Shaking Table Tests Research Articles

Response of Building Frame to Vibrations Induced by Tunneling Study Using Shake-Table Tests

Response of Building Frame to Vibrations Induced by Tunneling Study Using Shake-Table Tests

Video comprehension-based approach for seismic damage recognition of freestanding non-structural components

With the emergence of seismic resilience concepts, the objective of buildings’ seismic design shifts from life safety to earthquake-induced functional consequences. The seismic damage of nonstructural components (NSCs) is paramount in economical loss assessment and post-earthquake functional recovery. To rapidly assess the seismic damage of NSCs, this paper leverages the video-comprehension techniques to customize a novel deep learning model (which is called two-pathway vision transformer for the damage state recognition, TPViT-DMSR) that can recognize the freestanding NSCs’ damage states through the video footage. This model includes a slow and fast pathways to analyze the object’s movement at different speeds. The two pathways are fused through a unidirectional connection, which allows damage information to be better shared across two pathways. To improve the robustness of the model, the trajectory attention mechanism is integrated. To demonstrate the model’s applicability and efficacy, a comprehensive video dataset that describes various freestanding NSCs’ movement behavior is compiled via a series of shaking table tests. The application result reveals that the TPViT-DMSR model performs at a desired level with the mean average precision achieving at 74.87%. The model is also applied to the video footage collected from past earthquake events. The application results highlight that the model can deliver a reliable estimate of the damage state for NSCs.

Shake table test on support uplift force of long-span cable-stayed bridge under longitudinal ground motions

Since the excessive seismic support uplift force may cause the support failure of long-span cable-stayed bridges, this study focused on the support uplift force at the auxiliary pier for a double-tower cable-stayed bridge with a main span of 1088 m. A shake table test was designed and performed based on the 1/35-scale test model scaled from the prototype bridge. Details of the test model, including the scale factor, structural member configurations, boundary conditions, and the numerical validation were briefly presented. The test results show that although only the longitudinal ground motion was applied, significant seismic support uplift and compression forces would be generated in the bearings at the auxiliary pier, resulting in the bearing uplift. The vertical vibration of the deck contributed by the first vibration mode of the test model was one of the main causes of the bearing uplift, but no rigid-like pounding effect occurred due to the vertical nonlinear mechanical behaviour of the bearing. Furthermore, the effect of the bearing uplift on the main seismic responses of the test model was negligible.

Numerical Simulation of Polymeric Strap Material Reinforced Walls Under Seismic Excitation

This paper presents a comparison between the two-dimensional finite element and experimental results of shaking table tests on six one-third-scale polymeric strap or polymeric geostrip reinforced walls performed under seismic excitation at given peak ground accelerations [Formula: see text]. The effects of initial tangent stiffness or the stiffness of polymeric strap material [Formula: see text] and the slope angle of the cohesionless backfill material [Formula: see text] on the maximum relative displacement, [Formula: see text], of the reinforced earth wall, the values of the horizontal incremental dynamic earth pressure [Formula: see text] with distributions, acceleration responses, horizontal dynamic active earth pressure coefficient [Formula: see text] and maximum dynamic tensile forces [Formula: see text] were assessed in this study. Moreover, the vertical dynamic active earth pressure coefficients [Formula: see text] and the angles of the resulting dynamic active force with horizontal [Formula: see text] were predicted from the numerical analysis. Closely matched responses between the experimental and numerical studies were attained. Data obtained from experimental and numerical studies illustrated that increasing the slope angle of the cohesionless backfill material resulted in an increase in the values of horizontal displacement in the walls, and in dynamic earth pressure and root mean square acceleration [Formula: see text]. Increasing the stiffness of the reinforcement material caused a decrease in horizontal reinforced earth wall displacement and increases in dynamic earth pressure. In addition, the conventional pseudostatic limit equilibrium methods overestimated [Formula: see text] values, whereas they underestimated [Formula: see text] values, and the recommended [Formula: see text] values by current design codes were not found to be compatible with the numerical and experimental results.

