山区桥梁设计风参数实测方法及与规范结果对比研究

Wind Parameters Measurement Method for Design of Bridges in Mountainous Area and Comparison with Code-Recommended Values

针对山区桥梁设计风参数难以确定的问题,提出结合地形模型风洞试验、现场风观测、气象站数据统计分析确定山区桥梁设计风参数的方法。采用地形模型风洞试验确定桥址风场空间分布;利用短期内桥址现场与气象站同步观测结果对比确定两地风速缩放关系;再根据气象站长期风速资料确定风速概率分布模型,并结合风速缩放关系、桥址风场空间分布得到桥址各位置的设计基准风速以及检验风速。以某拟建跨峡谷大跨悬索桥为背景,应用该方法确定了该桥设计风参数,并与《公路桥梁抗风设计规范》(JTG/T 3360-01—2018)计算结果进行对比。结果表明:山区桥址平均风速沿桥轴线呈不均匀分布,具有明显的方向性;桥址平均风速在高风速时以东南风向与西北风向为主,且东南风向形成负攻角,西北风向形成正攻角,风攻角正负具有明显的风向依赖性;平均风攻角随着风速的增加而降低,但仍明显高于我国规范规定范围;-3°~+3°小风攻角下,规范方法得到的检验风速高于实测方法,偏安全,对于大风攻角,规范方法偏危险。

The determination of wind parameters is quite critical to the design of bridges in mountainous area.In this paper,a method to determine the design wind parameters for bridges in mountainous area is proposed,which combines statistical analysis of the wind tunnel test with terrain model,field wind observation and data from weather station.The wind tunnel test was carried out to determine the spatial distribution of wind fields at bridge site,the parallel observation results from short-term field measurement and weather station registration were taken into account to calculate the wind speed scaling factors between two locations.With the long-term wind speed data from weather station,a wind speed probability distribution model was developed,together with wind speed scaling factors and wind field spatial distribution at bridge site,the design reference wind speed and checking wind speed at different locations of the bridge site were obtained.The method presented has been applied for the design wind parameter determination of a proposed valley-crossing long-span suspension bridge,and the values were compared with the values suggested in Wind-Resistant Design Specification for Highway Bridges(JTG/T 3360-01—2018).As per the analysis,the mean wind speed at the bridge site showed sign of non-uniform distribution along bridge axis,with predominant direction.At the high wind speeds,the southeast and northwest winds are the basis of the mean wind speed,and the former creates negative attack angle,and the latter the positive attack angle,indicating that the negative and positive wind attack angles are highly dependent on wind directions.The mean wind attack angle reduces as the wind speed increases,but still higher than the stipulated range in the Chinese code.When the wind attack angles are at-3°to+3°,the checking wind speeds obtained using the method suggested in the code are higher than the measured values,relatively safe,but for the large wind attack angle,the values attained by the method suggested in the code are hazardous.