TAIPEI (CNA) — An investigation into the collapse of Nanfang’ao Bridge in Yilan County last year found corrosion in several of the bridge’s steel cables, while the impact of other factors, including road construction projects and overloading, is still being studied, the Taiwan Transportation Safety Board (TTSB) said Tuesday.
Three fishing boats were crushed when the 140-meter suspension bridge in Taiwan’s northeastern Su’ao Township collapsed on Oct. 1 last year, resulting in the deaths of six crew members.
Nine other sailors, one tanker truck driver and three rescue workers were also injured in the incident.
At a press conference Tuesday, the TTSB announced the initial results of its investigation into the facts of the case, but did not conclusively state what caused the collapse.
A draft of a comprehensive report on the subject is scheduled to be completed in August.
According to the TTSB report, surveillance camera footage showed abnormal movement in one of the bridge’s arches before the collapse, which dislodged the casings on five of the bridge’s 13 suspenders.
The western end of the bridge then dropped by eight degrees, causing the deck of the bridge to fracture, the report said.
TTSB investigators found deficiencies in several of the bridge’s suspenders, including rust damage and steel strands which had “escaped” from their anchors on the bridge’s arches and deck.
However, because of the bridge’s design features, safety inspectors would not have been able to see the rust damage with the naked eye, and failed to establish additional inspection standards taking this into account, said Wang Hsing-chung (王興中), a senior TTSB investigator.
Yilan County Government inspected the bridge a total of seven times from 2001-2016. On April 28, 2016, responsibility for the bridge was transferred to the Maritime and Port Bureau, and no further inspections were conducted, the report said.
Larger questions surrounding the bridge’s collapse, including the possibility of improper construction and the extent of the rust damage, require further investigation, the TTSB said.
In the next phase of its investigation, the safety board said it will also analyze road construction and overloading on the bridge as possible contributing factors.
Between 2005-2019, the report noted, the bridge underwent 60 road construction projects, which nearly doubled the thickness of some portions of the road to 17.5 centimeters.
Meanwhile, from October 2016-September 2019, Su’ao port authorities transported concrete tetrapods across the bridge four times for use in coastal seawall construction.
Yilan County Government likewise used the bridge while transporting gravel for construction projects from September 2018-January 2019, the TTSB said.
In response to the report’s publication, the state-owned Taiwan International Ports Corporation, which was responsible for the bridge’s maintenance, said Tuesday it is conducting an internal review and will submit a list of punishment recommendations to the Ministry of Transportation and Communications (MOTC) within seven days.
In terms of local reaction, Su’ao Township Mayor Lee Ming-che (李明哲) urged the government to fulfill its promise to rebuild the bridge within three years, saying the collapse has severely impacted local businesses and caused traffic congestion.
Huang Chih-liang (黃志良), commissioner of Yilan County Transportation Department, said that in light of the impact, the government should consider expanding the project to include the revitalization of the Su’ao business district and port area.
The MOTC’s Directorate General of Highways said in a press release Tuesday that the three-year reconstruction timeline is on schedule, with a new bridge expected to be completed by Oct. 1, 2022.