6.

Reference to TTHSB / locknut procurement

• Tors-shear type high-strength bolts (TTHSB) have a pintail or Bolt tip (gripping portion) at
the end that takes the reaction force of the tightening torque. Since the base of the pintail
breaks at a certain torque, the tightening torque can be easily controlled
• Today, it is widely used in Japan as installation and post-installation inspection is easier
than high strength friction grip bolt (HSFGB).
• On the other hand, quality control of the manufacture of TTHSB is crucial since the
introduced axial force cannot be adjusted by the tightening torque at site. Variations in the
bolt product itself directly connects to variations in the axial tightening force.

Inner Socket : Pin-tale • A special fastening machine generally consists of a motor,

transmission, and two sockets that hold the nut/pintail
Head and transmit torque.
• The inner socket holds the pin tail of the bolt and
Thread transmits the reaction force of the tightening torque.
Washer Both sockets are designed to rotate in opposite
Outer Socket :
directions.
Nut
Nut • In the initial stage of tightening, the outer socket rotates
Pin tale/bolt tip to tighten the nut. The inner socket rotates until the
Notch notch is cut due to plastic deformation of the notch area.

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6. Reference to TTHSB / locknut procurement

Inner socket

Outer socket

Installation 1. Tightening 2. Base of bolt tip 3. Bolt tip shear break

near shear break and target torque applied

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6. Technical Specification – Manufacture

• Contract main text for TTHSB are in Section VI-3, Bidding Documents – Part 2
Material to be used : Clause 6.2.1 pp75
Material testing and acceptance : Clause 6.3 b) 3) pp80

• Detail of Inspection for TTHSB is written in Page 173, Appendix.9 which specifies
3 inspection categories for manufacture.
1. Dimensional, visual, mechanical properties inspection

2. Defect on surface inspection

3. Axial tightening force inspection

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6. Installation at site – Erection

After Assembly
Girder

Temporary bolt for assembly

Splice plate

Drift pin

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6. Installation at site – Erection

1st tightening & marking

Marking

Detail

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6. Installation at site – Erection

1st tightening complete

1st Tightening
Machine
Marking Sample
Ex : https://www.sg-partners.co.jp/product/pdf02/09_renchi_toruku.pdf

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6. Installation at site – Erection

Tightening Final tightening

Machine

Final tightening
Machine

Ex : https://www.sg-partners.co.jp/product/pdf02/09_renchi_toruku.pdf

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6. Installation at site – Erection

Snap/marking inspection
Only nut
rotating

OK

Washer rotating Bolt rotating NG

together together

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6. Installation at site – Preliminary test

Tension indicator

Bolt insert hole

Fixing jig

Bolt tension measuring device

Example of Preliminary test
(Example: https://tonetool.co.jp/support/pdf/IM-KI013.pdf)

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6. Installation at site – Preliminary test
High Tension Bolt Preliminary Test Sheet
Project name
Contractor name
Bolt supplier name
Scheduled tightening section
Bolt type
Test date
Lot number
Weather and temperature
Standard tension force
Inspector name
Tightening machine number
Tension measuring device number
Test report Record of each measurement result
Average, C.V., Final result

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