雷暴冲击风下输电塔风荷载特性与风振响应研究

Thunderstorm downburst is an intensive downdraft air that induces very strong wind in all directions when striking the ground. The maximum wind speed of downburst is near the ground, which has a strong destructive to the transmission tower. Unfortunately, the wind loads used in Chinese codes and most countries' codes are based almost entirely on the conventional boundary layer vertical profile, downbursts have not been taken into account in current Chinese design standards for wind loads because of lack of statistical analysis and knowledge for wind load and wind-induced vibration characteristics of transmission tower under downburst. In the current project, the conventional boundary layer wind tunnel is used to simulate the wind profiles of thunderstorm downburst, and based on a new displacement measurement technology, system studies on the wind-induced vibration characteristics of transmission tower with different types subjected to downbursts are conducted to clarify the wind-induced response law of downburst by using aeroelastic model wind tunnel tests. Based on the overall displacement responses of transmission tower measured from aeroelastic model tests, the aerodynamic damping and the aerodynamic loads role in the structure are further identified to analyze the variation of aerodynamic damping with wind speed and the distribution characteristics and action mechanism of aerodynamic loads, respectively. Moreover, a new experimental analysis method for three-dimensional equivalent static wind loads model of transmission tower system is also proposed based on the overall displacement responses of transmission tower. Through this project, theoretical basis and design guidance will be proposed for downburst wind-resistent design of transmission tower.

雷暴冲击风是短时间内冲向地面并沿雷暴中心向外围迅速扩散的高强气流，其最大风速出现在近地面附近，对输电线塔具有极强的破坏性。目前针对雷暴冲击风下输电塔风荷载和风振性能的研究较少，包括我国在内的大多数国家的荷载规范基本上仍采用常态大气边界层剖面风荷载作为设计荷载，并未体现雷暴冲击风的作用。本项目通过输电塔气弹模型风洞试验，在边界层风洞中模拟雷暴冲击风风场，采用新的位移测试技术对输电线塔雷暴冲击风作用下的风振特性进行系统的研究，分析不同类型的输电塔在冲击风作用下的风振响应规律。基于输电塔气弹模型整体位移响应的测量结果，进行气动阻尼参数和作用于结构上的气动荷载识别，研究输电塔结构气动阻尼随风速的变化规律和气动荷载的分布特征与作用机理，建立输电塔结构三维静力等效风荷载的新的试验分析方法，为输电塔抗冲击风设计提供理论依据和设计指导。

雷暴冲击风的最大风速出现在近地面附近，对输电线塔具有极强的破坏性。当前针对雷暴冲击风下输电塔风荷载和风振性能的研究较少，导致输电塔的风毁事故时有发生。包括我国在内的大多数国家的荷载规范基本上仍采用常态大气边界层剖面风荷载作为设计荷载，并未体现雷暴冲击风的作用。本项目采用自主开发的雷暴冲击风模拟装置，在常规边界层风洞中实现了雷暴冲击风的模拟。基于输电塔气弹模型风洞试验，采用非接触位移测试技术对输电线塔在冲击风场下的风振特性进行了系统研究。总结了不同类型的输电塔在不同尺度冲击风作用下的风振响应规律，并对比分析了常规风场和冲击风场下塔头、塔高等因素对输电塔风振响应的影响。基于输电塔气弹模型位移响应的测量结果，研究输电塔气动荷载的分布特征，类比于荷载响应相关法，建立了输电塔结构三维静力等效风荷载的新的试验分析方法。研究结果表明，冲击风下的输电塔风振响应与常规风场下的响应并未有明显区别，均以一阶模态振动为主。不过，由于冲击风的低湍流度特征导致脉动响应偏小。输电塔风振响应随高度和风速的增大而增大，同时随风向角变化呈现规律性的特征，最大风振响应基本发生在15o～30o。风场和塔高相近的条件下，干字型塔楼的平均和脉动响应均高于猫头型输电塔。输电塔的等效静风荷载成分组成说明，对于镂空的输电塔结构，其平均荷载占有绝对优势，背景响应和共振响应占次要地位。