Study On The Far-filed Long-period Ground Motion Intensity Index And Spectrum Characteristic Index

In recent years, with the development of social economy, super high-rise buildings, tall structure, large span bridges and more long-period structure have been built, it is easily produce resonant response with far-field long-period ground motion,casing strong vibration and even serious damage,So when aseismic design of long-period structure should pay attention to the influence of the far-field long-period ground motion. At present,the seismic time history analysis need a index to select and adjust the ground motion input,but now the index of research for long-period structure is relatively few, so it is necessary to further study the ground motion intensity index and spectrum characteristic index of the long period structure. In this paper, using ANSYS finite element software to establish a simplified model of super high rise structure, input far-field long-period ground motion on the model to obtain top displacement and the maximum inter story displacement of structure model by the time history analysis. The correlations of the ground motion intensity index, the spectral characteristic index and the peak displacement, the maximum inter story displacement of the structure respectively were analyzed, then the structure of the period and damping ratio was changed to get the correlation with the change of the structure period and damping ratio. The main work and conclusions are as follows:1.The principle of choose far-filed long-period ground motion was determined,then choose 19 far-field long-period ground motion for the study and correct the ground motion,the ground motion intensity index and spectral characteristics index of ground motion were extracted.2.Five different heights(50,75,100, 120 and 150 layer)of the high-rise structure model were established using ANSYS software, Time history analysis is carried out on the five models and damping ratio was changed to get the top displacement and the maximum inter story displacement.3.The correlations of the ground motion intensity index, the spectral characteristic index and the peak displacement, the maximum inter story displacement of the structure respectively were analyzed.The results show,on the aspect of ground motion intensity index:The correlation cofficient between PGA, Sa(T1), Sd(T1) and top displacement of structure increases with damping ratio ξ increases, the correlation between PGV, PGD and top displacement increases with damping ratio ξ increases on the whole, the damping ratio effect on the correlation betweenaS and top displacement is not abvious, The correlation between Sa(T1) and top displacemen is maintained at more than 0.8, and the varition cofficient is low,so the Sa(T1) was recommend to characterize the top displacement of high-rise buildings; The correlation between PGA, PGD,aS, Sd(T1) and the maximun inter-story displacement withincreases damping ratio ξ increases, the damping ratio effect on the correlation between PGA,Sa(T1) and the maximun inter-story displacement is not abvious.the collection of PGV index is stable in each period, and remain above 0.84, so the PGV was recommend to characterize the maximun inter-story displacement of high-rise buildings. on the aspect of specture characteristic intensity index:the damping ratio effect the correlation between specturm characteristic index and top displacement is not abvious before T=8s, after the correlation between specturm characteristic index and top displacement decreaseswith damping ratio ξincreases except Tpv,the correlation between Tmf and top displacement up to 0.75 and the varition cofficient is 0.35, so Tmh was recommend to characterize the top displacement of high-rise buildings; the collection cofficient of PTA、Tc、gT 、PTD is increases with damping ratio ξ increases, the correlation between PTA, Tmh and the maximun inter-story displacement are less affected by damping ratio, the correlation cofficient between Tg, Tmf and inter-story displacemen is decreases with damping ratio ξ increases after T=8s, the collection cofficient of Tmf is stable in each period and remain around 0.65, it varition cofficient is low, so the Tmf was recommend to characterize the maximun inter-story displacement of high-rise buildings.