Study On Simplified Calculation Method Of Seismic Vulnerability For Skew Highway Bridges

China is an earthquake-prone country.As an important infrastructure and lifeline engineering,bridges are vulnerable in the earthquake.In recent years,the number of skew highway bridges is increasing rapidly along with the development of urban road construction.However,investigations into the earthquakes’ damages indicate that the skew bridges are more vulnerable than the straight bridges which caused the seismic vulnerability of skew bridges to become one of the key issues for study.In the study,the skew highway bridges were taken as research object.The current state and development of seismic damage characteristics to skew bridges was discussed,and the seismic fragility of straight bridges and skew bridges were summarized.In the dissertation,the main work and conclusions are as follows:(1)The technical process of seismic vulnerability analysis for bridge based on the IDA(Incremental Dynamic Analysis)method was introduced.Pier,bearing and abutment were selected as vulnerability components based on the damage characteristics of skew bridges.The qualitative limit state was divided into five levels,and the ultimate value of vulnerability components at each level was determined.The method of generating the system seismic vulnerability from components was discussed.(2)A skew highway bridge was taken as a benchmark bridge,and 4 new skew bridge samples were designed with skew angles ranging from 0° to 45°.The finite element models of bridges described above were built with OpenSees and the seismic vulnerability analysis was conducted.The seismic vulnerability parameters of skew bridges and straight bridges were compared;the results showed that the seismic vulnerability parameters have no obvious change when the skew angle is less than 30 degree,the median value decreases with the increase of skew angle when the angle is more than 30 degree.(3)The skew bridges were divided into 8 classifications by different types of column,the upper-structure supporting forms and codes,total 240 bridge elementary samples were built up.The new samples were generated by changing the skew angle 13 times on each elementary sample.The seismic vulnerability analysis of the same angle samples was conducted and the relationship between the seismic vulnerability parameters and the skew angles was discovered.The results showed that the median value decreases with the increase of angle and the logarithmic standard deviation changes in the opposite trend.(4)Based on the analyze data and the revised method FHWA proposed,a new correction formula of the median value was fitted which suited to the current skew highway bridges situation of our country.The recommended value of logarithmic standard deviation was given.The seismic vulnerability simplified calculation method of skew highway bridges was generated by the new correction factor and recommended value.The result of the research is beneficial to the seismic risk assessment and retrofitting codes of skew bridges.