Soil Dynamics and Earthquake Engineering最新文献

The effects of scour depth on the seismic responses of rock-socketed single pile foundations and 2 × 2 pile group foundations were investigated by shaking table tests, and the seismic performance and differences of these two foundation types were analyzed. The test results show that increasing scour depth causes liquefaction to occur earlier but also accelerates the dissipation of pore water pressure. Pile acceleration, pile top displacement, and pile bending moment all increase with increasing in scour depth. The pile top acceleration and amplification factor of the pile group increase steadily and linearly with increasing scour depth, while those of the single pile increase abruptly at the anchorage ratio of 4.6. The acceleration amplification effect is also susceptible to the types of soil layers and the stiffness of the pile body. The stability of pile group deformation is assessed to be superior to that of single pile based on the amplification intersection line. The maximum bending moment of the pile body arises at the interface between saturated sand and strongly weathered granite, and its location does not shift with increasing scour depth. Increasing scour depth not only amplifies the adverse effects of seismic excitation on pile acceleration, pile top displacement, and pile bending moment but also amplifies the differences in seismic performance and liquefaction resistance of these two foundation types. Based on the research results, pile group foundations have better seismic performance than single pile foundations because of the load-sharing effect of the pile group under different scour depths. Therefore, pile group foundations can provide more stable support in scour-prone areas.

In conventional designs, the pile and pile cap are typically considered rigid connections. However, this type of connection experiences a concentrated force during earthquakes, leading to frequent damage at the pile heads. To mitigate pile head damage, semirigid pile‒pile cap connections are proposed. Centrifuge shaking table tests were conducted to investigate the seismic response of the superstructure‒pile foundation system. Two layers of Toyoura sand, including a moderately dense upper layer and a denser bottom layer, were used as the foundation soil. The superstructure was simplified as lumped masses and columns with two different heights and periods. The foundation consisted of a 3 × 3 group of piles. Rigid and semirigid pile‒pile cap connections were evaluated. The experiments investigated the effect of connection type on the distribution of bending moments in the piles and analyzed the acceleration and displacement responses of the superstructure under different pile‒pile cap connections. According to the results, semirigid connections reduced the peak bending moment at the pile head by 50–70 %, especially for low-rise superstructure cases. The influence depth of the connection type on the pile bending moment reaches approximately 10 times the pile diameter. For low-rise superstructure cases, semirigid connections slightly reduced the natural frequency of the superstructure, leading to a decrease in the superstructure acceleration during earthquakes with a short dominant period. The semi-rigid connections reduce the rotation of foundations but promote the translational displacement of foundations. For the mid-rise superstructure cases, semirigid connections reduce the translational displacement and increase the rotational displacement of the foundation. These experiments provide insights into the seismic performance of superstructure‒pile foundation systems with different pile‒pile cap connections and can serve as a reference for seismic design in similar engineering practices.

Coastal bridges, as vital components of transportation networks, are vulnerable to damage from successive earthquake-tsunami (EQ-TS) events in rapidly developing coastal hazard-prone cities. Understanding how these bridges perform under the combined effects of earthquakes and tsunamis is crucial. Though studies have investigated coastal buildings facing these hazards, there is limited research on bridges experiencing extreme EQ-TS events, especially on the generation of load sequences, dynamic structural responses, and cumulative damage assessment. To overcome these limitations, this study aims to thoroughly examine the dynamic behavior of reinforced concrete coastal bridges subjected to successive EQ-TS hazards. To generate practical sequential EQ-TS loads, records of the 2011 Tohoku earthquake and resulting tsunami heights, which are calculated based on the earthquake magnitude and epicentral distance, are utilized for analyses. The tsunami wave load time series for each earthquake record is created using a high-fidelity computational fluid dynamics model. Nonlinear time-history analyses are then performed for the bridge model in OpenSees under the synthetic EQ-TS sequences, quantifying structural responses and cumulative damage. Moreover, the comparative results of structural performance under single and successive hazard scenarios are presented and discussed. Results indicate that successive EQ-TS hazards not only induce much larger structural responses as compared to a single EQ hazard, but also produce considerable residual displacements for both bearings and decks. The wave height is more appropriate than the peak ground acceleration as an individual intensity measure for predicting the cumulative damage of bridges under cascading EQ-TS hazards. Relying solely on peak responses for assessing the dynamic performance of piers under successive EQ-TS sequences may underestimate the actual damage.

