【作者】 成琛；

【导师】 张开银；

【作者基本信息】 武汉理工大学 ， 道路与铁道工程， 2011， 博士

【摘要】 预应力混凝土桥梁是我国已建桥梁中数量较多的一类桥梁。虽然预应力混凝土桥梁结构的形式和跨径在不断地创新,数量在不断地增加,但是很多运营中的大跨径预应力混凝土桥梁跨中下挠、箱梁开裂现象十分普通,使得部分桥梁过早地失效或破坏,对桥梁结构的造成较大威胁。预应力混凝土连续梁桥在运营过程中的混凝土梁体伸长,说明很多桥梁结构中存在的下挠,开裂等病害均与《公路规范》中结构有效预应力估计不足有关；而施工中预应力混凝土连续梁桥预应力长索在设计张拉力下伸长量不够,反映出现行预应力计算公式不能很好的描述预应力束的张拉变化规律。本文从《公路规范》中预应力摩阻损失公式出发,基于弹性力学中赫兹(Hertz)接触理论,对预应力混凝土连续梁桥中弯曲孔道的有效预应力进行理论分析与试验研究。具体内容如下：1、预应力结构弯曲孔道预应力损失研究。首先指出《公路规范》在预应力摩阻损失公式的推导过程中的问题,并基于力学平衡条件,推导了任意应力分布模式下弯曲孔道摩阻损失公式。通过连续圆弧孔道与非连续圆弧孔道预应力损失理论分析计算,证明了弯曲孔道内预应力摩阻损失不可加,应以相对独立的弧段为单元进行摩阻损失计算。讨论了管道摩阻系数对摩阻损失计算的影响,利用弯曲孔道摩擦阻力试验及实桥的测试数据证明了目前通用损失计算公式的不合理性。最后给出了预应力钢束与与管道壁之间的摩阻损失公式。2、预应力钢束与混凝土接触的有限元分析。借助通用有限元分析软件ANSYS对弯曲孔道预应力钢束和混凝土的受力性能进行分析,得到弯曲孔道预应力摩阻损失的分布规律,以及预应力钢束和混凝土的界面接触应力分布模式。通过规范公式、本文简化公式和有限元计算结果比较,发现当弯曲孔道圆心角度小于120°时,可利用简化公式计算弯曲孔道的预应力摩阻损失；当弯曲孔道圆心角度大于120°时,必须考虑B值项对摩阻损失的的影响。假定界面接触应力沿圆弧长度呈三段直线分布,在此基础上推导本文公式中B值项的表达式。从理论上为预应力钢束的摩阻损失计算提供了参考,且证明了只要接触应力分布模式假设正确,本文推导公式将给出准确的摩阻损失值,进而验证本文推导摩阻损失公式的适用性。3、预应力摩阻损失公式的参数识别。在前述推导的孔道预应力摩阻损失简化公式的基础上,基于实际桥梁结构施工过程中管道摩擦系数μ和管道偏差系数k的不易确定性,结合桥梁现场实测数据,利用BP神经网络的非线性拟合功能,对参数μ和k进行识别；计算结果表明,采用BP神经网络算法用于摩阻参数的识别是可行的,利用识别参数计算的摩阻损失与试验值吻合较好,证明了本文推导公式用于预应力摩阻损失计算的有效性。对于计算平曲线预应力钢束摩阻损失和空间曲线预应力钢束摩阻损失计算也是可行的,并且精度比规范公式要高。根据环向预应力钢束的应变测试结果,给出了弧段内指定点的摩阻损失计算的简化方法。4、预应力损失的实桥设计应用与比较。结合某大跨径连续刚构桥梁,对预应力钢束的损失值进行了分析研究。计算了摩阻损失、弹性压缩损失、收缩徐变损失、钢束松弛损失等损失在总预应力损失中所占的比例,得出了预应力钢束与与管道壁之间的摩阻损失和混凝土收缩徐变引起的损失是对预应力钢束影响较大损失的结论。针对管道中摩阻损失,考察了结构挠度和应力随摩擦系数μ和管道偏差系数k变化的敏感性,同时比较了本文摩阻损失公式与规范损失公式的差别对结构的影响程度。更多还原

