Study On The Far-field Long-period Ground Motion Selection And Characteristics

In recent years, with the development of economy, super high-rise buildings, tallstructure, large storage tank, large span structure, and more long-period structure have beenbuilt or building from all over the world, it is easily produce resonant response with far-fieldlong-period ground motion, causing strong vibration or serious damage. Structural seismicresponse depends mainly on the common work, which composed of the ground motioncharacteristics and dynamic characteristics of structure. At present, a little thesis study on thecharacteristics of far-field long-period ground motion, at home and abroad, it is necessary tofurther study on its engineering properties.Based on achievements of studying thecharacteristics of far-field long-period ground motion, this paper analyzed what it caused. Andcombined with the existed long-period evaluation parameters, determined the principle ofchoose far-field long-period ground motion base on K-NET and KIK-NET from the M9.0earthquake which occurred in the northeastern Japan, March11,2011. On the basis of this,this paper select out two big data, the choice set and the control set, and the data processing.Then, studied the main factors of the far-field long-period ground motion, and use theimproved HHT method to discuss what different from the choice set and the control set, suchas dynamic characteristic, the time-frequency characteristic, spectrum period characteristicsand instantaneous power spectrum. The main work and conclusions are as follows:1. Combined with long-period ground motion with far-field sites, taken the M9.0earthquake as data base, determined the principle of choose far-field long-period groundmotion, classified the data according to NEHRP standards of USA, and corrected the groundmotion.2. Studied the influent factors of the far-field long-period ground motion, mainlyincluding propagation distance and site conditions. The results show that the parameters PGA,PGV and PGV/PGA of the far-field long-period ground motion change with propagationdistance have different laws. The same distance, the parameters PGA, PGV and PGV/PGAhave different regularity under the different sites C, D and E. It depends more on sitecondition and propagation distance. But restricted by data, this article does not discuss theeffects of the magnitude and focal mechanism.3. Studied the parameters characteristics and parameters of different componentsbetween the ground and downhole motion records, which come from the far-field long-periodground motion. Results show that the parameters PGA, PGV and PGV/PGA of ground anddownhole motion records have different laws. With changing depth, there is a big differentbetween the curve of horizontal and vertical component. 4. Studied the characteristics of the far-field long-period ground motion, such as dynamiccharacteristics, the time-frequency characteristics, spectrum period characteristics andinstantaneous power spectrum by the improved HHT, which based on the choice set and thecontrol set. At the same time,37ground motion records selected to study their spectrumperiod characteristics and its correlation between parameters. Results show that the marginaland Fourier spectrum of the choice set mainly distributed in0.1~5Hz range. While the controlset distributed more evenly in0.1~30Hz or greater range. Compared with the marginalspectrum, the Fourier spectrum underestimated the amplitude of the ground motion in the lowfrequency part, and overestimated in the high frequency part. The instantaneous powerspectrum of choice set distributed relatively concentrated and smaller than the control set. TheFourier spectrum average period Tmfhas great correlation than the marginal average period Tmh, theproposal use Tmfas evaluation period parameter for far-field long-period ground motion.