Bridges

The existing Newmarket Viaduct was built in 1966 and has played a vital role in the Auckland motorway network for the last 45 years. The viaduct carries more than 160,000 vehicles per day over several key arterial roads and the North Auckland railway line. Increased traffic volumes and structural deficiencies created the need to replace the existing six lane viaduct with a new, stronger, seven lane viaduct 690m in length. The new viaduct comprises two box girders joined with an insitu median stitch to form one continuous structure. The box girders are made from precast segments erected by the balanced cantilever method using a launching gantry. This paper describes the design issues and technical challenges that were overcome. The key design objective was maintaining the motorway operations while building the new viaduct. Detailed construction stages were incorporated into the design so that the new viaduct could be constructed within the same corridor as the existing structure; requiring the new box girders to overlap with the existing viaduct by up to 1m, with motorway traffic less than 1m away. The design also considered effects such as: significant construction loads from the 800t launching gantry, different motorway traffic load cases for each construction stage, differential creep and shrinkage effects caused by joining the two new box girders to create one viaduct, significant seismic demands and substructure founding conditions ranging from shallow, fractured basalt to deep Waitemata Sandstone.