Compressive strength of existing masonry

[SteveHarris]

Greetings all,

I'm in the process of submitting structural calcs to building control for an extension.
One of the steel beams that will support the first floor joists will be supported from the existing (external) brickwork. Everything is sized except for the padstone that will need to go into the existing brickwork.

I understand the compressive strength of "unknown" masonry is 0.43N/mm2 - but that this is based on poor quality victorian london bricks. This gives me a padstone of about 1400mm long! Has anyone any experience of what building control are likely to accept for a rather more modern 1973 brick and mortar, or are they likely to require it tested?

Also for my own piece of mind, does anyone know how much testing costs?

Cheers

 

[hotrod]

Hi Steve,

In situations like your's (old victorian masonry and steels/padstones etc) our LABC are often satisfied with 4-5 courses of new concrete commons (20N/mm²) extended underneath a 440x215 padstone. Obviously the padstone size will depend on your steel spec.

hth

 

[Shytalkz]

Try moving your decimal point along! It's 4.3N/mm² for 15MN bricks in group IV mortar, which is a reasonable one to take for Vic bricks.

You then apply a bearing factor, which depends on the type of bearing that you have and there is a also a materials safety factor (3.5 for old stuff like this). As a rule of thumb, if the load is a service load (ie not already factored up) then:

padstone length = (1.5 x reaction x 10³ x 3.5)/brick strength x 1.25 x padstone width)

If the answer is less than 215, then direct bearing to the all is ok, or just use a single engineer brick.

If the loading is factored up already, lose the 1.5.