OTIRA VIADUCT

The Otira Viaduct carries Highway 73 through the mountainous terrain of Arthur’s Pass National Park on the South Island of New Zealand.

The structure is a cast-in-place bridge built in balanced-cantilever with form travelers. The viaduct consists of three balanced cantilevers and four spans measuring 87, 134, 134, and 87 meters for a total length of 442 meters.

Threaded through a steep valley above the Otira River the viaduct contains a sweeping s-curve and a superelevation that varies from -6% to 3% and a steep grade that varies from 11.7% to 14%. The Otira Viaduct contains New Zealand’s longest reinforced concrete box-girder bridge span. Each cantilever has sixteen segment pairs, each 4.0 meters in length with a 9.0 meter deck width and box depth that varies from 7.75 meters at the pier to 2.75 meters at mid-span. Counterweights were used during cantilever erection to control the out-of-balance loading and the interior spans were jacked apart prior to pouring the midspan closures.

Construction on the viaduct started in February 1997. The project was completed in January 2000 with a cost of $25 million.