Despite the complexity of real earthquake motions, the incident wavefield excitation for soil-structure interaction (SSI) analysis is conventionally derived from one-dimensional site response analysis (1D SRA), resulting in idealized, decoupled vertically incident shear and compressional waves for the horizontal and vertical components of the wavefield, respectively. Recent studies have revealed potentially significant deviation of the 1D free-field predictions from the actual three-dimensional (3D) site response and obtained physical insights into the mechanistic deficiencies of this simplified approach. Particularly, when applied to vertical motion estimation, 1D SRA can lead to consistent overprediction due to the refraction of inclined S waves in the actual wavefield that is not correctly accounted for in the idealized vertical P wave propagation model. However, in addition to the free-field site response, seismic demands on structures and non-structural components are also influenced by the dynamic characteristics of the structure and SSI effects. The extent to which the utilization of vertically propagating waves influences the structural system response is currently not well understood. With the recent realization of high-performance broadband physics-based 3D ground motion simulations, this study evaluates the impact of incident wavefield modeling on SSI analysis of representative building structures based on two essential ingredients: (1) realistic spatially dense simulated ground motions in shallow sedimentary basins as the reference incident motions for the local SSI model and (2) high-fidelity direct modeling of the soil-structure system that fully honors the complexity of the incident seismic waves. Numerical models for a suite of archetypal two-dimensional (2D) multi-story building frames were developed to study their seismic response under the following incident wavefield modeling conditions: (1) SSI models with reference incident waves from the 3D earthquake simulation, (2) SSI models with idealized vertically incident waves based on 1D SRA, and (3) conventional fixed-base models with base translational motions from 1D SRA. The impact of these modeling choices on various structural and non-structural demands is investigated and contrasted. The results show that, for the horizontal direction, the free-field linear and nonlinear site amplification and subsequent dynamic filtering of the base motions within the structure can be reasonably captured by the assumed vertically propagating shear waves. This leads to generally fair agreements for structural demands controlled by horizontal motions, including peak inter-story drifts and yielding of structural components. In contrast, vertical seismic demands on structures are overpredicted in most cases when using the 1D wavefields and can result in exacerbated structural damage. Special attention should be given to the potentially severe vertical floor accelerations predicted by the 1D approach due to the combined effects of fictitious free-field site amplification and significant vertical dynamic amplification along the building height. This can pose unrealistic challenges to seismic certification of acceleration-sensitive secondary equipment necessary for structural and operational functionality and containment barrier design of critical infrastructures. It is also demonstrated that vertical SSI effects can be more significant than those in the horizontal direction due to the large vertical structural stiffness and should be considered in vertical floor acceleration assessments, especially for massive high-rise buildings.

We propose a test procedure to quantify the response of dry sand to cyclic compressional loading under constrained conditions. The test procedure is designed to represent the response of sand layers to upward propagating P-waves during an earthquake event. Such P-waves are prominent within the vertical component of earthquake ground-motions, which is often ignored or simplified in common practice of seismic hazard analysis, despite its potential damaging effects. In the proposed method, the lateral deformation is restrained within a triaxial device, through variations of the cell pressure, thus maintaining pure compression while allowing moderate to large axial strains. Both dry and saturated samples are tested, and the compressive stiffness is computed from the full stress-strain loops. We show that as long as drained conditions are maintained and volume changes are allowed - the response of a saturated sample to slow cyclic loading is representative of the response of dry sand to seismic loading, despite the differences in saturation and in strain rates. Finally, we compare the proposed method to cyclic loading within a rigid cell and discuss the differences and limitations that the new proposed method overcomes.

The objective of this study is to explore the seismic fragility of reinforced concrete bridges, specifically in response to the vertical components of ground motions, utilizing fragility surfaces. The examination of bridge responses involves the application of optimally selected intensity measures through three-dimensional nonlinear time-history analyses, encompassing uncertainties in both superstructure materials and soil-structure interaction effects. In this investigation, an extended Probabilistic Seismic Demand Model (e-PSDM) is employed, leveraging fragility surfaces to concurrently consider vertical and horizontal excitations. The results obtained from this approach are compared with traditional fragility curves. This study emphasizes Pile-cap displacement and drift ratio as pivotal engineering damage parameters, acknowledging their sensitivity to the influences of both soil-structure interaction effects and vertical ground motion. The fragility surfaces derived from the study reveal a correlation between increased vertical spectral accelerations and elevated probabilities of surpassing both slight damage and collapse limit states. These observations underscore the critical significance and practical utility of fragility surfaces in the context of performance-based seismic assessment and design for reinforced concrete bridges. The findings from this research contribute valuable insights into the nuanced behaviour of reinforced concrete bridges under seismic conditions, emphasizing the relevance of incorporating vertical components in fragility assessments for a more comprehensive understanding of structural vulnerability.

Owing to global warming, the rise in sea temperature is causing degradation of submarine permafrost, which has an impact on the seismic responses of submarine strata. Based on the revised dynamics of nearly saturated frozen porous media, a simplified model of the vertical seismic responses of submarine permafrost is established considering the degradation of its upper layer, and an analytical solution is obtained using the Laplace transform method. The governing equation of a single-degree-of-freedom system on the seafloor is further proposed, and the vertical response spectrum is obtained using the numerical inverse transformation method. The numerical results show that the vertical ground motions of the seafloor agree well with those of saturated and nearly saturated soil layers with a free surface on land and under deep-water conditions. Parametric studies show that saturation strongly affects the vertical ground motions of the seafloor, and this effect is closely related to the water depth ratio. In addition, the structural stratum parameters, including the active layer thickness ratio, permafrost thickness, and temperature, have significant effects on the vertical ground motions of the seafloor and the vertical response spectrum of the submarine lumped parameter system. Therefore, attention should be paid to the impact of submarine permafrost degradation on the vertical seismic responses of oil and gas exploitation systems in polar oceans. (c) 2022 Elsevier Ltd. All rights reserved.