Seismic Response And Seismic Vulnerability Analysis Of Lightweight Aggregate Concrete Bridges

China is located between the Pacific Rim Seismic Zone and the Eurasian Seismic Zone.The seismic fault zone is very active because of the compression of the Pacific plate,the Indian plate and the Philippine Sea plate.From the point of view of the past earthquake damage,the traditional concrete materials can no longer meet the needs of seismic fortification.It is particularly important to find materials that can improve the seismic performance of structures.As a lightweight and high strength concrete material,whether the application of concrete in bridge construction in strong earthquake area can reduce seismic response and improve seismic performance of structures remains to be studied.Therefore,this paper takes a typical small and medium-span continuous beam bridge in strong earthquake area as the research object,and designs four schemes,namely,full-bridge ordinary concrete bridge,bridge with light aggregate concrete only in superstructure,full-bridge light aggregate concrete bridge and bridge with light aggregate concrete only in lower structure.OpenSEES,a finite element software developed by University of California Berkeley,is used to carry out the research.Research on the following aspects:(1)Comparing the dynamic characteristics of bridge structures under four schemes,the results show that the vibration modes of different schemes are basically the same,but the period and frequency as well as the contribution rate of vibration modes are different.The first three natural vibration periods of the bridge with lightweight aggregate concrete in the upper structure or the whole bridge are smaller than that of the ordinary concrete bridge,and the first three natural vibration periods of the bridge with concrete in the lower structure are larger than that of the ordinary concrete bridge.Concrete bridge.Bridges with lightweight aggregate concrete in upper structure converge fastest in longitudinal and transverse cumulative mode contribution rate,followed by ordinary concrete bridges and full bridge lightweight aggregate concrete bridges,and those with lightweight aggregate concrete in lower structure converge slowest.(2)Seven seismic waves in accordance with three types of sites are selected to analyze the non-linear time history of the four schemes of bridges,and the displacement of pier top,the bending moment of pier bottom and the bending moment of pile top are studied.The results show that only the upper structure,only the lower structure or the whole bridge using lightweight aggregate concrete can reduce the seismic response of the bridge,of which the lightweight aggregate concrete bridge is the most effective.(3)Static design(calculation by Sap2000)and seismic design of the bridges under the first three schemes are carried out and their economy is compared.The results show that the use of lightweight aggregate concrete bridges under the three schemes can significantly reduce the consumption of materials when the ratio of structural function value to capacity requirement is basically the same and meets the requirements,but it can not reduce the cost of construction,mainly because of light bone.The unit price of concrete is higher.(4)Selecting 100 seismic waves from the Pacific Seismic Database of the United States which meet three types of sites,the paper carries out non-linear time history analysis of four kinds of bridges.The seismic vulnerability curve is generated by linear fitting method based on probabilistic seismic demand analysis,and the seismic performance of lightweight aggregate concrete bridges is analyzed by probabilistic method.The results show that compared with ordinary concrete bridges,lightweight aggregate concrete bridges can significantly reduce the damage probability of supports,but the damage probability of piers and pile foundations is increased;lightweight aggregate concrete bridges can significantly reduce the damage probability of piers and pile foundations,but can not reduce the damage probability of bearings;lightweight aggregate concrete bridges can significantly reduce the damage probability of piers and pile foundations.Concrete bridges can significantly reduce the damage probability of piers,pile foundations and supports,as well as the overall damage probability of bridges.