Shaking Table Experiments Research Articles

Theoretical Model and Shaking Table Experiment of Eddy Current–Enhanced Friction Pendulum Tuned Mass Damper

ABSTRACTTraditional pendulum tuned mass dampers (PTMDs) necessitate substantial vertical space, and conventional friction pendulum systems (FPS‐TMDs) struggle to balance low activation thresholds with adequate damping levels due to their reliance on friction forces. This study presents an innovative eddy current–enhanced friction pendulum tuned mass damper (ECEFP‐TMD), which capitalizes on eddy current damping to lower the activation threshold effectively. Simultaneously, incidental friction damping provides a complementary dual–damping scheme. We developed a robust theoretical model, underpinned by shaking table experiments, to demonstrate the ECEFP‐TMD's superior vibration mitigation. Findings reveal that eddy current damping not only diminishes the activation threshold but also streamlines the adjustment of damping levels. The integrated dual–damping mechanism substantially augments energy dissipation, thus reducing the acceleration response of structures subjected to seismic activity. Particularly, for FPS‐TMDs with minimal friction coefficients, the inclusion of eddy current damping substantially elevates seismic resilience, mitigating stick–slip behavior typically induced by excessive friction damping.

Seismic Resilience of Geogrid Reinforced Concrete Earth-Retaining Wall of Various Incremental Panels Based on Physical and Numerical Modelling

The dynamic response for different earth-retaining walls having geogrid as a reinforcement, combined with cohesionless granular material for backfill to mitigate earth pressure, has been examined through scale-down shaking table experiments and full-scale 3D FE analysis, utilizing ABAQUS as the finite element software. The scale factor is 1/4th for scaled-down. This study included various physical modelling experiments using different geogrid-reinforced earth retaining (GRER) walls (1m height, 7.5cm, thickness, and length 1m). Additionally, comprehensive 3D finite element analysis were conducted with the configurations measuring (4m, height 0.3m, thickness, and length 4m). This study examines hollow prefabricated concrete panels with shear key (PC-W), stone masonry walls of gravity type (GM-W), and traditional reinforced concrete (RC-W) walls. It also presents comparative investigations, such as lateral horizontal displacement of the wall, lateral pressure to the backfill, backfill soil settlement, and settlement of the wall foundation of various (GRER) walls. The accuracy of the Finite Element simulation framework has also been assessed in the shaking table experiment, as well as the FE analyses. According to the results, a PC-W wall with a shear key is the most effective type because it shows more resistance toward displacement. As per the comparison of the test models, GRER walls’ seismic response was more affected by the earthquake waves from the far field having long-term high acceleration values. In contrast, seismic waves from the close field had a smaller impact on the walls’ seismic response. However, the geogrid could improve the GRER seismic resilience deformation. Geogrid layers may reduce backfill pressures and backfill settlements. The geogrids located in the central portion within the reinforced soil and the geogrid roots connected to the walls were essential to the seismic design of the geogrid-reinforced earth retaining wall. To evaluate the reliability of the findings, the models have a predicted R2 variance below 0.1, indicating a consistent relationship between these two variables.

Innovative earthquake resistant school building typologies for earthquake-hit areas of Nepal

The 2015 Gorkha earthquake in Nepal devastated over 50,000 classrooms across 14 rugged districts, many accessible only by foot trails. Rebuilding multi-hazard resilient school buildings in these remote areas posed unique challenges, including adherence to restrictive building codes, logistical hurdles in transporting modern construction materials and financial constraints. This study innovatively addressed these challenges by advocating for the utilisation of local materials and craftsmanship in line with the 'Build Back Better' initiative. Through a blend of literature review, field surveys, structural assessments, and stakeholder consultations, an overall framework of the research was prepared and is presented in this paper. This framework included an attribute-based approach for the selection of locally suitable construction materials, techniques and building types. Four novel multi-hazard resilient building prototypes are proposed, rigorously tested for compliance with Nepalese building codes using shaking table experiments and numerical simulations. By challenging conventional engineering norms, the findings of the findings of this study not only resulted in the development of pragmatic alternatives but also illustrated the significance of locally driven solutions for school infrastructure resilience, both in Nepal and also for regions worldwide where similar geographical and multi-hazard constraints are encountered.

