Search Results (44)

Tall-pier girder bridges with fluid viscous dampers (FVDs) are widely used in earthquake-prone mountainous areas. However, the influence of higher-order modes and near-field earthquakes on tall piers has rarely been studied. Based on an asymmetric tall-pier girder bridge, a finite element model is established, and the parameters of FVDs are optimized using SAP2000. The higher-order mode effects on tall piers are explored by proportionally reducing the pier heights. The pulse effects of near-field earthquakes on FVD mitigation and higher-order modes are analyzed. The optimal FVDs can coordinate the force distribution among tall piers, effectively reducing displacement responses and internal forces. Due to higher-order modes, the internal force envelopes of tall piers exhibit concave-convex distributions. As pier heights decrease, the internal force envelopes gradually become linear, implying reduced higher-order mode effects. Long-period pulse-like motions produce the maximum seismic responses because the slender tall-pier bridge is sensitive to high spectral accelerations in medium-to-long periods. The higher-order modes are more easily excited by near-field motions with large spectral values in the high-frequency range. Overall, FVDs can simultaneously reduce the seismic responses of tall piers and diminish the influence of higher-order modes. Full article

The dynamic control of vibrations in skyscrapers is a critical consideration in sustainable building design, particularly in response to environmental excitations such as wind impact or seismic activity. Effective vibration neutralisation plays a crucial role in providing the safety of high-rise buildings. This research introduces an innovative concept for an active vibration damper that operates based on fluid dynamic transport to adaptively alter a skyscraper’s natural frequency, thereby counteracting resonant vibrations. A distinctive feature of this system is an adjustable-length cable mechanism, allowing for the dynamic modification of the pendulum’s effective length in real time. The structure, based on cable length adjustment, enables the PTMD to precisely tune its natural frequency to variable excitation conditions, thereby improving damping during transient or resonance phenomena of the building’s dynamic behaviour. A comprehensive mathematical model based on Lagrangian mechanics outlines the governing equations for this system, capturing the interactions between pendulum motion, fluid flow, and the damping forces necessary to maintain stability. Simulation analyses examine the role of initial excitation frequency and variable damping coefficients, revealing critical insights into optimal damper performance under varied structural conditions. The findings indicate that the proposed pendulum damper effectively mitigates resonance risks, paving the way for sustainable skyscraper design through enhanced structural adaptability and resilience. This adaptive PTMD, featuring an adjustable-length cable, provides a solution for creating safe and energy-efficient skyscraper designs, aligning with sustainable architectural practices and advancing future trends in vibration management technology. The study presented in this article supports the development of modern skyscraper design, with a focus on dynamic vibration control for sustainability and structural safety. It combines advanced numerical modelling, data-driven control algorithms, and experimental validation. From a sustainability perspective, the proposed PTMD system reduces the need for oversized structural components by providing adaptive, efficient damping, thereby lowering material consumption and embedded carbon. Through dynamically retuning structural stiffness and mass, the proposed PTMD enhances resilience and energy efficiency in skyscrapers, lowers lifetime energy use associated with passive damping devices, and enhances occupant comfort. This aligns with global sustainability objectives and new-generation building standards. Full article

Given the critical role of electrical cabinets in the post-earthquake recovery and emergency response of nuclear power plants (NPPs), a comprehensive assessment of their seismic performance is essential to ensure operational safety. This study analyzed seismic behavior by fabricating an electrical cabinet model based on the dynamic characteristics and field surveys of equipment installed in a Korean-type NPP. A shaking table test with simultaneous tri-axial excitation was conducted, incrementally increasing the seismic motion until damage was observed. A numerical model was then developed based on the experimental results, followed by a seismic response analysis and comparison of results. The findings verified that assuming fixed anchorage conditions in the numerical model may significantly overestimate seismic performance, as it fails to account for the nonlinear behavior of the anchorage system, as well as the superposition between global and local modes caused by cabinet rocking and impact under strong seismic loading. Furthermore, damage and impact at the anchorage amplified acceleration responses, significantly affecting the high-frequency range and the vertical behavior, leading to substantial amplification of the in-cabinet response spectrum. Full article

