| Historic timber structure is a living witness of China’s 5000-year history and culture.It has precious historical value,cultural value and scientific research value.The existing historic timber structure our country have been damaged by wars,earthquakes,weathering and so on.Their performance has been damaged to varying degrees,and the seismic risk has been increasing,which brings great challenges to the protection and repair of ancient buildings.Because of its long history,the uncertainty of ancient wooden structures deserves more attention.Therefore,considering the uncertainties of knowledge and nature,it is of far-reaching significance to study the seismic risk of ancient buildings for the protection and repair of wooden structures of ancient buildings.In addition,the mature ancient building insurance industry also urgently needs to conduct in-depth research on the risk loss of ancient building timber structure.Taking Xi’an Bell Tower as an example,based on performance-based seismic engineering theory(PBEE),the probabilistic seismic risk and probabilistic seismic loss risk of Xi’an Bell Tower are analyzed.The main research contents are as follows:(1)Based on the analytic function of seismic vulnerability,the seismic capacity and seismic demand of bell tower are analyzed.The damage state of ancient timber structure is divided and its threshold is determined.The seismic capacity model of the bell tower is established on the assumption that the seismic capacity of the bell tower obeys normal distribution.Latin sampling is used to generate 10 bell tower finite element samples to consider the structural uncertainties of the bell tower,and 10 ground motions are screened and amplitude modulation is used to consider the seismic uncertainties.Seismic ground motion and finite element samples are matched to 700 pairs of ground motion-structure samples,and the relationship between ground motion parameters PGA and maximum displacement angle between stories is obtained by dynamic time history analysis.The seismic demand model of bell tower is obtained by logarithmic linear fitting.(2)By convoluting the seismic demand model and the seismic capacity model of the bell tower,the vulnerability function of the bell tower considering only the essential uncertainty and the knowledge uncertainty is obtained.The probability of conditional failure of bell tower is analyzed.The results show that the probability of moderate damage and collapse of bell tower under moderate earthquake is close to 0,but the probability of slight damage under small earthquake is more than 50%.At the same time,the influence of capacity uncertainty on seismic vulnerability is analyzed.The results show that ignoring capacity uncertainty will lead to unsafe evaluation results.(3)Based on the power exponential seismic risk function,the probability seismic risk of the bell tower is analyzed,and the seismic risk curve of the bell tower is obtained.Referring to the "three-level" fortification requirements of the national seismic code,the probability of minor damage,moderate damage and collapse within 50 years is defined as 63.2%,10% and 2%(exceeding probability within 50 years of small,medium and large earthquakes),respectively.The seismic risk analysis results of bell buildings show that the probability of minor damage and moderate damage in 50 years is over 63.2%and 10%,respectively,but the probability of collapse occurs.The probability is far less than 2%,which is consistent with the seismic response of bell tower and the characteristics of earthquake disaster of ancient wooden structure.(4)The probabilistic earthquake loss risk of the bell tower is analyzed with the annual expected loss as the index,and the time curve of the expected earthquake loss rate of the bell tower is drawn.The framework of socially acceptable risk line for earthquake is established,and the seismic risk loss of the bell tower is evaluated.The results show that the seismic risk of the bell tower can be accepted under the current social and economic level in China. |
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