预应力砼塔筒截面刚度降低系数与预应力度的关系

在预应力混凝土塔筒的挠度和裂缝宽度计算中 ,截面的刚度是必不可少的基本资料。虽然我国《混凝土结构设计规范》给出了截面刚度的计算公式 ,但由于其形式复杂 ,原高耸结构设计规范没有采用 ,而是给出了一个适用于普通钢筋混凝土塔筒的刚度降低系数。为了适应预应力高耸结构变形和裂缝宽度计算的需要 ,本文在混凝土结构设计规范公式的基础上 ,提出了利用预应力度来求解截面刚度降低系数的简单方法。由混凝土结构设计规范给出的公式可以看出 ,刚度降低系数与预应力、外荷载及截面配筋率等很多因素有关。而预应力度是一个把外荷载和预应力及截面配筋率联系起来的量 ,因此本文利用了预应力度的这个特点 ,通过选取承受不同荷载的各种塔筒截面 ,计算其在不同预应力度配筋情况下的刚度降低系数值。根据计算的结果 ,分析了预应力塔筒截面刚度降低系数随预应力度的变化趋势 ,并拟合出刚度降低系数与预应力度之间的关系曲线和计算公式。为预应力高耸结构的设计计算提供了参考。

The Relationship between the Dropping-coefficient of Stiffness and Prestress Degree of Prestressed Concrete Tower Drum

To do the calculations for the deflection and the flaw width of pre stressed concrete tower drum,the stiffness of the cross sections is essentially basic data.Our government's Design Code for Concrete Structures offers some calculating formulas for the cross section stiffness,however,because of the complexity in the form,these formulas were not adopted by previous Design Code of High structures.Instead a stiffness reduction coefficient was given which was only applied to reinforced concrete.In order to meet the calculating needs for pre stressed high structure deformation and flaw width,the author of this paper,in accordance with the formulas for concrete structure design criterion,puts forward a simpler calculating method by which the cross section stiffness reduction coefficient can be got if prestress degree are given. The formulas offered by the Design Code for Concrete Structures indicate that the dropping coefficient of stiffness is related with many factors such as prestress degree,exterior loads and reinforcement percentage.The prestress degree is a quantity which relates exterior loads with reinforcement percentage.The author takes full advantages of characteristics of pre stressing forces,and by means of selecting various cross sections bearing different loads,calculates the dropping coefficient of stiffness under different prestress degree.With the calculation results,the author analyzes the changing tendency of cross section stiffness reduction coefficient under different pre stressing forces,and works out the curve and calculating formulas for the inter relation between dropping coefficient of stiffness and prestress degree.And all these can be used as a reference for the pre stressed high structure design and the related calculations.