The seismic design of underground or aboveground structures is commonly based on the free-field assumption, which neglects the interaction between underground structures–soil–aboveground structures (USSI). This simplification may lead to unsafe or overly conservative, cost-intensive designs. To address this limitation, a series of shaking table tests were conducted on a coupled USSI system, in which the underground component consisted of a subway station connected to tunnels through structural joints to investigate the “city effect” on-site seismic response, particularly under long-period horizontal seismic excitations. Five test configurations were developed, including combinations of one or two aboveground structures, with or without a subway station. These were compared to a free-field case to evaluate differences in dynamic characteristics, acceleration amplification factors (AMFs), frequency content, and response spectra. The results confirm that boundary effects were negligible in the experimental setup. Notably, long-period seismic inputs had a detrimental impact on the field response when structures were present, with the interaction effects significantly altering surface motion characteristics. The findings demonstrate that the presence of a subway station and/or aboveground structure alters the seismic response of the soil domain, with clear dependence on the input motion characteristics and relative structural positioning. Specifically, structural systems lead to de-amplification under high-frequency excitations, while under long-period inputs, they suppress short-period responses and amplify long-period components. These insights emphasize the need to account for USSI effects in seismic design and retrofitting strategies, particularly in urban environments, to achieve safer and more cost-effective solutions. Full article

In the context of autonomous environmental monitoring, this study investigates a surface acoustic wave (SAW) sensor designed for selective carbon dioxide (CO₂) detection. The sensor is based on a LiTaO₃ piezoelectric substrate with copper interdigital transducers and a polyetherimide (PEI) layer, chosen for its high electromechanical coupling and strong CO₂ affinity. Finite element simulations were conducted to analyze the resonance frequency response under varying gas concentrations, film thicknesses, pressures, and temperatures. Results demonstrate a linear and sensitive frequency shift, with detection capability starting from 10 ppm. The sensor’s autonomy is ensured by a piezoelectric energy harvester composed of a cantilever beam structure with an attached seismic mass, where mechanical vibrations induce stress in a piezoelectric layer (PZT-5H or PVDF), generating electrical energy via the direct piezoelectric effect. Analytical and numerical analyses were performed to evaluate the influence of excitation frequency, material properties, and optimal load on power output. This integrated configuration offers a compact and energy-independent solution for real-time CO₂ monitoring in low-power or inaccessible environments. Full article

This study aims to overcome the technical bottleneck of non-invasive differentiation between the rammed earth layer and pebble layer in complex shallow subsurface environments, particularly focusing on the challenge of detecting highly heterogeneous pebble layers with complex wavefield characteristics. Using the western city wall of the Baodun site (Xinjin, Sichuan, China) as a case study, we introduce a high-resolution seismic detection technique combined with controllable high-frequency seismic source excitation to investigate the response characteristics of high-frequency components and energy variations of seismic waves in different strata, thereby revealing differences in physical properties between the rammed earth layer and pebble layer. Through high-frequency data acquisition, specialized processing, and interpretative analysis of seismic data, we successfully distinguish the two strata and delineate pebble-related anomalous zones. The results also indicate that, due to complex geological conditions, the reflection and refraction patterns of seismic waves in the pebble layer are exceptionally intricate. Moreover, the interplay of abrupt seismic velocity variations, interference waves, and other contributing factors leads to pronounced heterogeneity and strong scattering characteristics in the seismic data across the time, frequency, and phase domains. This research overcomes the limitations of conventional geophysical methods and confirms the applicability of high-frequency seismic techniques to complex near-surface archaeological contexts. It provides robust scientific support for the archaeological study of the Baodun site and offers a methodological reference for subsurface mapping of pebble layer in prehistoric urban landscapes. Full article

