Footing load bearing calculation

[Ben100]

Hi guys,

 

I'm currently looking at load bearing capacity of footings. I have a lot of structural steel beams and columns in my design, and my SE has given me details on loads. I was planning to bolt the columns straight onto the concrete footings, but someone suggested that this might not be the best option and I may need some kind of cast concrete pillar. This got me thinking about the loads at various points on the footings and how to calculate the correct depth/area. Up to this point the footing design was simply to go down around 1m and 600mm wide, make sure we him hard ground, and fill with at least 300mm of concrete. Most of the ground around here is very hard and compact stone gravel and sand, so good for building on. The guy from building control also seems not concerned with the depth of the footings as long as it's 1m down and on the hard ground.

 

Is this something I should look into more or is 300mm of concrete on hard compact sand/gravel enough?

 

Cheers!

[Oz07]

Why only 300mm of fill is that the bare minimum? Had around 600mm on last pour 

[Ben100]

300mm is the minimum, while some areas go up to around 600mm. This is mainly due to the internal floor level being dropped by 375mm too, so making the trench on the internal level shallower in some places. We intend to build up from the concrete footings with blocks then timber frame once out of the ground.

[Ben100]

Reading into this a bit more, it seems like the concrete in 'strip foundations of 600mm wide and 250mm deep' is sufficient for most domestic builds. I'd be interested in others opinion on this though.

[A_L]

3 hours ago, Ben100 said:

I'd be interested in others opinion on this though.

I do not have the experience to have an opinion, but you may find the attached, although no longer 'current' informative (sections 1.C.3 & 1.C.6).

Small_Buildings_Structural_Guidance.pdf

[Mr Punter]

300mm thick is fine for domestic up to 3 storey and the 1m depth is often just frost protection / rule of thumb but if you have point loads from columns you may need thicker / wider and / or rebar. Your SE should advise.  We have had to do 1000 x 1000 x 400d  concrete pads for some columns.

[Temp]

Perhaps see Table 10 in Approved Document A Structure. Gives guidance on foundation width vs load for various soils.