【作者】 郭琦；

【导师】 贺拴海；

【作者基本信息】 长安大学 ， 桥梁与隧道工程， 2008， 博士

【摘要】 从二十世纪三十年代开始,预应力技术已广泛地应用于桥梁结构工程之中,世界桥梁中有70%以上都采用了预应力混凝土结构。然而,在预应力技术大量地应用于桥梁工程的实践过程中,尤其对于服役多年的大、中跨径预应力混凝土桥梁,有相当一部分结构产生了严重病害,主要表现在混凝土劣化和力筋缺损等方面。目前关于预应力筋典型缺损状况中关于有效预应力衰减程度的检评技术研究仅停留在简单结构体系的室内模型试验阶段,与实桥工程应用的目标还有很大距离。本文以西部交通建设科技项目—“大、中跨径混凝土桥梁预应力检测技术研究”(项目编号：2005 318 812 15)之专题五—“预应力筋有效预应力的检测方法、设备与评价技术研究”为依托,针对在役混凝土桥梁的有效预应力衰减状况进行了预测理论与方法的系统研究,得到以大跨径混凝土连续梁(刚构)桥为典型代表的具有复杂预应力体系桥梁的有效预应力标准化检测技术及其模拟预测方法,并建立起了完备的测评指标体系,以全面推动预应力有效值检测的实用化进程。文中方法同样适用于以中等跨径桥为代表的简单预应力体系桥梁的有效预应力检测及评价。本文完成的主要研究工作内容如下：(1)基于分项预应力损失算法的解构分析,通过有效预应力实际纵向沿程变化规律预测的反问题开展理论研究,建立起由钢束测值分析和有效预应力分布状况模拟两大模块构成的钢束有效预应力预测理论与方法。其中,核心研究成果主要体现在以下四方面：①通过大量实桥中常见预应力钢束的布置类型及几何特征的归纳统计,将关键服役钢束分为表层测试钢束及间接预测钢束两大类并完成了与直接法检测技术(DD)相匹配的钢束标准化测试分类研究。在以弯曲半径、空间包角及投影长度作为特征参数进行影响因素分析的基础上,定义钢束应力沿程界限波动率(LSFR)—β作为判定指标,将表层测试钢束分为波动束及平缓束两类；②通过同一截面内基准测试钢束有效预应力测试值与预测钢束有效预应力预测值之间的相关关系的建立,得到涵盖几何对称束与几何非对称束两种钢束类型的截面内有效预应力预测方法；③将以波动束为代表的复杂类型钢束拆分为多个单一线型,通过对现行规范中预应力摩阻相关损失的简化计算方法改进,获得了具有通用性的组合线型钢束拟摩阻损失函数σlana(x)的算法并编制了配套的《预应力筋拟摩阻损失等效参数求解程序》(PresPS V1.0),进行了计算机软件著作权登记,实现了波动束有效预应力实际分布状况模拟；④针对以平缓束为代表的简单类型预应力钢束,通过预应力分布从属的三种模式(等比、等差和混合模式)判别,建立起束筋有效预应力实际值与理论值偏差的相关关系,以此为依据得到了基于钢束当前张力测值的平缓束有效预应力纵向沿程分布规律的模拟。(2)基于截面分析的方法,开展了关键测试截面的有效预应力衰减程度整体化评价方法研究,建立了有效预应力整体衰减评价理论与方法,其中关键研究成果主要体现在以下三方面：①通过考虑由钢筋及混凝土组成的复合材料截面间由于混凝土收缩、徐变、温差及预应力筋松弛等时变因素的影响,以预应力体系建立时刻与桥梁服役期内预应力检测时刻为关键时间点状态,结合由此引起的截面内应力重分布的特点,在截面静力平衡的基础上建立了由钢束当前应力测值向有效预应力值转化的解析方法；②分别通过检测状态下截面边缘可测钢束的预应力当前测值及关键截面的释放应力测值两条技术途径,建立了基于预应力测值和截面释放应力测值的截面应力合效应分析模型；③与现行设计规范中基于截面分析的方法相衔接,将理想设计状态下与服役状态下的桥梁控制截面内有效预应力储备度λ的偏差加以量化,建立起分级评价指标体系用于有效预应力衰减程度及影响分析；(3)基于静力学测试原理研发了针对混凝土桥梁预应力筋(钢绞线)预应力有效值的实时检测专项设备—预应力钢索张力测试仪(型号：LCZL-50),并申请了发明专利。该设备有针对性地攻克了在小范围局部扰动梁体混凝土及波纹管状态下钢束张力检测的各项技术难关,为预应力检测技术提供了硬件支撑。(4)规划设计了测量预应力钢绞线张力的基础性专项试验,并在预应力张拉试验台上完成了全过程试验实施,积累了丰富的数据资料。试验中首次以局部扰动混凝土范围及边界支撑方式作为重点模拟参数,进行了钢绞线静、动力指征数据的直接法量测。同时借助数学手段及试验回归分析方法消除了系统测试误差并获得了计入模拟边界工况下的推荐修正公式,分别形成了“静力参数静测法”(SPLM)及“模态参数动测法”(MPIM)两套实用检测技术。静力方法适用于以后张法施工工艺建立预应力体系的在役桥梁预应力检测,而动力方法对于采用先张法施工工艺的在建空心板、梁式桥及体外预应力桥梁的预应力检测更有优势。(5)参照公路混凝土梁桥预应力钢束的常见几何类型及布束方式,设计制作了室外大比例模型梁并开展了试验研究。在实际工程中预应力损失发生、发展机理及变化状态的真实模拟状况下,进一步标定了预应力钢索张力测试仪及配套的测试装置,整合和校正了组配的动力测试系统,验证了修正公式的工程精度,完成了检测方法的适应性研究；通过试验揭示出的实际钢束有效预应力纵向沿程分布规律,得到与瞬时损失相关的预应力损失推论验证。(6)以涵盖常见大中跨径预应力混凝土梁式桥梁结构的五座桥梁作为背景工程,进行了依托工程的实桥应用研究。在此基础上,对建立的有效预应力衰减预测方法重点进行了数值仿真及其影响的对比分析,促进了研究成果更好的推广应用于工程实践。综上所述,文中具有的创新点为：1、首次基于预应力束筋有限点上有效预应力的测值,建立了钢束有效预应力预测模型。该模型由钢束测值分析和有效预应力分布状况模拟两大模块构成,解决了关键服役钢束实际有效预应力量值的预测及沿程分布规律的模拟问题；2、首次提出了控制截面有效预应力衰减整体评价理论与方法。该方法分别依据直接法检测(DD)与应力释放法检测(RD)两条并行技术路线建立了截面应力合效应分析模型,并在此基础上以有效预应力储备度为指标完成了具有复杂预应力体系的梁式桥整体化分级评价；3、首次基于预应力钢绞线静动力指征参数的直接法量测,形成了两套局部扰动混凝土的拟边界状况下钢束张力的实用检测技术—“静力参数静测法”(SPLM)和“模态参数动测法”(MPIM);4、自主研发了预应力钢索张力测试仪(型号：LCZL-50)。通过该设备首次实现了在小范围局部扰动梁体混凝土状态下,针对预应力筋(钢绞线)索力值的抓、握、拔、测一体化实施。更多还原

【Abstract】 Since the 1930s, prestressing technology has been widely used in bridge engineering and more than 70 percent of bridges are of the prestressed concrete structures at present. However, in the procession of its practical application, serious defect have been found out in a considerable number of PC (Prestressed Concrete) bridges, especially to those existing bridges via many years. Altogether the material disease is mainly shown in two aspects:one is concrete deterioration and the other is steel tendon defect. Current studies about inspection and evaluation on attenuation degree of effective prestress are confined to the experimental datum on simply-supported beams. Therefore it still has a long way to go.The research is sponsored by the science & technology program for west communication construction of MOC which is the project of NDE (Nondestructive Examination) on prestress tendon for mid-span or long-span PC bridges (Grant No.2005 318 812 15). This paper relies on the fifth sub-project of the programm focusing on the inspection study of effective prestress for