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RE: Prestressed Double T Camber

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A contractor once told us that he saw this in prestressed bridge beams.  His crew would grumble when they got “Saturday beams” – beams that were cast on Saturday, and hence left in the forms an extra day when the plant was shut down over Sunday.  They would have noticeably different camber than the other (“weekday”) beams, and they’d have to accommodate for it when they set their precast deck panels.

 

-- Joel

 

SHW Group, Inc.

Plano, TX

 


From: Wontae Kim [mailto:kimwontae(--nospam--at)email.com]
Sent: Wednesday, July 23, 2008 10:41 PM
To: seaint(--nospam--at)seaint.org
Subject: Prestressed Double T Camber

 

Hi!

 

Recntly we measured cambers of 10' wide, 60' long precast prestressed double tees for parking garage.

Generally, camber is about 3" to 4" for this kind of DTs.

But, this time all DT cambers are about 1".

Only difference in production condition is they stayed in mold more than three days because of holiday;

 typically we strip precast members within 8 hours of steam curing after pouring concrete.

 

I heard that detensioning is required immediately when concrete drying shrinkage or temperature shrinkage may cause

severe damage to long members like bridge girders.

But, I have never heard delayed detensioning could cause 'significantly' less camber.

Will these DTs have eventually the similar camber of DTs which were stripped 8 hours later?

 

If you have any experience or info, please let me know.

 

Thanks!

wontae


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