| Earthquake is a kind of common natural disaster.When the seismic response of structure is too large,it will cause structure damage even to collapse,resulting in a lot of life and property losses.How to reduce the seismic response of the structure and improve the seismic performance of the structure is a very important research topic.As a classical passive energy dissipation and seismic mitigation device,the viscoelastic damper has the advantages of strong energy dissipation,simple structure,easy installation and low price,which is widely used in structural damping and seismic control.At present,the domestic and foreign scholars have conducted a lot of researches on viscoelastic damping and seismic control technology of building structures and have made many achievements.But there are still some problems that need to be further studied,especially that the investigations of the viscoelastic damper at micro-and meso-scale are rare.Therefore,based on the multi-scale research method,the mechanical behavior and energy dissipation mechanism of viscoelastic materials are investigated in micro-and meso-scale,as well as the dynamic mechanical performance test and finite element analysis,mechanical model of viscoelastic dampers,and the seismic mitigation analysis of viscoelastic damping structures.The main research work is as follows:(1)Spatially simplify the micro-configuration of the molecular chain network of viscoelastic materials.The influence of cross-linked chains,the constrain effects of surrounding molecular chains,entangled network chains and entangled-like network chains on the mechanical behavior of viscoelastic materials is studied.The effects of free molecular chains,non-equilibrium entangled network chains,non-equilibrium entangled-like network chains and filler network on the energy dissipation of viscoelastic materials are researched.The results show that the mechanical properties and energy dissipation capabilities of viscoelastic materials are closely related to the microscopic molecular structures and the filler network system of the rubber matrix.(2)The molecular dynamic simulation method is used to simulate the mechanical behavior of the viscoelastic material in the microscale,and the effects of molecular chain length,ambient temperature and loading rate on the mechanical behavior of the viscoelastic material are analyzed.The representative volume element method and the finite element calculation with the aid of ABAQUS software are utilized to investigate the mesoscale mechanical behavior and energy dissipation performance of the carbon black filled viscoelastic material.The enhancement effect of filler structure on the modulus and energy dissipation capacities of viscoelastic materials is verified.(3)Based on the mechanical behavior and energy dissipation mechanism researches of viscoelastic materials in micro-and meso-scale,the viscoelastic material and damper with good mechanical properties and energy dissipation capabilities are developed.The dynamic mechanical properties of viscoelastic dampers are tested under different ambient temperatures,displacement amplitudes and loading frequencies,and the effects of temperature,displacement and frequency on the mechanical properties and energy dissipation capacities of the damper are analyzed.The results show that the developed viscoelastic damper has good energy dissipation performance under different conditions,and the temperature,frequency and displacement amplitude have a significant effect on the mechanical properties and energy dissipation capacities of the damper.(4)The dynamic mechanical properties and energy dissipation capacities of the viscoelastic damper are further analyzed by using the finite element method.The size variation influence on the damper performance is studied,and the self-heating phenomenon of the damper under sinusoidal displacement excitation and the damper properties change during the heating process are discussed.The cracking failure of the damper in the working process is researched.The results show that the equivalent stiffness,equivalent damping and single-loop hysteretic energy dissipation of the viscoelastic damper are greatly affected by the size change of the damper.When the loading circle number increases,the self-heating phenomenon of the viscoelastic layer turns obvious,and the internal temperature increment of the material has a great influence on the damper performance.The maximum shear strain,loading rate and initial crack length greatly affect the generation and propagation of cracks at the interface.(5)Based on the microscopic molecular configuration of viscoelastic materials,the viscous damping properties of the materials are characterized by the fractional-order mechanical model.The temperature-frequency equivalent principle and amplitude-temperature equivalent principle are used to study the influence of temperature and displacement amplitude on the dynamic mechanical properties of the damper.The equivalent fractional multi-layer network chain model and the equivalent fractional micro-scale structure mechanical model of viscoelastic dampers are proposed.The comparisons with the experimental results show that the proposed models can well describe the influence of loading frequencies,ambient temperatures,displacement amplitudes,filler and molecular chain network microstructures on the damper performance.(6)Based on the rod model of the reinforced concrete frame structure,the elastoplastic time-history analysis program of viscoelastic damping structure with and without control is compiled.By analyzing the storey response of the structure under common and rare earthquakes,viscoelastic dampers are used to design the seismic mitigation and retrofit of the reinforced concrete frame structure.Considering the safety and economy of seismic mitigation and retrofit schemes,the genetic algorithm is used to optimize the number and installation locations of viscoelastic dampers,and the earthquake mitigation effects of the viscoelastic damping retrofit schemes are verified.The innovations of this paper are as follows:(1)The mechanical behavior and energy dissipation mechanism of viscoelastic materials in micro-and meso-scale are revealed.The influence of cross-linked chains,the constrain effects of surrounding molecular chains,entangled network chains and entangled-like network chains on the mechanical behavior of viscoelastic materials is discovered.(2)Through the systematic performance test of the viscoelastic damper in the wide temperature range(-10??40?),it is found that the dynamic parameters such as equivalent stiffness and damping change rapidly in low temperature region but slowly in high temperature region,and finally tends to a uniform value.The extending law of the damage crack in the viscoelastic layer are investigated simultaneously.It is found that the maximum shear strain,loading rate and initial crack length have significant influence on the generation and propagation of cracks at the interface.(3)The microstructure based mechanical models that can well describe the dynamic mechanical properties and energy dissipation capabilities of viscoelastic dampers with different temperatures,frequencies and displacements are proposed. |
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