NEW DELHI: The heart-wrenching bridge collapse tragedy in Gujarat on Sunday evening, which left at least 134 people dead, has triggered an outpouring of grief across the country. It has also raised some important questions, such as the reasons behind the bridge collapse and the load capacity of a suspension bridge.
Here’s all you need to know …
What is a suspension bridge? How does it work?
Saptadip Sarkar, a structural engineer working with Delhi-based Engineers India Limited, explained the functioning of a suspension bridge in an interview to PTI.
The deck of the suspension bridge, which bears the weight of the people walking on it in addition to its own weight, is held in place by the means of vertical suspenders which are made from ductile material and subjected to tension.

These suspenders are then connected to the main cable which is also ductile and subjected to tension.
The main cable, which spans between the points connected by the bridge and is intermediately supported by vertical main column piers, has two functions. The first is to support the vertical suspenders and the second is to maintain the verticality of the piers.
Overall, the weight of the deck, including the traffic of people, is transferred to the ground through the vertical piers, which are in compression, explained Sarkar.
What may have led to the bridge collapse?
The more than a century-old bridge on the Machchhu river in Morbi, located around 300km from the state capital Gandhinagar, collapsed around 6.30pm on Sunday.
Due to the Diwali vacation and being a Sunday, there was a rush of tourists on the bridge, a major tourist attraction.
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Eyewitnesses said there were 400-500 people on the bridge when it snapped, plunging hundrends into the river below. The bridge had a capacity of around 150.
Before the tragedy occurred, some people were also seen jumping on the bridge and pulling its big wires, an eyewitness said, adding that the bridge may have collapsed due to the “huge crowd” on it.
Moreover, the bridge was reopened after a gap of nearly 6 months and was yet to receive the municipality’s “fitness certificate,” a civic official said.
An FIR registered by the Gujarat police blames the “callous approach” of the private firm that was responsible for the renovation of the bridge.
Two managers and two ticket booking clerks of Oreva group that was managing the bridge have been arrested.
At what points is such a type of bridge the most vulnerable?
Quite a few, it turns out.
“To begin with, the main cable, suspenders and the points at which the suspenders connect to the bridge deck are all vulnerable to failure,” Sarkar said.
“In fact, the main cable requires the most attention in terms of regular checks and maintenance over the service period of the bridge. The reason for this being the fatigue load that it is continuously subjected to during its service,” he said.
Fatigue load refers to continuously subjecting a material to some force until it develops a crack.
Referring to the suspension bridge in Morbi, Sarkar said its cables are of a highly ductile material and should have stayed in place much longer, despite the kind of deflection being deliberately created by the people seen in the video (CCTV footage).
“Also, the bridge that failed was recently renovated, so fatigue failure can be safely ruled out as a possible cause,” observed Sarkar.
So then what was it that gave way?
The connection points where the vertical suspenders meet the deck of the bridge are next in line to warrant attention, the structural engineer said.
“It is through these points that the loads of the deck and people are together transferred to the suspenders. The suspenders, in turn, transfer the loads to the main cable,” he elaborated.
“As I understand it, the dynamic loading created by the synchronous and deliberate movements of the people on the bridge created excessive deflection from the point of view of the joint of the suspender to the bridge deck,” he added.
On the transmission of forces to the ground, Sarkar further said that the main cables are in slope and so the tension in the cable at the pier junction has a horizontal and a vertical component.
“While the horizontal component of this force is catered to by the cables anchored at the two ends through tension, the vertical component creates a compression in the pier,” he said.
“Failure occurs when the structural integrity at any of these points described is compromised,” he concluded.
(With inputs from PTI)