8 . CABLE BAND BOLT REPLACEMENT
Cable band bolts form a small but vital part of the suspension bridge . Their primary function is to generate sufficient friction to prevent slippage of the bands down the main suspension cables under loads applied by the hangers .
In the main span there are typically 4 bolts per cable band which increases to 6 near the towers where the cable is steeper . The heavier side spans typically have six bolt bands except near the main and side towers where there are 8 and 4 bolts respectively .
In 1995 a hanger rope was found to be frayed , and tests on some other ropes showed concerning deterioration .
It was decided to replace all of the hangers . At the same time the original cable band bolts were replaced as well . The works were completed in 2000 .
In 2007 during a routine inspection one nut was found to be cracked and during further checks in 2008 and 2009 nine failed nuts were found .
In March 2012 during inspection of the cable following completion of the dehumidification project a further 17 cracked nuts were found . It was decided to undertake the replacement of all 944 bolt assemblies on the bridge , in order to reinstate the structural integrity of the hanger system and minimise the risks to traffic .
Figure 11 : Example cracked nut as found Figure 12 : Example cracked nut after removal
9 . MAINTENANCE OF THE MAIN EXPANSION JOINTS
In each carriageway of the suspended spans , at both main towers , there are two joints . Each of these joints ( in total eight ) is of the roller shutter type whereby a series of plates slide over fixed curved girders .
Roller shutters of this type have a typical design life of 20 to 30 years . In 1975 a detailed inspection was carried out . It was reported that the joints were generally performing well with some evidence of wear .
Figure 13 : Long section through the joint
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