开孔开槽交通标志板风荷载风洞试验

Wind Tunnel Tests of Wind Loads on Traffic Signboards with Holes and Slots

为了研究局部开孔或开槽等措施对减小交通标志板风荷载的影响效果,设计了可以实现多种开孔开槽方式的标志板试验模型。通过刚性模型测压风洞试验,得到16种不同开孔、开槽方式下的非均匀开孔板表面风压数据,获得不同工况下板表面的平均风压分布特性,分析单排孔位置、单列孔位置、多排多列孔位置及单槽双槽等因素对交通标志板表面平均风压分布、阻力系数和扭矩系数的影响规律,进一步分析各工况下板平均阻力系数随孔隙率的变化规律,以及扭矩系数随风向角的变化规律。研究结果表明:风向角为0°～45°时,板的阻力系数变化很小,风向角为45°～90°时,板的阻力系数呈线性减小;0°风向角下,开孔或开槽板迎风面风压系数基本不变,背风面孔或槽附近平均风压系数幅值增大;当孔隙率小于5%时,板阻力系数对孔隙率、孔位置和开槽数量均不敏感,标志板风荷载减少的主要原因在于受风净面积的减少;孔隙率较大时,减小板阻力系数的效果相对明显;给出了非均匀开孔情况下,板阻力系数与孔隙率的建议公式;板在45°斜风向下产生最大扭矩系数,开孔或开槽都能够显著减小斜风向下绕板竖向中心轴和边缘竖轴的平均扭矩系数,其中45°风向角时影响更为显著;孔隙率较大时,扭矩系数减小效应更为显著。

The effects of drilling holes or slots in partial areas of traffic signboards on reducing wind loads were investigated. A test model was designed to employ one model to make different kinds of drilling holes or slots. Based on wind tunnel tests of the rigid model, pressures on signboards with 16 kinds of holes or slots were obtained. Characteristics of the mean wind pressures on signboards under different cases were then acquired, and the influence of single row holes, single column holes, multi-row holes, multi-column holes, and single and double slots on the characteristics of mean wind pressure, drag force coefficients, and torsion coefficients on the traffic signboard was analyzed. Finally, variations of the mean drag force coefficients with porosity and variations of the torsion coefficients with wind direction were investigated. The results show that the drag force coefficient of a signboard varies little for wind directions between 0° and 45°, however it decreases almost linearly when the wind direction moves from 45° to 90°. For the 0° wind direction, the wind pressure coefficients on the windward face of the signboard with holes or slots tend to be stable, whereas there is a small increase of the amplitude of the mean wind pressure around the hole or slot. When the porosity is less than 5%, the drag force coefficients are not sensitive to the porosity and the position of holes or slots, and the effects on reducing wind loads on signboards are attributed to the reduction of the net area of the signboard. When the porosity is greater than 5%, the reduction of drag force coefficients is relatively obvious. A fitted formula of the mean drag force coefficients with the porosity of the signboard with non-uniform holes was proposed. The maximum torsion coefficient appears at the 45° wind direction. The mean torsion coefficients along the side vertical axis or the center vertical axis of the signboard with holes or slots are much smaller than those of the solid slab for oblique wind directions, and such reduction effects are more remarkable for the 45° wind direction or for the signboard with a large porosity.