What weight can a 3.7N block support?

[epsilonGreedy]

According to my maths the answer is 16.6 tons which is just silly. Could someone spot the error in the following arithmetic?

1. A 3.7N rated block should cope with a compressive load of 3.7N per mm squared.
2. The surface area of a standard 100mm wide block is 100mm x 440mm = 44,000 mm squared.
3. Therefore a block can support 44,000 x 3.7N = 162,800N before it is at risk of crumbling under the total load above.
4. There are 9.8N in a Kg* which means a block can support 162,800 / 9.8N = 16.6 tons.

 

* For the scientifically pedantic this might not apply in Cornwall or on Planet @SteamyTea.

[Mr Punter]

But when you run over them with a telehandler they crumble to dust.

[Temp]

Calculations look right to me. I believe you need to reduce the result by a safety margin. Factor of 2?

 

I think the compressive strength of blocks is mainly a concern where you have beams and lintels that concentrate loads onto the bearing ends. 

 

I'm not an SE though.

 

[epsilonGreedy]

20 hours ago, Temp said:

Calculations look right to me. I believe you need to reduce the result by a safety margin. Factor of 2?

 

I think the compressive strength of blocks is mainly a concern where you have beams and lintels that concentrate loads onto the bearing ends. 

 

 

I was thinking about the inner block wall that contributes to supporting a 1.8m all chimney on a hipped roof. The corbeled plinth for this is built over three blocks and I reckon it takes about 500Kg of the total 780Kg weight of the chimney when wind pressure is zero.

 

If my calculation of 16.6 tons per 3.7N block is correct, then my 780kg chimney is many factors within the 50 ton support limit of those 3 blocks even allowing +10% for a rain sodden chimney and wind pressure.

 

I still like the idea of enhancing the lateral stability of the block wall with 12mm cement board like Hardiebacker. 

[Temp]

I'd take advice from an SE. I really don't like the idea of using hardibacker board for this!

 

Our SE specified 7N blocks with 14N blocks for our chimney and some pillars because we have a beam and block first floor.