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!

*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.

Jobs

Local thickening of a slab on grade

Local thickening of a slab on grade

(OP)
Hello, I havent done this before so Im asking for some guidance and suggestions.

When Im dealing with slabs on grade I choose thickness (ussually 250 mm thick for residental structures) and this is sufficient most of the time.
But in this case Im dealing with large single loads (from columns) that are acting on a slab on grade so shear breakthrough - punching shear is a problem.

Is it allright to locally increase thickness of a slab as shown in view a-a in attached image?

Should I reinforce this thickened part as a spread footing?

Is this expensive to do in a field?


RE: Local thickening of a slab on grade

Quote (gmd255)

Is it allright to locally increase thickness of a slab as shown in view a-a in attached image?

Yes

Quote (gmd255)

Should I reinforce this thickened part as a spread footing?

I would.

Quote (gmd255)

Is this expensive to do in a field?

No

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/

RE: Local thickening of a slab on grade

Here's a detail for a holddown anchor that is located in the 4" thick section of a ribbed slab. You could just calc the required spread footing reinforcement and modify.

RE: Local thickening of a slab on grade

The main issue (beyond the pure strength design) on thickened slabs-on-grade is that under the higher pressure from walls and columns, that portion of the thickened slab will deflect differently than the relatively unloaded slab adjacent to them. So you may get slab cracking due to the differential movements. In most cases these are minor but depending on the stiffness of the subbase material you could have a very pronounced crack and vertical offset at the crack.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: Local thickening of a slab on grade

JAE, but is there a better / another option for this? I dont see one...

RE: Local thickening of a slab on grade

The other option would be to construct independent footings under columns and walls where the top of footing is located at the bottom of the slab.
The walls and/or columns are then separated by expansion joint material to allow the footings to settle somewhat independently from the slab.

However, I say "somewhat" because if a footing settles, the earth under it and adjacent to it will also be affected by that settlement and the slab may still settle down as well.
The slab cracking would just be less severe.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close