Ngā Hau MāngereA strategic connection and an iconic community feature

Known during construction as the Old Māngere Bridge replacement, the bridge has recently been gifted the name Ngā Hau Māngere by mana whenua to reflect the cultural history and landscape in which it sits. In translation it means the 'gentle lazy winds'.

The Old Māngere Bridge was both a cherished community asset and an important piece of engineering history – it is believed to be the oldest reinforced concrete bridge crossing a harbour in Aotearoa New Zealand. Retaining the history and character of the old bridge was an important theme through the community feedback, so salvaged pieces of the old structure feature in a heritage garden alongside native planting on the northern side of the bridge.

Recognising the bridge’s intent as both a strategic connection and a place for the community, seats are located across the bridge deck in three different designs to allow individuals, couples, or groups to view both the Manukau Heads and Waitakere Ranges. Bold use of colour on the bridge deck loosely demarcates areas of movement and pause – with purple used for the anti-slip coating in seated spaces and black applied in walking and cycling areas.

Innovation needed to solve engineering challenges

The bridge’s distinctive curved aesthetic was challenging to design and construct. As the arch is on one side of the deck only and inclines outwards, there are opposing forces acting on the structure – compression forces in the arch and tension forces in the deck. To understand the internal flow of these forces and validate our design, our team created a full finite element model.

The arch’s cross section varies in both depth and width throughout its length, making analysing its propensity to buckle difficult using local design standards. Aurecon applied international design standards and advanced analysis to calculate and understand the capacity of the arch.

Developing the construction staging for the incline pier columns which support the arch was challenging, due to the significant structural demands generated by the shallow angle needed to match the arch. To manage this, our team used post-tensioning both within the piers themselves and externally to connect the top of the piers together.

The complex geometry between the arch and pier meant there was limited space available to provide arch support, while at the same time there is a large structural demand created by the vertical loads and horizontal tie forces. This meant a conventional reinforced concrete corbel to transfer loads was not practical in the space available.

Aurecon developed an innovative design based on thick steel plates embedded into concrete to transfer the loads.