Okura River Bridge

OTHER ENTRANTS

Okura River Bridge

Submitted by:  Bridge Concepts

Owner:  Okura River Residential Society

Consulting Engineer:  Airey Consultants Ltd

Contractor:  Bridge Concepts

Sub-contractors:  Duracrete Products  /  C & D Concrete  /  Bill Harvey  /  Gibbons Contractors

Summary:

Masonry arches transmit structure loads to their abutments and foundations by transferring compression forces through the arch ring.

Arch bridges have proved themselves to have lives typically 10 times greater than other types. Some have been in use for 2000 years. They became expensive to produce and the ability to design them was lost. Believing that they could be re-engineered for economy and speed, the Bridge Concepts team set about developing a new arch bridge for New Zealand markets.

The bridge at Okura River represents a major step in that process. It is built from 6 x 1 m wide lightweight precast concrete ring sections which are lifted together to form an arch which then has a dense concrete saddle applied. The concept of making lightweight sections that are still strong enough to carry the load of the saddle is entirely new. So is the system of analysis created for dealing with earthquake loading.

A load test showed the bridge to deflect about 1mm under a 10-tone axle load. That is 1/7000 of the span or about 1/20th of the deflection of normal designs.