【作者】 高昂；

【导师】 孙璐；

【作者基本信息】 东南大学 ， 道路与铁道工程， 2016， 硕士

【摘要】 现代预应力技术发展迅速,应用广泛。预应力混凝土在土木工程,特别是在大跨度的桥梁结构中应用越来越广泛。但是由于受到施工、材料性能及环境条件等因素的影响,预应力钢筋中的预加应力会逐渐减少,从而也使混凝土中的预应力相应减少。预应力钢筋中这种预加应力减少的现象称为预应力损失。预应力损失计算的准确与否,与结构的抗裂性、裂缝、挠度和反拱等使用性能有密切的关系,而且当前预应力混凝土桥梁中有效预应力检测也没有较为成熟实用的方法。因此研究准确便捷的预应力桥梁有效预应力的检测方法和精确的预应力损失计算方法,对于确保桥梁结构的安全有极大的研究价值。本文从现行规范中的预应力摩阻损失计算方法和钢筋回缩预应力损失计算方法出发,对预应力损失的计算公式进行了理论推导公式和有限元仿真模拟研究,并通过有限元模型对现存预应力和梁体自振频率相关性进行分析,论文主要研究内容如下：(1)预应力钢筋弯曲孔道摩阻损失计算方法。目前采用的预应力损失计算公式考虑的主要因素为管道摩擦系数和偏差系数,其摩阻损失的成因还包括施工质量和施工工艺造成孔道质量过低引起的阻力,但由于孔道质量阻力引起的损失难以从理论上推导分析,同时会对摩擦系数和偏差系数造成影响,本文采用孔道质量影响系数来反应对摩擦系数和偏差系数的影响,并给出基于孔道质量影响系数的摩阻损失公式。现阶段预应力损失计算公式基于刚体假设,忽略弯曲孔道受挤压产生变形的影响,其接触应力分布与实际不符,但接触压力分布与材料的本构关系密切相关,推导了三种假设分布压力下的摩阻损失公式,并采用有限元软件设计孔道接触摩阻损失的数值模拟实验,通过理论计算、实验数据和有限元仿真结果比较,验证本文推导的摩阻损失公式的适用性。(2)预应力钢筋回缩预应力损失计算方法。首先根据摩擦反向和边界条件,推导出回缩影响范围内的钢筋预应力方程,并根据变形协调条件,基于不同的基本假设,归纳总结了目前的使用的简化计算方法和分段近似计算方法,对其计算方法进行进一步的研究改进,并提出了更为精确的曲线计算方法。最后针对有限元软件中模拟该项预应力损失给出了数值计算公式,实现在有限元中模拟预应力钢筋回缩损失(3)现存预应力与梁体自振频率的相关性分析。首先基于初始荷载效应考虑预应力对混凝土弹性模量的影响,以无粘结和有粘结预应力混凝土梁为研究对象,采用ANSYS建立相应的有限元模型,在对混凝土弹性模量进行修正后对梁体进行动力仿真分析,并将计算结果进行拟合,分析了钢筋面积、偏心距、预应力钢筋弹性模量因素对梁体自振频率的影响规律。并采用了简化假设推导了梁体自振频率的理论计算公式,并与有限元计算结果进行对比验证。最后分析了预应力梁不同有效预应力作用下的挠度值,建立了预应力与梁体挠度的定量关系式,提供了另一种检测梁体预应力损失的方法思路。更多还原

【Abstract】 With the development of modern prestressed concrete technology, it is widely applicated. The prestressed concrete is widely used in the civil engineering, especially in the long span bridge structure. However, affected by the factors of construction, material properties and environmental conditions, the prestressing force in the prestressed reforcement will be gradually reduced, thus reducing the prestressing force in prestressed concrete. The reduction of the prestressing force in the reforcement is called prestress loss. Whether the calculation of the prestress loss is accurate or not, has a close relationship with the service performance, such as the crack resistance, crack, immunity and anti arch. Besides, there is no mature and practical method for the effective prestress detection in the prestressed concrete bridges. Therefore, to ensure the safety of the bridge structure, the research of accurate and conveninet effective prestress detection and accurate calculation method has great research value.In the paper, Based on the calculation mehod of the prestress loss of friction and reinforced retraction in the current criterion, the prestress loss calculation formula is derived and researched through the finite element simulation. The correlative factor analysis between the effective prestress and natural frequency of vibration of the beam is performed.. The main contents of this paper are as follows:(1) The calculation method of the frictional loss for the prestressed dust. At present, the main factors considered by the the prestress loss calculation formula are pipe friction coefficient and the deviation coefficient, but the friction loss also includes resistance casued by the poor quality of hole due to the construction quality and construction craft. However the loss caused by the quality of the hole is difficult to analysis in theory, also affecting the friction coefficient and the deviation coefficient. The paper use the quality coefficient to react the influence on the friction coefficient and the dviation coefficient, and the friction loss formula based on the quality coefficient is presented. Now the prestress loss calculation formula is based on the assumption of rigidity, neglecting the influence of hole deformation.The contact stress distribution is inconsistent with the actual situation, for the contact stress distribution has relationship with the constitutive behavior of the material. The paper derives friction loss formulas under three kinds of hypothesis pressure distribution. The numerical simulation is designed by the finite element software to get the friction loss in curved duct. Verifying the applicability of the derived friction loss formula by comparing the results of the calculation reuslts, test data and the finite element calculation results.(2) The calculation method of the prestress loss for retraction of tendons. According to the reverse friction and boundary conditions, the equation of the prestress in the tendon is derived within the range of retraction. Based on the condition of deformation compatibility and different assumptions, the paper summarizes and improves the simplified calculation method and the piecewise approximate calculation method. The higher precision of the calculation formula of prestress loss is established in this paper. And to simulate this kind of prestress loss in the finite element software, the numerical calculation formula is presented.(3) The correlation analysis of the existing prestress with the vibration frequency of beam. First, based on the initial load effect, the influence of prestress on the elastic modulus of concrete is considered. To study the unbounded and bonded prestressed concrete beam, the corresponding finite element model is established by using ANSYS. The dynamic simulation analysis of the model based on the correction of the elastic modulus of concrete is carried out. the calculation results are fitted. And the influences of the area, eccentricity and the elastic modulus of the tendon on the natural frequencies of beam are analyzed. The theoretical calculation formula of the natural frequencies of the beam is derived based on simplifying assumptions, compared with the finite element calculation results. Finally, the deflection of the prestressed beam under different prestress is analyzed, which the quantitative relationship between the prestress and deflection is established. So another way to detect the prestress loss of tendon is provided.更多还原