To improve the output damping force of the eddy current damper, a multilayer magnetic field rotary eddy current inertial damper (MMF-RECID) is proposed. The MMF-RECID is an inerter-based eddy current damper. A prototype device of the MMF-RECID is manufactured and tested, and its mechanical properties are systematically investigated. Firstly, the configuration of the MMF-RECID is described, and the calculation formulas of the axial force are derived. Secondly, an MMF-RECID prototype is designed and fabricated, and the apparent mass and energy dissipation performance under recycled axial loading are investigated. Three-dimensional transient numerical simulations of eddy current damping are conducted using the ANSYS Electronics Desktop. The results show that the eddy current damping force exhibits velocity nonlinearity, and the test results are consistent with the simulation results. Next, the study focuses on parameters influencing the maximum eddy current damping torque generated by the copper plate and the corresponding critical rotating speed. These parameters encompass the number and size of the magnets, the thickness of the copper plate, and the air gap. Finally, the earthquake-reduction effect of a six-degree-of-freedom structure equipped with MMF-RECID is analyzed. This study demonstrates that the ball screw system of MMF-RECID achieves a multiplicative effect of apparent mass and eddy current damping force, the eddy current damping force of a multi-layer magnetic field versus a single-layer magnetic field conforms to the law of linear superposition, and the hysteresis curves are stable. The eddy current damping torque can be improved by increasing the number and size of the magnets, and decreasing the air gap. The thickness of the copper plate significantly affects both the maximum damping torque and the critical speed, and the optimal thickness range is between 2 mm and 4 mm.

The mechanical properties and constitutive model of unsaturated soils under cyclic loading are crucial for understanding the behavior of foundations and slopes subjected to dynamic motions such as earthquakes and traffic loading. In this study, multilevel strain-controlled cyclic simple shear tests of unsaturated weathered red mudstone (WRM) were conducted. The detailed investigation focused on cyclic responses, including shear stress-strain behavior and volume change, strain-dependent secant shear modulus and damping ratio, and stress–dilatancy behavior. This study revealed the significant influences of the degree of saturation and vertical stress on these responses, with the initial static shear stress mainly affecting the shear stress-strain behavior and volume changes at the initial loading stage. Based on the experimental observations, a cyclic constitutive model was proposed for unsaturated WRM. The model incorporates a slightly revised Davidenkov model and Masing criterion to generate shear stress-strain hysteresis loops with or without initial static shear stress. Additionally, a stress-dilatancy equation was included to capture the volume changes during cyclic loading. The proposed model was verified by comparing representative test data and calculation results, demonstrating the excellent performance of the proposed model in modeling the main features of unsaturated WRM under cyclic loading.

Proper representations of ground motion characteristics and prediction of rock-to-ground amplification factors (AFs) of intensity measures (IMs) are crucial in site-specific probabilistic seismic hazard analysis (PSHA). By using spectrally equivalent pulse-like and non-pulse-like ground motion suites within the convolution-based PSHA framework, this paper aims to (i) investigate the amplification patterns and AF prediction efficiency for 16 typical IMs; and (ii) evaluate the sensitivities of AF and PSHA to the pulse-characteristic, rock-IM type, and AF functional form. The results reveal that IMs are generally amplified, whereas de-amplification occurs at soft sites for IMs largely dominated by high-frequency content (e.g., Arias intensity). Specific rock-IMs for predicting AFs are recommended through efficiency criterion. The results for pulse-like and non-pulse-like suites are found to be not significantly different; hence, including pulse-like records is generally not essential in convolution-based PSHA as long as the bedrock spectra designed with pulse-type features have been matched. Meanwhile, the similar AF predictions from the linear and nonlinear models indicate that the choice of functional form is of secondary importance. Instead, the selection of rock-IM is of higher importance, especially for soft sites and high-frequency dominated IMs. This study could provide useful insights into ground motion selection and AF prediction for site-specific PSHA.

Aftershocks frequently induce further damage to slopes that have already been compromised by mainshocks. Most of the current research concentrates on the case-based studies of structural response to the mainshock-aftershock sequences (MAS), however, the influence of the MAS parameter characteristics has not been adequately considered. In this study, the peak characteristic, spectrum characteristic, cumulative characteristic and polarity effect of the MAS were considered, the correlation between 21 MAS parameters and slope response were analyzed, and the response characteristics of soil slope under the MAS action were comprehensively and systematically revealed. The results show that: (1) Aftershocks can induce significant incremental damage to slopes, with the extent of this damage being contingent upon the severity of damage caused by the mainshock; (2) Among the MAS parameters, the Cumulative Absolute Velocity (CAV_ma) and Peak Ground Velocity (PGV_ma) are optimal for assessing the response of soil slopes under MAS conditions. Furthermore, the incremental damage caused by aftershocks can be predicted using the displacement increment ratio (δ_D); (3) The polarity of the MAS has an impact on the displacement of the slope, following the pattern: MAS along-slope direction > mainshock along-slope direction and aftershock reverse-slope direction > aftershock along-slope direction and mainshock reverse-slope direction > MAS reverse-slope direction; (4) The MAS polarity also affects the correlation between the MAS parameters and the slope displacement response, especially for the aftershock displacement. The research results aim to provide a foundation for the selection of evaluation factors and the analysis of soil slopes stability under the MAS action.

