Joshua Macabuag

Estimating Tsunami-Induced Building Damage through Fragility Functions: Critical Review and Research Needs

Tsunami damage, fragility and vulnerability functions are statistical models which provide an estimate of expected damage or losses due to tsunami. They allow for quantification of risk, and so are a vital component of catastrophe models used for human and financial loss estimation, and for land-use and emergency planning. This paper collates and reviews the currently available tsunami fragility functions in order to highlight the current limitations, outline significant advances in this field, make recommendations for model derivation, and propose key areas for further research. Existing functions are first presented, and then key issues are identified in the current literature for each of the model components: building damage data (the response variable of the statistical model), tsunami intensity data (the explanatory variable), and the statistical model which links the two. Finally, recommendations are made regarding areas for future research and current best practices in deriving tsunami fragility functions (section 6). The information presented in this paper may be used to assess the quality of current estimations (both based on the quality of the data, and the quality of the models and methods adopted), and to adopt best practice when developing new fragility functions.

Building Damage Assessment and Implications for Future Tsunami Fragility Estimations

Abstract This chapter summarizes perspectives on building damage assessment and their implication for future fragility estimations using damage data from recent tsunamis, including the 2011 event in Japan. Causes of building damage, i.e., a combination of hydrostatic and hydrodynamic forces, debris impact and foundation effects, are explained. Damage scales used in previous studies are introduced, including the scale used for the 2011 tsunami, and possible future damage to be considered in the construction of tsunami evacuation shelters is discussed. Fragility estimations methods are presented, including the PTVA/BTV methods and fragility functions. Fragility functions provide superior, quantitative information compared to other tools, and are thus discussed in depth, from statistical considerations (differences between each model, including the traditional liner models and the new generalized linear models), to the factors affecting the structural performance of buildings. These factors include the type of construction material and the buildings height, function and surroundings. Future improvements and applications of fragility functions considering model diagnostics, additional tsunami parameters, additional building characteristics, and damage scale improvements are also considered. In this sense, research on fragility functions that cover both the preceding earthquake induced damage and the subsequent damage by tsunami represents a challenging future research topic.

Tsunami design procedures for engineered buildings: a critical review

Tsunamis have the potential to cause enormous loss of life and socio-economic impacts on coastal communities. Central to tsunami risk mitigation is the protection of critical infrastructure and evacuation-designated buildings, which are often necessarily located within tsunami inundation zones. As such, these must be designed to withstand and remain fully or partially operational after a tsunami. Guidance documents for tsunami design of buildings exist in the USA and Japan, including the recent release of the US ASCE 7 chapter 6 on tsunami loads and effects. This paper outlines the key engineering principles of tsunami design of buildings, summarises and compares how these principles are addressed by US and Japanese standards, and outlines considerations not yet covered.

Advances in the Assessment of Buildings Subjected to Earthquakes and Tsunami

Currently, 8 out of the 10 most populous megacities in the world are vulnerable to severe earthquake damage, while 6 out of 10 are at risk of being severely affected by tsunami. To mitigate ground shaking and tsunami risks for coastal communities, reliable tools for assessing the effects of these hazards on coastal structures are needed. Methods for assessing the seismic performance of buildings and infrastructure are well established, allowing for seismic risk assessments to be performed with some degree of confidence. In the case of tsunami, structural assessment methodologies are much less developed. This stems partly from a general lack of understanding of tsunami inundation processes and flow interaction with the built environment. This chapter brings together novel numerical and experimental work being carried out at UCL EPICentre and highlights advances made in defining tsunami loads for use in structural analysis, and in the assessment of buildings for tsunami loads. The results of this work, however, demonstrate a conflict in the design targets for seismic versus tsunami-resistant structures, which raise questions on how to provide appropriate building resilience in coastal areas subjected to both these hazards. The Chapter therefore concludes by summarizing studies carried out to assess building response under successive earthquakes and tsunami that are starting to address this question.

Sensitivity Analysis of Different Capacity Spectrum Approaches to Assumptions in the Modeling, Capacity and Demand Representations

Several capacity spectrum assessment methods exist for determination of structural performance of building models subjected to earthquake loading. The repetition of such analysis for earthquakes of increasing intensity will result in the derivation of analytical fragility functions. A comparison of three capacity spectrum assessment approaches (N2, SPO2IDA and FRACAS) has been carried out, highlighting the advantages and limitations of the approaches. Two experimental case studies have been chosen to evaluate the IM-EDP (Sa-Sd, ISDmax%) estimates obtained from the three different capacity spectrum procedures, as well as from non-linear time-history analyses (NLTHA). It is found that all three approaches perform well in estimating the response of a simple steel frame, but that FRACAS provides the best estimate of the response of an irregular reinforced concrete frame. It is concluded that further comparisons of the capacity spectrum approaches with large-scale experiments on structures are required to draw more general conclusions.