Large-scale Shaking Table Tests Research Articles

A Stand-Alone Smart Camera System for Online Post-Earthquake Building Safety Assessment.

Computer vision-based approaches are very useful for dynamic displacement measurement, damage detection, and structural health monitoring. However, for the application using a large number of existing cameras in buildings, the computational cost of videos from dozens of cameras using a centralized computer becomes a huge burden. Moreover, when a manual process is required for processing the videos, prompt safety assessment of tens of thousands of buildings after a catastrophic earthquake striking a megacity becomes very challenging. Therefore, a decentralized and fully automatic computer vision-based approach for prompt building safety assessment and decision-making is desired for practical applications. In this study, a prototype of a novel stand-alone smart camera system for measuring interstory drifts was developed. The proposed system is composed of a single camera, a single-board computer, and two accelerometers with a microcontroller unit. The system is capable of compensating for rotational effects of the camera during earthquake excitations. Furthermore, by fusing the camera-based interstory drifts with the accelerometer-based ones, the interstory drifts can be measured accurately even when residual interstory drifts exist. Algorithms used to compensate for the camera’s rotational effects, algorithms used to track the movement of three targets within three regions of interest, artificial neural networks used to convert the interstory drifts to engineering units, and some necessary signal processing algorithms, including interpolation, cross-correlation, and filtering algorithms, were embedded in the smart camera system. As a result, online processing of the video data and acceleration data using decentralized computational resources is achieved in each individual smart camera system to obtain interstory drifts. Using the maximum interstory drifts measured during an earthquake, the safety of a building can be assessed right after the earthquake excitation. We validated the feasibility of the prototype of the proposed smart camera system through the use of large-scale shaking table tests of a steel building. The results show that the proposed smart camera system had very promising results in terms of assessing the safety of steel building specimens after earthquake excitations.

Study on Identification of SSI Damping System Based on Large-Scale Shaking Table Test

Damping system represents the energy dissipation characteristics of the overall structural system. The correct identification of damping system is not only the premise of selecting dynamical analysis method, but also the foundation of obtaining accurate results in seismic analysis. Traditionally, the identification of damping system under dynamic action is based on material properties. However, this method is lack of theoretical and experimental research. Based on fundamental identification method, the paper presents the study on the consistency of dynamic characteristics between different parts by shaking table test. The changing law of SSI damping system in different dynamic processes is investigated. The experimental results indicate that SSI system manifest obviously classical energy dissipation characteristics under certain conditions and can be considered as an approximate classical damping system.

Validation of numerical model based on large-scale shaking table test of liquefied site

Based on the completed large-scale shaking table test of liquefaction free field, the OpenSees computational platform was used to establish a numerical model of liquefiable free-field shaking table test in this study. In the numerical modeling, simulation of soil displacement and pore pressure using two-phase fully coupled u-p form. The comparison of shaking table test results shows that the established numerical model can reasonably simulate the seismic response of liquefiable soils, and further verify the reliability of the numerical model. At the same time, the distribution characteristics of soil excess pore water pressure at the critical moment were analyzed. This paper provides an effective numerical method for dynamic response analysis of liquefied soil.

Experimental study on the dynamic characteristics of low-angle loess slope under the influence of long- and short-term effects of rainfall before earthquake

Landslides on low-angle slopes can be caused under the coupled effect of rainfall and earthquake. In order to investigate the influence of duration of time between rainfall and earthquake on the scale and failure mode of landslides, a low-angle loess slope at Lanzhou New Area was adopted as a prototype, and a large-scale shaking table test was performed. By using self-designed artificial rainfall equipment, 30 mm of rainfall 12 h before shaking and 20 mm rainfall immediately before shaking were exerted on the slope model to investigate the responses and determine the differences in the failure mode of the low-angle slope under different rainfall cases. To measure the dynamic response of the test model at each working condition, 18 acceleration sensors, 7 soil-pressure sensors, 10 pore water-pressure sensors, and optical measurement techniques were used. The results show that the acceleration amplification effect increased with increasing intensity and the soil pressure increased with decreasing elevation under the long-term effects of rainfall before earthquake, but the value on the slope surface decreased under the short-term effects of rainfall before earthquake. The dynamic pore pressure value varied considerably between positive and negative and the maximum displacements at slope surface increased about 69.7% under the short-term effects of rainfall before earthquake. Large displacements and deep cracks occurred on the surface of the slope, mainly caused by the loess losing its strength and the large inertial force on the surface owing to the long-term effect of rainfall before the earthquake. The damage to the low-angle slope was mainly caused by liquefaction and the loss of loess strength under the influence of short-term rainfall before the earthquake. The failure of the slope was soil flow, which was similar to the sliding process of the Yongguang village landslides. Finally, we note that the effect of coupled effect on the low-angle slope should be evaluated in future work from two aspects: the intensity of rainfall and earthquake and the time when rainfall occurred before the earthquake.

