China Earthquake Reconnaissance Report: Performance of Transportation
Structures During the May 12, 2008, M7.9 Wenchuan Earthquake
LESSONS LEARNED FROM THE POSTEARTHQUAKE RECONNAISSANCE
The bridge damage caused by the May 12, 2008, Wenchuan Earthquake reminded the researchers of damage suffered in California during the February 9, 1971, San Fernando Earthquake. In the early 1970s, the highway network in the United States was expanding in ways similar to current the expansion occurring in China. Before the San Fernando earthquake, Caltrans' maximum seismic coefficient was 0.10 g (0.98 m/s2), the same as China's current maximum seismic coefficient. After the San Fernando earthquake, Caltrans greatly increased the seismic hazard used to design California's bridges, and following the 1995 Kobe earthquake, Japan increased the hazard for its bridges. Hopefully, this earthquake will have the same significance for China's bridge engineers and the seismic hazard for areas near known faults will be increased.
In addition, the bridges studied had few seismic details such as long seats, large shear keys, or tightly spaced transverse reinforcement. These details would greatly reduce bridge damage during earthquakes. The various fault traces through the region need to be carefully identified, and bridges should be designed for the seismic hazards at the bridge site, based on a low probability of the hazard being exceeded during the life of the bridge. Such efforts would ensure that China could rely on its highway infrastructure during the earthquakes that frequently strike the country.
Based on the field reconnaissance, the following observations can be made:
- The collapse of most arch and girder bridges was associated with surface rupturing of the faults in the Longmen-Shan thrust zone. A significant portion of roadways and bridges were pushed away or buried by overwhelming landslides in the steep slopes of mountainous terrain.
- The representative damage types in bridge superstructure included unseating of girders, longitudinal and transverse offset of decks, pounding at expansion joints, and shear key failure.
- The bearings of several girder bridges were either crushed or displaced significantly.
- The substructure and foundation of bridges were subjected to shear and flexural cracks, concrete spalling, stirrup rupture, excessive displacement, and loss of stability.
- More damage occurred in simply supported bridges than in continuous spans. Curved bridges either collapsed or suffered more severe damage.
- Evidence of the directivity effects on the bridges near the earthquake epicenter was observed during the earthquake.
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