【作者】 薛鹏飞；

【导师】 项贻强；

【作者基本信息】 浙江大学 ， 桥梁与隧道工程， 2009， 博士

【摘要】 海工建筑物和公路桥梁常因氯盐等环境因素引起钢筋锈蚀而使结构性能退化、承载能力降低,甚至毁损破坏,不得不花费巨资维修甚至重建,造成巨大的经济损失和严重的社会影响。本文结合“大跨度移动模架现浇箱梁裂缝控制技术及耐久性研究”项目,以广州珠江黄埔大桥引桥段预应力混凝土连续刚构桥为工程背景,对移动模架施工的薄壁混凝土箱型桥梁结构的耐久性进行试验分析、状态评估、寿命预测,同时考虑材料性能退化,对其运营阶段结构的极限承载能力进行分析预测研究,主要的研究成果如下:(1)确定了黄埔桥的主导腐蚀环境—氯离子侵蚀。讨论了氯离子对混凝土结构的侵蚀机理和破坏形式,采用NEL法测定黄埔桥引桥段墩身和箱梁混凝土氯离子的扩散系数,并根据混凝土渗透性评价标准,对黄埔桥引桥段的墩身和箱梁混凝土的渗透性等级进行评定。(2)基于Fick第二扩散定律,通过参数定义综合考虑氯离子扩散系数的时随效应、混凝土的氯离子结合能力,混凝土自身的材料缺陷对氯离子在混凝土中扩散过程的影响,建立了多因素作用下的氯离子在混凝土中扩散的修正模型,研究给出了模型中各参数的取值,利用该模型,结合已有研究的实测数据对该模型进行了验证,取得了较为满意的结果。(3)基于上述扩散模型,以钢筋表面的氯离子浓度达到临界值导致钢筋开始锈蚀作为结构寿命终结的标志,采用不同的方法进行结构寿命预测:定值法,即将扩散模型中的若干参数作为常变量处理,取一代表值直接计算;利用经典概率论方法,考虑参数的随机特性,推导了基于概率的混凝土结构工作寿命期望值及相应失效概率的计算公式;引入可靠度概念,把临界浓度的氯离子侵入深度看作环境荷载,保护层厚度看作结构抗力,采用蒙特卡洛法进行可靠度计算,通过引入目标可靠度进行结构的寿命预测。采用上述三种方法,针对黄埔大桥钢筋混凝土引桥段的墩身和箱梁混凝土进行基于耐久性的寿命预测,不同方法的预测结果能够相互吻合。(4)基于灰色关联和模糊识别理论,采用非线性的归一化处理方法,引入信息熵和复合权重的概念,综合考虑专家经验和检测数据自身的重要性,建立了混凝土构件的耐久性评估模型,并给出了工程算例。该评估模型可一次对多个构件进行评估,且具有广泛的适用性,不仅局限于对混凝土耐久性能的评估。(5)基于材料性能的退化,以黄埔大桥的预应力混凝土连续刚构桥为背景,从空间单元模式、预应力空间效应分析、阶段模型应力处理、材料非线性的考虑等方面对在役预应力混凝土桥梁结构的极限承载能力及退化规律进行了分析研究。结果表明材料的性能退化对结构的极限承载能力有较大影响,破坏时的载荷因子出现大幅下降,且破坏时的脆性特征加剧,有从整体破坏向局部破坏转化的趋势。更多还原

【Abstract】 Marine structures and highway bridges usually suffered environmental loads, such as chloride ion corrosion. It caused structural behavior degeneration、bearing capacity decreasing, even structural failure, and lead to tremendous economic loss and severe social impact. According to the item of "Study on crack control technology and durability for cast-in-place box girder by large span Movable Scaffolding System (MSS)", on the background of Huang-pu Bridge project, aiming at P.C. continuous rigid frame bridge with thin-walled box section, the series studies were carried out - including experimental analysis of material durability, condition assessment, life prediction, ultimate bearing capacity analysis and prediction on service stage based on material degradation. And the primary achievements are listed as follows:(1) Chloride ion was identified as main erosion environment of Huang-pu Bridge. Corrosion mechanisms of chloride ion and damage modals of concrete structures suffered chloride erosion were discussed. The NEL method was adopted, and the chloride ion diffusion coefficient of piers & box girders of approach bridge was measured. According to the assessment standard of concrete permeability, the permeability grade evaluation of piers & box girders were performed.(2) Based on Fick’s second law, a new chloride diffusion model in concrete was formulated, in which the factors of time-dependence of chloride diffusion coefficient, chloride binding capacity of concrete, and self-defects of concrete were taken into account. And the parameters value in the model was given for practical application. The model was verified by long-term field data that are available in published literatures. The practical data agreed with the calculated results very well.(3) Based on the diffusion model, three different life prediction methods were presented, with the state that chloride ion concentration on rebar surface reached the threshold value was regarded as a sign of end of life. The first method assumed parameters in diffusion model as constant, the representative value was employed to calculate; And based on classical probability theory, the parameters randomness was considered, then expected value of service life and corresponding failure probability of concrete structure were further deduced in second method; By introducing the concept of reliability, the chloride ion penetration depth in limit state was taken as environment load, and the cover thickness was taken as resistance, monte carlo method was adopted to calculate reliability of structure. Through the introduction of target reliability, life prediction could be easily performed. By using above methods, aiming at piers & box girders of approach bridge of Huang-pu Bridge, service life prediction were carried out and the results could be matched each other.(4) Based on grey correlation and fuzzy recognition, a durability assessment model of concrete members was established, in which nonlinear normalization processing method was adopted. By introducing combinatorial weight, the importance of expert experience and inspection data were taken into account. The model was testified by practical engineering example at last. By using this model, several concrete members could be evaluated at one time, and it has widely applicability, not only confined to concrete durability assessment.(5) With a case study of P.C. continuous rigid frame bridge of Huang-pu Bridge , on the basis of material performance degradation, the ultimate bearing capacity analysis of P.C. bridge structures was carried out from several aspects: space element mode, spatial prestressing effect, treatment of stage model stress, and material nonlinear effect. The results showed that material degradation has great impact on ultimate load capacity of structure: the load factor on limit state dropped rapidly and brittle characteristics was aggravated at the same time.更多还原