Assessment of foundation damage during earthquakes using acoustic emission monitoring: An experimental study on the shaking table test

Assessing structural foundation damage following an earthquake is critical for safety evaluation. However, assessing the damage to pile foundations with traditional visual inspections and non-destructive testing methods is challenging. This study evaluated the use of acoustic emission (AE) monitoring for damage detection and location in foundation structures during earthquake simulations by conducting shaking table experiments. Scaled models of foundation structures with and without surrounding soil were used in the experiments, and the performance of the AE monitoring system was evaluated by comparing the AE parameters via visual inspection. The experimental results showed that the AE monitoring system could effectively predict the initiation of cracks in foundation structures that experienced an earthquake. In addition, an appropriate filtering criterion for the shaking table experiments was established based on the AE characteristics of the foundation structures during the earthquake simulation, thereby improving the performance of the AE monitoring system for damage location. Consequently, this study contributed to a better understanding of the applicability of AE monitoring systems to foundation structures during earthquakes.

Numerical Simulation of Nuclear Power Plant Pile Foundation Damage Under Earthquake Action

This study investigates the pile foundation of a nuclear power plant situated on medium-soft soil. It employs an improved viscoelastic artificial boundary unit to accurately simulate the boundary conditions of the calculation area. The research utilizes a constitutive model of concrete damage plasticity for the pile foundation and an equivalent linearized model for the soil layer. Through large-scale shaking table experiments and numerical simulations, we explore the internal force distribution within the nuclear power structure’s pile foundation and assess the extent of the damage. The results indicate that damage primarily occurs in the medium-soft ground, concentrating in the upper part of the pile and affecting the entire cross-section. Subsequent numerical analyses were conducted after reinforcing the soil layer around the top of the pile. The findings demonstrate that this reinforcement leads to a more uniform and rational distribution of internal forces along the pile, significantly reducing damage. Notably, there is no severe damage extending across the entire cross-section after reinforcement. This outcome highlights the potential for improving the force distribution in the pile foundations of nuclear power structures through appropriate soil layer reinforcement. The insights gained from this study provide valuable guidance for the seismic design of nuclear power structures.

A novel biaxial shaking table and its performance when investigating seismic actions

AbstractThe design of a new type of biaxial shaking table is presented. The shaking table is able to apply horizontal and vertical movements to models using two actuators. It is novel in that the two actuators are horizontally aligned, through its use of a scissor mechanism, and because of its compact design which permits simple anchorage to a laboratory strong floor. The scissor mechanism translates the movement of one of the actuators to a purely vertical movement at the table. The other actuator, which moves horizontally the scissor mechanism and its supports, causes the horizontal movement of the table. The horizontal and vertical movements are applied and controlled independently, individually or simultaneously. The capability of the shaking table to control and replicate a variety of uniaxial and biaxial movements is verified by conducting several shaking table experiments. This is done when the table is naked and when it supports a payload having a nonlinear dynamic response. Very good agreements between achieved and desired uniaxial and biaxial movements are attained. Rigidity of the scissor arm mechanism and connections, and preloaded roller bearings and rail blocks, are central to its success. Displacement errors, rolling, pitching and yawing of the table's top plate are negligible. The new table type is slightly more expensive than a uniaxial system, and substantially less expensive than a six degrees‐of freedom system, meaning biaxial vertical and horizontal shaking capability can now be achieved in a laboratory at reasonable cost.

Study on dynamic post-buckling stability of fast reactor vessels subjected to vertical vibration

Abstract As a lesson learned from the Fukushima nuclear accident, the importance of accident mitigation for Beyond Design Basis Events (BDBEs) is recognized. Excessive earthquake is a typical BDBE. During such events, the Fast Reactor Vessel (FRV) is vulnerable to buckling. The safety goal of FRV under excessive earthquake is to achieve a stable post-buckling state. Our previous study on bending buckling confirmed a global response stability under horizontal vibration. As a parallel study, this paper focuses on axial compression buckling under vertical vibration. Shaking table experiments using thin-walled cylindrical models (R/t=260) are carried out. Similar methodology is applied to investigate the buckling and post-buckling behavior. It is found that axial compression buckling shares an extensive similarity with bending buckling in both buckling mode and post-buckling behavior. Similar global response stability is confirmed due to phase-inverse phenomenon. After buckling, buckling failure becomes stable and does not progress further even when an intense input amplitude is continuously applied. The vibrational load acts as a displacement-controlled load in the out-of-phase domain such that immediate collapse is prevented. Most input energy is dissipated in hysteresis loops rather than being carried by the mass. These mechanisms are independent of input waveform and can be applied to an arbitrary seismic input. In addition, a conservative limit displacement for global response stability is identified. Moreover, the effect of the input frequency ratio, the initial geometrical imperfection and the gravitational force on the post-buckling behavior are clarified.

