Bridge design is pushing the boundaries of engineering ingenuity across the full range of project scales.
When it comes to the newly opened Russky Bridge in Vladivostok the boundaries have been pushed another 16 metres. With a central span of 1,104 metres, the cable-stayed bridge has set a new world record in its category, beating the 1,088 metres of China’s Sutong Bridge.
Central to the design is the incorporation of shock resistors at the bottom of each cable, which reduce movement and enable the bridge to withstand winds of up to 250 kilometres per hour.
To ensure their calculations were correct, French engineers Freyssinet tested a scale model of the bridge design in a wind tunnel at the Scientific and Technical Centre for Building (CSTB) in Nantes, France. The end of the orthotropic steel deck was held by stays connected to “A” towers made of C60 high-performance concrete. At 320 metres high, the towers were the same height as the Eiffel Tower.
Mike Tapley, Aurecon’s bridges leader for the Asia region believes engineers can go even further.
“The successful adoption of advanced bridge technology on the Russky Bridge has demonstrated that cable stayed bridges can readily span 1,200 metres and with a few minor adaptations 1,500 metres is achievable,” he said. “Subject to adequate financing being made available, it is not inconceivable that in the next 30 years, we will see other forms of bridges with spans of four kilometres and longer.”
Another massive bridge project that has caused a stir in the engineering profession is the Taizhou Bridge in China, which has just won the Supreme Award for Structural Engineering Excellence, as well as the Award for Highway or Railway Bridge Structures at The Structural Awards 2013.
With a pair of 1,080-metre main spans carrying six lanes of traffic, it straddles the two navigation channels of the Yangtze River and is the world’s first long-span, three-tower suspension bridge. The most unique feature of the bridge – the asymmetric live loading – required extensive research and development by the structural design team of Jiangsu Provincial Communications Planning and Design Institute and AECOM Asia Company Ltd. The central tower solution straddles the fine line between stiffness and flexibility needed for the project to succeed.
“This enormous project was an extraordinary achievement, pushing the frontiers of suspension bridge technology to new heights,” said the judges of the Structural Awards. “It lays out an excellent model for the future development of long-span bridges across the world.”
At the other end of the size scale is the Pembroke College Footbridge in the UK.
Providing a walkway between the existing college and the new building opposite, the bridge deck employs the more unusual monocoque technique. Monocoque, which means ‘single shell’ in French, involves the use of an external skin to support most of the load, morphing from triangular into rectangular cross-section with internal rib strengthening exposed along the soffit to express the load paths of the structure. A single sheet glass panel provides the balustrade.
With access levels already fixed on either side, the maximum structural depth was just 135 millimetres over the street below to achieve the required traffic clearances.
In Bolivia, the innovation pursued by the engineers of Bridges to Prosperity has an entirely different motive. Their goal is to simplify designs to improve constructability, allowing the use of common manual labor skills and materials and developing a model which could be replicated in other poor and remote parts of the Andes.
The Chari Chari Bolivia Cable-Supported Pedestrian Bridge is 520 feet long. Situated in challenging and remote terrain, the first innovation was to re-design the cable anchorages to better utilize existing subsurface conditions. The second innovation was to integrate the masonry towers into the anchorage design, thereby significantly reducing the excavation and concrete required while still providing a high level of confidence in the design solution.
The approach is now helping communities in the region, as well as in other poorer nations around the world, to develop critical bridge infrastructure.