Boltight perfect for suspension bridges
23 May 2017
Bolts connecting cables to the decks of today’s suspension bridges should be tightened simultaneously to minimise operator’s influence on the tightening result, reports Nord-Lock Group.
In other words, if an operator starts at one end of the bridge – tightening the bolts as they go along – by the time they reach the other end, the first bolts tightened are likely to have started loosening. In the worst case, uneven lift of the deck could cause elements of the bridge to warp and crack.
To manually tighten all bolts on a bridge simultaneously would take a huge amount of manpower acting in exact concert and in constant communication. This needs to be coordinated via radios or by a foreman. Even in this situation, there is a good chance of human or mechanical error, as well as the need for expensive equipment to reach a sufficiently high pre-tension of the bridge bolts. Even after the operation is complete, all bolts must be checked in order to make sure they have reached their load. Insufficient tightening of the bolts could be disastrous for the bridge’s structural integrity.
Boltight hydraulic tensioning offers a far better solution to the problem of achieving pre-tension in a number of cables and bolts – simultaneously. Boltight tensioners can be fitted to all the bolts
requiring tension, which are then connected to the same hydraulic pump. The pump is brought up to pressure, producing an axial load and causing the bolt to be stretched axially. At this point, the operator can simply run the nuts down to the normal position against the element to be clamped with little effort. This is because the bolt is already in its stretched condition, so rotating the nut to its ‘tight’ position can be performed with zero resistance and little effect of friction.
Once the required tension is achieved, the hydraulic pressure is released. Tightening is achieved to a very high tolerance and often at a very high percentage of the bolting yield strength. Boltight hydraulic tensioning tools are lightweight, compact and easy to use, with an inherent focus on safe operation and product quality.
As a result of its efficiency, the Boltight solution has proven popular on a number of bridges, including the Bosphorus Bridge Project in Turkey, the Hammersmith Flyover in London and the Oakland Bay suspension bridge.