Signature Bridge: Important Aspects of its Design and Construction

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The Signature Bridge represents the culture of India through its "Namaste" shape, a gesture representing reverence and respect. Bridges are usually constructed with a symmetrical shape so that the entire length of the bridge bears the weight, and further reduces the stresses on the foundation. However, the Signature Bridge has an asymmetric shape and is India's first asymmetric steel cable-stayed bridge.

The Signature Bridge crosses river Yamuna at Wazirabad, New Delhi. The main span of the bridge is 251 m and the overall length of the bridge is 575 m. The bridge is double the height of the Qutab Minar and is recognized as the tallest structure of New Delhi.

The bridge deck is a composite of steel and concrete, the deck consists of a dual carriageway with four lanes having a total width of 14 m. Its dramatic inclined steel pylon with a height of 154 m, and elegant stayed cable design make it an attractive and imposing addition to the Delhi skyline.

The bridge pylon consists of stairs and lifts for access to the top of the pylon for maintenance and sightseeing purposes. It is also equipped with a sophisticated structural health monitoring system, which monitors the weather loading (e.g. temperature, storms), earthquake, and structural response of the bridge.

1. Location of Signature Bridge

The Signature Bridge connects Wazirabad to East Delhi. This bridge was primarily constructed to reduce the travel time between north and northeast Delhi.

2. Foundations Details

The following points describe the foundation details of the Signature Bridge:

1. Profile of the rock bed below the bridge keeps varying drastically, due to which the design of the foundation was quite complex.
2. Open and well foundation were provided for the piers of the bridge.
3. The primary foundations over which the bridge pylon is supported are comprised of two big circular open foundations. The diameter of each circular foundation is 23 m.
4. Specifically designed sheet pile cofferdams supported with toe pinning and bracing arrangement were used to excavate the foundation level.
5. Well foundation was built using jack down approach for fast and speedy sinking.

3. Materials Used for Construction

The following points describe the materials used for the construction of the Signature Bridge:

1. Structural steel of grade S355J2 for thickness up to 80 mm and steel of grade S355NL for thickness above 80 mm was used for the construction.
2. A total of 6500 and 7000 metric tons of steel was used in the fabrication work of pylon and the deck, respectively.
3. To improve the deformation properties of a highly stressed zone line of pylon and pylon base, steel of grade S460 NL was used.
4. Concrete grades of M-40 to M-60 were used for foundation and deck construction.

4. Construction of Superstructure

The two main components of the Signature Bridge are the pylon and the deck. A pylon is a complicated three-dimensional structure inclined at all the planes. It is composed of irregular panels bonded with different steel plates of various grades. The deck of the bridge is a composite of steel and concrete. Construction details of the pylon and the deck of the bridge are discussed below:

4.1 Fabrication Work

The following points describe the fabrication work required for the construction of the Signature Bridge:

1. In a preliminary study, it was decided to use the segments of pylon of 6.5 m x 6.5 m x 15 m size. The weight of these segments was varying from 60 to 560 metric tons.
2. Later, it was realized that the transportation of such oversized and bulky segments from the fabrication shop to the site was almost impossible. Also, setting up a sophisticated fabrication workshop at the site was not feasible due to time constraints.
3. To overcome the restrictions on transportation, the pylon was divided into sub-panels of transportable sizes by introducing additional splices.
4. Sub-panels of the pylon were fabricated in established workshops and transported to the site. At the site, these sub-panels were reassembled to make segments of the required size.
5. For maintaining the quality of products, a variety of non-destructive testing (NDT) techniques, such as dye penetration test, ultrasonic test, etc. were conducted.

4.2 Pylon and Deck Erection Work

The following points describe the pylon and deck erection work for construction of the Signature Bridge:

1. As the Signature bridge is an asymmetrical cable-stayed bridge, the structure was unstable throughout the erection process due to its asymmetry. Therefore, special supports were created for supporting the structure and maintaining the correct geometry.
2. A unique tie-down set up at the base of the pylon was installed to support the preliminary stage of pylon erection. Further, the pylon was supported by a specially designed temporary strut and after the construction of the pylon, permanent cables were installed.
3. A crawler crane of 1250 tons capacity was used for the erection of the pylon.
4. The construction of the deck girder was achieved with the help of a Goliath gantry installed over a temporary open braced framework of a horizontal beam, which was further supported by two pairs of sloping legs.

