Naeem Hussein, global leader for bridge design at Arup, discusses the art and future of this iconic branch of civil engineering.
Since the 1990’s there has been considerable development in the design and construction of bridges ranging from boutique footbridges to long span bridges and large sea-crossings. Widespread use of computers and involvement of architects has improved both the engineering quality and aesthetic appeal of bridges.
In many parts of the world waterways whether wide rivers, bays and estuaries have meant large detours and/or use of ferries thus severely hindering the movement of people and goods and limiting socio-economic development. This has led to the bridging of these waterways with road and rail bridges and since the 1990’s several large sea-crossing bridges have been built mainly in the Far-East. In North America many large bridges are reaching their service life which has been as short as 70 years and these need replacing. In the next few decades this trend is set to continue with more aesthetically appealing bridges and very large sea-crossings such as between Java and Sumatra, between Hainan Island and the mainland in China, between China and Taiwan, the Berring Starits linking Russia to Alaska, the crossing across the Red Sea linking the Arabian Peninsula to Africa, the Gibraltar crossing.
In engineering terms the major development has been the increase in span of cable-stay bridges which are set to replace suspension bridges up to a span range of 1500m. Beyond 1500m it will invariably be suspension bridges, and in both types, multi-span bridges will make large sea-crossings possible.
But whatever type of long span bridges are used there needs to be and will be a radical re-thinking on how bridges are constructed, inspected, maintained and replaced. Bridge technology will need to adapt techniques and materials being used in the off-shore, shipping and aircraft industry. Over-reliance on traditional materials like steel and concrete will be replaced by use of lightweight composites for parts of the structure and use of synthetic materials such as kevlar for cables, will enable longer spans to be realised. Just like in the automobile and aircraft industry, parts of the bridge will be designed to be replaceable. It can even be forseen that robust foundations with a life-span greater than 300 years will be designed and built, whilst other parts of the bridge can have lower design life and be replaceable. This will increase the longevity of the bridges and lead to more sustainable bridges.
A major development in sea crossings across deep water will be the use of off-shore technology such as is being considered for the pioneering design and construction of the E39 motorway across the deep fjords in Norway. Suspension bridges with spans in excess of 2500m with towers supported on floating tension-leg caissons are in an advanced stage of study and realisation. This technique along with use of composites will be the revolutionary break-through in bridge engineering.
The return on capital expenditure on large bridges can and will be increased by enabling foundations of long marine viaducts to also support wind turbines. Political will is required to enable this to be realised but public pressure for renewables and sustainability will force procuring agencies to invest in multi-use large crossings.
Fast evolving digital technology will be increasingly adopted in the design and construction of bridges. Structural Health Monitoring is now a norm in bridge engineering but wireless technology will enhance this and along with drones will enable more focussed inspection and mintenance to be carried out. 3-D printing of bridge parts, off-shore fabrication in factory conditions and use of robots in assembling the bridge will lead to safer work, reduction in capital expenditure and longer useable life of bridges.
The prospect for break-throughs in bridge technology are encouraging and realisation of academic ideas into reality are within reach.