Research On Crack Of Steel Bridge Deck Asphalt Pavement Under Coupling Action Of Water-temperature-traffic Load

Based on the steel bridge pavement system under the influence of water temperature driving load,the dynamic expansion model of transverse and longitudinal cracks is established.The sensitivity analysis and dynamic expansion of stress intensity factors are carried out.Finally,BP neural network model is established to analyze the influence of different thickness and modulus of steel bridge pavement on fatigue life.Firstly,the temperature field model under low temperature environment is established by DFLUX and FILM temperature field subprograms,and the maximum tensile stress is 2.076mpa.The temperature field at this time is used as the predefined field to import into the dynamic model.Based on the sequential thermal coupling model,the stress condition of different positions on the pavement surface is analyzed and the most unfavorable position is found.The results show that:the transverse tensile stress is greater than the longitudinal tensile stress,and the longitudinal crack will occur first in the pavement layer of steel bridge,while the longitudinal crack is most likely to appear on the upper surface of the pavement which intersects the center of two adjacent diaphragm plates and the top of stiffener web,and the transverse crack appears on the upper surface of the pavement near the diaphragm top and the load.Then,based on the most unfavorable position,the transverse and longitudinal cracks are set up,and the changes of stress-strain and stress intensity factors at different times are analyzed.The results show that the maximum tensile stress and strain will be increased when cracks occur;The closer the crack tip,the greater the curve change trend of stress and stress intensity factor;The maximum value of K_Ⅰis greater than K_Ⅱand K_Ⅲ,and the open instability crack is the main part;Because the longitudinal cracks are set between two adjacent diaphragms,the stress intensity factor curve shows symmetrical distribution;The stress intensity factor curve under transverse crack is asymmetric distribution.Secondly,the crack propagation model under the coupling of thermal and water temperature driving load is compared.It is found that the dynamic water pressure increases the crack growth of type I and type II to some extent.Then,according to the transverse and longitudinal crack propagation models under the coupling action of water temperature driving load,the sensitivity analysis of stress intensity factors is carried out.The results show that for the crack depth,the longitudinal crack will decrease first and then increase with the increase of the crack depth,and the transverse crack will increase first and then decrease with the crack expansion process;The increase of speed,load and pavement modulus will increase the stress intensity factor to some extent;The effect of the increase of pavement thickness on crack growth is more obvious than other factors.Based on sensitivity analysis,it is found that under the condition of satisfying the road performance and safety,the pavement thickness of 50mm is the most economical choice,and the selection of pavement modulus should be as low as possible.Finally,according to a large number of fracture model data under the coupling action of water temperature driving load,the relationship between the equivalent stress intensity factor and the crack depth of pavement is fitted.Based on the model data of different bridge deck system structural parameters,BP neural network model is obtained by training samples of BP neural network.Then,the fatigue expansion parameters of asphalt mixture are determined according to the literature.The fatigue extension life of pavement is calculated by Paris formula.The sensitivity of the fatigue life of steel bridge pavement under longitudinal and transverse cracks is studied.The results show that increasing the thickness of the pavement layer,or reducing the modulus,load and speed of the pavement layer properly,can improve the fatigue life of the steel bridge pavement,among which the increase of the thickness of the pavement will increase the fatigue life of the steel bridge pavement.