INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

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!

Join Eng-Tips
*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 from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

20 Kip Point Load over a 7' Square Concrete Slab

20 Kip Point Load over a 7' Square Concrete Slab

(OP)
Do anyone has the formula for a point load on a simply supported slab using the "theory of elasticity". AASHTO has a very simple formula but it is around 25% conservative. Essentially there are both torsional moments and bending moments that resist the point load. The crossing beam analogy is the simplest most conservative way to determine the moments in both directions. Any tips will be greatly appreciated.

RE: 20 Kip Point Load over a 7' Square Concrete Slab

Do you have a copy of Roark?

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
No

RE: 20 Kip Point Load over a 7' Square Concrete Slab

What are your boundary conditions, and slab dimensions?

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
Simply Supported on 4 sides, 7 foot square slab, 10 inches thick, 20 kip load in center.

RE: 20 Kip Point Load over a 7' Square Concrete Slab

I'm coming up with a bending stress of 256psi - using Roark.  I am assuming your 20k point load is spread over a 16.8"x16.8" area to conform to the table.

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
I am looking for the bending moment in kip-feet.  

RE: 20 Kip Point Load over a 7' Square Concrete Slab

About 29.9K-ft

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
Seems quite high to me. If you take the 20 kip load and divide that by 2 you have PL/4 or 10*7/4 = 17.50 kip-ft.
This is based on a simplified 2 way distribution of the load.

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
Per AASHTO formula 3.24.6 for conc.load in center of a square slab distributes 50% each way. The formula is p=b^3/a^3+b^3 where a and b are the same dimensions for a square.

RE: 20 Kip Point Load over a 7' Square Concrete Slab

Cap4000-

I agree with EIT and get around 260 psi using Roarke and another method.  For a bending moment, I get a peak moment of 4.4 k'/ft.  The 17.5 k' is a average over the entire width of the plate.  

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
miecz

I agree with the 260psi but I disagree with the 4.4k-ft/ft.

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
miecz

AASHTO E = 4 + 0.06(S) or E = 4.42ft as the effective width
Using 10k/4.42' = 2.26K Load. PL/4 = 3.95k-ft/ft
Does this really apply to a 7' x 7' area??

RE: 20 Kip Point Load over a 7' Square Concrete Slab

cap4000

I don't believe the AASHTO provision (3.24.3.2) is really meant for two way slabs.  I think it is meant for one way slabs with the supporting stringers perpendicular to the direction of traffic.  That said, I think it can give a close enough approximation the way you use it.  We only differ here by 10%, 4.4 k'/ft vs 3.95 k'/ft.  I have one other reference that gives 4.4 k`/ft and another (Seeley & Smith Advanced Mechanics of Materials Article 74) that gives 3.6 k'/ft.

RE: 20 Kip Point Load over a 7' Square Concrete Slab

(OP)
miecz

Thanks Alot. Done Deal.

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!

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