Shaking table test of seismic responses of anchor cable and lattice beam reinforced slope

As a combined supporting structure, the anchor cable and lattice beam have a complex interaction with the slope body. In order to investigate the seismic behaviors of the slope reinforced by anchor cable and lattice beam, a large-scale shaking table test was carried out on a slope model (geometric scale of 1:20) by applying recorded and artificial seismic waves with different amplitudes. The acceleration and displacement of the slope, the displacement of lattice beam and the axial force of anchor cable were obtained to study the interaction between the slope and the supporting structure. The test results show that: (1) the acceleration responses of the slope at different relative elevations display obvious nonlinear characteristics with increasing of the peak ground acceleration (PGA) of the inputted seismic waves, and the weak intercalated layer has a stronger effect on acceleration amplification at the upper part of the slope than that at the lower part of the slope; (2) the frequency component near the second dominant frequency is significantly magnified by the interaction between the slope and the supporting structure; (3) the anchor cables at the upper part of the slope have larger peak and residual axial forces than that at the lower part of the slope, and the prestress loss of the anchor cable first occurs at the top of the slope and then passes down; (4) the peak and residual displacements inside the slope and on the lattice beam increase with the increase of relative elevation. When the inputted PGA is not greater than 0.5 g, the combined effect of anchor cable and lattice beam is remarkable for stabilizing the middle and lower parts of the potential sliding body. The research results can provide a reference for the seismic design of such slope and the optimization of supporting structure.

Failure modes of slope stabilized by frame beam with prestressed anchors

A large scale shaking table test was carried out to study the failure modes of the slope stabilized by frame beam with prestressed anchors. Based on the Hilbert–Huang Transform (HHT), the damage identification analysis was performed by using the marginal spectrum obtained from the acceleration responses. The results from the tests show that the seismic damage of the slope stabilized by the frame beam with prestressed anchors mainly occurs at the top of the sliding mass and on the free surface of the slope. The upper part of the sliding layer begins to damage under the seismic excitation with low amplitudes. Because of existing anchor cable and frame beam, the middle and lower parts of the slope display better seismic performance. The seismic failure mode of the slope stabilized by frame beam with prestressed anchors is mainly expressed by the penetration of tensile cracks and longitudinal cracks at the top of the sliding mass, collapse and hollowing of free surface at the upper part of the slope, and overall slippage of sliding mass. The slope has an elevation amplification effect on the amplitude of the Hilbert energy spectrum and changes the time-frequency distribution of the energy spectrum.

Experimental study on seismic response of soilbags-built retaining wall

The seismic performance of soilbags-built retaining wall model was studied experimentally. A series of small-scale shaking table tests with the input of different amplitude sinusoidal waves and a large-scale shaking table test in a designed laminar shear box with the input of the Wenchuan earthquake wave were carried out on soilbags' retaining wall models. For comparison, the small-scale shaking table tests were also conducted on horizontally reinforced retaining wall models. The horizontal acceleration responses, the Fourier spectra, the dynamic earth pressure and the lateral displacements of soilbags' retaining wall models were investigated in shaking table tests. The results show that the seismic response of the soilbags' retaining wall is equivalent to or even slightly better than that of the horizontally reinforced retaining wall. The fundamental frequency and the Fourier spectral characteristics of the soilbags’ retaining wall are similar to those of backfill sands. The dynamic earth pressure of the wall model fluctuates almost synchronously with the input Wenchuan wave and no residual earth pressure is induced by the seismic loading. The permanent lateral displacements are small when subjected to multiple shakings, providing a proof that the retaining wall of soilbags has a good seismic performance.

Identification of SSI Damping System Based on Large-Scale Shaking Table Test

Damping system represents the pattern and characteristics of energy dissipation in a dynamical system. The correct identification of a damping system is not only the premise of selecting dynamical analysis method but also the foundation of obtaining accurate results in seismic analysis. Traditionally, the identification of a damping system under seismic waves is based on material properties. However, this method is the lack of theoretical and experimental research. Based on the most fundamental identification method, the paper presents the study on the consistency of dynamic characteristics between different parts and continuity of motion states at the interfaces of the SSI (Soil-Structure Interaction) system by shaking table test. The changing law of SSI damping system in different dynamic processes is investigated. The experimental results indicate that the SSI system manifests obviously classical energy dissipation characteristics under certain conditions and can be considered as an approximate classical damping system.

