The Chenab Bridge is an arch bridge under construction in India. It spans the Chenab River between Bakkal and Kauri, in Reasidistrict of Jammu and Kashmir. When completed, the bridge will be 1,315 m (4,314 ft) long, with a 480 m (1,570 ft) trussed arch span, 359 m (1,178 ft) above the river Chenab and a 650 m (2,130 ft) long viaduct on the Kauri side.[2][3]
The bridge is part of several bridges and tunnels which makes up the Katra-Laole Section of the JUSBRL Project in Jammu and Kashmir. Another, smaller, arch bridge in the link will be the 657 m (2,156 ft) long, 189 m (620 ft) high Anji Khad bridge between Katraand Reasi over the Raavi river.
The Chenab Bridge was originally scheduled to be completed in December 2009.[4]However, in September 2008 it was announced that the Chenab bridge had been cancelled due to fears over its stability and safety.[5] Work on the bridge restarted in 2010 and once construction is completed in 2015 the Chenab Bridge is expected to be theworld's highest rail bridge.[6][7] [8]
Introduction and topography
Indian Railways has undertaken the mega-project of construction of a new railway linein the state of Jammu and Kashmir, fromUdhampur to Baramulla, which has been declared a national project.[9] The alignment is a culmination of a large number of tunnels and bridges which are to be implemented in highly rugged and mountainous terrain, with the difficult Himalayan geology. The alignment crosses a deep gorge of the Chenab River, near Salal Hydro Power Dam,[10] which necessitates construction of a long span bridge. After many deliberations, the configurations of steel arches were found most suitable, on account of aesthetics, economy, and availability of local expertise and construction materials.
The Chenab Bridge, 359 m (1,178 ft) above river bed, will be the highest arch bridge in the world, and longest span for a BG rail line with arch span of 480 m (1,570 ft).[11] This bridge is in the most difficult part of the project which has been assigned to the Konkan Railway Corporation Ltd. It is being constructed by Afcons.[12] Many experts throughout the globe, based on their versatile and relevant experience, have been involved, in order to make this project a success.
National codes of India, Indian Railway Standards (IRS), Indian Road Congress (IRC) and Indian Standards (IS) have been supplemented with International standards; British Standards (BS), International Union of Railways (UIC) and Euro, as national codes, were found inadequate for such large spans. The Quality aspect has been emphasized, as the quantum of fabrication and welding is colossal. Mostly indigenous material has been planned to be used, whereas for the design, international codes have been referred, which means the Quality Control work is still difficult.
Regular painting of such bridges is an intimidating task; hence, a painting scheme has been developed, having life over 15 years, compared to 5 to 7 years (approx.) of life in most of the Indian railway bridges. The erection scheme for the bridge is a project in itself, where two pylons (about 130 m and 100 m high) are to be erected on either side of the river, and two auxiliary cable cranes (Capacity 80T each), consisting of self-propelled equipment, will be running on the carrying ropes across these pylons.
Special considerations
The structural concept of the bridge over the river Chenab is a large span arch over the river, with approach viaducts on either side. The proposed arch is a two-ribbed arch, fabricated from large steel trusses. The chords of the trusses will be sealed steel boxes, filled with concrete to assist in controlling wind-induced forces on the bridge. Another advantage of concrete filling is that internal painting will not be required. The boxes will be stiffened internally.
The numbers of bearings have been minimized, particularly on the approach viaduct, through the use of continuous construction. This is advantageous, as it reduces the maintenance and inspection efforts, and improves the riding quality. The viaduct piers are of concrete, while the piers near the arch are in steel.
The design of major arch rail bridges requires considerations of a number of additional parameters, such as fatigue, global stability, second order effects, composite action, etc. It also requires that such a bridge is designed to achieve a consistent level of reliability for all load cases, and that the design standards match the construction standards.
The Indian Railway Standards (IRS) is primarily intended for simply supported bridges with spans up to 100m (although these have been successfully used for higher spans up to 154m). The spans proposed for this bridge greatly exceed this limit, and are continuous. In order to provide these additional features, it will be necessary to augment the design with additional international codes and standards that enable the designer to produce a safe design.
Following are some of the special features of structural design for the bridges:
- Limit state philosophy of design has been decided to be followed as per BS codes.
- Computation of wind load effects as per Wind tunnel tests
- Site specific seismic spectra developed by Indian Institute of Technology (IIT) Roorkee.
- Provision of Euro code 8 for ductility detailing of very tall and hollow rectangular RCC piers.
- Provision of long welded rail (LWR) over the bridges and resulting force calculation as per UIC – 774-3R guidelines.
- Blast resistant design has been used.
- Design checking for fatigue as per BS codes.
- Deformation limits as per comfort criteria of UIC – 776-2R and UIC 776 -3R guidelines.
- Redundancy provided in the structures, for lower level of operation during mishaps and against collapse in extreme cases of one pier failure.
Anji Khad Bridge
The alignment is a culmination of large number of tunnels and bridges which are to be implemented in highly rugged and mountainous terrain, with mostly difficult Himalayan geology. The alignment crosses deep gorges of Anji-Khad near Reasi, which necessitates construction of a long span bridge. After many deliberations, the configurations of steel arches were found most suitable on account of aesthetics, economy, and availability of local expertise and construction materials.
Anji Khad Bridge, with its 265m-long main arch span, at a height of 189m from the bed level, is perceptible. Many experts throughout the globe, based on their versatile and relevant experience, have been involved in order to make this project a success. National codes (IRS, IRC and IS) have been supplemented with International standards (BS, UIC and Euro), as national codes were found inadequate for such large spans. The Quality aspect has been emphasized, as the quantum of fabrication and welding is colossal.
The material procurement has been done as per IS codes, whereas for the design, international codes have been referred, which means the Quality Control work is still difficult. Regular painting of such bridges is an intimidating task; hence, a special painting scheme has been developed, having life over 15 years, compared to 5 to 7 years of life in most of the Indian railway bridges.
Construction Site of Anji Khad Bridge - See construction on two hills on extreme left
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