International Journal of Structural Stability and Dynamics

To exactly study the riding comfort of passengers in urban rail transit trains, a coupling vibration model, including passengers, train, and bridge is proposed in this paper. According to the Lagrange Equation, the differential equations of motion of each part are derived, which are coupled with each other through displacement and dynamic interaction forces. A corresponding calculation program is compiled by the Fortran language. A representative steel-concrete composite girder bridge on Beijing Metro Line 5 is selected as the research background, the dynamic responses of passengers and train are simulated in detail, and the dynamic response differences between the passenger and carriage are compared. The passengers’ riding comfort is evaluated according to ISO-2631 Standard based on the simulated data. The result shows that passengers in the middle carriages of the train feel better than those in the head and tail ones. While in the same carriage, passengers on the middle seats feel better than those on both ends of it. If only vibration is considered, passengers will feel better in a fully loaded carriage than those with few passengers. The riding comfort of passengers will be gradually reduced with the increase of the train speed.

So far, wind loads on structures are almost exclusively evaluated by Extended Pressure Systems (EPS) cyclone models according to design codes. However, there is evidence that downburst wind fields, originating from thunderstorms (TSs) events, may have caused or contributed to the collapse of transmission line towers around the world. In this context, this work proposes a complete methodology to simulate a wind field from combined EPS (synoptic) and TS (nonsynoptic) storms. The proposed combined wind field model is applied to a real transmission line segment and the results are compared with those of the system subjected to the equivalent static loading method proposed in the IEC 60826/2003 code. The finite central differences explicit method is adopted for dynamic integration, taking into account nonlinearities. The assessment confirmed the localized and transient nature of the TS phenomenon. The results indicated that, for most of the elements analyzed, the equivalent static method for synoptic winds of IEC 60826/2003 resulted in a lower response than that obtained through the proposed combined model, which considers a TS carried by an EPS background wind. Thus, the proposed method to combine synoptic and nonsynoptic wind fields might be a useful tool to assist in the design of structures, such as transmission lines, which are susceptible to the effects of combined EPS and TS wind fields.

Collapse hazards occur frequently in mountainous areas. Geosynthetics-reinforced soil (GRS) wall, combing the damping characteristics of soil and the tensile properties of reinforcement materials, can effectively resist rockfall impact through its flexible deformation. However, excessive deformation is easy to occur near the impact point of reinforced soil retaining wall subjected to impact loading, resulting in instantaneous instability and long repair time as well as high repair cost of the structure. Therefore, the prestressed GRS wall with buffer layer was proposed in this paper. Four retaining walls with different types and the impactor consist of pendulum device and solid steel ball was designed to study the impact resistance and dynamic stability of the retaining wall. The results show that the cumulative deformation of the wall panel experiences acceleration phase, deceleration phase and stable stage subjected to the impact loading. The application of buffer layer and prestress member can effectively improve the impact resistance and dynamic stability of retaining wall, and further control the deformation of retaining wall under the impact loading, in comparison with ordinary reinforced retaining wall. The peak impact stress of the retaining wall and the responsive strain of the reinforcement increase gradually as the distance between the measure point and the impact point decreases. The research results can provide reference for the design and the application of prestressed GRS wall under the impact of rockfall.

Indeed, base isolation systems have gained significant attention from researchers and designers over the last few decades. Within this context, various technologies were developed to improve the performance of structures under strong earthquake shaking intensities. Recently, a new generation of multi-stage friction pendulum (FP) bearings known as “Quintuple Friction Pendulum” (QFP) was introduced to the literature to attain high energy dissipation capability. The main advantages of this bearing come from its ability to achieve complex multi-stage adaptive behavior with smoothed loading and unloading when subjected to lateral forces owing to its five effective pendula and nine operation regimes. On the other hand, investigations that studied the influence of the bearing properties and the impact of various ground motion characteristics on the performance and behavior of this isolation system are scarce. Thus, this research aims to conduct a parametric assessment that highlights and quantifies the effect of the various isolator properties and earthquake characteristics on the behavior of the base-isolated structure. As a part of the study, finite element models considering the nonlinearity of the isolation system and the superstructure will be developed in OpenSees. Generally, the study results have shown that the behavior of the isolator is significantly influenced by its properties and the type of earthquake being applied.

