After the sudden collapse of the Nanfang'ao Bridge in Taiwan's northeastern county of Yilan today (Oct. 1), the structure's steel cables are at the center of the initial investigation.
As of 1 p.m., the Ministry of the Interior's National Fire Agency said that of the 10 people requiring hospitalization, six were Filipinos, three were Indonesians, and one, the truck driver, was a Taiwanese citizen.
Up to six fishermen are still believed to be trapped beneath the bridge inside their fishing boats. Divers have reportedly heard knocking sounds apparently coming from inside the boats, and Marines have been dispatched to the scene to aid with the rescue.
(CNA photo)
As for the reason why the bridge suddenly imploded, the initial assessment is that its vertical suspension cables, known as "hangers," snapped, causing the bridge's deck to plummet six stories below. After the collapse, badly frayed cables could be seen strewn across the deck of the bridge.
Sung Yu-chi (宋裕祺), dean of the School of Engineering at National Taipei University of Technology, was cited by the Liberty Times as saying that one possible reason is that the bridge is close to the ocean, thus the salt content of the air is very high.
Prolonged exposure to salinity could cause the steel cables to rust, weakening their integrity, according to Sung. Another possibility could be long-term vibrations caused by wind, resulting in fatigue and causing their anchors to loosen, said Sung.
Ultimately, the balanced force could no longer bear the weight of the bridge deck and the cables snapped, postulated Sung. He noted that the bridge had more than 10 cables and that if one broke, the load-bearing capacity should have depended on the rest of the cables.
In this case, however, it appears that the additional load placed on the other cables was in excess of their carrying capacity. Sung said that this led to a domino effect "like setting off a string of firecrackers, one after another."
Sung said this sequence of snapping cables eventually led to the bridge collapsing. When the bridge's deck collapsed, the original balance force between the steel-reinforced concrete at the base and the steel girders was also destroyed, causing the arch to fall.
Yilan had been buffeted by heavy rain and pounding winds from Typhoon Mitag on Monday, and on top of that, a magnitude 3.8 earthquake struck at 1:54 a.m. this morning, registering an intensity level of 4. Sung emphasized that a thorough investigation will be necessary to assess the causes of the bridge's failure in detail.
The bridge, which spanned Nanfang'ao Fishing Port, was completed in 1998 and was the only steel single-arch bridge in Taiwan, the first bifurcated single-arch bridge in Asia, and one of only two such bridges in the world. It was 140 meters in length and 15 meters in width.
Video showing the moment the bridge collapsed
Source：Taiwan News
