Research On Prestress Loss Based On Friciton, Retraction And Natural Frequency

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.