Bridges play a key and controlling role in transportation systems. Steel bridges are favored for their high strength, good seismic performance, and convenient construction. As important node connectors of steel bridges, high-strength bolts are extremely susceptible to damage such as corrosion and loosening. Therefore, accurate identification of bolt loosening is crucial. First, a new type of adhesive piezoelectric sensor is designed and prepared using PMN-PT piezoelectric single-crystal materials. The PMN-PT sensor and polyvinylidene fluoride (PVDF) sensor are subjected to steel plate fixed frequency load and swept frequency load tests to test the performance of the two sensors. Then, a steel plate component connected by high-strength bolts is designed. By applying exciter square wave load to the structure, the vibration response characteristics of the structure are analyzed to identify the loosening of the bolts. In addition, a piezoelectric smart washer sensor is designed to make up for the shortcomings of the adhesive piezoelectric sensor, and the effectiveness of the piezoelectric smart washer sensor is verified. Finally, a bolt loosening index is proposed to quantitatively evaluate the looseness of the bolt. The results show that the sensitivity of the PMN-PT sensor is 21 times that of the PVDF sensor. Compared with the peak stress change, the natural frequency change is used to identify the bolt loosening more effectively. Piezoelectric smart washer sensor and bolt loosening indicator can be used for bolt loosening identification. Full article

This study investigates the seismic performance of the V3.0 220 kV standard-designed substation of the Southern Power Grid, located in a high-intensity seismic zone, with a focus on the application of seismic isolation technology. Seismic isolation and structural analysis were conducted and shaking table tests were performed on both isolated and non-isolated structural models. A total of 40 tests were carried out using three levels of ground motion intensity (i.e., 140 gal, 400 gal, and 800 gal) and in three directions (unidirectional, bidirectional, and triaxial). The dynamic characteristics, seismic response, and isolation effectiveness were evaluated. Results indicate that the test models exhibit strong agreement with theoretical and numerical predictions, with an average frequency deviation of 10.98%. The fundamental period of the isolated structure was extended by a factor of 2.33 compared to the non-isolated configuration. As the peak ground acceleration increased, structural frequency decreased, and the period increased. The isolated structure showed a lower first-period growth rate (4.82%) than the non-isolated structure (15.38%). Even under 800 gal excitations, the isolated structure remained within the elastic range. Seismic isolation significantly reduced structural response, with a control effectiveness exceeding 50%, enabling a one-degree reduction in seismic design intensity. A vulnerability analysis based on 200 simulated earthquake cases revealed that the isolated structure exhibited lower failure probabilities across four performance states. At 600 gal PGA, the failure probability in the LS3 state was reduced by 27.8%. These findings confirm the effectiveness and reliability of seismic isolation design for substations in high seismic intensity regions. Full article

The study of vibration isolation devices has become an emerging area of research in view of the extensive damage to buildings caused by earthquakes. The ability to effectively isolate seismic vibrations and maintain the stability of a building is thus addressed in this paper, which evaluates the effect of horizontal ground excitation on the response of a structure isolated by a coupled isolation system consisting of a non-linear damper (QZS) and a friction pendulum system (FPS). A single-degree-of-freedom system was used to model structures whose bases are subjected to seismic excitation in order to assess the effectiveness of the QZS–FPS coupling in reducing the structural response. The results obtained revealed significant improvements in structural performance when the QZS–FPS system uses a damper of optimum stiffness. A 30% reduction in displacement was recorded compared with QZS alone for two signals, one harmonic and the other stochastic. The response of the QZS–FPS system with soft stiffness to a harmonic pulse reveals amplitudes reaching around eight times those of the pulse at low frequencies and approaching zero at high frequencies. In comparison, the rigid QZS–FPS coupling has amplitudes 0.9 and 3.5 times higher than those of the harmonic signal. Thus, the resonance amplitudes observed for the QZS–FPS system are lower than those reported in other studies. This analysis highlights the performance differences between the two types of stiffness in the face of harmonic pulses, underlining the importance of the choice of stiffness in vibration management applications. The stochastic results show that on both hard and soft soils, the new QZS–FPS system causes structures to vibrate horizontally with maximum amplitudes of the order of 0.003 m and 0.007 m respectively. So, QZS–FPS coupling can be more effective than all other isolators for horizontal ground excitation. In addition, the study demonstrated that the QZS–FPS combination can offer better control of building vibration in terms of horizontal displacements. Full article

