While girder bridges may cost less to construct, they tend to need more maintenance and incur higher repair fees. In the event of a collapse, huge compensation has to be paid to those who are affected, while the reconstruction of such bridges costs even more, Yao said.
Apart from bridge design, equally important is environmental protection. Yao, who led a team last week to investigate why a large number of bridges in Chiayi County failed, said the main reason behind the collapse of so many bridges before water levels reached officially set alarm levels lay in the fact that the huge amounts of silt, soil, rocks and driftwood washed into the rivers by typhoon-triggered flash floods and landslides enormously increased the impact of the river flows.
“Silt, soil and driftwood from the mountains are testimony to illegal logging, excessive land development and residential construction on mountain slopes,” Yao said. “If rampant overuse of slopeland and riverside agriculture cannot be halted, bridges will be doomed to continue collapsing, no matter how advanced the technology used to build them.”
To solve the root of the problem, Yao said, some areas should no longer be inhabited.
“Land planning and river management should be addressed to resolve bridge safety problems once and for all,” he said.
While Taiwan has one of the world’s highest densities of bridges, it is sadly lacking in manpower for bridge maintenance and management. Before the deadly earthquake of Sept. 21, 1999, the DGH had a bridge supervisory system that was in charge of 4,564 provincial highway bridges.
After the 921 earthquake, Yao said, the Ministry of Transportation and Communications commissioned the National Central University’s bridge research center to conduct a nationwide survey, which found Taiwan had 20,000-plus bridges, but only a limited number of staff to oversee them. For instance, Chiayi County had 993 bridges, but only one full-time engineering official and several contract workers to manage them.
Meanwhile, bridge experts said that the government should conduct a nationwide bridge examination and single out dangerous bridges.
Chen Ming-huang, president of the National Federation of Construction Industry Associations, said many bridges, particularly those in rural townships or villages, were situated on narrow rivers and were dilapidated.
“Environmental and climatic changes might have undermined their structures. Even though they remain standing after the typhoon, they might nonetheless require maintenance,” Chen said.
Also See: Constructing ‘intelligent bridges’ an option: group
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