Abstract: On the basis of the thermal shrinkage effect,the ultra-long isolated structures may undergo seismic action during their operation period.Combination of the isolation layer displacement under the combined action of thermal-shrinkage-seismic was studied to ensure the safety and economy of ultra-long isolated structures design.Firstly,a combined method for the isolation layer displacement under the combined action of thermal-shrinkage-seismic was proposed based on the total probability theorem.Secondly,methods for determining annual exceedance probability function and thermal shrinkage displacement of the isolation layer were presented.Using a ultra-long isolated structure in a cold region as an example,the non-linear relationship between spectral acceleration (S_a(T₁)) and seismic displacement of the isolation layer was determined using incremental dynamic analysis (IDA) method.The annual exceedance probability function of the horizontal two-way maximum seismic displacement of the isolation layer was then obtained.A monthly root mean square temperature correlation model of the isolation layer was established to provide a basis for temperature prediction of the isolation layer during operation period.Using temperature and humidity data from the project site over the past 55 years,a probabilistic distribution model was obtained for the horizontal two-way maximum thermal shrinkage displacement of the isolation layer.The displacement of the isolation layer under the combined action of thermal-shrinkage-seismic was combined.The results show that as the horizontal two-way seismic displacement fractile values of the isolation layer increase,the combination value coefficient of the horizontal two-way maximum thermal shrinkage displacement gradually decreases.However,this decrease is limited and the dispersion of the combination value coefficient of the maximum thermal shrinkage displacement of the isolation layer is very small.For the sake of structural design and performance analysis,it is proposed that the combination value coefficient for the maximum thermal shrinkage displacement of the ultra-long isolated structure is set at 0.393.