【作者】 唐国斌；

【导师】 项贻强；

【作者基本信息】 浙江大学 ， 桥梁与隧道工程， 2011， 博士

【摘要】 混凝土桥梁生命周期内,受荷载作用、钢筋锈蚀、混凝土碳化和开裂等因素的影响,其全寿命性能始终处于变化状态。本文结合浙江省交通运输厅科技计划项目“预应力混凝土连续箱梁底板开裂原因分析及防治研究”(项目编号2008H38),对施工过程中的裂缝,服役过程中的荷载—环境耦合作用及时变承载力等混凝土箱梁桥全寿命设计理论的若干问题进行探索,并以典型箱梁桥为背景进行应用研究。主要的研究工作如下。(1)建立预应力混凝土箱梁桥的空间弹塑性分析的整体和局部模型,对其底板开裂的成因及影响因素进行了详尽的分析研究,表明混凝土箱梁下缘横向应力过大是开裂的直接原因；合龙束孔道对底板截面的削弱及普通受力钢筋配置的不合理,将直接导致底板混凝土横向抗剪不足,是其开裂的根本原因。(2)提出了箱梁施工过程中底板开裂除纵向开裂、预应力束局部崩出、底板孔道间混凝土竖向拉裂等三类开裂形态外,横向剪切裂缝也是一种主要开裂形式,并针对不同裂缝形态,提出了相应的抗裂设计方法。(3)考虑服役过程中荷载—环境的相互作用,提出锈蚀钢筋的名义弹性模量和锈蚀系数以反映钢筋在锈蚀过程中的变形特征；同时结合已有的锈蚀速率模型,推导了不同锈蚀速率下钢筋的锈蚀系数,通过对锈蚀变形规律的研究,将荷载与环境共同作用下,钢筋变形特征分为加速型和衰减型；在此基础上,构建了锈蚀过程中钢筋的时变本构模型。(4)提出荷载—环境耦合效应分析的数学模型,推导了混凝土分离式和组合式两种模型中的耦合分析的有限元方程,利用单元内部开裂应变和保护层厚度的比值控制开裂混凝土单元内钢筋的锈蚀；采用Fortran语言编程实现和嵌入上述模型,并给出了计算实例进行验证。(5)基于混凝土结构裂缝面的力学特征,推导了开裂混凝土的本构关系矩阵及其工程显式,同时对三维分析时,开裂区单元的屈服准则和加、卸载准则等进行探讨,并编制程序予以实现,通过已有构件试验对模型进行验证。(6)综合考虑各种因素及耦合的影响,结合某预应力混凝土连续箱梁桥的工程实例,运用所提出的理论及方法,对服役过程中荷载—环境的耦合效应和时变承载力进行研究,分析表明,在一般大气环境和正常使用荷载下,预应力混凝土连续箱梁桥在服役100年后仍具有较高的超载潜力,从承载力退化的曲线来看,在结构服役的初期,是极限承载力变化最快的时期,其主要原因是混凝土强度快速发展；在服役的中期,承载力退化较为稳定,因为在这一阶段混凝土的强度比较成熟,并且钢筋的锈蚀速率也较小；而在服役的后期,由于多种材料的劣化最终加剧承载力的退化。更多还原

【Abstract】 The life-cycle performance of concrete bridge varies with external factors, such as load effect, reinforcement bar corrosion, concrete carbonation and cracks, et al. The research project "Cracking mechanism and control measurement of crack in bottom plate of prestressed concrete continuous box girder bridge" has been supported by the scientific and technological plans of Zhejiang communications department. According to the project, this paper focuses on the life-cycle design method for concrete box girder bridge. The cracking mechanism in construction stage, the load-environment coupled effect in service stage and the time-dependent carrying capacity of box girder are investigated in this thesis. The primary work and achievements are as follows.(1) The cracking mechanism and parameters study are discussed according to numerical analysis of local and integral module of box girder. The exaggerated transverse stress by the downward radial force leads to the crack in bottom plate. In addition, the shortage of shear capacity due to the ducts and unreasonable reinforcement play crucial roles in the cracking of the bottom plate.(2) Transverse shearing crack is one of the most common crack during the construction of the box girder bridge, as well as longitudinal cracking, concrete cover spalling and vertical tensioning crack. And design methods for cracking control are proposed according to the crack patterns.(3) Nominal elastic module of corroded reinforced bar and corrosion factor are presented to illustrate the deformation process of steel bar during the service of bridge. According to the existing corrosion rate module, the corrosion factor of bars are deduced and compared. And the deformation characteristics are generally divided into acceleration type and degeneration one. Then, the time-dependent constitutive relation of steel bar is advanced.(4) The approach for load-environment coupled effect analysis of concrete bridge is proposed, and the finite element equation for separated element and combined element are deduced respectively. In order to take into account the effect of cracks, the ratio between crack strain and concrete cover depth is used to control the initial corrosion time of cracked element on some assumptions. The above approach is implemented in FORTRAN language, and tested by a reinforced concrete beam test.(5) Based on the characteristic of crack plane, the constitutive relation of cracked reinforced concrete is deduced according to the microscopic study of concrete crack. For the convenience of three dimensional problem, yield criterion and loading and unloading criterion are discussed. By compared the numerical result with experiment ones, the promoted method are tested, and well agreement is obtained.(6) Combined with project case, the load-environment coupled effect and the time-variable capacity of a continuous box girder bridge are studied by the promoted method. The numerical results indicate that the bridge has preferable overloading capacity after 100 years’ service. And from the capacity degeneration curve, early in the service is the fastest-changing period due to rapidest development of concrete strength. During the middle period of the service, the degeneration of capacity becomes stable, because of the stabilized concrete strength and the lower corrosion rate. And in the late time, the capacity has a sharp deterioration caused by various materials degradation.更多还原