This study investigates how structural dynamic characteristics affect the response to high-frequency dominant seismic excitations, using a 3D numerical analysis considering soil–structure interaction (SSI). For this purpose, an SSI analysis was conducted using the finite element analysis software LS-DYNA, incorporating four representative Korean geotechnical characteristics and the 2016 Gyeongju earthquake, characterized by dominant high-frequency components. A comparison was conducted between a fixed-end model without considering SSI and an embedded model with SSI for a high-rise structure (40 stories) with low natural frequencies, and a low-rise structure (5 stories) with high natural frequencies. The analysis focused on key dynamic responses, including the natural frequency, frequency of maximum response, and maximum relative displacement of the structures, to identify differences in the SSI effect based on the structures’ dynamic characteristics and the soil types. The analysis generally revealed that the SSI effect lowers the natural frequencies of structures and increases the damping effect. It was also found that depending on the match between the dominant frequency range of the seismic excitations and the range of the structure’s natural frequencies, larger dynamic responses were calculated when SSI was considered, suggesting that it may be necessary to consider SSI for conservative design results. Full article

This study investigates the dynamic performance of a road sign equipped with a multi-material electronic signboard subjected to mining-induced seismic tremors. The key innovative aspect lies in providing new insights into the dynamic performance of multi-material electronic signboards under high-energy mining tremors, enhancing their safety assessment in mining areas. Experimental modal analysis and finite element analysis were conducted, and the numerical model of the sign was calibrated by adjusting ground stiffness to align experimental and computational data. The fundamental natural frequencies and their corresponding mode shapes were identified as 2.75 Hz, 3.09 Hz, 8.46 Hz, and 13.50 Hz. Numerical results were validated using MAC methods, demonstrating strong agreement with experimental values and confirming the accuracy of the numerical predictions. Damping ratios of 3.79% and 3.71% for the first and second modes, respectively, were measured via hammer tests. To evaluate the sign’s dynamic performance under high-energy mining-induced tremors, two events were applied as kinematic excitation of the structure. These tremors, recorded in different mining regions, exhibited significant variations in peak ground acceleration (PGA) and dominant frequency range. A key finding was that frequency matching between the dominant frequencies of the tremor and the natural frequencies of the sign had a greater impact on the sign’s dynamic response than PGA. The Szombierki tremor, with dominant frequencies of 1.6–4.8 Hz, induced significantly higher stress and displacement compared to the Moskorzyn tremor (5–10 Hz) despite the latter having twice the PGA. These results highlight that a road sign structure can exhibit widely varying dynamic behaviors depending on the seismic characteristics of the mining zone. Therefore, a comprehensive assessment of mining-induced tremors in relation to the seismicity of specific areas is crucial for understanding their potential impact on such structures. The dynamic performance assessment also revealed that the electronic multi-material signboard did not undergo plastic deformation, confirming it as a safe material solution for use in mining areas. Full article

