The 460-feet long bridge, which opened in 1998, was built to replace a lower bridge that prevented large fishing vessels from passing underneath.

The collapse of the Nanfangao Bridge in Yilan County, Taiwan, on Tuesday morning might have been due to rusted anchoring points, the Taipei Technology College of Engineering said.

Video footage showed that the vertical cable at the center of the bridge’s steel arch was the first to snap, noted the engineering school’s dean Sung Yu-chi.

However, the bridge is suspended by 10 or more steel cables and theoretically, the other cables should have been capable of evenly distributing the weight the broken cable had borne, he said.

However, it looks like the snapping of the vertical cable caused a domino effect. The bridge was continuously exposed to salty air, which would have rusted the cables, reducing the amount of weight the span could support, a report indicated.

Long-term exposure to wind could have also loosened the anchor points, making them unable to sustain the bridge’s weight.

Two overseas Filipino workers died while five were injured. Another OFW is still missing as of posting time.

Two Indonesians were also reported killed.

The collapse of the arch was caused by the dissolution of the force equilibrium between the bridge and the arch, although an investigation is needed to confirm the cause.

Bridges are designed with safety factors and mechanisms taken into account, and routine inspections and precise equipment calibrations are required to maintain normal operations.

Wang Chung-yu, a professor of civil engineering at National Central University, also said the cables could have rusted.

Strong winds brought by Typhoon “Mitag” would have caused the cables to sway constantly, which could have forced the cables to the point of snapping, Wang said.

An site inspection to determine which anchor point broke first is required. Authorities should make precise records of the site to compare with the records of the bridge’s last inspection, which could help clarify what happened.

The bridge was an older design, created when the idea of protection from natural erosion was not yet popular, and it was possible that maintenance checks could have overlooked such possibilities, he added.

However, he believes that Mitag also contributed to the collapse.

Taiwan International Ports Corp (TIPC) said it has conducted routine annual maintenance since the bridge was completed 21 years ago and, per regulations, each cable cord was inspected every four years.

The last inspection was conducted in 2016, when the Yilan County Government awarded the commission to Chien Hsin University of Technology and Science, TIPC said.

The university’s report suggested reinforcing the bridge body with concrete, removing rust from the cable beams, repairing the downspouts and replacing the expansion joints of the angle iron, it said.

It budgeted NT$10 million ($322,113) between 2017 and 2018 to cover the repairs and reinforcements noted in the report. (Taipei Times)