5. Time Delays and Cost Overrun

The initial estimation of expenses for the construction of the bridge was INR 464 crores in 2005. In 2006, it was authorized for a financing of INR 459 crores. Later on, the design of the bridge was altered from a simple one to a landmark bridge. The quote was modified to INR 1131 crores in 2010 and further to INR 1575 crores in 2015.

For phase-1, the tender was initiated in the year 2007. It was decided to complete the work before the 2010 Commonwealth Games. However, the changing designs and dimensions of the project increased the cost of the project. After that, the work was again granted in 2010. This time, it was decided to complete the project before December 2013. However, it missed out on the due date again because of a contractual issue. Finally, the construction of the Signature Bridge completed in 2018, and it was opened to the public on 4 November, 2018.

6. Major Concerns During Construction and Execution Phase

The following points describe the major concerns during the construction and execution phase of the Signature Bridge:

1. Pile foundation was adopted at the beginning of the project. However, after the detailed soil investigation, it was discovered that varying rock strata exist below the location of the piers. This led to a change in the foundation design.
2. The integrated pile foundation was changed to well foundation. Therefore, the change in the design of the foundation led to delay in the construction of the project. This was due to the failure in holding the detailed geotechnical survey of the area before the execution phase.
3. A big crane was needed to be set up for the massively unbalanced steel pylons. However, there were problems in establishing the crane as the bearing capacity of Yamuna bank soil was low and the crane had to carry heavy loads.
4. For lifting and transporting the precast segments, a gantry crane was used. However, due to a massive storm in June 2016, the working of the gantry crane got badly affected and had to be redesigned and re-fabricated. Therefore, the work was impacted until December 2016 and this caused a delay in the positioning of girder pieces.

The construction of the bridge was delayed for over ten years due to several factors, such as contractual issues, environmental clearances, etc. These factors are discussed in detail in the subsequent section.

6.1 Contractual Concerns

The agreement for the approach of the bridge was granted to Gammon India in 2008. After a series of delays, the tender for the bridge was granted to the Gammon-ConstrutoraCidade-Tensacciai in 2010. Out of the three partners, Gammon is an Indian company, and the other two are Italian and Brazilian, respectively.

However, Gammon India was also involved in other projects at that time, like the construction of the Delhi metro. During the time, a major accident of a pier failure of Delhi metro occurred, which led to questioning of the credibility of Gammon India as an in-depth examination had revealed the company to be primarily accountable for pier failure during the metro construction. This incident further led to the cancellation of the contract to Gammon India and therefore caused a delay in the construction of the Signature Bridge.

6.2 Environmental Clearances

Delhi government initially applied for environmental clearance from the ministry of environment and forests (MOEF) in 2007. MOEF notified the Delhi government that such jobs did not need an environmental impact assessment (EIA) as bridges are not categorized under the EIA notification- 2006.

However, in 2014, the National Green Tribunal (NGT) filed a petition stating that the bridge could not be a standalone project and that such projects are part of highway projects. Moreover, the Signature Bridge has an overall construction area of more than the permissible limit of 1,50,000 m², and it falls under the area redevelopment category of EIA notification-2006. Thus, NGT directed the state government environmental assessment committee to conduct the environmental impact assessment of the project. This led to a further delay in the construction of the bridge. However, NGT had notified that no demolition of the signature bridge was needed.

Later on, the state government environmental assessment committee gave the environment clearance in 2017 with a series of limitations on certain activities.

6.3 Supplier Issues

A Chinese company Jiangsu Zhongtai Bridge Steel Structure Co., Ltd (ZTSS) had the contract of supplying steel girders and pylons. However, the comptroller and auditor general (CAG) had discovered some specific concerns about obtaining the steel pylon from China. The legal obligation of the contractor and also the quality of the steel frames were questionable.

This led to the delay in the shipment of the steel pylon. The very first consignment of the steel pylon was received in September 2013.

6.4 Social and Legal Issues

The residents of Delhi supported the construction of the Signature Bridge because it would drastically decrease the travel time between north and northeast Delhi. Due to several delays in the project, an activist from Delhi had filed a litigation in the Delhi high court against the delay in completion of the project.

This led to the formation of a committee by the court to look into the causes of delays in the project. Due to the highest level of scrutiny, each and every construction activity had to be overlooked by the legal committee, which increased the time span of construction. Thus, the project faced legal and social issues and got delayed.

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