Professors Dipankar Chakravorty and Arup Guha Niyogi of Jadavpur University inspect the collapsed part of the VIP Road flyover on Thursday. Picture by Sanjoy Ghosh
The collapsed deck slab of the VIP Road flyover has suffered “severe internal damage” and can hardly be used again, said a team of Jadavpur University experts that visited the crash site on Thursday.
The team led by professors Arup Guha Niyogi and Dipankar Chakravorty inspected the fallen structure, part of which is still in the Kestopur canal, and conducted a series of tests before concluding that it could not be used again.
“The metal’s elasticity has been damaged beyond repair,” said one of the experts.
The 128ft-long structure, which collapsed early on March 3, has around 260-tonnes of “mild steel”. If the metal has suffered irreparable damage and cannot be used again, bridging the flyover gap would be costlier than expected as it will involve using new metal.
“There is a stress limit for any metal after considering the amount of strain it can bear. The moment the limit is crossed, the metal tends to acquire the character of plastic and loses its elasticity,” explained Guha Niyogi of JU’s civil engineering department. “The ripped-off portion has become a piece of junk.... There are tell-tale signs of the intrinsic crystalline alignment of the metal having undergone a change under the impact of crash.”
“A close look at some of the nuts on the collapsed structure reveal that there has been a searing because of the fall,” said Chakravorty, also of JU’s civil engineering department.
“The thrust was so immense that it seems to have brought about a change in the internal configuration of the metal. This is our observation.”
The probe team conducted three types of tests on the metal. First, it examined the micro-structure after taking photographs of the metal’s surface using a microscope. Then sound waves were sent through the structure to ascertain the rebound time (if there is a crack in the structure, the rebound time will be more than what has been specified) and finally, a hardness test of the metal was conducted.
What now? “The structure will be split into parts and removed. This is necessary to restore the flow of the canal,” said a team member.
The JU experts regretted that they were yet to get necessary details of the structure from the CMDA, the implementing agency of the project. Guha Niyogi and Chakravorty both said they had taken up the matter with the agency.