10 . FRACTURED TRUSS END LINK AND REOPENING OF THE BRIDGE
The photographs on this page show the location of the failed truss end link , on the south side of the north main tower and a close up of the failed member showing the crack .
The truss end link carries vertical loading into tower bracket , it accommodates longitudinal truss end movement . Live load is dominated by traffic loading , wind and temperature .
On 1 December 2015 during an inspection a broken link was identified . The failure caused loss of vertical support for a 400t section of the truss and created a cantilever supported by nearest hanger .
There was the potential for the corner of the truss to drop by approximately 250mm if the remaining section
of the damaged link failed . This situation would result in severe damage to the bridge and risk of injury to users so it was decided to close the bridge to traffic on 3 December . Following the installation of a temporary support at the location of the damaged link , the bridge reopened to cars and light vehicles on 23 December 2015 , and to all traffic , including heavy goods vehicles , on 20 February 2016 .
The repair had two phases :
Phase 1 : Repair – allowed all traffic to return except HGVs ( 23 December 2015 )
Design included specification of main loads , identification of structural requirements on repaired link and construction considerations .
Following repair load testing was carried out , the bridge was monitored using 150 strain gauges and displacement sensors and 4 data units .
Phase 2 : Support – allowed all traffic to return ( 20 February 2016 )
Additional bracket was bolted to tower face above road / carriageway level , spreader beam installed below carriageway level and bridge cables / strand jacks were installed to support the truss .
After opening the bridge , Phase 3 : Works follows : � Existing truss end link member and post are removed . � New post , support bracket and bearing are installed . � Concrete is poured to strengthen the tower .
Structural health is constantly monitored by strain gauges , displacement transducers and temperature sensors . WIM data are provided .
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