| With the rapid development of arch bridge construction technology,CFST arch bridge has been widely used in infrastructure construction in western mountainous areas.The western mountainous area is an area with high incidence of earthquakes,and most of them are located on the earthquake fault zone.Under the action of near fault earthquake,the inclined buttresses of the arch ribs of concrete-filled steel tube arch Bridges may have great stress,which leads to the risk of buckling instability.How to reduce the inclined buttress stress effectively and improve the seismic performance of the Bridges is very important.Firstly,taking a long-span concrete-filled steel tube arch bridge with a main span of 500 m as the engineering background,MIDAS Civil is used to establish the finite element analysis model of the full bridge.Secondly,the nonlinear dynamic time history analysis method is used to study the influence of near-fault earthquake on the seismic response of concrete-filled steel tube arch bridge,and the flexural capacity of the key section of the bridge is checked.Then,based on the energy dissipation principle of the buckling restrained brace,the influence law of the buckling restrained brace location and design parameters on the damping effect of the structure is discussed,and the seismic performance analysis and flexure capacity demand calculation of the proposed optimal damping scheme are carried out.Finally,based on the curve fitting method of the demand capacity ratio model,the seismic vulnerability curve of the component is established,and the difference of damage probability between the buckling restrained brace damping scheme and the original design scheme is analyzed.The main work and conclusions of this paper are as follows:(1)Based on the PEER strong earthquake database,14 near-fault pulsed and non-pulsed earthquakes were selected,and the spectral characteristics of the two types of near-fault seismic waves were compared and analyzed.By introducing the seismic response amplification factor,the effects of near-fault pulsed and non-pulsed earthquakes on the seismic performance of long-span concrete-filled steel tube arch Bridges were compared.The results show that the near-fault pulse earthquake contains more low-frequency components,which will increase the seismic response of the medium-long period structure.The seismic response of the whole structure will be increased in different degrees,and the internal force of the arch foot section and the displacement of the vault will be increased significantly.(2)Buckling restrained brace is used to replace inclined bracing with high stress between ribs under earthquake action.Based on the two-stage seismic design method,the specific parameters of buckling restrained brace are designed.Under the combined action of pulsed seismic envelope and dead load,the influence law of the layout position and design parameters of buckling restrained brace on the seismic internal forces and displacement response of the bridge is studied.The results show that when the buckling restrained brace is arranged in the upper chord section of the arch(L/4～2L/5,3 L/5～3L/4),the yield capacity is 13900 k N and the steel type of the core plate adopts Q195,the seismic internal forces and displacement response of the whole bridge are better.(3)Based on the optimal damping scheme and the original design scheme,the internal forces and displacements of the key parts of the structure were compared and analyzed,and the flexural capacity requirement ratio(CDR)of the key section of the arch rib was calculated.The results show that the anti-buckling supports in the damping scheme all reach yield displacement and yield bearing capacity,and have good hysteretic energy dissipation performance.The stress of the buckling restrained brace decreases to different degrees on the whole,which can effectively solve the problem of diagonal brace stress overlimit.In the damping scheme,the flexural CDR of arch rib section with buckling restrained brace is reduced,but the flexural CDR of arch foot and arch top section is significantly increased,which makes the safety reserve of the key section of the structure more balanced.(4)The incremental dynamic analysis(IDA)method is used to analyze the seismic vulnerability of the arch rib and inclined brace in the damping scheme and the original design scheme respectively.Based on the curve fitting method of the demand capacity ratio model,the vulnerability curves of the weak members of the whole bridge are established,and the damage probability control effect of the damping scheme on the weak members of the structure under different intensity levels of earthquakes is studied.The results show that the buckling restrained brace can effectively reduce the damage probability of arch rib and inclined brace members,and significantly reduce the damage probability of arch rib at the arch foot and inclined brace at the arch top.When the local seismic wave PGA is 0.1g～0.2g,the damage probability of arch rib and inclined brace of the main bridge is significantly reduced by the damping scheme,which indicates that the buckling restrained brace has a good damage control effect on arch rib and inclined brace under the design earthquake. |