Study on deformation patterns of tunnel isolation layers and seismic response of a shield tunnel

Tunnel seismic isolation is an effective measure to reduce the seismic response of tunnels; however, the unclear mechanism limits the popularization and application of this measure. In this study, the deformation patterns of tunnel seismic isolation were investigated using theoretical analyses and shaking-table experiments. The analytical solution for the dynamic response of the seismic isolation tunnel under SH-wave incidence was derived using the wave-function expansion method. A novel loading device based on the reaction-displacement method was used to study the mechanism of the tunnel seismic isolation layer. It was found that the seismic isolation layer helped reduce and spread the deformation from the outer surface to the inner surface, effectively minimizing the deformation affecting the lining. The DSCF response of the lining is subsequently reduced. Moreover, the installation of seismic isolation did not result in a significant alteration in the acceleration response of the tunnel. These results provide a reference for the seismic isolation design of tunnels.

Seismic Wave Amplification Characteristics in Slope Sections of Various Inclined Model Grounds

The collapse of slopes caused by earthquakes can lead to landslides, resulting in significant damage to both lives and structures. Seismic reinforcement of these slopes can protect social systems during an earthquake. In South Korea, where more than 70% of the land is mountainous, the stability of slopes is of paramount importance compared to other countries. While many seismic designs are based on peak ground acceleration (PGA), there is relatively little consideration given to the extent of PGA’s influence, and few studies have been done. This study aims to assess the seismic amplification of slopes with multilayers using a 1 g shaking table and verify the results through numerical analysis after confirming the impact of PGA at specific points. Typically, slope model experiments are conducted on single-layered ground models. However, actual ground conditions consist of multiple layers rather than a single layer, so a multi-layered model was created with different properties for the upper and lower layers. Two multi-layered ground models consisting of two layers were created, one with a flat ground surface and the other with a sloped surface. The properties of the two layers in each model were configured as a single layer to create the slope models. The peak ground acceleration (PGA) of the four ground models was compared, revealing that seismic wave amplification increases as it moves upward, and the amplification is even greater when transitioning from the lower to the upper ground layers, leading to different dynamic behavior of the slope. Through the contour lines, the influence of PGA was further confirmed, and it was found that approximately 60% of the PGA impact occurs at the topmost part of the slope on average. Analysis of the earthquake waves showed that the top of the slope experienced an average amplification of about 31.75% compared to the input motion, while the lower part experienced an average amplification of about 27.85%. Numerical analysis was performed using the ABAQUS program, and the results were compared with the 1 g shaking table experiments through spectral acceleration (SA), showing good agreement with the experimental results.

A self-powered and self-sensing hybrid energy harvester for freight trains

Freight trains, being crucial for economic development, often face challenges due to the lack of electrical infrastructure. In this study, a self-powered and self-sensing hybrid energy harvester system (SS-HEH) is proposed, it consists of an electromagnetic generator (EMG), a piezoelectric energy harvester (PEH), and an energy input module. The proposed EMG utilizes a rolling magnet to intersect the square coil, thereby better adapting to the operational conditions of freight trains and producing higher electrical energy output. Additionally, the PEH converts bogie vibration signals into electrical signals to detect bogie operations. The EMG acts on the PEH, inducing bending and generating electrical signals. Conversely, the PEH acts on the EMG to maintain it horizontally, enhancing its ability to absorb the vibration energy of the bogie and forming a bistable system. Furthermore, at a speed of 40 km/h, the EMG voltage with PEH increased by 43.75 % compared to the scenario without PEH. The electrical performance of the SS-HEH was assessed through shake table experiments, yielding an RMS voltage of 11.5 V and output power of 74.1 mW. In addition, combined with deep learning, SS-HEH has an accuracy of 97.41 % in detecting the operating status of bogie.

