Experts blame poor design, quality for flyover collapse

The collapse of an under-construction flyover here on Wednesday which left at least 24 people dead and nearly 100 injured was poorly planned and executed, said experts.

While forensic scientists have identified the faulty portion, top engineers blamed bad planning and poor quality material for the tragedy. Though much of the rubble was cleared by Friday morning, with personnel from the army and National Disaster Response Force (NDRF) working throughout the night, two subsided flanks of the structure could not be cleared apprehending further damage. According to forensic scientists, who visited the site on Friday, a girder that joined the two flanks of the flyover was what caused the collapse. “There was too much pressure on the pillars. Any decent engineer would have noticed it,” said a miffed forensic expert.

Expert engineers from the army, leading defence contractor Garden Reach Shipbuilders & Engineers (GRSE) and public-private joint venture engineering firm, Rail Vikas Nigam Limited, inspected the site throughout the day.

Top engineers from private sector infrastructure majors, Larsen & Toubro, Gammon and Afcon, involved with several important infrastructure projects in Kolkata, lent a hand. An engineer questioned the need for having two pillars on either side of the columns to bear the flyover’s total weight.

He explained that the flyover stood on two pillars that look like a “T” divided in half, bearing the load of the flyover’s two flanks. “This is the only such flyover in Kolkata. The need to design it like this is questionable,” said a GRSE engineer.

He pointed out that while the flyover’s girders were divided in segments and installed on top of the pillars, instead of using box stiffeners, plate stiffeners were used.

“The contractor must have used plate stiffeners to save on cost because box stiffeners are expensive,” he said.

While a plate stiffener is a girder, fabricated by welding plates together to create the desired shape, a box stiffener is more resistant to twisting even under extreme pressure, the GRSE engineer explained.

“Despite having put bolts, the girders were also welded. The project engineers must have known the structure was weak and needed the precaution,” he said. He added that the thickness of the steel sheets used to make the girders was also compromised. “Instead of the more appropriate 25 mm thick sheets, 12-14 mm steel sheets were used,” he added.