Study On The Structural Performance Change Of Concrete Frame Beams Strengthened With External Prestressing

In the various methods of reinforcement and reconstruction of existing buildings,the external prestressing reinforcement technology has its unique advantages.Based on the traditional external prestress technology,The paper mainly carries out the theoretical analysis,numerical simulation and experimental study,based on the technology of external reinforcement of tilted belly poles,the finite element software ABAQUS to establish the frame model and the experimental frame model established in the laboratory,combined with the National Natural Science Foundation of China.(1)Based on the finite element method and the external web as the research object,the axial force change of the web under the bolt torque load is analyzed,and the deformation compatibility equation between the web and the cable is deduced.Based on the static equivalent principle,the equivalent node load of the web to the beam is deduced,which is the external prestressed cable-web.The reinforcement system provides a theoretical basis for overall analysis.(2)Under vertical load,the stress changes of steel and concrete,the stress distribution of external abdominal bars and the plastic development of beams are analyzed with nonlinear methods: 1)after the reinforcement of the frame beam,the stress is redistributed,the stress of the mid-span concrete decreases,and the peak stress is concentrated at the beam end and anchor hole of the external cable;2)the stress of external abdominal bar increases with the increase of mid-span deflection of beam;3)according to the analysis of the plastic deformation cloud map,the plastic zone of the unreinforced beam first appears in the mid-span region,and gradually extends to the shear bending section as the external load increases,and the plastic zone gradually appears at the beam end.The plastic development of the reinforced beams changes,and the middle span is no longer the first region of plastic development.(3)Under the action of horizontal load,the stress change of frame load-displacement curve,steel bar and concrete and the development law of web stress are analyzed: 1)the stiffness of the whole frame is relatively higher than that before the reinforcement after the external prestressed reinforcement;2)compared with the unreinforced frame,the reinforced concrete in the area of negative bending moment at the end of the beam is less damaged,and the reinforcement stress is less.3)the external abdominal bar stress does not change significantly with the increase of the frame displacement,and the prestress tends to reduce.Therefore,after aperiod of time of test,the prestressed bar should be re-tensioned.(4)A full-scale three-layer two-span frame model was produced in the laboratory,and vertical load was applied to it.The test data was used to verify the frame model established by finite element software ABAQUS,which indicated that the finite element frame model could be used for the frame reinforcement design and analysis.