Jadavpur University estimates that lifting the collapsed portion of the VIP Road flyover from the Kestopur canal would be equivalent to picking up 167 full-grown Indian elephants at one go.
The jumbo task, the first important step in the process of rebuilding the flank that came crashing down along with a marble-laden truck early last Sunday, has prompted the JU duo probing the collapse to suggest the feasible alternative of breaking up the 500-tonne concrete and steel slab (in picture, by Amit Datta) into pieces.
“Only the railways and the port authority have cranes that can lift loads of 500 tonne… Transporting these cranes to the site is going to be a challenge. Besides, there will also be the problem of parking such cranes in that area,” professor Arup Guha Niyogi told Metro on Wednesday.
An adult Indian elephant weighs around three tonne, which means 167 of them would together weigh as much as the slab lying in the canal.
Apart from investigating the reasons for the collapse, the JU team will be looking at ways to remove the slab and suggest how the flyover can be rebuilt.
The team, formed at the state government’s request, is expected to submit its report on how to remove the slab from the canal in a week.
Officials of the Calcutta Metropolitan Development Authority (CMDA) admitted they couldn’t figure out how to remove the 500-tonne slab from the canal. A CMDA engineer on the verge of retirement said he couldn’t recall another such Herculean task in his 30-year career.
Guha Niyogi and colleague Dipankar Chakravorty say a more feasible option than trying to lift the slab in one piece is to shear it of concrete, which they estimate would reduce the weight by half. “People can crush the concrete portion using jackhammers,” Guha Niyogi said.
Chakravorty said the idea of shedding the concrete first was “common sense”.
“It will then be easier to lift the remaining structure. However, nothing has been decided. We are considering all aspects.”
Even after the concrete is broken into pieces, the composite steel box girder would weigh around 250 tonne, approximately the weight of 83 Indian elephants. “Lifting this weight too is an extremely difficult proposition as none of the state government agencies possesses a crane sturdy enough to do the job,” a CMDA engineer said.
The engineer, who has been associated with flyover construction for several years, said the available cranes could lift load up to 70 tonne.
Parminder Singh of Singh Crane Services in north Calcutta said the maximum capacity of those on hire in the city was 110 tonne. “There are cranes in Haldia that can lift 250 tonne but transporting them to Calcutta is easier said than done,” said Singh.
During construction, cranes lifted the smaller portions of the frame so that they could be hinged together. After erecting the pier caps, the steel girders were fitted with bearings on a concrete pedestal, atop which the deck was laid.
Guha Niyogi suggests unhinging the joints before breaking the girder into fragments that can be lifted separately. Another option is to use a gas cutter and break up the girder. Since most of the collapsed structure is above water, unhinging or using gas cutters won’t be much of a hassle, according to the JU team.