World's tallest bridge gets 1,100 C fireproof armor

As Guizhou province prepares to unveil what will be the world's tallest bridge, its main suspension cables are receiving a fire-resistant and anticorrosion treatment, which is said to be able to withstand temperatures of up to 1,100 C for a full hour without so much as a singe.

Measuring 2,378 meters, the main cables of the Huajiang Grand Canyon Bridge are vital components designed to bear the bridge's weight. Once installed, however, these steel giants are nearly impossible to replace or repair without undertaking a full-scale rebuild. That vulnerability makes fire a particular concern.

"In a fire, cables can be seriously damaged," explained Wu Huijuan who is responsible for the fire-treatment project. "High temperatures can change the cable's properties and structure, risking collapse."

Wrapped in protective wire and multiple protective layers, the cables are engineered to resist rust and extreme heat. A single main cable consists of 217 compacted strand bundles, which in turn contain 91 high-strength, 5.7 mm steel wires.

Since April 1, nearly 100 workers have labored around the clock on the bridge's catwalks to complete this monumental task.

"Fire-resistance standards take into account the worst-case scenario, such as an oil tanker catching fire on the bridge deck," Wu said. "A burning fuel truck can raise temperatures to around 1,000 C. That's why we set our design threshold at 1,100 C."

"Even if a tanker burns for an hour, the cables remain unscathed," she added. "Our firefighting systems and protocols ensure that rescue crews can always arrive within that window."

Technician Tian Hongrui of the Guizhou Bridge Construction Group detailed the process of how they first wrapped the main cable in tightly spun wire using a specialized machine, creating a sealed barrier against moisture, rain and corrosion, and then up to five layers of fire-resistant material were applied, depending on the location of the cable.

According to the work-zone chief Li Ping'an, despite 11 fireproofing steps and five layers of protective material, the total added thickness is under one centimeter, leaving cable performance unaffected.

Recent high-profile bridge fires have spurred this emphasis on cable protection. Last year, a van caught fire on the cross-sea Shenzhen-Zhongshan Link near the main cable, with official reports confirming no damage to its cables.

"Bridge fires are rare, so fireproofing hasn't always been a priority," Wu said, revealing that Guangzhou's Huangpu Bridge in Guangdong province was the first in China to install fire-resistant protection on its stay cables.

The Huajiang Grand Canyon Bridge is expected to open in the second half of this year.

Contact the writers at liuboqian@chinadaily.com.cn