Study On Aerodynamic Interferences Of Long-Span Bridges With Twin Separate Parallel Decks

Highway bridges with Twin Separate Parallel decks (TSP decks) are designed frequently in order to accommodate increase of traffic volume. Due to small net distance, there exist aerodynamic interferences between TSP decks. Static wind load, characteristic of vortex-induced vibration, flutter stability of TSP decks are different from those of single deck because of such aerodynamic interferences. Aerodynamic interferences have become one of the key problems in wind-resistant design of long-span bridges with TSP decks.The research status of aerodynamic interferences of long-span bridges with TSP decks was firstly summarized in detailed in present paper, then aerodynamic interferences of long-span bridges with TSP decks were studied systematically based on research of three representative sections (rectangular section, Π shaped section and streamlined section) and some actual bridge models through wind tunnel experiments and numerical simulations. The main contents of this thesis are as follows:1. A quantitative analysis method of aerodynamic interferences of TSP decks was developed. Interference factor (IF) is defined as a ratio of aerostatic coefficients, maximum vortex-induced vibration amplitude or flutter critical wind speed of TSP decks to that of single deck. IF<1means a decreasing aerodynamic interference effect and IF>1means an increasing aerodynamic interference effect. Interference factor formulae of representative sections were fitted through experimental and numerical study in smooth flow field. Wind tunnel experiment results of some actual bridge models show that interference factor formulae are of certain applicability.2. The aerodynamic interference rules of representative sections in smooth flow field are as follows.(1) Aerodynamic interferences on aerostatic coefficients are mainly attributed to shielding effect. Mean value of drag coefficient of leeward section is smaller than that of single section. Compared with streamlined section, shielding effect on bluff sections (rectangular section and Π shaped section) is more significant.(2) Vortex-induced vibration amplitudes of both forward and leeward bluff sections are larger than that of single bluff section. Vortex-induced vibration amplitude of forward streamlined section is close to that of single streamlined section. Vortex-induced vibration amplitude of leeward streamlined section is larger than that of that of single streamlined section.(3) Flutter critical wind speed of twin bluff sections is lower than that of single bluff section when D/B<1(D is net distance of twin sections, B is width of single section) and slightly higher than that of single bluff section when D/B=1. Flutter critical wind speed of twin streamlined sections is lower than that of single streamlined section and decreases with smaller net distance.3. Influences of turbulence intensity on vortex-induced vibration and flutter stability of both single and twin representative sections were investigated through wind tunnel experiments in turbulent wind field produced by uniform grids. Aerodynamic interferences on vertical vortex-induced vibration of twin Π shaped sections become more noticeable with larger turbulence intensity. Aerodynamic interferences on vertical vortex-induced vibration of twin streamlined sections are not appreciably affected by turbulence intensity. Aerodynamic interferences on flutter stability of twin Π shaped sections become weak gradually with larger turbulence intensity. Aerodynamic interferences on flutter stability of twin streamlined sections become weak gradually with larger turbulence intensity when net distance is smaller and little affected by turbulence intensity when net distance is larger.4. Due to deficiency of study on aerodynamic performance of bridge decks in turbulent wind field using Renolds Averaged Numerical Simulation method and Large Eddy Simulation method, a flat-plate boundary layer flow was simulated by using Direct Numerical Simulation code DNSUTA. This work has offered a useful preliminary exploration for application of Direct Numerical Simulation method in wind-resistant research of bridge decks in turbulent wind field.