湖南大学博士学位论文混凝土斜拉桥施工期的时变可靠性研究姓名：刘扬申请学位级别：博士专业：结构工程指导教师：尚守平20050401I摘 要 混凝土桥梁结构的生命全过程可分为施工期、使用期、老化期三个阶段，现行规范主要针对正常使用阶段，对施工期的可靠性研究还很少。近年来调查分析表明，结构施工期的平均风险高于使用期。 论文研究了混凝土斜拉桥施工期构件抗力的概率模型、 施工期荷载的调查统计、时变可靠度分析以及施工期体系可靠度计算等问题，主要工作内容包括以下几个方面： 1 针对混凝土斜拉桥采用的高强混凝土，在施工现场进行高强混凝土早龄期力学性质的试验研究，分析了早龄期轴心抗压强度和弹性模量的截口概率分布类型，对试验数据进行非线性最小二乘回归分析，基于随机过程理论建立了混凝土早龄期轴心抗压强度和弹性模量的平均值和变异系数的历时变化模型，并根据试验结果，提出了早龄期混凝土轴心抗压强度和弹性模量的关系式。 2 考虑抗力的随机性和时变性，采用非平稳随机过程模型来描述混凝土斜拉桥构件施工期抗力，获得了混凝土斜拉桥构件施工期抗力的平均值函数和标准差函数，并且分别采用离散采样法和假定抗力服从独立增量过程的连续函数法计算了早期抗力的自相关函数，同时对影响斜拉桥构件抗力的各变量进行了参数敏感性分析。 3 针对混凝土斜拉桥的施工特点，对各施工工序的主梁活荷载进行分类并进行现场调查，获得了一批现场数据，分析了施工期活荷载的分布规律，基于工序时间域获得了施工期活荷载的均值函数和标准差函数。 4 基于施工控制的参数反馈识别技术，对反映荷载效应的斜拉桥主梁参数如容重、刚度等物性参数进行了实时识别，分析了该参数在施工过程中的波动规律。针对现行规范中大跨度桥梁施工质量评定缺乏反映结构荷载效应的评价指标的问题，提出了反映结构荷载效应的斜拉桥施工期新的施工质量评价指标等效容重波动率和等效弹性模量波动率。并且分别采用控制图和工序能力指数进行施工质量评价，在控制图法中建立了分别考虑等效弹性模量和等效容重的一元质量控制图和考虑两者相关性的二元质量控制图。同时，根据工序能力指数提出了等效弹性模量波动率和等效容重波动率的建议评价标准。 5 在混凝土斜拉桥这一类复杂结构的可靠度计算中，极限状态函数一般是隐式函数，本文提出了一种高效的改进虚拟中间变量法，直接在标准正态空间内重构极限状态函数，可以对施工期斜拉桥结构的失效曲面进行高精度重构，II显著地提高了拟合精度和运算效率，具有很大的优越性，并通过实例验证了这种算法的高效性和精确性。 6 将可靠度分析模块与施工控制分析程序相结合，提出了混凝土斜拉桥施工期的时变可靠度的实用计算方法，该方法可以直接利用现有的施工控制分析程序，将结构的力学分析和可靠性评价两部分合理统一。同时，基于结构可靠度的一次二阶矩法原理，分析了施工阶段斜拉桥时变可靠度的主要参数的敏感性，在此基础上可以明确斜拉桥施工过程中应重点控制的施工参数，以提高施工质量控制的主动性。 7 采用改进的约界法限制分枝规模，寻找并识别对结构体系可靠度起主导作用的主要失效模式，考虑各主要失效模式间的相关性对施工期斜拉桥的时变体系可靠度进行了合理分析。 主题词：混凝土斜拉桥；施工期；时变可靠度；概率模型；抗力；荷载 IIIAbstract The life cycle of concrete bridges consists of three periods, i.e., construction period, service life and degradation process. The failure probability of cable-stayed bridges during construction is higher than that during service life. However, the existing codes provide no uniform safety requirement for bridges during construction and nearly all of the existing literature is not particularly surprising since very little is known about the structural performance of a bridge during its construction based on structural reliability theory. This dissertation studies the probabilistic model of structure member resistance for concrete cable-stayed bridges during construction, the probabilistic analysis method of load during construction, time-dependent reliability analysis, and evaluation of system probability of failure based on time-dependent reliability. The main work is as follows. 1. On the basis of in-site experimental results for the concrete cable-stayed bridges, the early mechanical properties of high-strength concrete are studied. Probability distributions of the early strength and elastic modulus of concrete are analyzed. Time-dependent models of mean and variation coefficient of early strength and elastic modulus are developed respectively. Also the relationship between the early strength and elastic modulus of concrete is analyzed. 2. Considered of the randomness and the time-dependence of resistance during construction, a unbalanced random process is introduced to describe member resistance. The mean and variance function as well as self-correlation coefficient of resistance for flexural member of concrete bridge during construction are determined by taking the independent increment process as the probabilistic model of resistance. And the two methods of calculating the standard auto-correlation function are introduced: the method of discreteness data and the method of continuum function assuming resistance as independent increment random process. Additionally, the influence of parameters on structural resistance is studied. 3. Based on the in-site investigation and statistical analysis of live loads during construction, the changing law of construction live load of main beam with the changing cantilever length is studied, and the probabilistic model of live loads on cable-stayed bridge is established. It is found that the mean value of live loads submits to exponential distribution and standard variance of live loads submits to IVlogarithm distribution. 4. The two parameters, density and elasticity module, are identified used ANN. The two new parameters which represent load affects, i.e., equivalent density and equivalent elasticity module, are suggested to evaluate the workmanship during construction. And the unitary quality control method and the duality quality control method are used to evaluate the stability of workmanship. 5. An modified virtual intervening variable method is introduced to deal with the reliability analysis of cable-stayed bridges, the performance functions of which are implicit. The performance function approximation is implemented in the standard normal space of random variables. The efficiency and accuracy of the proposed algorithm are demonstrated by several examples. 6. Combined with the Construction Process Analysis Program for Bridges, an efficient algorithm is proposed to calculate the time-variant reliability index of cable-stayed bridge during construction. Based on principle of first order and second moment method, the formulas are introduced. The parameters sensitivity is studied for time-variant reliability of cab