International Journal of Structural Stability and Dynamics

The pulse effect of near-fault ground motion has asevere threat to high-speed railway train running on bridge. Current research generally relies on numerical simulation and lacks physical test data. In this paper, a scale indoor physical test of high-speed train running on bridge is conducted and dynamic characteristics of high-speed railway train–track–bridge system under near-fault pulse-type ground motion are explored. The bridge of the physical test is excited by shaking table with lateral inputs of near-fault pulse-type ground motion, pulse-free ground motion and far-field ground motion. A corresponding numerical model is established and validated by the test data. Then, the influence regularities of pulse effect on system dynamic response and running safety indexes are explored under different peak ground acceleration (PGA) and train speeds using data of the physical tests and the numerical simulation comprehensively. Results suggest that compared to the near-fault pulse-free ground motion and the far-field ground motion, the near-fault pulse-type ground motion leads to larger lateral beam displacement, lateral train acceleration, and running safety indexes in different degrees. And from the data results of this paper, its lateral wheel–rail force and derailment coefficient are the first to break through the limit values. By studying the parameter sensitivity of lateral train acceleration, it was found that under the near-fault pulse-type ground motion, the lateral train acceleration is significantly more sensitive to changes of train speed and PGA. From the perspective of energy, the near-fault pulse-type ground motion results in spectrum intensity (SI) indexes which are larger and improve faster with the increase of PGA than other ground motions. This indicates that it inputs significantly more energy into the high-speed railway train–track–bridge system, although it may not excite larger lateral beam acceleration.

In this research, the nonlinear response including amplitude and phase angle of a functionally graded inextensional rotating shaft is studied under the electromagnetic load. Three types of porosity distributions through the radial direction are considered in this work. For the rotating shaft with nonlinear curvature and inertia, the governing equations and corresponding boundary conditions are derived. The Galerkin and the multiple scales methods are used to obtain the modulation equations. The effect of the power law index for a functionally graded shaft fabricated from the mixture of ceramic and metal is presented in the frequency response diagrams for primary resonance under electromagnetic force. Numerical simulations include the effects of the power law index of functionally graded material (FGM), porosity distribution, air-gap length, electromagnetic load, and vibration modes of a rotor on the phase angle and amplitude of steady state responses.

Compared to ground supported tank, column supported tank has the advantages of saving land space, having strong adaptability and making gas transmission cost small. It can be mass-produced in the center of a city, which has been widely used in practices. However, its seismic responses are much different from those of cylindrical tank. Limited research works and standard codes involve uplift effect and retrofitting measure of column supported tanks. Therefore, a shaking table test is conducted with a model tank designed by quasi-dimensional analysis method. To solve the problem of the anchored tank that may suffer damage under severe earthquake, a designed resilient tank is presented with mild steel dampers. The seismic responses of those two tanks are compared with each other, including the structural displacement parallel to excitation direction, the strain of tank walls and columns, the uplift displacement and the structural force. The results show that due to the uplift effect and the energy dissipation of dampers, the resilient tank has larger horizontal displacement, but less base shear and overturning moment than the anchored tank. Its strains of columns and walls in excitation direction decrease obviously, while those in perpendicular direction increase but with small variation, resulting in more balanced force allocation of the resilient tank. When encountering plastic failure, the dampers can be replaced in a very short time, making the normal use of the tank quickly even extreme condition. The resilient tank can save repairing time and cost. It can help resume the gas supply function of a city quickly after severe earthquake.

Used extensively in structural dynamics analysis, the energy method is advantageous for transforming boundary value problems of differential equations into variational extremum problems. Recent applications include analyzing the wave and vibration characteristics of track structures. However, traditional energy methods for dynamic modeling and analysis of ballastless track structures require obtaining the global stiffness matrix and mass matrix of the entire coupled system, which decreases computational efficiency. The EM-CMS algorithm for frequency domain dynamic response analysis of ballastless track structures has been proposed to address this issue. The core of EM-CMS is the development of model reduction strategies within the framework of the energy method to reduce matrix dimensions and thereby improve computational efficiency. Specifically, the steel spring floating slab track is the focus of this research. Utilizing the energy functional variational method, the modal properties of the rail and floating slab structures are obtained, and truncation is performed. A reduced-order model for the steel spring floating slab track is established by considering the boundary conditions between the rail-floating slab and the floating slab foundation (connected through fastener springs and steel springs, respectively, and considering the springs’ elastic potential energy). Comparatively, the computational efficiency of EM-CMS is approximately ten times greater than that of the energy method. The method’s accuracy is also carefully validated against finite element simulations.

