Metro pillar crashed due to inadequate support: Report

Published on Jan 23, 2023 12:15 AM IST

Prof J M Chandra Kishen of the civil engineering department at IISc, who conducted the inquiry, submitted the report to the Bangalore Metro Rail Corporation Limited (BMRCL) on Saturday. He inspected the accident site twice and spoke to three junior engineers, an executive engineer, a chief engineer and some workers at the construction site.

Inadequate support structure for the tall reinforcement cage is the main reason behind the collapse of a metro pillar in Bengaluru (ANI)
Inadequate support structure for the tall reinforcement cage is the main reason behind the collapse of a metro pillar in Bengaluru (ANI)
ByPriyanka Rudrappa, Bengaluru

The inadequate support structure for the tall reinforcement cage is the main reason behind the collapse of a metro pillar in Bengaluru, killing a techie and her son earlier this month, an inquiry report by the Indian Institute of Science (IISc) has stated.

Prof J M Chandra Kishen of the civil engineering department at IISc, who conducted the inquiry, submitted the report to the Bangalore Metro Rail Corporation Limited (BMRCL) on Saturday. He inspected the accident site twice and spoke to three junior engineers, an executive engineer, a chief engineer and some workers at the construction site.

The accident occurred on January 10 near HBR Layout in the city when the reinforcement cage of pier number 218 of the KR Puram-Airport metro line collapsed on a motorcycle, killing two people. The BMRCL, facing flak over the incident, roped in IISc to investigate the reason behind the mishap.

Lack of adequate support to the metro reinforcement cage is the primary reason for the mishap, Prof. Kishen said.

“These bars come in a length of 12 metres. Here, the pillar was itself 18 m. So, the reinforcement comes from the foundation. About 2 m gets into the foundation, and you are left with about 10 m above. So, to achieve this 18 m, they had to make a connection, take another rod and join,” the professor stated.

“Whenever it is joined, the joint region forms a weak link. It is a weaker zone. When lapping is done there is a natural tendency for the bars to bend. Ideally, when there is a self-supporting pillar, all the weight goes to the ground. But when it starts to bend, the load has to be carried by some other mechanism. So, the mechanism used here is called ‘guy wires’, where steel wires are tied up in four different directions. This is fine as long as the pillar is vertical. But when it starts to bend, these guy wires become slack it will not carry any load. The load gets carried to the remaining two, which will be under tension. So, because of the extra load, it has snapped,” he added.

He further explained that the workers use scaffolding, on which they stand to tie the reinforcement. Afterwards, they remove the scaffolding to create space for column boxes to pour concrete.

“They were removing the scaffolding from the top, and this reinforcement column started to bend. They should have supported it with a crane. This arrangement was not made. So, it started to bend, and two of the guy wires weakened, and the other two had an extra load on them which led to the breakage. This led to the collapse. So, it’s basically due to inadequate support.”

“Had the guy wires been much stronger, the other two could have held it. But since the diameter was only about 10mm, and because of the excess load due to bending, it got cut and fell,” he added.

Kishen further said that the mishap could have been averted if adequate safety measures were taken during the construction work. However, he ruled out any possibility of poor-quality materials being used and said the responsibility lies with everyone working at the site.

“The workers are not experienced. This is an unusual structure. The reason that it is so high is there is a flyover there, and the metro has to be higher than the flyover. That is why the height is above 18 meters. In this case, they should have taken much more precautions. They should have done concreting in two stages instead of giving a connecting bar. But I think the crane would have been the best mechanism,” he said.

“In my report, I have given details like what could have averted this accident. One, it should have been supported by a crane. The concreting should have been done in two stages, or the guy wire system should have been designed well. There are different things which could have been done,” Kishen said.

In the report submitted to the BMRCL, Prof. Kishan said there are two different sections regarding the safety measures going forward.

“One is during metro work, and the other one in general. Metro work is going on in many cities in India. Tall structures like this are unusual. They should classify them as special structures. Even structures which experience heavy winds or rains should be classified as special structures.”

“Secondly, the special structures should have a complete method statement on how it should be done, every aspect should be defined - supporting system, what material, what diameter rod, every detail should be specified. Third, only experienced workers should be hired for such structures. They should have at least 5-10 years of experience in handling it. They should also have some lessons regarding safety measures in local languages. Workers come from either Tamil Nadu or Bihar, and they don’t understand our local language. In their local language, they should have some special lessons,” he said.

“Also, the junior engineers appointed here should undergo some safety examination. On how to deal with such things, how to deal with natural hazards like rain, other hazardous materials, etc. Some courses on safety in all respects should be given. Some short-term courses should be given every six months or so. Some of the engineers working there are quite smart and good. When they come with some suggestions, they should be awarded for it,” he added.

Meanwhile, BMRCL managing director Anjum Parvez appeared before the police for questioning on Saturday in connection with the collapse. According to police officials, police questioned Parvez at the Bengaluru east deputy commissioner of police’s office for nearly two hours. So far, nine people, including the construction company Nagarjuna Construction Company (NCC), have been named in the FIR filed by the police.

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