Catastrophic earthquake and tsunami events that resulted in significant loss of life and property over the past two decades have raised the global awareness regarding the need to understand the response of communities and their built environment to multi-hazard extreme events. In recognition to this impending threat to the coastal communities, a new chapter \Chapter 6: Tsunami Loads and Effects" has been introduced for the first time in the current edition of ASCE/SEI 7 (ASCE 2016), \Minimum Design Loads and Associated Criteria for Buildings and Other Structures". This new standard, which was adopted by the International Building Code IBC (2018) will soon affect the building design specifically on the west coast of the United States of America. This warrants the probabilistic performance assessment of buildings designed to these new provisions for future earthquake-tsunamis. Moreover, though a large number of studies have investigated the impact of different multi-hazard events (e.g., seismic mainshock-aftershock, hurricane and earthquake hazard, scour and earthquake hazard) on the performance of different structural systems, there is a lack of studies in existing literature that systematically evaluate the effect of accumulated damage due to earthquake ground shaking and its impact on the vulnerability of structures under subsequent tsunami inundation, especially in a probabilistic manner. To address this knowledge gap, a probabilistic methodology to assess the risk of structures in coastal regions prone to cascading earthquake-tsunami hazards is presented in this dissertation. To achieve this goal in a systematic manner and to cover the effect of the whole spectrum of the earthquake-tsunami multi-hazard on the performance of structures, three individual probabilistic performance assessment studies of buildings are performed in this dissertation, respectively, for earthquake only hazard, for tsunami only hazard, and for earthquake-tsunami multi-hazard.
In the first manuscript (Chapter 3), a formulation for incorporating model class uncertainty in probabilistic seismic demand assessment (PSDA) of structures is developed. Model class uncertainty relates to the use of different structural analysis models to predict the physical response of structural systems when subjected to different loading. The application of the formulation is illustrated through the assessment of a modern code-designed reinforced concrete (RC) frame building with unreinforced masonry (URM) infills. Results of this study indicate that incorporating model class uncertainty is important when estimating the uncertainties in the drift demand hazard of structures when subjected to earthquake hazard.
In the second manuscript (Chapter 4), a probabilistic framework is developed for determining physics-based parameterized tsunami fragility functions, accounting for structural member failures. Results of the study indicate that explicit consideration of structural member failures is of paramount importance because the fragility functions based on global failure criteria (which is a common practice in tsunami engineering) tend to overpredict damage state capacities. Among
the several sources of uncertainty considered in this study, breakaway openings in the building are found to be the dominant contributor to the uncertainty in the structural capacity. Moreover, the estimation efficiency of several scalar and vector-valued intensity measures as predictors of structural damage is evaluated.
In the third and final manuscript (Chapter 5), a probabilistic framework is developed to assess the structural risk of structures in coastal regions prone to cascading earthquake-tsunami hazards. Three design variants of a four-story and an eight-story reinforced concrete (RC) special moment resisting frame (SMRF) office buildings are developed based on the earthquake and tsunami provisions per ASCE/SEI 7-16 (ASCE 2016) and ACI 318-14 (ACI 2014): (i) Design-I is based on earthquake only previsions; (ii) Design-II is based on earthquake and tsunami provisions and single column design; and (iii) Design-III is based on earthquake and tsunami provisions and multiple column designs. These design variants are used as application examples to illustrate the structural risk assessment framework developed. Advanced three-dimensional (3D) nonlinear finite element models (FEMs) of the buildings are developed in OpenSees (McKenna et al. 2010) to simulate cascading earthquake-tsunami response of structures through sequential nonlinear response history analyses (NRHA) and nonlinear static pushover (NSP) analyses at multiple seismic and tsunami intensity levels. The multitude of structural response obtained in the three-phase nonlinear response analyses comprising of Earthquake phase, Free vibration phase, and Tsunami phase is used to develop several scalar and vector-valued earthquake-tsunami fragility functions, which are then used with a site-specific earthquake and tsunami hazard analysis (PSTHA) results at three potential building sites within a coastal community to assess geospatial variation of the multi-hazard earthquake-tsunami structural risk of different design variants of the application example buildings.
Funding Statement (additional comments about funding)
Support for this dissertation was provided by: (i) as part of the cooperative agreement 70NANB15H044 between the National Institute of Standards and Technology (NIST) and Colorado State University through a subaward to Oregon State University, and (ii) Kearney Faculty Scholar Grant in Civil and Construction Engineering of Oregon State University.