Aiming to enhance the accuracy, stability, and noise robustness of swarm intelligence-based algorithms for structural damage identification (SDI), a novel improved dragonfly algorithm (IDA) is proposed. The IDA integrates the dragonfly algorithm (DA) with three key strategies including enhanced Lévy flight, optimal solution bidirectional search, and greedy preservation. These strategies are introduced to enhance the exploration capability of the original DA and improve the IDA’s capacity to obtain global optima. An objective function is defined using frequency change ratio and flexibility assurance criterion (FAC). Additionally, trace sparse regularization is also incorporated into the objective function since most of the damages in structures tend to be sparsely distributed, so that a sparse result is ensured to improve SDI accuracy. To evaluate the performance of the proposed algorithm, a comparison of the original DA and IDA is conducted using four benchmark functions. The results demonstrate that the proposed algorithm achieves improved convergent rate and accuracy. Furthermore, numerical simulations are performed on a 10-element simply-supported beam and a 31-element planar truss to validate the effectiveness and efficiency of the proposed algorithm in SDI. Significantly, the utilization of IDA instead of DA leads to a substantial reduction in the average calculated relative error for the truly damaged element within the considered damage cases of the simply-supported beam, decreasing from 13.05% to 6.15%. Moreover, an experimental simply-supported beam structure with several assumed damage cases is fabricated in the laboratory. The experimental results further confirm the robustness and capability of the proposed method in real-world SDI applications.

In this paper, the dynamic response of an infinite Euler beam that was mounted on a fractional-order Pasternak viscoelastic foundation subjected to a moving point load was investigated. An analytical solution to the problem was derived using Fourier and Laplace transforms. Numerical results obtained by numerical Laplace inversion were analyzed to explore the impact of various parameters on the system’s response. The findings indicated that increasing system damping led to a decrease in maximum deflection and a more visible deformation hysteresis with an increase in fractional derivative orders. Additionally, all parameters of the foundation and shear layer were observed to have a significant effect on the deflection. The study confirmed that the fractional-order model predicted damping and dynamic deflection more accurately than the conventional integer-order foundation model. The research contributed to the understanding of the behavior of Euler beams mounted on viscoelastic foundations and provided valuable insights into the design of such systems.

Damage localization is very significant in engineering applications. The existing method based on the chi-square distribution of an autoregressive moving average with exogenous inputs (ARMAX) model residual is not applicable for these realistic excitations except Gaussian excitation. To solve the above problem, this paper presents a structural damage localization method based on the empirical probability mass function (EPMF) of the ARMAX model residual and Kullback–Leibler (KL) divergence. In detail, we employ empirical data analysis (EDA) approach to estimate the EPMF of the ARMAX model residual of the data generated by the arbitrary excitation because EDA does not need any a priori knowledge about the model residual. Moreover, the KL divergence is introduced to measure the dissimilarity of the EPMFs in undamaged and damaged states to prove that our method is effective for arbitrary excitation. Finally, the semi-parametric extreme value theory is used to estimate the reliable threshold for localizing the damage. Numerical simulated and experimental results illustrate that the proposed method localizes the damage under different excitations, respectively.

This research elucidates the influence of the 60N rail profile on the dynamic interaction between wheel and rail, and the dynamic performance within the turnout. The influence of the 60N profile on the long-term service efficiency of turnouts was scrutinized. Subsequently, an optimization approach for the 60–60N rail combination profile was suggested. The main conclusions are as follows: (1) During the passage in the main direction, the 60N rail profile enhances driving stability and mitigates the progression of wear. However, it causes focalized wheel–rail contact on the rail head and escalates contact stress. (2) During the passage in the branch direction, the 60N rail profile amplifies the lateral dynamic force and rail wear rate in the closure panel, engendering two-point contact and increased contact stress. (3) In the early stage of field service of turnouts, a robust correlation exists between the contact band and the rail profile. In the fragile cross-section of the point rail, the contact band of the 60N rail profile turnout fully occupies the rail head, potentially causing stress concentration on the non-working edge position. By the stable service period, the wheel–rail contact band is mainly influenced by total weight. (4) An optimization method for the 60–60N combination profile was proposed with the corresponding machining tool profile designed. This strategy can avoid the profile transition before and after the turnout, reduce field maintenance workload, enhance running stability of straight passage through the turnout, and preclude fatigue damage in the weak cross-sections of the point rail.

