Grafton Bridge comes together, one giant bit at a time
THE new Grafton Bridge is growing again, with concrete segments beginning to be joined to the existing pier.
The pairs of concrete segments will connect the bridge together and are currently being added to pier three, which is the second pier in the water off the southern bank.
The process is called cantilevering, a vital part of the bridge design and where it takes its description from - a balanced cantilever bridge.
The 176 pre-cast segments, which weigh between 60 and 70 tonnes each, are being poured locally in the Through St facility.
Once complete, 13 segments will arch across each side of the pier to meet in the middle.
This stage of the project will progress from the southern side of the river to the north, with up to two segments lifted into place daily by a crane operating from a barge on the river.
Once in place, segments are checked to ensure they align with the adjoining segment. An epoxy resin, like super-strength glue, is then applied to the face of the segment, bonding it to the next.
As each segment is installed, temporary post-tensioning is applied that 'bolts' the segments together. After four segments are installed, two each side of a pier, multiple steel cables of about 15mm in diameter are threaded through ducts in the segments and stretched to lock in energy to compress the segments together.
More than 200km of steel cable will be used for the new bridge.
This process is expected to take seven months to complete, weather permitting, after which the temporary jetty on the southern bank of the Clarence River will be dismantled.