Broomfield river bridge was delivered by leading the bridges team located in geographically separate offices in Auckland, New Zealand and Brisbane/Cairns, Queensland , developement and management of the detailed design to the Technical Brief for the 110m long multi-span prestressed psc composite deck unit bridge for crossing the Bloomfield River. The structure is geographically remote requiring the extensive use of precast concrete crossheads and deck units. This approach minimises the time required for working in the watercourse which is subject to high stormwater event flows, (design event 1 year ARI).
Durability of the structure in the exposure classification C environment was a major consideration for the developed design. Another facet of the project has been difficult ground conditions, scour susceptible material overlying very hard rock with the site accessibility on the existing road network proved a challenge for the mobilisation of heavy piling plant required for the large diameter bored cast in place piled foundation solution.
The superstructure solution modified a typical QTMR bridge form utilising a reinforced concerete insitu deck, with modified 750mm QTMR psc deck units. The modification of the units allowed for the reduction in the mumber of beams by 50% for the six span structure. This was a reduction from 108 psc deck units to 54. Reducing the number of vehicle movements on the inner developement road.
In addressing future maintenance requirements significantly fewer hydraulic jacks will be required for the bearing replacement anticitated to be required at year 35.