By Dr. Bharat Thakkar-
(Dr. Bharat Thakkar is an eminent expert on safety of systems and quality control with several papers to his name. He is a Chicago-based retired professor of mechanical engineering who taught for decades at major U.S. universities.)
The report of the Special Investigation Team (SIT) into the October 30, 2022, Morbi bridge disaster, that killed 135 people in the Indian state of Gujarat, makes a sobering reading.
While at one level it vindicates my assessment first reported by indica just one day after the bridge collapse over the Machchhu River, it also highlights the woeful lack of not just timely maintenance of infrastructure in India but an absence of maintenance sensibility.
The SIT’s preliminary findings say that nearly half of the wires making up one cable had corroded over the decades but practically nothing was done to repair those, clearly underscoring apathy towards the maintenance of structures.
The SIT findings quoted by the Indian media say, “It was observed that out of the 49 wires (of that cable), 22 were corroded, which indicates that those wires may have already broken before the incident. The remaining 27 wires recently broke.”
Seven strands constituted each cable with each comprising seven steel wires. Thus 49 wires formed the cable, the SIT report said.
Another finding points out the problem of welding of old and new suspenders which created a significant structural weakening. The welding of the old and new suspenders was obviously problematic but it was carried out as part of repairs.
I had pointed out in the immediate aftermath of the collapse that with its Factor of Safety (FOS) being way lower than it should have been the Morbi bridge was in a sense a disaster waiting to happen.
The FOS of the Morbi bridge was set at 5 or 6 which for the 600 people it carried at the time of the collapse was too low for any kind of bridges. In the US and elsewhere globally, the Factor of Safety should be between 30 to 50 with a lifespan of at least 50 years. In my reckoning the Morbi bridge’s FOS was 10, which was alarmingly low.
There is something called graceful failure or graceful degradation in design engineering as part of which as design fails it does so without its core functionality being lost that results in as little collateral damage as possible.
Here are a couple of examples of what graceful failure is. As a rule a car tire, for instance, does not immediately go flat when air leaks out of it because of a puncture. That leak is part of graceful failure to minimize casualty. Older car tires had tubes in them which, when punctured, would cause a major accident on highways.
Another example of graceful failure is a short circuit caused by a blown fuse to protect homes or equipment from catching big fires.
FOS is essentially a load-carrying capacity of a structure beyond what the structure supports. It is about how much stronger a structure should than what is required. The Morbi bridge was designed and built during the British colonial times. It must have been designed keeping in mind the standards of those days. Over the decades since its maintenance was not properly enforced.
I am not qualified to go into what leads to such negligence, whether corrupt practices were involved or there was any political motivation to throw open the bridge. My concern as an engineer is only to point out that the FOS of 5 or 6 is unacceptable for any bridge.
At the heart of the rationale behind FOS is that any structure be built stronger than what is deemed necessary in order that it withstands any emergency of the kind the Morbi bridge experienced in terms of overload.
No one will ever build for the FOS with 5 or 6. The bridge was built for 150 people maximum for daily use. It collapsed when 500 to 600 people were on it.
The designers must consider dynamic effects. This Morbi bridge experienced a dynamic effect due to people walking and playing with it because it was a hanging bridge. It is not people’s fault for playing with the structure. Anyone would like to test it out of curiosity because it was newly opened to the public. However, even a scratch in wires can cause stress concentration up to 100 times.
The broader question after the preliminary SIT report is how to create a nationwide culture that minimizes negligence to its lowest even while creating a steadfast maintenance culture. As India progresses and builds large public infrastructure, it cannot afford to continue with its traditional apathy in this area. It does not help to find a few scapegoats at lower levels after a tragedy like Morbi.
What is urgently needed is consciously create a university discipline of maintenance. There ought to be both federal and state programs which focus on maintenance as an ongoing exercise which is outside political point-scoring. Otherwise, India will continue to witness ever larger infrastructural catastrophes.
