Experts question repeated metro rail bearing pad failures despite viaduct's weight

 
After the fatal metro rail accident, questions are mounting over how a bearing pad -- which supports viaducts weighing hundreds of tonnes -- could fall off again, just 13 months after a similar incident.

Even the Road Transport Advisor Fouzul Kabir Khan, raised the question, noting that last year's accident caused no casualties but exposed design vulnerabilities that remain unresolved.

Experts explain that bridge or flyover bearing pads are not mechanical bearings as used in vehicles, but thick layers of neoprene or natural rubber designed to absorb vibration between a pier and viaduct joints. Some pads are reinforced with internal steel plates and can weigh over 100kg, reports bdnews24.com.

Engineer Moniruzzaman, who has long worked on bridge condition surveys, said: "During construction, a concrete seat is built on the pier to hold the rubber pad in place. Sometimes it's also glued -- it depends on the design. But since the viaduct's weight presses down with immense force, it rarely comes loose."

He added that such incidents are sporadic: "I've seen a few cases where bearing pads shifted due to tilting or floods -- only in very old structures."
So how could this happen twice within a year on a brand-new metro line?

Moniruzzaman suspects a possible gap formed beneath the viaduct, reducing pressure on the pad. "That gap could be one reason," he said. On Sunday afternoon, a bearing pad fell near Khamarbari, killing 36-year-old Abul Kalam.

BUET civil engineering Prof Shamsul believes the fatality points to a construction flaw left uncorrected. "It's unsafe to resume operations without a full safety audit. This has created fear -- people will now look up whenever a train passes overhead," he said.

"Dhaka residents already live with too many anxieties. We must not add another one hanging above their heads."

Hoque said rubber pads are never installed alone: "They're fixed within a frame to prevent shifting -- this is century-old technology that has evolved greatly. Yet ours falls off in a crowded city." He said Japan's consultant firm took about Tk 11 billion for advisory work.

"If the Japanese consultants failed to ensure proper installation, they share responsibility," he said.

Hoque warned that if such failures occur during the system's "honeymoon period", future risks could be greater.

"Metro rail is a mature science, perfected over a hundred years. There's no excuse for compromise -- this death demands accountability."
Metro rail authorities say recommendations from last year's probe were implemented.

"All pillars were inspected by experts," said DMTCL Managing Director Faruque Ahmed.

Standing beside him at the scene, Advisor Fouzul pointed to the structure and asked: "Then how did it happen again?"

Faruque said the earlier incident had occurred within the defect liability period, and the contractor had been allowed to fix it.

"They assured us it was corrected," he said.

Fouzul confirmed that the same Japanese contractors were responsible and that a five-strong probe committee has now been formed to investigate Sunday's fatal collapse.