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New bridge-building method used

A road built with a new and more environmentally friendly technology jointly developed by National Applied Research Laboratories and the University of Buffalo hugs a mountainside in the US. PHOTO: COURTESY OF NATIONAL APPLIED RESEARCH LABORATORIES

In regions with low seismicity such as Europe and parts of the US, many bridge superstructures borrow ideas from Lego blocks in that segments are pre-cast and assembled at the final construction site.

Now the technique has been modified and could be applied in earthquake-prone Taiwan, the National Center for Research on Earthquake Engineering announced yesterday.

The new technique will be used for the first time in Taichung, where two bridges will be built to connect the Formosa Freeway (Freeway No. 3) with Taichung City's expressway system, with construction beginning as early as May.

"Building pre-cast segmental bridges offers several advantages," said project leader Chang Kuo-chun (張國鎮), professor and chairman of the National Taiwan University Department of Civil Engineering.

Because pre-cast bridge segments are fabricated in factories, they are solid in quality when compared with bridges that are constructed on-site, Chang said, adding that while traditional bridges average a 50-year lifespan, the pre-cast segmental bridges may last up to 75 years.

"The bridges have accelerated construction time and better work environments for workers because less construction occurs in high-rise settings. Also, there is less traffic disruption because of the shorter construction time," he said.

But one of the biggest advantages of pre-cast segmental bridges is that because they are only assembled on-site, less land is required for construction, so the bridges create a reduced environmental impact, he said.

As a result, pre-cast segmental bridges abroad are mostly built in environmentally sensitive regions, such as the famous Linn Cove viaduct in North Carolina in the US, where the bridge blocks were suspended in a top-down style and the bridge hugs the belt of the cove loosely to preserve the original beauty of the scenic area, he said.

The key to making pre-cast segment bridges work in Taiwan lies in padding them with complementary seismic isolation systems, or threading energy dissipating (ED) reinforcement steel rods through the blocks after assembly, Chang said.

"We have made three types of bridge columns: one with no ED rods, one with moderate ED rods and one with high ED rods," he said.

A computerized earthquake test revealed that the third type with high ED rods demonstrated the best seismicity resistance, Chang said, adding that whether the second type or third type better suits the needs of Taiwan required more research and experimentation.

"However, the first type of columns [no ED rod] can be built in the least amount of time, which is good for places where construction time needs to be tightened, like when bridges are built in urban areas with heavy traffic," Chang said, adding that such columns would need to be fitted with seismic isolation systems.

The new bridges to connect the Formosa Freeway and the Taichung City expressway system will use exactly that, said deputy director of the Taiwan Area National Expressway Engineering Bureau design division Chen Kuo-long (陳國隆), adding that the combination would be the first in the world.

Asked whether the Suhua Freeway construction team might consider the newest technique, Chen said the change would "require a whole new drafting of the construction plan."

"However, it is true that this technique is good for environmentally sensitive regions," he said.
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