Soil Dynamics and Earthquake Engineering最新文献

Under strong earthquakes, subway station structures situated in potentially liquefiable soils may experience complex seismic response scheme when the structure base slab is embedded in non-liquefiable soils while the sidewalls and top slab are buried in liquefiable soils (hereinafter referred to as a “liquefiable sites”). This paper investigates the dynamic seismic responses of multi-story underground structures in liquefiable sites employing an advanced three-dimensional nonlinear finite element model. The results indicate that the seismic response of underground structures is primarily determined by the soil displacement and the soil-structure stiffness ratio. In addition, the seismic response of the soil-underground structure system is strongly influenced by the distinct characteristics of the input ground motion. Seismic input motions rich in low-frequency components are more likely to cause saturated sand layers to liquefy and are likely to trigger more pronounced flow deformations, leading to severe damage to underground structures. Generally, liquefied soils are prone to significant horizontal displacements (i.e., lateral spreading); however, due to the reduced soil-structure stiffness ratio, the soil ability to induce shear deformation in the structure is diminished, and hence the structure does not undergo large horizontal deformations same as that of the soil. Additionally, structures may exhibit a slight tendency to uplift after the earthquake. These observations can inform the seismic design of underground structures in liquefiable sites.

Here, we describe a technique for probabilistic seismic hazard assessment based on a combination of a characteristic earthquake model and an areal seismic source model. One of the active regions in the Middle East, the Gulf of Aqaba, was used as an example. Five active faults located inside the Gulf of Aqaba (GA), representing the southern part of the Dead Sea Transform fault system, were included in the characteristic earthquake model. The hazard estimations were obtained using the Monte Carlo approach, consisting of the generation of a set of synthetic earthquake catalogs and the calculation of ground motion from all earthquakes in all catalogs. It is assumed that the large earthquakes with magnitudes M > 6.5 may happen on the GA active fault system, while earthquakes with magnitudes M ≤ 6.5 are distributed inside the areal GA zone. This technique considers individual as well as combined faults. The stochastic catalogs generated using the characteristic earthquake model showed conformity with the recurrence of large (M > 6.5) historical earthquakes that have occurred in the studied region over the last 1000 years. The seismic hazard maps obtained using the characteristic earthquake model clearly reflected the location and influence of the considered faults. It seems that the areal source model, in which a single zone is used for the entire Gulf of Aqaba, does not adequately describe seismic hazard. For practical applications, we suggest calculating the hazard from separate faults and their combinations and then constructing the final seismic hazard map using a weighted average scheme.

This study investigates dynamic earth pressure on basement walls by considering soil-structure interaction, a factor that is often overlooked by conventional methods like Mononobe-Okabe, Seed and Whitman, and Wood. Superstructure, basement, and soil were numerically simulated in a single model to evaluate the inertial and kinematic effects of buildings on dynamic earth pressure on the basement walls. The numerical model was validated using data from a centrifuge test and an instrumented building. Then, a parametric study was performed, with the height, width, and basement depth of the building varied with six input motions. The results showed that the inertia of the building increased dynamic thrust. Furthermore, the dynamic thrust showed a similar trend with the displacement response spectrum curve of the ground surface acceleration as the building height increased, while the distribution shape transitioned from triangular to inverted triangular. Additionally, wider buildings had increased dynamic earth pressure, while deeper buildings exhibited smaller normalized dynamic thrust.

The effects of subsurface heterogeneity on liquefaction phenomena during earthquakes are discussed using case histories and nonlinear dynamic analyses with different subsurface modeling approaches. The importance of geologic and anthropogenic controls and the effects of stratigraphic heterogeneity, lithological heterogeneity, and inherent soil variability at the project site scale are discussed. The results of these studies reinforce lessons regarding the importance of subsurface characterization and its representation in analyses for evaluating liquefaction-induced ground deformations and their impacts on civil infrastructure.

In this study, the impact of the second-order effect on the pipe pile's lateral dynamic responses is investigated by Novak's thin layer method. To derive the pile's axial force function, the vertical static equilibrium equations governing the pipe pile expressed in terms of displacements are rigorously solved. The lateral motion equations of the inner and outer soils are decoupled by introducing the potential functions, and the lateral soil resistance is subsequently determined. The pipe pile is idealized as an Euler-Bernoulli beam embedded within a half-space continuum. Based on the lateral vibration equilibrium equation, the solution for the pipe pile's dynamic responses is theoretically derived. By comparisons with the existing theoretical solutions in the absence of vertical loads, the correctness of the solution is verified. Parametric analysis is executed to delve into the impacts of side friction, vertical load, pile-soil modulus ratio, dimensionless frequency, Poisson's ratio, as well as length-diameter ratio on the lateral dynamic responses. Our results indicate that neglecting side friction leads to an overestimation of internal forces, including bending moments and shear forces; vertical load redistributes the pipe pile's displacements and internal forces.

