| Energy dissipation technology is to set energy dissipating devices（such as dampers）in some parts of the structure（such as connections,shear wall,etc.）to consume seismic energy and reduce the seismic responses of the major structure through friction,buckling,elastic-plastic hysteretic deformation,so as to reduce the damage of the major structures.The friction damper is favored by domestic and foreign scholars because of its excellent characteristics including clear force,stable energy dissipation,simple structure and convenient installation.However,the traditional friction dampers have some disadvantages such as unchangeable friction force and lack of the ability of recentering.In this paper,the traditional sliding friction damper is improved.Two friction dampers,VFD and SC-VFD,are proposed based on the structure of slope sliding plates and belleville springs,which can improve the shortcomings above.A series of hysteretic performance studies are carried out for the two types of energy dampers.At the same time,the variable friction damper is applied to the self-centering prestressed concrete beam-column connectons in which shear resistance is provided by hidden corbel and the hysteretic behavior of HC-VFD-SCPC beam-column connections is analyzed.The main research contents and conclusions are as follows:（1）The structure of the two kinds of variable dampers are analyzed and their working mechanism is expounded.Through the combination of slope panels and bolts,the effects of variable initial sliding force and variable friction are realized,and the variable friction damper can also have a recentering force.According to the stress balance equation,the working mechanism of the slope surface is analyzed,and the theoretical formula of the output of the damper in each stage under the ideal state is derived.The theoretical hysteretic model of the variable friction damper is established and the calculation formulas of the parameters in the model are given.（2）In order to verify its working mechanism and optimize the structure details,a reciprocating tension test is carried out for a VFD.The tests of optimized VFD and SC-VFD are carried out respectively,and the hysteretic performance,energy consumption,equivalent viscous damping ratio and other parameters are studied by considering variable parameters such as preload force of bolts and belleville springs stiffness.In addition,three-dimensional elaborate finite element models are built in ABAQUS to verify the rationality of the design of the variable friction damper.It shows that the theoretical hysteretic model is in good agreement with the test and simulation,and the the damper has strong energy dissipation capacity and variable friction performance.Through the rational design of slope angle,initial preload and other parameters,the expected energy dissipation effect of variable friction can be realized.Aiming at the phenomenon of uneven opening of SC-VFD during loading,a simplified"spring-bearing"model is established and calculated in MATLAB,which can be used to analyze the deformation form of uneven opening.The validity of the simplified model is also verified.（3）A new type of HC-VFD-SCPC connections is proposed and designed by combining the variable friction damper with unbonded post-tensioned prestressed concrete beam-column connections,which has the advantages of being self-centering,variable friction,strong shear resistance and high assembly efficiency.The detailed structure of HC-VFD-SCPC is optimized and the parameters of friction force,axial shear moment,rotational stiffness and self-resetting coefficient are derived in every working stage according to its working performance.A theoretical hysteretic model of connection is established,which is an improved flag-like curve with two corners,three stiffness and adjustable energy dissipation.According to the performance of HC-VFD-SCPC connections,three performance objectives and processes are proposed,and one connection is designed.（4）The three-dimensional detailed finite element model of HC-VFD-HCPC connections is established to analyze the hysteretic behavior of the connections and the parametric analysis of the model are carried out.The results of finite element analysis show that when the interlayer displacement angle reaches 4%,the HC-VFD-HCPC connections remains elastic and self-centering as expected.Design parameters,such as initial preload of bolt p,stiffness of belleville springs KCBS,initial post-tensioned force Fpt,number of post-tensioned tendons n,distance of plane section L,etc.have great influence on hysteretic performance indexes.Considering the design parameters comprehensively,the connections can be well designed to meet the performance requirements under different seismic intensities. |
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