What was the Reason Behind the Nangang’ao Bridge Collapse?

By: | March 18th, 2020

Image Source: 玄史生

In October 2019, the Nanfang’ao bridge in eastern Taiwan suffered a catastrophic collapse without a warning or any signs of an impending structural failure. Unfortunately, at the time of the collapse, a truck was crossing it and boats were passing from underneath. As a result, twelve people were injured and another six were killed. Investigations were launched immediately to figure out why the tied-arch bridge that was commissioned only 22 years ago and was built to last for 50 years, fell apart so soon.

The video from the collapse showed that the vertical cable at the center of the bridge snapped, and the rest followed quickly although they should be able to still carry the additional load. Instead, a domino effect occurred, with all cables snapping one after another, followed by the deck dropping, the steel-reinforced concrete base retreating to the sides, and eventually the 320-ton arch falling down.

Engineers believe that the Typhoon Mitag that struck the area just a day before the collapse of the bridge may have weakened its structural elements. In addition to that, in the morning before the collapse, a 3.8 magnitude earthquake occurred. Another problem with the Nangang’ao bridge according to other experts was the lack of proper maintenance which could have helped secure the structure that day. 

Since its opening in 1998, the bridge was inspected only once, in 2016. The report from the Chien Hsin University of Science and Technology engineers who performed the inspection talked about apparent warps and signs of damage in the expansion joints of the bridge. These are meant to link the deck parts while safely absorbing temperature-induced expansion, wind movement, seismic activity, sudden load distribution changes, etc. The Taiwan International Ports Corporation (TIPC) reacted to the report by conducting remediation work on the joints, but these fixing efforts may have been inadequate. 

Bill Toulas

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