International Journal of Structural Stability and Dynamics

Hybrid damping systems are becoming increasingly popular in longitudinal vibration control of longspan bridges under various excitations such as traffic and seismic loads. However, their diversity and complexity make efficient parameter analysis challenging. This study proposes a Simplification-Equivalence-Optimization(SEO) parameter design approach without time history analysis for the Combined Viscous-Steel Damping System (CVSDS), in which the vibrations induced by traffic loads and earthquakes are separately suppressed by the viscous fluid damper (VFD) and the steel yielding damper (SYD). The suspension bridge was simplified to a single-degree-of-freedom (SDOF) system, and the excitations were equivalently converted in the longitudinal direction. The SYD was optimized by stochastic seismic analysis and weighted Pareto optimization. Incorporating the stiffness effect of the SYD, the VFD was further optimized based on harmonic steady-state responses when considering train loads and stochastic responses when considering vehicle loads. Shake table tests were conducted to verify the feasibility of the structural simplification. Numerical time history analysis was performed to validate the proposed optimization approach and investigate the performance of the optimal damper. The results illustrate the efficiency of the proposed SEO method. The SDOF system provides an accurate reproduction of the longitudinal movement of the bridge girder. The optimal CVSDS significantly reduces structural displacement response. VFDs for resisting train loads are more powerful and nonlinear than those for vehicle loads. The initial stiffness of the SYD contributes the most to the vibration control capacity of the CVSDS under earthquakes.

This paper simplifies the tunnel lining section as a straight-curved coupled beam structure, with the tunnel lining and surrounding rock modeled as a straight-curved coupled beam system supported by a soil layer of limited depth to analyze its dynamic response. A refined model of the tunnel-soil coupling system is developed based on Timoshenko curved beam theory, straight beam theory, and the motion equation for an elastic foundation. The finite element method (FEM) is used to validate the numerical solution of the coupled system’s steady-state response, obtained using the transfer matrix method (TMM) and the fourth-order Runge-Kutta method. Through numerical simulations and parameter analysis, the effects of subgrade reaction coefficient, soil thickness, and the tunnel crown’s arc angle on the vibration characteristics of the coupled system are investigated. By applying the symmetry simplification method from structural mechanics, the study demonstrates that this approach is suitable for developing structural dynamic models. The results show that when considering the soil movement around the tunnel, doubling the soil thickness reduces the natural frequency of each order by approximately 15%, while significantly increasing the displacement resonance amplitude. The resonance frequency is most sensitive to the subgrade reaction coefficient in the lower modes, and the overall stiffness of the coupled system decreases as the arc angle at the tunnel crown decreases.

Various adaptive friction pendulum isolators with complex configurations have been developed to meet the increasing engineering demands. However, studies on the influence of temperature and velocity effects on the mechanical properties of new friction pendulum isolators are limited. In particular, equivalent linearized models that consider such friction-dependent effects are scarce, making traditional equivalent linearization methods unable to meet these requirements. In this study, a double-curved adaptive variable friction pendulum isolator (DCAVFPI) is developed that doubly enhances displacement capacity and maintains a small size while considering temperature-induced coefficient of friction deterioration. Meanwhile, its refined mechanical model expression is derived based on the friction dependency theory, which can simulate the effects of frictional heat and velocity on the friction coefficient, unlike the mechanical model directly based on the Coulomb friction model. The proposed mechanical model was validated through experiments on its mechanical properties. Nonlinear response history analyses determined the potential range of the nonlinear parameters and optimal equivalent damping ratio using particle swarm optimization. Nonlinear regression analysis proposes an equivalent linearized model expression for DCAVFPI based on ideal equivalent damping ratio. In conclusion, when evaluating the peak displacement of DCAVFPI, the accuracy of the proposed method can be stably controlled at -10% to 20% better than the existing equivalent linearization with an accuracy of -20% to -50%. Additionally, the proposed mechanical model accurately simulated the effects of temperature and velocity variations.

The computational delay is a key problem in real-time hybrid testing (RTHT). The restart loading technique provides the possibility for non-real-time numerical calculation of RTHT. However, the RTHT based on restart loading technique (RTHT-RLT) requires the experimental substructure to return to the initial state for overall reloading, which requires a significant time cost. To solve this problem, a new RTHT based on partial restart loading technology (RTHT-PRLT) is proposed in this paper. The proposed method carries out partial restart loading in a time-increasing way to reveal the mechanical performance of the experimental substructure accurately and efficiently. Firstly, the RTHT-PRLT is proposed. Furthermore, the effectiveness and accuracy of the proposed method are verified through numerical simulations and experimental tests on a three-story frame structure, modeled by refined finite elements, with a viscous damper. The results of simulation and experiment show that when the number of restart loading steps of the RTHT-PRLT is 50 steps, the viscous damper obtains the same mechanical state quantities as those in the RTHT-RLT. Meanwhile, the experimental efficiency of RTHT-PRLT is more than 50% higher than that of RTHT-RLT.

