Tiwai Bridge Replacement Project

Award:  Other Entrants

Project:  Tiwai Bridge Replacement Project

Entrant:  Structex Ltd

Owner:  Invercargill City Council

Consultant:  Structex Ltd

Contractor:  Fulton Hogan Civil South

Structex was engaged by Fulton Hogan to assist in delivering a 490m replacement deck to the Tiwai Bridge.  Being the only access to NZ Aluminium Smelter's Tiwai Point plant, the bridge has significant economic benefits to the people of Southland.  The clever use of concrete components delivered a superb result with minimal interruption to this estimated $3million a day production facility.

The justification for the project was based on the existing superstructure having suffered durability issues and reached the end of its useful life; and being significantly short of meeting the requirement of HN-HO-72 loading requirements, being only 80% of Class 1.

The use of concrete, specifically a Double Hollow Core (DHC) deck solution, enabled all of the following functional requirements of the project to be met or exceeded:

1.  The new superstructure had to be within 127% of the weight of the existing superstructure.

2.  The existing deck soffit clearance from the underside of the bridge to the water below had to be maintained.

3.  For the purpose of the smelter maintaining production, closures of the bridge had to be kept to a minimum.

Using concrete as opposed to other materials, coupled with efficient construction methods, enabled all of the above requirements to be met within the constraints presented.  In addition, Structex/Fulton Hogan were able to present an option to increase the bridge to two full, 3.5m wide lanes without any cost penalty.