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Housing - New Build: Shuttering reuse

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  1.  
    • CommentAuthorEd Davies
    • CommentTimeNov 22nd 2014
     
    Is it nutty to even think about the possibility of reusing timber used for shuttering in the actual house? Perhaps wrap it in polythene to keep the worst of the concrete off it?
  2.  
    Hundreds of croft houses across Scotland built that way over the last hundred years. Boards were used for shuttering and concrete (and stones from the shore, bits of barbed wire, bedsteads etc) poured a bit at a time then when they got to the top the boards were used as sarking. You can use mould release oil to help get them off.
    • CommentAuthorEd Davies
    • CommentTimeNov 22nd 2014 edited
     
    Thanks Willie. Good point about the sarking board. I was thinking of some 145×45 C16 which would go in the floor (above the C24 really structural bit) but sarking board's probably a bit cheaper if it does get messed up and less critical in actual application.

    It's to go round the 500×500 foundation pads where they stick out of the ground and I'll have to have 541 mm bits of the C16 to go as sort-of-dwangs between the JJI rafters at the wallplate anyway so they'd do for both jobs. Longer joists for the sides to keep the pads nicely aligned.

    (Colour code: light brown: C16, darker brown: C24 and ply (for the 25 mm packing pieces (can't think of the right word) in the I-beams.))
  4.  
    Yes the larger section timber a better idea to keep the formwork as straight as possible, poured croft houses never did have a reputation for flat wall! Ebay good source for 100 and 150mm screws (velocity ones are good), use this as an excuse to get yourself an impact driver if you haven't already got one, it will be invaluable for your build. Are you planning on using wax cones and hold down bolts or are you going to be drilling them later using resin and studding to hold the steel?
    • CommentAuthorEd Davies
    • CommentTimeNov 22nd 2014
     
    I was originally thinking to set studding in the concrete as it was poured having seen that approach used quite happily for telescope pillars but on reflection I got bothered about doing it accurately (builder most likely doing the foundations agrees) so drilling and resin is the plan now.

    With Segal-like builds getting the posts in the right place is key, I think - if they're right everything else more-or-less falls into place; if they're wrong the whole thing becomes impossible. x & y matter, z can be tweaked by trimming the post heights.
    • CommentAuthorskyewright
    • CommentTimeNov 22nd 2014
     
    Posted By: Ed Daviesply (for the 25 mm packing pieces (can't think of the right word) in the I-beams.)

    If it's the bit I'm thinking of the word 'web' comes to mind? I-beams typically have a 'flange' top & bottom to handle the major compressive & tensile forces, with a 'web' between.
    • CommentAuthorowlman
    • CommentTimeNov 22nd 2014
     
    I don't know if the steel support plates are just for illustration purposes Ed. But if not I'd be tempted to weld in a couple of triangular webs in a cruciform fashion at their bases, or if not then alternate the orientation along the whole length of the house. One parallel and one crosswise to add a bit of stiffness and mitigate deflection esp. for wind loading. As they are there's not much strength if they are all the same orientation IMO.
    Maybe there are other supports you are using also?
    • CommentAuthorEd Davies
    • CommentTimeNov 22nd 2014 edited
     
    Posted By: skyewrightIf it's the bit I'm thinking of the word 'web' comes to mind? I-beams typically have a 'flange' top & bottom to handle the major compressive & tensile forces, with a 'web' between.
    Yep, web and flange for the actual I-beam (shown in OSB colours and white respectively) but I was thinking of the extra material fixed where the I-beam attaches (birdsmouthed on to the C24 in this case) to spread the point or small-area loads out on to the flanges and web. The JJI document just calls them blocks which is reasonable but a bit generic - I had a feeling there was something a bit more specific.
    • CommentAuthorEd Davies
    • CommentTimeNov 22nd 2014 edited
     
    Posted By: owlmanI don't know if the steel support plates are just for illustration purposes Ed. But if not I'd be tempted to weld in a couple of triangular webs in a cruciform fashion at their bases, or …
    That's drawn as specified by the SE. 8 mm steel, to be galvanized. I too am a bit surprised as another little plate welded from the base up to the flanges supporting the post, even just on one side, would contribute a lot of strength but I have to assume he knows what he's doing.

    There are four rows of these things so there will be very little twisting load on that bottom joint - it'll only really have to take a side load caused by wind. There are (or will be) 36 of the things under the house.

    With an A-frame as this will be with the ridge oriented east-west, the racking strength north-south is huge but it's not so good east-west. These plates are therefore oriented east-west to feed some racking strength up to the posts. I think I'd be making a bad mistake by ignoring his drawing and putting any with the tongue plane north-south.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 23rd 2014
     
    Would they call those blocks 'spacers'?
  11.  
    My SE called them web stiffeners for my Steico I-beams.
  12.  
    Sorry for the poor drawing but hopefully it will convey my thinking...

    Not sure if this is exactly what owlman has in mind but additional triangular webs welded on to your base plates would surely stiffen them up immensely and deal with any possible movement from winds in the north south direction.

