Elegance meets form and function

A new landmark pedestrian swing bridge for South Africa’s oldest working harbour

Project

V&A Waterfront Swing Bridge

Year

2020

Location

South Africa

Client

V&A Waterfront Holdings (Pty) Ltd

60
The swing bridge is capable of operating in up to 60 km/h wind speeds
4
The new 4m wide swing bridge has a span of 40m
90
The swing bridge opens in 90 seconds and closes in 100 seconds
500
The spine beam is 500 mm wide and has a total depth of 800 mm

Situated in South Africa’s oldest working harbour, the V&A Waterfront is a mixed-use development, offering visitors a world-class experience when it comes to entertainment, shopping, dining and accommodation.

The waterfront already had a pedestrian swing bridge that was well-used and well-loved. It was an efficient structure that opened and closed up to 60 times a day, carrying up to 2.4-million people per year. The 2 m wide walkway, which once seemed appropriate, could no longer cope with the rising foot traffic. To keep pace with demand, a new, wider bridge was commissioned.

“The bridge’s integrated form is simple and unique. It is no more nor less than it needs to be, which gives it an elegance that is hoped will be timeless. It serves as an important link and is considered a positive landmark for both the V&A Waterfront and Cape Town.

– John Anderson, SMEC Functional General Manager, Structures

The challenge
SMEC South Africa’s Structures team was engaged by V&A Waterfront Holdings (Pty) Ltd as the lead design firm and structural engineers for the replacement of the old swing bridge. Our team worked in conjunction with architectural design firm, COA Architects; engineering design consulting firm, Eadon Consulting; and multidisciplinary construction group, Stefanutti Stocks.

The challenge set by the client was:

  • The new bridge had to be equally quick and efficient, effective and reliable as the existing bridge;
  • The construction cost had to be within a tight budget; and
  • The works had to limit disruption to the public, the harbour and the environment.

Leveraging technical expertise to identify fit for purpose solutions
The design team worked through various options for the new link. Among those considered were a bascule and lift bridge; however, it was deemed that a swing bridge would still be the best solution in terms of the speed of operation and electrical energy needed to operate it. Important performance specifications included the bridge being capable of operating in wind speeds of up to 60 km/h, that it be designed for impact by a vessel from both directions and swing free in such an instance so as to protect the mechanical equipment.

Both steel and Fibre Reinforced Polymer(FRP) were considered at the early stages of the project as the only materials that were light enough to limit the loads on the moving mechanical parts and to limit the foundation size. However, as the design progressed the use of steel was the obvious choice.

The new 4 m wide swing bridge has a span of 40 m. The deck is cable-stayed with a single plane of four locked coil cables connecting to a central, upstand spine beam. The spine beam is 500 mm wide and has a total depth of 800 mm, but only 470 mm protrudes above the top of the deck. The reclining pylon is in the continuity of the main central beam and its stiffness transfers the cable loads into the piled substructure. The steel with timber deck is rotated on a slewing bearing, which is stressed down onto a doughnut-shaped pile cap by 34 vertical Freyssibars. The bridge is supported on eight piles, positioned in a ring.

The slew bearing and hydraulic motors are in a plant room, created by the pile cap ring. By forming the pile cap in this way, it was possible to house the mechanics within the depth of the foundations. This reduced the required excavation depth and kept the foundations above sea level, which was advantageous from a durability perspective. It also limited the construction impacts on the historical quay wall.

A slew bearing option was preferred as it was considered to offer a more sustainable solution. Slewing bearings are tried and tested in both pedestrian bridge and industrial applications. Their large diameter allows them to resist overturning moment and hence a cable stayed bridge with no backstays could be conceived. This was attractive in that it limited the works that had to be done on the quayside. It also allowed the bridge superstructure to be fabricated and assembled off site and then barged and lifted into place, complete, on a single day.

Industry recognises outstanding project outcomes
The project, which was delivered within very tight commercial and time constraints, were split into two stages to ensure that construction works did not run into the V&A’s peak periods. The piling works was first built under one contract and then buried in sand and the area re-paved until the superstructure contract was activated the following year.

The Project Team together with the V&A Project Managers put significant thought and effort into minimising disruption to the area. Safe access across the cut for the public was maintained using the old swing bridge for all but four weeks of the construction works – a major achievement that required innovative thinking and expertise. The new V&A Waterfront swing bridge was officially opened to the public on 11 July 2019.

In 2020, the project was named joint winner in the Technical Excellence category of the South African Institute of Civil Engineering (SAICE) National Awards, 2020. It also won both the Bridges category and was recognised as the Overall Winner (across all categories) at the Southern African Institute of Steel Construction (SAISC) Steel Awards, 2020.

Project

V&A Waterfront Swing Bridge

Year

2020

Location

South Africa

Client

V&A Waterfront Holdings (Pty) Ltd

60
The swing bridge is capable of operating in up to 60 km/h wind speeds
4
The new 4m wide swing bridge has a span of 40m
90
The swing bridge opens in 90 seconds and closes in 100 seconds
500
The spine beam is 500 mm wide and has a total depth of 800 mm

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