Bridges are the most important element in a surface transport network. Once built, they are extremely difficult to replace and it becomes challenging even to close them for a few days for essential repair work. A sudden failure disturbs normal life, affects development and causes economic losses. So it’s important for the public to be aware of the reasons for their failure and raise voices to prevent them.
Bridges have failed across the world for long. In developed countries, such failures are analysed, the studies shared and the lessons recorded to prevent recurrences. In India, the trend has been to form enquiry committees without checking the technical competence of the members and hide the proceedings in confidentiality, keeping the public uninformed. Reports are often allowed to ‘disappear’ to protect those responsible.
The classical case of the Tacoma Narrows bridge failure in the US in 1940 was instantly shared across the world; the video of the failure became standard teaching material for engineering students across the world. The result: there has been no such failure ever and every engineer knows that a lightweight, long-span bridge needs to be checked for aerodynamic stability and model tests have to be done in a laboratory.
The failure of the West Gate bridge in Australia in 1970 was similarly explored; the enquiry commission came out with a comprehensive analytical report that became a bible for the makers of design codes across the world. People came to know of the problems with thin-walled box girders made with steel plates that had become the favourite of engineers trying to cut steel consumption. Such failures never recurred.
In our country, the much publicised failure of the Morvi bridge, an unstiffened suspension bridge that tends to wobble with people walking on the deck, was widely circulated by the media. Despite the high casualties, we have not learned the lesson—none of the several unstiffened suspension bridges in the lower Himalayas have been intensively inspected or their rehabilitation initiated, as far as public knowledge indicates.
The spectacular failure of the Majherhat bridge in Kolkata has been all but forgotten. No analytical studies were done and no mandatory notification issued to authorities across the country to ensure that the wearing coat on the bridge deck should not be allowed to go beyond design thickness—a common folly of bridge maintenance teams and widely believed to be the root cause of the failure. We can expect to witness more such failures.
Technical knowledge of bridges is globally shared and countries follow identical design norms that are openly shared and updated. Bridges of an earlier era used to be girders put on piers in the form of beams or trusses, supported on bearings put on piers. The need to elongate spans led to the use of arches and bowstring girders, such as for the Sydney Harbour bridge.
With a thrust on sustainability after the Second World War, the choice moved to bridges supported by cables. Across the world, cable-stayed bridges (Signature bridge in Delhi) and extra-dosed bridges (Nivedita Setu in Kolkata) have become popular. With these changes in technology, engineering knowledge needs upgrading. There have been widely-circulated reports of distress observed on cables across the world; for example, a bridge in Genoa named after its fabled Italian designer Riccardo Morandi had a spectacular failure due to corrosion of cables.
For understanding the reasons for bridge failures, one has to first recognise the various types of failure. There are failures that happen after years of operation, sometimes due to inadequate maintenance. They can also result from adopting a technology without a proper appreciation of long-term deterioration not accounted for in the design. Cable-supported bridges come under this category, as there is inadequate understanding of the deterioration of cables that are subjected to constant exposure to rain, sun and frost; the protective layer on cables by epoxy chemicals and UV-protected sheathings are yet to reach perfection.
In our country, of late, failures during and immediately after construction are becoming commonplace. Although official investigation results are not made public, the evident reasons are that the construction agencies do not always have the requisite experience, and more often the responsibility is transferred to subcontractors with little experience after the job has been secured based on the past capabilities of the original selected contractor.
The list of the apparent faultlines that have made the country a claimant for maximum bridge failures will be long, but let us highlight the important ones.
• The practice of choosing the lowest-cost bidder, despite official claims of disregarding it, leads to awarding contracts at unworkable prices. That is the main motivation for compromising on the quality of materials, deployment of unskilled work teams and adoption of unsafe practices—often with tacit consent of the supervising authority. Adoption of quality-based selection for specialised jobs should be the norm.
• In engineering, procurement and construction contracts, the authorities must check the credential of the design consultants and sub-contractors of the successful bidders as deficiency in capability can lead to failures.
• The agencies deployed, including academic bodies entrusted with proof-checking the design, must be made accountable when failure occurs.
• Every important bridge must have a maintenance manual created with the help of the designers and its implementation must be mandatory, with penalties fixed for non-compliance.
• Budgets need to be allotted for maintenance and staff identified to carry out systematic maintenance. Updating the skills of those deployed for bridge work on a regular basis by agencies like the Institution of Engineers, Consulting Engineers Association and Association of Consulting Civil Engineers under regulatory bodies like the All India Council for Technical Education is essential.
It is unfortunate that in our country, engineering is not yet regulated as a profession. Any graduate from an engineering college is entitled to issue construction documents and approve construction work from day one, unlike other professionals like lawyers, accountants and doctors. An Engineers Bill, in the works for more than 50 years, is yet to become a reality.
Engineers—whether in private organisations like consultancies and contractors, or with public authorities—require upgrading of skills by selected agencies throughout their careers. The ultimate goal is to implement safe practices and guarantee an optimum use of our poor country’s resources.
Amitabha Ghoshal | Former President, Consulting Engineers Association of India; lifetime achievement awardee, ING, International Association for Bridge and Structural Engineering
(Views are personal)