Shaking table tests on deformation pattern and failure mechanism of fault-crossing tunnels in non-rupture scenario

Tunnels, as critical underground infrastructures, often intersect with faults. Field investigations have underscored the susceptibility of fault-crossing tunnels to extensive damages during earthquakes. Hence, large-scale shaking table tests are conducted to investigate the deformation pattern and failure mechanism of fault-crossing tunnels under transverse excitation, particularly in non-rupture scenarios. The dynamic behavior of the tunnel, as expected, is dominated by the surrounding strata. Acceleration responses vary notably across different regions of the fault site. The disparity increases with the increments of seismic intensity and input frequency. The tunnel section at the interface between the fault and the hanging wall manifest the strongest acceleration, where the largest strains of the tunnel and most of the lining cracks also occur, highlighting its vulnerability to seismic vibrations. The damage-induced non-linearity of the tunnel is then identified by the decreasing dominant frequency thereof. The fault-crossing tunnel exhibits unique three-dimensional shearing-torsional deformations, elucidated through the test data and an analytical model. This deformation pattern provides a better understanding of the seismic responses of fault-crossing tunnels under seismic vibrations.

Shaking table tests of a one-quarter scale model of concrete hollow block masonry houses retrofitted with fiber-reinforced paint

Unreinforced masonry (URM) buildings are prone to significant damage when subjected to ground motion. Some strengthening methods have been proposed to increase the seismic capacity. However, the widespread adoption of these methods faces various challenges, including economic constraints experienced by common people in developing countries, the complexity of implementation, efficiency, and seismic safety of each technique. This paper introduces a new retrofitting method of fiber-reinforced paint using fiberglass as the primary reinforcing material. The advantage of this technique lies in its simplicity and ease of application, with the added benefit of using the paint to improve the appearance of the house. Two 1:4 scale concrete hollow block (CHB) masonry houses were constructed to represent unreinforced masonry and retrofitted masonry structures using fiber-reinforced paint (FR-Paint). The shaking table test results indicate that the retrofitted house model showed improvements of up to 18 times in deformation capacity and up to 13 times in energy dissipation compared to the non-retrofitted house model. FR-Paint has a robust performance even in high input motion at a seismic intensity JMA of 7 (Japan Meteorological Agency). This confirms that this retrofitting method has a high earthquake-resistant performance.

Numerical and experimental study of a suspension bridge with combined viscous-steel damping system under train and seismic loads

The longitudinal dynamic performance of long-span bridges with passive vibration control devices when subjected to vehicle and seismic loads has raised extensive attention of the civil engineering community. This study aims to provide numerical and experimental assessments of the dynamic performance of a railway suspension bridge with the Combined Viscous-Steel Damping System (CVSDS) under various excitations. The deck is simplified to a single-degree-of-freedom (SDOF) system according to the longitudinal vibration characteristics of the suspension bridge. The Dynamic Equation Method (DEM) and Fourier Expansion Method (FEM) are suggested for the equivalence of the spatiotemporal variable train loads to horizontal excitations. A simplified two-stage analytical model is proposed to simulate the restoring force characteristics and fuse-lock function of the CVSDS. Shake table tests are conducted to further illustrate the feasibility of the simplified model and evaluate the effectiveness of the CVSDS. The results indicate that the SDOF system is reasonable and satisfactory in simulating the deck displacement. The two-stage working mechanism of the CVSDS is verified by both the simulation and experiment, i.e. the viscous fluid damper works under train loads and the steel yielding damper operates under earthquakes. The vibration mitigation effectiveness of the CVSDS is remarkable.

