Study On The Mechanical Behaviorof Steel Deck Pavement In Continuous-Span Suspension Bridges Based On Random Traffic Flow

In recent years,the research and application of multi-tower suspension bridges have attracted the attention of scholars and engineers at home and abroad.Most of the studies on the multi-tower suspension bridge focused on the fields of seismic resistance,wind resistance and vehicle-bridge resonance of the whole bridge,and the structural safety of the whole bridge or steel box girder was mainly studied.However,limited studies on the mechanical response of pavement layer under the combined influence of load and bridge have been conducted,which needed to be demonstrated.Based on National Technology Support Program project "The structural behavior characteristics of super large-span continuous flexibility bridge deck and the key technology of its pavement"(No.2009BAG15B03),taking Taizhou Yangtze River Highway Bridge as example,this paper presents the mechanical behavior of steel bridge deck pavement under random traffic loads.The regularity of the mechanic behavior of orthotropic steel bridge deck and asphalt pavement system under random traffic loads for multi-tower suspension bridges were obtained by numerical simulation and experimental tests.Moreover,suggestions for structural parameters design of the steel-deck pavement of multi-tower suspension bridges were also proposed.Firstly,statistical analysis method and forecasting principle of random traffic flow of bridges were studied systematically.Combined the traffic forecast data of Taizhou Bridge and actual measured data of Jiangyin Bridge for statistical analysis result of measured data,vehicle load parameters including the type,weight and following distance were analyzed.It indicates that the vehicle is in accordance with the bi-modal normal distribution,the vehicle weight is in accordance with the extreme value I type distribution,and the vehicle spacing is in accordance with the exponential distribution.Based on the Monte Carlo method combined with MATLAB program,a random traffic load simulation program was presented.And the random traffic load model of Taizhou Bridge was constructed.Secondly,the whole bridge numerical model of Taizhou Bridge was built using the finite element numerical simulation method,the reliability of the bridge model was verified by comparing with the modal analysis results from the design file of Taizhou Bridge.The obtained random traffic load was loaded onto the multi-tower suspension bridge,mechanical responses of the whole bridge model under random traffic flow and normal load were compared and analyzed.The mechanical responses of Taizhou Bridge under various working conditions were studied.Compared with the single-span suspension bridge,the existence of the middle tower makes the stiffness of the multi-tower suspension bridge structure and the base vibration frequency smaller.The middle tower position is the most dangerous position of the bending moment of the pavement layer,and the negative bending moment(the upper part of the main beam is pulled)is 32.54% smaller than the road-I load.;the torque response sensitive area at the bridge end and the middle tower.The maximum torque amplitude under random traffic load is 38.34% larger than that under road-I load.The spatial position and stress of the most dangerous beam section subjected to random traffic flow were also obtained,which provided basic data for investigating the mechanical response of steel bridge deck pavement under the influence of random traffic load and bridge type.Thirdly,finite element refinement model of the steel bridge deck pavement composite structure was built in view of random traffic load and the whole bridge effect using multi-level analysis method of “the whole bridge-local box girder-orthotropic plate” based on equivalent transformations of boundary conditions and loads.Among them,the local girder model was built by using the hybrid-element method.The contribution of pavement layer to the stress of steel box girder under boundary conditions with external stress was studied.The influence of moment and torque on stress response of local girder and the influence of random traffic flow and normal load on the mechanical response of local beam sections were demonstrated.The mechanical responses of bridge deck under standard two-wheel load and wheel load considering whole bridge effect were studied by building the high level fine chemical sub model of orthotropic plate.The influence of temperature load on stress response of steel deck pavement with initial stress condition was studied furtherly.These results can provide references for experimental model design of the mechanical responses of composite structure of steel box girder bridge deck and pavement under random traffic flow.Considering the influence of random traffic load and the whole bridge type,the extreme value of the stress near the hanging points of the steel box girder increases by about 34%~42%,and the extreme value of the stress away from the hanging point increases by 15%~135%.The value of the traffic load and the structure of the lifting point must be considered in the design of the pavement system;the random traffic flow must be considered in the design of the steel box girder and pavement.The combined effect of load and bridge type avoids excessive longitudinal tensile stress of the pavement system under negative bending moment.Fourthly,full-scale test model of composite structure composed of steel box girder bridge deck and pavement was conducted considering the equivalent of stress extreme value.The mechanical response behavior of bare deck of steel box girder subjected to random load flow and the same level of static load was studied by load test system and multi-channel strain,displacement test system.Then,mechanical response behavior of composite structure under the effect of random traffic load and same level of static load was studied to obtain the mechanical response behavior of composite pavement structure under random load flow.It is shown that under different loads,the strain response and change trend of the test points in bare steel plate are exactly the same,the strain value under static load is slightly larger;the strain response and change trend of steel bridge deck before and after paving is basically the same,but it is numerically attenuated to about 1/2 after paving.Lastly,the influence of parameter changes of deck system and pavement under random traffic load on mechanical response of pavement system was studied by setting different bridge deck configurations and construction dimensions using orthogonally analysis method.On this basis,suggestions were proposed for values of various parameters in bridge system design to reduce the mechanical response of pavement layer and bridge deck.It is recommended to use the random vehicle flow load to the design of multi-tower suspension bridge deck pavement,adopt the pavement material with relatively high modulus and the bonding layer material with good tensile performance,and avoid the improve the thickness of the deck.