Seismic safety of highway bridges is one of the critical issues for the functionality of transportation lifelines after severe earthquakes. Skewed highway bridges are found to be more vulnerable due to the irregular distribution of seismic demands on the bridge components. Moreover, scour induced loss of soil material and hence reduction in lateral support around the foundation piles can amplify the seismic effects on the structural components of water crossing bridges. A numerical study was conducted to investigate the seismic performance of skewed and straight highway bridges with varying scour depths and two different scouring types around the bridge piles. Analytical models of straight (0°) and 45° skewed bridges were created using the OpenSees program and a series of nonlinear response history analysis was carried out under the effect of recorded strong ground motions. In the first scouring type which was called as Case-1, scour depth was assumed the same around all piles and varied uniformly. In Case 2, two different non-uniform scouring types with linearly varying scour depth around the piles were investigated. The uncertainty in the earthquake ground motion excitation direction of the two horizontal components was also studied by considering the variable incidence angle of ground motion pairs. The maximum seismic demands of the members at different ground motion incidence angles were evaluated and compared to the demands obtained for the critical ground motion incidence angles suggested by Caltrans. Superstructure displacement, curvature demands of bridge column and shear force demands of pile elements are the seismic demand parameters examined within the scope of the study and were compared for each scour condition for both straight (0°) and 45° skewed bridge.

The long-term performance of pavement structures is heavily reliant on the sustained load-carrying capacity of the subgrade soil. Under repetitive traffic loads, permanent deformation (PD) gradually accumulates in the subgrade due to plastic yielding and soil particle rearrangement, which can compromise the serviceability and durability of overlying pavement layers. This study aimed to enhance the understanding of compacted clay response under long-term cyclic loads through a systematic repeated load triaxial (RLT) testing approach. The proposed approach considered depth-dependent static and dynamic stresses exerted on compacted clay beneath pavement structures and traffic loads. A series of RLT tests were conducted to investigate the impact of key factors, including soil properties (moisture content and compaction degree), stress conditions (confining pressure and deviator stress), and load characteristics (load duration and rest period), on the PD behaviour of compacted clay subgrade. Stress-strain hysteresis loops and damping ratios were analyzed to enhance the fundamental understanding of subgrade PD evolution. The results showed that higher moisture content and lower compaction degree significantly increased PD, with the PD response transitioning from plastic shakedown to plastic creep. Greater deviator stress also exacerbated PD accumulation. Variations in loading duration and rest period influenced the PD behaviour, demonstrating the importance of accurately simulating the stress history experienced by subgrade soil elements under traffic loading. The findings provide valuable insights to optimize subgrade design and implement performance-based management of pavements.

Stiffened deep cement mixing (SDCM) piles present excellent engineering performance compared with conventional pipe piles and thus are often applied to the structure foundation in coastal soft-soil area. This study intends to explore the vertical dynamic behavior of a SDCM pile in unsaturated soil by developing an analytical approach. In the proposed approach, the SDCM pile divides into two parts. The first part is considered as a composite pile formed by a prestressed high-strength concrete (PHC) pipe pile and a cement mixing pile through high-strength bonding, and the second part formed by the PHC pipe pile and an unsaturated soil column. The closed-form solution for the dynamic impedance of the SDCM pile has been determined and then verified by contrasting with the existing solutions, where the dynamic impedance is mainly characterized by dynamic stiffness and dynamic damping at SDCM pile head in the vertical direction. Numerical discussions are finally implemented to analysis the dependence of physical parameters of cement mixing pile, PHC pipe pile, and unsaturated soil on the vertical dynamic impedance of SDCM pile. It can be concluded that increasing the depth, radius and elastic modulus of the cement mixing pile at relatively low load excitation frequencies is beneficial for enhancing the vertical vibration resistance of the SDCM pile, while the reverse is true at higher load excitation frequencies. Quantitatively, under relatively low load excitation frequencies, the reinforcement depth of the cement mixing pile should not exceed 2/3 of the length of the PHC pipe pile, while its elastic modulus should be 5 ‰ to 2 % of the elastic modulus of the PHC pipe pile.