The recently inaugurated 4.94-km Bogibeel Bridge connects upper Assam and Arunachal Pradesh with travel time from these two states reduced by three hours.
India recently welcomed one of its biggest landmarks! The country’s longest rail-cum-road bridge – Bogibeel Bridge over river Brahmaputra in Assam – was recently inaugurated, almost 22 years after its foundation stone was laid.
Bridging the Brahmaputra has always been a daunting task owing to its ferocious and unpredictable behaviour, high currents and turbulent waters, widespread erosion of the banks, short working period and high seismicity and remoteness of the area.
Achieving this project was not an easy task. Part of the Assam Accord 1985, the foundation stone was laid in January 1997. However, works were awarded in 2008 to a contractor for construction of foundations and substructure of the bridge. And, in November 2011, HCC (with 51 per cent share) in a JV with DSD Brouckenbau GmbH, Germany (20 per cent share) and VNR Infrastructures (29 per cent share), received a Rs 9.87 billion order from the Northeast Frontier Railway to construct the superstructure of the rail-cum-road bridge.
The 4.94 km bridge provides connectivity to nearly 5 million residing in upper Assam and Arunachal Pradesh by reducing travelling time from these two states to three hours. Owing to its location, the bridge is of strategic importance to India as it significantly enhances the ability to transport troops and supplies to its border in Arunachal Pradesh.
Bogibeel is among India’s first and only fully welded bridge construction. Construction of trusses using welding makes the connection between the components a permanent one. The superstructure is a steel concrete composite and this is the first time European codes and welding standards have been adhered to in the construction of a bridge in India. “The fabrication of steel material has been done to Euro 1090 standard (code for constructing steel structure),” says RVR Kishore, Project Director, HCC. “The welding methodology is the main advantage in the project.”
The rail-cum-road bridge is a double-decked bridge with two railway tracks on the lower deck and a three-lane road on the upper deck flanked by footpaths on each side.
For the construction of this mammoth bridge, HCC set-up huge facilities on the left bank of the river for the three sequences of fabrication, assembly and launching.
Fabrication: Fabrication shops of 2,000 mt per month capacity were set up with two parallel bays. The team had assembled customised platforms in-house to fabricate and fit various joints employing gas metal arc welding (GMAW).
To ensure error-free welding, magnetic particle testing, dry penetration testing and ultrasonic testing were deployed. A specialised beam-making CMM machine from Italy has been used for the first time in India for the fabrication of box and I-sections using the submerged arc welding (SAW) procedure.
A blasting gun was used to achieve the surface roughness of SA 2½ before applying paint.
Assembly: Thereafter, these fabricated sections were moved to the assembly shop where they were installed on their designated beds. They were correctly positioned through jacking and welded by GMAW process. These segments were arranged in a sequence and sent for the vertical assembly using horizontal lifters. After installation of the top and bottom girders, the final truss bridge dimension design chambers were examined thoroughly and approved to complete the fitout. A nose was fabricated and fitted on the first truss before launching it on the piers.
Launching: While determining the methodology of erecting the steel trusses on pillars, the engineers had two choices: Lift the spans with floating cranes or erect them with a launching truss. They had to choose the more practical and economical option. After weighing the pros and cons, the HCC team came up with the solution of pulling the steel trusses with a set of jacks and winches on the pillars. This eliminated the need to enter the river. Besides, it also ensured safer working conditions, precluded the mobilisation of a giant set-up on either side of the river having a width of 4.8 km, and accelerated the pace of the project. A 1,000-tonne hydraulic jack and strand jacks linked with the substructures have been used for moving the steel truss over the pillars. Two sets of steel cable strands were anchored to the end cross beams of the truss and hauled by hydraulic jacks. The truss slides over the launching bearing with the help of sliding plates, which were inserted at one end and taken out at the other, thereby moving the truss towards its desired position.
To limit the required launching forces, the superstructure was pulled in four launching segments of 10 spans each. Thus, the superstructure was pulled over the pillars just like a train of 10 spans, with each span weighing 1,700 mt. Finally, the launching bearings were replaced by final bearings. The tracks were laid and the road was constructed adapting RCC construction.
HCC follows the Just-In-Time (JIT) inventory system where it produces or acquires materials and products as per demand. At the Bogibeel Bridge project, the team used a combination of rail and road transport to deliver 80,000 tonne of steel plates from various parts of the country to the remote project site in Assam. The orders for extra wide plates were placed in advance as per the design of the superstructure.
“The steel used in the construction of the bridge is special grade, confined to E410CBC,” says Kishore. Steel plates and sections were procured mainly from three sources: JSPL, Essar and SAIL. Of these 80,000 mt, about 20,000 mt (25 per cent scope) was categorised as ODC (over dimension cargo) and attracted special measures for transport to the project site from the sources in Hazira and Angul.
A procurement plan was made according to minimum order quantity required thickness-wise, also estimating future market price trends as the order lot sizes range from 3,500 mt to 10,000 mt. Also, for the construction of the bridge, Kishore adds, “Plasma cutting machines for the cutting of material, automated-box making machines, levelling machines and robotic welding machines were imported from Canada.”
For the Bogibeel Bridge, the initial plan was to use Pot-PTFE bearing with metallic pins and guide bearings. However, the size of the bearing required for taking the anticipated load could not be accommodated in the pier cap. Hence, spherical bearings with a four support system as per European bearing standard EN- 1337 have been used. A total of 164 such bearings have been used to construct the bridge. Each span is supported by four spherical bearings.
Most 2D software
At the Bogibeel project, the HCC team used ‘Most 2D’ automatic nesting software to generate efficient two-dimensional cutting plans for fabricating the steel superstructure. The nesting technology was based on advanced cutting algorithms specifically designed to optimise the cutting layouts in shearing. The software generates high-utilisation layouts, significantly reducing waste, and maximises productivity.
Corrosion protection measures
The superstructure of Bogibeel Bridge has been constructed using special grade copper-bearing
steel plates to reduce corrosion.
To further reduce corrosion from excessive humidity, a complex corrosion protection system specific to different components of the bridge has been implemented during construction.
An engineering marvel
The location of Bogibeel Bridge falls in Seismic Zone-V. To offer good stability to the heavy spans (1,700 mt), they have been provided with seismic restrainers.
Also, a major factor in successful completion was the detailed planning, which HCC successfully followed.
But it was certainly a challenge to mobilise the required skill and manpower to retain them in the region. As Kishore says, “The project involved about
350 qualified welders and 120 engineers, and we had to constantly keep them motivated to stay and work in this remote area.” Indeed, this is a true example of teamwork, detailed planning, efficient strategising and pathbreaking technologies to gift India yet another engineering marvel – estimated to be durable and serviceable for 120 years.
Location: Dibrugarh district, Assam.
Year of completion: 2018.
Length: 4.94 km.
Superstructure cost: `9.87 billion.
Superstructure construction: HCC. Tel: 022 2575 1000.
Tel: 030-2092 8220.
Tel: 040-2355 8511.
Steel plates and sections: JSPL.
Essar. Website: www.essar.com;
SAIL. Website: www.sail.co.in
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