This Rapid Response Research (RAPID) award provides funding to carry out an exploratory study focused on modeling of structural damages of selected bridges subjected to long duration, high intensity earthquakes (including both mainshock alone and mainshock plus aftershocks), and strong earthquake followed by tsunami wave force by using actual input data of the March 11, 2011 Japan earthquake off the Pacific coast of Tohoku. The PIs will work with their Japanese research partners who are collecting ground motion and tsunami wave force records as well as other useful perishable information; and will identify instrumented and damaged bridges that are suitable for preliminary investigations on the correlations between structural damages and long duration earthquake load effects as well those due to cascading hazard effects. Based on information available, special emphasis for field data collection in this exploratory study will include some or all of: (1) the structures designed according to comparably strict seismic design codes of Japan, but damaged in the mainshock earthquake most likely due to the characteristic of long duration; (2) the bridges survived in mainshock earthquake with minor damages, but damaged more severely or even collapsed in sequential aftershock earthquakes (including earthquake and/or tsunami introduced soil liquefaction effects); (3) damaged or collapsed bridges near coast in hazard region due to combined actions of the mainshock earthquake, tsunami water wave forces associated with the impact forces from floating debris objects, cars and ships to impact the structures; (4) the bridge failure as a result of degradation or loss of function of structural protection systems implemented on the bridge.
The results of this exploratory research will be presented to an NSF workshop for considering future research opportunities related to multiple extreme hazard (including cascading events) mitigation of civil infrastructure systems. The study will also contribute to continued US-Japan cooperative earthquake engineering research and expanding the scope to multiple extreme event engineering. Additionally, this study will provide an opportunity to train post-doctoral and graduate students to understand the complex nature and challenges to develop multi-hazard resilient structures.
In recent years, catastrophic and destructive natural hazards world-wide have highlighted the need to understand better the dynamic responses of engineered structures due to different extreme hazards and to establish design principles and methodologies based on an integrated, reliability-based approach. Currently, design against the effects of different natural hazards is typically an individualized approach based on different philosophies and criteria, with very limited historical data, especially those involving cascading effects due to one type or different types of hazard events. The March 11, 2011 Japan disaster represents a typical example of cascading events (main shock, tsunami and aftershocks) that may provide a rare opportunity to identify and develop important research agenda. In collaboration with research partners from Japan and Taiwan, and the support of the FHWA, an international cooperative project was established on cascading effects of extreme events through the RAPID grant in the last year. Structural damage to bridges columns due to the cascading earthquake and tsunami actions were the primary focus of this investigation. Japanese collaborators (Dr. Kunimoto Sugiura, Professor and head of Civil Engineering, Kyoto University and Dr. Yasuo Kitane, Associate Professor of Civil Engineering, Nagoya University) provided hazard information and data. The prototype bridge for FEM study selected was the Koizumi Hashi railway bridge. The collaborators provided a report of the bridge information and analysis results. These results suggest that the maximum model column top displacement under the Tohoku earthquake was roughly 15% of the column yield displacement, and the residual displacement at model column top after the earthquake was approximately 0.1% of the column yield displacement. This implies that the Japanese model bridge column remained in elastic range after the earthquake and the damage caused by earthquake was small or negligible. In contrast, the simulated tsunami wave force was capable of destroying the model column alone. The variation of the sinusoidal wave amplitude has little influence on the failure of the model column. The instantaneously invading tsunami wave force controlled the failure. As the wave-force impact time increases, both the maximum model top displacement and maximum base shear decrease. Our partner researcher in Taiwan, Professor Ou and his team, reported that the bridge column, under the long duration protocol (i.e., Tohoku earthquake ground motions) showed a significantly greater stiffness and strength degradation compared to a typical response under the conventional strong earthquake loading protocol. A technical paper will be published in 2013 by the Journal of Structural Engineering of the American Society of Civil Engineers.
