In Situ Assessment Of The Fundamental Period Of Site Based On Strong Motion Data

One of the main reasons for the damage of building structures caused by earthquakes is that the natural period of the site is just close to the one of the building structure in the earthquake,generating resonance and causing serious damage.The site amplification and the fundamental period of the site need to be estimated during site selection and design of buildings and engineering facilities.Two studies were carried out using the ground motion records from Center for Engineering Strong Motion Data(CESMD)in the US and KIK-NET in Japan.One is the application comparison of the methods for estimating the fundamental period,and the other is the relationship between the fundamental frequency of different site classes and the change of PGA or PGV.The purpose of this research is to reveal the applicability of different assessment methods and the influence law of intensity of ground shaking on the fundamental frequency,so as to provide a scientific basis for earthquake fortification of construction projects.The main results are as follows:1.The in-situ methods for estimating the fundamental period are studied,including shear wave velocity method,ground to borehole spectral ratio method,horizontal to vertical spectral ratio method and mode identification(CMIF)method.2.Treasure Island Geotechnical Array(Class E),Delaney Park Geotechnical Array(Class D),Obregon Park Geotechnical Array(Class C)and IWTH23 Geotechnical Array(Class B)selected from the CESMD and KIK-NET are used as research cases,and the six methods introduced in this paper are used for the fundamental period assessment.The results show that the peaks of the site amplification corresponding to the fundamental frequencies identified by the ground to borehole spectral ratio method are clearer,the standard deviation of the fundamental periods of the assessed site is the smallest,and the method has high stability,which is widely applicable to sites with uphole and downhole strong motion observation data.The method can be used to study the law of the fundamental frequencies of the site changing with the intensity of ground motion.3.Selecting the data that meet the requirements of the signal-to-noise ratio from the more than 800,000 sets of three-component ground motion observation records recorded by the KIK-NET strong motion observation network in Japan from October 1997 to June 2021.The downhole spectral ratio method evaluates the fundamental frequency of the ground under different ground motions.Forty-five arrays that recorded ground motion data with PGA higher than 500 cm/s2 were selected first for research,and the fitting results of the fundamental frequency of the site with PGA and PGV were obtained according to different site types.The relationship between the fundamental frequency of the site and the ground motion intensity(PGA and PGV)both satisfy the hyperbolic model:(?)...