Large post-liquefaction deformation of sand: mechanisms and modeling considering water absorption in shearing and seismic wave conditions

Large deformation of sand due to soil liquefaction is a major cause for seismic damage. In this study, the mechanisms and modeling of large post-liquefaction deformation of sand considering the significant influence of water absorption in shearing and seismic wave conditions. Assessment of case histories from past earthquakes and review of existing studies highlight the importance of the two factors. Based on the micro and macro scale mechanisms for post-liquefaction shear deformation, the mechanism for water absorption in shearing after initial liquefaction is revealed. This is aided by novel designed constant water-absorption-rate shear tests. Water absorption in shearing can be classified into three types, including partial water absorption, complete water absorption, and compulsory water absorption. Under the influence of water absorption in shearing, even a strongly dilative sand under naturally drained conditions could experience instability and large shear deformation. The mechanism for amplification of post-liquefaction deformation under surface wave load is also explained via element tests and theoretical analysis. This shows that surface wave–shear wave coupling can induce asymmetrical force and resistance in sand, resulting in asymmetrical accumulation of deformation, which is amplified by liquefaction. A constitutive model, referred to as CycLiq, is formulated to capture the large deformation of sand considering water absorption in shearing and seismic wave conditions, along with its numerical implementation algorithm. The model is comprehensively calibrated based on various types of element tests and validated against centrifuge shaking table tests in the liquefaction experiments and analysis projects (LEAP). The model, along with various numerical analysis methods, is adopted in the successful simulation of water absorption in shearing and Rayleigh wave-shear wave coupling induced large liquefaction deformation. Furthermore, the model is applied to high-performance simulation for large-scale soil-structure interaction in liquefiable ground, including underground structures, dams, quay walls, and offshore wind turbines.

Intelligent identification of moving forces based on visual perception

The task of identifying moving forces presents a challenging inverse problem for bridge health monitoring and condition assessment. Existing methods for identifying moving loads rely on complex structural response measurement equipment, resulting in inefficiency and elevated costs. To address these challenges, this study introduces an innovative intelligent identification method for moving forces on bridges using visual perception techniques. The proposed method utilizes cameras to capture displacement changes at specific points on the bridge surface to reconstruct moving forces in the time domain. Initially, numerical simulations were conducted to ascertain the feasibility and robustness of identifying moving forces based solely on the structural displacement response. This phase also investigates the influence of different measurement point combinations on identification accuracy. Subsequently, the accuracy of the proposed method in measuring the dynamic displacement response of the structure was carefully evaluated by an outdoor shaking table test. Furthermore, a meticulously designed simply supported beam model was fabricated, followed by the execution of precise vehicle-bridge coupling dynamic experiments. This phase rigorously validates the effectiveness and accuracy of the proposed moving force identification method at varying vehicle speeds. The obtained results substantiate the proposed approach's capability not only to comprehensively capture bridge response data for full-area monitoring but also to consistently and reliably identify information on moving vehicle forces. This study underscores a pioneering application of intelligent visual perception technology in the field of identifying moving forces. The introduced noncontact intelligent identification method is an effective solution for monitoring moving forces on bridges, which has a wide range of applications in the future.

Shaking table test for seismic performance of rock slope reinforced by C&S–R anchor cables

To investigate the seismic reinforcement performance of compression and self-recovery (C&S–R) anchor cables, a series of shaking table comparison tests were conducted on rock slopes reinforced by two types of anchor cables: C&S–R anchor cables and conventional anchor cables, under different seismic intensities. During the tests, multiple accelerometers, displacement meters and strain gauges were synchronously arranged to monitor the strain of anchor cables and the dynamic response of the anchored slopes. The test results reveal that C&S–R anchor cables had better seismic performance. Compared to conventional anchor cables, C&S–R anchor cables had a peak axial strain reduction of approximately 23.0% and an increase in seismic intensity of 0.1g–0.2g. The final natural frequencies of the slope reinforced by C&S–R anchor cables and that of the slope reinforced by conventional anchor cables were 31.25 Hz and 26.1 Hz, respectively, confirming that C&S–R anchor cables reduce the internal damage of the anchored slopes during earthquakes. The results provide guidance and basis for the seismic optimization design of anchored slopes.

