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Tsunamis are low-probability high-consequence events, usually caused by an earthquake in the ocean and can result in high casualty rates and billions of dollars in damage. Tsunamis can be divided into two main categories: near-field and far-field tsunamis, based on the location of their origin with respect to the site of interest. To perform risk assessment of communities subjected to tsunamis, the current approach would be to use empirical data from historical events, making the data site specific. Recently, researchers have developed approaches to estimate the risk of structures subjected to far-field earthquake generated tsunamis using a simulated tsunami force on a structure numerically. However, for near-field tsunamis, ground motions caused by the earthquake will reach the structure earlier than the tsunami, damaging the structure, which can substantially impair its structural performance in the following tsunami. The multi-hazard case of tsunami following earthquake is discussed herein and a physics-based approach to estimate the risk of structures subjected to them is presented. An illustrative example is presented to elaborate the methodology for a steel building. Successive nonlinear analyses are used to develop fragility functions based on joint earthquake-tsunami intensity measures (spectral acceleration-flow depth-flow velocity). These functions are used in combination with hazard analysis of a specific location to obtain loss estimates. Three different approaches were used for this process and the results showed that the use of the joint three intensity-measure fragilities is essential for the accuracy when estimating damage or structural loss and neglecting their interaction results in substantial errors. [ABSTRACT FROM AUTHOR]

The damage caused by tsunamis to coastal communities is often not only the result of the flowing water itself, but also of transported debris. Although there have been efforts to characterize forces from single-debris impacts, a more general scenario of multiple-debris impacts has not been studied experimentally. To address this need, experimental studies were performed, considering the effect of debris orientation and the number of debris field components on peak impact and damming forces on coastal structures. These forces are evaluated both qualitatively and quantitatively to provide insight into the nature of these impacts. For a few selected cases, a number of trials were conducted and an initial statistical study of the debris field collision phenomena performed. Observed forces and results are presented in terms of normalized quantities using analytical equations commonly used to calculate impact or drag forces. The lessons from this work provide an initial data set that can be used to guide further experimental and numerical studies on debris-laden tsunami flows. [ABSTRACT FROM AUTHOR]

A large-scale physical model was constructed in the Large Wave Flume of Hinsdale Wave Research Laboratory (HWRL) at Oregon State University to develop a dataset of measured pressures and forces acting on an elevated, coastal structure, representing a two-story building with an elevated foundation, due to tsunami-like wave impacts. Two wave cases, unbroken and broken long waves, were investigated by changing the still water level, resulting in cases without and with an air gap between the still water level and the bottom of the test specimen, while maintaining the base of the test specimen at the same elevation. Horizontal and vertical pressures and forces were measured on the faces of the test specimen and between the test specimen and its supports, respectively. Three pressure gauge layouts were used to measure the distribution of pressures around the test specimen for each wave case. Regression surfaces of the pressure gauge measurements illustrate the shape of the pressure distributions on the test specimen. The maximum vertical forces were measured during the unbroken-wave case. However, the streamwise, horizontal force was maximized when the structure was subjected to the broken wave. The findings and data presented here are intended for use by numerical modelers for future validation analyses that can be used toward enabling tsunami-resistant designs of coastal elevated building structures. [ABSTRACT FROM AUTHOR]

Large earthquakes and tsunamis can damage or lead to the collapse of lifeline bridges, resulting in human and socioeconomic losses as well as prolonged recovery times. Although many simulation models are available for the individual effects of earthquake and tsunami hazards on bridges, there are limited modeling approaches for predicting damage from sequential earthquake and tsunami hazards. A bridge modeling approach, which includes soil-foundation-structure interaction effects, is developed within the finite-element framework OpenSees to quantify sequential earthquake and tsunami-induced damage. Multihazard interaction diagrams that relate earthquake and tsunami intensity measures to bridge system damage show that the residual effects of earthquake loading on the bridge system reduce resistance to subsequent tsunami loading. [ABSTRACT FROM AUTHOR]

Annual exceedance probabilities of the maximum tsunami inundation depth, hMax, and momentum flux, MMax, conditional on a full-rupture event of the Cascadia Subduction Zone (CSZ) were used to estimate the probability of building damage using a fragility analysis at Seaside, Oregon. Tax lot data, Google Street View, and field reconnaissance surveys were used to classify the buildings in Seaside and to correlate building typologies with existing fragility curves according to the construction material, number of stories, and building seismic design level based on the date of construction. A fragility analysis was used to estimate the damage probability of buildings for 500-, 1000-, and 2500-year exceedance probabilities conditioned on a full-rupture CSZ event. Finally, the sensitivity of building damage was estimated for both the aleatory and epistemic uncertainties involved in the process of damage estimation. Probable damage estimates from the fragility curves based on hMax and on MMax both generally show higher damage probability for structures that are wooden and closer to the shoreline than those that are reinforced concrete (RC) and further landward of the shoreline. However, a relatively high and somewhat unrealistic damage probability was found at the river and creek region from the fragility curve analysis using hMax. Within 500 m from the shoreline, wood structure damage shows significant sensitivity to the aleatory uncertainty of the tsunami generation from the CSZ event. On the other hand, RC structure damage showed equal sensitivity to the aleatory uncertainty of the tsunami generation as well as the epistemic uncertainties due to the numerical modeling of the tsunami inundation (friction), the building classification (material and date of construction), and the type of fragility curves (depth or momentum flux type curves). Further from the shoreline, the wood structures showed similar aleatory and epistemic uncertainties, qualitatively similar to the RC structure sensitivity closer to the shoreline. [ABSTRACT FROM AUTHOR]

Tsunamis are rare destructive phenomena caused by the sudden displacement of a large amount of water in the ocean and can result in enormous losses to coastal communities. The resilience of coastal communities to tsunamis can be improved through the use of risk-informed decision making tools. Performance-Based Engineering (PBE) approaches have been developed for different natural hazards including earthquake, fire, hurricane, and wind to perform probabilistic risk assessment for structures. In this study, a probabilistic Performance-Based Tsunami Engineering (PBTE) framework based on the total probability theorem is proposed for the risk assessment of structures subject to tsunamis. The proposed framework can be disaggregated into the different basic analysis phases of hazard analysis, foundation and structure characterization, interaction analysis, structural analysis, damage analysis, and loss analysis. An application example consisting of the risk assessment of a three-story steel moment frame structure was performed using the proposed framework. The probability of exceedance of the total replacement cost including structural, nonstructural, and content losses were computed. [ABSTRACT FROM AUTHOR]