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Reinforcing Steel in House foundations

Reinforcing Steel in House foundations

Reinforcing Steel in House foundations

I am interested in the need for reinforcing steel placement in house foundations that are constructed on good engineered fill material properly compacted to 98% of proctor density and certified as capable of supporting 150Kpa.  What level of precaution is necessary to avoid future foundation settlements or wall cracking?  Some advice is to place 2-15 or20m bars in the footing (450mm X 150mm) only and some to place additional bars in the top of foundation wall.  This assumes the engineered fill was placed properly and protected from frost and moisture penetration or softening during foundation excavation.

RE: Reinforcing Steel in House foundations

Two very different questions have been asked.  

The reinforcement requirements for a concrete foundation depends upon the degree of foundation 'stiffness required and characteristics of concrete (shrinkage). A minimum amount of reinforcing is always required but, the amount of foundation 'stiffness' will usually control the final amount.  Of course, we are not trying to overcome bad subgrade problems by adding more reinforcing steel but, working on improving the subgrade soils with the structural fill.

The amount of settlement the foundation will undergo is a function of the applied building and live loads and the characteristics of the supporting soil.  

You say the site has structural fill. The structural fill has been compacted and is 'certified as capable of supporting 150 Kpa'. How much settlemnt was considered acceptable at this load?  You must remember that soil is a compressible, variable material.  

What are the inplace conditions of the underlying soil?  The whole fill matte may undergo settlement due to compressible or worse subgrade soils. Is this possible subgrade settlement figured into the fill 'capacity?

The amount of reinforcing steel in the foundation can only affect differential foundation settlement, depending on how 'stiff' the foundation is designed.

The Structurals on this site can provide some reinforcing information but, You will need to provide some more information regarding the structure, single story?, 2 or 3 story? Construction type?  

RE: Reinforcing Steel in House foundations

I'm trying to think of the conditions under which I'd "certify" that a fill would support, with no affects that might in the future be considered unacceptable, any load.

Can't do it.  Would wonder about anyone willing to do so unless they had total control over sampling, testing and construction.

But, on point (and this is not something I've dealt with for a very long time) I wonder if the old ACI "plain concrete" criteria could not be used.  Wouldn't it be a function of what the local codes required?

Bill Holt

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