This study investigates the effect of concrete-steel debonding on the modal dynamic properties, i.e. frequency values and vibration mode shapes, and deals with the identification of interfacial debonding zones in CFST columns. In this context, debonding, defined as a decrease in concrete stiffness at the connection with the steel tube by a depth of 3 mm, was analyzed through the frequency analysis of the column. The findings indicate that debonding results in a discernible disparity between the primary and secondary mode shapes, as assessed by the Modal Assurance Criterion (MAC). Furthermore, there is a reduction in the frequency values across all modes. This paper proposes the irregularity detection indices of the Modal Curvature Index (MCI), Modal Curvature-Slope Index (MCSI) and Modal Curvature-Curvature Index (MCCI) using the concept of curvature to detect the debonding zones. These indices indicate the relative extreme values of irregularities in debonding zones for all modes, such that the MCSI and MCCI show an increase in the height of irregularities regardless of negative or positive signs in a debonding zone as the damage severity in that zone increases.

The relatively uncontrolled dynamic behavior of a rigid block resting on a flat surface under ground motion has been well studied. In contrast, a block with a gently inclined V- or W-shaped sliding key would ensure dynamic self-centering or resetting performance under various seismic conditions. To better understand the nonlinear responses of rigid blocks having this type of interface where both rocking and sliding movements are possible, an event-based algorithm is put forward to cover various types of motions, including the transition stages between different types of motions. A comprehensive study is carried out to examine the dynamic responses of blocks of different sizes and aspect ratios. Moreover, the simplified pure rocking model and pure sliding model are also adopted to obtain rough estimates of dynamic response for comparison. The results show that the simplified models are reliable for some special cases only, e.g. squat blocks and slender blocks. The study also evaluated the influence of the coefficient of friction and slope inclination on the resetting capabilities of typical sliding-prone and rocking-prone systems. For those cases that are prone to toppling or excessive sliding under strong earthquakes, the provision of vertical post-tensioning can effectively ensure stability and resetting performance. Such findings provide insight into the performance of precast segmental bridge columns with resettable sliding joints.

A novel metamaterial periodic multi-span beam with elastic supports and local resonators is designed and studied. The vibration characteristics of the designed metamaterial multi-span beam structure are investigated by the spectral element method (SEM) combined with the transfer matrix method (TMM). The accuracy and feasibility of the theoretical methods are validated by the finite element method (FEM) and vibration experiment. It is demonstrated that the metamaterial periodic multi-span beam with elastic supports can produce local resonance bandgaps in the low-frequency regions and Bragg bandgaps in the middle- and high-frequency regions. For some support stiffnesses, the amplitudes and widths of the bandgaps for the proposed structure are larger than those of the metamaterial multi-span beam with simply supported boundaries. Thus, the positions and ranges of the Bragg bandgaps can be adjusted by changing the stiffness of the elastic supports so as to improve the vibration reduction performance of the structure.

In this paper, based on distributed transfer function method (DTFM), the closed-form analytical solutions for vibrations of Euler–Bernoulli beam and frame structures with arbitrary number of cracks are studied. First, generalized DTFM is employed to characterize the dynamical model for a single cracked beam and its analytical solutions for eigenvalue problem and frequency response are obtained. Then, a new DTFM cracked element that encapsulates one crack of arbitrary location inside the beam is proposed. Using the DTFM cracked element and global dynamic stiffness matrix assembly technique, damaged frame structures of arbitrary form can be modeled for vibration analysis. Previous analytical methods only addressed low-frequency vibration of simple cracked beam structures, the proposed method can yield analytical solutions in the medium- and high-frequency regions, which is critical for the small crack detection in complex frames. Lastly, three numerical examples are given to illustrate the correctness and effectiveness of the DTFM in analyzing natural frequencies, modal shapes and frequency responses for cracked structures. By comparing with the Finite Element Method (FEM) and benchmarks from literatures, we proved that the DTFM has better performances in terms of accuracy and efficiency.