Calcutta: Aurobindo Setu, the 43-year-old flyover between Ultadanga and Gouribari in north Calcutta, has been diagnosed with acute stress and diminished load-bearing capacity after ploughing on with the same set of bearings for almost three times their lifespan.

"The bearings of a flyover or bridge should be replaced every 10 to 15 years, which means those under the Aurobindo Setu have been living on borrowed time," said a member of the consultancy team that had inspected the structure.

Bearings offer a resting surface between the deck of a flyover and its piers, enabling transfer of load from top to bottom. This function is crucial to reducing structural stress.

When a curved section of the VIP Road-Bypass flyover collapsed in 2013 under the impact of an accident, engineers had attributed it partly to the failure of the bearing assembly.

Aurobindo Setu's deck rests on 40 to 45 bearings, almost all of which have exceeded the stipulated replacement date, an official in the urban development department said.

The Calcutta Improvement Trust used to maintain the flyover before the baton passed to the Calcutta Metropolitan Development Authority (CMDA).

According to civil engineers, the reinforced concrete structure of a bridge or flyover can last decades without a hitch if maintenance is regular. In Calcutta, concrete structures with a high load factor like Aurobindo Setu's show signs of stress in 25 to 27 years because of little or no maintenance.

RITES, the engineering consultancy contracted to evaluate the structural stability of Aurobindo Setu, has not only recommended a change of bearings but also an overhaul of the flyover's surface. "The concrete is showing signs of ageing and some of the pedestals have started crumbling. The structure is currently very weak and vulnerable," a representative of the consultancy said.

Several more flyovers in the city are said to be in a similar condition.

The urban development department had engaged RITES to monitor the health of flyovers and bridges across the city after a deck slab of the incomplete Vivekananda Road flyover collapsed in March 2016, killing 26 people.

Aurobindo Setu's condition was among the red flags in the report, but nobody seemed worried till some cracks on the sidewalls grabbed urban development minister Firhad Hakim's attention last November. Heavy vehicles were temporarily diverted through Ultadanga Road and Canal East Road to reduce the flyover's load. The repairs were cosmetic, though.

"We are now looking at an overhaul that will require anything between two-and-a-half months to three months," a CMDA official said. "We might need to close the flyover to traffic in phases."

Officials in the urban development department said bids would be invited soon to select a reputable infrastructure company to replace the bearings of Aurobindo Setu and reinforce its surface.

The cost of repair has been estimated at Rs 3-4 crore.