Bridges

The New Old Mangere Bridge (NOMB) replaces what is understood to be the oldest reinforced concrete bridge across a harbour in New Zealand. Pedestrianised in the 1970’s, the existing bridge has become a much loved landmark for the local community and serves as a link for pedestrians and cyclists, and a popular fishing location. At 100 years old, the bridge is in a very poor condition and has reached the end of its service life.

Extensive consultation was undertaken to determine the requirements of the replacement structure. Designed in collaboration with an architect, an urban designer and two local artists, the solution provides a delicate balance of attributes to meet the varied stakeholder expectations. The design provides an agreed minimum width of 8m with localised widenings to allow for fishing and a form of community space. Navigation access to the upper harbour is improved through increased clearance, a 60m main navigation span, and allowance for the future retrofit of an opening span.

The main navigation span consists of a single steel tied arch that supports an 8m wide, 1m deep steel box girder deck to match the approach spans which are of integral concrete hollowcore girders. The arch itself varies in section and leans outwards at 22o to the vertical. The deck is supported via eleven proprietary hangers, and the whole span is supported on concrete “V piers”. The V pier legs splay both vertically and horizontally and are post tensioned to ensure crack widths in the splash zone are adequately controlled.

The paper will present:

• Concept design development (geometric and form finding) including the use of physical and virtual reality modelling
• Aesthetic considerations
• Structural requirements and design
• Durability solutions for a marine environment.

Detailed design is complete with construction due to commence in 2017.