冷却塔风振响应时程计算和风振系数分析

Wind induced responses of a hyperboloidal cooling tower in time-domain and gust effect factor analysis

为全面获得冷却塔塔筒的风致动力响应特征,探究各响应包括内力和位移的峰值因子g、动力放大系数D以及用于结构设计的风振系数β的取值和各参数在不同响应间的差异,以某大型冷却塔为例,经风洞试验获得塔筒表面风压时程,采用时程方法进行结构动力响应计算。分析表明,作为空间结构,不同位置不同响应的g值和D值有较大差异,难以直接应用;但结合各响应的时程特征、塔筒结构特性及配筋设计原则,可以将塔筒的g值和D值从环向和子午向的二维分布简化为仅沿子午向的一维分布,由此所得各响应的D值可达工程实用范围,但用法与现行设计方法仍不一致;根据环向和子午向配筋设计的独立性,并考虑风致各内力在结构设计中的不同权重,在实用中对D值可仅区分环向内力和子午向内力独立取值,但环向内力的D值要大于子午向内力。此时,环向和子午向的D值即可作为风振系数β参与结构设计。

Studies were conducted for wind induced dynamic responses of a hyperboloidal cooling tower, gust factor g and dynamic amplification factor D of its different internal forces and displacements. The gust effect factor β, a concept of the equivalent wind load used for structural design was included as well. The tower, s wind-induced dynamic analyses in time domain were conducted based on the wind pressure data obtained from wind tunnel tests on a rigid model of a large hyperboloidal cooling tower. The results showed that g and D of all responses both vary greatly with tower shell positions in latitude and meridian directions, and therefore they can’t be applied in practice conveniently; however, the two dimensional distributions of g and D can both be simplified into one dimensional distributions just along meridian height; this simplification is based on the characteristics of time domain responses, structure behavior and structural design principles; meanwhile, the amplitudes of D can be applied practically but the application method is not consistent with that of the current design codes; furthermore, according to the structural design independence in latitude and meridian directions and different weights of wind induced internal forces in structural design, two Ds are adopted for the internal forces in latitude and meridian directions, respectively, but the former is much higher than the latter; consequently, the two Ds can be used as in the two directions, respectively in structural design as usual.