| As a common form of urban overpass,curved girder bridge plays an important role in transportation.In the process of bridge operation,the safety accidents caused by accidental explosion and terrorist attacks can not be ignored.When explosives explode at key locations on the bridge,the bridge may collapse as a whole,causing traffic paralysis and huge losses to the economy.Therefore,it is of great significance to study the damage and dynamic response of curved bridges under the explosive load on the bridge deck,and similaly it is very significant to use reasonable and accurate safety assessment methods to timely evaluate the safety level of curved bridges based on the damage of the bridge after the explosion,so as to provide theoretical basis for bridge anti-blast design and post-disaster reinforcement.In this thesis,a four-span continuous curved box-girder ramp bridge in Zhongmu County was used as the engineering background.The curved girder bridge,explosives and air model were established.The fluid-structure coupling method and the"three-stage method"were used to study the top of the bridge deck.Research variables includes different positions,vehicle types,proportional distances,contact explosion above and below the box girder,and internal explosion.The damage shape and dynamic response of the curved girder bridge at different positions of the same section were analyzed.According to the member strains of the bridge under explosion,a method for evaluating the safety of the bridge after explosion is proposed.The main conclusions are as follows:?1?By comparing the damage patterns and dynamic responses of different positions above the bridge deck to the curved girder bridge,the cross-central axis position of the bridge is the weakest part of anti-explosion,which should be considered first when carrying out anti-explosion defense.?2?According to the scale of the car bomb and the height of the chassis,the car bombs are classified,the damage mechanism of the curved girder bridge under different types of explosions is analyzed,and the damage patterns are divided into three categories:explosion into pits,explosion penetration,and explosion impact cut.Studies have shown that when the proportional distance Z<0.18 m·kg-1/3,the total volume of the failure element of the bridge have a linear relationship of y=70.75·x-5.7975 with the proportional distance.The safety impact on the curve bridge was ranked as follows when different models explode from low to high:car bomb<small passenger car bomb<small truck bomb<truck or tank bomb.When the tank truck exploded,the curved bridge deck collapsed entirely.?3?By changing the explosion height,the effect of proportional distance on the curved bridge is analyzed.With a fixed explosive volume of 750 kg TNT,the destruction form and dynamic response of the curved bridge are analyzed when the explosion center is 1.23,2.23,and 3.23 m from the bridge deck.The results show that when the charge is the same,the smaller the proportional distance,the more serious the curve bridge is damaged.The linear relationship between the total volume of the failure element of the curve bridge and its existence is as y=-11.5·x+4.82333 under different proportional distance explosions.?4?Using the analytic hierarchy process?AHP?,the curved girder bridge is evaluated from four levels of member-component-unit-bridge,the safety index S of the curved girder bridge is calculated,and the safety grade of the bridge is evaluated according to the safety index.The security degree is classified into four levels.The maximum TNT equivalent weight that the bridge can withstand through safety assessment is 1000 kg.Exceeding 1000 kg TNT equivalent weight the bridge may overally collapse,and the safety level will be reduced to level five. |
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