Contrastive analysis of dynamic response of tailings dam with and without geofabriform by shaking table model test

Construction using geofabriform is a new promising technology to build fine grain tailings dam. Large-scale shaking table tests are conducted in this study to investigate the dynamic performances in terms of horizontal acceleration and displacement of the tailings dam with and without geofabriform subject to horizontal earthquakes. Test results indicate that the seismic performance of the tailings dam with geofabriform is significantly better than that of tailings dam without geofabriform. The two types of tailings dams have different failure modes under the action of earthquake. The acceleration amplification factor(Am), vertical displacement and horizontal displacement of the tailings dam with geofabriform under the same seismic acceleration input are smaller than that of the tailings dam without geofabriform, the maximum attenuation amplitude of the Am at the dam slope reaches to 81%. The horizontal displacements of the two types of dams are nonlinearly distributed in the height direction and the geotextile bags of the tailings dam have an upward displacement and are tilted upward. According to the failure mode of the tailings dam with geotextile bags, it is recommended to strengthen the drainage measures and set up anti-slide piles at the bottom of the geotextile bags body to strengthen the tailings dam.

Seismic performance of helical piles in dry sand from large-scale shaking table tests

Recent earthquakes have highlighted the need for safe and efficient construction of earthquake-resilient structures. Meanwhile, helical piles are gaining popularity as a foundation not only for new construction, but also retrofitted structures, owing to their advantages over conventional driven pile alternatives. In addition, several structures supported by helical piles in New Zealand sustained minimal damage during the Christchurch earthquake, proving that helical piles can be a suitable foundation option in highly seismic areas. However, there is a knowledge gap concerning their seismic performance. Therefore, the current study investigates the performance of helical piles through a full-scale shaking table test programme – the inaugural large-scale seismic testing programme performed on helical piles. The experimental set-up involved installing ten steel piles with different configurations and pile head masses in dry sand enclosed in a laminar shear box mounted on the Network for Earthquake Engineering Simulation at University of California, San Diego (NEES/UCSD) large high-performance outdoor shaking table (LHPOST). The loading scheme consisted of white noise and two earthquake time histories with varying intensity and frequency content. The experimental results are presented in terms of the natural frequency and response of test piles (peak deflections). The effects of loading frequency and intensity and the pile's geometrical configuration and installation method were evaluated.

Responses of reinforced soil retaining walls subjected to horizontal and vertical seismic loadings

Vertical ground acceleration is a component in an earthquake loading, and in some cases, the vertical to horizontal acceleration ratio (V/H ratio) may be very large. However, the influences of the vertical seismic loading on the responses of reinforced soil retaining walls are still not clear. In this study, a Finite Element procedure was further validated by a large-scale shaking table test subjected to both horizontal and vertical seismic loadings. It was then employed to investigate the seismic responses of two models considering a large range of earthquake loading scenarios. The results showed that the vertical ground acceleration might alter the shear wave propagation in the reinforced soil, but the Arias intensity at the top of the reinforced soil correlated well with the maximum reinforcement load. The vertical seismic loading mostly increased the reinforcement load, but reduced the residual facing displacement. The reduction of lateral facing displacement may have come from the increase of the confining pressure and the change in the far-field lateral displacement due to the vertical seismic loading. Some limitations of the present study are also discussed.

Graphene sensing meshes for densely distributed strain field monitoring

The objective of this study is to design and validate distributed strain field monitoring using a patterned nanocomposite “sensing mesh” that is coupled with an electrical impedance tomography (EIT) measurement strategy and algorithm. Although EIT has been used in other studies and in conjunction with a piezoresistive thin film for spatial damage detection, different strain components cannot be directly extracted from reconstructed EIT conductivity maps. Therefore, this study seeks to address this issue by patterning piezoresistive graphene-based thin films to form a mesh-like pattern. The high aspect ratio of each nanocomposite grid interconnect acts as a linear distributed strain sensor, capable of resolving strains along the entire length and direction of the element. This study first began with the design, fabrication, and characterization of the strain sensing response of a graphene-based thin film of high strain sensitivity. Second, the strain-sensitive film was spray-coated onto patterned polymer substrates to form the sensing meshes, which were then subjected to load tests. Upon validating distributed strain field monitoring through EIT, its applicability for field implementation and damage characterization was also demonstrated by instrumenting sensing meshes in the column of a seven-story reinforced-concrete building subjected to shaking table earthquake excitations. The large-scale shaking table test results successfully validated distributed damage detection.

