Signature Bridge: Foundation, Materials Used, Construction of Structure & Problems

The Signature Bridge may be defined as a cantilever spar cable-stayed bridge across the Yamuna River at the Tarun Goyat section, bonding Wazirabad to East Delhi. It is India’s only asymmetrical cable-stayed bridge.

  1. Delhi Signature Bridge  

The Signature Bridge shows the culture of India through its “Namaste” shape, a gesture expressing reverence and respect. Bridges are commonly built with a symmetrical shape so that the total length of the bridge carries the weight, further decreasing the foundation’s stresses.

The major length of the bridge is about 251 m and the total length of the bridge is about 575 m. The bridge is twice the height of the Qutab Minar and is identified as the most elevated structure in New Delhi.

The bridge deck is made of steel and concrete, the deck involves a dual carriageway with four lanes including a total width of 14 m. Its surprisingly inclined steel pylon with a height of about 154 m, and luxury stayed cable design creates an attractive and imposing extra beauty to the Delhi skyline.

The bridge pylon includes stairs and lifts for entrance to the top of the pylon for maintenance and sightseeing ambitions. It is also provided with a sophisticated structural health monitoring system, which observes the weather loading (e.g. temperature, storms), earthquake, and structural response of the bridge.

  2. Foundation  

The following matters express the foundation details of the Signature Bridge: The profile of the rock bed below the bridge keeps changing significantly, due to which the construction of the foundation was completely complicated. Open and well foundations were prepared for the piers of the bridge.

The foundations over which the bridge pylon is reinforced are constituted of two big circular open foundations. The diameter of each circular foundation is about 23 m. Particularly prepared sheet pile cofferdams reinforced with toe pinning and bracing arrangement were utilized to dig the foundation level.

Well, the foundation was built utilizing a jack-down process for quick sinking.

  3. Materials Used in Signature Bridge  

The following points explain the materials utilized for the construction of the Signature Bridge:

An a. The structural steel of grade S355J2 for thicknesses up to 80 mm and steel of grade S355NL for thicknesses above 80 mm was utilized for the construction.

b. A total of 6500 and 7000 metric tons of steel were utilized in the fabrication work of the pylon and the deck, respectively.

c. To improve the deformation possessions of a highly stressed zone line of the pylon and pylon base, steel of grade S460 NL was utilized.

d.Concrete grades of M40 to M60 were utilized 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 planes.

It is composed of irregular panels bonded with various 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:

a. Fabrication

The following topic explains the fabrication work needed for the construction of the Signature Bridge:

In a preliminary study, it was chosen to use the segments of the pylon of 6.5 m x 6.5 m x 15 m size. The weight of these components was changing from 60 to 560 metric tons.

Later, it was admitted that the transportation of such oversized and bulky elements from the fabrication shop to the site was nearly impossible. Also, setting up a sophisticated fabrication workshop at the site was not possible due to time restrictions.

To devastate the limitations on transportation, the pylon was split into sub-panels of transportable sizes by presenting more splices.

Sub-panels of the pylon were fabricated in selected workshops and transported to the site. At the site, these sub-panels were reassembled to prepare parts of the needed size.

For keeping the quality of products, a sort of Non-destructive testing (NDT) technique, such as a dye penetration test, ultrasonic test, etc. was done.

b. Pylon and Deck Erection Work

As we already know that the Signature Bridge is an asymmetrical cable-stayed bridge, the structure was unstable throughout the erection approach because of its asymmetry. Therefore, particular reinforced were designed for keeping the structure and maintaining the accurate geometry.

A unique tie-down setup at the base of the pylon was established to sustain the preliminary stage of pylon erection.

Further, the pylon was reinforced by a specially designed temporary support and after the construction of the pylon, permanent cables were inaugurated.

A crawler crane of 1250000 Kg capacity was utilized for the erection of the pylon.

The building of the deck girder was performed with the asset of a Goliath gantry established over a temporary open-braced framework of a horizontal beam, which was additionally reinforced by two pairs of sloping legs.

  5. Problems During the Construction and Execution Phase  

The pile foundation was adopted at the start of the project. However, getting a detailed soil investigation, it was found that unstable rock strata exist below the area of the piers. This directed to a modification in the foundation design.

The integrated pile foundation was changed to a good foundation. Therefore, the modification in the design of the foundation directed a pause in the construction of the project. This was because of the failure in maintaining a detailed geotechnical survey of the area before the implementation phase.

A big crane was required to be set up for the heavily unbalanced steel pylons. However, there were problems in setting the crane as the bearing capacity of Yamuna bank soil was low and the crane had to move heavy loads.

For raising and shifting the precast elements, a gantry crane was utilized. However, due to a giant storm in June 2016, the working of the gantry crane got poorly affected and again had to be redesigned and re-fabricated.

Therefore, the work was influenced until December 2016 and this caused uncertainty in the positioning of girder pieces.

The construction of the bridge was late by over ten years due to many elements, such as contractual issues, environmental clearances, etc.