The Chitpore Bridge was repaired using anti-corrosive treatment, rebuilding of concrete section with micro concrete and polymer, followed with strengthening by using SRM C-wraps and SRM C- Laminates of carbon fiber. After successful completion of repairing and strengthening work, the bridge was open for the public.
Dr M.V. Joshi, PhD IIT Bombay, CEO of SSSPL; Vivek S V, M-Tech IIT Kharagpur; and J. D. Bhanushali, MSc in Civil Engineering, IIT Tirupati

The Chitpore Bridge has contributed to the economic growth of Kolkata city from as early as 1843. It was constructed under the leadership of John Thomson, who was the superintendent of canals and the agent for iron suspension bridges. The bridge spans 99 feet and has a roadway which is 24 meters wide. It was popularly referred to as the Bagbazar Bridge and is one of the earliest examples of the bowstring bridge (Figure 1).

The Kolkata Metropolitan Development Authority KMDAFigure 1

KMDA conducted structural inspection of Chitpore Bridge
Deterioration is a common problem in bridges and Chitpore Bridge is no exception.

The Kolkata Metropolitan Development Authority KMDA, conducted structural inspections of several bridges in Kolkata and found that Chitpore Bridge falls under the category of “vulnerable bridges and flyovers” and therefore needed immediate repair and restoration to avert any major mishap.

Non-Destructive Tests Performed on Chitpore Bridge
In August 2019, LASA was awarded consultancy services for Chitpore Bridge. The condition of the bridge was surveyed and non-destructive tests were performed. The seemingly healthy bridge revealed active corrosion in selected areas. The NDT test revealed the following:
  • In the vertical hangers, steel reinforcement had lost its diameter at several locations
  • Spalled portions and discontinuous rebars were visible in hanger columns, under the deck slab and on cross beams (Figure 2)
  • The structural strength of sectional members was compromised by corrosion
  • Pitting corrosion of the embedded steel in the vertical hangers and in the beams supporting the deck
The Kolkata Metropolitan Development Authority KMDAFigure 2: Spalled portions show exposed and discontinuous rebars in hanger columns, under deck slab, and on cross beams

Adding to its already distressed condition, was the nearby Tala Bridge, which was closed down, sending substantial traffic to Chitpore Bridge. To prevent a catastrophe, an immediate strengthening of the structural system was necessary. It had to be done fast with due diligence. That’s when Sanrachana came to the rescue.

Repair and Retrofitting of Chitpore Bridge Executed by Sanrachana
Sanrachana is one of the pioneers in the area of structural retrofitting and protection in India and has decades of experience in executing bridge repairs across the country. It has served clients on over 2000 commercial properties, industrial facilities, energy plants, and public infrastructure, and many other projects of varying size and scale.

Overview of work executed:
  • Sandblasting, anti-corrosion treatment
  • Providing additional rebars, micro-concreting
  • Strengthening of hangers, deck & cross beams with SRM carbon laminates & SRM C-wraps
  • Post-tensioning 4 Mac-alloy bars with 5 tons each, to counteract tension on each hanger.
The team started repair work with sandblasting in Chitpore to get clarity on the underlying distressed concrete (Figure 3). Delamination and spalling were detected and removed with hammer and chisel. The exposed rebars of the hangers were treated for corrosion. The section was rebuilt with high-strength micro concrete. The underside of the bridge was made accessible with platforms supported by a structural steel section.

The Kolkata Metropolitan Development Authority KMDAFigure 3: Illustration of repairing scheme for Chitpore Bridge

The strengthening of hangers, decks & cross beams was done with SRM C-Lam carbon laminates and SRM C-wraps as shown in Figure 4.

The Kolkata Metropolitan Development Authority KMDAFigure: 4 Application of SRM carbon laminates & SRM C-wraps

The base of the hangers was armored with a 1.2m cover block. Structural steel sections were used on top of the hangers above the RCC arch. Connecting these, high-strength MC Alloy threaded bars were installed. The tensioning mechanism was to be operated from the top of the hangers.

The Kolkata Metropolitan Development Authority KMDAFigure 5: Illustration of strengthening activities using MC Alloy Bars

Mechanism of post-tensioning
The Kolkata Metropolitan Development Authority KMDAFigure 6: PT application on MC Alloy bars
Upon tightening the top nuts of the McAlloy bars, tension force gets developed in the bar, because of which a reaction force of compression is generated on the RCC hangers. Post tensioning in this manner keeps the concrete under compression while the McAlloy bars handle the tension. Typically, while post tensioning, PT force is applied using hydraulic jacks. The advantage of using McAlloy bars is that PT force can be applied without such machinery. The trained workforce of Sanrachana is seen applying PT force manually by using spanners (Figure 6). With the application of protective coating, the work was completed. All the contract criteria were met by Sanrachana.

References
  1. American Concrete Institute, Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures (ACI 440.2R-2017), ACI, Farmington Hills, MI, 2017.
  2. getbengal.com - (https://www.getbengal.com/details/chitpur-bridge-the-bridge-that-protected-kolkata-from-maratha-bargis).
Remotely Piloted Aerial Vehicle (RPAV) Based Bridge Monitoring
Dr. Naveet Kaur, Senior Scientist, Bridge Engineering & Structures Division, CSIR-CRRI, New Delhi, shares information on the various types of applications of RPAV technology in BHM, including visual inspection, non-destructive testing, and structural health

Read more ...

