We are looking at a contractor's method statement for needling an existing 327mm brick wall and he is proposing 203UC needles at 1m cc. The wall is 9.6m tall above the opening to be needled. That means that the stress in the bricks from the selfweight of the wall alone is 0.22N/mm2. For historic london brick construction the CIRIA guide allows a bearing stress of 0.42N/mm2. The wall is also carrying some load from floors so we end up with a brick stress of around 0.30N/mm2. So if the wall is to be needled, the needles would need to occupy more than half the area of the wall which seems a bit much. Even if we assume we can increase the bearing stress by the local factor of 1.5 to get 0.63N/mm2 allowable we would still need 203UC needles at 400mm centres which is way more than allowed for. I asked one of the needle suppliers and they said they don't normally bother checking. They just put needles at 1m centres and it works! What do temp works engineers normally allow for masonry bearing stress on needles?
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