Earthquake Engineering and Engineering Vibration最新文献

Several popular time-frequency techniques, including the Wigner-Ville distribution, smoothed pseudo-Wigner-Ville distribution, wavelet transform, synchrosqueezing transform, Hilbert-Huang transform, and Gabor-Wigner transform, are investigated to determine how well they can identify damage to structures. In this work, a synchroextracting transform (SET) based on the short-time Fourier transform is proposed for estimating post-earthquake structural damage. The performance of SET for artificially generated signals and actual earthquake signals is examined with existing methods. Amongst other tested techniques, SET improves frequency resolution to a great extent by lowering the influence of smearing along the time-frequency plane. Hence, interpretation and readability with the proposed method are improved, and small changes in the time-varying frequency characteristics of the damaged buildings are easily detected through the SET method.

A trigger system is typically employed in active seismic testing to trigger and synchronize multichannel surface wave data acquisition. The effect of the trigger system on the dispersion image of surface waves is empirically known to be negligible, however, theoretical explanation regarding the effect of the trigger system is insufficient. This study systematically examines the theory for surface wave dispersion analysis and proves that the effect of the trigger system on a dispersion image is negligible via a solid theoretical explanation. Subsequently, based on the new theoretical explanation, an alternative method that uses only the relative phase difference between sensors to extract dispersion characteristics with better conceptual clarity is proposed. Two active surface wave testing cases are considered to validate the theory and method. The results indicate that (1) an accurate trigger system is not necessary for surface wave data acquisition, and (2) it is unnecessary to assume that the impact point is the generation point of the surface waves for the experimental dispersion analysis.

The auto-parametric resonance of a continuous-beam bridge model subjected to a two-point periodic excitation is experimentally and numerically investigated in this study. An auto-parametric resonance experiment of the test model is conducted to observe and measure the auto-parametric resonance of a continuous beam under a two-point excitation on columns. The parametric vibration equation is established for the test model using the finite-element method. The auto-parametric resonance stability of the structure is analyzed by using Newmark’s method and the energy-growth exponent method. The effects of the phase difference of the two-point excitation on the stability boundaries of auto-parametric resonance are studied for the test model. Compared with the experiment, the numerical instability predictions of auto-parametric resonance are consistent with the test phenomena, and the numerical stability boundaries of auto-parametric resonance agree with the experimental ones. For a continuous beam bridge, when the ratio of multipoint excitation frequency (applied to the columns) to natural frequency of the continuous girder is approximately equal to 2, the continuous beam may undergo a strong auto-parametric resonance. Combined with the present experiment and analysis, a hypothesis of Volgograd Bridge’s serpentine vibration is discussed.

Vertical mass isolation (VMI) is one of the novel methods for the seismic control of structures. In this method, the entire structure is assumed to consist of two mass and stiffness subsystems, and an isolated layer is located among them. In this study, the magnetorheological damper in three modes: passive-off, passive-on, and semi-active mode with variable voltage between zero and 9 volts was used as an isolated layer between two subsystems. Multi-degrees-of-freedom structures with 5, 10, and 15 floors in two dimensions were examined under 11 pairs of near field earthquakes. On each level, the displacement of MR dampers was taken into account. The responses of maximum displacement, maximum inter-story drift, and maximum base shear in controlled and uncontrolled buildings were compared to assess the suggested approach for seismic control of the structures. According to the results, the semi-active control method can reduce the response by more than 12% compared to the uncontrolled mode in terms of maximum displacement of the mass subsystem of the structures. This method can reduce more than 16% and 20% of the responses compared to the uncontrolled mode in terms of maximum inter-story drift and base shear of the structure, respectively.

Evidence from recent earthquakes has shown destructive consequences of fault-induced permanent ground movement on structures. Such observations have increased the demand for improvements in the design of structures that are dramatically vulnerable to surface fault ruptures. In this study a novel connection between the raft and the piles is proposed to mitigate the hazards associated with a normal fault on pile-raft systems by means of 3D finite element (FE) modeling. Before embarking on the parametric study, the strain-softening constitutive law used for numerical modeling of the sand has been validated against centrifuge test results. The exact location of the fix-head and unconnected pile-raft systems relative to the outcropping fault rupture in the free-field is parametrically investigated, revealing different failure mechanisms. The performance of the proposed connection for protecting the pile-raft system against normal fault-induced deformations is assessed by comparing the geotechnical and structural responses of both types of foundation. The results indicate that the pocket connection can relatively reduce the cap rotation and horizontal and vertical displacements of the raft in most scenarios. The proposed connection decreases the bending moment response of the piles to their bending moment capacity, verging on a fault offset of 0.6 m at bedrock.

