Study On Response Spectrum Of Wenchuan Earthquake

M. A. Biot presented response spectrum theory at the third decade of 20th century, and until the fifth decade of 20th century, G. W. Housner developed the first seismic design response spectrum. From then on, response spectrum method is widly accepted internationally, which indicate that the development of earthquake engineering come into response spectrum theory phases, and research on response spectra continues to today. At present, most countries of the world use seismic design response spectra calculating earthquake action on building structures. Usually, the form of smooth seismic design response spectrum is calibrated by several characteristic parameters, among which the most important are the peak platform value and characteristic period of response spectrum. In the study of response spectra, a lot of work is how to scientifically determine the two characteristic parameters. Site condition is an important factor effecting response spectrum characteristic parameters, but the code for seismic design of our country just consider site condition effects to the response spectrum characteristic period but not the peak platform value of response spectrum. One of the most important reasons is short of ground motion records with site condition.On May 12, 2008, at 14:28 PM local time, a great earthquake of Richter magnitude 8.0 occered near Wenchuan town in Sichuan province, and this earthquake was the most devastating, the most widely spread and the most difficult relief earthquake disaster, since the founding of New China, and it resulted in great tragedy for Chinese. In the"Tenth Five"plan of China, China Earthquake Administration set a great deal of strong motion instruments on the North-South earquake zone. These strong motion instruments net got abundant high quality digital ground motion records. Many of these ground motion records had detailed site condition, and this provides us abundant basic information for our research on spectra and site condition effect on parameters of resonse spectra. This dissertation comprehensively and systemically summarized the results of the current forefront of the field and related literature. Based on collatting strong motion records information of Wenchuan earthquake, it analyzed response spectrum of Wenchuan earthquake and its characteristic parameters statistically, did in-depth reseatch on methods of calibrating seismic design response spectrum, explored the relationship between the response spectrum parameters and site conditions and other factors. The investigation of this work includes:(1) Comprehensively collected and collated strong motion records of Wenchuan earthquake. Collected strong motion records, site condition of stations and station coordinates of 158 soil stations and 16 bedrock stations in Sichuan, Shanxi and Gansu province. Caculated peak ground acceleration and peak ground velocity of each strong motion record.(2) Researched and advanced a new method of calibrating seismic design response spectrum. Methods of calibrating seismic design response spectrum correlate with determination of redponse spectrum characteristic parameters. Based on summarizing many methods of calibrating seismic design response spectrum, this dissertation advanced least square fitting method based on coordinate transformation, and by comparing different calibrating methods, pointed out that least square fitting method is simple and logical calibrating method. Using this method, this dissertation caculated the characteristic parameters of Wenchuan earthquake strong motion records.(3) Researched the effects of site condition and distance from the fault to response spectrum characteristic parameters. Peak platform value of response spectrum denotes the strength characteristic of ground motion, and this parameter relates with a variety of factors. This paper statistically analyzed the peak platform value of response spectrum in different site condition and different distance from the fault subarea. It pointed out that site conditions have a great impact on the peak platform value of acceleration response spectrum. With the soft site, the peak platform value of acceleration response spectrum increases. It caculated the coefficients of site effects of the peak platform value of acceleration response spectrum on different site conditions with different grouping method.(4) Researched the spectrum characteristic of Wenchuan earthquake strong motion. Characteristic period of response spectrum reflects strong motion's characteristic. By statistically analyzing the relationship between the characteristic period and the predominant spectral period and the smoothed spectral predominant period with site conditions and distance from the fault, this paper pointed out that these three kinds of period increase with the soft site, and increase with the incease of the distance from the fault. It also fit the empirical relationship between the characteristic period and the predominant spectral period and the smoothed spectral predominant period.(5) Reasearched the vertical response spectrum of Wenchuan earthquake strong motion. Caculated the ratio of vertical response spectrum to horizontal response spectrum near fault and far fault, and analyzed its different characteristices and factors. Point out that near fault the ratio of vertical response spectrum to horizontal response spectrum obviously affected by"hanging wall"effect. On short periods the ratio of vertical response spectrum to horizontal response spectrum on the hanging wall are bigger than the foot wall, and on the long periods the ratio of vertical response spectrum to horizontal response spectrum on the hanging are smaller than the foot wall. Far fault, on short periods and long periods the ratio of vertical response spectrum to horizontal response spectrum minish with the soft site, and minish with the far distance from the fault.(6) Researched the effects of site condition and distance from the fault to the peak platform value of vertical response spectrum and vertical response spectrum characteristic period. Research found that the peak platform value of vertical response spectrum is smaller than the peak platform value of horizental response spectrum with the same conditions. Caculated the coefficients of site effects of the peak platform value of vertical acceleration response spectrum on different site conditions. The results show that vertical response spectrum characteristic period is smaller than horizental response spectrum near fault, and vertical response spectrum characteristic period is larger than horizental response spectrum far fault.Any disaster of the world compensate to the prograss of the human socity. Wenchuan earthquake brought us great disaster, and people in disaster area suffered huge economic losses, but it provided us with abundant seismic information, and gave us a great chance to research earthquake disaster. Sum-up and study of the damage in Wenchuan great earthquake, depth researth of strong motion's characteristics, have great significance to improve the seismic capacity. The conclutions of this paper are only come from research on Wenchuan earthquake strong motion data, and some results may be inconsistent with our usual understanding. Science is an exploration, and exploration will make mistake, please point out the inadequacies.