预应力混凝土构件时变预应力损失计算  

Computation of time-dependent prestress losses in prestressed concrete members

作　　者：胡狄 李雨洁 余志武[1] HU Di;LI Yujie;YU Zhiwu(School of Civil Engineering,Central South University,Changsha 410075,China)

机构地区：[1]中南大学土木工程学院,湖南长沙410075

出　　处：《铁道科学与工程学报》2024年第7期2852-2859,共8页Journal of Railway Science and Engineering

基　　金：高铁联合基金资助项目(U1934217)。

摘　　要：较准确预测混凝土收缩徐变和预应力筋松弛引起的时变预应力损失是进行预应力混凝土结构抗裂性和变形控制的基础,预测值过高或过低均直接影响设计配筋及结构的服役性能。包括设计规范给出的现有各种时变预应力损失公式均为近似式,这些公式的表达形式并不一致,对是否考虑普通钢筋配筋等参量影响存在较大差别。同时各公式中引入的简化系数值及简化项亦不相同,且所有这些公式均不能严谨体现收缩徐变与松弛的耦合影响,因此其时变预应力损失的预测精度难以保证。根据任意时刻截面内力增量平衡和变形协调条件,运用按龄期调整的有效模量法,建立预应力混凝土受弯构件时变预应力损失统一计算方法;结合预应力筋时变应变变化特点和松弛折减系数分析模型,推导松弛折减系数求解方程,从而获得了预测时变预应力损失的实用公式。计算式全面考虑了预应力筋与普通钢筋截面配筋率、钢筋位置等各个影响因素,并能体现混凝土收缩徐变与预应力筋松弛的耦合影响。该公式的计算值、各规范公式值与长期预应力损失试验值比较表明,AASHTO规范与EN 1992-1-1规范的公式理论值比试验值大17%~24%,TB 10092—2017与JTG 3362—2018规范的公式理论值则比试验值少9%~21%,该公式的计算值与试验值差别在6%以内,说明该公式具有良好计算精度。The accurate prediction of time-dependent prestress losses due to concrete shrinkage and creep and tendon relaxation in prestressed concrete structures is important for controlling cracking and deflection,over-or under-estimation of prestress losses affects the prestressing-tendon design and the structural performance in service.The presented formulae including those provided in the codes for time-dependent prestress losses are approximate which hold significant differences in expressions and in whether to consider the influence of parameters such as non-prestressed steels.In addition,the values of the introduced simplified coefficients and the simplified terms in each formula are also different,and they cannot rigorously reflect the coupling effect of shrinkage,creep,and relaxation,making it difficult to ensure the prediction accuracy of time-dependent prestress losses.Based on the equilibrium and deformation coordination conditions for internal force change in cross-section at any time,a unified calculation method for time-dependent prestress losses in prestressed concrete flexural members was presented by using the age-adjusted effective modulus method.Considering the characteristic of time-dependent strain variation in prestressed tendons along with the analytical model for relaxation reduction coefficient,the corresponding equation was derived.A practical formula for predicting time-dependent prestress losses was obtained.All the influence factors,such as prestressed and non-prestressed steel ratio and their locations in the section were taken into account.The coupling effect of concrete shrinkage and creep and tendon relaxation was certainty illustrated.The comparison between the values by the formulae calculation proposed in this article and the values in the specifications,and the experimental values in the long-term prestress loss tests were carried out.The theoretical values of the AASHTO and EN 1992-1-1 formulae are 17%to 24%higher than the tested values,while the theoretical values of the TB 10092—2

关 键 词：预应力损失 徐变 收缩 松弛 松弛折减系数 

分 类 号：U448.35[建筑科学—桥梁与隧道工程]