huangyhg

posttesnsioning eqipment calibration before or after transpo
please,
what is your oppinion??
on page 326, section 20.2.3 stressing, of the post-tensioning institute's post-tensioning manual, 6th edition, it says: stressing equipment should be accompanied by calibration records that are no more than six months old and should indicate the proper hydraulic gauge pressure to which the tendons are to be stressed to achieve the required final effective force.
page 89, section 4.4.7.2.1 stressing equipment says: for each ram and gauge unit used on the job site, the post-tensioning supplier must furnish certified calibration charts to the design engineer prior to stressing. the post-tensioning supplier must further verify that ram and gauge serial numbers match those listed on the calibration sheets.
the problem is how do we understand the use of "prior" for me it means after delivery, and imidiatelly before stressing not before the transportation half way around the world.
the contractor think different as you may expect.
(to get it right assume you are wrong)
from a previous post you stated that this is a multistrand ram for bridge girders...multistrand rams are pretty big beasts (eg 31 strand multistrand ram weighs close to 900 lb).
calibrations for us bridge projects are usually conducted by nist-traceable certified and experienced labs and can cost several thousand dollars and usually are independent labs. after transportation "half way around the world", i am going to guess that such independent and experienced labs may not be available.
we always pre-calibrate our rams before we transport them to remote areas.
based upon the evidence you have from the pt contractor, why do you feel the ram/s are not in calibration?
if the project specifications state the ram shall be calibated prior to use (and say within the last 6 months) and they comply (written and signed calibration certificates), then unless you have some visible or other evidence that the rams are not in calibration, let them stress and check the tendon elongations. the onus is on the pt contractor to verify stressing force usually via gauge pressure and tendon elongation. if the results are more than +/- 5% then the ram calibration may be the issue. it may also be four or five other variables too that explain out-of-tolerance elongations.
good luck.

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