Effect of installation geometry on dynamic stability of small earth dams retrofitted with a geosynthetic clay liner

Geosynthetic clay liners (GCLs), used to repair small earth dams, are typically installed with the GCL panel placed parallel to the upstream slope of the dam or on the surface of benches cut into the upstream side of the earth dam fill. While the former requires less earthwork, leading to a more cost-effective and rapid construction, it can potentially introduce a plane of weakness if the interface shear strength between the GCL and the cover soil is less than the shear strength of the cover soil. The inclusion of benches in the upstream slope of an earth dam can potentially be an effective strategy for reducing the significance of this preferential failure plane, resulting in an increased seismic performance during earthquakes. However, the expected increase in seismic performance has not yet been quantified in large-scale shaking table tests. In this study, a full-scale shaking table test on an earth dam with a GCL installed parallel to the upstream slope of the dam is reported and compared to previously published results from tests on an identical earth dam with the GCL placed in the benched configuration under the same seismic boundary conditions. The results indicate that, for the configuration tested, the seismic deformation of the benched installation was half of that of the earth dam with the GCL installed parallel to the slope, providing significant motivation for adopting the benched installation method.

Seismic response of irregular underground structures under adverse soil conditions using shaking table tests

A series of large-scale shaking table tests were performed to investigate the seismic response of an underground subway structure with irregular sections in adverse soil conditions (soft and liquefiable sites). Emphasis is placed on the influence of the adverse soil conditions on the response of the irregular underground structures and over areas of soil-structure interface, involving buildup of pore pressures and resulting large deformations. The results indicate that the seismic responses of the structure and the soil were sensitive to input motions with richer low-frequency components. The seismic damage of the underground structure was more significant in the soft site as compared with that in the liquefiable site. The liquefiable site worked as a natural seismic isolation system for the underground structure, significantly reducing the damage potential to the model structure. Under the action of a strong earthquake, the horizontal displacement response of the liquefiable site sharply increased compared with that of the soft site. With respect to the structure response, the interlayer displacement of the structure in the soft site was approximately twice that in the liquefiable site. The lateral deformation of the structure was greater in the soft site and the interior structure column was more prone to damage. Correspondently, the peak and the residual strains in the structural components in the soft site were higher than those in the liquefiable site were. The results provided insights into the site effects of adverse soil conditions on the seismic response of underground structures, especially on the seismic damage process and the failure mechanisms of the structure members.

Comparative Analysis of Dynamic Responses of Different Rock Tunnel Slopes

Large-scale shaking table tests and numerical simulations are performed to analyze the commonality and difference of the seismic responses between two rock tunnel slopes. One is a slope with a single tunnel, the other is a slope with small spacing tunnel, and both have the same slope size and tunnel size. Two recorded ground motions with different amplitudes are applied in three directions. The results show that the acceleration amplification effect of two slopes both presents obvious nonlinear characteristics along the height of slope. The acceleration amplification effects of two slopes mainly appear at the middle-upper part of slope under horizontal seismic excitation, whereas those mainly appear near the slope crest under vertical seismic excitation. Whether in horizontal or vertical excitation direction, the acceleration amplification effect of the slope containing small spacing tunnel is greater than that of the slope containing single tunnel. There is a significant difference in seismic response between small spacing tunnel and single tunnel. The maximum horizontal displacements of two slopes are on the slope crest. With the increase of the input earthquake amplitude, the peak displacement of the slope containing small spacing tunnel is gradually approaching and exceeding that of the slope containing single tunnel. The arch springing, the tunnel vault, the middle rock pillar and the slope foot of the slope containing spacing tunnel require special enhancements for seismic design, whereas the special reinforcement area of the slope containing single tunnel is the arch springing and the tunnel vault.

Research on Crossing Tunnels’ Seismic Response Characteristics

A large-scale shaking table test system and corresponding numerical model are designed to study the seismic characteristics of crossing tunnels. The calculated results are in good agreement with experimental data, both the results suggest that: Loading the El-Centro seismic wave, the maximum acceleration in upper tunnel’s crossing center section is located in the crown, the maximum strain is located in the haunch; meanwhile, the maximum acceleration and strain in underpass tunnel’s cross center section are both located in the crown. Affected by the underpass tunnel, at the side wall bottom of the upper tunnel, tests data reveal that the crossing center’s maximum acceleration is reduced for 30.9% and the strain was enlarged 170% than the normal section. Affected by the upper tunnel, at the haunch of the underpass tunnel, tests data reveal the crossing center’s maximum acceleration is enlarged by 10.0% and the strain is 27.2% reduced than the normal section.

