Heat from slum fire melts Durgapur Bridge bearings, experts advise replacement
Times of India | 28 December 2024
12 Kolkata: A leading structural engineer who designs bridges says the fire that scalded the Durgapur Bridge in New Alipore on Saturday may have caused the moisture from the concrete to evaporate and left the bridge's superstructure brittle. Also, he says several rubber bearings that cushion the motorable deck on the piers may have melted in the intense heat caused by the fire and will need to be replaced to prevent deformity in the bridge.
Biswajit Som, who has designed several bridges and is a visiting faculty member in the construction engineering department at Jadavpur University, observed a change in the colour of the concrete when he visually inspected the Durgapur Bridge on Thursday. While concrete is usually ash in colour, Som observed that sections of the concrete exposed to the fire on Saturday turned to a buff colour, indicating that the temperature may have been around 400°C to 500°C.
"I was told there was a lot of wood piled up below the bridge that caught fire. Also, there were sounds of exploding LPG cylinders. Hence, there was enough combustible material for heat to develop. Deterioration of concrete begins at 250-300°C. First, the pore water evaporates. This turns the concrete acidic and brittle. Surface concrete flaking happens. The colour in some sections also changed to buff, indicating a possible alteration in the concrete's structure," said Som, who was the first to warn about the deflection of the superstructure of the right turn flyover at Beleghata nearly a decade ago.
Som also said the intense heat caused by the fire would certainly cause the bearings attached to pedestals on the piers to melt, thereby reducing the articulation of flexibility of the bridge. The bridge's motorable deck atop the girders sits on the bearing. "The bearings that are affected will have to be changed so that when vehicles brake or accelerate on the bridge, deformity and cracks do not appear in the bridge," he said.
While the bridge expert did not notice any deficiency in the structural system of the bridge, Som said the bridge will have to undergo tests, including non-invasive ones like ultrasonic pulse velocity and core cutting, to determine further measures that may need to be taken. "As of now, the bridge is safe. Its longevity may have been affected by the fire, but if the bearings are changed and flaking segments are repaired, there is no immediate threat to the bridge," Som added.
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