关键词: 地震反应谱, 地震动, 抗震设计, 桃夭门大桥

Abstract: With the construction of more and more super-high buildings and large scale flexible structures,great attention has been paid to information about long-period response spectrum exceeding 4～6s,which is the basis of anti seismic design of large scale flexible structure. However,most of current anti-seismic codes,such as the anti-seismic design codes for highway construction used for the basis of large highway bridge design,are inadaptable just due to shortage of available information of the spectrum noted above. In consideration of the need of long period spectrum in the design of Taoyaomen large bridge in Zhoushan City,this paper focuses on the investigation and analysis of the basic characteristics of seismo-geologic environments of the bridge site and presents the state of art of the research of long period ground motion spectrum. On the basis of the analysis of the basic characteristics of long period component of 72 ground motion records chosen from 11 representative strong earthquake records,as well as in the light of the determining method of ground spectrum for specific sites of the Nuclear Safety Code [HAF0101(1)],the long period response spectrum based on middle response spectrum is established in this paper through statistic analysis method. According to the basic forms and characteristics of the average spectrum of strong motion records,this paper utilizes zigzag spectral form to represent the average spectrum of strong motion records under various ground condition. In consideration of the reliability of strong motion records,especially the long period part,the average value of seismic response spectrum of the bedrock within period field spectrum is processed separately: those of less than 4.0s period build on data from all samples,and those of greater than 4.0s period build on more reliable ground motion records,involving mainly the samples with PGA of above 100gal (0.1 g ). Moreover,comparison has been made with some standard seismic response spectrum related to the Taoyaomen site,which includes: 1) horizontal and vertical average probabilistic spectrum obtained from ground probabilistic earthquake risk analysis; 2) Probabilistic spectrum (50yrs,above 10% exceeding probability) for Fuchi Island near the Taoyaomen large bridge presented in the report of earthquake safety assessment of the bank area of Yeyashan-Cezi Island,Zhoushan City submitted by Institute of Crustal Dynamics,China Seismological Bureau in 1988. The comparison shows that the average spectrums of bedrock records of the period of 6～10s,whether the mean spectrum or the mean plus 1σ one is much higher than the probabilistic spectrum of the site. The following two factors are considered: 1) the site where Taoyaomen large bridge is situated belongs to low seismicity and relatively stable area,and the basic earthquake intensity for the area is assigned to be Ⅵ Degree; 2) As a whole,the standard of seismic design of highway architecture is lower than that of nuclear facilities and hydro constructions,so taken the 3% exceeding probability per century as the basic estimation of large bridge deformation is approximately equal to the seismic activity level of one event per 3000～4000years. Therefore,6～10s long period response spectrum can be used for the design spectrum of Taoyaomen bridge,similar to the determination method used in most of the engineering seismic design regulations. The comparison of the results shows that it is feasible to use long period response spectrum based on middle response spectrum as the basis of design spectrum of Taoyaomen bridge in Zhoushan City. From the point of view of the present research situation of long period ground motion response spectrum and the rapid growth of the need of long period design spectrum in engineering design,this research topic is not only of universal significance,but also provides operable reference for seismic design of engineering that needs the long period design spectrum. In consideration of the certain limitation of frequency characteristics of simulated strong-motion records.

Key words: seismic response spectrum, strong ground motion, seismic design, Taoyaomen Bridge