【作者】 黄胜前；

【导师】 杨永清；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2014， 博士

【摘要】 大跨度预应力混凝土箱梁桥在运营中过量下挠和普遍开裂一直困扰着桥梁工程师,是一个亟待研究解决的问题。过去,人们习惯从受力角度去分析和研究这一问题,虽然取得了一些成果,但没有解决根本问题。本文紧紧抓住材料破坏的形变本质,从研究混凝土材料形变与破坏的关系出发,建立混凝土的形变破坏准则,探讨大跨度预应力混凝土箱梁桥开裂的形变机理。1、对国内部分大跨度预应力混凝土箱梁桥的典型裂缝进行了调查研究,分析了导致这些裂缝的荷载因素和变形因素,总结了国内外的既有研究成果,指出从受力分析不能很好地解释部分裂缝的成因,提出从形变角度来研究大跨度预应力混凝土箱梁桥的开裂问题。2、将固体材料在应力作用下的形状和体积变化定义为形变,在直角坐标系下以应变张量表示,推导了在八面体上和在Haigh-Westergaard坐标系下的形变量。指出混凝十的形变包括瞬时形变和徐变形变,建议使用非线弹性正交异性本构模型计算瞬时形变,按依时本构模型计算徐变形变。本文在总结混凝土在单轴、双轴和三轴等不同应力状态下空间徐变规律的基础上提出了基于徐变泊松比的单徐变度依时本构模型；在分析混凝土徐变机理的基础上,提出了球徐变度和偏徐变度的概念,建立了混凝土的双徐变度依时本构模型。3、指出固体材料破坏的本质是形变超过自身的承受能力而发生形体失稳,在此基础上探讨了混凝土材料的形变破坏理论。研究了混凝土材料形变与破坏的关系,分别以应力空间破坏准则推导了混凝土形变破坏准则,根据以试验数据直接建立的应变空间破坏准则建立了考虑徐变形变的混凝土形变破坏准则。4、为了验证混凝土形变破坏准则,提出并建立了一套基于单轴加载设备实现混凝土立方体试件双轴加载和基于普通应变计实现混凝土立方体试件空间应变测试的方法,试验结果与计算结果随应力发展的趋势吻合较好,但应变值在高应力水平时存在一定偏差。根据试验和计算得到的形变结果,分别计算形变破坏判断指标r/r*,在应强比σ3/σ3f较小时,二者吻合较好,应强比σ3/σ3f较大时有一定偏差,这是由于试验测试应变存在偏差造成的。整体上,形变破坏判断指标r/r*随应强比σ3/σ3f变化的趋势吻合较好,在σ3/σ3f<0.90～0.95时,r/r*<1,可以判定混凝土未破坏,在σ3/σ3>0.90时,r/r*随σ3/σ3f迅速增大,在接近极限强度点时r/r*超过临界值,可以判定混凝土破坏,较好地验证了本文提出的混凝土形变破坏准则。5、比较研究了几种常用的收缩徐变模型,根据考虑因素、适用范围及预测结果优劣,选择GL2000模型用于分析大跨度预应力混凝土箱梁桥的收缩徐变效应。提出了考虑箱梁截面非均匀收缩的结构收缩效应计算方法,考虑混凝土空间徐变的结构徐变效应计算方法。在研究混凝土箱梁的口照辐射温度场和比较研究国内外几种梯度温度模式的基础上,分析了大跨度预应力混凝土箱梁桥的结构温度效应。6、以一座大跨度预应力混凝土箱梁桥为例,应用本文提出的结构效应计算方法采用实体单元有限元对结构进行了分析,根据计算结果利用形变破坏准则从形变角度很好地解释了腹板斜裂缝的形成机理。更多还原

【Abstract】 The problem of excessive downward and cracking of long span prestressed concrete box-girder bridges in service has not been realized by the bridge engineers, and it needs to be solved urgently. In the past, people have made some achievements by analyzing and studying this problem on stress according to the custom, but not found the essential reason. This dissertation built a shape-change failure criterion for concrete and researched on the shape-change mechanism of cracking of the long span prestressed concrete box-girder bridges from studying the relationship between shape-change and failure of concrete material by holding the shape-changing failure essence of material.i. By investigating the typical cracks of some long span prestressed concrete box-girder bridges at home, this dissertation analyzed the load factors and deflection factors which induced to crack, pointed out that it was hard to explain the cracks on stress analysis by summarizing the existing research results at home and abroad, and put forward the way of shape-change to study the cracking problem of long span prestressed concrete box-girder bridges.ii. The shape-change is the change of shape and volume of solid material, can be expressed by strain tensor in the spatial rectangular coordinate system. This dissertation deduced the shape-change variable on the octahedral and in the Haigh-Westergaard coordinate system. It pointed out that the shape-change of concrete including instantaneous shape-change and creep shape-change, can be calculated according to nonlinear elastic orthotropic constitutive model and time-dependent constitutive model respectively. On the basis of summarizing spacial creep regularity of concrete under uniaxial, biaxial or triaxial stress, it built time-dependent constitutive model with single compliance function for creep based on creep Poisson’s ratio. On the basis of analysing the creep mechanism of concrete, it put forward the concept of spherical compliance function for creep and deviatoric compliance function for creep, and built time-dependent constitutive model with double compliance function for creep.iii. It pointed out that the failure essence of solid material was the shape and volume instability when the shape-change exceeded its bearing capacity, and discussed the shape-change failure theory of concrete material. It studied the relationship between shape-change and failure of concrete material, deduced the shape-change failure criterion from the stress spatial failure criterion for concrete, and built the shape-change failure criterion for concrete with consideration of its creep based on the strain spatial failure criterion directly built by test data.iv. To check the shape-change failure criterion for concrete, this dissertation put forward a test method which realized biaxial loading on cube concrete specimen with fixtures and uniaxial loading equipment and testing the spatial strain of the cube concrete specimen with ordinary strain gauge. The variation tendency of the test result of spatial strain with the change of stress was consistent with its computing result, but its value had some deviation when the stress was large. The shape-change failure index r / r can be caculated by the test result or the computing one of shape-change respectively. They were consistent when σ3 / σ3f was little, but had some deviation when σ3 / σ3f was large due to the test deviation of spatial strain. In general, the variation tendency of the shape-change failure index r / r with the change of σ3 / σ3f was consistent. When σ3 / σ3f ＜ 0.90-0.95, r / r ＜ 1, one can accurately judge that the concrete was not failed; when σ3 / σ3f ＞0.90, r /r grew quickly with σ3 / σ3f , and it exceeded critical value when closing to the bearing capacity point of concrete, one can accurately judge that the concrete was failed. So this test proved that the shape-change failure criterion for concrete in this dissertation was correct.v. A comparative study had been done on several usual shrinkage and creep model for concrete in this dissertation. Baded on considering factors, application scope and the quality of the predicted results, the GL2000 model was choosed to analyse the shrinkage and creep effect of long span prestressed concrete box-girder bridge. It put forward a method to calculate structure shrinkage effect with consideration of the non-uniform shrinkage of box girder section, and a method to calculate structure creep effect with consideration of the spacial creep of concrete. By the study on solar radiation temperature field and comparative study on temperature gradients model at home and abroad, the temperature effect of a long span prestressed concrete box-girder bridge was analysed.vi. A long span prestressed concrete box-girder bridge, for example, its structual effect was analysed using the method put forward in this dissertation with solid element, and the formation mechanism of web crack was explained well with the shape-change failure criterion for concrete.更多还原