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Thread: How safe are houses made of bricks

  1. #11
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    Quote Originally Posted by veronica View Post
    the majority of brick houses, chimneys and walls that went down were older than 1970, after that there was an earthquake bit added to the building code. the old brick houses had a very weak mortar (cement) mix so under the shaking the bricks didn't hold together. The new houses (and a few of the old) have a much better building spec. We have a timber and tin house and although timber is great it didn't stop the Bay windows parting company with the main house.
    That's interesting about the mortar mix. I tend to think of mortar in relation to it's ability to react to ground movement of a more gentle persuasion like settlement. Earthquakes have never occurred to me. Obviously had a sheltered life.

    I take it when you say brick houses you mean they are timber frame clad with bricks?

    Have you managed to reunite your windows with your house? Sounds horrendous.

  2. #12
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    Hope that you are no longer boarded up Veronica.

    We had a collapsing brick problem, in the landlords' side of the house. The house is a timber frame construction with brick skin.....with very inadequate ties!! I believe from talking to a colleague that even pre EQ inspections were done as brick walls were going up...he had photos taken as his extension was built as they wanted to get it completed.

    However the base structure of the house is fine...it no longer has an outside wall..which is currently covered in weatherproof ply (glad no one is living in it over winter). The end we are in has block over what my OH belives is timber frame. It has held with no problems ...windows though were a completely different matter.............

  3. #13
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    Quote Originally Posted by Origems View Post
    I'm referring to a concrete masonry internal skin tied to brick masonry external skin. This is the most popular construction type in the UK. I know that the majority of New Zealand homes are timber frame with cladding (often in brick as mentioned above) and I just wondered if building with two layers of masonry is possible under the code without being too uneconomic compared to timber frame. I assume the masonry structure being heavier and more rigid than timber would need adaptation to it's design for it to be as suitable for withstanding earthquakes and this could prove costly.
    Blocks here in NZ are generally hollow blocks to be reinforced and filled with concrete. You could use them as the inner wythe and then adding insulation, cavity and an outer wythe of brick, tied into the blockwork.
    (In Europe a block house is often meant to be a solid timber log house, as also often seen in Scandinavia or Canada.)

  4. #14
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    The problem with mortar, grout and concrete is that it is very good in compression but quite weak in tension. The direction (vertical or horizontal) does not matter. Its strength increases by using more and certain cement but only so far. Thus the practice of using reinforcement or ties in these materials which is very good in resisting tension.

  5. #15
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    Quote Originally Posted by ralf-nz View Post
    What is an earthquake prone area? All regions in NZ have a hazard factor. I think I addressed it already in one of the other breads. There is no region with '0.0' in this category.
    Also what do we actually really know about this? The factor for Canterbury will now have to be changed.
    The factor for Canterbury will have to change but it was always an earthquake prone area; there are many faults running under the plains and the main fault exit running through Marlborough has been shifting southward over time with more earthquakes to the south of the fault and fewer to the north.

    In terms of areas that aren't earthquake prone I would say most places north of the Bombays. Obviously we have other hazards here; and do get a few small earthquakes but they are few and far between and the bulk of these aren't felt. I doubt that our chance of a 5 or other is too much greater than, say, the Midlands in the UK.

  6. #16
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    Quote Originally Posted by James 1077 View Post
    The factor for Canterbury will have to change but it was always an earthquake prone area; there are many faults running under the plains and the main fault exit running through Marlborough has been shifting southward over time with more earthquakes to the south of the fault and fewer to the north.

    In terms of areas that aren't earthquake prone I would say most places north of the Bombays. Obviously we have other hazards here; and do get a few small earthquakes but they are few and far between and the bulk of these aren't felt. I doubt that our chance of a 5 or other is too much greater than, say, the Midlands in the UK.
    As I wrote here http://www.enz.org/forum/showthread.php?t=33504:

    Canterbury 'has already been considered "prone" before these earthquakes! ...The exact hazard factors "Z" per NZS 1170 are for Auckland 0.13, Christchurch 0.22 and Wellington 0.40. The factor of 0.13 is the lowest within this standard; the highest is 0.60 for Otira and Arthur's Pass'.