DEVELOPMENT OF A HIGH-SPEED VIDEOGRAMMETRIC MEASUREMENT SYSTEM WITH APPLICATION IN LARGE-SCALE SHAKING TABLE TEST

Abstract. The high-speed videogrammetric measurement system, which provides a convenient way to capture three-dimensional (3D) dynamic response of moving objects, has been widely used in various applications due to its remarkable advantages including non-contact, flexibility and high precision. This paper presents a distributed high-speed videogrammetric measurement system suitable for monitoring of large-scale structures. The overall framework consists of hardware and software two parts, namely observation network construction and data processing. The core component of the observation network is high-speed cameras to provide multiview image sequences. The data processing part automatically obtains the 3D structural deformations of the key points from the captured image sequences. A distributed parallel processing framework is adopted to speed up the image sequence processing. An empirical experiment was conducted to measure the dynamics of a double-tube five-layer building structure on the shaking table using the presented videogrammetric measurement system. Compared with the high-accuracy total station measurement, the presented system can achieve a sub-millimeter level of coordinates discrepancy. The 3D deformation results demonstrate the potential of the non-contact high-speed videogrammetric measurement system in dynamic monitoring of large-scale shake table tests.

Effects of pulse-like earthquake motions on a typical subway station structure obtained in shaking-table tests

A series of large-scale shaking table tests on a typical subway station structure were carried out for pulse-like earthquake motions. The propagation of earthquake motions in soils is explored. The effects of velocity pulse parameters (i.e., pulse shape, pulse frequency (fp), and pulse duration (Tpd)) on dynamic responses of the structure are analyzed from the viewpoint of the dynamic characteristics of soils. It is found that the site amplifies the frequency components of dynamic excitation in specific frequency bands (i.e., the amplification frequency band, AFB). With an increase in earthquake motion intensity, the AFB gradually moves towards low frequencies. Additionally, the bandwidth gradually narrows. The velocity pulse increases the amplitude of the first-mode shear deformation of soils and thus the seismic internal force response of underground structures. In addition, the effect of a one-sided pulse in terms of increasing the first-order shear deformation amplitude of soil is more pronounced than the effect of a two-sided pulse. Pulse-like earthquake motions with long pulse duration and multiple pulse cycles may trigger remarkable resonance-like phenomena of soils and further aggravate soil and structure responses when the main pulse frequencies are located in the AFB of soils.

Damping effects of different shock absorbing materials for tunnel under seismic loadings

Circular tunnels are widely used in infrastructure. Under the action of earthquakes, the destruction of circular tunnels will result in a large number of economic losses and casualties. Therefore, the study on shock absorption of tunnels is important. However, the research has not been sufficient on the effect of the damping layer on seismic response of a circular tunnel in sand. In this paper, the influence of the damping layer on the seismic response characteristics of circular tunnels in sand is studied by large-scale shaking table test. The actual El-centro wave is loaded to the model system in three directions during the tests. The input peak seismic acceleration values are 0.05 g, 0.1 g and 0.2 g. Then the effects of two different damping materials on the dynamic response characteristics of circular tunnels are analysed quantitatively. The test results show that the damping layer reduces the seismic response of the circular tunnel. The response accelerations of the tunnel bottom and crown without damping layer are greater than that with the damping layer, which indicates that damping layer absorbs the energy caused by the seismic motion. When the sponge rubber is used, the circular tunnel dynamic response is more attenuated than that with foam board. In conclusion, the shock absorbing layer can effectively reduce the seismic response of tunnel. As a result, the damage of the tunnel decreases under the earthquake. This study has clarified the isolation mechanism of the shock absorbing materials. It is recommended to use sponge rubber material as the shock absorbing layer.

A New Seismic Response Control Technique for Buildings Using Block And Tackle

The author proposed a new seismic response control system using a block and tackle (hereinafter, referred to as a dynamic pulley damper system) developed especially for the high-rise buildings. The proposed system has a configuration where a damper is installed on the track of the cable-stayed wire, amplifying the amount of movement of the wire by using a movable pulley that increases the damping effect to reduce the vibration of a building. we apply this system to connect the core structure (parking tower) and the surrounding frame (housing part) of a high-rise building. This system aims to reduce the earthquake response of the building by the force of the damper attached to the core structure. To verify the effectiveness of this response control system, two types of shaking table tests were conducted; one is the large-scale shaking table test using a magnetic damper, an-other one is the small-scale shaking table test using a steel damper. The mathematical model of the dynamic pulley damper system to implement the frame analysis was developed and the results of simulation analysis are compared with the experiments.