Shaking table simulation of soft sediment deformation structures in lacustrine sediments

Soft sediment deformation structures (SSDSs) in lacustrine sediments could record paleoearthquakes in tectonically active areas. However, their interpretations of deformation and triggering mechanisms still exist disagreement due to the lack of understanding of natural formation processes of SSDSs. In this study, two large shaking table experiments of saturated lacustrine sedimentary sequences, including Model 1 (simple stratigraphic system of thick silty-clay and sand layer) and Model 2 (stratigraphic systems of thin silty-clay and sand alternating layers) were carried out at the different peak ground accelerations (PGA) in order to simulate the earthquake-triggered SSDSs on the basis of field investigation in Tashkorgan of western China. The results showed that there were no SSDSs formed at the PGA 0.125g, and the excess pore-water pressure ratio (γμ) measured in the sand layer was lower than 0.1; sand volcanos, pipes and sand veins were formed at the PGA 0.25g, and the γμ value of the sand layer reached about 0.2 with the maximum liquefied depths of nearly 30 cm, indicating that weak liquefaction occurred in the sand layer; sand volcanos, pipes, sand veins, diapirs, load and flame structures, ball-and-pillow structures, silty-clay deformation structures were formed at the PGA 0.5g and 0.8g, and the γμ value of sand layer reached about 0.91 and 0.94 with the maximum liquefied depths of nearly 60 cm and 100 cm, respectively. The γμ value of silty-clay layers measured in all the tests was lower than 0.1, indicating that little liquefaction but thixotropy happened in the silty-clay layers. The tests showed that liquefied SSDSs could form at the PGA 0.25g, while thixotropic and gravity-driven SSDSs could form until the PGA reached 0.5g. This study also provided insights for single or closely spaced shaking events being responsible of superposed deformed beds. The simulated SSDSs have striking resemblance to that of ones identified in the field, supporting the earthquake triggering of SSDSs in the Tashkorgan area.

Integrating low-cost GNSS and MEMS accelerometer for precise dynamic displacement monitoring

We assess the performance of the self-developed receiver coupling dual-frequency low-cost GNSS chipset and IMU MEMS sensor. The system also comprises software dedicated to vibration monitoring based on relative kinematic positioning in a post-processing mode. The observation assessment reveals high accuracy of low-cost GNSS and MEMS accelerometer data. The Septentrio Mosaic X5 chipset exhibits competitive to high-grade receivers’ phase observation noise, outperformance in code noise level and observation auto-correlation at a level that may be neglected even in high-rate applications. The evaluation of the MEMS accelerometer data proves that the sensor accuracy is adequate for vibration monitoring. With the shake table experiment, we examine the performance of vibration recovery. An advantage of the coupled solution over a GNSS-only one is documented with a 15 % reduction of the amplitude error. The backward smoothing of coupled solutions drives the next 20 % error drop. Finally, the high performance of the coupled solution based on low-cost GNSS & accelerometer is confirmed by a mean amplitude error of 0.4 mm. The frequency analyses indicate that both coupled and single-sensor solutions precisely detect the vibration frequencies; however, they also confirm the outperformance of the former over the latter. The power spectra of the recovered displacement time series accentuate the benefits of GNSS + accelerometer fusion and backward filtering for reducing displacement noise.

Enhancing Building Stability and Seismic Resilience with Water-Added Tuned Mass Dampers

These days, the construction industry is increasingly producing buildings with extremely low damping values. Under structural vibrations caused by storms and earthquakes, structures can collapse easily. There are now several methods for reducing structural vibrations, and one of the methods currently employed is the Tuned Mass Damper (TMD). Research is being conducted to determine its performance and importance. The entire damper was tuned for various constructions. An eight-story model specifically designed for the structure was used in this study to observe the structure's response with and without TMD during shaking table experiments. Compared to passive control devices (PTMDs), Active Tuned Mass Dampers (ATMDs) are more efficient as they are active control devices powered externally. By maintaining the structure's frequency, damping, and stiffness constant, other variables such as the percentage reduction in structural capacity can effectively control structure vibrations. The findings and observations from TMD studies can be used to address challenges in earthquake structural control considering current technological limitations and energy demands. The results illustrate significant improvements with damping: the damped structure experienced a 21% increase in acceleration, a 17% increase in velocity, and a 79% reduction in displacement compared to the un damped structure. These findings underscore the effectiveness of damping in mitigating earthquake-induced vibrations.

