Elasticity coeff / slab design

[mathias_peron]

Hi everyone,

I'm designing today a concrete slab on the ground but I don't have the geotechnical report yet. In other words, I don't know the composition of my soil.

It will be my first time that I'm using Robot for a ground slab design.

Is there a conservative value that I can use as Elasticity coefficient of the soil in order to run the calculations?

Have a nice day,

Mathias.

[mathias_peron]

Tell me if I'm wrong,

K = R / u

with R: reaction (total foundation load) [kN/m3] ; u: maximum displacement [m]

So if I take u = 30 mm, it's a pretty conservative value, isn't it?

Have a nice day,

Mathias.

[mathias_peron]

With R: reaction (total foundation load) [kN/m2]

[Anonymous]

According to Bowles "Book: Foundation Analysis and Desing", you can also determine K with this formula:

[mathias_peron]

Thanks a lot,

So for exemple if I'm using a bearing capacity of 150 kN/m², I just use : ks = 40 x 150 = 6000 kN/m3.

There is not a problem with the units here? 

Have a nice day,

Mathias.

[Anonymous · Accepted solution]

There is not a problem.

You forgot the Safety Factor

ks = 40 x 150 x (SF) =

Check this example from the book: 

[HoshangMustafa]

Hi

You forgot to include SF, that's safety factor.

You can use two approaches in soil:

1- Spring (ARSA depends on Boussinesque equation), it includes winkler model, Pasternak model...

2- Finite element: more exact model

[mathias_peron]

Ok ok, I understand.

Can I take the safety factor equal to 2 in any case?

About the 2 approaches,

I'm using the Slab wizzard included in Robot (screenshot attached). I don't know which method it is using.

Thanks again for all these precious answers.

Mathias.

[Anonymous]

You can put the value in the box, or calculate it with the Robot´s procedures.

[Anonymous]

Hi All,

Can anyone please advise on how the software calculates kz from the soil profile, estimated load and dimensions? It would appear from this thread that an assumption on displacement is used to determine kz but this is not a user input.

I have an allowable bearing pressure from a Soil Investigation Report but this is based on an allowable displacement. Therefore, without knowing the assumed displacement used in Robot I cannot compare my output soil reactions to my allowable bearing pressure.

Thanks very much for the help.

Craig

[Refaat]

Hi

I hope you will find an answer for your inquiry in these links :

http://help.autodesk.com/view/RSAPRO/2017/ENU/?guid=GUID-68C071E7-7318-4A5D-9FC7-43D02F547892

http://help.autodesk.com/view/RSAPRO/2017/ENU/?guid=GUID-797045CF-F656-4635-A467-848A57314256

Refaat