    And also that
    '"our code not only uses the hazard factor "Z" as mentioned in an earlier post but there are more factors e.g. for "site subsoil class", being "near [a] fault", "importance of a structure".'

    Of course the near fault factor will need to be changed, and probably also the general hazard factor.

    However as per code/NZS ALL regions in NZ are earthquake prone, to a different degree though of course.

  7. #17
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    If you want a stronger build house resistant to earthquake, then you would look to commercial designs. You may be looking at the wrong tree when considering the type of exterior cladding or brick / block walls. Look at what holds the walls up and how the walls are tied together. In this case, you can only rely so much on standard 100mm thick concrete slab with 665 steel mesh. To go a more commercial route, you would choose "Rib Raft" type of foundation. However, maybe 1 in a 1000 houses will use this method of construction due to it's high cost of construction. Spec houses will ONLY use raft foundation if required by engineers.

    Brick ties too can only go so far in adding rigidness to the exterior wall cladding. Again, single story residential houses have their timber frame stud width at 600mm apart. So basically there isn't a lot of brick ties due to the wide stud widths. To go a higher spec (& higher cost), keep the stud widths down to say 400mm wide or less. Then plywood brace the whole wall. But realistically, when looking to buy a house, there's no way of knowing so these improvements can be thrown out the door.

    People who have invested more than the normal cost to build a home typically do not sell so quickly. Certainly, with all the houses i've looked to buy in the past, these are houses that are standard build in terms of structure. You can have all the bling bling interior design in the house you want but it all doesn't mean a thing when the Gib wall linings keep cracking.

  8. #18
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    Quote Originally Posted by ralf-nz View Post
    Of course the near fault factor will need to be changed, and probably also the general hazard factor.
    Yesterday we received a paper CHRISTCHURCH SEISMIC DESIGN LOAD LEVELS - INTERIM ADVICE from SESOC (Structural Engineering Society NZ) on this. Apparently this paper can currently not be accessed on the internet.

    Amongst others it reads:
    'SESOC has recommended to the Department of Building and Housing that the hazard factor in the Canterbury region is increased to a minimum of:
    Z = 0.3 ...

    The revised z factor is intended only for use for the design and assessment of buildings and structures, pending further research.'

  9. #19
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    Quote Originally Posted by Super_BQ View Post
    In this case, you can only rely so much on standard 100mm thick concrete slab with 665 steel mesh. To go a more commercial route, you would choose "Rib Raft" type of foundation. However, maybe 1 in a 1000 houses will use this method of construction due to it's high cost of construction. Spec houses will ONLY use raft foundation if required by engineers.
    Again the question which system/material to use:

    (Concrete) slab on grade or suspended (composite or timber) floor on piles.

  10. #20
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    I'm speaking within the past 10+ years how houses are being built.

    On the flat, concrete slab poured over screed stone tailings. No one uses compacted hard fill on residential builds anymore. No one uses piles and no one uses timber. They use a digger to excavate the footing, put in 2 bars of steel and pour the concrete. Then they may install 665 mesh steel (rebar) and pour concrete which makes up the slab. You might be lucky if they use the vibrator.

    Rib Raft requires a different specification. Materials isn't the issue as the steel work gone into building the foundation is tied in - meaning the whole poured area has steel work is connected like a 'raft'. Super strong against earthquakes. But the problem is the amount of labour to construct could be 4 folds to conventional 100mm slab foundation as described above.

    At the end of the day, it doesn't matter what kind of exterior finish the house has. If the geo-tech soil tests show the ground is soft and proned to earthquakes, then you require a foundation that is designed for it. If the gound is hard shingle / gravel base, then it might be overkill to go above the the standard.

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