基于反应谱方法的双曲冷却塔地震响应特征分析

Seismic response features of hyperboloidal cooling towers based on response spectral analysis

为明确冷却塔结构的振型特征、不同振型在地震响应中贡献及地震内力环向分布特点,便于冷却塔结构设计,以某大型双曲冷却塔为例,在动力特性分析基础上采用反应谱方法进行地震响应计算,并与其它荷载作用下内力进行对比。研究表明,冷却塔振型可据其形状、方向分为环向与子午向谐波耦合振型、侧向弯曲振型、竖向伸缩振型及竖向扭转振型4类。第1类振型为冷却塔主振型;水平、竖向地震响应贡献分别来自第2、3类振型,第1、4类振型对地震作用均无贡献。侧弯振型的截面变形特征决定水平地震作用下塔筒内力在环向呈正弦或余弦分布。无论水平或竖向地震作用,塔筒中主要产生双向轴力,在下支柱主要产生轴力及弯矩,且水平地震作用产生的内力远大于竖向地震。较其它荷载作用效应,地震作用对塔筒的关键效应为塔筒中下区段内子午向拉力及塔筒顶端0.2HS范围内环向拉力,且地震效应对下支柱影响明显大于对塔筒影响。

In order to illustrate the features of free vibration modes of hyperboloidal cooling towers （HCTs） and their contributions to seismic responses, response spectral analysis was conducted for a certain HCT and its dynamic feature analysis was done too. Then, latitude distributions of its internal forces were discussed. Comparative study under other load effects was also presented to identify the status of its seismic responses for structure design. It was shown that according to their shapes and directions the modes of the HCT can be classified into four types including coupled modes between latitude and meridian hrmonics, lateral bending modes, vertical stretching modes and vertical torsion modes; the first type is the most dominant, but it has no contributions to seismic responses just like the forth type ; the contributions to horizontal and vertical seismic responses all come from the second type and the third one, respectively; all internal forces are in sine or cosine distribution along the latitude direction, depending on the cross section deformations of lateral bending modes; the prominent internal forces in the shell are axial forces in latitude and meridian directions for horizontal or vertical seismic inputs, the corresponding prominent internal forces in columns are axial force and moment; the horizontal seismic responses are much larger than the vertical seismic responses; based on the comparison with other load effects, the key seismic responses for structure design of the shell are the latitude axial force at the top of the shell and the meridian axial force in the lower half shell, and the seismic responses of columns are more significant than those of the shell.