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RE: Limit on Pour Height

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Title: Limit on Pour Height

Jim,

 

I believe the columns of that building down on Pike or Pine Street used 10,000 psi concrete pumped from the bottom (sorry I don't know the specific building).

 

We just did a deep concrete reservoir with external vibrators and it worked well after de-bugging.  If I had it to do over again, I would have specified that the contractor do a test pour with external vibrators to prove his means and methods before production.

 

Bob Garner, S.E.

 


From: Jim Lutz [mailto:Jim.Lutz(--nospam--at)bhcconsultants.com]
Sent: Wednesday, November 19, 2008 8:29 AM
To: seaint(--nospam--at)seaint.org
Subject: Limit on Pour Height

 

In my experience, the biggest concern with tall pours is not form blowout or deflection, which you can design for, but how to get good consolidation. I mostly run into this in the context of tanks, where walls are poured tall with no horizontal joints. If the walls aren’t very wide, there are issues with dangling a vibrator down a deep form and trying to see, much less control what you are doing. For externally prestressed circular concrete tanks, which have fairly thin walls and not a lot of conventional reinforcement to get in the way, it is typical to cut pour windows in the forms at vertical intervals of about five feet so the form can be easily accessed with vibrators. The windows are then closed up as the pour advances. Some pretty tall walls have been built this way.

I have also heard of the concrete being pumped into the form from the bottom, but have never done it myself. It’s also important to be able to access the bottom of the form where consolidation is especially critical, near the waterstop. For tall walls on rectangular tanks this doesn’t work, because there is generally so much steel in the way you can’t get past the curtain to do anything. In situations like this, it’s a good idea to consider wall thickness to make sure you have some space between the curtains. It’s usually cheaper to go with a little wider wall to reduce steel percentage anyway, at least for conventionally reinforced rectangular tanks.

Jim Lutz, PE, SE

Senior Structural Engineer

1601 5th Avenue, Suite 500

Seattle, WA  98101

Ph: 206-505-3400

Fax: 206-505-3406

www.bhcconsultants.com