From “the wrong” materials to lack of inspection to indifference to standard engineering practices, numerous factors doomed Indonesia’s “Golden Gate Bridge,” which collapsed catastrophically in November, the official report shows.
The 10-year-old Mahakam II suspension bridge, also known as the Kutai Kartanegara bridge, collapsed “in less than 20 seconds” Nov. 26 due to an accumulation of problems that included brittle bolts, lack of standards, fatigued materials, and improperly performed maintenance that applied fatal stress to the bridge, investigators announced recently.
Cahyo Sukaryo / Lockerz
|The Kutai Kartanegara was the third suspension bridge built in Indonesia. Engineers had little knowledge of suspension bridge technology, officials said.|
The three-span, 2,329-foot bridge was built from 1995 to 2001 by state-owned corporation Hutama Karya. Maintenance work was underway when the $11.7 million bridge collapsed, hurling dozens of vehicles into the Mahakam river, which is up to 40 yards deep.
More than 20 people died, and dozens more were injured.
Stress, Maintenance Cited
The official report by the Evaluation and Investigation Team, appointed by Indonesia’s Ministry of Public Works, traced the immediate cause to shear failure in too-brittle bolts connecting the steel hanger and the bridge truss near the deck. Officials said the failure occurred when engineers were jacking underneath one side of the bridge deck at mid span.
That final break, however, was the culmination of many factors, said the team, led by Professor Iswandi Imran, of Bandung Institute of Technology (ITB).
Among the contributors, Imran said: structural stress caused by previously undetected problems, exacerbated by maintenance that had been not managed correctly.
‘They Did Not Follow Any Guidelines’
Photographs taken two days before the collapse showed a subsidence in the asphalt surface of the middle span, said the investigation team, which consisted of nine engineers from three universities and a representative from the Ministry of Public Works.
However, before beginning maintenance, the company “failed to make structural checks on the bridge to analyze what impact the jacking procedure would have on the bridge,” reported New Civil Engineer magazine, which reviewed the report.
Robet Eko Mardiantho / Lockerz
|The bridge collapsed in less than 20 seconds on Nov. 26, killing more than 20 people.|
Engineers even noted before maintenance began that the foundation of one tower had shifted by 200mm, but they did not investigate further or explore how this shift would be affected by jacking.
Workers first began jacking on the upstream side of the bridge two days before the collapse, officials said. After raising it by 150mm, they began jacking on the downstream side, triggering the shear failure.
In an interview with NCE, Professor Bambang Budiono, another team member, said the maintenance crew should have jacked up the bridge deck at both sides and closed the bridge to traffic. But, he added, that was only one of a series of errors and irregular practices.
‘Lack of Knowledge’
The larger problem, officials conceded, was the general lack of expertise behind the original construction. Suspension bridge technology is rare in India—the Kutai Kartanegara was only the country’s third bridge of that type—and “even in the U.S., there have been no specific standards yet for hanging or suspension bridges,” said Iswandi.
“They did not follow any guidelines or good engineering principles,” said Budiono. "The main reasons why the bridge collapsed was lack of knowledge [about the forces running through the bridge], an over-simplified approach [to repairing the bridge], and lack of maintenance and repair.”
The bridge was not even inspected for three years after opening, due to lack of funds, alleges the report.
‘The Wrong Choice of Material’
Officials also found that engineers had used poor quality bolts to connect the hangers to the bridge deck and suspension cable.
“They used a very brittle material manufactured locally, which was not covered by the codes,” Budiono said.
The bolts were used of a cast-iron grade that was “brittle and sensitive to impact loading,” NCE reported. Budiono called this “the wrong choice of material.”
Indonesia’s Department for Public Works “has accepted the conclusions of the report and is reviewing its procedures,” NCE said.