    Won't make for any additional work in bolting to the wooden blocks and will also strengthen what could possibly be a breaking point at the lower bolt holes.
    • CommentAuthorowlman
    • CommentTimeNov 23rd 2014 edited
     
    That's exactly the sort of thing I had in mind Chris. With the existing drawing every thing rests in a series of in-line 8mm welds.

    P.S.
    As an alternative you could use a large "U" channel for the vertical element. That may also make fabrication easier and more accurate, as the "U" sections could be very accurately water jet/plasma/laser cut at right angles. This means they only have to be centrally placed on the flat bottom plate before tack welding in place in a very accurate 90 degrees.
    With the existing design the welder has to jig them up in the vertical before tacking to achieve a good right angle. The room for error is greater.
  14.  
    Was also going to suggest that it could be fabricated from H section which would make it easier to fabricate. Some of the material would be superfluous as it wouldn't be transferring any load but what the hell....
    • CommentAuthorowlman
    • CommentTimeNov 23rd 2014
     
    "H" section is even better as you suggest. Poor Ed will soon be wishing he never posted that pic.:wink::bigsmile:
  16.  
    There wont be a bending moment on the flitch plates but possibly shear forces, in which case 8mm x 36 means a total cross section of 29 cm of steel. I think thats enough to counter any shear forces across the bottom of the A frame.

    The entire A frame would be much stronger if it was the bottom of the I beams of the A frame that were anchored directley onto the concrete pads,
    • CommentAuthorEd Davies
    • CommentTimeNov 23rd 2014 edited
     
    Yep, I was thinking of a fillet like this, one side or both. I wouldn't like brackets as Crispy suggests as letting any moisture which gets into the wood by any means get out again is essential.
  18.  
    For me the crucial joint is connection at the corner of the A frame triangle, as it is this that will determine if the structure moves or not, not the metal base plate.

    Or to put it another way, if there is problem stress on the the metal base plate, its because there is unwanted movement at this connection.
    • CommentAuthorowlman
    • CommentTimeNov 23rd 2014
     
    The top plate upon which the timber is resting, would IMO, allow moisture to accumulate and enter the vulnerable end grain.
    • CommentAuthorEd Davies
    • CommentTimeNov 23rd 2014
     
    Posted By: bot de pailleThere wont be a bending moment on the flitch plates but possibly shear forces, in which case 8mm x 36 means a total cross section of 29 cm of steel. I think thats enough to counter any shear forces across the bottom of the A frame.
    Yes, that's pretty much as I think of it. Imagine trying to break an 8 mm thick sheet of steel which is 5.4 metres long (36 off, 150 mm across) purely with shear forces.
    • CommentAuthorEd Davies
    • CommentTimeNov 23rd 2014
     
    There's a lot of C24 (220 x 45) holding the posts upright. NS beams connected with 2 × M16 bolts, EW edge beams with 1 × M16 bolts with the inner two on SAI hangers. It'll be pretty stiff before the JJI rafters go on but, yes, they'll need to be more than just resting on: “JJI rafters at 600c/cs. Birdsmouthed around edge beam as shown and fixed with 2nr HD9090 angle brackets.â€Â
    •  
      CommentAuthordjh
    • CommentTimeNov 23rd 2014
     
    Posted By: owlmanThe top plate upon which the timber is resting, would IMO, allow moisture to accumulate and enter the vulnerable end grain.

    It does seem likely that capillary action could draw in any water draining down the post. And there are some connectors that only have a very small plate, presumably to act as a position stop whilst bolting. But all the Simpson Strongtie post bases seem to have such a plate, for example, so is it a problem in real life? Ed's drawing shows the plate being a little smaller than the timber, so there's the possibility to form a drip edge if necessary.

    Posted By: Ed DaviesThere's a lot of C24 (220 x 45) holding the posts upright. NS beams connected with 2 × M16 bolts, EW edge beams with 1 × M16 bolts with the inner two on SAI hangers.

    Presumably there's OSB or something to provide racking resistance as well?
    • CommentAuthorEd Davies
    • CommentTimeNov 23rd 2014
     
    Posted By: djhEd's drawing shows the plate being a little smaller than the timber, so there's the possibility to form a drip edge if necessary.
    That's right. Those flanges are 60 mm so the total width is 128 mm giving 11 mm of exposed end-grain to breath on each side.
  24.  
    Posted By: Ed DaviesI wouldn't like brackets as Crispy suggests as letting any moisture which gets into the wood by any means get out again is essential.

    The sides of the H section don't need to butt up against the timber so there will be no more contact than with your original upright.

    You could in fact use longer lengths of steel H section set them in the ground build your floor and when everything is square and level pour your concrete into the shuttering around the the H section to secure them and create your pads.

    Dispenses with the need to fabricate anything just chop some steel beam to length, no drilling concrete, no bonding bolts, has to be cheaper all round and a few taps of a sledge here and there and a few wedges ensures everything lines up precisely.

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