Liquefaction and earthquake damage to coral sand sites can cause engineering structure failure. Both testing and analyzing the seismic response characteristics of pile groups on coral sand sites are highly important for the seismic design of engineering structures. To address the lack of research on the seismic dynamic response of group pile foundations in coral sand sites, this study analyzes the characteristics of the seismic dynamic response of vertical and batter pile foundations for bridges in coral sand liquefaction foundations via the shaking table model test and investigates the variation patterns of acceleration, excess pore water pressure (EPWP), and the bending moment and displacement of foundations, soil, and superstructures under different vibration intensities. Results show that the excitation wave type significantly affects liquefaction: at 0.1 g of peak acceleration, only high-frequency sine wave tests liquefied, with small EPWP ratios, while at 0.2 g, all tests liquefied. Vertical pile foundations had lower soil acceleration than batter piles due to differences in bearing mechanisms. Before liquefaction, batter piles had smaller EPWP ratios but experienced greater bending moments under the same horizontal force. Overall, batter piles showed higher dynamic stability and anti-tilt capabilities but endured larger bending moments compared to vertical piles in coral sand foundations. In conclusion, batter pile foundations demonstrate superior seismic performance in coral sand sites, offering enhanced stability and resistance to liquefaction-induced failures. Full article

The generation of an earthquake and a tsunami is a coupled process of radiating seismic waves and exciting tsunamis, and the two types of waves are simultaneously recorded by ocean-bottom pressure sensors. In order to constrain the earthquake source and evaluate the tsunami hazards, it is necessary to separate the tsunami waves. It is traditional to apply a low-pass filter such that the seismic waves are filtered and the tsunami waves remain. However, filtering may also cause distortion of the tsunami waves. In this study, we first use the finite-element method to simulate the generation of seismic and tsunami waves and show that the coupling is a linear superposition of the two waves. We then propose a new method to extract the tsunami waves. First, a low-pass filter with relatively high cutoff frequency that does not affect the tsunami waves is adopted, so that only tsunami waves and low-frequency seismic waves remain. The low-frequency seismic waves satisfy a theoretical equation $p=\rho ha$ (p pressure, $\rho$ water density, h water depth, and a seafloor vertical acceleration), and they can be predicted and removed by utilizing the records of ocean-bottom acceleration. We demonstrate the procedure by numerical simulations and show that the method successfully extracts clean tsunami signals, which is important for earthquake source characterization and tsunami hazard assessment. Full article

To study the influence of random seismic responses on the structure of a large-span double-deck steel truss cable-stayed bridges under the effects of high-intensity rare earthquakes, a new power spectral model was proposed based on improvements to existing power spectra for fitting the improved power spectra of random seismic responses. The bridge finite element model established using ANSYS was employed as an engineering example for computational analysis to investigate whether the improved spectrum exhibited better adaptability and feasibility under high-intensity rare earthquake compared with other power spectra. The results indicated that the power spectral model, based on improvements to the original power spectra, had a more pronounced filtering effect on the low-frequency and high-frequency portions. Moreover, under the consistent three-dimensional excitation, the vertical displacement of the main beam was the greatest, indicating that the improved spectrum had better adaptability than other power spectra in studying the high-intensity rare earthquakes affecting bridges. It also reflected the feasibility of using the improved spectrum for studying the random responses to high-intensity rare earthquakes, providing a reference for bridge design concerning rare earthquakes in large-span bridges. Full article

The accurate and timely acquisition of high-frequency three-dimensional (3D) displacement responses of large structures is crucial for evaluating their condition during seismic excitation on shaking tables. This paper presents a distributed high-speed videogrammetric method designed to rapidly measure the 3D displacement of large shaking table structures at high sampling frequencies. The method uses non-coded circular targets affixed to key points on the structure and an automatic correspondence approach to efficiently estimate the extrinsic parameters of multiple cameras with large fields of view. This process eliminates the need for large calibration boards or manual visual adjustments. A distributed computation and reconstruction strategy, employing the alternating direction method of multipliers, enables the global reconstruction of time-sequenced 3D coordinates for all points of interest across multiple devices simultaneously. The accuracy and efficiency of this method were validated through comparisons with total stations, contact sensors, and conventional approaches in shaking table tests involving large structures with RCBs. Additionally, the proposed method demonstrated a speed increase of at least six times compared to the advanced commercial photogrammetric software. It could acquire 3D displacement responses of large structures at high sampling frequencies in real time without requiring a high-performance computing cluster. Full article