Concrete slab on subgrade

[dbest69er]

Hi guys. I'm an undergraduate civil/structural engineer doing vacation work at a firm. I was assigned a project by one of the senior structural engineers to create a spreadsheet which designs the thickness of a concrete slab on soil. I'm just trying to create a general solution with tables to read off thicknesses depending on the load and grade of concrete.

I was told that when soil is used as a support it acts as though multiple springs are supporting it. My question is how do I do the analysis of this case (never seen this before). Is it statically determinate? How do I work out reaction forces and bending moments etc.? I obviously need this before I can move onto the actual design process.

 

[racookpe1978]

Well, that's why he gave you the assignment, and - hopefully, the pay as well. 8<)

Hint: Figure out how to do it by hand from the book.

Hint: The reason he wants a spreadsheet from you is so he doesn't have to do it by hand from the book each time something changes, so be able to change the major parameters ONCE for each analysis at ONE place up conveniently located in upper left-hand corner, properly labelled with units and assumptions, ready to print with spreadsheet file name and archival (printed) output into the firm's folders.

Hint: I did the same thing as you're doing, but to calculate generic heat vertical exchanger stresses and skirt loads under different wind loadings for varying wall thicknesses, heights, and diameters. In 1975. Before there were (computer-based) spreadsheets and printers.

Assume a size, a load-per-square-unit to be carried, a soil resistance and a concrete strength and rebar mat specification. Then calculate. Rinse, repeat. By the third time you do it, you'll have the spreadsheet mentally designed and optimized.

THEN - and only when you've done it by hand for a 3 meter x 3 meter (Yes, be able to set your spreadsheet up for both ANSI and metric) surface 10 cm thick)

 

[dik]

Try to find a publication by the Concrete Society, titled "Concrete Industrial Ground Floors, A Guide to Design and Construction", Technical Report No. 34.

this has a lot of information as well as design formulae.

Dik

 

[dbest69er]

Thanks for the help guys!

@racookpe1978, yeah I'll do it by hand first a few times to get the hang of it

@Dik - I managed to find this book online and am reading through it now. Definitely the best resource I've seen by far for what I need.

 

[dik]

There are a few of them... there's another free one that is put out by the US military... I'll post the title tomorrow sometime... it on my office machine...

Good luck... when I make up spreadsheets, I often do them in Metric and Imperial combined... column for both values and units... and convert between the two depending on the units of the publication.

Dik

 

[dik]

See attached...

Dik

 

[asixth]

These books are a good starting point. It really becomes important for high live loads or sloppy subgrade. And where slabs on grade are used to support formwork which is overlooked most of the time. From what I remember, the formulas are mainly emperical based rather than analytical as a slab supported by many "springs".

 

[amecENG]

There is a pretty good spreadsheet for slab on grade design available at:

http://www.steeltools.org/STEELTOOL...+on+grade&SearchMatch=any&ProductList=Library

 

[ooox]

The Cement Concrete & Aggregate Association of Australia have developed a spreadsheet based on the principles in their manual, 'Guide to Industrial Floors and Pavements'

http://www.ccaa.com.au/publicationextras/

You'll need the ISBN of the manual to download the spreadsheet.