prestressed reinforcement. Therefore, the research objectives of this paper are getting standard testing technology on effective prestress and setting up unified theoretical system of prediction on its attenuation, which may cover both long-span bridge with complicated prestressing systems like continuous rigid frame bridge and mid-span bridge with simple prestressing systems for practical application.Main research contents of this paper are as follows:(1) Based on comparatively sophisticated prestress loss method in current code, combined with study on the inverse problem to the principle of longitudinal distribution for effective prestress, model for predicting on attenuation of effective prestress was built up which included both analysis module and simulation module. Altogether there existed four key aspects as follows:a) According to the route of summing up characteristic types and geometry of prestressed reinforcement in a large number of highway bridges, for the sake of matching with the DD (Directly Detection) testing technique, standardization and classification on effective prestress inspection had accompolished. The prestressed reinforcement was divided into two categories, namely, the directly-measured prestressed reinforcement and indirectly-predicted ones. As far as the directly-measured prestressed reinforcement was concerned, its LSFR (Limited Stress Fluctuating Rate)βalong longitudinal direction used as index of testing classification was defined, which considered the influence of spatial geometry factors such as radius, angle and length of projection and so on to the prestress losses. This type of tendon was categorized as VT (Violent Tendon) and MT (Moderate Tendon). This academic route has greatly strengthened normalization of the inspection technology.b) Numerical method for effective prestress prediction between facial tendon and inner tendon in the same section was built up, through which effective prestress for each tendon could be deduced. This method was suitable not only for tendons with symmetric geometry types but also for asymmetric ones.c) Through decomposition of geometric types and simplified analysis on prestress losses for VT, the algorithm for virtual frictional loss functionσlana(x) was put forward in a universal way. On this basis, software named Prestressing Parameter Solution to virtual frictional loss function (PresPS V1.0) was programmed and copyright of the software had been registered. Thus the analogy method for VT was got eventually. Numerical analysis showed that the method was more accurate and easier in use than the simplified method in current code.d) Aiming at the analogy method for MT, different cross section types, construction techniques and prestressing forms were concluded. Furthermore, three subordinated modes including GM (Geometric Mode), AM (Arithmetic Mode) and FM (Functional Mode) were put forward. After recognition on these modes, distribution regularity and effective prestress value for moderate tendon could be simulated.(2) Based on section analysis, studies of the integral methods for evaluation on attenuation of effective prestress were conducted. Altogether there existed three key aspects as follows:a) Researched on the influence of time-dependent effects such as shrinkage, creep and prestressing relaxation upon composite PC cross-section, a simplified analytical method of stress transformation analysis was presented according to the features of cross-section stress redistribution during the period between the end of construction and the start point of inspection.b) Two practical analysis models for resultant force were available through DD (Direct Detection) and RD (Relieve Detection) testing techniques separately. It made up for the deficiency in nonlinear analysis when applying finite element method for beam structures and possessed advantages of practicability.c) Quantitative analysis for the deviation of Prestress Reservation Degreeλin critical sections between ideal state and service state was executed based on cross-section analytical method. By means of grading index system for deficit of effective prestress, evaluation of PC bridge performance had accomplished and was verified by a synthesis example.