The jury is still out on mode of rehabilitating flyover

A technical team from the Vigilance and Anti Corruption Bureau inspecting the damaged Palarivattom flyover in Kochi on Tuesday.

A technical team from the Vigilance and Anti Corruption Bureau inspecting the damaged Palarivattom flyover in Kochi on Tuesday.  

IIT Madras team to submit comprehensive report this month

Over two months since the Palarivattom flyover was closed for repair works, dilemma continues on whether it can be rehabilitated using techniques like carbon-fibre wrapping or whether the entire lot of girders have to be pulled down and rebuilt.

Metroman E. Sreedharan had submitted a report to the State government a week ago suggesting rehabilitation works worth ₹18.71 crore to ensure structural safety of the flyover which was commissioned in 2016. “This would involve replacement of all the girders and bearings since cracks up to 0.3 mm have been reported in almost all the girders within this short time span,” said structural engineering experts who have been keeping tab of developments regarding the flyover.

This process would take upto 10 months, as pointed out in Mr. Sreedharan’s report. Another option would be to strengthen the existing structure using techniques like carbon-fibre wrapping, a process which would take three months.

Since the piles (foundation) and piers (pillars) of the structure are intact, the wrapping process would mainly involve the damaged girders.

A comprehensive report on the mode to be adopted to rehabilitate the structure is awaited later this month, when structural-engineering experts of IIT Madras submit it to the government.

Anil Joseph, a city-based structural engineer, said that it has to be ascertained how the IIT and technical experts from the Vigilance and Anti-Corruption Bureau collected concrete samples from the flyover.

“It is a very challenging process and only samples measuring 67 mm could be taken in the place of 75 mm samples due to intermittent steel bars. It appears that samples from a few spans show weaker concrete, while those from most others show that concrete was used as per norms.”

In this circumstance, a load test (in which a much heavier load than the design load is carried over the structure) must be done as per Indian Roads Congress (IRC) norms, to assess deflection and other parameters of the flyover.

Rehabilitation using carbon-fibre wrapping can be done if the flyover emerges successful after the test. Else, the option of replacing the girders might have to be considered, Mr. Joseph said.

Whatever be the case, the design and execution of deck-continuity method (which was hitherto not tried out in Kerala) to construct the flyover has not been done in a professional manner. Problems like deflection beyond the permissible limit must be rectified to ensure safety of commuters and pedestrians, he said.

Another expert in the field, Prof George Mathew of Cusat, a doctorate holder in structural engineering, spoke of how utmost caution must be exercised even when rehabilitating the flyover.

“In carbon-fibre wrapping, care must be taken so that there is proper bonding between the protective sheet that is wrapped around the girders and the surface of girders.

“The epoxy-like material that is used for bonding the two surfaces must be of excellent quality.”

The quality of workmanship must never be compromised when executing the work, failing which the structure would be prone to further deterioration. The cracks on girders and undue deflection are the main concerns about the structure, Prof. Mathew said.

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Printable version | Feb 23, 2020 7:29:35 AM | https://www.thehindu.com/news/cities/Kochi/the-jury-is-still-out-on-mode-of-rehabilitating-flyover/article28336505.ece

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