Study On Fire Behavior Characteristics And Structural Thermal-mechanical Response In Curved Tunnel Under Different Wind Speeds

In addition to the development of design method and construction technology,the operation environment and safety management in tunnel engineering have become heated issues,where tunnel fire is one of the most harmful safety problems.Due to the poor ventilation of tunnel,toxic gas and high temperature gathered in the fire will pose a serious threat to life safety and bring serious damage to tunnel structure itself.Forced ventilation,as a control strategy for tunnel fire,is used in many countries and regions in the world,but its advantages and disadvantages have not yet reached a consensus,while the differences of its effect on straight and curved tunnels have not been ascertained.In this paper,scale experiments and numerical simulations are used in combination to study fire behavior characteristics and structural thermal-mechanical response in curved tunnel under different wind speeds,and the above problems are divided into the following three parts for research:(1)CFD numerical simulation is used to clarify the similarities and differences of flow field distributions between straight and curved tunnel with various radii and inlet wind speeds.The influence of vehicle blockage on local flow field and the principle of vortex generation are expounded.1D model is adopted to analyze pressure drop and functional relation between effective resistance coefficient and inlet wind speed is constructed.(2)A 1:7 scale test bench is set up to carry out the fire experiments of curved tunnel with different radii and wind speeds,in which four variables are introduced: fire position,fire power,angle of curve segment and inlet wind speed.After the integration of experimental data,data tables of tunnel ceiling temperature are established and contour maps of temperature are drawn.Based on flow field analysis,the specific reasons for temperature distribution change are clarified.Through dimensionless analysis,the expressions of maximum temperature rise under windless and windy conditions are established,respectively.The effects of above variables on flame length and inclination angle are studied as well as equations are created.(3)Using ANSYS software for numerical simulation,models of straight and curved tunnels are set up.The experimental temperature data obtained from different working conditions are loaded by thermal convection to clarify the influence of forced ventilation on tunnel temperature distributions.Temperature nonlinearity of concrete material properties is introduced.Then,the damage degree of high temperature to lining structure of straight tunnel and curved tunnel is compared.In conclusion,the feasibility of forced ventilation for fire control is finally determined.