Contact US

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.

Students Click Here

prestressed/ precast lift slab capacity

prestressed/ precast lift slab capacity

prestressed/ precast lift slab capacity

I am trying to determine the capacity of an existing (1968) precast/prestressed lift slab (24'x24' column spacing).  It seems the original engineer did not include some significant equipment loads and my client would like to add some heavier equipment.  If there is a simplified method or software out there please let me know how I can acquire it.  Thank you!!

RE: prestressed/ precast lift slab capacity

The warning by other answering this post in other channel about punching shear is the most serious one for lift slab. Lift slab -and steel columns, even with collars- are insets in the floors, and very sensitive to vertical dynamic shakeout.  That the static capacity may be astounding as many tests may show does not diminish what above stated. Upon shakeout the connections are to suffer severily. This a child that has pierced a paper with a stick very well knows. It is like the failed joint in the sunk floating offshore norse structure, if the failure is what Collins and Mitchell indicated, heck, to seam parts 1,5 m thick one cannot use 20 cm insets in each side, whatever the calculations may say about the length of necessary embedment.

RE: prestressed/ precast lift slab capacity


I hope that you have access to the original structural drawings.

If the slab was post-tensioned then you can use any current P-T software. I use RAPT for 2D analysis and SCS-FLOOR for more complex situations where FEA is required. I would think that a 2D analysis based upon equivalent frame would be sufficient and adequately able to model the structure.

BUT you will need to review the original details of the column/floor connection. The shearhead collar connections were often proprietry, with channel, angles and steel adjustment wedges welded permanently after the floor slab elevation was set.

You will need to check ACI 318 (if the project is in the US) where the code required a minimum of 2 tendons in each direction through the critical shear section over the columns.

I am sure that you are aware that several LIFT SLAB projects collaped during lifting, in both the US and UK.

Also, consider that for a P-T floor system built in 1968 with unbonded (?) P-T, depending on the exposure and environment,  corrosion may be present in the tendons with possible strand breakages. You may need to do a bit of investigation to see the "real" condition of the structure.


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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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