Blast-induced ground motions (BIGM) can cause significant damage to the structure, leading to loss of life and economy. Previous studies proposed the use of base isolation system to prevent such adverse effects of blast loading on the structures. This study explores the effect of parametric uncertainty on the performance of shape memory alloy-assisted lead rubber bearing (SMA-LRB) isolator for the vibration control of building, under the BIGM. Nonlinear time-history analyses are performed to estimation responses, and compared them with the LRB isolated building. The building is modeled as a linear system, and nonlinear force–displacement behavior of LRB and SMA has been modeled via Bouc–Wen model and thermo-mechanical material model. To identify the critical design parameters and study the effect of parameter uncertainty, sensitivity analysis and Monte Carlo (MC) simulation are performed. Study results reveal that, compared to LRB, SMA-LRB reduces the peak floor acceleration by 20% with an added benefit of 35% and 67% reduction in peak and residual isolator displacement. Parametric uncertainty causes noticeable increase in mean responses of LRB isolated system than deterministic case, which get diminishes for SMA-LRB isolation system. This increase in the mean value of peak floor acceleration, peak, and residual isolator displacement are 64%, 68%, and 60% less for SMA-LRB than LRB isolated building. Further, compare to the LRB, SMA-LRB reduces standard deviation by 77% for the peak floor acceleration and peak isolator displacement, and 85% for the isolator residual displacement. Thus, conjunction of SMA with the LRB isolator enhances the performance and provides robust control effect under parameter uncertainty.

Considering the internal and external disturbances, i.e. coupling effect, model uncertainties, and external excitation of an all-clamped piezoelectric plate, a two-loop nonsingular terminal sliding-mode controller (NTSMC) based on extended state observer (ESO) is developed to suppress the two-mode structural vibration. First, a state space model of the structure is established based on system identification with an auxiliary variable method. Second, a three-order ESO of each individual mode is drawn to estimate and compensate the lumped disturbances via feedforward channel in real-time. Third, the NTSMC based on ESO for each single mode is designed to obtain vibration suppressing performance. In addition, the two-mode vibration control is decoupled into single-mode independent control through the proposed ESO. The stability of whole closed-loop system is analyzed by using a Lyapunov stability criterion. Finally, the experimental platform based on NI-PCIe device for a piezoelectric structural vibration control is set up to verify the effectiveness and superiority of the proposed two-mode vibration control method. Compared with the conventional ESO-based sliding-mode control (SMC) method, the experimental results of two-mode structural vibration demonstrate that the vibration suppression performance of first two modes is improved from 8.94dB to 11.7dB and 9.2dB to 14.75dB, respectively.

The construction of high-speed railways continues to extend in seismic prone areas, but there is limited research on the seismic-induced track irregularities occurred in positions where high-speed railway bridges are involved. Taking a five-span high-speed railway simply supported beam bridge as the engineering example, the corresponding nonlinear system model, with CRTS II slab ballastless track, is established by using ANSYS finite element analysis software. The distribution mode of post-earthquake track residual irregularity is studied, the statistical characteristics of its power spectral density are analyzed, and a representative seismic-induced track geometric irregularity spectrum is constructed. The effects of the site categories and the epicenter distance on seismic-induced track spectrum are also discussed. The results show that after the earthquake, the alignment irregularity is significant, while the vertical, cross-level and gauge irregularities can be ignored. The amplitude of track geometric irregularity, caused by earthquake, increases significantly with the increase of ground motion intensity. The seismic-induced track spectrum obeys lognormal distribution at all frequencies. The track spectra almost coincide for all five site categories, thus, the impact of site categories on the seismic-induced track spectrum of high-speed railway bridges is considered negligible. Due to the pulse effect, the seismic-induced track spectrum of near-field earthquakes is significantly larger than that of far-field earthquakes.

This paper examines the differences in hysteretic behavior of buckling-restrained brace subsystem frames (BRBFs) with concentric and out-of-plane eccentric configurations. First, a quasi-static experiment was carried out on steel plate BRBF specimens to study the differences in mechanical properties, stability, and energy dissipation capacity between BRBFs with concentric and out-of-plane eccentric configurations. Second, a numerical simulation was carried out using the same steel plate BRBF specimens to study the difference in the stress distribution and high-order deformation patterns between the BRBFs with concentric and out-of-plane eccentric configurations. The test and numerical results showed that the out-of-plane eccentric BRBFs under in-plane quasi-static loads have different mechanical properties, larger compression strength adjustment factors ($\beta$) under larger loading amplitudes, higher $\beta$ value increasing rates, lower equivalent viscous damping ratios ($\zeta$), different yield processes, and different generation processes of high-order core deformation compared with the concentric BRBFs.

