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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

High-Concept Bridge Skips Lightly Across Singapore Waterway

By Catherine A. Cardno, Ph.D.

Under a recently released plan, a pedestrian and bicycle bridge would be tucked underneath a gently curved highway bridge originally designed to allow clearance for seafaring vessels.

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OOZN, a Singapore-based architecture firm, has created a high-concept design for a sustainable and efficient pedestrian and bicycle bridge that bounds lightly across Singapore’s Marina Reservoir, anchored underneath an existing highway bridge. OOZN

October 20, 2015—In 2008, the completion of the Marina Barrage in Singapore created an engineered boundary between the sea and the mouths of five rivers. With the construction of the dam, the risks posed by rising tides and flooding in low-lying urban areas ended and the estuary was transformed into a fresh water reservoir that could provide drinking water as needed. Within this newly created reservoir, crossings that had been built with clearances to allow seafaring vessels to pass underneath have instead became memorials to the city's past. The Singapore-based architecture firm OOZN has taken this unique context to create a high-concept, sustainable, efficient pedestrian and bicycle bridge that would seem to bound lightly across the water, anchored underneath an existing highway bridge. The highway crossings' piers have been reimagined as small, shaded public parks.

"The bridge aims to represent the next phase in sustainability by improving the city via the adaptive reuse of an existing iconic structure," explained Peter Morris, RIBA, an architect and a cofounder of OOZN who served as the project leader for the design. Morris wrote in response to written questions posed by Civil Engineering online. "We are unaware of another bridge that utilizes this concept, perhaps because this particular bridge has a unique set of circumstances that make our proposal possible," he noted. 

The highway crossing—the Benjamin Sheares Bridge—is a concrete road bridge completed in 1981 that extends 1.8 km over Marina Reservoir, carrying the East Coast Parkway. It is supported by rows of H-shaped columns. The columns rest atop concrete podiums that extend above the waterline. Reaching a height of 20 m, the bridge clearance far surpasses anything currently needed on the waterway, according to Morris. 

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The highway bridge was built to provide clearance for seafaring ships, but a dam built across the mouth of the bay in 2008 has turned the estuary into a large freshwater reservoir that does not require the same clearance heights for vessels. OOZN

The pedestrian and cycle bridge would piggyback onto the highway bridges' foundations, threading its way between the bridge's columns. The project would also involve turning  the above-water podiums into small, green public parks accessible by dedicated ramps from the pedestrian and cycle crossing.

In addition to its height, the existing bridge was designed to withstand ship impacts. This "overcapacity" of height and structural strength would easily allow the bridge to support a relatively lightweight, secondary pedestrian and bicycle bridge, according to Morris. "The bridge is conceived as a simple structural arch suspended from the existing column structure, clad in lightweight aluminum panels to give [a] sleek, simple effect," Morris said. "The intention is to minimize the loading transferred to the existing structure," he noted. 

The symbiotic design is more cost-efficient and sustainable than a stand-alone structure because it reuses the existing foundations. The architects are also quick to point out that such a design is also beneficial from an urban planning perspective because it reduces the "visual weight" of the pedestrian and bicycle bridge in this location compared to a stand-alone structure. 

Singapore has been developing an extensive system of parkland and bicycle paths around the reservoir and along the coast. With the development of the Gardens by the Bay on one side of the reservoir, and the 21 km long East Coast Park on the other, bicycling would be convenient method of commuting to work, according to the architects. Within the last few years, two 6 km loops have been added around the Marina Reservoir. However, the lack of a bridge at the Sheares crossing increases by at least 4 km any journey from the eastern side of the reservoir into the northern city center, according to Morris.

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The pedestrian and bicycle bridge would thread its way through the existing highway bridge’s H piers, while the bridge’s concrete podiums, which extend above the waterline, would be transformed into small public parks. OOZN

Despite the distance that must be traveled, Morris estimates that hundreds of recreational and commuting walkers and cyclists pass through Garden by the Bay each hour at peak times. With the addition of the new crossing, "we anticipate a large increase in [bicycle] traffic during the week with a boost in recreational users at the weekend," Morris said. This could also improve the flow of vehicular traffic on the main bridge by encouraging drivers to cycle instead.

While the design is currently in the concept design phase, "a conventional standalone bridge was proposed in this location as part of the original Gardens by the Bay master plan," Morris said. "A pedestrian link in this location is still included in the Singapore planning authority master plan, though a construction date has yet to be confirmed.

"OOZN hopes that their more sustainable and cost-effective solution will increase the chances of turning the project into reality," Morris noted. The firm is currently negotiating with several government stakeholders in the hopes of doing just that.

 

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