How did a bridge in Mumbai collapse on Thursday, killing six people and injuring 31, just six months after a structural audit report had pronounced it to be in “good condition”?

This was one of the many questions that emerged in Mumbai on Friday, the day the collapse of a big section of a 35-foot pedestrian bridge on Dadabhai Naoroji Road outside Chhatrapati Shivaji Terminus, one of Mumbai’s busiest railway stations. This was the sixth railway bridge mishap in the city in two years.

The foot-over-bridge at CST had undergone a structural audit in 2016 and the report on this exercise was published by Mumbai’s municipal corporation in September 2018. Soon after the tragedy on Thursday, Maharashtra Chief Minister Devendra Fadnavis ordered a “high-level inquiry” into the accident. A preliminary report by the Brihanmumbai Municipal Corporation pinned the blame on an “irresponsible structural audit”. The Mumbai police also filed a First Information Report booking the Brihanmumbai Municipal Corporation for causing death by negligence.

On Friday, as details about the structural audit surfaced, structural engineers that Scroll.in spoke to pointed out several gaps and flaws in the narrative that has emerged so far. This raises concerns about the ability of Mumbai’s civic authorities to provide safe infrastructure to the city, they said.

‘Minor repairs’?

The foot-over-bridge, constructed in 1990, is located a stone’s throw away from the headquarters of the Brihanmumbai Municipal Corporation.

In 2016, after a bridge collapse on the Mumbai-Goa highway, the municipal corporation contracted several structural engineering firms to conduct safety audits of 314 bridges, skywalks and subways in Mumbai. The municipality submitted the final audit reports in September 2018, after two other major bridge accidents took their toll on the city: in September 2017, a stampede on a narrow railway foot-over-bridge at Elphinstone Road station killed 23 people and in July 2018, one woman was killed and four injured when a portion of a railway bridge in Andheri collapsed onto the tracks.

The audit of the bridge outside Chhatrapati Shivaji Terminus, or CST as it is popularly known, was conducted by DD Desai Associate Engineering Consultants. The head of the firm, Neeraj Desai, told the Mumbai Mirror that the report had marked the bridge as being “in need of minor repairs”. He also claimed that weeks before the audit was conducted, the munipality had beautified the bridge with new tiles and fresh paint. As a result, he was only able to inspect the “accessible portions” of the bridge. “There is a chance that because of the tiles and the paint, the corrosion in the structure was not detected,” Desai told the newspaper.

Kiran Dighavkar, the assistant municipal commissioner of the A ward, under whose jurisdiction the bridge falls, told Scroll.in that he was the one who oversaw the beautification of the structure. “I had got the cosmetic repairs done in 2016 – I had the tiles changed and got new paint put on the bridge,” said Dighavkar. “After the audit, the bridge was classified as C2B [under the BMC’s classification of dangerous buildings], which means it needed minor repairs.”

Those repairs have not yet been carried out, but Dighavkar claimed that a bridge or building need not be closed to the public in order for minor repairs to be undertaken.

However, when television news channel Republic TV on Friday accessed a document it claimed was the structural audit report, it made no mention of “minor repairs” anywhere. In fact, the report claims that the bridge is in “good condition”. Why, then, have civic officials and the auditor himself been claiming that the bridge needed “minor repairs”?

Scroll.in was unable to contact Neeraj Desai or the municipal corporation’s chief engineer for bridges despite several attempts.

Inadequate audit

Structural engineer Mithilesh Dalvi highlighted a number of problems with claims made by the Dighavkar and the auditor. One problem is the confusion over the civic body’s classification of dangerous structures into categories C1 (for dilapidated buildings that need immediate evacuation), C2A or C2B, and C3.

The authorities are claiming that the bridge falls under the C2B category “but also say that the bridge needed minor repairs”, said Dalvi, the executive director of engineering firm Tech-N-Eco. However, he noted that the C2B category is for structures that need major repairs. “C3 is for minor repairs,” he said. (C2A, meanwhile is a category for structures that need to be partially demolished).

“If the bridge was indeed in the C2B category, then it must have needed major repairs, and then it should not have been open for public use,” he said. “So there are some contradictory statements being made.”

Another problem is the thoroughness of the structural audit of the CST bridge. According to structural engineer Alpa Sheth, the first stage of a structural audit typically involves a detailed visual assessment of a structure to evaluate whether it has gone through any damage or degradation.

“In the case of steel structures, corrosion is the biggest culprit for degradation, and prima facie that seems to be one of the possible reasons behind this bridge collapse,” said Sheth, a managing partner at the firm VMS Consulting Engineers in Mumbai. “Going by the photos [of the collapse], the degradation seems to be have been quite extensive, and to me it’s a wonder that the bridge did not collapse earlier. I am puzzled why such corrosion was not picked up in a detailed structural audit.”

While Neeraj Desai claims that the municipality’s new tiles and paint made it difficult to see the extent of corrosion, Sheth believes that structural audits are often not performed as exhaustively and thoroughly as they are meant to be. An auditor should have a comprehensive checklist that ensures that nothing is missed out. “The auditor has all the powers to ask for some of the tiles or a precast slab or two to be removed to check the condition of connections below,” she said.

According to Dalvi, if an auditor finds their inspection of a structure obstructed by elements of beautification, like paint or tiles, they should also specifically mention this hindrance in their audit report. “But the BMC [Brihanmumbai Municipal Corporation] or the Railways should also not carry out cosmetic work on structures before they are audited and repaired,” said Dalvi. “If you are living in a building with damages, are you going to paint it first or repair it?”

Also read:

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CST tragedy: Anger in Mumbai as city witnesses sixth railway bridge accident in two years

‘Spirit of Mumbai has collapsed’: Rage and frustration on social media after CST bridge mishap