Many of the advances in performance-based seismic design (PBSD) originated in Seattle, where a community of structural and geotechnical engineers specialize in tall building design and code development. This paper presents the history and practice of the geotechnical engineer’s role in performance-based seismic design of tall buildings in the greater Seattle area, including the characterization of the seismic hazard in the Puget Sound region and development of ground motions that are used in nonlinear dynamic structural models. The standard of practice for geotechnical seismic design continues to evolve with changes to codes and increased understanding of the seismic hazard and geologic conditions in the Puget Sound region. This paper provides an overview of the conditions under which PBSD is used and the evolution of design standards (from FEMA 356 through ASCE 7-16) used in practice. A technical overview is presented regarding the seismic setting in the Seattle area (including near-source effects of the Seattle Fault and basin amplification effects). Discussion of some of the technical aspects of PBSD, such as the development of site-specific spectra (uniform hazard, uniform risk, and conditional mean spectra), and the selection, scaling, and use of ground motion records for nonlinear response history analysis is included as well.

The accumulation of liquefaction-induced volumetric strains leads to ground settlement. Volumetric strain is estimated using empirical models based on laboratory data, and settlement is computed as the integration of volumetric strain with depth in the liquefied materials and calibrated using field data. Currently, the assessment of liquefaction-induced free-field ground settlement (S_v) generally follows a deterministic or a pseudo-probabilistic approach. In both cases, the assessment of the ground motion intensity measure (IM) is decoupled from the computation of S_v. For example, a hazard curve for the IM is developed through a probabilistic seismic hazard assessment that accounts for all relevant earthquake scenarios in a pseudo-probabilistic approach. A design hazard level for the IM is defined, and S_v is computed based on this design IM. A key assumption in this approach is that the hazard level of the IM is consistent with the hazard level for S_v. However, this assumption is not always valid. A performance-based approach for the assessment of S_v is developed in which the hazard evaluation for the IM is explicitly incorporated in the assessment of S_v by combining the hazard curve for the IM with the probability of exceeding different S_v levels. Hence, the sources of variability contributing to the IM are incorporated in the assessment of S_v. The variability in the inputs to the empirical model for S_v can also be included through a logic-tree approach. As a result, the hazard curve for S_v is developed, which directly links different hazard levels with their corresponding values of ground settlement. Conventional approaches used currently do not always produce values of settlement that are compatible with design hazard levels.

Variable or unknown ground conditions are a major contributor to uncertainty in a geotechnical project and arise as a result of the geomorphological processes that shaped the land. The planning of a ground investigation programme can be thought of as a sampling optimisation problem, seeking to balance precision, accuracy, and costs through selection of an investigation density that achieves a degree of residual uncertainty that is sufficient for the intended purpose. This study draws on detailed observations of the patterns of liquefaction-induced land damage mapped across Christchurch City during the 2010 – 2011 Canterbury Earthquakes, and uses the variability in the observed damage as a proxy for variability in the underlying shallow ground conditions. The correlation between investigation density and residual uncertainty in ground conditions is examined using a Monte Carlo approach, varying size of the study area and the investigation spacing. The hypothesis is that as the total area investigated increases, the spacing between investigations can be increased while still achieving the same degree of residual uncertainty in the ground conditions. The results of this study were used to set the minimum investigation density recommendations for land use planning and subdivision in the New Zealand guidance on geotechnical investigations for earthquake engineering.

The classical problem of earthquake induced sliding of rigid bodies is revisited. Apart from the intrinsic lack of uniqueness in the inversion of sliding response to back-calculate the earthquake excitation, a key obstacle in understanding the mechanics of frictional sliding lies in the need to integrate twice the acceleration time history for displacements – a non-trivial problem which, for actual earthquake recordings, is treated almost exclusively by numerical means. This study presents, for the first time, an exact graphical method for determining the sliding response of a rigid block under seismic excitation that overcomes the need for numerical integration and greatly simplifies the analysis. To this end, it is demonstrated that the problem of frictional sliding can be treated as a problem of finding the shear force and bending moment diagrams in a cantilever beam under transverse loading ("beam analog"). The method is extended to treat the inverse problem of obtaining the seismic motion from the recorded peak sliding response. The role of acceleration, velocity and duration of seismic motion are highlighted, and the lack of uniqueness in the solution is discussed. Application examples are provided.

