Seismic and Tsunami Reliability Analysis of Bridges Subjected To the Anticipated Nankai Trough Earthquake

Abstract eng:
The 2011 Great East Japan earthquake (i.e. Off Pacific Coast of Tohoku Region, Japan earthquake) with the magnitude of 9.0 occurred at 2:46 p.m. (local time) on March 11, 2011. The giant tsunami due to the 2011 Great East Japan earthquake inflicted substantial damage to many coastal communities in Japan, including their critical port facilities, residential and commercial buildings, and infrastructures. Many bridges and embankments of the transportation networks collapsed due to the resulting impulsive pressures of breaking waves and hydrodynamic pressures associated with water velocity. Because tsunami effects have not been taken into consideration in the seismic design and retrofit specifications in Japan, code provisions regarding tsunamis need to be established based on the failure mechanisms observed in the tsunami-induced damage to bridges. A probabilistic framework for seismic design, assessment and computational prediction of structures has been developed over the last two decades. However, a probabilistic estimation of tsunami impact on bridges is still in the early stages of development. In this paper, the procedure for estimating the bridge reliability subjected to tsunami caused by the anticipated Nankai Trough earthquake is presented. The occurrence of a huge earthquake along the Nankai Trough and the subsequent giant tsunami are considered in Japan as possible events. It is expected that the damage and the economic loss resulting from Nankai Trough earthquake and its associated tsunami will be larger than those resulting from the 2011 Great East Japan earthquake. Based on the probabilistic tsunami propagation analysis using the fault parameters of anticipated Nankai Trough earthquake, the probabilistic density function (PDF) of tsunami wave height at the bridge location is estimated. A number of tsunamis with the same height but different periods and velocities are generated to take into consideration the tsunami pressure fluctuations using the CADMUS-SURF software. The PDF of the hydrodynamic forces given the tsunami height can be identified based on Monte Carlo Simulation. Then, the hydrodynamic horizontal forces are applied to bridges. When estimating the bridge reliability, a push-over analysis using hydrodynamic forces given tsunami height is performed to compare the capacity with the demand. In an illustrative example, the effect of the bridge elevation on the tsunami reliability is investigated. In addition, the seismic reliability of the bridge subjected to the anticipated Nankai Trough earthquake is compared with tsunami reliability of the same bridge. The need to consider the tsunami effect in the design of coastal bridges is also discussed.

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