Traffic Safety Study Of Mountain Highway Bridge And Tunnel Connecting Segment Under The Wind Environment

With the continuous expansion of the scale of highway construction, and with thecontinuous increasement of the construction mileage and density, the highway is graduallydeveloping to the mountains and hills areas. However, with the continuous development ofChina’s highway, the traffic safety issues are also increasingly prominent. In addition, thesituations of both bridge and tunnel clouded, and bridge and tunnel connection areas alsoraised new challenges to the mountainous highway traffic safety. Under bad weatherconditions and special geographical environment, the probability of traffic accidents on thehighway is very large, while harsh weather conditions is also extremely unfavorable for theaccident rescue and traffic safety control work. At the present stage, the majority ofresearches on mountain highway roads are concentrated on the description of security issuesthemselves and on the qualitative analysis of the cause of the accident. The impact on severeweather conditions are focused on the study of rain, snow, fog etc. It lacks the research on theimpact of wind on driving security. When a car drives on bridge and tunnel connectingsegment of the highway on the mountain, it is influenced severely by the wind environment.The wind flow rate will be accelerated when it flows through the canyon. At the same time, alarger fluctuating wind is caused by the influence of the ground surface, and flows with theaverage wind.Particularly, when the vehicle drives at a high speed, the pneumatic lateral forceunder the action of strong winds will cause wheel cornering and unsteady steering. Therefore,canyon winds have significant impact on traffic safety.Since the academic world at home andabroad lacks systematic research in this area, this paper attempts to reveal the mechanism ofthe influence of upwind characteristics at bridge and tunnel connecting segments to the trafficsafety research.In order to study the impact of the wind in mountainous sections of the canyon on trafficsafety at the bridge and tunnel connection, this paper utilizes three-dimensional N-S equationand k-turbulence model which is viscous, unsteady and incompressible. It applies finitevolume method to set up the numerical model of the effect of canyon wind at bridge andtunnel connection segment in the ambient air flow field. It also based on the theory of windengineering to analyze wind characteristics on the bridge and tunnel connection. Under the effect of the canyon wind in the absence of vehicles, this paper analyzes the flow field ofbasic wind environment under the effect of dual role of the line-environment. It also put thebridge and tunnel connecting section as the research object to simulate the wind speedchanges, and lays the foundation data for the traffic safety feasibility research. In addition, theauthor proposes the equivalent wind speed and crosswind reduction factor concept above thebridge deck to better reflect the wind characteristics, and quantitatively reflects the law ofirregular change of the wind characteristics along the heights and horizontal distance to bridgecentral location at the bridge and tunnel connection.This paper applies numerical simulation method on automotive external flow field, andchooses the driving car on the highway bridge and tunnel connecting segments as the researchobject. On the basis of assumptions and simplifications it also utilizes GAMBIT software tobuild a three-dimensional automotive model for numerical simulation, and uses dynamic gridtechnique and C++programming. In addition, according to mountain highway speed limit toselect the appropriate vehicle speed, this paper simulates vehicles on such wind filedenvironment, and researches the changes of related impact indicators and automotive externalflow field pressure distribution Furthermore, it quantitatively studies the aerodynamiccoefficients of vehicles under the state of motion. It provides intuitive understanding of thepressure distribution and separation of flow field around and vortex generation anddevelopment.This paper utilizes more often used concrete barrier, under the impact of the unfavorablefactors, to access the basic law of impact of guardrail to the bridge wind environment.Learned from long-span bridges continuous wind barrier set, and for the features where windspeed is high in between and low on sides at bridge and tunnel connecting segments onmountain highways, the author designed and implemented measures to improve the windenvironment at bridge and tunnel connecting segments on mountain highways, under theconsideration of different sizes, porosities and the lengths of the start-stop. This paperproposed different types of wind barriers, and chosen the degree of deceleration andturbulence intensity as the appraisal indicators, to quantitatively analyze its slowing effect andto determine the most appropriate measures to improve the wind environment at bridge andtunnel connecting segments on mountain highways. With dynamic grid technique simulates vehicles on such wind filed environment, and researches the changes of related impactindicators and automotive external flow field pressure distribution, to verify the effectivenessof the improvement measures.Using fuzzy theory to evaluate traffic safety on bridge and tunnel segments, and bymaking a comprehensive analysis of factors affecting traffic safety on bridge and tunnelsegments, this paper utilizes Analytic Hierarchy Process to divide factors into two layers toevaluate, and uses Analytic Hierarchy Process and BP neural network to analyze and calculateeach layer. It establishes model using MATLAB software and finally uses Xian-Hanzhonghighway as experimental samples for verification. Eventually, using wind tunnel tests andexperimental samples to establish the Xian-Hanzhong highway bridges and tunnelsconnecting the mountain highway traffic safety model instance segment analysis, numericalsimulation to verify the accuracy of the effectiveness of the effectiveness of recommendationsto add facilities and post-evaluation methods.