This paper presents an analysis of the vibration performance of composite shells with doubly-curved shapes embedded with a damping layer. First, the geometric equation and governing equation of composite sandwich doubly-curved shells (CSDCSs) are deduced using the first-order shear shell theory and Hamilton's principle. Subsequently, the Navier solution is applied to solve the deduced governing equation of CSDCSs, and the findings obtained by ANSYS are used to validate the validity and accuracy of the solutions. Finally, this paper graphically provides the vibration performance of CSDCSs with the structural as well as the physical parameters, as follows: With the change of the thickness ratio of the upper and lower layers, the frequency of hyperbolic shell decreases and then increases, while the loss factor increases and then decreases. As the aspect ratio rises, the frequency and loss factor of the spherical shell gradually decrease; the frequency of the parabolic shell shows a trend of gradually decreasing, while the loss factor shows a trend of increasing. Increasing the length-to-radius ratio, the loss factor decreases significantly, but the frequency only decreases slightly. When the shear coefficient takes a value greater than a certain value, CSDCSs can obtain both a better structural stiffness and a larger loss factor.

This research analyzes the dynamic behavior of a viscoelastic beam using the Kelvin-Voigt model and frequency-dependent method under the moving mass, which is crucial for the design and construction of various types of bridges, employing the quasi-3D theory of shear deformation. Viscoelastic materials have intricate molecular chains that influence macroscopic characteristics, including stiffness and damping. The system's equations are established via the Hamilton’s principle. The equations of motion are solved using Navier's analytical technique in the spatial domain and Newmark's numerical method in the temporal domain. To verify the correctness of the produced findings, comparisons with established responses for specific scenarios will be provided. The difference between the Kelvin-Voigt model and the frequency-dependent model is analyzed on the dynamic response and critical velocity of the moving mass, and the influence of various parameters on the dynamic response and critical velocity of the moving mass for both models has been examined and studied. One of the significant findings of this research is that the frequency-dependent method demonstrates greater suitability and reasonableness for the investigated structure compared to the Kelvin-Voigt model, as evidenced by the latter's critical velocity being 18% lower. This underscores the advantages of the frequency-dependent approach in accurately modeling the system's behavior.

An MS 7.4 earthquake struck China Maduo County in 2021, and it was a typical strike-slip rupture earthquake with clear directionality. A near-fault bridge named as the Yematan No.2 Bridge suffered severe seismic damage in the Maduo earthquake. To analyze the seismic damage mechanism of the Yematan No.2 Bridge, the detailed finite element model of the bridge upline and downline was established in this study. To analyze the coupled effects of soil liquefaction, traveling wave effects, and seismic inertial forces, and to make the numerical simulation results better reflect structural seismic responses under real-site liquefaction conditions, this paper proposes a simplified method for simulating ground motions in liquefiable sites. This method integrates key effects induced byliquefaction into the ground motion simulation process. The detailed finite element model of the bridge upline and downline was established in this study. Then, the near-fault seismic bedrock motion of three directional components was synthesized by using the velocity pulse method to simulate the low-frequency pulse component and the stochastic finite-fault method to simulate the high-frequency component. The seismic ground motion was inversely computed by the equivalent linear method, and the field residual displacement measurement was used to optimize the seismic ground motion amplitude. Furthermore, to study the soil liquefaction effect on the bridge seismic damage, a simplified model based on planar one-dimensional wave theory was employed, and the seismic ground motion on the soil liquefaction site was computed through the site transfer function by using the inverse Fourier transform. Finally, the bridge seismic response analysis was conducted under non-uniform seismic excitation to consider the seismic traveling wave effect. The results show that the bridge severe seismic damage is caused by the following multiple factors: (i) the fault rupture directionality of the near-fault earthquake results in the significant girder displacement along the bridge; (ii) the differential displacements between the upline and downline are also attributed to the soil liquefaction effect; (iii) the seismic traveling wave effect of strong seismic motion exacerbates the bridge seismic damage.