Numerical Simulation Of Seismic Responses Of A Scaled Single-Layer Spherical Lattice Shell Structure Isolated With Friction Pendulum Bearings Considering Variable Friction Coefficients

Friction pendulum bearings(FPBs)are widely used spherical sliding friction isolation devices,and their friction coefficients have significant impacts on the isolation performances of this type of isolation bearing.It should be noted that the friction coefficients vary with different contact pressures,horizontal sliding velocities,and lubrication conditions.Sliding friction mechanisms under heavy loads of full-sized multistory buildings and bridges have been extensively studied so far.However,for the scaled models of FPB-isolated structures,their sliding friction behaviors and related parameter calibrations under relatively low pressures have been rarely attracted scholars.Consequently,quasi-static experiments were conducted on a scaled FPB specimen under multiple low pressures in this study.Variable friction coefficient models at device-and structure-levels were developed using the obtained experimental results,respectively.The seismic responses of a scaled test structure of single-layer spherical lattice shell with FPBs were numerically simulated considering the influence of variable friction coefficients.The main contents of this thesis are listed as follows:(1)A scaled FPB specimen for shaking table tests of an isolated lattice shell model was adopted as the research object.A series of quasi-static experiments was performed on this isolator specimen to obtain its cyclic responses.During this experimental study,various loading conditions,such as low contact pressures,sliding velocities,and lubrication states,were applied to the FPB specimen.The results indicate that the friction coefficients of the FPB under low pressures are not a constant,but variables related to the aforementioned loading conditions.(2)Based on the experimental data,the hysteretic characteristics and mechanical performance parameters of the FPB specimen were discussed.The variation laws of the sliding coefficients were summarized considering the influence factors including the contact pressures,sliding velocities,and lubrication states.According to a previously proposed model describing variable friction coefficients,corresponding parameter values for non-lubricated and lubricated conditions of the sliding surface of FPB were determined,respectively.(3)A user subroutine program incorporating the variable friction coefficient model was implemented into ABAQUS,which can be used for the numerical simulation at a device-level.In addition,the variable friction model of OpenSees was employed to simulate FPBs at a structure-level,and the related parameters were calibrated using the experimental data.The numerical simulation results obtained by the two software are in good agreement with the test results,and the errors between them and the corresponding measured friction coefficients are less than 5%,which can accurately predict the sliding friction behavior of FPB.(4)A numerical model of a test structure of FPB-isolated spherical lattice shell was constructed using OpenSees,and Coulomb and variable friction coefficients were used to define the friction properties of the FPBs.The influences of different friction coefficient models on seismic performances of the isolated test structure were compared and analyzed through simulation of structural seismic responses.The research results indicate that the error between the simulated results using the variable friction coefficient model and the experimental results can be reduced by 5% compared to the Coulomb model,indicating that the numerical model of FPB isolation structure with variable friction coefficient can more accurately simulate the seismic dynamic behavior of the test model compared with the Coulomb model.