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

Concrete columns Supporting PT slab drop cap retrofit

Concrete columns Supporting PT slab drop cap retrofit

Concrete columns Supporting PT slab drop cap retrofit

I was hired to perform a structural evaluation of the existing construction on a 6 building condo development.  the development is a subgrade garage with concrete columns and PT slab above supporting up to two stories of wood framed construction.  Originally it was only the distress report, but as my investigation revealed considerable construction defects, the owner then asked me to perform structural calculations on the existing structures to verify they were engineered correctly.  Everything was OK, until I got to investigating the punching shear capacity of the PT slab at the columns.  I hadn't noticed it before, but the concrete columns supporting the PT slab were only 12" square....with NO drop caps.  As a result the punching shear force is about 35% higher than the punching shear capacity.  Now my question, I need to attach a drop cap to the concrete column, but am unsure of the best way.  With the connection force being around 70k on some columns, I don't think I can attach the retrofitted drop cap to the concrete column without a million bolts.  I was thinking of fabricating bent plates that would sandwich around the concrete columns and then welding them together, thus providing a direct path to the foundation.  I would like to hear if anyone else has any better/more cost effective ideas.  I was looking into FRP, but couldn't find any examples of FRP and attaching drop caps on the internet.

RE: Concrete columns Supporting PT slab drop cap retrofit

Make the columns bigger if you can.

RE: Concrete columns Supporting PT slab drop cap retrofit

Hokie66, thay was also an option we considered. However, the columns currently stick out 6" into the parking spaces, adding an extra 6" - 9" to the sides of the column (which is about what I have calculated I will need depending on the column) would ruin the parking space. We can't lose any parking spaces because there are currently two spaces per unit without any extras.

RE: Concrete columns Supporting PT slab drop cap retrofit

couldn't you add the new dimension along the length of the car park so new column would be 12"x36"?

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

RE: Concrete columns Supporting PT slab drop cap retrofit

RE's solution is what I meant.  Having recently reviewed another engineer's proposal for solving a punching shear issue, I am convinced that making the columns larger is the best approach.  Installing steel brackets is cumbersome, involves a lot of head scratching about consistent deflections, and is likely impossible for such a small existing column.

RE: Concrete columns Supporting PT slab drop cap retrofit

I misunderstood your first post and it has been clarified by rowingengineer's post.  In the review you recently did, how was the new column portion connected to the exiting column?  I am somewhere in the order of 70k deficiency on some columns, seems like i would still be stuck with a lot of dowels to tie them together.

RE: Concrete columns Supporting PT slab drop cap retrofit

Are the PT slabs supporting parking or something else?  Not sure what the floor area tributary to the column is, but LL reduction could get you some of the way.  

Do you have enough headroom to retrofit on a capital?  Anything on  a 12" column is going to be tough

RE: Concrete columns Supporting PT slab drop cap retrofit

The PT slabs are supporting wood framed living space above, some 2 story some single story.  Live load reduction has helped out some.  i was even able to reduce the roof live load a little bit.  There is enough room to retrofit a capital or drop cap, which is what I was hoping to get some ideas on here.  The 12" columns do make it tough, which is one reason why we were looking at surrounding the concrete columns with steel columns and providing steel cap and base plates to increase the punching shear.

RE: Concrete columns Supporting PT slab drop cap retrofit

I don't think the connection of the new adjacent columns to the existing needs to be cumbersome.  Some nominal dowels...or even a gap between them.  As long as the new column can take its share of the load and the total shear perimeter is increased as required, I would be comfortable with this solution.  You could use steel columns, but fire rating issues may make the concrete more attractive.  Either way, non-shrink grout should be used to ensure complete bearing.    

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


eBook - Integrating the Engineering Ecosystem
Aras Innovator provides multiple options for integrating data between systems, depending on the scenario. Utilizing the right approach to meet specific business requirements is vital. These needs range from authoring tools, federating data from various and dissimilar databases, and triggering processes and workflows. Download Now
Research Report - Simulation-Driven Design for SOLIDWORKS Users
In this engineering.com research report, we discuss the rising role of simulation and the paradigm shift commonly called the democratization of simulation. In particular, we focus on how SOLIDWORKS users can take advantage of simulation-driven design through two analysis tools: SOLIDWORKS Simulation and 3DEXPERIENCE WORKS. Download Now
White Paper - Industry 4.0 and the Future of Engineering Education
With industries becoming more automated, more tech-driven and more complex, engineers need to keep their skills and knowledge up to date in order to stay on top of this wave—and to be prepared for the Industry 4.0 future. The University of Cincinnati offers two online Master of Engineering degree programs designed specifically for practicing engineers. Download Now
eBook - The Design Gridlock Manifesto
In this eBook, you’ll learn 6 ways old CAD technology slows your company down and hear how design teams have put those problems to rest. “The Design Gridlock Manifesto” shares first-hand modern CAD experiences from 15 companies around the world. 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