Research On Time-Varying Vulnerab Ility Of Base-Isolated Buildings In Southwest Alpine Region

The southwest alpine region has always been one of the regions with the strongest seismic activity in the country.For a long time,earthquakes have occurred frequently,posing a huge threat to the safety of people’s lives and property.From the perspective of earthquake damage,the top priority is to improve the resistance level of local building structures.The technical conditions for seismic isolation of buildings are relatively mature,and the effects of earthquake prevention and disaster reduction have been tested worldwide,and seismic isolation bearings have many advantages such as simple installation,easy construction,and high economic efficiency,making it a building in the region to improve seismic tolerance Ideal choice.According to the different positions of the seismic isolation support,it can be divided into ground,underground,indoor,outdoor and other methods.During the service period,the mechanical properties of the seismic isolation building will change with the increase of service time.The resistance of buildings will inevitably decline.For example,the rubber material is the active molecule in the shock-isolating support,and the support gradually deteriorates in the long-term contact with the external environment.At the same time,there are many uncertain factors in the main structure of the seismic isolation building.The coupling effect of structural randomness and time-varying properties reduces the reliability and safety of the structure,loses the performance margin it should have at the beginning of the design,and has a negative impact on the resistance of the structure.Therefore,the evaluation of the resistance of the seismic isolation building after the performance declines Have certain practical needs.In this paper,the equivalent simulation freeze-thaw degradation test is used to study the time-varying characteristics of the mechanical properties of the shockisolating support rubber material in the southwest high-cold freeze-thaw environment;select suitable steel,rubber,and lead materials in the lead-core rubber shock-absorbing support The constitutive relationship,and the expression of the random time-varying constitutive relationship of the rubber is introduced;then,the finite element model of the lead-core rubber isolation bearing is established to analyze the vertical and horizontal performance of the bearing,and the time-varying law of the equivalent damping ratio;Based on the probability density evolution theory,the equivalent horizontal stiffness is used as the evaluation index to solve the freeze-thaw time-varying reliability of the two types of supports;finally,a seven-story base isolation frame building（the support is above ground/outdoor layout）is used as For example,systematically studied the time-varying vulnerability of the structure under different freezing and thawing times.The main research contents and conclusions are as follows:（1）Through experiments to simulate the actual freezing and thawing environment in the southwestern alpine region,it is feasible to degrade the performance of the rubber material of the vibration isolation support.The temperature range of the freezing and thawing machine should be controlled during the test to avoid aggravating the crystallization of rubber.The mechanical parameters of rubber samples are significantly affected by the freezing and thawing environment.After 50 years of freezing and thawing,the mechanical parameters of the rubber samples degrade significantly.（2）In the finite element software,the Mooney-Rivlin constitutive relationship can be used to better simulate the change process of the mechanical properties of the rubber sample when it is stretched.It is found during simulation that the vertical and horizontal mechanical performance parameters of the seismic isolation support after freezing and thawing have different degrees of decline,and the parameters of the large-diameter support have a relatively significant decline.（3）The Latin hypercube algorithm and probability density evolution theory are used to calculate the dynamic reliability of a frame structure,which verifies that the latter has high analysis efficiency and accuracy when dealing with compound random problems,and can describe the probability of structural response.Evolution information.Based on the probability density evolution theory,the time-varying reliability of the lead-core rubber isolation bearing is solved,which proves that the reliability of this type of bearing has dropped significantly after 20 years of service in a freeze-thaw environment.（4）Taking a multi-layer isolation frame structure as an example,comprehensively consider the randomness of the main structure parameters and the time-varying and randomness of the seismic isolation support parameters.After defining the limit damage limit of the structure,draw the time-varying vulnerability curve（surface）of the structure under various service periods and various performance levels.It shows that the variability of the vulnerability curve of the structure increases with the increase of the performance level judgment index;the vulnerability curve of the structure shows obvious difference under different freezing and thawing times;When a strong earthquake occurs,the development trend of the vulnerability curve is different,which proves that this type of structure has greater survivability in the event of a strong earthquake.