×
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

When to consider Main Floor Dead Load

When to consider Main Floor Dead Load

When to consider Main Floor Dead Load

(OP)
I know there are many ways to design foundations although the client is leaning towards this one. It is a two story residential building. He is looking for a thickened slab design with screw piles. I currently have the screw piles embedded in the concrete thickening at approximately 8'-0" spacing.

My question is whether I need to consider the concrete slab as a dead load on my piles. Normally main floor is not accounted for as there is a joint separating the concrete slab to the pile/gradebeam, although in this case they are well tied together. My initial instinct was yes I would need to consider the dead load although after further looking into it I'm second guessing.

I would say that the piles would tend to settle more since there would be significantly more load on them. If this were the case then the concrete slab would only reduce the loading on the piles although this may not always be the case. If there were to be settlement of the slab right after pouring the slab there may be settlement from the weight of the concrete alone.

It worthy to note that the slab were to be held in place by the piles while the soil underneath settled then the slab would not be able to handle the loading and would fail. (Slab on grade only and not structural slab).

Let me know your thoughts. Much Thanks

RE: When to consider Main Floor Dead Load

I think that's a bad plan either way. You should either separate the slab-on-grade from what will essentially be a grade beam between piles, or change it to a structural slab. Otherwise you'll end up with some pretty unsightly cracking when the screw piles settle but the slab doesn't.

RE: When to consider Main Floor Dead Load

Personally, I wouldn't bother with the slab on grade contribution. And, were I to, I'd just assume something simple like 10X the slab thickness as tributary.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: When to consider Main Floor Dead Load

(OP)
So I should recommend to the client to go with Pile and Gradebeam, and skip the slab thickening altogether since it would be more prone to cracking from differential settlement.

RE: When to consider Main Floor Dead Load

If the soil below the slab is bad enough to require screw piles to support the loads, I would be designing the slab as suspended and the piles would have to support it all!

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