Buses and minibuses will not ply on the Tallah bridge as no one from the various agencies, which ran a health check on the structure, agreed to allow them on it.
At two separate meetings in Nabanna on Tuesday, engineers from consultancy firm RITES, railways and the PWD said the “frail structure” could not bear the load of any vehicle weighing more than three tonnes and that any additional load could “prove disastrous”.
Chief minister Mamata Banerjee then declared that the ban on the movement of heavy vehicles on the bridge would continue, brushing aside a police suggestion to allow buses and minibuses during the puja.
The ban will remain in force till October 12.
“We are unable to run buses. Engineers from RITES have said it would not be proper to run buses on the bridge,” Mamata said on Tuesday. “We will meet on 12th and take stock of the situation.”
Buses, minibuses and lorries have been banned on the bridge since September 29.
The toll of the resulting detours could be felt on VIP Road in the east and on Bally bridge in the west throughout Monday and Tuesday. The city’s lifeline, Metro, struggled with extra load of passengers.
On Tuesday, the decision to continue with the ban came after two rounds of meetings. The first was presided over by chief secretary Rajiva Sinha and was attended by engineers from RITES, railways, PWD and the Calcutta Metropolitan Development Authority. The other was chaired by the chief minister.
Engineers later said banning heavy vehicles like buses and minibuses was not enough. The 57-year-old bridge is in such a “precarious condition” that even cars should be stopped, they said.
The prestressed cables that hold the girders of the bridge have buckled under pressure and are jutting out of the concrete at multiple places in the underbelly of the bridge, above the railway tracks.
Water has been seeping inside the concrete and the cables have corroded, some of the PWD engineers said.
“We will not be able to allow vehicles above three tonnes to ply on the bridge,” Mamata said after the meeting.
The Tallah bridge stands on 39 girders and each is about 25m long. The cable ducts in eight of the bridge’s spans have corroded. Of these, two are in the middle of the bridge over the tracks. The concrete in these spans have cracked, while in the others it has started to come off.
“The bridge is like a piece of chalk. Even the residual strength of the structure is not enough to bear any load,” a PWD engineer said. “The malleability of the cables is gone. We have to be extremely careful even with the repairs.”
Engineers from RITES have started collecting samples from the bridge. These will be sent to their materials testing centre in Bangalore. An analysis will provide specific indications on the condition of the bridge, an engineer said.
A separate team has started working on a new design with pictures of the existing concrete and prestressed cables.