High strength bolts torque values
High strength bolts torque values
(OP)
Hi all ,
In Australia, to follow the standards AS3990 and AS4100, what should be the torque values for HSS bolts (grade 8.8) using a torque wrench?
for example I think it should be 580Nm for M20 galvanised bolts .
However everybody seems to use 370Nm
I have calculated as follows for M20:
1- T = K x Fi x D
2- Fi = 87 / 0.6 = 145 Kn. Minimum bolt pretension as per appendix F in AS3990. This is to drive the bolt to proof stress as i can see
3- K = 0.2 for galavanised
4- D = 20
therefrore T=580 Nm
this way all the threads are engaged and the bolt can actually surpass it s yeild strength and not be subjected much for fatigue, this is why the code prohibits using already torqued bolts.
In Australia, to follow the standards AS3990 and AS4100, what should be the torque values for HSS bolts (grade 8.8) using a torque wrench?
for example I think it should be 580Nm for M20 galvanised bolts .
However everybody seems to use 370Nm
I have calculated as follows for M20:
1- T = K x Fi x D
2- Fi = 87 / 0.6 = 145 Kn. Minimum bolt pretension as per appendix F in AS3990. This is to drive the bolt to proof stress as i can see
3- K = 0.2 for galavanised
4- D = 20
therefrore T=580 Nm
this way all the threads are engaged and the bolt can actually surpass it s yeild strength and not be subjected much for fatigue, this is why the code prohibits using already torqued bolts.





RE: High strength bolts torque values
The US methods do permit a calibrated wrench installation method, similar to what is described in Appendix K of AS4100, however the target torque must be established daily by running a series of tests in a calibration device.
There are no prepublished values available for torque installation that would be precise enough for general use.
RE: High strength bolts torque values
http://www.FerrellEngineering.com
RE: High strength bolts torque values
Pretensioning to design values causes yielding of the bolt which is why they can not be reused.
RE: High strength bolts torque values
RE: High strength bolts torque values
Not entirely correct. If you stop at Design, you are still in the elastic range, deep into the elastic range. Torquing/tensioning slightly past Design will usually cause yielding, plus some coatings [galvanizing, yellow zinc, etc] increase the probability of cracking. Thus the general prohibition for reusing fasteners.
RCSC and AISC allow reuse of A325 non-galvanized bolting, if there is assurance that they were not overtorqued/overtensioned.