In seismology and earthquake engineering, it is fundamental to identify and characterize the pulse-like features in pulse-type ground motions. To capture the pulses that dominate structural responses, this study establishes congruence and shift relationships between response spectrum surfaces. A similarity search between spectrum surfaces, supplemented with a similarity search in time series, has been applied to characterize the pulse-like features in pulse-type ground motions. The identified pulses are tested in predicting the rocking consequences of slender rectangular blocks under the original ground motions. Generally, the prediction is promising for the majority of the ground motions where the dominant pulse is correctly identified.

A shaking table test for a bridge foundation reinforced by anti-slide piles on a silty clay landslide model with an inclined interlayer was performed. The deformation characteristics of the bridge foundation piles and anti-slide piles were analyzed in different loading conditions. The dynamic response law of a silty clay landslide with an inclined interlayer was summarized. The spacing between the rear anti-slide piles and bridge foundation should be reasonably controlled according to the seismic fortification requirements, to avoid the two peaks in the forced deformation of the bridge foundation piles. The “blocking effect” of the bridge foundation piles reduced the deformation of the forward anti-slide piles. The stress-strain response of silty clay was intensified as the vibration wave field appeared on the slope. Since the vibration intensified, the thrust distribution of the landslide underwent a process of shifting from triangle to inverted trapezoid, the difference in the acceleration response between the bearing platform and silty clay landslide tended to decrease, and the spectrum amplitude near the natural vibration frequency increased. The rear anti-slide piles were able to slow down the shear deformation of the soil in front of the piles and avoid excessive acceleration response of the bridge foundation piles.

Soil nonlinear behavior displays noticeable effects on the site seismic response. This study proposes a new functional expression of the skeleton curve to replace the hyperbolic skeleton curve. By integrating shear modulus and combining the dynamic skeleton curve and the damping degradation coefficient, the constitutive equation of the logarithmic dynamic skeleton can be obtained, which considers the damping effect in a soil dynamics problem. Based on the finite difference method and the multi-transmitting boundary condition, a 1D site seismic response analysis program called Soilresp1D has been developed herein and used to analyze the time-domain seismic response in three types of sites. At the same time, this study also provides numerical simulation results based on the hyperbolic constitutive model and the equivalent linear method. The results verify the rationality of the new soil dynamic constitutive model. It can analyze the mucky soil site nonlinear seismic response, reflecting the deformation characteristics and damping effect of the silty soil. The hysteresis loop area is more extensive, and the residual strain is evident.

Extensive high-speed railway (HSR) network resembled the intricate vascular system of the human body, crisscrossing mainlands. Seismic events, known for their unpredictability, pose a significant threat to both trains and bridges, given the HSR’s extended operational duration. Therefore, ensuring the running safety of train-bridge coupled (TBC) system, primarily composed of simply supported beam bridges, is paramount. Traditional methods like the Monte Carlo method fall short in analyzing this intricate system efficiently. Instead, efficient algorithm like the new point estimate method combined with moment expansion approximation (NPEM-MEA) is applied to study random responses of numerical simulation TBC systems. Validation of the NPEM-MEA’s feasibility is conducted using the Monte Carlo method. Comparative analysis confirms the accuracy and efficiency of the method, with a recommended truncation order of four to six for the NPEM-MEA. Additionally, the influences of seismic magnitude and epicentral distance are discussed based on the random dynamic responses in the TBC system. This methodology not only facilitates seismic safety assessments for TBC systems but also contributes to standard-setting for these systems under earthquake conditions.

Seismic isolation effectively reduces seismic demands on building structures by isolating the superstructure from ground vibrations during earthquakes. However, isolation strategies give less attention to acceleration-sensitive systems or equipment. Meanwhile, as the isolation layer’s displacement grows, the stiffness and frequency of traditional rolling and sliding isolation bearings increases, potentially causing self-centering and resonance concerns. As a result, a new conical pendulum bearing has been selected for acceleration-sensitive equipment to increase self-centering capacity, and additional viscous dampers are incorporated to enhance system damping. Moreover, the theoretical formula for conical pendulum bearings is supplied to analyze the device’s dynamic parameters, and shake table experiments are used to determine the proposed device’s isolation efficiency under various conditions. According to the test results, the newly proposed devices have remarkable isolation performance in terms of minimizing both acceleration and displacement responses. Finally, a numerical model of the isolation system is provided for further research, and the accuracy is demonstrated by the aforementioned experiments.