Influence Of Spacing And Wind Attacking Angle On Vortex-induced Vibration Characteristic Of Twin Separate Flat Box Girders

Modern bridges across the river with twin separate parallel box girders are designed frequently in order to accommodate increase of traffic volume. The characteristic of vortex-induced vibration of twin separate box girders is different from those of single deck because of such aerodynamic interference. In some cases, the vortex vibration amplitude would be even greater and the probability of occurrence of vortex vibration could be higher of twin separate box girders. In order to avoid separation of double box girder bridge large amplitude of vortex-induced vibration, the urgent need for further study of the vortex vibration characteristics.Based on a domestic separate double flat box girder bridge as the background, a series of pressure-measured and vibration sectional model wind tunnel test was performed. Firstly, the vortex vibration characteristics of single flat box girder was studied under different wind angle of attack, then the vortex vibration characteristics of twin separate parallel decks at +5° wind angle of attack was carried out between 16 different distance, finally, four typical spacing was picked according to the test results of +5° wind angle of attack, the vortex vibration characteristics of twin separate box girders was studied under different wind angle of attack in four typical spacing.The content of this paper includes the following:(1)The vortex vibration characteristics of single flat box girder under different wind angle of attack was studied. Study found that, the vortex vibration performance of single flat box girder under negative wind angle of attack is better than positive wind angle of attack, under positive wind angle of attack, the vortex vibration performance worse gradually with the increase of wind Angle of attack, the vortex vibration amplitude is bigger and the vortex vibration locking range is longer.(2)The vortex vibration characteristics of twin separate box girder under different spacing was studied at +5° wind angle of attack. Study found that, at +5° wind angle of attack, the vortex vibration characteristics of forward girder and leeward girder can be roughly divided into four intervals.(3)The interference of wind attacking angle on vortex vibration characteristics of twin separate flat box girders was studied under four typical spacing. Study found that, under a few wind angle of attack that single flat box girder with vortex vibration(+5°, +4° and +3° wind angle of attack), the vortex vibration characteristics of double flat box girder showed regularity of broadly similar, this suggests that under the wind angle of attack, interference of spacing on vortex vibration characteristics of twin separate flat box girders can be divided into four interval, but the division of the interval is slightly different. Under some wind angle of attack(such as +2° wind angle of attack) that a single flat box girder did not happen vortex vibration, twin separate flat box girders has vortex vibration phenomenon obviously in certain spacing, this shows that, compared with single flat box girder, the probability that vortex vibration happened to twin separate flat box girders is higher.