The paper presents a feasibility study on the Capacity Spectrum Method (CSM) (widely used in structural design), applied on Soil-Structure Interaction (SSI) systems. A bridge pier founded on two distinct Reinforced Concrete (RC) pile groups, is employed as an illustrative example. Finite Element (FE) models are used to perform (monotonic and cyclic) static pushover and nonlinear time-history analyses. The CSM method predicts the seismic performance of the studied system by comparing the capacity to the demand diagram. The first corresponds to the monotonic pushover analysis, while the latter is the combined acceleration-displacement elastic spectrum of each input motion. The intersection of the two curves represents the expected performance point. Iterations, required to account for increased damping of the SSI system, are possible using the results of the cyclic pushover analyses. The predictions of the CSM method are comparatively assessed to the results of nonlinear FE time-history analysis and are shown to be in good agreement. Thus, the application of the CSM for the design of bridges on pile groups is considered promising. Allowing for parametric investigations, such an approach can contribute towards performance-based design, as an alternative to the computationally demanding time-history analyses.

In recent years the applications of metamaterials for building protection have garnered considerable attention. In this study a new device for the seismic protection of new and existing structures based on resonant metamaterials has been presented. This device, called Periodic Foundation Piles, applies to deformable soil deposits in order to filter shear waves in a specific frequency range and consists of an array of vertical periodic and relatively small resonators, suitably tuned to one or more natural frequencies of the soil deposit. The performance of this system in reducing the amplitude of a seismic motion has been shown by using a non-linear one-dimensional shear beam model subjected to real acceleration records at the base. A soil deposit with increasing shear wave velocity profile has been considered; the nonlinear behavior of the soil has been modeled through the Iwan model which has been calibrated using a normalized secant shear modulus curve. Numerical results are shown in terms of peak ground acceleration, horizontal displacements and shear strain profiles, as well as in terms of Fourier amplitude and response spectra. The results of the analysis indicate that periodic foundation piles may provide efficient seismic protection for both new and existing structures.

In this paper, a case study involving the seismic evaluation of an existing anchored sheet-pile quay wall in the Ravenna port area is presented. A well-known geotechnical setting, in addition to the data of an extensive field and laboratory investigation carried out lately in the area for upgrading works, allowed to perform both simplified and detailed seismic analysis. The site-specific earthquake ground motions are defined through 1D equivalent-linear site response analysis in which the outcropping bedrock motion time histories are selected based on regional probabilistic seismic hazard studies. A simplified seismic analysis, based on the pseudo-static method outlined in the new generation of Eurocode 8 (draft version), has been carried out applying a seismic coefficient defined accounting for spatial variation of the ground motion along the wall height. On the other hand, the seismic performance of the quay wall is evaluated through a 2D FEM non-linear dynamic analysis. The results of a detailed dynamic analyses and the pseudo-static analysis were compared pointing out the relevance of defining an appropriate seismic coefficient for simplified seismic analysis.

Seismic design employs the seismic-intensity method. In this study, the ultimate vertical bearing capacity of building foundations on sandy soils subjected to inclined and moment loads is evaluated using the rigid plastic finite element method. The study takes into account the size effect of the foundation to assess its stability during earthquakes. The ultimate bearing capacity is simulated by gradually increasing vertical and horizontal loads simultaneously, aiming to ascertain the impact of inclined load. The analysis findings suggest that a high-order function can effectively describe the foundation size effect. Discrepancies between the analysis results and the AIJ evaluation formula are discussed. The findings of the study revealed that the reduction formula, which utilizes the ultimate bearing surface by Nova, aligns well with the obtained analysis results while considering the influence of eccentricity and inclined loads.