The January 2011 floods that swept through Queensland had a lasting impact on the state and its capital.
In addition to the extensive damage to thousands of properties, many of the public ferry terminals on the Brisbane River were at the heart of the devastation and were either destroyed or severely damaged.
Brisbane City Council and the Queensland State Government were quick to react. In the aftermath of the flooding events, the city and state held an open competition to design new ferry terminals that would be more resilient to future flood events.
The competition attracted 65 submissions, including the winning concept from Aurecon and Cox Rayner Architects. “Aurecon and Cox Rayner was up against some strong competition, which included people from around Australia and the world,” says Richard Woollard, Marine Structure Engineer at Aurecon, who worked on the project.
“The idea for the concept was to come up with a flood resilient design that was also compliant with the Disability Standards for Accessible Public Transport (DSAPT).” Not only that, but the team’s ambition was to deliver a modern and elegant architectural design that avoided the traditional array of pontoon guide piles.
Brisbane City Council praised Aurecon and Cox Rayner’s combination of all of these ideals, surmising in a statement at the time that the winning design: “integrates technical innovation, flood resilience and elegant form to deliver terminals that will become iconic features of our river city.”
Mr. Woollard says that the submission for the competition in 2011 was a general concept, and Aurecon and Cox Rayner subsequently working on the detailed design had to expand on that basic idea while adhering to the stringent requirements of the brief set out by Brisbane City Council.
The design team looked at the failures of the previous terminals in flood events in order to gain some insight into the structural vulnerabilities they needed
to eliminate.
They found that the pontoon restraints failed to provide support at the height of the flood, the hydrodynamic performance of the existing box-shaped pontoons was poor and debris build-up and its impact led to damage and loss.
Aurecon and Cox Rayner’s response to the council’s vision to create flood resilient and accessible terminals required a drastic change in design approach. “It was a very big step away from traditional design,” says Mr. Woollard. “We had to start from scratch with everything.”
The project required a range of expertise and skills in different fields, including maritime, industrial mechanical and architectural disciplines.
Mr. Woollard explains that there were a number of high level constraints and challenges on the project, including how to plan the structure with a high degree of flood resilience, but avoiding visible piles around the terminal.
Further challenges revolved around achieving compliance with the DSAPT requirements for slope gradient and length between horizontal landings on the gangways. The ramps had to be at no more than 1:14 grade for a maximum of six metres between horizontal landings for 80 per cent of the time. The ramps, however, vary in slope through the tidal range, making it near impossible to comply with these conditions.
Not only were there many technical issues to consider, the new terminals had to be visually stunning and embrace the natural surroundings of the river.
To face these design conundrums, Mr. Woollard says the team had long conversations with various experts from different disciplines to come up with a resilient and long-lasting terminal design.
These meetings came to fruition, and the project drew inspiration from some unlikely sources, including offshore coal export terminals. Mr. Woollard explains that the concepts behind large-scale mechanical functions and systems on coal shiploaders, for instance, were suitable for the terminal design in mind and were scaled down to suit the function of the terminals.
“In that concept design phase there were a lot of ideas thrown around,” says Mr. Woollard. The consensus was to go for a simple, sustainable approach.
The hull of the pontoon was designed with a boat-like aspect, making it streamlined. This reduced the drag force of the river and minimised the risk of debris impact. “We needed to think about how all those objects would impact the structure,” says Mr. Woollard.
He says the flooding events in 2011 saw objects sailing down the river at various speeds, the impact of which needed to be taken into account in the new terminals’ design. The team undertook physical model testing at the Australian Maritime College in Tasmania to optimise the form of the pontoon and confirm suitable hydrodynamic performance in flood flow speeds.
The terminals’ design eliminates the traditional restraint pilea through the use of a single upstream pier structure. The steel and precast concrete pier is designed to absorb the energy of and deflect heavy objects away from the terminal. This unique addition helped to avoid the ‘forest’ of piles required in conventional design. The gangway acts as a radial arm to provide the second point of lateral support.
Further innovation comes in the form of the gangway itself, which is automatically released from the land-side when a flood hits. “A lot of the original gangways weren’t there at the end of the flood in 2011. The new design can just float up with the pontoon to the top of the flood,” says Mr. Woollard. Flotation incorporated within the gangway allows it to become buoyant in floodwaters, and a pivoting mechanism allows it to rotate behind the pontoon, out of the path of any moving debris.
The difficult task of making the gangway compliant with the DSAPT requirements was also met with a unique solution – a ‘hanging floor’ within its structure.
The hanging floor combines pinned parallelogram frames connected to intermittent fixed triangular frames. The intermittent frames maintain the floor of these segments horizontal, regardless of any variation in slope of the structure. This ensures that the gangway can cope with the tidal range of the river and comply with the DSAPT conditions. Mr. Woollard asserts that Aurecon and Cox Rayner believes this to be a world-first technique in addressing accessibility with tidal variations in maritime public transport.
The terminals are designed to withstand a 1-in-500-year flood event due to the extensive resilience measures incorporated into the design.
The final design for the Ferry Terminals was completed in March 2014 and they were completed between January and June 2015.
The outcome showcases the unique and bold approaches taken by the Aurecon and Cox Rayner design team, in collaboration with Brisbane City Council. The innovation and expertise demonstrated in the project has garnered praise, winning the Gold Award in the Design Innovation category at the 2015 Consult Australia Awards for Excellence in December last year.
While the task of ensuring the design met the specific brief criteria brought some major challenges, Mr. Woollard also sees it as one of the most rewarding projects he’s worked on. “I’m proud to have been a part of the team that delivered these iconic terminals that add a new level of visual presence, resilience and accessibility to the Brisbane River-scape.”
This story has appeared in the Roads & Civil Works February/March 2016 edition – get your copy here today!