EM Bypass: The urban development department has started replacing the expansion joints of Ambedkar bridge, which runs over a canal near Ruby Hospital.

This is the first time the joints are being replaced since the bridge was inaugurated more than 30 years ago.

Expansion joints are mid-structure separations designed to relieve stress on building material caused by movement triggered by thermal expansion and contraction because of temperature changes.

The bridge has eight expansion joints. The new ones will have gaskets in between to enable transfer of vehicular load from the deck to the pillars.

A Bhopal-based company, which manufactures bridge expansion joints, has been entrusted with the job.

"The joints had long outlived their utility... the change was necessary considering the load the bridge bears," a CMDA engineer said.

The agency is overseeing the work that would take around two months.

The bridge is crucial for vehicular movement on the Bypass, considering the volume of traffic it handles daily during rush hour, a traffic police officer said.

Engineers were trying to figure out the condition of the bridge when engineering consultancy company RITES carried out a safety audit of bridges and flyovers in Calcutta in 2016.

This bridge featured on a list of five that needed immediate repairs. The other bridges are Bankim Setu in Howrah, Sealdah flyover, Baghajatin rail overbridge and Chingrighata flyover.

A laser study of the bridge's structures, including the pier cap and deck slabs, had apparently revealed that the joints needed immediate replacement, a RITES official said. Without the new joints, the heavy traffic load could take a toll on the piers of the bridge through which the load is transferred.

"We have decided to bore around 370mm of the bridge surface and 780mm in width to reach each of the expansion joints," an engineer of the Bhopal-based company said. "We found all the expansion joints are in a very damaged state."

The repair work has posed a challenge for cops controlling rush-hour traffic headed to Science City on the Bypass.

A portion of the Bypass is already covered for the Garia-Airport Metro work and a slight drizzle could make matters worse, a traffic police officer said.

The police have created a channel on the Ruby-bound flank of the bridge for small cars headed for Science City.

More traffic cops are posted during the morning and evening rush hour, the officer said.