Bridge expert: The smallest design parts are the most satisfying

On Friday, the Destructor Bridge in Bath was awarded ‘as a fine example of how to succeed in bridge design" at the prestigious Structural Awards in the UK. Project managers John Banks and Matthew Cartwright share some of their insights about the challenging solution.

23.11.2017

Designed by COWI and Knight Architects and constructed by Britannia Construction, Bath’s Destructor Bridge connects the revitalised area of Bath Western Riverside with the A4 Upper Bristol Road over the River Avon in the UK.

The 400 tonne bridge was launched across the river earlier this year, in a complex operation involving a self-propelled modular transporter driving the bridge from the rear, while the front end was supported by rollers on temporary towers.

Here is a brief interview with John Banks, PM for planning phase and Matthew Cartwright, PM for detailed design and construction phases, about the challenges and design choices:

What was the main structural challenge to the project and how did you overcome it?

A significant challenge was to select the most efficient and elegant structural form in response to the specific constraints of the site.

The site, together with the conceptual design of the bridge, was carefully appraised at the outset, working closely with the architect, to satisfy all of the characteristics of the site. In doing so, the unconventional asymmetric arch design was conceived.

How did designing a structure of a UNESCO World Heritage City affect the works/ design (if at all)?

Although the UNESCO World Heritage status of the city was an important factor, the local industrial heritage at the bridge site played arguably an even more crucial role.

Situated on a site that had been home to heavy engineering and metal works trades for generations, the bridge is a crafted structure that reflects the skill and inventiveness of the engineering processes synonymous with the area.

It was important to remain sensitive to the nearby Victoria Bridge. Indeed, the gentle arching curve of the top chord is perfectly complementary to the similarly proportioned sag curve of the Victoria Bridge suspension chains.

How could other lessons learned in the design and construction of the bridge be applied to other structures?

Elegant design does not need to be expensive. It can be made in such a way that simplifies construction processes to facilitate high quality output.

Some of the most satisfying parts of the design are also the smallest, such as detailing of the parapet handrail, which accommodated both modular design and simple, elegant and hidden connections.

About the Destructor Bridge

The Destructor Bridge was primarily built to replace an aging, single lane truss bridge to service the new Bath Western Riverside residential development with 2000 planned new homes.

The primary traffic usage will be from local residents.The new structure is a 48m long asymmetric steel tied arch bridge with two box girders. It will accommodate a two-lane highway for vehicles, a wider pedestrian walkway, and a cycleway. The steel arch supports a composite deck through flat plate hangers. The prefabricated units were welded on-site in 24 pieces.

About the Structural Awards

The Structural Awards celebrate the role of structural engineers as innovative, creative design professionals and to showcase the world’s cutting edge engineering projects.

The judges base their decisions on the structural engineering excellence of the project; the creativity, innovation, elegance and detailing within the structural design, alongside the sustainable techniques and technologies incorporated and the value of the project - both in terms of economic viability and value for money in the structural solution, as well as non-financial indicators of value.

Speaking of Destructor Bridge, the judges said:
"Designed in proximity to older, more established heritage bridges, the Destructor Bridge is an understated but expertly considered, detailed and executed vehicle, pedestrian and cycle bridge. The engineers have produced a bridge of delightful simplicity and technical accomplishment that serves as a fine example of how to succeed in bridge design."

Source: IStructE.org