双层桥面桁架梁软颤振特性风洞试验研究

随着城市交通量的日益增大,双层桥面桁架梁的应用需求日益增加,研究其颤振特性有助于提升该类加劲梁的抗风设计水平。以武汉杨泗港长江大桥双层桥面桁架主梁为对象,利用节段模型自由振动风洞试验,测试了该主梁模型在不同工况下的软颤振特性,对比了不同风速条件下软颤振形态的异同。研究表明,双层桁架梁在试验中表现出了明显的软颤振特性,其振幅也随风速增加而增大。在0°风攻角的各级试验风速下,软颤振形态均表现为偏心扭转运动;在3°和5°风攻角下,起初表现为弯扭耦合运动,随着风速增大,弯扭耦合运动相位差逐渐减小;当风速增大到某个值后,弯扭耦合相位差为零,耦合颤振转变为偏心扭转颤振。无论是在连续的升风到降风过程中,还是在固定风速下给予不同初始激励,模型的软颤振振幅与折算风速之间具有唯一对应关系,不存在同一折算风速对应不同振幅的情况以及不同折算风速对应相同振幅的情况。最后从气动阻尼同时随振幅和折减风速变化的角度初步解释了双层桁架梁软颤振的发生机理。

Wind tunnel tests for soft flutter characteristics of double-deck truss girder

The application requirements of double-deck truss girders increase in bridge engineering with increase in urban traffic volume, and studying their soft flutter characteristics is helpful for improving their wind-resistant design level. Here, Yangsi Port Yangtze Bridge in Wuhan was taken as the study object, and wind tunnel tests were conducted for its segment model to measure soft flutter characteristics of its girder model under different working conditions, and compare similarities and differences of soft flutter forms under conditions of different wind speeds.The test results showed that double-deck truss girder reveals obvious soft flutter characteristics in tests, its flutter amplitude increases with increase in wind speed; under different wind speeds and 0° wind attack angle, soft flutter forms all are eccentric torsional motion; under 3° and 5° wind attack angles, soft flutter forms initially reveal typical bending-torsional coupled motion, with increase in wind speed, phase difference of bending-torsional coupled motion gradually decreases; when wind speed increases up to a certain value, bending-torsional coupled motion phase difference is zero, coupled flutter transfers to eccentric torsional one; in process of wind speed continuously increasing or decreasing, or under a constant wind speed, vibration amplitude of soft flutter is independent of initial excitations and related to a unique reduced wind speed, there are no phenomena that the same reduced wind speed corresponds to different amplitudes, or different reduced wind speeds correspond to the same amplitude; the occurrence mechanism of double-deck truss girder’s soft flutter is explained from the view point of aerodynamic damping varying with variation of both reduced wind speed and flutter amplitude.