×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Concrete slab on subgrade

Concrete slab on subgrade

Concrete slab on subgrade

(OP)
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.

 

RE: Concrete slab on subgrade

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)  

RE: Concrete slab on subgrade

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

RE: Concrete slab on subgrade

(OP)
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.

RE: Concrete slab on subgrade

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

RE: Concrete slab on subgrade

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".

RE: Concrete slab on subgrade

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

www.ccaa.com.au/publicationextras/

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources