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To reveal the failure mechanism of resonance effect on long-periodic structures, the spectrum characterization of nonlinear and non-stationary long-periodic ground movements are studied. Firstly, the period and energy characterizations about IMFs (intrinsic mode functions) of ground movements are analyzed. Then, an energy-weighted average period is proposed to indicate the long-periodic characterization on different types of ground movements. Lastly, the simplified method on the low-frequency time history for long-periodic ground movements is proposed and verified. The research conclusions show that, various Hilbert amplitude spectra analysis can expose all the inherent information of nonlinear and non-stationary long-periodic ground movement accurately and comprehensively. The proposed periodic parameter that characterizes different earthquake classifications can help to efficiently and conveniently filter out long-period ground movements, and it also can be used as a quantitative indicator to identify long-period ground movements. The suggested simplified method can facilitate in-depth and accurate analysis of the low-frequency components of long-periodic ground movements. Effective and accurate evaluation on the low-frequency components of long-periodic ground movements plays the key role to uncover the nonlinear dynamic behavior of long-periodic structures, and it is of great scientific research significance in the field of earthquake engineering and structural engineering. • The spectrum characterizations of long-periodic ground movement can make up for the deficiencies of linear signals analysis. • The suggested periodic parameter can be used as a quantitative indicator to identify long-period ground movements. • The proposed simplified method can facilitate in-depth and accurate analysis on the long-periodic ground movements. [ABSTRACT FROM AUTHOR]

Most of hybrid test researches utilizing OpenSees are based on the hybrid test system framework software OpenFresco. Such software is convenient but can only be connected to specific test control systems, which limits the widespread application of hybrid test. In this paper, a new hybrid test system based on Matlab-OpenSees combined programming is developed, and the details of hybrid test system including core architecture, test facilities and Matlab-OpenSees system are described. Then, the performance verification of test facilities and Matlab-OpenSees system is conducted. Next, the mechanical properties of viscoelastic damper are tested under different amplitudes, frequencies and temperatures. Finally, the hybrid tests of three-dimensional viscoelastic damping structures are implemented by the developed hybrid test system for the first time. The feasibility and accuracy of hybrid test system based on Matlab-OpenSees combined programming are verified by the seismic response comparison of viscoelastic damping structures obtained by the hybrid test and the finite element numerical simulation. A good damping effect of viscoelastic dampers on the structures under earthquake excitation is demonstrated by comparing the results of the damped and undamped structure. • A new hybrid test system based on Matlab-OpenSees combined programming is established. • The Matlab-OpenSees interface is developed based on TCP/IP communication protocol and network communication principle. • The test facilities can high-precisely track the displacement commands and meet the requirements of displacement control in hybrid test. [ABSTRACT FROM AUTHOR]

Viscoelastic (VE) damper exhibits significant mechanical nonlinearity under dynamic loads due to variations in the temperature, excitation frequency, and the occurrence of large strains. However, in the existing research literature, such nonlinearity is barely considered, and its effects on the aseismic behaviours of viscoelasticlly damped structure (referred to as VE structures) are also unclear. In this paper, a modified equivalent fractional Kelvin model is established to depict the mechanical nonlinearity of VE damper with the introduction of internal variable parameters. Through the comparison with the existing mathematical models for the performance of an individual VE damper, it is found that the proposed model has a high prediction accuracy, especially in the large-strain working condition. To incorporate the effects of real-time change of the mechanical properties of VE dampers on the seismic responses of structures equipped with such dampers, an approximate method is devised for the numerical calculations. Two representative VE structure with proportionally and non-proportionally damped system are analysed with consideration of the time-varying mechanical nonlinearity of VE dampers. The discrepancy between the seismic responses of the VE structure with and without considering the nonlinearity is discussed. The results indicate that the mechanical nonlinearity of VE dampers could introduce a negative effect on the actual seismic resistance capacity of a VE structure, leading potentially to the structure not meeting the design requirements of codes when the mechanical nonlinearity occurs. The study concludes that it is necessary to take the mechanical nonlinearity into account in the design and performance evaluation of VE structures. • A modified equivalent fractional Kelvin model with high prediction accuracy is established to depict the viscoelastic nonlinearity of VE damper. • An approximate method is devised to incorporate the effects of mechanical properties of VE dampers on the seismic response of VE structures. • The viscoelastic nonlinearity can introduce a negative effect on aseismic capacity of a VE structure, leading potentially risks to the structure. [ABSTRACT FROM AUTHOR]

The variable friction self-centering energy dissipative (VF-SCED) device is proposed to solve the challenge for the developed SCED braces on the weak energy dissipative capacity or too complex energy dissipative system, and the conflict between the self-centering ability and energy dissipative ability. The composition and working principle of the VF-SCED brace are described, the theoretical equation for controlling brace performance is developed, and the key parameters are identified. Two VF-SCED brace specimens were fabricated and tested. Furthermore, the finite element (FE) model of the VF-SCED brace was established and analyzed. The parametric analysis is carried out based on the verified VF-SCED brace FE model. The experiment results show that the hysteresis loop of new device performs typical flag-shaped and almost no residual displacement after tested. The simulation results are close to the experimental and theoretical results, and the FE model can effectively reflect the working properties of the VF-SCED device. The parametric analysis shows that increasing spring stiffness and preload length have a positive effect on the energy dissipative ability and self-centering capacity of the brace. The increase of tan θ has a negative effect on the energy dissipative capacity but a positive effect on the self-centering capacity. Increasing the magnitude of wedge blocks and friction coefficient μ 2 has a positive effect on the energy dissipative capacity but a negative effect on the self-centering capacity. The increase of static friction coefficients μ 1 and μ 3 will reduce the energy dissipative capacity of the VF-SCED brace, but the influence is small. The research shows that the energy dissipative and self-centering capacity of the VF-SCED brace have a large variable range, and the key parameters can be determined according to engineering application and design requirements. • The novel variable friction self-centering energy dissipative device is developed and introduced. • The details and working mechanism of the new system are described, and the theoretical equation is identified. • The specimens were fabricated and tested, and the finite element and theoretical model were established and verified. • The parametric analysis is carried out based on the verified finite element model. [ABSTRACT FROM AUTHOR]

Evaluating the performance degradation of the earthquake-damaged structure and optimizing the placement of dampers is important for retrofitting post-earthquake structures. In this study, a damage evolution model is developed to evaluate the degradation of strength, stiffness, and energy dissipation capacity for earthquake-damaged structures. The proposed damage model is validated using previous experimental results based on the nonlinear finite element analysis. Then, research on the optimal design of damper parameters and quantity is carried out. Considering the optimization range of earthquake-damaged structures, a genetic algorithm with multi-objective functions is developed to determine the optimal placement of viscoelastic dampers in damaged structures. The results demonstrate that the proposed damage model can effectively describe the performance degradation of damaged structures. The control effects of the acceleration response increase exhibited a maximum enhancement of 3.38 times after accounting for the optimization range of earthquake-damaged structures. The optimization results of the multi-objective function with the optimization range are better aligned with the objectives of designers. • A damage model is developed to evaluate the degradation of strength, stiffness, and energy dissipation for structures. • Understanding of the beneficial effect of the viscoelastic damper on the seismic response for earthquake-damaged structures. • A genetic algorithm with multi-objective functions is developed to optimize the design and placement of VE dampers. • The control effects of the acceleration response increase exhibited a maximum enhancement of 3.38 times. • The optimization results of the proposed method are better aligned with the objectives of designers. [ABSTRACT FROM AUTHOR]

The harmful vibration of the building structure usually can lead to huge casualties and property losses, it is necessary to reduce and eliminate the detrimental effect through effective vibration control device. In this paper, the viscoelastic damping limb-like-structure (VE-LLS) device is proposed by combing the viscoelastic (VE) damper and the limb-like-structure (LLS) together, which possesses coupling nonlinear characteristic that is benefit for improving the vibration control performance for building structure. Firstly, the property experiment is carried out to study mechanical performance of the proposed VE-LLS device, and the results show that the proposed device has better energy dissipation capacity and stability, the final failure mode of the device usually is caused by destruction of the VE damper. Next, the hysteretic curves of experimental results are plotted and discussed, and equivalent stiffness K e and equivalent damping C e are calculated to study the nonlinear influence of geometrical parameters on mechanical properties of the proposed device. Then, the mechanical model of the proposed device is established by considering the viscoelastic force and the friction force together. Lastly, the experimental and numerical results are compared and discussed together, and the results indicate that the established mechanical model has excellent accuracy and can precisely describe mechanical property of the proposed device. • The viscoelastic damping limb-like-structure device with coupling nonlinear characteristic is proposed by combing the viscoelastic damper and limb-like-structure firstly. • The property experiment of the proposed device is performed. The test results show that the proposed device has good energy dissipation capacity and stability;. • The mathematical model of the proposed device is established, which has excellent accuracy to describe the mechanical property of proposed device. [ABSTRACT FROM AUTHOR]