Seismic performance of railway bridges with novel ductile piers under near-fault earthquakes

The destructive force of near-fault earthquakes presents a significant challenge to railway bridges. To enhance the seismic resilience of railway bridges under such conditions, a novelly designed ductile pier is introduced herein, accompanied by a analysis of its stiffness, damping characteristics, and shear capacity. The analysis reveals that the ductile pier exhibits reduced stiffness and increased viscous damping ratio when compared to the traditional pier. Subsequently, a finite element model of a typical railway simply-supported girder bridge is established and verified through shaking table tests. Furthermore, the near-fault seismic wave synthesis method is introduced, and the synthesized near-fault seismic waves are input into the traditional pier model and the ductile pier model for seismic analysis. The findings demonstrate that the ductile pier effectively diminishes girder acceleration and bearing displacement while enhancing pier energy dissipation. Additionally, the ductile pier is proved effective in safeguarding the core concrete during significant seismic events.

Multi-axial computational model for simulating the seismic behavior of concrete columns including axial collapse

This paper describes a coupled multi-axial material model that can capture the interaction between axial/shear/flexure and simulate the lateral cyclic response of non-retrofitted and retrofitted concrete columns under seismic loads up to complete loss of lateral and axial strength. The new material model is intended for use within two-dimensional lumped-plasticity framework and implemented in the open-source simulation software OpenSees as CMACA2D. The material model was calibrated using a newly compiled database of 719 cyclic and monotonic pushover column tests and only requires the input of column geometric and material properties. It includes several capacity models to capture all the salient lateral and axial strength-degradations including flexure, shear, flexure-shear, splice, up to complete axial collapse. These capacity models for each axial/shear/flexure degree-of-freedom (DOF) depend on the boundary conditions and applied demands in its own and other DOFs and constantly change during the analysis so the governing strength-degradation mode is not known a priori of the analysis. The material model employs an energy dissipation term to define the cyclic behavior response and to adjust the strength damage rate observed in test data. Finally, the performance of the proposed computational tools is compared with results from shake table tests.

Rubber-sand infilled soilbags as seismic isolation cushions: experimental validation

This study proposes the use of soil bags filled with a rubber sand mixture (SFRSM) to address the issue of weak stability associated with rubber-sand layers for seismic isolation. To evaluate the dynamic characteristics of the SFRSM, large-scale cyclic simple shear tests were conducted to investigate the effects of rubber content, vertical pressure, shear displacement amplitude, fill percentage, and laying scheme. Furthermore, shaking table tests were carried out to evaluate the impact of vibration intensity and frequency on the seismic isolation of SFRSM layers. The results indicate that (1) Compared to the rubber-sand layer, the SFRSM exhibits a lower shear modulus and higher damping, indicating its potential for greater seismic isolation and energy dissipation. (2) The dynamic characteristics of the SFRSM were significantly influenced by the fill percentage and laying scheme, suggesting that an effective isolator capable of withstanding various external conditions could be developed. (3) The isolating effect of the SFRSM layer is attributed to its ability to dampen high-frequency vibration components effectively. Additionally, the threshold frequency required to trigger attenuation decreases with an increasing number of SFRSM layers. In summary, these experimental results provide evidence that the proposed innovative strategy enhances the strength and vertical stiffness of the original rubber-sand layer, making it well-suited for seismic design applications in low-rise buildings in less-developed regions. Highlights 1. A novel seismic isolation strategy using the soil bags filled with rubber-sand mixture (SFRSM) was proposed. 2. Large-scale cyclic simple shear tests were conducted to evaluate the dynamic properties of SFRSM. 3. The influence of key parameters on the dynamic shear modulus and damping ratio of SFRSM was analysed. 4. The proposed strategy is well suited for the seismic design of low-rise buildings in less-developed regions.

