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Old 15th May 2017, 02:19 PM   #2
motorphotos
Senior Member
 
Join Date: Apr 2011
Posts: 44
Default Re: Concrete Pad For column

Hi

The program does not design concrete foundations (FYI columns are concrete and stanchions are steel this is how we were taught to remember them)

This is what I do in these situations

At the bottom of the page that has the section size on it there is a box that allows you to type in a notes - this could be the section size etc

So I would type in something like

allowable ground bearing pressure taken as 100 kN/m2 (this is the allowable bearing pressure of the ground) this depends on the type of ground you are on

Then I would type ' foundations load (load on stanchion plus say 10 or 15 kN for the self weight of the pad and depends on how large the stanchion load is as the bigger the foundation required the more it would weigh) so lets assume the stanchion load is 50 kN so this would give a foundation load of 60 kN

Area of pad required 60 /100 = 0.6 m2 (take the square root of this)

Provide 800 x 800 x 400 thick mass concrete pad foundation off suitable virgin ground depth to be agreed on site with bco

unreinforced foundation design is basically load / area which must be less than the allowable ground bearing pressure and I always have the thickness half the length so for 800 wide pad its 400 thick and for 1000 wide it would be 500 thick and so on so that the load spreading through at 45 degrees will always pass through the side of the concrete pad foundation and give an even pressure on the ground. I assume its off the centre line of the stanchion but you could reduce the concrete thickness by taking the 45 degree load spread line from the baseplate BUT this means that if the stanchion is not placed centrally the load spread might not be even over the full plan area of the pad

What worries me is that this is basic stuff do they not teach this at college now ? (it must be different to the late 1970's)

If you are taking the rear wall of a house out then you probably have 2 beams side by side ? its all very well designing a single stanchion but you need to think of how the beams are fixed to the top of the stanchion - it could be easier to provide 2 stanchions one under the outer beam and one under the inner beam this allows the beams to be joined over the stanchion and keeps the loads on the centre lines of the stanchions. You also need to consider lateral stability of the rear wall - the building regs require 550 returns for stability of the side walls and if you don't have this it might mean the stanchion needs to take lateral loads as well as vertical ones - what I am saying is there is more to structural design that just coming up with beam sizes

I always remember a disclaimer when computer programs were first coming out in the late 1980's that went along the lines of ' this program (which ever one it was I cannot remember) will assist competent engineers to design economic solutions but bad engineers to design dangerous structures with the minimum of ease'

Hope this helps and any numbers used are for illustration only as I don't have the loads you are using and this is intended or guidance only

regards

motorphotos
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