Subgrade Modulus Paper

[BigH]

Fattdad: Regarding your post on the paper by Duncan, can you post it here - or email it to me? [blue] bohica dot fries at bigfoot dot com [/blue]. They don't like the "posting" of emails in the main forums but here is okay (I understand).
Cheers.
The other question - is how big does a slab have to be before you actually go into the modulus values? You don't hear about it for footings - but what is the cut-off between "footing" and "raft".

 

[fattdad]

Note to self: Look at this thread after vacation.

Later. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[fattdad]

BigH,

Duncan's paper emailed along with a few other comments.

f-d

¡papá gordo ain’t no madre flaca!

 

[fattdad]

Current ACI 360, pertaining to design of slabs on ground has a reference to "long-term" subgrade modulus. One of the participants (whom I don't know) is an engineer named Wayne Walker. He has done some research on the use of long-term k values, based on computer modeling of Westergaard stress distributions. I have not reviewed his work, I'm just posting this for anybody that's trying to get more information on the use (or misuse) of "long-term" k values. I'd rather just call it what it is, soil compression (or consolidation) and leave it to the geotechnical engineer to properly model. Then again, I'm bias - ha.

f-d

¡papá gordo ain’t no madre flaca!

 

[Mccoy]

The issue is that structurals have their softwares which require specific input. one of these inputs is subgrade modulus. Often there are no elastic properties of soil to be crunched into the PC.

The use of a long-term modulus is something which I have discussed at lenght with colleauges.

Some engineers contend that long-term deflections are less harmuful to the structure since RC has its ways to rearrange and distribute stresses and moments. In the words of a professor of civil engineering: "reinforced concrete is like a good householder, it won't leave his family (the structurals) in trouble..."

Rantings aside, how to get a copy of Duncan's paper?

 

[fattdad]

To the extent that there is such a thing as a "long-term" subgrade modulus, it would relate to the interaction between the slab and the subbase/subgrade condition within a foot or so of the base of the slab. To attempt to address the vertical movement of the slab due to changes in stress within the soil profile (likely extending 10s of feet) just doesn't make sense to me - bearing in mind that I'm a geotechnical engineer. . . .

f-d

¡papá gordo ain’t no madre flaca!