An active negative stiffness regulation and precision micro-vibration isolation technology (ANSVIT) based on composite feedback of acceleration and velocity is proposed to realize the low-frequency isolation of air floating isolators with heavy loads. Adjustable negative stiffness generated by acceleration feedback realizes low-frequency isolation, and absolute velocity feedback is combined to reduce the peak vibration transmissibility and improve isolation performance. The effects of feedback coefficients in the frequency domain are analyzed based on the dynamics model. And the relationship of feedback coefficients that achieves low natural frequency and lower peak vibration transmissibility than passive vibration isolation is derived to guide design. Furthermore, the effects of ANSVIT on vibrations in the low-frequency region, resonance region, and isolation region are investigated numerically in the time domain. Finally, an experimental setup is built, and experiments are conducted. Experimental results show that the introduction of ANSVIT attenuates the natural frequency by 61.54% and achieves lower peak vibration transmissibility and higher vibration level than passive vibration isolation. The promise of the proposed ANSVIT for improving the isolation performance is verified.

This research aims to evaluate the dynamic interaction between a cable-stayed bridge (CSB) and operating trains during earthquakes. A three-dimensional finite element modeling approach has been used to analyze the H-shaped pylon CSB along with soil–pile interaction. The train model has been developed using a dynamic system having 10 degrees of freedom. The contact forces between the wheels and the track illustrate the dynamic interaction between the bridge and the train. A Matlab program has been built to receive train–bridge interaction responses. The nonlinear dynamic analysis was performed on CSB using the Bhuj earthquake time history. The structure’s response can then be used to assess the safety of running trains during seismic activity. The dynamic response of the train–bridge interaction system, including the derailment and offloading variables related to the train’s running safety, is evaluated using varied spectral acceleration scaling. The results demonstrate that the acceleration response of the train during seismic events is substantially higher than when there are no earthquake inputs. The operating train’s safety is influenced by both the intensity of the earthquake and the train’s running speed. The operating safety of a moving train during a seismic event is guaranteed by the threshold curve. The proposed bridge modeling technique and simulated results prove that the proposed formulation can accurately envisage dynamic train responses with acceptable computational errors.

A hybrid method is presented to obtain the analytical approximate solution to the primary resonance of harmonically forced strongly nonlinear oscillators. This hybrid method combines the classical perturbation method and the classical harmonic balance method. With the proposed splitting procedure some free parameters are introduced, more accurate and reliable analytical approximation compared to the results obtained by the classical harmonic balance method are presented. The proposed method is not based on the small parameter assumption when perturbation method is applied. It is found that the corrections to erroneous solution when harmonic balance method and Floquet theory are adopted in stability analysis is necessary. The proposed method gives excellent stability results compared to those obtained by using harmonic balance method and Floquet theory. Two examples are presented to illustrate the applicability, validity and convergence of the proposed method. The convergence of the solution in stability analysis by the proposed hybrid method are compared with that obtained by using the Floquet theory and the harmonic balance method. The results obtained by the proposed method are verified by the numerical simulations.

The empirical envelope (EE) method based on the amplitude-modulation and frequency-modulation (AMFM) decomposition is effective for identifying the modal parameters of time-varying and weakly nonlinear systems. However, the identification accuracy of the EE method is sensitive to noises which often exist in vibration measurements of real structures. In this study, an improved empirical envelope (IEE) method is proposed to achieve robust modal parameter identification from noisy measurements. Specifically, the idea of sliding window threshold denoising is introduced to reduce the error in the instantaneous envelope induced by abnormal extreme points, and a moving average filter is utilized to reduce the error in the instantaneous frequency induced by high-frequency noises. Two numerical examples and an experimental example of a full-bridge aeroelastic model are analyzed to validate the accuracy of the IEE method and highlight the superiority of the IEE method relative to the original EE method. It is concluded that the IEE method is robust to measurement noises (the considered signal-to-noise ratios include 5–90dB) and that the IEE method is more accurate than the EE method. Hence, the IEE method serves as a promising alternative for modal parameter identification of time-varying and weakly nonlinear systems.