As part of the NZ$500m Auckland Electrification Project, which delivered an electrified rail network to Auckland, KiwiRail commissioned WSP to design the replacement of five bridges: Browns Road, Jutland Road, Station-Lupton, Morrin Road and Mt Wellington Highway Road Bridges, which carry local roads over the North Island Main Trunk (NIMT) rail line.
Innovative solutions were developed based around the concept of using Accelerated Bridge Construction (ABC) principles to minimise the bridge construction periods and associated disruption to road and rail users. This involved the extensive use of precast elements with innovative techniques to connect the precast elements. To minimise the associated road works and avoid resource consent triggers, slender construction techniques were used for the design of the bridge decks, including a conventionally reinforced 325mm deep twin portal and fully integral and simply supported beams with slenderness ratios of 35 and 32 respectively.
COLLABORATION ACROSS THE COMMUNITY
The numerous stakeholders included local boards and service providers, with Auckland Transport, owners of the bridges requiring replacement, as the key stakeholder. Auckland Transport also represented the interests of the local communities. As the key stakeholder, Auckland Transport was integrated into the project team and worked collaboratively with KiwiRail and WSP to determine best-for-project solutions. One of Auckland Transport’s major requirements was for the bridges to be widened to either allow for separated cycle lanes or future proof for planned route widening.
As Mt Wellington is a major arterial route and within 200m of SH1, Auckland Transport required the project to maintain a minimum of three operable lanes for the duration of the works, with the exception of the Christmas weekend where this could be reduced to two lanes. For all bridges, except Mt Wellington Highway, Auckland Transport was agreeable to using accelerated construction framework with full road closure for the duration of the bridge replacements, which was between 4-7 weeks. Due to the close proximity of Browns, Jutland and Station-Lupton Road Bridges to each other, only a maximum of two bridges could be taken out of service at any one time.
Constructability through design was the key to the successful delivery of this project and minimising any errors was paramount. A decision was taken early on in the project to three dimensionally model all of the bridges which provided extra certainty that the dimensions of the precast elements were all correct and allowed the project team to provide exact set out information for individual bars where required. They also provided the constructor with a visualisation of what they were to build. A further step to increase the transfer of knowledge and understanding on this project was the creation of detailed construction sequence drawings. This allowed the constructor to plan their resources appropriately and comprehend the design philosophy of the structures.
WHAT SUCCESS LOOKED LIKE
Accelerated Bridge Construction was fundamental in achieving KiwiRail’s project objectives of minimising cost and disruption, while maintaining the highest standards of environmental and health and safety principles. The key to the success of the ABC design philosophy on the project was the ability of the design team to integrate constructability within the design solutions, and forming a collaborative working relationship with the constructor.
The most innovative and impressive element of the project is the detailing of a fully integral connection using ABC technology. Integral bridges are normally considered more time consuming to construct than the more conventional simply supported structures. Given the whole of life benefits from removing bridge joints and bearings this is an area of focus for New Zealand bridge