Research Of Observation Environment Impacting On The Strong-motion Records

Stipulation on China Digital Strong Motion Network makes the following provisions for the location of fixed strong motion stations: Fixed strong motion stations should be located in the free space avoiding major changes in the location of the local terrain, such as a hill, ridge or river valley that might create ground motions not expected to be experienced by nearby sites of interest. At the same time, it should be sited a distance of at least one major structural dimension (height or length, whichever is greater) from any large building likely to cause significant soil-structure interaction effects that will contaminate the data. With the development of town planning and construction of high-rise structures, the location of some stations haven't meet the requirements of Stipulation on China Digital Strong Motion Network: some on the edge of scarp, some on the hill, and some near the valley sides, while others have relatively flat topography, but have a little distance to tall building. The records obtained by this way could be amplified or reduced comparing with records of free space. This article takes it as a starting point, selecting some stations in Sichuan Province, combining their acceleration records obtained in Wenchuan ML8.0 Earthquake on May 12th,2008 and the damage surveys within 500 meters around these station, using numerical simulation, discussed the observation environment impacting on the records of strong ground motion under SV wave vertical incidence as follows:(1) Local site terrain effect impacting on the strong motion records. Taking the river valley of Bajiao strong motion station in Shifang for instant, this paper established a finite element model to analyses the changes of peak ground acceleration and spectrum property with the distance to the valley edge using uniform excitation. So it provided a theoretical basis for the location of strong motion stations under the valley terrain;(2) Taller structures impacting on the strong motion records. Taking the signal tower around Jiangyou strong motion stations for instance, this paper established a finite element model to analyses the changes of peak ground acceleration and spectrum property with the distance to the tower using uniform excitation, and combined with the damage surveys within 500 meters around this station. The result proved that the records of Jiangyou station had been amplified.(3) Strong motion observation room and the pier of accelerograph impacting on the strong motion records. According to the specification of Stipulation on China Digital Strong Motion Network on the strong motion observation room and the pier, this paper established relevant model to prove that the strong motion observation room had a little influence on the records, while the impact of the of the pier's height was larger.