Shaking Table Experiment and Numerical Simulation Research on Earthquake Safety of Wheelchair Users

<p>由過往的研究得知，輪椅使用者在地震時可能會面臨到的輪椅振動行為包含(傾斜角度由小到大)： Walking(走步)，Rocking(搖擺)，以及最危險的行為Overturning(翻覆)；其中翻覆還可分成側向翻覆以及向後翻覆。而受到不同的激振加速度振幅、頻率(可對應到各建築物樓高自振頻率)，則會觸發不同的輪椅振動行為發生，其中激振加速度振幅愈大、頻率愈低(高樓層建築物)愈容易造成輪椅的翻覆。本研究透過實驗以及建立數值模擬的方式發現，在同樣的加速度振幅作用下，當激振頻率低於輪椅翻覆的最高頻率時，輪椅亦會翻覆。因此，輪椅的翻覆頻率為一段範圍區間而非一特定值。當加速度振幅增加時，輪椅翻覆的頻率範圍也會提升。因此，對應到不同的加速度振幅，會有不同的輪椅翻覆頻率範圍。最後，由本研究的振動台實驗結果得知，以外部束制去固定輪椅後方的兩個把手，最能夠避免輪椅向後與左右傾倒。</p> <p> </p><p>Based on previous research, it has been found that wheelchair users may experience different wheelchair vibration behaviors during earthquakes, ranging from walking, rocking, to the most dangerous behavior—overturning, which can occur in sideways or backward directions. Corresponding to different acceleration amplitudes and excitation frequencies related to the natural frequencies of different building heights, different wheelchair vibration behaviors can be triggered. Among them, higher excitation accelerations and lower frequencies typically associated with taller buildings are more likely to result in wheelchair overturning. This study, through experiments and numerical simulations, has discovered that under the same acceleration amplitude, when the excitation frequency is lower than the highest overturning frequency of the wheelchair, the wheelchair can still overturn. Therefore, the overturning frequency of the wheelchair is within a range of values rather than a specific value. As the acceleration amplitude increases, the highest overturning frequency of the wheelchair also increases, and the low-frequency range expands accordingly. Consequently, different acceleration amplitudes correspond to different ranges of wheelchair overturning frequencies. Finally, the shaking table experimental results of this study indicate that fixing both handrails of the wheelchair with external restraints can effectively prevent the wheelchair from overturning in both backward and sideways directions.</p> <p> </p>

Tunable High-Static-Low-Dynamic Stiffness Isolator under Harmonic and Seismic Loads

High-Static-Low-Dynamic Stiffness (HSLDS) mechanisms exploit nonlinear kinematics to improve the effectiveness of isolators, preserving controlled static deflections while maintaining low natural frequencies. Although extensively studied under harmonic base excitation, there are still few applications considering real seismic signals and little experimental evidence of real-world performance. This study experimentally demonstrates the beneficial effects of HSLDS isolators over linear ones in reducing the vibrations transmitted to the suspended mass under near-fault earthquakes. A tripod mechanism isolator is presented, and a lumped parameter model is formulated considering a piecewise nonlinear–linear stiffness, with dissipation taken into account through viscous and dry friction forces. Experimental shake table tests are conducted considering harmonic base motion to evaluate the isolator transmissibility in the vertical direction. Excellent agreement is observed when comparing the model to the experimental measurements. Finally, the behavior of the isolator is investigated under earthquake inputs, and results are presented using vertical acceleration time histories and spectra, demonstrating the vibration reduction provided by the nonlinear isolator.

Seismic behavior of piles-supported pier-superstructure to liquefaction-induced lateral spreading considering variability of soil permeability

This study characterizes the effect on different engineering demand parameters owing to lateral spreading caused by liquefaction. 1 g large-scale shaking table experiments were conducted along with efficient numerical simulations of the piles-supported pier-superstructure system response to strong earthquakes. An integrated nonlinear numerical method was established and evaluated with the results of the shake table experiments, and the seismic response characteristics of the system was discussed by combining the experimental and numerical results. The influence of the initial soil hydraulic conductivity on soil liquefaction was evaluated and the inertia and kinematic effects were evaluated employing cross-correlation analyses. The results indicated that soil softening diminished as the permeability coefficient increased, and consequently the lateral displacements of soil and superstructure decreased, and the superstructure acceleration demand increased. Increased permeability coefficient shifted the fragile location of the piles-supported pier-superstructure from the liquefiable soil bottom to the pier bottom. Finally, the inertial effect increased on pile curvature near pile head while the kinematic effect decreased as the permeability coefficient increased.

