Placing a RSJ on a 3.6N AERATED CONCRETE BLOCK (Thermalite)

Discussion in 'Building' started by OrangeJuice09, 26 Nov 2021.

  1. Dereekoo

    Dereekoo

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    And based on a maximum bearing reaction of 2.4N/mm2. OJ fyi the 51.4 KN isn't the factored load the 73.74 Kn derived from this is the factored load
     
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  3. Dereekoo

    Dereekoo

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    And based on a maximum bearing reaction of 2.4N/mm2. OJ fyi the 51.4 KN isn't the factored load the 73.74 Kn derived from this is the factored load
     
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  4. Dereekoo

    Dereekoo

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    Good spot
     
  5. OrangeJuice09

    OrangeJuice09

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    Originally on the inside there was a brick column, this is how the calcs were created. The Architect then removed it and did not update the padstone size. Nor by the looks of it the calcs. I have asked the architect several times about this but he does not respond. :(
     
  6. RonnyRaygun

    RonnyRaygun

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    Yes, which probably means a larger pad stone is required.
     
  7. Dereekoo

    Dereekoo

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    Original calcs worked on sizing padstone based on allowable bearing of 2.4 N/mm², since padstone is 100 instead of 150 then actual bearing would increase to 3.6N/mm². However since you propose using a 440 long padstone the bearing is reduced to 1.7N/mm²
     
  8. RonnyRaygun

    RonnyRaygun

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    He needs a minimum 500mm long by 100mm wide by 225mm deep pad stone (allowable bearing for a 3.6N block wall is 1.5N/mm2 allowing for the partial safety factor and enhanced bearing factor).
    It's very tight at 0.4h, but considering a material partial safety factor of 3.5 is used in addition to the load factors there is arguably a little bit of leeway there...
     
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  9. tony1851

    tony1851

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    In which case presumably thermalite won't do, so the builder would probably be best putting one layer of two 7N blocks immediately under the padstone?

    PS just spotted Ronny's post above, so yes, longer padstone would be needed if keeping to aac block.
     
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  11. Dereekoo

    Dereekoo

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    Another good spot, I was still running with original designers bearing fig of 2.4N/mm2
     
  12. ^woody^

    ^woody^

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    You can't use Superbeam and SE in the same sentence, as they are not mutually compatible.
     
  13. RonnyRaygun

    RonnyRaygun

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    :D:LOL::ROFLMAO:
     
  14. Dereekoo

    Dereekoo

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  15. RonnyRaygun

    RonnyRaygun

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    Obviously the wall has to be designed for the load coming onto it. For a bearing, we can take an enhanced factor locally, the actual value of which depends on the position and orientation of the beam.

    However, BS5628 also states that the wall should be checked for normal stresses 0.4 times the height of the wall down from the bearing. This means that the localised load can spread out somewhat, the extent of the spread depending on the position of the beam and the length of the panel (or the length between any openings, recesses etc that might interfere with the load spread). It's assumed that the load spreads at 45 deg.

    So if the beam is positioned 2.5m above floor level, the stresses are checked directly under the beam (or padstone) and then again, 1m down, allowing the load to spread out, but not taking the enhanced local bearing factor into account.

    The reason three courses of stronger blocks won't help in that respect is that three courses of blocks won't come down 1m to where the additional check is carried out.
     
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  16. OrangeJuice09

    OrangeJuice09

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    I can't find a suitable padstone size - I can get hold of a 600 long x 100 wide x 140 deep (This reduces bearing to 1.2 N/mm2), will this work or does it need to be 225mm deep also?

    About the 0.4h check- there are no openings in the wall and wondering if this check is needed?

    Applogies, but I'm a bit lost on this thread, I'm tempted to have this part of the wall replaced from dpc with 7N blocks or can I get a way with the existing thermal blocks?

    Thanks again for your assistance.
     
    Last edited: 28 Nov 2021
  17. RonnyRaygun

    RonnyRaygun

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    Use a precast concrete lintel, 600mm (or longer). In fact, why not make it 900mm long (length of two blocks). This will be stiff enough at 140mm deep and will help spread the load further. The 225mm depth is the depth of a block (actually 215mm) and allows a 45 deg spread from the edge of the beam flanges to the end of the unreinforced pad stone. The reinforcement in the lintel makes it stiff enough to spread the load along its length. Use a course of bricks under the lintel to make up the depth.

    Don’t have the wall rebuilt. It’ll be fine.
     
    Last edited: 28 Nov 2021
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