topic Re: Kz elastic foundation coefficient - what it really means? in Robot Structural Analysis Forum

Kz elastic foundation coefficient - what it really means?

sweapon — Sun, 11 Oct 2015 09:41:10 GMT

Hi Everyone,

I'm trying some examples with RSA (just practicing) on trying to design some foundations, but i have a question, what does it really mean the Kz (elastic coefficient of the soil) and how its calculated, I suppose it must be dependant of the Friction angle and the cohesion, but i cannot find any relation, i have tried looking on the web for any information on this but couldnt find anything, hope anyone can help.

Regards,
Alex

Re: Kz elastic foundation coefficient - what it really means?

Anonymous — Sun, 11 Oct 2015 13:32:53 GMT

Hi Sweapon, check this thread.

http://forums.autodesk.com/t5/robot-structural-analysis/elasticity-coeff-slab-design/m-p/5801173/highlight/true#M37352

You can find more information in these books:

-Soil Mechanics in Engineering Practice: Karl Terzaghi

-Foundation Analysis and Design: Joseph E. Bowles

Re: Kz elastic foundation coefficient - what it really means?

sweapon — Sun, 11 Oct 2015 14:04:44 GMT

Thanks,

I checked some books and robot help material, found it in most books as "Ks" elastic reaction, i hate when this happens some time, when variables change between different books.

Cheers

Re: Kz elastic foundation coefficient - what it really means?

Anonymous — Thu, 23 Mar 2017 09:16:36 GMT

The Kz (Uz) coefficient is stated as units (kPa) as in kN/m^2....how does this directly relate to the ks factor given as force/m^3?

Is this exactly the same factor? If so, why isn't the kz units shown accordingly?

Re: Kz elastic foundation coefficient - what it really means?

Artur.Kosakowski — Thu, 23 Mar 2017 09:28:10 GMT

The units depend on the type of the foundation. Could you attach the screen capture so that it is clear what exactly your question relates to please?

Re: Kz elastic foundation coefficient - what it really means?

Anonymous — Thu, 23 Mar 2017 09:49:41 GMT

Re: Kz elastic foundation coefficient - what it really means?

Artur.Kosakowski — Thu, 23 Mar 2017 11:35:50 GMT

This is for unit length of a bar considering it width so kN/m3 * 1 m = kN/m2

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Re: Kz elastic foundation coefficient - what it really means?

Anonymous — Thu, 23 Mar 2017 10:34:47 GMT

so for example, if my site corresponded to a value within this table;

ks (kN/m^3) x 1m = kz (Uz) (kPa)?

Re: Kz elastic foundation coefficient - what it really means?

Artur.Kosakowski — Thu, 23 Mar 2017 11:33:49 GMT

In terms of a bar (e.g. 0.3 m wide ground beam) you should also consider its width so for 1 m length it will be:

KZ (kN/m2) = ks* 0.3 (width)

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Re: Kz elastic foundation coefficient - what it really means?

sweapon — Sat, 25 Mar 2017 06:47:36 GMT

Thanks Artur, for lighten up us all, i have seen most of your videos on youtube which i find very good for the higher experinced in robot

Re: Kz elastic foundation coefficient - what it really means?

Anonymous — Thu, 28 Feb 2019 16:44:07 GMT

Sorry Arthur,

I know that maybe the post is old, but I just in this problematic at moment, and because I'm in Spain at moment, I had Geotechnical report showing some K30 value called BALLAST COEFFICIENT. Is this same coefficient that I need in Robot called Kz??

Usually I'm calculating this value automatically with the procedure in Robot, but in this case I need to use those values specified in the Report.

Thnaks,

Carlo

Re: Kz elastic foundation coefficient - what it really means?

Artur.Kosakowski — Thu, 28 Feb 2019 16:52:51 GMT

Hi @Anonymous

looking at page 245 from

https://books.google.pl/books?id=ygKio-Ks0doC&pg=PA245&lpg=PA245&dq=BALLAST+COEFFICIENT&source=bl&ots=AJ8-nDxgyk&sig=ACfU3U0JspS2lhHcodezcrg_PC3ZtuDTBQ&hl=pl&sa=X&ved=2ahUKEwjA-KXb8N7gAhW7RhUIHfZPC20Q6AEwCHoECAQQAQ

it is the same.

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Re: Kz elastic foundation coefficient - what it really means?

Anonymous — Fri, 01 Mar 2019 09:50:58 GMT

Thanks.

Re: Kz elastic foundation coefficient - what it really means?

memoalcr — Fri, 08 Nov 2019 15:43:28 GMT

Just to be clear, and I am not a geotechnical engr. is the "elastic foundation coefficient" Kz used in Robot the same as the "modulus of subgrade reaction" ks? or do I have to transform ks into Kz? How do you do the conversion?