(3) A special instrument named Stretching Force Tester for prestressing strand (model: LCZL-50) was invented, through which real-time acquisition of effective prestress force could be realized and the patent had been applied. It provided powerful support for the basic experiments on "static parameter" testing under the condition that bellows were locally split.(4) Special experiment for measuring the tension force of prestressed steel strand was implemented on static load anchoring platform. Both of the damage range and boundary condition were considered as the key index through which the directly-detected measurement on static and dynamic parameters was applied. Simultaneously, test errors were minimized by the aid of mathematic and regression method. Two of the practical techniques for prestressing force inspection which called SPLM (Static Parameter Loading Method) and MPIM (Modal Parameter Incentive Method) separately were got ultimately. Noticeably, SPLM was suitable for existed PC beam and MPIM was privileged in pre-tensioned voided slab respectively.(5) Consulting the common geometry type and disposal way of prestressing tendon in highway bridges, large-scale beam model was made and experimental study had been launched. By simulation of taking place, developing and changing state of prestress losses, the precision for empirical formula was tested and their adaptability study were accomplished. Meanwhile through experiment on actual distribution principle of inherent prestressed tendon along longitudinal direction, a significant deduction correlated with instantaneous prestress losses was demonstrated.(6) Taken five engineerings which composed of common types of PC beam bridges as the background project, the research results were put into practical use. On this basis, numerical simulation and comparative analysis on the key techniques for system of inspection and evaluation on effective prestress were applied to engineering practice successfully so as to fulfill the expected research target eventually.Generally speaking, four innovative points of this paper are summed up:(1) For the first time, model for predicting on attenuation of effective prestress was built up which included both analysis module and simulation module. It solved the problem of simulation on practical value and deviation regularities for effective prestress.(2) For the first time, the integral methods for evaluation on attenuation of effective prestress were put forward based on critical section analysis. In this method, double resultant force models were built up according to two of the parallel ways which are DD (Direct Detection) and RD (Relieve Detection) testing techniques. Furthermore, grading index system for deficit of effective prestress was set up and performance evaluation of beam structures with complicated prestressing systems had been accomplished.(3) For the first time, two of the practical techniques called SPLM and MPIM were got ultimately, which could execute prestressing force inspection on the condition of splitting the concrete and bellows locally.(4) A special instrument named Stretching Force Tester for prestressing strand (model: LCZL-50) was invented. For the first time, it integrated griping, holding, drawing and detecting on prestressing strand to realize real-time acquisition of effective prestress force.更多还原