This research aimed to develop data-driven models using deep neural networks (DNNs) that can rapidly predict the seismic drift responses of reinforced concrete (RC) wall structures in building frame systems, aiming to overcome the challenges of costly seismic performance evaluation of building structures. A total of 46 RC wall structures ranging from four to 40 stories were analyzed and subjected to 1,000 ground motions including far-field, near-field-pulse, and near-field-no-pulse types. Two input sets were investigated initially. The first input set comprises peak ground acceleration (PGA), spectral accelerations at 1 s–6 s with 1-s intervals, and the first five natural periods of the wall structure. The second input set contains PGA and spectral accelerations at the first five natural periods of the wall structure. The DNN model developed based on the first input set demonstrated superior accuracy achieving an $R^2$ value of 0.880, and slightly outperformed other reputable machine learning models. To enhance the applicability of the developed model, the ground motion type was incorporated as an additional variable to the first input set, which led to an $R^2$ value of 0.869. Ultimately, two DNN models, one based on the first input set and the other considering the ground motion type, were proposed in this study. Finally, the two models were applied to quickly predict seismic drift responses of a new 24-story RC wall structure, and the predicted results were then utilized to efficiently construct the fragility function. The findings highlight the potential of DNNs as an efficient solution to address complex and costly challenges in the earthquake engineering domain.

Underground structures can significantly affect the ground motion and further influence the seismic design of aboveground structures around them. Although this issue has been well recognised and studied, it is not thoroughly addressed as a large number of factors are involved. This paper focuses on ground motion amplification induced by twin circular tunnels embedded in saturated poroelastic soil. The saturated poroelastic soil is modelled as a two-phase medium to consider parameters characterising the fluid phase. Three-dimensional scattering features of the twin tunnels for obliquely incident seismic waves are numerically investigated by a 2.5D finite element and boundary element hybrid model. It is shown that the presence of the twin tunnels can lead to significant modifications of the free-field motion, in terms of its magnitude and distribution. The three-dimensional oblique incidence scenario presents a more general perspective on the ground motion amplification. Moreover, the effects of saturated poroelastic soil parameters on the ground motion amplification, including soil permeability, groundwater levels, and the degree of saturation, are parametrically investigated. The differences in ground motion amplification patterns between the saturated poroelastic and dry poroelastic soil scenarios are notable, highlighting the effects of parameters characterising the fluid phase.

The effect of past earthquakes (e.g., the 1995 Kobe and 2016 Kumamoto earthquakes) on the space structures revealed the fact that the assumption of the invulnerability of these structures is incorrect despite their light self-weight and high degree of redundancy, and space structures may suffer severe damage during strong ground motions. Therefore, special attention should be paid to the design of this type of structure in high seismic-risk regions. Nevertheless, the existing seismic design codes have not provided the seismic design parameters (i.e., the seismic response modification factors), including the behavior factor, R, and the displacement amplification factor, C_d for space structures. This research aims to extract the seismic design parameters of double-layer diamatic domes (DLDDs) to answer the challenges that structural engineers face in the design of this type of structure. For this purpose, 16 DLDD models with different rise-to-span ratios (RSRs) and span lengths were considered. After designing the models and performing the nonlinear time history analysis using the simultaneous effect of the three transitional components of ground motions, the target displacement at the control node was determined. Then, the pushover analysis was carried out to derive the capacity curve of the structures and calculate the seismic response modification factors in both horizontal and vertical directions. The results indicate that the domes with RSRs of 1/7 and 1/5 should be designed such that they remain in the elastic state in the horizontal direction. Then, with the growth of RSR, the value of R increases and reaches 1.792. Finally, equations were presented in this study for the period, behavior factor, and displacement amplification factor of DLDD structures in both horizontal and vertical directions using the nonlinear regression analysis.

The current research on evaluating the response modification factor $R$, related to the lateral strength demand of structures, has been generally based on inelastic single-degree-of-freedom systems. Nevertheless, most structures have more than one main analysis component and will be subjected to bidirectional ground motions. In this study, the results of the parametric evaluation of the response modification factor considering the bidirectional interaction ($R_b$) of inelastic two-degree-of-freedom systems (2DOF) are presented. The effects on the factor $R_b$ of the vibration period, the ductility capacity, the hysteretic model, the seismic incidence angle, and the period ratio were evaluated. Analysis results show that the bidirectional interaction could increase the lateral strength demand of the 2DOF systems because of the coupling effect of the two components’ responses. To make this research useful for improving engineering practice and code provisions, the main contribution is the proposal of a simplified expression for estimating the factor $R_b$.

Accounting for uncertainties in seismic site response is crucial to improving the performance of one-dimensional (1D) ground response analyses (GRAs) at downhole array recording sites. In addition to site effects, uncertainties in 1D-GRAs can also be contributed from the seismic source and/or path. Though often representing not more than one percent of the distance (path) from the source, site conditions are known to have an enormous influence on ground shaking. In this study, we focus on the site shear-wave velocity (V_S) structure, which is the main ingredient for estimating the variability of site response. As such, V_S can manifest aleatory uncertainties related to the effects of small-scale spatial heterogeneities within the near surface, thus V_S can substantially modify ground shaking during earthquakes. We apply a novel V_S randomization approach to propagate the small-scale heterogeneities of V_S to estimate seismic site response within a non-stationary probabilistic framework. The randomization approach generates samples of V_S profiles that are used to perform several 1D-GRAs and obtain an averaged site response and related variability. The proposed method is implemented on data recorded at two downhole array sites with different subsurface soil conditions: a soft soil site on Treasure Island (California, United States of America) and a rock outcrop site in Cadarache (South-East France). We show that synthetic surface-to-borehole transfer functions from 1D-GRAs provide an acceptable fit to the empirical transfer functions from low-motion earthquake records and succeed in reproducing most of the site-specific seismic response variability. The remaining mismatch between transfer functions is likely due to insufficient precision on the seismic bedrock and the impedance contrast. The variability in site response is discussed with emphasis on the role of V_S small-scale heterogeneities, attenuation, and input motion incidence angle in ground motion variability for the site and soil conditions at both locations.