The world has progressed beyond imaginations. Similar to the field of IT, Civil Engineering has also taken several steps forward to bring out innovative technologies to meet challenges of this world’s aspirations. Going forward from just meeting out the functional needs, construction speed has become an important aspect. Led by the inspirations of high speed computers, fast track construction is found inevitable, even though it may not be the cheapest. When it comes to BOT project, economics lies in speed of construction apart from materials cost, so that Toll earnings can be realized faster by the concessionaire/owner. It has also become equally important to have an inception of aesthetics, especially in the case of urban structures, for obvious reasons. Recently, a trend is picking up, wherein architects are engaged in bridge architecture. Lastly, every country wants to create a landmark and world record by constructing largest span bridge on its land. Of the available technologies, Cable Stayed technology, Extradosed Bridge technology and Suspension Bridge technology have led to largest span ranges. Largest span in Cable Stay technology is about 1200m, that in Extradosed technology is about 250m and that in Suspension Bridge technology is about 2000m. A far reaching imagination will entail a span that would bridge different cities.
When it comes to aesthetics in bridges, the first and common form, usually thought of is Arch Bridges. One of the simplest form of arch bridge can be seen in the award winning project of Dodan Nallah bridge (see fig. 1), wherein aesthetic matching with the surroundings has turned out to be an eye catching feature. In case of Rottwell Arch Bridge in Germany (150m span), the arch rib has been constructed using Stay Cantilevering Technique and the deck has been constructed using Incremental Launching Technique (See fig.2).
Similarly, in the case of 180m span Tennessee Route Bridge in the USA, the deck was constructed using Balanced Cantilever Construction Technique (see fig.3).
Learning from the international experience, a 120m span arch has been constructed over turbulent river Parvati in Himachal Pradesh, India (see fig. 4). The 30m high Arch Rib was constructed using Stay Cantilevering Technique, as any staging placed in the river bed would be washed off due to highly turbulent waters. The 45m high temporary steel pylons (see fig. 5) has been provided with Back Stays at 30m height and 45m height connected to reaction blocks to carry horizontal and vertical force components. The forward stays support the arch rib at all stages of its construction. Once the arch rib is joined, all temporary pylons, back stays and forward stays are removed. Thereafter, the deck slab was cast using formwork hanging with wire suspenders (see fig. 6). These hangers later formed part of permanent suspension for the deck slab. An arch bridge has its own charm in hilly terrain.
AIIMS flyover in Delhi has successfully conveyed that even a fat structure can be made to look aesthetically pleasing, which is a must in an Urban Infrastructure Project (see figs. 7, 8 & 9). The piers have been architecturally camouflaged with the corresponding superstructure. High seismicity of the area has been taken care of by incorporating separate seismic attachments, while the main POT bearings carry only the vertical loads.
Girder Slab Bridges
This is one of the most common, simplest and cheapest forms of bridge superstructure. The project of Delhi-Gurgaon Expressway in Delhi (see fig. 10 & 11), has made use of 1800 nos. Precast Pretensioned Girders for continuous superstructure. Similarly, Kuantan River Bridge in Malaysia (see fig. 12) has made use of 40m span, closely spaced Precast Post-Tensioned Girders for continuous superstructure.
This section of the article is only available for our subscribers. Please click here to subscribe to a subscription plan to view this part of the article.