December 01, 2011
Surabaya. A clearer picture is emerging of the structural flaws that led to the deadly collapse on Saturday of the Mahakam II Bridge in East Kalimantan’s Kutai Kartanegara district.
Priyo Suprobo, a structural engineer at the Sepuluh Nopember Institute of Technology (ITS) in Surabaya, said on Wednesday that an investigation by a team from the university found that the anchor blocks for the suspension bridge’s pillars had shifted 10 centimeters. He added this was in addition to a 20-centimeter shift that maintenance engineers had discovered in 2006.
Priyo said that as a result of the bridge’s foundation shifting, the pillars themselves were earlier this year found to be warped by 15 centimeters. In turn, that led to the deck of the bridge sagging by 75 centimeters.
What triggered the collapse of the already badly strained bridge, he posited, was the repair work being done to level out the sag.
“They’d managed to jack up one end of the bridge by 15 centimeters, and the other by 10 centimeters,” Priyo said, adding this led to uneven loading conditions along the span of the bridge.
“Coupled with the steep rate at which they were jacking up the deck, it was inevitable that the structure would fail,” he said.
“My hypothesis is that one of the linchpins along the deck sheared because of the uneven loading, which caused shock loading that resulted in the other linchpins also shearing.”
Priyo said the theory was based on the discovery of a sheared linchpin thrown some 50 meters from the bridge. He also said the actual cables had not failed, as was widely reported, and that witnesses reported hearing gunshot-like pops just before the collapse, likely from the linchpins shearing.
He added that the work of leveling out the sag should have involved jacking up several points along the deck, and not just the two ends, to ensure an even raise and uniform loading across the entire structure. “And they should have been raising it slowly, by a centimeter at a time across the whole deck,” he said.
The collapse sent dozens of vehicles plunging into the Mahakam River below. On Wednesday, search-and-rescue officers pulled another body from the water, bringing the official death toll from the incident to 19. However, rescuers say at least eight cars remain buried in the riverbed beneath the ruins of the deck, and could yield even more bodies.
Sutopo Purwo Nugroho, a spokesman for the National Disaster Mitigation Agency (BNPB), said the search for victims was being hampered by the murky waters and torrential rains causing the river to flow much faster.
Officials plan to raise the deck from the river by yoking it to 60 balloons capable of lifting a combined 50 tons. As of Wednesday, the balloons were already set up at the site. Officials plan to use a crane and tugboats to remove the cars now littering the riverbed.
In Jakarta meanwhile, the company responsible for building the bridge, state-owned Hutama Karya, continued to absolve itself of any responsibility for the accident, saying it was only legally liable for the structure for the first 180 days of its life.
(as read in the JG)
wo 30 nov 2011 - 20:24