Analytical Tools for Resilience of Lifeline Highway Bridges to Tsunami Events

Abstract

Extreme tsunami events in the 21st century, particularly the 2004 Indian Ocean and 2011 Great East Japan events, have put the vulnerability of coastal transportation infrastructure to tsunamis at the front of bridge engineering design and assessment. The 2011 Japan event was particularly eye-opening because its infrastructure was designed to resist very high seismic risk; however, many bridges were washed away or rendered unserviceable due to wave loading. In response to these events, several experimental and analytical research projects have been undertaken to improve the resilience of transportation infrastructure to tsunami attack. Detailed, time consuming analyses are required to capture fluid-structure interaction during tsunami runup and inundation and the results are highly variable due to uncertain boundary conditions and uncertain wave loading scenarios. The intended result of these experiments and analyses is, among other things, to develop loading equations for engineers to quickly assess the impact of tsunami loading on bridges. In this project, simplified analytical models and loading conditions are developed in order to estimate horizontal tsunami loads on bridge superstructures. Comparisons are made with wave flume experiments made available by the Public Works Research Institute (PWRI) in Japan. In addition, the role of connections and/or substructure flexibility is explored and response spectra are developed. The results indicate the simplified approach reasonably predicts peak horizontal forces, but without any clear trends. As expected, the simplified analyses are not able to capture high intensity impact forces owing to pressure shocks. In addition, as the natural period of the bridge system increases, e.g., due to added flexibility, the forces in the connections and/or substructure tend to increase. Again, the simplified analysis ignores the interaction of structure and fluid as flexibility is added to the system. The simple analytical approach offers a framework for developing and defining tsunami loading equations and it can also be applied to equations for uplift and downward force.