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Re: Prestressed Double T Camber
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Prestressed Double T Camber
- From: "Wontae Kim" <kimwontae(--nospam--at)email.com>
- Date: Fri, 25 Jul 2008 07:07:16 -0500
Thank you for your responses!
I did not know that late stripping of prestressed members from the mold would cause severe camber difference.
Though, this deviation is within product tolerance (0.25"/10ft , max 0.75"/10ft) according to PCI Design Handbook;
I got 2" while 0.75x60'/10'=.45", which is very big number!
I understand camber is related with E and E is eventually affected by f'c.
In my case, when I ran a program to compare how f'c affects camber using 3500psi (@stripping)/5000psi(@28-day)
and 6000psi(@stripping)/8000psi(@28-day), cambers were only 0.5" difference.
I am still puzzled at what caused 2" camber difference.
In most precast plants, steam curing is popular and I think concrete strength does not change much between 12 hours
and 36 hours after concrete placement
because like my company weekend concrete mix may be used and steam is not provided during weekend.
Here is my conclusion:
we have to cut strands if prestressed members stay in the mold for extended hours in order to prevent strand failure and/or concrete spalling
and excessive camber variance.
I did not know second part was so important.
PS: Jim G., I appreciate your remedial advice!
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