Seismic response of permafrost slopes supported by the thermal anchor pipe frame: Theoretical analysis and shaking table test verification

To study the seismic response of the thermal anchor pipe frame supporting permafrost slope system, the coupled dynamic interaction model of the permafrost slope with the thermal anchor pipe frame in thawing and freezing periods was established by taking into account the stratification characteristics of the permafrost slope in different typical seasons, respectively. Based on D'Alembert's principle and Dirac's function, the coupled vibration equilibrium differential equations are given and the seismic response of the system is analyzed for different periods. The reliability of the proposed model was further verified through shaking table tests. The results show that the acceleration response at different positions during both freezing and thawing periods is similar to the initial loading seismic wave shape. The peak acceleration and velocity during the thawing period is greater than that during the freezing period. The shear force and bending moment of the frame column are distributed alternately positive and negative along its height. The incremental dynamic shear force and bending moment are greater during the thawing period. However, the peak bending moments and shear forces are greater during the freezing period when the combined effects of frost and earthquakes. The peak bending moment occurs at the position of the first layer of the thermal anchor pipe, and the shear force suddenly changes near the thermal anchor pipe. In seismic design, attention should be paid to checking the internal force of the frame column during the freezing period to prevent plastic bending failure. The results contribute to further understanding the dynamic interaction mechanism of the thermal anchor pipe frame permafrost slope system, which has important practical significance for its seismic resistance.

Friction-based connectors with wooden dowels for timber shear walls: Shake table and time-dependent test

Prestressing in wood connection, due to frictional forces, improves mechanical properties of the connection. This paper presents novel friction-based connectors, and corresponding tests at the connection and system levels. The friction-base connector is composed of a softwood or hardwood dowels inserted into the wood-based material and tightened to generate frictional force. Long-term performance was evaluated by stress relaxation tests and time-dependent connection tests. To evaluate dynamic performance of shear walls with friction-based connectors, shake table tests were conducted. The shake table tests showed that the restoring force characteristics of the wood friction shear walls were bilinear reflecting the behaviors of the friction-based connectors. The strength degradation of the wood friction shear walls due to cyclic input was small that more seismic inputs could be applied before any significant damage to the wood friction shear wall. Results of stress relaxation tests, for periods of 1 to 3 years, showed that the stresses were maintained at 70–90% under uncontrolled environment. On the other hand, the results of time-dependent connection tests, for 1 to 6 years, showed high initial clamping stresses caused large performance loss, but high performance could be maintained when tightened below the allowable stress for sustained loading.

A Hybrid Perspective of Vision-Based Methods for Estimating Structural Displacements Based on Mask Region-Based Convolutional Neural Networks

Abstract Vision-based methods have shown great potential in vibration-based structural health monitoring (SHM), which can be classified as target-based and target-free methods. However, target-based methods cannot achieve subpixel accuracy, and target-free methods are sensitive to environmental effects. To this end, this paper proposed a hybrid perspective of vision-based methods for estimating structural displacements, based on Mask region-based convolutional neural networks (Mask R-CNNs). In proposed methods, Mask R-CNN is used to first locate the target region and then target-free vision-based methods are used to estimate structural displacements from the located target. The performances of proposed methods were validated in a shaking table test of a cold formed steel (CFS) wall system. It can be seen that Mask R-CNN can significantly improve the accuracy of feature point matching results of the target-free method. The comparisons of estimated structural displacements using proposed methods are conducted and detailed into accuracy, stability, and computational burden, to guide the selection of the proper proposed method for the specific problem in vibration-based SHM. Proposed methods can also achieve even 1/15 pixel-level accuracy. Moreover, different image denoising methods in different lighting conditions are compared.

Experimental Study on Impulse-Induced Liquid Sloshing Modes and Frequencies in Rectangular Tanks

Storage tanks are extensively used containers in various industries for storing diverse liquids. The sloshing of liquid in these containers, often caused by earthquakes, is an emerging issue in the context of damage sustained by tanks. Thus, the seismic resilience of a tank is a critical performance criterion in tank design. Given the complexity of liquid sloshing, the fundamental characteristics of this phenomenon must be examined to gain insights into fundamental sloshing behavior. Liquid sloshing typically involves a combination of fundamental and higher sloshing modes, and the modes and frequencies of liquid sloshing are therefore crucial for assessing this complex behavior. In this study, a shaking table test was employed to analyze the characteristics of liquid sloshing modes. The shapes of the first three sloshing modes under unidirectional excitation were determined and used to validate their symmetry. The findings indicate that the first sloshing mode exerts a more pronounced influence on liquid sloshing during free oscillation induced by unidirectional and horizontal excitation. The modal contribution factor of the first sloshing mode escalates with an increase in the ratio of the liquid level to the length of the tank parallel to the shaking direction, eventually converging toward a constant value.

