Good spotWhy is the padstone shown yellow marked as 150 wide? Is the inner skin blockwork 100 thick? If so, part of the padstone will be overhanging one side or the other, and the effective contact area would be 300 x 100, which would be OK for 7N block, but the extra width seems pointless.
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/mm²Originally 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.
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?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
Another good spot, I was still running with original designers bearing fig of 2.4N/mm2In 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.
The only question that remains is whether the wall is strong enough with the load spread at 0.4h (as Tony mentioned). Three courses of concrete blocks won’t help there either/QUOTE]
Could you enlighten me on this statement as I don't understand the relevance of 0.4h. Thankyou.
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...
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.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.
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