Dynamics of a rocking bridge with two‐sided poundings: A shake table investigation

AbstractDuring strong earthquakes, the footing of a rockable bridge can temporarily and partially separate from the support. This rocking motion can activate rigid‐like motions, reducing the deformation along the height of bridge piers and leading to smaller bending moments. As a result, rockable footing has been considered as a possibility for low‐damage seismic design of structures. For bridges, the seismic‐induced interaction between girders and adjacent abutments can change the structural dynamics due to the impeded girder movements. Although bridges with rockable footing, for example, the South Rangitikei viaduct, have been constructed, research on rockable bridges mainly focused on a single‐segment case. Physical experiments on rockable bridges considering pounding are very limited. In this work, large‐scale shake table experiments were performed on a two‐segment bridge model with abutments. The cases without pounding and with girder‐girder pounding alone were considered as references to help interpret the results. To investigate the consequence of footing rocking, the results of the rockable bridge on a rigid base were compared to that of the fixed‐base bridge. The study reveals that compared to a fixed‐base segment, the girder of a rockable segment is easier to move laterally. This change in dynamics due to rocking leads to less maximum pounding forces and thus reduces the damage potential to girders and abutments.

Numerical analysis on seismic response and failure mechanism of articulated pile–structure system in a liquefiable site from shaking-table experiments

Numerical analysis on seismic response and failure mechanism of articulated pile–structure system in a liquefiable site from shaking-table experiments

Structural Stability Evaluation of Natural Fiber Retrofitted Low-Cost Rammed Earthen Houses Under Seismic Loading

Earthen houses constructed using the rammed technique have long served for housing across the globe. However, despite their environmental benefits, these houses may pose unacceptable earthquake risks for the communities. To address this, the current study focuses on investigating the seismic response of unreinforced and retrofitted rammed earth model houses using unidirectional shaking table experiments. Retrofitting is performed using two different approaches. The first method is the traditional way using cement, lime and natural fibers like straw and jute mixed with soil. The second method is a new and innovative approach that uses bitumen-treated natural fibers such as jute and bamboo strips as external encasing reinforcement along with special L-shaped corner reinforcement using jute and bamboo sheets. The study shows that rammed earth houses retrofitted using the proposed novel and low-cost methods with jute/bamboo fibers demonstrate promising results in terms of structural strength and ductility compared to the stabilized counterpart. The fundamental period of the retrofitted and unreinforced houses is found in the order of 0.08 and 0.12 indicating an enhancement in lateral stiffness depending on various level retrofitting methods. The study provides valuable insights and points toward potential changes in the seismic design guidelines for low-cost rammed earthen houses.

Pore-pressure-dependent performance of rocking foundations

This study explores the concept of rocking foundations to mitigate damage during seismic events. By weakening the footing intentionally, the foundation acts as a “fuse” to prevent plastic hinges from forming in columns. Shake table experiments were conducted on a lightweight prototype deck mass-column-footing model founded on a fine, medium-dense sand, in two states of nearly dry and saturated. Kinetic energy dissipation, hysteresis, and decay are examined for various structure masses, for two nominal low and high motion frequencies. Findings suggest that energy dissipation is higher in saturated sands ― as compared to nearly dry and despite the absence of liquefaction ― due to fluctuating pore water pressure and a suction effect that evolves beneath foundations’ edge. Where the substrate retains its original porosity, flow of water and subsequent damping becomes pivotal mechanisms to enable the rocking motion. In dry sands, energy dissipation occurs mainly through rotation, and enhances with motion frequency (from testing 3–5 Hz). In saturated sands, energy dissipation occurs predominantly through plastic settlement, and becomes less effective with motion frequency. Lighter structures experience greater rotational movement, especially in the case of dry sands. That enhanced rotational movement is drove by lower rotational stiffness. Overall, lighter structures facilitate the re-centring of the foundation upon rocking motion.