huangyhg

direct tensioning of anchor bolts
hello,
i will be going to site next week to witness the direct tensioning of quite a few anchor bolts to make sure everything's going okay. well, i haven't done anything like this before and i don't know what to pay attention for, i'm still green in the belly with just slightly over a year of experience. friends, i could really use a few pointers.
from what i understand, the nuts are loose, and will therefore apply a breaking force of 50% of the anchor bolt capacity. i don't quite understand this procedure, would appreciate your input.
regards,
clansman
also,
what could have possibly caused the nuts to loosen? a colleague threw around the term "relaxation"
direct tension indicating washers have teats or raised bumps that smash down when correct tension is applied, (some splash bright color dye when tensioned). bolt torques are also calibrated for impact wrenches that automatically shut off after reaching the preset torque. the correlation between the torque and the tension is what is calibrated, (changes almost daily with temperature, number of air hoses, location of compressor, length of air hoses, etc.) most designs are attempting to achieve 90% of yield for the high strength bolt. i do not understand the 50% referenced to breaking.
tensioning a bolt involves stretching the free length. i suppose it is possible to "tension" a bolt enbedded in concrete and after a time the portion of the bolt in the concrete "slips" causing loss of the pretension. it seems to me that pretensioned bolts need to be sleeved or at least greased.
why pretension the bolts at all? is it a cantilevered stack or vessel?
anchor bolts embedded into concrete are generally not "tensioned" in the same sense as high strength connection bolts. most anchor bolts nuts are tightened to consistent contact with the
clansman,

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