World’s Tallest Railway Bridge – Chenab Bridge

Written by Harsh Sharma

Construction is an important part of any country’s infrastructure and industrial growth. In India, construction is the second main economic activity after agriculture. Our blooming communications sector is fuelling demand for all kinds of construction equipment. Our country’s economic growth and trade are based on transport. No production can take place unless and until such as raw materials, labor, and fuel can be moved to and from different locations. And for this, the development of the transportation is necessary. And for the transportation purposes, the Railways is the most essential and most reliable means of transportation huge masses of raw materials and also connecting the various parts of the country. India,with its huge topographical variations, including the hilly areas of Himalayas to the barrens of the Thar deserts to the deccan plateau in the southern India, presents a big challenge for the transportation.

A big challenge was faced by the engineers during the construction of the railway line in Jammu and Kashmir between the Udhampur to Baramulla. This railway track is proposed to consist of a huge number of the tunnels and bridges which is to be implemented in highly rugged and mountainous region. The alignment crosses a deep gorge of the Chenab river, that necessitates the construction of the long span bridge whose height is approximately five times the height of the QutubMinar.

Chenab Bridge project started in 2004 and was proposed to be completed in December 2009. However, in September 2008, due to the safety reasons the bridge project was cancelled. But the work restarted in the 2010 and was proposed to be completed in 2015. Yet, there were many hurdles faced by the engineers in the construction of this bridge.

An official committee headed by E Shreedharan expressed serious concern about the stability of the structure since this area is earthquake prone and construction in this much height in the seismic active area is a huge risk itself.

The Chenab bridge has a total length of about 1315 m. It is an arch bridge and the span of the arch is 469 m across the Chenab river. The height of the bridge is about 359 m above the river bed of the Chenab river which is approximately 5 times the height of QutubMinar and 39 metres taller than the Eiffel Tower of Paris. Once constructed, it will become the tallest railway bridge of the world, breaking the present record of the France’s Tarn river railwaywhich is about 340 metres high from the river bed.

The approximated cost of this mega structure is about Rs. 650 crores. And it needed about 25,000 million tonnes of steel in the construction of this bridge. The bridge is to be constructed considering various parameters that are unique. The some of the considerations are high wind forces on this much height, the location of the bridge in the highly seismic zone of the country, possibility of the terrorists attacks, provisions for the future attacks and the continuous monitoring systems etc.

The main span of the bridge will be an arch which is made of the steel trusses. The chords of the trusses will be sealed steel boxes, filled with concrete to assist in controlling the wind-induced forces on the bridge. The boxes will be stiffened internally. Also a great emphasis is laid on the structural response to the wind forces. For this various wind load tests had been conducted in the Force Laboratory in Denmark.

Arch Design

The arch and the arch piers are being made from large steel trusses. The chord of trusses and the diagonal were made of the shape of the sealed steel boxes and all the other members including the secondary members are made of circular shape. In the arch portion, the superstructure is supported on the steel piers with a height of upto 120 metres.

Construction Innovation

Bridges all over the world are incrementally launched either on the straight alignment or on the curved alignment of uniform radius. The bridges are never incrementally launched from one end when the bridge is partially straight and partially curved and more so when the bridge is on the transition curve of varying radius. The deck on the viaduct of the Chenab is partially in straight and partially in circular and transitional curve. This is the first time that the incremental launching is attempted on the transitional curve. The arch span is to be constructed using the cable cranes, the largest cranes ever used.

Safety Measures

The bridge is constructed for the heavy wind pressure and the earth quake zone IV as per relevant IS codes. IIT Roorkeehas also played an important role in conducting the tests. Bridge is designed for the blast loading as per IS 4991-1968 and contact blast load on the deck of the arch. Bridge is provided with various alarming systems such as anemometers, accelerometers, temperature monitors, central control to monitor the induced strains due to wind and seismic loads through computerized systems with automatic comparison with permitted limits in the design. The paint used is also Akzonobel’scorrosion resistant paint that lasts for 15 years.

The Chenab Bridge will be the biggest and highest railway arch bridge with the longest span ever built in the world. Its design offers great challenges but they will be more demanding before the gap between the main arch halves is filled. The project once completed, will be a feather in the cap of Indian and International engineers, for having built the tallest bridge in the world in a geologically active area and with peculiar functional demands.