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Footing Design

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Title: Samsung Enterprise Portal mySingle
I have one doubt regarding the design of combined footing.

suppose we are designing a combined footing with two columns  

_____|_|_______|_|_______ ( Diagram)

now the bending moment diagram will have 3 maximum moments ,  one positive and two negative

-ve Max- --+vemax---- -vemax


when we are designing the footing slab why do we consider only the negative moment( on the cantilever portion at the edges)  and find the depth and steel considering that moment, even if the positive moment is more than the negative moments on the cantilever portion.

and how do we account for the transverse bending of the footing slab.

in a footing when it is isolated and combined, in which direction do we considered the bending of the footing for designing it? in longitudinal direction ( the direction of the line joining the centres of the columns)  or in transverse direction ? for finding the depth.



Mandeep Singh. GET






------- Original Message -------
Sender : akester(--nospam--at)<akester(--nospam--at)>
Date : Oct 22, 2009 08:18 (GMT+09:00)
Title : SOG Cracks

Harold et al,
This is a bit of a loaded question, but I just want to test the waters on this. I have my ideas...

What are your opinions as to the possiblity of settlement (slight, say, less than 1" over 10ft or so) causing hairline to 1/16" wide cracks in typical, residential, concrete slabs-on-grade (I don't like the new slab on "ground")? What if there were micro to hairline existing cracks, do you think settlement could exacerbate them?

I know there is a difference in a floating slab that buts against a CMU stem wall, but for the most part I mean single story, thickened edge monolithic slab-foundations, supporting wood frame and CMU.

Part 2: what about standard residential pool deck slabs and driveway slabs? Take into account that many times the pool deck slab is placed over the pool shell wall and a bond forms.

Part 3: Could ground vibrations due to construction activity cause or exacerbate cracks in concrete SOG?

I know, who cares, all SOG crack and are non structural. Poor workmanship, not enough CJ, better design mix and curing, proper placement of WWR, etc etc. But please humor me...

Could you direct CC me your opinions also at akester(--nospam--at) ?

Thanks list,
Andrew Kester, PE

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