Microtremor tests and finite element numerical simulations were used to analyze the seismic ground motion effects of the Yunnan Dayao sedimentary basin. The results of the microtremor relative to the reference point spectral ratio (HS/HR) method showed that the spectral ratio curves of each observation point in Dayao basin show multipeak characteristics, indicating that the site consists of different soil layers; the predominant frequencies of each observation point mainly are 6~9 Hz in the basin and there are lots of differences in the predominant frequencies of different observation points, which indicate that the site stiffness of each observation point is different; the differences of spectral ratios between the east–west directions (EW) and the north-south directions (NS) reveal the site’s anisotropy. The amplification coefficient characteristics of each observation point in the basin obtained by numerical simulation show that the predominant frequency is 6~9 Hz; the amplification coefficients of each observation point are different; the edge effect and the focusing effect amplify the seismic ground motion in the basin; the different amplification coefficients of the two sub-basins reflect the significant effect of the basin soil layers’ differences on the seismic ground motion, the site is softer and amplification coefficients are larger; the slope degree of basin edges significantly affects the seismic ground motion near the basins edge, the amplification coefficients of the slope steeper and amplifica- tion coefficients larger. This study demonstrates that the microtremor test spectral ratio (HS/HR) method has good reliability applied to the analysis of basin effect and combining the finite element numerical simulation method is more effective in revealing the basin effect mechanism.
This study evaluates gravity-induced progressive collapse performance and damage mitigation strategies in modular steel buildings (MSBs) A typical three-dimensional six-story structure was modeled and analyzed using the finite element method, focusing on the instantaneous removal of a corner module. The study includes a parametric evaluation of the influence of beam moment capacity on progressive collapse and investigates the effect of using concrete as an infill for square hollow section columns. Additionally, the effectiveness of short K-shaped braces in limiting gravity-induced collapse was assessed. A response/damage index (DI) was proposed to quantify the overall structural response. The findings indicate that semirigid beam-column connections outperform fully rigid connections. Both concrete-filled columns and K-shaped braces mitigate structural damage, with K-shaped braces proving more effective in preventing collapse. Although increasing the beam moment-resisting capacity reduced the DI, improvements were marginal beyond 50% of the fully rigid connection capacity. Higher beam moment capacities reduced local vertical displacement at the corner joint but led to undesirable lateral deformations. Reducing beam rigidity/capacity by 25% mitigated global structural deformations. The optimal beam moment capacity was identified as 75% of the total section capacity when using concrete-filled columns. K-shaped braces applied at the column midpoint entirely prevented progressive gravity-induced collapse and no lateral deformations were observed in braced structures with fully rigid beam-column connections, unlike unbraced structures. Concrete-filled columns offer a cost-effective solution for preliminary production of MSBs, while K-shaped braces are suitable for retrofitting existing buildings. Further research is necessary to address other parameters influen cing the mitigation of progressive collapse in MSBs.
Stochastic subspace identification (SSI) stands as one of the most extensively employed algorithms for modal parameter identification within the domain of bridge structural health monitoring. However, when confronted with non-stationary signals, it often generates numerous false modes in the stability graph, consequently impeding the accuracy of modal parameter identification. To address this challenge, an algorithm combining the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and covariance-driven SSI (COV-SSI) has been proposed in this research, referred to as the CEEMDAN-SSI algorithm. The CEEMDAN-SSI algorithm first decomposes the structural vibration acceleration into intrinsic mode functions (IMFs) and then selects the pertinent IMF component for signal reconstruction using the Pearson correlation coefficient. Subsequently, the reconstructed signal undergoes analysis using the coV-SSI algorithm, effectively mitigating the occurrence of false modes. Furthermore, the research focuses on a large-span continuous rigid frame bridge with elevated piers situated in Toutunhe, Xinjiang Province, currently under construction. Modal parameters of the rigid frame bridge under various wind speed conditions are compared and analyzed using both COV-SSI and CEEMDAN-SSI algorithms. The findings reveal that the CEEMDAN-SSI algorithm markedly diminishes false modes while enhancing the strength of stability axes for each mode, thus affirming the feasibility and robustness of the CEEMDAN-SSI algorithm.
When the seismic source is shallow or the wind turbine structure is moderately distant from the epicenter, it is necessary to consider the oblique incidence of planar body waves. To investigate the dynamic response law of wind turbine structures under oblique seismic wave incidence, this study establishes an integrated approach for analyzing the dynamic response of wind turbine structures considering oblique seismic wave incidence, incorporating one-dimensional time-domain site response analysis and viscoelastic artificial boundaries. By using the above seismic input method, the dynamic response law of a 5MW monopile wind turbine under the obliquely incident P and SV waves are analyzed in detail when different characteristics, incident angles, propagation angles and vibration directions of waves are considered. Numerical studies show that the above factors have an important influence on the seismic response of the wind turbine structure.
The restrainers in the friction pendulum system (FPS) may experience brittle failure during an earthquake. Strong nonlinear behavior should be considered to precisely assess the seismic performance of the railway beam bridge under an earthquake. A seismic vulnerability assessment was performed based on a typical simply supported railway beam bridge. Three different models of the FPS in fixed direction were considered: elastic restrainer model, brittle restrainer model, and nonrestrainer model. Through dynamic analysis, the responses of the railway beam bridge were obtained, including the force and displacement of the FPSs, the curvature ductility at the pier bottom, and transverse dislocation at the beam gap. The analysis results pointed out when the earthquake intensity exceeded the fundamental intensity, the brittle failure of the restrainers was very likely to happen. The sudden release of energy introduced a displacement pulse to the FPS. The elastic restrainer model overestimated the force demand and damage probability of the substructures but underestimated the FPS displacement and dislocation at the beam gap. The nonrestrainer model seriously under-estimated the force demand of the substructure and the FPS displacement under strong earthquakes. The brittle restrainer model could reflect the nonuniform failure of the restrainers and provide a more accurate estimate of the transverse dislocation at the beam gap.
