Section Model Wind Tunnel Experiment And Numerical Simulation Of A Long-span Rail-cum-road Cable-stayed Steel Truss Bridge

With the increase of traffic flow and the gradual decrease of the available land area,the long-span rail-cum-road cable-stayed truss bridge has become the main scheme in the design of bridge over river and sea.The structural system has a lot of components and strong spatial characteristics.Due to the arrangement of double-deck,there are many traffic lines on it,making the aerodynamic flow around the bridge complex.This paper takes the Shanghai-Suzhou-Nantong Yangtze River Bridge with a main span of 1092 m as the engineering background.The section model wind tunnel test and the related numerical simulation of aerodynamic behavior were carried out.The main research contents and conclusions are as follows:(1)The aerostatic tri-component force coefficients of the vehicle-bridge system was measured when a single train passed through the truss beam.The aerodynamic characteristics and their change trend of the vehicle-truss beam system were studied under multiple cases.Based on the measurements,the CFD models of both the vehicle and the truss were established.Accordingly,the characteristics of the wind field around the vehicle-bridge system were analyzed,so as to provide parameters for subsequent research.(2)The aerostatic tri-components force coefficients of the vehicle-bridge system were measured under multi-line and multi-train cases.The influences of the train meeting spacing,the bridge tower as well as the wind attack angle on the aerodynamic characteristics of the vehicle-bridge system were analyzed when two trains and three trains passed through the truss beam.In addition,the characteristics of the surrounding wind field were analyzed by numerical simulation.(3)The aerostatic tri-component force coefficients of the vehicle-bridge system was measured and compared when a train respectively passed through the truss beam and box beam..The calculation formula of equivalent wind speed suitable for truss structure was derived.The spatial distribution of the equivalent wind speed as well as the crosswind reduction coefficients inside the truss were simulated with the help of the CFD software,which layed a foundation for the comprehensive evaluation of the aerodynamic characteristics of the train passed through the truss.(4)The CFD model of the truss girder structure was established.The influence of different aerodynamic stability measures on the aerodynamic characteristics of the truss beam was therefore studied.According to the time history results of the computed tricomponent forces of the truss beam,the user-defined module of the Fluent software was re-developed using the C language,based on which the vortex vibration amplitude of the truss beam was obtained.Finally,the effect of different aerodynamic stability measures on the magnitude of the vortex vibration of the truss beam was analyzed.The results show that:(1)When a train moves from the windward track to the leeward,the drag coefficients of the vehicle and the truss gradually decrease,while the lift coefficient of the vehicle and the moment coefficient of the truss reach the maximum on the leeward track.(2)As a train passes through the tower,the average surface wind pressure of the shielded vehicle will be significantly reduced,and the shielding effect is most obvious when it is on the windward track.However,the surface wind pressure near the tower edges fluctuates remarkably.(3)As two trains meet on the bridge,the drag and lift coefficients of the vehicle increase with the meeting spacing.As three trains meet on the bridge,the drag and lift coefficients of the vehicles behind the windward train decrease significantly.The middle train has the smallest lift coefficient and a negative drag coefficient.As the number of trains on the bridge increases,the drag and lift coefficients of the truss increase gradually,while the moment coefficient remains almost the same.(4)The shielding effect of the truss structure on the train is obvious.The average wind speed is significantly lower than the incoming wind speed,but high winds appear near the centroids of the two rightangled triangles in each truss panel,which coincides with the centroid height of the vehicle.(5)It is beneficial to install a central stabilizer and wind nozzle measures on the bridge for effectively reducing both the horizontal and vertical vortex vibration amplitudes of the bridge.