Experimental and numerical study on dynamic response of offshore wind turbine subjected to earthquake loads

In order to investigate the response of offshore wind turbines (OWTs) under earthquake, shaking table test is conducted using a 6.45 MW OWT as prototype. The effective length of the embedded steel pile is determined using the equivalent embedment method, and a scale model with a similarity constant of 1:15 is designed. The dynamic characteristics of the scale model are evaluated through position-shift and white noise. Three earthquakes with different spectrum characteristics are utilized as inputs, and subsequently, an analysis is performed to assess the earthquake response of the OWT. The results demonstrate that the dynamic characteristics between the scale model and the prototype model meet the similarity constants. Due to the eccentric mass, torsional vibrations are induced when subjected to bidirectional excitation, resulting in the occurrence of ‘beat vibration’ phenomenon. The acceleration is significantly influenced by the excitation spectrum, with the maximum occurring at either the top or 2/3 height, and Darfield with wide spectrum result in a more pronounced stimulation. The displacements are all observed at the pinnacle of the tower. The Imperial and Kocaeli, characterized by shorter duration and higher energy concentration, elicit more pronounced displacement. Stress concentration occurs at the lower 1/3 due to sudden stiffness change.

Seismic fragility of vertically irregular gravity column-core tube structure subjected to pulse-like ground motions

The effects of the pulse-like ground motion and structurally vertical irregularity on the seismic fragility of the new gravity column-core tube structural system are investigated. Based on the shaking table test, the finite element parameters are verified. By changing the stiffness ratio of the first story to the second story, the typical vertically irregular gravity column-core tube structure models of 20-, 30- and 40-stories are established. Selecting 10 pulse-like and 10 corresponding non-pulse-like ground motion records, the incremental dynamic analysis and seismic fragility analysis are performed to these structures employing CANNY program. The results show that the maximum inter-story drift ratio (θmax) and the probability of exceeding the limit state (Pf) of each structure under pulse-like cases are significantly greater than those under non-pulse-like cases. From slight damage to approaching collapse state, the difference in seismic fragility curves between pulse-like cases and non-pulse-like cases is gradually amplified. It is suggested that the seismic strength reduction factor of these new type of structures be reduced properly to consider the pulse-like ground motion effect. With the stiffness ratio decreases, θmax and Pf have an increasing trend. However, the increasing quantity is small, which may be due to the effect similar to the isolation in the first story. As a limit value of vertical irregularity in the first story, the stiffness ratio of 1.5 provisioned in the code is conservative. To give consideration to both the safety and the economy, it is recommended to lower the limit value to about 1.2 for the gravity column-core wall structures with stiffness irregularity at the first story.

Seismic Performance Analysis of Ancient Palace-Style Timber Structure Considering Column Rocking Effect

ABSTRACT The seismic response of palace-style timber structures is closely related to the rocking characteristics of column. To accurately describe the dynamic characteristics of timber structures, a nonlinear rotational spring is employed to simulate the rocking behavior of column base joints under seismic excitation. Firstly, a spring-rigid rod analysis model that comprehensively considers the nonlinear properties of column base joints, mortise-tenon joints, and bracket set joints is proposed, and a simplified lumped mass model is obtained through centroid method and equivalent stiffness method. The accuracy of the simplified model is verified through shake table tests, and nonlinear dynamic response time-history analysis of the structure is conducted. Based on the verified simplified model, the influence of tenon-mortise joint reinforcement on the seismic displacement response of the structure was further investigated. It was found that carbon fiber sheets reinforcement increased the initial stiffness of the joints by 1.45 times and reduced the displacement response of the structure by 15%. Additionally, the optimal stiffness enhancement of column frame mortise-tenon joints range from 4 to 6 times.