Running Safety Of Vehicles On Bridges Under Complex Flow Of Mountainous Region

With the proposal of the Belt and Road Initiative,western China has gradually become the construction focus of economy,and the transportation network also will be extended to the western region.The complex and changebale mountain canyon is common in the western region of China.To ensure the safety of wind-induced driving of vehicles,the determination of windinduced driving in bridge site and the safety of vehicle wind-induced driving have become more and more prominent.In this paper,the field measurement and wind tunnel test are used to study the complex wind characteristics and vehicle driving safety in mountainous areas.Firstly,a 50 m high meteorological mast with three set of ultrasonic anemometers which was installed at 10 m level,30 m level and 50 m level respectively was erected in a deep-cut canyon.Based on the long-term monitor data,the wind characteristic parameters at a certain place including average and fluctuating wind characteristics and coherence between different heights are investigated.The results are as follow: The influence of topography on wind characteristics cannot be ignored,and the wind characteristics in complex mountainous areas are quite different from flat areas.The dominant wind direction which depends on the topography is consistency with the direction of river.Although the wind speed corresponding to the dominant wind direction is relatively large,the wind speed corresponding to the non-dominant wind direction cannot be ignored.The attack angle of wind is mainly less than zero,and its probability distribution obeys Gaussian distribution.In addition,the wind attack angle has a strong correlation with the wind direction.The negative attack angle appears mostly in the south wind,and the positive attack angle appears mostly in the north wind.The gust factor has a similar change law of attack angle.With the increase of the height of the measuring point,the turbulence intensity of the horizontal direction decreases,while that of the vertical direction increases.The wind spectrum of complex mountain area is more consistent with von Kármán model.Davenport coherence function can be applied to mountain environment.With the increase of distance,the decay factor increases.At the same time,the decay factor of low altitude area is larger.Secondly,taking a complex truss bridge in the western mountainous area as the object,the wind characteristics of different positions of the bridge deck are analyzed by means of field measurement,and the relationship between the wind characteristics of the bridge deck and the incoming wind is discussed.The results show that the wind speed above the bridge deck will increase with the affiliated facilities of the bridge deck,and with the lane moving to the leeward side,the wind speed will increase gradually.As for the wind speed,the wind speed of the bridge deck has a strong correlation with the incoming wind speed.The wind direction above the bridge deck is consistent with the dominant wind direction of the incoming wind.With the increase of wind speed,the turbulence intensity of local wind field of bridge deck decreases gradually.The affiliated facilities of bridge deck will increase the turbulence intensity of local wind field,especially in the horizontal direction.The ratio of lateral,longitudinal and vertical turbulence intensity of complex truss fluctuates about 1:1.4:0.8,which is quite different from the existing bridge specifications.The traditional exponential distribution or logarithmic distribution cannot reflect the distribution of the wind profile of the bridge deck,and the wind profile of the local wind field of the bridge deck is more consistent with the polynomial distribution.According to the fitted polynomial wind profile,the equivalent wind speed and the equivalent action point of wind load in the vehicle height are calculated.The equivalent action height of wind load is far higher than the height of vehicle center of gravity.The measured power spectral density function of the bridge deck is quite different from the common wind spectrum.For the complex truss and double-box girder sections,the fitted spectrums are given respectively.Thirdly,the influence of wind barrier parameters including the porosity,height and opening type on the local wind field was investigated by large-scale wind tunnel tests.The results show:The porosity of the wind barrier has a significant impact on the local wind field of the bridge deck.No matter which cross-section form,the wind barrier can effectively reduce the wind speed behind the wind barrier and increase the turbulence intensity of the bridge deck.Due to the different porosities between the wind barriers and the railings,the wind speed behind the railing will increase to a certain extent due to the installation of the wind barrier.In general,the lower the porosity is,the better the windproof effect is,and the lower the equivalent wind speed of the bridge deck is.The effect of the opening form of the wind barrier on its windproof effect is limited,and it is related to the section form of the main beam.When the bridge adopts the truss form,the round hole type wind barrier is better,and when the bridge adopts the double width box girder,the strip type wind barrier is better.In addition,the higher the wind barrier is,the larger the wind protection range is.Fourthly,the wind profiles above embankment-cutting connection section and viaductcutting connection section are investigated by large-scale wind tunnel tests.The results show:the air flow near the road juncture is very disordered,and the wind profiles at different heights are quite different.For embankment-cutting connection section,the wind speed at different height is domained by road type.When the height is less than 150 mm,the wind speed at the road junction is dominated by the cutting,while the height is greater than 150 mm,the wind speed at the road junction is dominated by embankment.As for the viaduct-cutting connection section,when the wind barrier is not installed,the change of wind profile at the road junction is complex,and the wind speed growth gradient is large,which is unfavorable to the running safety of raod vehicle.When the wind barrier is installed,the wind barrier can effectively improve the local wind field at the road junction,and reduce the growth gradient and the maximum wind speed of the wind speed.Finally,through the method of wind-vehicle-bridge coupling vibration analysis,the influence of complex incoming flow in mountainous area on vehicle driving safety is discussed.The results show that the height of wind load will directly affect the safety of sideslip and rolling.When the equivalent action height of wind load is higher than the center of gravity of vehicle,the safety of sideslip and rolling will increase,and the influence will be more significant with the deterioration of road conditions.The speed of vehicle is the main reason that affects the vertical response of vehicle,the wind speed is the main factor that affects the lateral response of vehicle,and the coverage of the lateral dynamic response of vehicle expands with the increase of wind speed.When considering the influence of different incoming flow,it can be found that there are some differences in vehicle response under different wind spectrums.Through the establishment of the total vehicle safety impactor,the GA-BP combined evaluation model is used to evaluate the running safety of traveling buses and container trucks.