Research On The Mechanical Properties Of Polyline Pretensioned Beams With New Bend Component

The polyline pretensioned beams (PPSCB) is a new structure which combine the advantages of pre-tensioned and post-tensioned structure. It adopts the reasonable arrangement of prestressed reinforcement, solved the deficiency in span of the traditional pre-tensioned structure, avoided the shortcomings in construction technology and durability of the post-tensioned structure. Based on the peculiar mechanical properties of PPSCB, the local stress distribution in some key position is analyzed by the nonlinear finite element method, and the new bend component is developed by optimization corner radius which can adapt and improve the local stress characteristics. Then the law and mechanism of steel strand mechanical properties and prestressing loss due to friction affected by the new and traditional bend component is analyzed and compared by experimental method. Then, combined the experimental study with theoretical analysis and numerical simulation, the overall mechanical properties and local stress states affected by the new and traditional bend component is studied and compared. The significant improvement on the local stress states and overall mechanical properties by the new bend component is confirmed in difference ways. The main works of this paper is as follows:1. The analysis of local stress and optimization of corner radius. Based on the nonlinear finite element theory and the general FEM software ANSYS, the local mechanical properties and stress distribution at the polyline prestressed reinforcement inflection point is analyzed detailedly. The results show that the main influencing factor of the complicated local stress states and stress concentration phenomenon is the corner radius of the polygonal line prestressed reinforcement. Then the corner radius is optimized, and the reasonable radius is obtained.2. The development of new bend component and the experimental study of its effection on the mechanical properties of steel strand. Based on the optimization corner radius, the new bend component is developed which is simple structure and easy to assemble flexibility. Then the law and mechanism of steel strand mechanical properties and prestressing loss due to friction affected by the new and traditional bend component is analyzed and compared by experimental method, and the scientificity and practicability of the new bend component is confirmed. The uniform formulas of prestressing loss due to friction is presented based on test data, which take the affection factor of R into account. It provides some design reference and test basis to further research and application of the polyline pretensioned beams.3. The design of the test beams and the monitoring of construction. According the research purpose, the8test beams are designed and constructed, and the various mechanical properties parameter are monitored to provide the test data and analytical initial value for the later experimental study. Meanwhile, the prestressed loss is monitored and the practical formulas of prestressed loss due to anchorage deformation and retractation of steel strand is discussed clearly. The scientificity and practicability of the uniform calculating formulas of prestressing loss due to friction is confirmed too.4. The mechanical properties research of PPSCB under static loads. To research the mechanical properties of PPSCB and the influence of new bend component, the static load test of5PPSCB is designed and implemented. Combined the experimental study with theoretical analysis and numerical simulation, the mechanical properties of PPSCB, such as the ultimate loading capacity, deformation ability and ductility property, is analyzed clearly, as well as the load-deflection relationship, load-strain law, etc. The law of the crack formation and expansion is discussed and the failure pattern is observed carefully. Similarities and differences of the mechanical properties on the PPSCB with the new bend component and the traditional bend component are compared. The results show that the new bend component will significantly improve the ultimate deformation ability and ductility property of the PPSCB.5. The monitoring of local stress and the refined finite element analysis. Based on the peculiar mechanical properties of PPSCB and the general FEM software ANSYS, the refined FEA model of PPSCB is established by the sub-model technology which the bend component is simulated accurately. The local stress states at the bend component part is analyzed clearly and the similarities and differences on the PPSCB with the new bend component and the traditional bend component are compared. The simulation results verified the improvement of local stress states in PPSCB by the new bend component. Meanwhile, the local strain at the bend component part is monitored and analyzed based on self-designed local strain test component, and the test results is compared on the PPSCB with the new bend component and the traditional bend component. The test results confirmed the improvement of local stress states in PPSCB by the new bend component.6. The mechanical properties research of PPSCB based on fatigue test. The fatigue test of2PPSCB is designed and implemented to research the mechanical properties of PPSCB and the influence of new bend component. The effective laws of various mechanical properties by the fatigue load, such as the ultimate loading capacity, deformation ability and ductility property, is analyzed clearly, as well as the stain of steel strand, common reinforced, concrete on middle span and bend component part. Similarities and differences of the mechanical properties on the PPSCB with the new bend component and the traditional bend component are compared, and the results show that fatigue restraint ability of PPSCB will be improved significantly by he new bend component. It reconfirmed the improvement on the local stress states and overall mechanical properties of the PPSCB by the new bend component.