大型单立柱双面广告牌风荷载及风振响应分析

大型单立柱双面广告牌的风致破坏时有发生,为研究其在强风下的破坏机理,完善大型户外广告牌结构的抗风设计,本文以典型的双面广告牌结构作为对象开展了两类模型风洞试验.首先通过刚性模型的面板测压风洞试验,分析了上部结构平行面板方向、垂直面板方向和扭转荷载的风力系数随风向角变化规律,针对最不利工况,给出了沿面板长方向风压分布及整体结构风力系数,以及垂直面板方向和扭矩风荷载功率谱的建议公式;通过气动弹性模型的高频天平测力风洞试验,研究了双面柔性广告牌的基底力响应.综合静力刚性测压和动力气弹响应两阶段试验结果,给出双面广告牌垂直面板方向和扭转风振响应的理论计算方法.计算表明:对垂直面板方向风荷载的理论计算,荷载谱需考虑气动导纳函数的影响,对于扭转荷载谱,主要为湍流和漩涡脱落激励的贡献.气动阻尼对结构共振响应的影响非常显著.利用理论方法计算的风振响应与气弹动力试验的结果吻合良好,可用于户外广告牌风振响应的计算.

Experimental study of wind loads and wind-induced vibration on large single column-supported two-plate billboard

To study the wind-induced destroy mechanism and improve the wind-resistance design for outdoor large single-column billboards, two kinds of wind tunnel experiments were conducted on a typical two-plate billboard. Based on synchronous pressure measurement test, the coefficients of horizontal force that is parallel to and perpendicular to plate, and torque loads coefficients in different wind directions were investigated, the wind pressure distribution along width of board and wind force coefficient of structure at most unfavorable wind directions were diagramed, and the analytic power spectrums density (PSD) of the horizontal and torsional wind loads were given. According to the aero-elastic model test by utilizing high frequency force balance (HFFB), the wind-induced force responses at the bottom of the two-plate billboard with flexible column were analyzed. The theoretical methods that calculate billboard''s wind-induced dynamic responses in horizontal and torsional directions were proposed based on the analysis of experiments. The results indicate that the PSD of wind loading which is perpendicular to plate needs to take aerodynamic admittance function into consideration. The excitation from turbulence and vortex shedding are the main contribution to torsional load spectrum. The aerodynamic damping in two directions (i.e. perpendicular to plate and torsion) has a significant influence on wind-induced vibration of billboard. The theoretical approach is validated through the wind tunnel experiment, and it can be applied in predication for wind load effect on billboards.