大跨度PC刚构桥的徐变效应分析

发布时间：2018-03-03 06:33

本文选题：高强混凝土　切入点：连续刚构桥　出处：《重庆大学》2014年硕士论文　论文类型：学位论文

【摘要】：近年来，随着预应力混凝土结构，大跨度结构的蓬勃发展，，混凝土的强度不断提高，结构中的徐变现象也越来越受到人们的关注。徐变和收缩是很多材料的固有时变特性，特别是混凝土材料，徐变从养护时便开始发展，一直持续到结构服役期结束。随着混凝土强度、结构跨度的不断增大，徐变所产生的影响也越来越大，特别是在预应力混凝土结构以及大跨度混凝土结构中。徐变会造成预应力损失，从而影响预应力混凝土结构的使用性能，；大跨度结构中，徐变会降低预拱度，是挠度增大。结构的时间依存性变形主要由徐变、弹性变形、收缩和温度变形构成，而徐变变形大小可以达到瞬时弹性变形的2~4倍，因此，在结构设计中考虑徐变对结构使用性能的影响是十分必要的。而目前大多数收缩徐变的模型都是针对C20~C40的普通混凝土或者强度等级为LC30以下的轻骨料混凝土，但对于预应力混凝土和高强混凝土，适用性好、精度高、计算相对简便的模型目前并不存在，并且考虑预应力混凝土结构的大量使用这一客观事实，提出一个适合高强混凝土的收缩徐变预测模型迫在眉睫。在大量的资料和数据、混凝土试验以及工程实例的基础上，本文主要工作及成果如下： ①搜集对比国内外影响较大的各种收缩徐变预测模型，参考几种常见的徐变机理，对中国建科院模型(1986)，欧洲混凝土学会-国际预应力协会1978模型(CEB-FIP1978)，美国混凝土协会209委员会模型(ACI209(1982))，Bazant和Panula提出的BP系列模型(主要是RILEM B3模型)，GL2000模型以及日本土木学会推荐的日本《混凝土示方书》中的模型，共六种模型的考量因素、数学表达式形式、精度水准等进行了详细的定性对比分析。利用B3变异系数法，对各个模型的精度进行定量的对比分析，结果反映出GL2000模型整体性能最优，其次是B3模型和日本混凝土示方书中的模型。 ②在已知混凝土徐变模型的前提下，提出了对应力历史进行划分的阶梯法和脉冲法，以及对计算过程做相应基本假定的逐次法。同时，进行了高强混凝土的收缩徐变试验，通过对比，发现已有模型与试验结果不能很好地吻合。于是在日本规范的基础上，利用试验数据进行拟合，计算相应组合系数，得到修正的徐变预测模型，并编制程序计算徐变度，和试验值进行对比。 ③在对牛角坪大桥进行长期观测后，对得到的应变和挠度数据进行分析。利用Python和Abaqus Scripting Interface脚本接口，进行二次开发，根据符合牛角坪大桥使用的高强混凝土的徐变规律和ACI209（1982）提出的徐变规律创建新的材料属性，对徐变应变和挠度进行计算。得到了应变和挠度共同符合的变形发展规律，即在早龄期阶段，徐变应变和徐变引起的挠度均发展很快，一般1~3年内可以达到70~80%，之后随着时间推移，尽管应变和变形仍然在发展，但增长速率逐渐放缓。
[Abstract]:In recent years, with the rapid development of prestressed concrete structures, the strength of concrete has been improved, and the creep phenomenon in the structure has been paid more and more attention. Creep and shrinkage are the inherent time-varying characteristics of many materials. In particular, the creep of concrete materials develops from the time of curing until the end of the service period. As the strength of concrete and the span of the structure increase, the influence of creep becomes more and more great. Especially in prestressed concrete structures and long-span concrete structures, creep will cause prestress losses, thus affecting the performance of prestressed concrete structures, and in long-span structures, creep will reduce the pre-arch degree. The time dependent deformation of the structure is mainly composed of creep, elastic deformation, shrinkage and temperature deformation. It is necessary to consider the influence of creep on the performance of the structure in structural design. At present, most models of shrinkage and creep are aimed at ordinary concrete with C20C40 or lightweight aggregate concrete with strength below LC30. However, for prestressed concrete and high strength concrete, the models with good applicability, high accuracy and relatively simple calculation are not present at present, and the objective fact that prestressed concrete structures are widely used is taken into account. It is urgent to put forward a model for predicting shrinkage and creep of high strength concrete. Based on a large number of data, concrete tests and engineering examples, the main work and results of this paper are as follows:. (1) collecting and comparing various kinds of shrinkage and creep prediction models with great influence at home and abroad, referring to several common creep mechanisms, The BP series models (mainly RILEM B3 model, GL2000 model and Japanese civil engineering model) proposed by the Chinese Institute of Science and Technology, the European Institute of concrete and the International Prestress Association 1978 model CEB-FIP 1978, the American concrete Association 209 Committee Model ACI 209 / 1982 Bazant and Panula have been studied. The model in Japan's concrete Square Book will be recommended, In this paper, the factors of consideration, mathematical expression form, precision level of six models are analyzed qualitatively and qualitatively, and the accuracy of each model is compared and analyzed quantitatively by using B3 variation coefficient method. The results show that the overall performance of the GL2000 model is the best, followed by the B3 model and the model in the Japanese concrete square book. 2 on the premise of known concrete creep model, the step method and pulse method are put forward to divide the stress history, and the successive method to make the corresponding basic assumptions for the calculation process is put forward. At the same time, the shrinkage and creep tests of high strength concrete are carried out. By comparison, it is found that the existing model does not agree well with the test results. Therefore, the modified creep prediction model is obtained by fitting the test data and calculating the corresponding combination coefficients on the basis of the Japanese standard. A program was compiled to calculate the creep degree, and the test value was compared. 3After the long-term observation of Niujiaoping Bridge, the strain and deflection data obtained are analyzed. The secondary development is carried out by using Python and Abaqus Scripting Interface script interface. According to the creep law of high strength concrete used in Niujiaoping Bridge and the creep law proposed by ACI 209 / 1982), the creep strain and deflection are calculated. That is, at the early age stage, the creep strain and the deflection caused by creep both develop rapidly, and generally can reach 70 ~ 80 in 1 ~ 3 years, and then, with the passage of time, although the strain and deformation are still developing, the growth rate gradually slows down.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U448.23;U441

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