超高层建筑横风向气动刚度研究

ANALYSIS ON CROSSWIND AERODYNAMIC STIFFNESS OF SUPER TALL BUILDINGS

为了研究超高层建筑横风向气动刚度,进行了多自由度气弹模型试验,以直接测量模型在不同风速下的振动频率,用该频率相对于自振频率的改变量作为气动刚度的评估指标。分析了结构阻尼比、风场粗糙度、模型密度、折算风速、高宽比、涡振位移等因素对气动刚度的影响。结果表明:在共振临界风速附近,气动刚度造成风振频率改变量可达自振频率的10%;频率改变量随折算风速呈"V"字形变化,在折算风速小于8时,频率改变量通常为正,在共振临界风速附近频率改变量最大,折算风速大于12时,频率改变量保持稳定且略小于结构自振频率。由于涡振位移和气动刚度的相互作用,结构阻尼比越小、风场紊流度越小、模型高宽比越大、密度越小则频率改变量随风速变化的"V"字形越尖锐。最后提出了名义折算风速和实际折算风速的概念,并建立了气动刚度的简化估算模型。

To study the aerodynamic stiffness of super high-rise buildings in the process of vortex-induced vibration （VIV）, wind tunnel tests of multi-degree-of-freedom （MDOF） aero-elastic models were carried out to measure the vibration frequency of the system directly. The effects of structural damping, wind field category, mass density, reduced wind velocity （Vr）, as well as VIV displacement on the VIV frequency were investigated systematically. It was found that the frequency drift phenomenon cannot be ignored when the building is very high and flexible. When Vr is less than 8, the drift magnitude of the frequency is typically positive. When Vr is close to the critical wind velocity of resonance, the frequency drift magnitude becomes negative and reaches a minimum at the critical wind velocity. When Vr is larger than 12, the frequency drift magnitude almost maintains a stable value that is slightly smaller than the fundamental frequency of the aero-elastic model. Due to the self-limiting and nonlinear characteristics of the VIV mechanism and the relationship between the STD of VIV displacement response and the aerodynamic stiffness, the aerodynamic stiffness and drift magnitude of the system frequency are highly sensitive to the aspect ratio, mass density, inherent damping of structure, as well as the roughness of wind field. Finally, the concept of nominal reduced wind speed and real reduced wind speed were proposed. An empirical formula to assess aerodynamic stiffness was established.