混凝土桥梁耐久性评估与预测

发布时间：2018-08-22 11:25

【摘要】：混凝土桥梁是公路和城市桥梁的主导桥型。由于其材料自身和使用环境的因素，往往存在各种各样的耐久性问题，必须进行周期性的维修养护。由于工程实际问题的复杂性，混凝土结构耐久性评估和寿命预测会遇到大量随机、模糊以及不完整的信息，尚无理想的混凝土桥梁耐久性评估及寿命预测方法。在综述国内外相关文献的基础上，对混凝土桥梁耐久性相关问题开展了如下研究： 1.提出一种基于层次分析法和证据理论的混凝土桥梁耐久性状况群体评估方法。首先，将全桥划分为上部结构、下部结构和桥面系三部分，并进一步划分为一系列部件、构件；其次，各个层次上指标权重的确定和底层指标的耐久性状况评估均由评估专家群体分别完成，专家个体权重由专家个体评估结果与理想结果的模糊距离确定；然后，将专家的评估意见加权平均，获得专家组的评估意见；最后，采用证据合成理论，从底层开始，逐层评估，直至得出最终评估结果。采用该方法评估广清高速公路天坪岭大桥和湖南常宁茭河口大桥的评估，用于验证该方法的可行性。 2.在对既有混凝土结构碳化模型总结分析的基础上，提出预测碳化深度的贝叶斯更新方法。首先，选择几个碳化模型并平均赋以权重，以其加权平均值作为先验模型预测碳化深度；然后，应用工程检测信息，对模型的分布参数和权重进行更新；最后，用更新后的模型参数和权重进行碳化深度预测。用一个10年期自然碳化试验验证了该方法的有效性，并将其用于新华高架桥的耐久性评估。结果表明该方法可有效提高碳化深度计算的精确性。 3.提出一种能考虑CO2浓度、温度随时间变化的碳化深度计算方法。利用最新的气候变化数据和气候变化预测模型，研究了CO2浓度升高和气候变化对碳化深度、钢筋腐蚀概率、混凝土桥梁表面开裂面积比和承载能力可靠度的影响。结果表明：CO2排放和气候变化加速混凝土碳化腐蚀，A1F1和A1B排放策略下混凝土碳化速度分别提高33%和24%左右，A1F1和A1B排放策略下钢筋开始腐蚀概率和正常使用极限状态耐久性失效概率均较气候不变情形有所提高，其中保护层质量越差，失效概率提高幅度越大。 4.研究了气候变化对氯盐环境下混凝土桥梁耐久性的影响。首先提出一个计算混凝土中氯离子扩散的新方法，该方法不仅能考虑混凝土掺合料、龄期、温度、湿度、混凝土与氯离子结合能力的影响，而且能考虑混凝土结构服役期内大气温度、大气湿度和冻融损伤程度的时变效应。考虑劣化空间变异性特征，研究了A1F1和A1B排放策略对混凝土桥梁耐久性的影响。结果表明：（1）未来40年，A1F1和A1B排放策略比气候不变情形的锈蚀开裂比例分别提高15%和12%，严重锈蚀开裂比例分别提高19%和14%；（2）对完好混凝土桥梁，不同截面的失效具有高度相关性，，其体系可靠度可由关键截面如跨中截面的可靠度代替，而对劣化的钢筋混凝土梁，应考虑钢筋锈蚀的空间变异性。 5.基于等超越概率原则，根据混凝土桥梁的预期使用寿命和拓宽前既有桥梁使用年限，分析了拓宽混凝土桥梁的设计基准期、车辆荷载和设计人群的取值。考虑混凝土桥梁拼宽后新、旧组合结构的不同步劣化引起的横向分布系数时变性，建立了拓宽后新、旧桥梁的时变可靠性模型。以一座16m跨预应力混凝土简支梁桥拼宽钢筋混凝土简支梁桥为例开展研究，结果表明：（1）拓宽降低原桥的横向分布系数，提高老桥的时变可靠度；（2）原桥钢筋锈蚀后刚度下降，引起老桥横向分布系数均值变小，新桥横向分布系数均值变大，新桥和老桥的荷载横向分布系数变异系数均变大；（3）如考虑横向分布系数相对变化，老桥的时变可靠度略有上升，而新桥的时变可靠度指标显著下降。
[Abstract]:Concrete bridges are the dominant types of highway and urban bridges.Due to the factors of material itself and environment, there are often various durability problems and periodic maintenance is necessary.Due to the complexity of practical engineering problems, the durability evaluation and life prediction of concrete structures will encounter a large number of random, fuzzy and so on. There is no ideal method for durability assessment and life prediction of concrete bridges with incomplete information. On the basis of reviewing relevant literatures at home and abroad, the following researches are carried out on durability of concrete bridges:
1. A group evaluation method for durability of Concrete Bridges Based on AHP and Evidence Theory is proposed. Firstly, the whole bridge is divided into three parts: superstructure, substructure and deck system, and further divided into a series of components and components. Secondly, the determination of index weight at each level and the evaluation of durability of the underlying index. The individual weights of experts are determined by the fuzzy distance between the individual evaluation results and the ideal results. Then, the evaluation opinions of experts are weighted and averaged to obtain the evaluation opinions of the expert group. Finally, the evidence synthesis theory is used to evaluate from the bottom, layer by layer, until the final evaluation results are obtained. The method is used to evaluate Tianpingling Bridge on Guangqing Expressway and Changning River Estuary Bridge in Hunan Province, and the feasibility of the method is verified.
2. On the basis of summarizing and analyzing the existing carbonation models of concrete structures, a Bayesian updating method is proposed to predict the carbonation depth. Firstly, several carbonation models are selected and weighted equally, and the weighted average is used as a prior model to predict the carbonation depth. Then, the distribution parameters and weights of the models are calculated by using the engineering detection information. Finally, the updated model parameters and weights are used to predict the depth of carbonization. A 10-year natural carbonization test is carried out to verify the effectiveness of the proposed method and is used to evaluate the durability of Xinhua viaduct.
