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Re: PT Construction

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First I assure you the beams on the first floor have been tensioned, as well as the beams on the next levels.  The tails will not be cut off until the stressing records are approved, but they will definately have been tensioned.
Typical PT construction in multi-story slabs is to re-use the shoring at each new level.  In high rise table top forms are common.  Floor stressing takes place within three to five days.  The weight of the new wet level is too high to shore off a single level, so the most recently completed level is "re-shored" with the posts you see, and left in place for typically three floors.  Once this amount of shoring is reached, the system is rotated up through the structure, with the lowest re-shores pulled to reshore the newest level and the table tops set for the next wet level.  The weight of the new construction is distributed through the next lower three floors based on compatibility of deflection.  In this manner the shored portion of the building can be ten floors in the air while the follow-up crews are in the lower levels installing cladding, mechanical, electrical, finishes and so on.
Standard specification requires tensioning of the floor system prior to re-shoring and moving the forms up for the next level.
----- Original Message -----
Sent: Friday, April 29, 2005 10:22 AM
Subject: PT Construction

I know this is going to be a stupid question for a lot of you, but I am young and this is the first time I have seen this kind of construction actually going up.
I attached a link to a picture of a building under construction (it is not my project). It is a reinforced concrete slab supported by post tensioned beams in each direction.  
The shoring is not really being removed the way I would have thought it would be based on my very limited experience with post tensioning. None of the beams have been tensioned, and the shoring has been removed from the first floor only. It was my understanding that PT beams are normally designed to balance a certain percent of the dead load, and the untensioned beams on the second floor are right now taking all the dead load on this floor plus some from the floor that is being poured at the highest level. I know there is a minimum amount of mild steel in the beams, but I wouldn't think it would be designed for this much dead load. Can anyone please explain what is going on here? What is the point of using post tensioned beams if there is enough mild steel to take all this load anyway?

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