| Backfill plays an active role in resisting longitudinal seismic force of the bridges in Wenchuan earthquake.The composite formed by filling sandy soil into the inner cavity of waste tires can exhibit higher compressive strength and shear strength than sandy soil.Negative Poisson’s ratio(NPR)bolt with the advantages of constant resistance and large deformation can effectively dissipate seismic energy.In view of this,a kind of NPR bolt and tire-soil composite backfill behind the abutment was proposed in this dissertation,its mechanical properties under different deformation ranges was determined through parameter analysis.A design method for simply supported girder bridges considering seismic absorption of backfill behind the abutment was established,and the seismic absorption effect and influencing factors of backfill behind the abutment were analyzed.The main accomplished work in this dissertation is as follows:(1)By referring to a large number of relevant literature,the research status of abutment-backfill seismic system,tire-soil composite and NPR bolt was summarized to find out the shortcomings of the current research.(2)The finite element simulation was carried out on the previous compression test of tire-soil composite backfill and NPR bolt to verify the reliability of the modeling method in this paper,the combination method of NPR bolt and tire-soil composite was determined.Finally,the integral finite element model of the tire-soil composite backfill behind the abutment was established.(3)The layout length,layout spacing,yield strength of NPR bolt and distance between abutment and tire-soil composite were analyzed.According to the deformation range of backfill,the reasonable layout of tire-soil composite under large deformation and small deformation were proposed respectively.The strengthening principle of the tire-soil composite backfill was put forward,and the development process of the failure surface of the backfill and the specific reason of the increase of its resistance was explained.(4)The calculation principle of equivalent linearization method was expounded,and a calculation method of equivalent stiffness and equivalent damping ratio of backfill was given.Based on the response spectrum method to calculate the seismic displacement demand of deck,a design method of simply supported girder bridges considering the influence of backfill was put forward,and the design calculation process of a real bridge was given.(5)A 3×30 m simply supported girder bridge model was established using Open Sees.Considering the impact of near-field ground motion,time history analysis was carried out on three cases,namely,without backfill,backfill of ordinary sand,and tire-soil composite backfill,respectively.On the basis of verifying the reliability of the simplified calculation method,the damping rate of backfill was studied.The results of study show that,when the backfill is considered,the collision force between adjacent girders will increase.The damping rate of backfill decreases with the increase of the gap at expansion joints.The damping rate of backfill under the action of no pulse seismic waves is higher than that under the action of pulse seismic waves. |
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