Return to index: [Subject] [Thread] [Date] [Author]

Re: PT Construction

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Well,  I almost didn't read this post - I assumed it was probably a discussion of something like whether illegal immigrants should be allowed to have driver's licenses.
As far as whether the beams were tensioned,  I would say they were,  even though it might not look like it.  I have only seen one instance of where a beam wasn't tensioned before shoring was removed.  It was a beam in a one-way slab and beam parking garage.  The engineer had (with good but misguided intentions)  specified that half of the tendons in each beam be stressed from each end.  The intent was to equalize prestress losses;  losses are greatest at the stressing end because of the wedge seating.
Unfortunately,  this is really not a standard way of doing things and people got confused.  One tendon didn't get stressed at all; but since the wedges had been hand-seated, the tendons got cut off.  The beam cracked all to hell within about 10 minutes after the shoring was removed.
With respect to prestress losses - creative procedures like this really aren't necessary;  the calculations are approximate enough to allow for these losses.
The tendon tails will tend to be sticking straight out if they are stressed.  However, if they are fairly long, they may sag under their own weight and look like they haven't been stressed.  If you can get close enough you can look for the paint marks that are used to measure the elongation.  Usually, they use something like a 2 by 4 to make the mark, so it starts at 4 in. away from the slab edge.  Once it is stressed,  it will be 4 in. plus the elongation (about 8 in. per 100 ft.)  If you can really close, and know what to look for,  you can look for the wedge marks.
Gail Kelley