| As an important transportation hub in western my country,Chengdu Tianfu International Airport is a complex space system composed of aviation,highways,and subways.Among them,Metro Lines 13,18 and Airport Light Automatic Guided Rail Transit(PRT)that cross the airport taxiway form a five-span and mid-span two-story "Pin"-shaped open-cut tunnel structure.The structure is multi-span horizontally,and the middle part is overlapped up and down.Under the coupling action of subway trains and PRT multiple dynamic loads,the structure and foundation force mechanism is complicated.How to evaluate the stress and reliability of structures under various types of reciprocating dynamic loads to meet operational safety requirements is an urgent problem to be solved in structural design.Based on this,this paper,through data investigation,theoretical analysis and numerical simulation,carries out research on the dynamic response characteristics and reliability of the "Pin"-shaped airport open-cut tunnel.The main research content and results of the thesis are as follows:(1)Through data research and analysis,obtain the method of determining the dynamic load of airplanes,subways,PRTs,and the response characteristics and laws of structural mechanics under different dynamic load types,combinations and operating speeds are studied.The results show that under a single type of dynamic load,the structural mechanics response caused by the aircraft taxiing is the largest;The operating speed of vehicles or airplanes mainly affects the stress and strain response amplitude of the tunnel structure,and has little effect on its distribution law;The operating speed has a more obvious influence on the acceleration response of the structure than the speed and displacement response;Under multiple dynamic load combinations,the aircraft + PRT + subway line 13 fully loaded is the most unfavorable combination.Under a single combined load,the stress,strain,velocity,acceleration,displacement and other mechanical responses of the structure are all within the safe allowable range,and the maximum shear stress response of the structure is the closest to the allowable value.(2)In view of the above-mentioned combination of the most unfavourable conditions,considering the deterioration of the foundation material at the bottom of the tunnel,the law of the settlement of the bottom foundation of the structure under reciprocating dynamic loading with time is analyzed.It can be seen that the accumulated settlement on both sides of the structure is obviously greater than that in the middle of the structure.At the same time,the accumulated settlement gradually increases with time,and the growth rate is relatively fast within 10 years and then stabilizes;The forced displacement method was used to analyze the structural force caused by the differential settlement of the foundation,and it was found that the maximum shear stress growth law of the structure was consistent with the cumulative settlement change trend;Using the principle of robust reliability based on the convex set theory and introducing non-probabilistic reliability indicators,a prediction model of the maximum shear stress of the tunnel structure considering the degradation of backfill materials is established,and the structural reliability of the "Pin"-shaped airport open-cut tunnel under reciprocating load is studied.It is found that the structural reliability index gradually decreases with the increase of time,showing a rapid decrease first,and then gradually tends to be stable with the increase of time.(3)Using the above-mentioned foundation settlement and structural reliability analysis method,according to the design service life of 100 years,different structural forms such as whether the cavity in the lower span of the "Pin"-shaped tunnel structure is closed,whether the cavity is backfilled,whether the backfill material,and whether the foundation is treated,etc.are compared and analyzed.The results show that the bottom of the lower abdominal cavity of the PRT channel is closed + foam concrete backfill + additional pile foundations are added to the tunnel base.Can significantly reduce the deformation amplitude of the structure under dynamic load,and can effectively reduce the maximum shear stress response of the structure,which can be used as a structural optimization plan;Considering the deterioration of the base and structural materials,analysis shows that the proposed optimization scheme has a structural non-probabilistic reliability index greater than 1 within 100 years of design service life,indicating that it meets the reliability design requirements. |
