All it takes is one look: The story of the V&A Waterfront’s new swing bridge

The serenity to accept what could not be changed, the courage to change what could, and the wisdom to know the difference, is why the V&A Waterfront’s updated swing bridge is a success.

 

“As designers we first had to learn about the constraints.
What you can’t change. We work from that,”

Explains Michal Korycki, an architect and director at Cape Town based Craft of Architecture (COA).

 

With the anticipation of the increased number of pedestrians crossing the channel to and from the Zeitz MOCAA and the popular Silo District the limitations of the old bridge were identified few years back. What was the solution? Well that was the question.

 

Called onto the project by respected bridge engineer John Anderson, SMEC’s Functional General Manager for Structures, the COA team knew it was going to be a learning  journey.

 

Recognised for their creative process and visual communication, COA were brought into a briefing process to perform site analysis, reviewing the existing bridge design and pedestrian movements. This research would reveal the project’s key features, opportunities and challenges.

The architects set out to build a 3D model of the entire site and the surroundings mapping out all relevant features. “This digital environment allows you to quickly test ideas and ‘what if’ scenarios drawing focus in the right direction,” Michal explains.

“Once the master plan concept is agreed upon we start the process again, repeatedly interrogating each design component until we get down to the smallest detail.”

In the urban form work phase we were plotting out every scenario including different types of bridges, augmenting the existing bridge and even installing the second bridge. Each option was scored on a matrix sheet plotting its cost and viability. The results led us to recommend that the new swing bridge be installed.

“We wanted to add to the urban environment and the experience of being in this celebrated precinct, and also to keep the view-line clear for those on the water, looking towards or away from the cut. We leant the bridge tower back to achieve both results,” explained Michal.

“As the V&A is a commercial environment, there could be no interruption in the switchover from the old to the new bridge. So, we decided to position the new bridge right alongside the old one so it could remain operational for five of the six installation months.”

 

It was far from plain sailing. Obviously there were lots of obstacles,” says John. “Among these were the harbour wall which we couldn’t strengthen,” noted Michal.

 

In the past, loose rocks and boulders were piled up and then cladded over to build the harbour wall. “There’s no great engineering in piling rocks on top of each other. The key was to not knock over this pile of marbles holding up the old quay wall,” says John.

 

They were able to stabilise the boulder mass by carefully drilling small holes into the bedrock, and injecting concrete to create “mini piles”, requiring the bridge to balance just right so that it would bear directly down into the rock.

Besides the foundations the team decided against any further land works. This freed them to build the bridge remotely, however instead of cables balancing the gravitational pull of the bridge as it swung out, the backwards-leaning tower was designed to take the load, allowing the whole bridge to pivot on its foundation.

 

“The bridge itself is planted on a giant slew bearing and as the bridge rotates it bears onto different piles.

 

In any position there are pile  in tension and compression. As it moves the tension is transferred into a vertical couple. This provides the restraint required: it’s pushing on one edge and being held back on another,” he said. Besides an  excellent level of function, the form had to be exquisite.

 

“We looked at the current bridge, and saw the contrast between the maritime designs of the time which had a lot of rigging and detail. We wanted to design a contemporary bridge influenced by modern maritime design so you could look at it once, and have the design guide your eye from top to bottom without being interrupted.

But, how do you bring a sideways swinging 42-metre, 55-ton bridge to a stop when your only resisting force to slow it is vertically downwards into a rock foundation surrounded by boulders leaning precariously on each other? “We paired pile couplings in the foundation, one to push and create tension, the other to pull and ease it,” explains John.

 

In part this meant no bulky hand railings, which previously contributed stability. Now the bridge had to be carried by the strength of a cantilevered beam along the centre which, decked with timber, now also provides a convenient place to sit. 

“Once we were more or less happy with the overall design we started looking at the visual experience of people nearby and those walking over the bridge. To help the eye rest on the beam and mast we made the balustrade as near to invisible as possible, as was the underside of the bridge.”

“Inspired by stealthy yachts and modern sailing boats we considered giving the bridge a dark colour, but we realised that seagulls would be quick to put white splats all over it. So it’s a light grey,” smiles Michal.  The teams’ intention was to answer this complex requirement with a simple design. “It needed to be refined, timeless, contemporary and unique,” said Michal.

Creating a bridge that could accommodate thousands of people crossing it every day, have manual operation if the power died and was simple to maintain throughout its lifespan, meant the architectural statement made by the new swing bridge is a beautiful answer to the question posed right at the beginning, of how exactly to do it.

When you next cross the bridge, taking it all in at a single glance, consider if this isn’t a picture worth a thousand words?

 

For more information on this project, see the V&A Waterfront Bridge project or view more of our award winning Bridges & Infrastructure projects.