Optimal implementation of frequency domain impedances in time domain simulations of building structures on embedded foundations

Soil-Structure Interaction (SSI) have been studied the last decades, and proper analysis for the linear elastic case in frequency domain has been established successfully. However, SSI is rarely considered in the seismic design of building structures. Regardless of its importance as a significant source of flexibility and energy dissipation, buildings are analyzed using a rigid base assumption, and the design is based on a response spectrum analysis, for which not only the soil, but also time are totally ignored. In a first attempt to improve and to incentivize time domain analyzes compatible with standard finite element packages for the engineering community, the state-of-practice introduces two major simplifications to transform the frequency domain analysis into a time domain analysis: (a) it assumes the frequency at which the impedance value should be read is the flexible-base frequency, and (b) it also assumes that the foundation input motion preserves the phase of the free field motion. Upon these simplifications, the following questions may arise: How does NIST recommendations perform in overall against a full finite element model? Are the embedment effects for shallow foundation not important so that the phase angle can be neglected? What is the best dimensionless frequency to estimate the soil impedance? Is it possible to make a better estimation of the dimensionless frequency to increase the NIST accuracy? In this study, we attempt to address these questions by using an inverse problem formulation

Ensemble Kalman Methods With Constraints

Ensemble Kalman methods constitute an increasingly important tool in both state and parameter estimation problems. Their popularity stems from the derivative-free nature of the methodology which may be readily applied when computer code is available for the underlying state-space dynamics (for state estimation) or for the parameter-to-observable map (for parameter estimation). There are many applications in which it is desirable to enforce prior information in the form of equality or inequality constraints on the state or parameter. This paper establishes a general framework for doing so, describing a widely applicable methodology, a theory which justifies the methodology, and a set of numerical experiments exemplifying it

Fragility Based Seismic Performance Assessment of Buried Structures

Fragility-based seismic performance assessment and design procedures are being refined and adopted for many civil structures. With recent advances in computational capabilities as well as broad improvements in ground motion characterization and inelastic modeling of structural and geotechnical systems, large-scale direct models for underground structures—e.g., tunnels, water reservoirs, etc.—can now be devised with relative ease and deployed in engineering practice. In this study, we present a fragility-based seismic performance assessment of a large buried water reservoir. We use existing documents/codes to define the performance criteria and develop fragility functions through a probabilistic seismic demand analysis (PSDA) procedure. The analyses incorporate inelastic/nonlinear behavior of soils and structural components, and account for uncertainties in the expected ground motions. The seismic performance assessment methodology presented herein can be applied to other large underground reservoirs