How to know if the strip foundations for our house are wide enough?


Postby Daca » Wed Feb 16, 2011 1:34 pm

Hello,

I am hoping someone can help with a foundation query.

We recently put in the strip foundations for our house and I am wondering if they are wide enough????

There is a 215mm wall built off the foundations going up to first floor level (approx. 3.4m) on top of this there are 2 precast concrete floor slabs resting. The load bearing capacity of the soil is 100N/M.

Would the foundation of 700mm wide by 300mm deep be sufficiet?

Thanks for any help!
Daca
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Postby stoneyboy » Fri Feb 18, 2011 6:06 pm

Daca,
Only the person who dug the foundations can advise you. eg if its made-up land then probably not. Presumably you had a BI involved and you had an inspection of the foundations before back-filling.
end
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Postby Daca » Sat Feb 19, 2011 1:14 pm

Thanks for the response. Yes, BC were involved and seemed happy. The ground was in good condition and seemed pretty solid (BC surveyor said that it would take a safe loading of 100KN/M2)

This means that the loading from the walls resting on it could be up to 70kn/m. Would a 215mm wall with 2 precast first floor slabs resting on it exceed 70kn/m?

In most books I have read it states that a typical two storey dwelling has a loading on between 30-50kn/m. But i assume this does not allow for precast floor slabs!
Daca
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Postby stoneyboy » Sun Feb 20, 2011 3:02 pm

Daca,
Allowing for the foundation width of 700mm, masonry walls and two floor slabs each 150mm thick and 6m wide supported either end you are unlikely to exceed 50kN per metre length of wall.
Structural calculations should have been made by your surveyor and your queries should be directed towards him if you are concerned.
end
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Postby andy01 » Sun Mar 13, 2011 8:03 pm

the proportions are correct so its doesnt need any mesh.

what span is the concrete floor?
what depth is the precast floor?
what depth os the screed?
are there any partitions on the floor? if so what are they made from?
does the ground floor also rest on this found?
etc

sorry not enough info to give an answer

ask the person who specified the founds
andy01
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Postby Daca » Mon Mar 28, 2011 6:05 pm

The span of the floor is 5m and the precast units are 200mm deep with a 75mm screed.

There are only a couple of minor partition walls constructed from dense blockwork.

The ground floor is solid so it will not rest on this foundation.
Daca
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Joined: Wed Feb 16, 2011 1:28 pm


Postby andy01 » Tue Mar 29, 2011 12:13 pm

I've assumed the roof spans onto the walls and included a min storage load in attic, but no water tank.

assume you have a cavity wall (brick and block)
assume ground bearing slab

used average loads not excessive ones

i quickly calced the line loads on the founds to be about 60kn/m

hence 700mm wide is fine

bucket sizes ae 450, 600, 750mm so supprised yours is designed to 700mm wide...

hope this helps you to worry less.

speak to the person who designed them. or read through their calcs, you have paid for them so you have a right ot look at them. and they are reqired for submition to BCO or NHBC
andy01
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Postby kaylee » Thu Oct 27, 2011 10:30 pm

perhaps the foundation is sufficient for a 700 mm wide by 300mm deep it would definitely consummate the entire area of the concreted floor. radically strip foundations can used to support a line of loads and line of columns need supporting where column positions are so close that individual pad foundations would be inappropriate.
kaylee
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