双曲线冷却塔施工期设计风荷载的确定

Design wind loads on hyperbolic cooling towers during construction

以结构可靠性设计的基本理论为基础,以双曲线冷却塔塔筒施工期和设计基准期内具有相同的可靠度为前提,研究塔筒施工期设计风荷载的取值标准问题。根据风荷载平稳二项随机过程模型的特点,利用结构可靠度的时段分析方法分别建立结构设计基准期及其间各时段可靠度的关系以及施工期及其间各时段可靠度的关系。从施工期与设计基准期的结构抗力成比例入手,按照规范中的分项系数设计方法的要求,得到施工期风荷载标准值与设计基准期风荷载标准值同样成比例的结论。建议了该比例系数即施工期风荷载因子的求解步骤,并针对冷却塔的实际受力情况和基本随机变量的不同分布类型做了计算。计算结果表明:施工期风荷载因子随施工期的延长而增大,随抗力分项系数的增大而减小,其与施工期的关系可用对数函数来拟合。根据施工期风荷载因子的拟合函数式或相应简化表格即可确定双曲线冷却塔施工期的设计风荷载。

The fundamental theory of structural reliability was used to predict the design wind load on hyperbolic cooling towers during construction to give the same reliability during construction as for the design reference period.The relationships between the reliability for the design reference period for various time intervals and the reliability during construction for various time intervals are given based on the time interval method for analyzing the structural reliability using the stationary binomial stochastic process model for wind loads.The structural resistance during construction is found to be proportional to that of the design reference period. The characteristic wind loads also preserve the proportionality relation with the wind load factor during construction defined in this paper using partial safety factor design expressions for these two periods.A general wind load factor solution procedure was given and the predicted wind load factors were computed for typical probabilistic distributions of the random variables.The wind load factor increases with the extension of the construction cycle or with a lower resistance partial safety factor.The relationship between the wind load factor and the construction time is well fit by a logarithmic function.The design wind load for hyperbolic cooling towers during construction can be determined with the correlations or simplified tables of the wind load factor.