Analysis Of Probabilistic Seismic Vulnerability Of Historic Timber Structure

Historic timber structure are precious history and culture legacy with a history of over 5000 years,which have extremely vales of historical,cultural and scientific.Those building’s performance is gradually weakened due to hundreds or more years of war,earthquake,weathering and the erosion of physical,chemistry as well as the destruction of human beings.The target to protect the legacy is facing great challenge.The seismic fragility analysis and research of historic timber structure,therefore,have important vale and profound significance on its evaluation,repair and reinforcement.Take Xi’an bell tower as an example,this paper do research on seismic fragility analysis on the basis of performance based seismic design.The main study contents are as follows:(1)This paper came up with the method of seismic vulnerability analysis which is aimed to historic timber structure based on PEER’s probabilistic assessment framework.The method simultaneously considered seismic oscillation and the structural instability and the later was considerate according to wood density,elastic modulus and Poisson’s ratio,the seismic oscillation instability was in accordance with 9 seismic oscillation records and its amplitude modulation equivalent.(2)The article discussed some related questions of seismic vulnerability analysis: 630 pieces of seismic oscillation-structure sampling was formed by using Latin sampling;peak ground acceleration(PGA)was chosen as seismic oscillation magnitude index(IM)and the maximum lateral displacement as damage index(DM)of the structure.The limiting value of the limit state property was given by performance levels of historic timber structure to represent anti-seismic capacity of the construction.(3)The study of the structure’s seismic vulnerability: The relationship of the damage index and seismic index was concluded by much dynamic time-history analysis;the regression analysis was adopted to predict probabilistic seismic demand model of the structure and we can further get different seismic intensities with different probability density functions of its demands,meanwhile,the fragility curve beyond the structures standard was given at last.(4)Contrastive analysis of the bell tower’s overall structure and vulnerability of the structure was only considered: the paper took modal analysis technic to contrast the structure’s two natural frequencies of which the influence of the high-platform to timber structure was analyzed then.By comparing the pillar’s top layer displacement of the structure,the paper drawn conclusion that the peak value of the high-platform’s overall structure was bigger and we found the damage under seismic action higher than wood structure’s in overall structure’s ultimate failure states through comparative analysis of the seismic demand probability density function and fragility curve.