Lachlans Line Bridge is a striking new pedestrian and cycle bridge ; Lachlans Line Bridge is a striking new pedestrian and cycle bridge ;

Christopher Cassaniti Bridge, Sydney

Embracing digital design for Sydney’s new double helix bridge

The Christopher Cassaniti Bridge is a first-of-its-kind – an organic, double helix bridge that will connect both Landcom’s new residential development and the Macquarie Park precinct to the North Ryde metro station in Sydney. It was formerly known as the Lachlan’s Line bridge.

Bold and bright blue, the bridge is a striking visual landmark as well as a busy active transport connection.

Arup’s design with KI Studio architects has transformed access to the site, currently bounded by one of Sydney’s busiest intersections – the M2 Motorway and Delhi Road. 

The roads have been optimised for the new structure to pass overhead and a new park area will provide green space for residents. Arup also provided civil and lighting services to ensure this is a liveable and well-connected part of the city.

Project Summary

170m long

5,000residents to have safe, easy access to mass-transit


The curved, fabricated box section construction takes helix design and fabrication to a new level with its irregular geometry and a more fluid shape – all enabled by Arup’s digital approach to structural geometry, engineering and design for the permanent design, temporary works and construction sequencing. 

The bridge alignment – defined by the minimum feasible length and pier locations - has driven a sinuous structural form.


The bridge is functional, fun and enhances its landscape. People are enjoy walking, cycling or passing by this bridge and it will bring a sense of wonder and inquisitiveness. ” Andrew Johnson Andrew Johnson Project Director

Image © Landcom

Coding for an efficient, effective and sculptural design

Inspired by parametric design principles, Arup captured the design process in an entirely digital workflow connected by computational code, creating efficiencies and unlocking opportunities for more fluid, inclusive and creative engineering.

Initially this digital approach was used to determine the shortest alignment for the pedestrian bridge while taking into consideration the busy roads below. The bespoke workflow then continued to evolve, with all design programs and models linked together. With parameters such as chord rotation between piers, helix density and helix diameter set by Arup’s engineers, a single modification – at any stage of the workflow – adjusts every subsequent model instantly.

With varying helical geometry and more than 3,600 unique steel plates, the workflow enabled the team to accommodate change more quickly than traditional means – updating in minutes, not weeks – and continuously innovate during the design process.

We recognised that to achieve a ‘first-of-its-kind’ over a busy intersection, we needed to be able to adapt designs quickly. Bespoke digital programming allowed us to navigate this. ” Xavier Nuttall Xavier Nuttall Structural Engineer

The workflow created architectural surfaces, defined the set-out and centre line geometry for analysis and fabrication, built and analysed a series of analysis models, assessed each steel plate within the helix and optimised the steel thickness and grade. It also updated Revit documentation and saved BIM models that contained all the steel data.

With efficiencies gained, additional focus could be placed on sustainability by minimising material usage and simplifying the construction process. 

For example, the use of curved plate fabricated box sections was more than an aesthetic choice: it enabled each side of the section to be optimised with different plate thickness responding to section demand, ensuring the absolute minimum quantity of steel was used.  Where design innovation pushed boundaries, the team applied stringent modelling, verification and prototyping to ensure the bridge would meet the highest standards of engineering.

The digital design also enabled more interactive engagement with client and community stakeholders, positive and timely outcomes around updates for the widening of Delhi Road and less impact on nearby vegetation.

Fabricating and erecting the structure

No two pieces are alike in this structure, with the steel varying in curvature, while maintaining uniform element sections. The length and geometry of the bridge were optimised as the shortest length between the two landing points, while achieving the necessary vertical clearances – the outcome being a sinuous form completely dictated by function. The helix varies 2.3m in diameter in relation to varying structural demand: it is 7.8m in diameter at its widest and 5.5m at its slimmest.

Arup worked with S&L, the project steel fabricators, to understand their requirements and to produce a 3D model of each piece of steel. 


The software developed by Arup analysed 164 unique doubly-curved node surfaces. To simplify fabrication, the software found their individual best fit equivalent cylinder, allowing us to provide simple roll radiuses and roll directions. This allowed the steel fabricator to unroll the geometry – imagine creating a flattened version of the 3D shape – and laser cut these shapes from a steel sheet.

Image © Landcom

The 170m steel structure has been built by the fabricator in four separate spans on a nearby site. 

Arup developed and designed transportation and lifting assemblies for each segment and part segment that enabled handling and transportation without overstressing the permanent elements.

The Christopher Cassaniti Bridge represents the meeting of engineering skill with digital knowledge, showcasing the possibilities for digital designs of the future.

Award wins

  • Good Design Australia Good Design Awards – Architectural Urban 2020

  • Good Design Australia Good Design Awards – Engineering 2020

  • ASI Steel Excellence Awards NSW Division – Engineering Projects 2020

  • Master Builders Association NSW Excellence in Construction Awards – Best Use of Steel 2020

  • Master Builders Association NSW Excellence in Construction Awards – Open Price Category 2020

  • Master Builders Australia National Excellence in Building & Construction Awards – National Civil Infrastructure Award over $25m 2020

  • ASI National Steel Excellence Awards – Engineering Projects 2020

Banner image © Landcom