Wind-vehicle-bridge coupled vibration analysis based on random traffic flow simulation

A wind-vehicle-bridge system can be regarded as an interaction result of wind-bridge interaction, wind-vehicle interaction and vehicle-bridge interaction, which is determined by nature wind, dynamic characteristics of vehicle and bridge structures, interrelationship between bridge and vehicle dynamic properties and so on. Firstly, based on the traffic loading investigation on the expressway bridge within 24 hours a day, all the critical parameters of traffic flow, such as the vehicle type, weight, separation space and speed are all recorded and analyzed to extract its statistical characteristics, which are used to work out random traffic flow simulation program RTF. This RTF program can be embedded with the other general FEM software. Secondly, a dynamic analysis module RTFWVB of the wind-vehicle-bridge coupling vibration under random traffic flow is presented, which can consider arbitrary number of vehicles, multi-lanes and traffic flow direction. Finally, Hangzhou Bay Bridge in China is selected as a numerical example to demonstrate dynamic interaction of the RTFWVB system. The results indicate that the traffic flow direction has just a little influence on bridge dynamic response, that the mean responses are mainly determined by the moving vehicle loads, and that the fluctuating components will increase with the increase of wind speed.

NUMERICAL SIMULATION ON EMERGENCY TUNNEL FIRES WITH TRANSVERSE VENTILATION

In case of an emergency fire in vehicle tunnel, the ventilation system should be operated effectively to control the thermal fume and smoke inside tunnel. However, it is quite difficult to predict every kind of emergency fire by fire tests because the actual movement of thermal fume and smoke is affected by many factors such as ventilation system, structure of the tunnel, etc., especially for tunnels equipped with transverse ventilation system on which rare experimental and numerical studies have been found so far. In this paper, a three dimensional numerical simulator using LES turbulence model is developed to simulate the movement of thermal fume induced by emergency fire in vehicle tunnel. The SMAC method is employed to calculate the pressure and velocity fields. The upwind differnece scheme with the third order accuracy is applied for the discretization of convection terms of the governmental equations. As the applications of the present simulator, the behavior of thermal fume induced by emergency fire in a vehicle tunnel with two direction traffic is analyzed. It is confirmed that the partial transverse ventilation system is more effective than the longitudinal ventilation system under large and small velocities of longitudinal bulk flow inside tunnel. Simulation result also shows that remaining the velocity of longitudinal bulk flow near zero around fire source can provide the best working condition for partial transverse ventilation system.