Hi Guys

Does anyone have allowable compressive stress values for bricks and blocks
used in 1970s construction please?
The blocks I have heard described as slag blocks - a bit like aero in
construction, but with black bits and solid chunks here and there.
Bit nasty to drill, but more solid/heavy that the modern thermalite jobbies.
The bricks I have heard described as Fletton (sp). Not sure if this is the
correct name, but these are bog standard 1970 house bricks.

Reason:

I am looking at an RSJ for ceiling joist support with one end landing on an
internal block leaf and the other landing on a
"previously-external-now-internal" brick leaf.
Need to assess end load support and any load spreading required.

TIA

Phil

On Mon, 13 Feb 2006 16:33:01 -0000 TheScullster wrote :
Does anyone have allowable compressive stress values for bricks and
blocks used in 1970s construction please?
The blocks I have heard described as slag blocks - a bit like aero in
construction, but with black bits and solid chunks here and there.
Bit nasty to drill, but more solid/heavy that the modern thermalite
jobbies.

Sounds like breeze blocks. I would treat them as 2.8N/mm2 blocks (this
is the crushing strength: the actual stress you can put on them is a
lot less than this)

The bricks I have heard described as Fletton (sp). Not sure if this
is the correct name, but these are bog standard 1970 house bricks.

Fletton near Peterborough was the place where the clay used to make
them was first found. It contains shale that burns during the firing
process thus reducing the amount of fuel required significantly (and
this making the bricks cheaper). On spec housing they are generally
laid frog down (to save mortar) so should be treated as 7N. Laid frog
up the full 21N crushing strength can be assumed.

Lots about Fletton bricks in a (PDF) Competition Commission report at
http://www.competition-commission.or...ext/088c05.pdf

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

Tony

Thanks for comprehensive reply!

One or two points arising:

Yes, now you mention them, the term breeze blocks is familiar - pretty sure
that's what I'm dealing with.
How can I use 2.8 N/mm2 for these, if the actual capacity is a lot less?
Do you have reference links/texts for figures quoted?
What is spec housing?


Phil


"Tony Bryer" wrote


Sounds like breeze blocks. I would treat them as 2.8N/mm2 blocks (this
is the crushing strength: *the actual stress you can put on them is a
lot less than this*)

On spec housing they are generally....

On Tue, 14 Feb 2006 08:48:56 -0000 TheScullster wrote :
Yes, now you mention them, the term breeze blocks is familiar - pretty
sure that's what I'm dealing with.
How can I use 2.8 N/mm2 for these, if the actual capacity is a lot
less?

Basically by reference to BS5628: the net allowable stress will be a
function of the block material (as above), thickness, mortar, bearing
type and assumed standard of workmanship. 0.7N/mm2 should be a safe
conservative figure for 100mm blocks.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

Thanks Tony
Much appreciated

Phil