Bolt Tension Measurement from Head Strain Data

Development and testing of a new method for continuous monitoring of tension in high strength bolts, based on head surface strain calibration, is described. The method overcomes access and interference problems associated with other methods. Radial and tangential head strain measurement are compared and the former is shown to be superior in terms of sensitivity and consistency. Calibration is linear up to at least 130% of proof load. Conditions in a calibration rig differ appreciably from those in a joint during tightening but it is shown from tests that the respective responses are related by a constant factor that depends only on the details of the joint. Correction factors are given for a variety of joint conditions.