混凝土结构中预应力筋摩擦损失与反摩擦损失简化计算
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摘要
由于计算摩擦损失须确定从张拉端到所考察截面预应力筋各相邻特征点(如张拉端、反弯点、计算截面等)的切线夹角之和,同时由于预应力筋不同区段摩擦损失曲线的斜率不同,使得预应力筋摩擦损失计算较为繁复。由于目前反摩擦损失计算的规范方法假定预应力筋各区段的反摩擦损失曲线斜率与正摩擦损失曲线斜率数值相等、方向相反,致使预应力筋反摩擦影响区长度lf及反摩擦损失的计算同样也十分繁复。针对这一突出问题,在对现行规范方法进行简要回顾之后,基于预应力筋摩擦损失的线性计算公式,提出了将预应力筋在张拉端至锚固端全长范围内的摩擦损失曲线与反摩擦损失曲线均分别统一取为单一斜率直线,且仍沿用正反摩擦损失曲线斜率大小相等、方向相反假定的简化计算方法(法Ⅰ);在对应用法I计算远离张拉端控制截面预应力筋摩擦损失量值偏大这一现象进行分析之后,提出对法I的修正方法(法Ⅱ);最后给出了将张拉端至锚固端预应力筋摩擦损失的指数曲线用连接二点的直线去替代,且仍沿用正反摩擦损失曲线的斜率大小相等、方向相反假定的简化计算方法(法Ⅲ)。介绍了三种简化方法的计算分析结果,并附算例。
As the summary of indications of the tangents of neighboring characteristic points (strssing point, inflection point and aim point) needs to be calculated in obtaining the friction loss and section slopes of the prestressing tendon are different, the calculation of friction is complicated. And calculation of the antifriction loss by the China Code method is the same intricate as a result of assuming that the magnitude of the friction curve slope of each section equals to that of the antifriction curve and the direction is reverse. To solve these problems, after briefly reviewing the code method, a simple method (method Ⅰ) is developed on the basis of the linear expression of the friction loss. The magnitude of the friction curve slope equal to those of the antifriction curve of the prestressing tendon from stressing point to dead end and the direction is reverse. Analyzing the phenomena that the result errors of method I are big in critical sections far from the stressing end, a modified method (method Ⅱ) is discussed for simplifying calculation. Moreover, method Ⅲ is presented in which the exponent expression of the friction loss between the stressing end and dead end is substiuted by a straight line between them. The analysis of the calculation results of these three methods are introduced, and calculation examples are included.
As the summary of indications of the tangents of neighboring characteristic points (strssing point, inflection point and aim point) needs to be calculated in obtaining the friction loss and section slopes of the prestressing tendon are different, the calculation of friction is complicated. And calculation of the antifriction loss by the China Code method is the same intricate as a result of assuming that the magnitude of the friction curve slope of each section equals to that of the antifriction curve and the direction is reverse. To solve these problems, after briefly reviewing the code method, a simple method (method Ⅰ) is developed on the basis of the linear expression of the friction loss. The magnitude of the friction curve slope equal to those of the antifriction curve of the prestressing tendon from stressing point to dead end and the direction is reverse. Analyzing the phenomena that the result errors of method I are big in critical sections far from the stressing end, a modified method (method Ⅱ) is discussed for simplifying calculation. Moreover, method Ⅲ is presented in which the exponent expression of the friction loss between the stressing end and dead end is substiuted by a straight line between them. The analysis of the calculation results of these three methods are introduced, and calculation examples are included.
引文
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[2]JTJ023—85,公路钢筋混凝土及预应力混凝土桥涵设计规范[S].
[3]JGJ/T92—93,无粘结预应力混凝土结构技术规程[S].
[4]郑文忠,王英.预应力混凝土房屋结构设计统一方法与实例[M].哈尔滨:黑龙江科学技术出版社,1998.7—13.
[5]郑文忠,王英,计学闰.现代(高效)预应力混凝土结构中预应力损失的合理预估[J].哈尔滨建筑大学学报,1996,29(6):48—52.
[6]Post TensioningInstitute.Post TensioningManual[M].USA.1985.
[7]杨宗放.曲线预应力筋锚固损失计算[A].见:华东预应力中心编.现代预应力混凝土工程实践与研究[C].北京:光明日报出版社,1989.117—120.
[8]陶学康.无粘结预应力混凝土设计与施工[M].北京:地震出版社,1993.28—34.
[9]陶学康.后张预应力混凝土设计手册[M].北京:中国建筑工业出版社,1996.24—34.
[10]郑文忠,王英.预应力混凝土结构中预应力筋损失的近似估算与简化计算[J].工业建筑.1999.29(3):5—8.
[11]郑文忠,曹大富,吕志涛.后张预应力混凝土平板 柱结构中预应力筋有效预应力的合理预估[J].建筑结构,1996,26(8):14—16
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