Bolts in pre-tensioned or slip critical joints must be tested to verify that the bolts can develop at least the minimum required bolt tension using a bolt tension measurement device. So, what is a bolt tension measurement device and how does it work?
It is a device capable of indicating bolt tension. There are two different bolt tension measurement devices, a hydraulic indicator, and a mechanical indicator. The hydraulic indicator has fluid inside its chambers and compresses during bolt tensioning which forces a needle to move thus indicating the bolt tension. The hydraulic unit must be calibrated at least annually. A DTI, such as a DuraSquirt Direct Tension Indicator (DSQDTI) may also be used as a bolt tension measurement device. The DSQDTI is a mechanical device that has bumps on it that correlate to bolt tension. We will provide a calibrated gap, for its DSQDTI, to confirm that minimum bolt tension has been achieved. Our DSQDTIs are calibrated for every lot that is manufactured. The DSQDTI bumps must be compressed until the calibrated gap is reached and orange media visible from all bump locations. This is known as complete indication and satisfies the pre-tensioning requirment.
If a hydraulic bolt tension measurement device, then three bolts from every lot and grade must be tested for the duration of a project. If a DSQDTI is used as your bolt tension measurement device then only three DSQDTIs need to be tested. Both methods work however the DSQDTI will make pre-installation faster and easier.
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