Discussion on Papers 9 to 11

Delegate

I want to talk about tension control bolts in terms of strengthening and maintenance and replacement. This will be nothing new to our Japanese visitors, because in terms of friction grip bolts the tension control bolt dominates the Japanese structure market, and many hundreds of thousands have been used over there.

It is a bolt with a rivet head and if you look down the other end beyond the nut you will see a small splined section and between the splined section and the end of the thread there is a small rebate. There is a special tool that engages the spline and the outer part of the tool engages the nut so the one pulls against the other to tighten the bolt. There is no problem about quality assurance because the bolt is so designed in terms of strength, lubrication and shape that when the spine section breaks off at the end of the bolt the tension in that bolt is correct. It is also made of better steel than BS 4395 HSFG general grade bolts, being grade equivalent to the HSFG higher grade. There are restrictions on the use of higher grade bolts in that standard, but the ductility of this bolt is guaranteed at 14% against 9%, I believe, for higher grade, and 12% for general grade (8.8 equivalent) HSFG bolts.