Bridge engineering has been making global headlines recently but for the most unfortunate of reasons.
As European civil engineers grappled with the aftermath of the Polcevera Bridge disaster in Italy, a similar tragedy unfolded in India in early September with the collapse of the Majerhat Bridge in Kolkata.
Majerhat Bridge connected Kolkata’s central business district with its residential and industrial areas, crossing over railways and a canal. The failure happened on the span across the canal, causing three deaths while injuring at least 25 others.
Sadly, this is not an isolated incident. Majerhat Bridge is the third bridge collapse in Kolkata in the past six years. It is disheartening to see how we continue to fail to keep our important infrastructure in good condition and safe for the people who use it. Once again, this collapse highlights the importance of systematic, controlled maintenance of critically important and capital-intensive infrastructure assets, particularly those which are older.
Opened in 1964, Majerhat Bridge was one of the first prestressed concrete girder bridges in the city. At the time, the design was forward-looking and addressed all the concerns of planners very well. Designed for the national highways loading standards of the 1960s, the bridge saw ever-increasing traffic loads for over 50 years. With the wearing course incurring frequent damage from heavy goods vehicles, and intense city traffic both day and night, the wearing coats were renewed often but perhaps had not been adequately tracked.
Investigations after the collapse have revealed a much larger thickness of bituminous wearing coats than the originally specified 125mm. This caused net tensions on the bottom flanges of the girders while the humid atmosphere above the canal area led to progressive corrosion.
The other likely reason for failure could be corrosion of the transverse prestressing wires. The joints were filled with mortars, which could have fallen off with time, making water ingress easier. Loss of prestressing could have adversely affected the orthotropic behaviour and imbalance in sharing of load carried by individual girders.
While the bridge belonged to the Public Works Department, control of the land underneath was divided between Railways, which managed the track portion, and Port Trust, which looked after the canal and its surroundings. The underside of the bridge’s girders was rendered inaccessible by the high voltage lines of the electrified rail tracks, affecting maintenance. There was also an absence of structural work manuals.
As we uncover exactly what went wrong in the past, clearly there are lessons to be learned for the future. We need to assess the condition of such structures and rehabilitate them long before accidents happen. We cannot accept long periods of reconstruction, causing a significant disruption to urban life. Above all, we cannot accept such a catastrophic loss of human life.
- Amitabha Ghoshal is an ICE Fellow