Inadequate supporting structures led to fall of Bengaluru metro pillar: IISc report
The under-construction pillar near Nagavara collapsed on January 10, killing a woman and her son who were travelling on a two-wheeler.
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Ideally, for such tall structures, the guy-wires should have a diameter of at least 20 mm. Here the diameter was only 10 mm, Kishen said. (PTI/File) Professor Chandra Kishen of the Bengaluru IISc, tasked with investigating the January 10 collapse of an under-construction metro pillar near Nagavara, has found that the inadequate supporting structures for its reinforcement cage led to the accident that claimed two lives.
Kishen submitted a 27-page report by email to the Bengaluru Metro Rail Corporation Limited on Saturday, after collecting, reviewing and analysing data related to the pillar’s 18m reinforcement cage. The report also details measures to be taken to prevent such accidents.
Speaking to The Indian Express, Kishen explained that the 18m structure was not a single-piece structure but a combination of reinforcement rods measuring 12 m each. “Since the rod is only 12m, the BMRCL lapped another reinforcement rod to it to achieve the height of 18 m. The lapping region becomes a weak link. When they join the rods for such a tall structure, the joint is bound to bend by the weight,” he explained.
“They have supported the reinforcement rods with the guy-wires. But guy-wires have a tendency to bend. So when such a tall structure bends, the self weight will pull it further and the load does not go to the ground but gets shifted. Then the weight comes on the guy-wires. Eventually the guy-wires will become slack and not be able to take the load, causing them to snap and ultimately the reinforcement cage collapses,” he added.
Ideally, for such tall structures, the guy-wires should have a diameter of at least 20 mm. Here the diameter was only 10 mm, Kishen said.
The professor also explained that the guy-wires must not be allowed to bend and that before adding the column rods, the reinforcement rods should be temporarily supported with a mobile crane, so that they do not collapse.
As for the solutions and recommendations, Kishen said that a detailed methodology on the supporting structures should be in place. He also recommended casting the reinforcement cage in two stages and concretising the structure before another rod is lapped.
“To manage special structures, there should be trained personnel. Workers should also be given lessons on safety, especially in the local language. Also, new engineers should attend safety courses and examinations,” he said.
Meanwhile, IIT Hyderabad, which has been engaged by police in their preliminary investigation, has also said that the “improper design of the supporting structures” may have led to the collapse of the reinforcement cage.
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