Prestressing Concepts, Systems & Technologies in Bridges
Prestressing works as an active force in the structure, opposite to applied tensions. There are several types of prestressing such as Internal Prestressing, External Prestressing, Bonded Prestressing, Unbonded Prestressing, etc. Pre-tensioning and Post-tensioning

Read more ...

Structural Integrity Assessment of Submerged Bridges Using Robotic Inspection and Scour Survey
In a developing country like India, roads, rails and bridges are amongst the most important infrastructure assets that connect every corner of the country. Roads and bridges tend to undergo wear and tear with aging. When they get submerged

Read more ...

Design Concept of Iconic Pedestrian Bridges - Atal, Sambhaji, and Deccan
Theme-based concepts of structural forms and designs of bridges are developed through collaborative efforts of the architects and engineers to maintain their aesthetics and structural efficiency. Any bridge or infrastructure is designed for

Read more ...

Construction of Balason Bridge in Darjeeling District @ West Bengal - An Engineering Feat
Situated amidst picturesque surroundings, Balason Bridge is located about 50 km from Siliguri Town, 17 km from Mirik Town and 80 km from Darjeeling Town. The Extension of Balason Bridge @ Dudhia is located 25 km from Siliguri Town in the state of West

Read more ...

Dextra supplies Mechanical Rebar Couplers and Post-Tensioning Bar Systems to new Zuari Bridge in Goa
An 8-lane cable-stayed bridge being constructed over the river Zuari in South Goa, has taken engineering to new heights. This is the second longest and widest cable-stayed bridge in India; it will serve Expressway NH-66 that runs between Panaji

Read more ...

Construction Industry - Progressing Towards A ‘Digital’ Future
The Indian construction and engineering industry is poised for significant growth with a projected expansion of 6.6% in real terms. As part of the ambitious Pradhan Mantri Gati Shakti Master Plan, worth $1.3 trillion, India’s infrastructure development

Read more ...

NHAI invites bids ₹244-cr six-lane flyover & two-lane ROB in Odisha
NHAI invites bids for six-lane flyover and two-lane ROB in Odisha with an investment of ₹244.32 crore. The Ainthapali junction project on NH-53 (Old NH-6) in Sambalpur involves the rehabilitation, upgradation, and augmentation

Read more ...

Synergising Aatmanirbhar Bharat and Operational Preparedness: Launch of Indigenous Modular Bridge in Sikkim
Enhanced operational preparedness along the borders and the need to be self-reliant are two major aspects that have seen a substantial impetus over the last few years. The Border Roads Organisation (BRO) has been a key contributor to the infrastructure

Read more ...

Architectural System for Arch Bridges
Dextra India’s architectural systems mainly include Tension Rods and Compression Struts, which creates functionally effective and aesthetically pleasing structures. Featuring a wide range of sizes and accessories in various steel grades and in both

Read more ...

Load Testing of Various Types of Bridge Superstructures
Er. Vivek Abhyankar describes the steps and aspects of load testing of various types of superstructures, along with some cautionary measures and points to ponder upon by the designers, site engineers, and testing agencies. The information provided will be

Read more ...

Innovative Steel Plate Girders With Corrugated Webs
Girders with corrugated steel webs represent a new innovative system which has emerged in the past decade. These girders have thinner webs, higher fatigue resistance, and are more economical, easier to fabricate, more aesthetic, and provide faster construction

Read more ...

My Tryst with the National Namaste Signature Bridge
The iconic National Namaste Signature Bridge in Delhi over the river Yamuna appears languid in perpetual motion in the tradition of the Calatrava’s Bridges in motion, symbolizing nationalism in its visual form. V N Heggade, FNAE, Structural Consultant, Mumbai

Read more ...

Construction of Foundation & Sub-Structure of Bogibeel Rail-Cum Road Bridge Over River Brahmaputra- An Engineering Marvel
The former Prime Minister of India Shri H D Devagowda laid the foundation stone of the Bogibeel Bridge on January 22, 1997 at Kulajan (Assam). After 5 years of laying of the foundation, on April 22, 2002 the Prime Minister of India Shri Atal Behari Vajpayee

Read more ...

Construction of World’s Tallest Rail Bridge in India
As part of Northeast Policy, the Ministry of Railways took up the project of providing rail connectivity to Imphal in Manipur state. As per the detailed survey, the rail alignment takes off from existing Jiribam

Read more ...

Construction of New Brahmaputra Bridge & Road Works Near Tezpur - An Insight...
Brahmaputra is one of the longest river in Asia with a total length of 2880 km & out of which 920km (approx.) lie in India. The New Brahmaputra Bridge @ Tezpur is one of the most challenging one, in the attempt to bridge

Read more ...

Slope erosion protection of bridge approach embankment
The road and railway crossing across the Brahmaputra on National Highway-52B is located at Bogibeel, about 17km downstream of Dibrugarh in Assam. The location is an area of high intensity rainfall (the annual rainfall ranges

Read more ...

Art & Science of Bridge Engineering - A World Scenario
The world has progressed beyond imaginations. Similar to the field of IT, Civil Engineering has also taken several steps forward to bring out innovative technologies to meet challenges of this world’s aspirations. Going forward from

Read more ...

Dhola Sadiya - India's Longest River Bridge
The bridge lies in the state of Assam, but this location is usually referred to as upper Assam as it is far away from Guwahati and bordering China. The nearest airport is Dibrugarh. Then there is a drive of 65km into the

Read more ...