Research On Response Spectrum Of Equipment Sliding Floor In Isolated Structure Equipment Combination System

In China,the current design codes for seismic testing of equipment based on the equivalent lateral force method,rely on the response spectrum calculation in seismic codes,for which the accuracy of the seismic checking of equipment depends on the accuracy of the response spectrum.However,the response spectrum given by the code was based on the premise of seismic structure,which is significant different from that of seismic isolated structure in terms of mechanical properties,resulting in a large error in the calculation results.On the other hand,when checking the isolated structure-equipment combination system,the interaction between the two is usually ignored,and the calculation results fail to meet the seismic requirements of equipment due to the higher seismic requirements of equipment in medical,electric power,communication and other industries.In this paper,the interaction between the main system of the structure and the sub-system of the equipment in seismic isolated structure-equipment combination system and the nonlinearity of the system were considered,and a simplified calculation method of seismic force of unanchored equipment based on the floor design response spectrum of isolated structure-equipment combination system was given by fitting and calibrating the response spectrum of floor design of isolated structure-equipment combination system,which provided some references for seismic isolation and shock absorption of equipment.The main research contents were as follows:(1)In consideration of the system nonlinearity and the interaction between the main system and subsystems,a mechanical calculation model of the isolated structure-equipment composite system was established based on the Bouc-Wen model to represent the system’s restorative force.What’s more,based on the Stribeck model,the motion equations of the main structural system and the equipment subsystem under the condition of equipment slip were established respectively.Accordingly,combined with the actual isolated structure and the time-history analysis with MATLAB programming,the mean response spectrum of the isolated structure-equipment combination system was calibrated,and the effects of six factors on the isolated structure-equipment combination system were selected,including the mass ratio of equipment mass to the floor,structural frequency,equipment position,site conditions,the ratio of static and static friction coefficient,and the transition coefficient of friction model.The findings showed: when the mass ratio between the equipment and the layer on which the equipment is located was greater than 1/10,the interaction between the sub-structure and the main structure cannot be ignored;with the increase of the frequency of the main system,the seismic response of the equipment also increased;the location and site conditions of the equipment also had certain influence on the seismic device response;the dynamic and static friction coefficient ratio had an obvious effect on the response of device in the low and medium friction region,while the influence in the high friction region was negligible;and the transition coefficient of friction model had little effect on the device response.(2)According to the spectral shape characteristics of the obtained mean response spectrum,the response spectrum was divided into low,medium and high zones,and calibrated by the least square method.In addition,the sample calculation was arranged in an orthogonal experimental design,and the visual analysis and residual analysis were carried out on the sample data to determine the influence of each factor on each parameter,fitted the specific mathematical expression of the parameters,and got the response spectrum of the floor design of the isolated structure-equipment combination system.By compared the fitting spectrum with the mean spectrum,it was found that the two tests were in good agreement,and that the response spectrum of the obtained floor design in the isolated structure-equipment combination system had a certain accuracy and rationality.(3)Through selected a practical isolated structure,designing three different isolation bearing arrangements,and selected nine different working conditions,based on the floor design response spectrum of the isolated structure-equipment combination system,the seismic force of the equipment was calculated.Accordingly,compared with the calculation results in time history analysis and specification,it was found that the error in this method and time history analysis was within 5%,while the mean error of the results obtained by standard and time-history analysis was about25%.It showed that under the premise of foundation isolation,the simplified calculation method proposed in this paper was more reasonable in the seismic checking calculation of floating release equipment,which provided a reference basis for seismic isolation of equipment.