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Is this ok ? Cutting 45 degree on either end of my steel

Discussion in 'Building' started by gasgas249uk, 6 Sep 2010.

  1. gasgas249uk

    gasgas249uk

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    My architect wanted a 254 x 146 steel RSJ , level with the plate from one side of this bunglow extention to the other , sitting on the inner skin.

    The problem is that the top of the steel will protrude outside ....through the roof

    The carpenter has suggested cutting it at an angle on both ends in line with the pitch of the roof , so its stays under the felt.

    In my eyes this weakens the bearing on both end.

    Is this normal to do this and will the building inspector have a baby over it? ;)
     
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  3. noseall

    noseall

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    It is acceptible and not unusual to have a chamfered cut to the top of a beam sitting in this location.

    However it would require sanction from an S.E.

    Otherwise, if the above scenario is not an option then the beam would need to be positioned so that it protrudes into the room below.
     
  4. gasgas249uk

    gasgas249uk

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    Thank you - sounds like good advice
     
  5. ^woody^

    ^woody^

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    This will weaken the bearings.

    It may be possible to reinforce the web or weld on a new flange, but this is something for an engineer to look at and not one for a builder with an angle grinder

    Incidentally, this is a perfect example of an Architect/designer not doing his job properly and leaving it for the builder to sort out on site and the client to potentially pay more for this messing about. Very annoying

    Who designs a steel that sticks out of a roof? :rolleyes:
     
  6. Deluks

    Deluks

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    Not unusual to see lead flashed protrusions at the side of roofs where the beam pokes through.
     
  7. studips

    studips

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    watched a large extension being built a while back - very reputable local builder - what an education.

    i loved the way the steel beam stuck through the roof tiles and then they whacked a huge amount of lead around it for a seal. lucky for him, it's in a position where the client would never see it (although i'm sure it was all above board, i'm also sure it was a cock up)
     
  8. Hitachimad

    Hitachimad

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    Usually dont get cut from the bottom flange to the top at 45, usually a bit left verticle from the bottom flange, about half way up the web then across at the right angle to suit the roof pitch.

    Getting the padstone height and the bearing right is key to not having to cut the beam.

    254, is a big ol beam, must be spanning a decent length.

    As said above, its all very well us aying what weve done in the past, but your SE needs to confirm.
     
  9. gasgas249uk

    gasgas249uk

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    254, is a big ol beam, must be spanning a decent length.

    The span is 5600.

    Bloody architect. Everything he touches is laiden with problems , glitches and complications , but he never thinks ahead of his next daft direction.
     
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  11. jeds

    jeds

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    This is standard cut and does not weaken the steel as long as you don't take too much away. Try to keep the bottom part of the cut at least half way up the depth if you can.
     
  12. Static

    Static

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    Would normally crank the beam ends into steel padstones / stub columns..
    Do as advised above get the SE to confirm how they see the beam ends sorted..
     
  13. RonnyRaygun

    RonnyRaygun

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    It shouldn't make any difference to the bearing capacity of the section. This is governed by the spread of load through the flange and root radius to the web and will not be affected by the depth of the section.

    Reducing the depth of the section will affect its shear capacity, although I have never known a domestic situation where shear has been the governing factor. Your SE will need to confirm but for the smallest 254x146 section, even if you reduce its depth by 50% at the bearing you will still have a shear capacity of 124kN.

    To put it another way, at 5.6m (and uniformly loaded) it would be impossible to exceed the 124kN shear capacity without the beam failing long before in bending and exceeding the limit for deflection.

    So nothing to worry about.
     
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  14. RedHerring2

    RedHerring2

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    I've got a very similar problem. The difference is that in this bungalow the ceilings meet the rafters about 500mm in from the walls, so that the ceiling slopes down by about 30 degrees at that point.
    This means that it's not possible to position the RSJ any lower 'cos it would be below head height.

    The architect did overlook this problem and when I brought it to his attention he suggested a kind of dormer structure on the roof to house the end of the RSJ. (Actually, I think he's written 152 X 89 RSC or RSE on the structural calculations, if that's possible).

    The RSJ will span 4.5 metres over the kitchen & bathroom extension so there'll be a pier and wall about 2.5 metres from the one end.

    I now have an agreement with the BI and the architect that when I open up the roof space/ceiling they'll come and agree the way forward.
    I'm hoping that a cantilevered RSJ will suffice, 'cos it only has to pick up the hip rafter. If we can use a cantilievered beam, then it won't need to go all the way to the external wall.


    [GALLERY=media, 25995][/GALLERY]
    [GALLERY=media, 25994][/GALLERY]
     
  15. RonnyRaygun

    RonnyRaygun

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    Red Herring, I wouldn't want to risk a 1.5m cantilever with only 2.5m between supports. You would need to be very careful there's no uplift at the first support. You would also want to make sure the end of the cantilever was very well restrained.

    Surely much better to weld a crank to the end of the beam and sit the end on a padstone?

    Up to your engineer though...
     
  16. RedHerring2

    RedHerring2

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    Sorry Gasgas, I didn't mean to hijack your thread.

    Thanks for the comments RR,
    There won't be a 1.5 metre cantilever, more like 750mm, as indicated in this drawing.
    The red line is the hip rafter and the blue, the proposed RSJ, but I suppose you didn't need me to explain that!
     
  17. Hitachimad

    Hitachimad

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    Ask him if 150x90 PFC will be acceptable :rolleyes:
     
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