Seismic Fragility Analysis Of High-speed Railway Bridge Subjected To Near-fault Ground Motions

The high-speed railways are constructed inevitably near seismic fault zones which are widely distributed in China.In recent years,more and more studies have concentrated on the seismic behavior of highway bridges under the near-fault earthquakes.However,the researches on high speed railway bridges are few.As an effective anti-seismic method,seismic isolation can minimize the structural damage.But most of scholars hold diverse views on the feasibility of seismic isolation to resist the near-fault ground motions.Therefore,it is of great practical significance to study the seismic performance of high-speed railway bridges and high-speed railway bridges with seismic isolation technology under near-fault earthquakes.In this paper,vulnerability analysis of high-speed railway bridge under near-fault region is carried out.Then a new seismic isolation bearing is proposed and a fragility analysis is did to a high-speed railway bridge with the bearing.Based on the vulnerability analysis,the effectiveness of seismic isolation for the resistance of highspeed railway bridges against near-fault earthquakes is evaluated.The main contents can be summarized as follows:(1)The vulnerability analysis is performed on high-speed railway bridges under near and far field earthquakes.The near-field and far-field seismic databases is established based on the IDA.Vulnerability curves of high-speed railway bridges under near-fault and far-field earthquakes is compared,and the corresponding conclusions is reached: With the same peak ground acceleration(PGA).Moreover,compared with far field earthquakes,near-fault earthquakes are more destructive and have greater hazards;Based on the characteristics of near-fault ground motions,at the same seismic intensity,the fling-step is more destructive than the forward directivity effect;The severe earthquakes will cause great damage to the high-speed railway bridges.To prevent super-intensity vibration,especially that with near-fault effects,the seismic fortification level of corresponding area should be improved.(2)In order to analyze the isolation of high-speed railway bridges,a new type of limited-seismic bearing is proposed.Based on traditional pot bearings,the new bearing integrates the limit function and shock isolation function.A full-scale model test is conducted on a new type of bearing and a numerical model is proposed.After the sensitivity analysis performed on the main parameters of the support,the following conclusions is drawn: The bearing simplifies the design and construction process and reduces the cost,then,a modularized design was applied to seismic vulnerable components,which could be easily repaired after earthquake.The bearing clearly clarifies the idea of isolation,and has a good effect in isolation design.In practical applications,the parameters of the bearing can be optimized in combination with the design and construction features of the structure to get better results.(3)The fragility of the high-speed railway bridges with the above-mentioned new bearing under near-field and far-field earthquakes is analyzed.The comparison between vulnerability curves of high-speed railway bridges and high-speed railway bridges with seismic isolation showed that,under the same earthquake intensity,the new seismic isolation bearings can reduce the seismic response of high-speed railway bridges effectively,especially under the near-fault earthquake.