×
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

Slab on grade design

Slab on grade design

Slab on grade design

(OP)
I need help to design a slab on grade.

I have a one story commercial building (90'x150'), and most of the loads are on the perimeter of the foundation (point loads spaced at 15' on center). I just need to design for relatively small uniform load of 100 psf.

Will 4" slab work with crack control joints at 12' on center and with minimal reinforcing for temperature and shrinkage.

Also, the soil report indicates a maximum PI = 8. I have read some articles indicating that beam spacing should not exceed 20'. Do I need any beams since the area is big (13,500 SF) Does this apply only for slabs on plastic/compressible clay (with high PI)?

The soil is mostly sandy silt/silty sand.

RE: Slab on grade design

Yes, the slab on grade will work if the subgrade is properly prepared.  Suggest 95% compaction, (Standard Proctor), for top 18" and 6" of granular base at 100%. Build slab in alternating strips of whatever width matches the joint spacing. Use perimeter foundation with isolation from the slab.

RE: Slab on grade design

When you say you have point loads at 15 ft on center, do you mean you have 22.5 kip point loads?

RE: Slab on grade design

(OP)
To civilperson,

Thanks a lot for your information because it is very helpful. Just one thing I would like to verify. When you say isolation from the slab, do you mean absolutely no dowels to tie the perimeter foundation with the slabs? Or just an isolation around each column? Thank you.


To jmiec,

The point loads are a result of the roof load spaced at 15' on center around the perimeter. Average point loads is about 15k.

RE: Slab on grade design

Oh, so you're not landing any of these loads on the slab?

RE: Slab on grade design

The slab and perimeter foundation will be loaded differently and will settle differently. Tied together wil crack one or the other. An expansion joint material between the slab and the perimeter will prevent the cracks cause by different loading.

RE: Slab on grade design

You might not be able to get away without providing reinforcement at columns to tie the slab. Your footing design is likely to be controlled by the horizontal loads due to wind, or earthquake, unless you provide a owefully large footing, overturning of the footing will be a concern. In such case, we used to tied the columns to the slab, and provide control/construction joint around the interface to minimize the effect of differential settlement.  

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