary sometimes reminds me of Owl in the Winnie the Pooh books. Still it is always encouraging to see signs of erudition on the internet.[:D] Link to comment Share on other sites More sharing options...
BIG MAC Posted July 17, 2011 Author Share Posted July 17, 2011 Toroidal? not sure I would describe re bar as a Toroid...to accept lower chords in a composite are under tension imposed by static load then the upper will be under compression.....not sure what the significance of mining works would be.Chancer is bang on with the norm for normal production of Pre- stressed RC lintels - the chords are tensioned off the mould ends which is why you can see the cut off 'Prestressed is a concrete lintel with smaller rebar comprising thin high yield steel tendons which are put into tension ie pulled apart as the concrete is cast. These are cut when the concrete has cured, which puts the concrete into compression as the wires try to shorten themselves. The reason for this is that concrete is strong in compression, weak in tension: it therefore reduces the tensile stresses in the concrete when a load is applied ie it's much stronger' Link to comment Share on other sites More sharing options...
Chancer Posted July 17, 2011 Share Posted July 17, 2011 Thanks for confirming that, I had always wondered as it looked like the ends were cut off flush when the beam was cut to length, your explanation makes complete sense.Now I will either have to get back to the job or find something else to ponder! Link to comment Share on other sites More sharing options...
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