Asphalt concrete is a foundational material in water conservancy projects, serving a critical function in the construction of impermeable structures such as dams. The seismic response characteristics and resilient safety of concrete dams are heavily influenced by the arrangement and evolution of the microscopic structure of the dam material. In this study, a high-precision computed tomography (CT) scanning technique, in conjunction with advanced numerical simulations, was employed to analyze the internal damage and crack extension mechanism of asphalt concrete. Microstructural images of the asphalt concrete specimen were accurately captured by CT scanning, followed by the construction of corresponding numerical models. Presented simulation results show that the displacement deformation of asphalt concrete reaches its maximum value in the top region of the model and subsequently decreases with depth. Material damage was first observed at the interface between aggregate and asphalt matrix, where microcracks emerge and extend to the entire asphalt matrix, resulting in a gradual deterioration of the model performance. The simulation results indicate that the overall strength of asphalt concrete is primarily influenced by the strength characteristics of its aggregates. The stress–strain curves obtained from the numerical simulations exhibit a hyperbolic relationship, which is in high agreement with the physical test results. This study not only enhances our comprehension of the mechanical behavior of concrete but also contributes to the analysis of seismic response and risk assessment in dam engineering through dynamic experimental testing and numerical simulation.
In December 2023, а 6.2 magnitude earthquake struck Jishishan, Gansu Province. This study utilized the Real-time Earthquake Damage Assessment using City-scale Time-history analysis (RED-ACT) system to analyze the seismic damage caused by the event. The analysis included assessments of strong ground motion records, building damage, and human acceleration feeling. The results indicate the following: (1) The earthquake-induced significant ground motion. The response spectrum at the 0–1.3s period range is far above the 7° design-based and maximum considered earthquake levels, and it also far exceeds the 9° maximum considered earthquake level. How to provide a more scientific and reasonable seismic design standard to ensure the anti-collapse performance of buildings still requires further in- depth research. (2) The RED-ACT analysis results indicate that the destructive power of this earthquake was significant. The strong ground motions recorded near the epicenter could cause a certain number of buildings to collapse, with the collapsed buildings mainly being raw-earth/wood structures and un- reinforced masonry structures. The main damage states of buildings assessed correspond generally with the actual earthquake damage survey results. (3) The RED-ACT system can provide assessment results of human feeling of acceleration at different locations, and the assessment results take into account the amplification effect of acceleration by different floors, which can provide a reference for post earthquake science popularization and for reducing post-earthquake panic among the population.
Due to the effects of complex fluid-structure interaction, deep-water bridges are more prone to damage under strong carthquakes. Quantification of seismic fluid-structure interaction can be crucial for evaluating the seismic performance of deep-water bridges. Currently, there is a lack of suitable methods for rapidly calculating hydrodynamic added mass for deep-water piers with complex cross-sectional shapes in the seismic performance assessment of deep-water bridges. In light of this, the present paper proposed an efficient and accurate method for calculating the hydrodynamic added mass of piers with different cross-sectional shapes. Taking circular, rectangular, and dumbbell-shaped piers as examples, the proposed method was employed to calculate the hydrodynamic added mass for deep-water bridge piers. Comparison of the seismic responses obtained from the analytical formula, fluid-structure coupling refined numerical model and the proposed method in this paper validated the accuracy of the proposed method. Finally, the hydrodynamic coupling effects of deep-water bridge piers were also investigated. It was concluded that the proposed method can be efficient and accurate for obtaining the added mass of deep-water piers.
As the Nairobi–Malaba Railway traverses the East African Rift Valley, it has complex engineering geological conditions due to the development of its geological formations. Since March 2018, four large ground fissures have occurred in the East African Rift Valley area crossed by the Nairobi–Malaba Railway engineering construction, posing a significant threat to the safety of the railway engineering. According to the field investigation, it is initially considered that the ground fissures are caused by the loss of strength of the lower soil layers. In view of the fact that the settlement occurred during the rainy season and no earthquake events were recorded in the local and nearby areas during that period, it is inferred that the ground fissures originated from the subduction of the underlying soil layer by the submerged erosion of groundwater. For this reason, a further field investigation was conducted and a geological trench was directly excavated to the underlying rock for the uneven ground settlement, which revealed that the overlying soil layers are mainly silty clay layers and volcanic ash layers, and there are some deep and long cracks of a certain width on the underlying volcanic rock layer and there is gas flow spilling from the cracks. The field investigation also found the existence of some penetrating holes in the volcanic rock layer and caves beneath the volcanic rock layer. Based on the field investigation and phenomenological analysis, it is concluded that during the rainy season, the alternating action phenomenon of downward seepage of water in the surface soil layer and upward reflux of water beneath the volcanic rock layer happened through the cracks and penetrating holes on the volcanic rock layer, and the alternating effect of groundwater flow causes some silty clay and volcanic ash particles to flow into the caves and cracks beneath the volcanic rock layer, which leads to the generation of ground fissures. In addition, to further confirm the reliability of this interpretation of the generative mechanism of ground fissures, related results of conventional geotechnical tests on the overlying soil were studied, which verified the conclusion obtained.