Asia is home to many of the world’s longest bridges and has a strong pipeline for future construction, much of it driven by the increasing prosperity and bold infrastructure programmes of the region’s developing economies. The natural environment of the region also presents several unique challenges, and as technology advances and expertise grows, increasingly innovative solutions are being engineered.
Japan is home to the longest suspension bridge in the world (which is actually made up of three suspension bridge structures), the 4 015 m Kurushima Bridge which links the islands of Honshu and Shikoku. The country also boasts the bridge with the longest span in the world, the Akashi Kaikyo Suspension Bridge, which has a span of close to 2 km.
However, both these record-breaking titles will soon be making their way across the East China Sea, where a flurry of bridge building activity is underway. China will eventually host five of the ten longest span bridges in the world, including the longest. But given the pace of infrastructure development worldwide, it’s unlikely these records will stay untouched for long.
The leading role of Japan, China and Hong Kong (which is home to Stonecutters Bridge, one of the most complex cable-stayed bridges in the world) in bridge building born out of geographical necessity. For Japan and Hong Kong there is the need to connect their many islands; while in China, the landscape is characterised by long and wide rivers. Crucially, Japan, China and Hong Kong also have the economic muscle to fund the large investment that long-span bridges require.
The issue of funding is an interesting point, and something of a Catch-22. Although bridges are a significant investment, governments understand that their creation can boost a nation’s prosperity, providing supply chain routes for goods, services and people. This is why we see developments such as the impressive Padma Bridge in Bangladesh get off the ground. The bridge, which will link Dhaka with the isolated western region of the country, is one of the largest bridges under development worldwide, yet Bangladesh remains one of the poorest countries in Asia.
A bridge of this scale, with an estimated construction cost of $3 billion, would normally be beyond the financial means of Bangladesh. But the government understands the economic benefits its creation will bring, and has concentrated efforts in guaranteeing its construction. The long-term value of the bridge will pay back its cost of construction many, many times over.
Elsewhere in Asia, fast-developing economies are focussing on bridge building programs. Both the Philippines (a network of islands) and Vietnam (criss-crossed by many long rivers) are in the middle of considerable development programs. In the Philippines, one of the most significant is the Cebu-Cordova Bridge, which will be the third bridge to serve the hugely popular tourist island of Cebu. Construction will start in 2017, with completion in 2020, and its introduction will further boost the flow of goods and people to the island, supporting economic growth.
Another interesting feature of bridge building in the developing economies of Asia is the advancement in design and building methods. Specifically, we’re seeing more designs that utilise precast concrete sections, rather than the traditional method of long precast beams with bridge deck sections cast in-situ. This is a more advanced way of bridge building and reflects the rising budgets and engineering skill levels. Using precast segmental construction requires higher levels of geometry control and the technical work for the cantilevering is more detailed, but with modern design programmes that work is becoming easier.
Design-wise, we see a stronger preference for cable-stayed designs versus suspension bridges, not only throughout Asia but worldwide. In general terms, there is a cost premium of 20% to 30% for a suspension bridge. At the same time we’ve seen a rapid acceleration in the span sizes for cable-stayed bridges. Whereas previously there might have been a limit of 300 m or 400 m spans for a cable-stayed bridge, that number is now closer to 1 km. Additionally, the relative ease of maintenance of cable-stayed bridges explains why such designs are preferred in all but the most exceptional cases.
One of the more intricate aspects to bridge design work in Asia is accounting for the environmental challenges inherent in this part of the world, particularly earthquakes and typhoons. In terms of seismic design, our industry has learnt much from recent events in Europe and Japan, which are reflected in the updated international codes of practice.
For example, the Akashi Kaikyo Suspension Bridge in Japan moved 1 m during construction in 1995 following an earthquake. It was one of a series of similar disasters that changed the way we design bridges as an industry. Our understanding of earthquakes, especially their geotechnics and soil mechanics, gives us much more insight into how it affects bridge structures. We are confident we can design bridges that will withstand earthquakes, even if surrounding buildings do not. While a bridge might be damaged during an earthquake, the structure is designed to be flexible so even if some elements fail, the overall structure will not. Therefore, in the event of a humanitarian crisis, the bridge will remain to provide much-needed supply access.
The approach to typhoons is similarly changing with our analysis becoming more sophisticated. For example, in many countries where long span bridges are planned, there is insufficient research on the loadings that will apply in the event of a major typhoon. In these instances we have to use whatever local data is available and adapt it for use within international design codes. We study the winds in the bridge’s location and also wind test the designs, first on the topography and then on the bridge itself.
Modern cable-stayed and suspension bridges are now very aerodynamic, and their designs allow air to move more easily over the deck sections, minimizing wind forces. With our wind analysis, we are able to model how wind behaves, using computational fluid analysis to see its effects around the structure. We also use wind tunnel testing, which is easier than before, and create physical models of the structures - increasingly using 3D printing. This allows for far more detailed modelling, both for the structure as a whole and for individual elements.
As creative architecture advances and demands more complex structures, more advanced analysis is required. But by using BIM technologies and the latest analytical tools, design consultants such as Aurecon are able to handle that analysis. The technology is a major progression, allowing our designers to understand structures better than ever before.
The increasing prevalence and affordability of modern technology can help in other areas of bridge engineering, such as asset management for existing bridge structures. On a recent project, Aurecon conducted a bridge-specific live load assessment, using video to record traffic. We used that video to calculate how the traffic was split by category, timing and more. This allowed us to determine the worst-case load scenario based on actual data, rather than simply applying the design parameters of the code, which are always the most conservative. This is a great example of how modern engineering can combine design codes and real-world data to deliver more accurate and functional results.
At Aurecon we take a design-led approach to our work, which we believe is essential to supporting the ambitious bridge development programme underway in Asia. Moreover, the challenge of creating long-span bridges here is not only about withstanding extreme events but also about connecting people and communities. The success of current and future bridge projects is crucial to the advancement of Asia’s economy. And in many ways, the continual growth in bridge scale remains a handy metaphor for the economic development of Asia overall.