【Abstract】 Prestressed concrete bridge has a large number in all kinds of built bridges in China. Although the structure form and the span of prestressed concrete bridge are in the constant innovation, the number is also constantly increasing, but the phenomenon of downwarping and cracking across the middle of box girder of many long span prestressed concrete bridge in operation is very common. These damages make some bridges failed or destroyed earlier, cause large threat to the bridge structure. The elongation of concrete beam of prestressed concrete continuous beam bridge in the operation indicates that downwarping, cracking and other diseases of many existing bridge structures have the matter with the insufficient estimation of effective prestress in the provision of Chinese "Highway Code". And during the construction of prestressed concrete continuous beam bridge the elongation of long cable under the designed tensile force is not enough. Both of these problems reflect the current formula does not give a good description of the tension variation of the pretress strands.Based on the Hertz elastic contact theory, this paper studies the formula of friction loss in the Chinese "Highway Code" and does some theoretical analysis and experimental studies on effective prestress of prestressed concrete continuous beam bridge in the curved duct. The main content includes:1. Study on the prestress loss of prestressed structure in curved duct. This paper pointed out problems of the prestressed friction loss formula of Chinese "Highway Code" in the deriving process at first. Based on force equilibrium conditions, this paper derived the friction loss formulas in any stress distribution mode. From the theoretical analysis and calculations of prestress loss of continuous and non-continuous circular of curved channel, this paper proved that friction losses of prestress in several curved ducts can not add up, but should be calculated in relatively independent arc as a unit. This paper then used the friction test of curved channel and the test data of a real bridge to prove the current general formula of prestresse friction loss unreasonable. Finally, prestressed loss formula between prestressed strands and pipe wall was shown.2. Finite element analysis of contact analysis between prestressed strands and concrete. With common finite element analysis software ANSYS, this paper analyzed the mechanical properties of prestressed strands and concrete in curved channel, and got the law of prestress friction loss and the interface contact stress distribution patterns between prestressed strands and concrete. Through the comparisons of the results by the code formula, the simplified formula and the finite element calculation, it is found when the central angle of the bend channel is less than 120°, we can use the simplified formula for friction loss of curved channel; when the central angle of the bend channel is greater than 120°, the results must be considered the value, of item B which can impact on the final friction losses. Assume that the distribution of contact stress along the arc is in three sections of lines, the value of item B can be expressed by a formula. This paper provided a reference of friction loss calculation in theory. It also proved derived formula will give an accurate value of friction loss as long as the assumption of contact stress distribution model is correct, and then validated the applicability of the derived friction loss formula.3. Parameter identification for formula of friction loss of prestress. For friction coefficientμand deviation coefficient k of the pipe is indeterminate in the construction process of a real bridge structure, this paper used the derived friction loss formula and field data to identify parametersμand k by BP neural network. The results shown that BP neural network algorithm for the identification of friction parameters is feasible; the values of friction loss by identification parameter are in good agreement with the experimental values. It proved the derived formula is effective for calculating prestress friction loss. The calculation of friction loss for flat curve and space curve prestressed strands were feasible and the accuracy is higher than the code formula. According to the strain test results of circular prestressed strands, it gave the calculation method of the specified point within an arc of curved duct.4. Design and comparison of prestress loss of a real bridge. Combined with a continuous rigid frame bridge, this paper analyzed the values of prestress loss. It calculated the prestress loss of friction, elastic compression, and looseness of strands, shrinkage and creep of concrete, and the ratios of the above four to the total prestress loss. This paper investigated the sensitivity of deflection and stress of the bridge structure with deviation ofμand k. It also compared the influence of derived friction loss formulas and the formula of current code.更多还原