3. A method of calculating the depth of carbonation considering the variation of CO2 concentration and temperature with time is proposed. The effects of CO2 concentration and climate change on the depth of carbonation, corrosion probability of steel bars, cracking area ratio of concrete bridge surface and reliability of bearing capacity are studied by using the latest climate change data and climate change prediction model. CO2 emission and climate change accelerated concrete carbonation corrosion. The carbonation rate of concrete under A1F1 and A1B emission strategies increased by 33% and 24% respectively. The corrosion probability of reinforcing bars under A1F1 and A1B emission strategies and the durability failure probability under normal service limit state were both higher than those under the same climate. The worse the quality of protective layer, the worse the failure rate. The greater the probability is.
4. The effect of climate change on the durability of concrete bridges in chloride environment is studied. A new method for calculating chloride ion diffusion in concrete is proposed. This method can not only consider the influence of concrete admixture, age, temperature, humidity, and the binding capacity of concrete to chloride ion, but also consider the atmospheric temperature of concrete structures in service. Considering the spatial variability of deterioration, the effects of A1F1 and A1B emission strategies on the durability of concrete bridges are studied. The results show that: (1) In the next 40 years, A1F1 and A1B emission strategies will increase the corrosion cracking ratio by 15% and 12% respectively, and the severe corrosion cracking ratio will increase by 12%. (2) For intact concrete bridges, the failure of different sections is highly correlated, and the reliability of the system can be replaced by the reliability of key sections such as midspan section, while for deteriorated reinforced concrete beams, the spatial variability of reinforcement corrosion should be considered.
5. Based on the principle of equal transcendence probability, according to the expected service life of concrete bridges and the service life of existing bridges before widening, the design reference period of widening concrete bridges, vehicle loads and design crowd values are analyzed. The time-varying reliability model of new and old bridges after widening is established. Taking a 16m span prestressed concrete simply-supported beam bridge as an example, the results show that: (1) widening reduces the lateral distribution coefficient of the original bridge, and improves the time-varying reliability of the old bridge; (2) the stiffness of the original bridge decreases after corrosion of steel bars, which leads to the lateral reduction of the old bridge. The mean value of the distribution coefficient decreases, the mean value of the lateral distribution coefficient of the new bridge increases, and the variation coefficient of the load lateral distribution coefficient of the new bridge and the old bridge increases. (3) Considering the relative change of the lateral distribution coefficient, the time-varying reliability of the old bridge rises slightly, while the time-varying reliability index of the new bridge decreases significantly.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U446

【参考文献】