Control of bolt pretension

The contractor is required to exercise strict control over the bolt tightening operations at the installation site and to submit reports on these controls for the review and approval of the supervising engineer. The supervising engineer can independently control the pretension of the bolts, either through a qualified laboratory or through a qualified laboratory. For high-strength bolts used in the design, the pretension force required to tighten the bolts is 55% of the ultimate strength of the bolt. It should be noted that by over-tightening the nuts, the bolt tension may be significantly increased from the above value, but this is not a problem.

In bolts that are pretensioned by over-tightening the nuts, after the bolts are fully tightened, a point on the bolt that is opposite each other is marked with a colored chalk and then it is checked that the over-tightening has been performed to a sufficient extent. To control the pretension of the bolts, a suitable torque wrench that has been previously calibrated in a laboratory accepted by the supervising agency should be used.