Study On The Theoretical Model Of Beam-cable Element After External Prestressing Reinforcement For Beams And Columns Of Concrete Frame

Because of the long-term use of building structures in life,the environmentalwill inevitably lead to some safety problems and resulting in the degradation of various functions.At the same time,the degradation of some component functions will lead to the reduction of the bearing capacity of the structure.The cost of building new houses is enormous,thus maintenance and reinforcement of existing structures is an effective measure to extend the service life of these structures,and is also the requirement of sustainable development strategy.To compare with other reinforcement methods,external prestressing technology has unique advantages in strengthening structures.In this paper,based on the principle of external prestressing simply supported technology,the principle of external prestressing hoop technology to strengthen joints and columns,the theoretical derivation and numerical simulation methods are used to analyze the frame beams,and 19 single frame structures are established by numerical simulation software ABAQUS.The research contents and conclusions are as follows:(1)Based on the moment-curvature relationship,the load-deflection curve equation of frame beams is deduced,and the internal force expression of cables and the curve expression of cables after deformation are deduced by means of the principle of force balance and the principle of point skew.The conclusion are as follows: the theoretical formula is based on a series of basic assumptions.To compare with the existing simulation and test data of our research group,it is concluded that the theoretical formula can guide practice in the elastic stage.After entering the plastic stage,due to the influence of material nonlinearity and geometric nonlinearity,theoretical formulas are significantly different from experimental and simulated data,and the accuracy is low.(2)Based on the literature,the theoretical model of frame beam is analyzed and the formula for calculating the bearing capacity of mid-span section is obtained.Assuming that the external cables are hinged with beams and webs and the cables are two-force bars,the element stiffness matrix of the external prestressing reinforcement bar in the linear elastic stage is solved,and the deformation increment of the cables is deduced by the cosine formula.The element stiffness matrix and the cable deformation increment are verified by Hooke's law.The results show that the relevant theories of frame beams have high applicability in three-web reinforced frame beams,and the accuracy of frame beams under external prestressing reinforcement system is low when the number of web members is large.(3)19 single frame structures were established by numerical simulation software ABAQUS.The beams of frame structures were strengthened by external prestressing simply supported technology with external prestressing tendons of different sag and cross-section area.The columns and joints were strengthened by external prestressing hoops of different cross-section area.The concrete and reinforcement of frame beams before and after strengthening were analyzed.The variation of stress nephogram under external loads is analyzed,and the influence of different factors on load-deflection curve of frame beams is analyzed.The conclusions are as follows: 1)To compare with the unreinforced single frame model,the application of external prestressing simply supported technology to reinforce beams,ring stirrups to reinforce columns and joints can greatly improve the bearing capacity of frame beams;When compared with the frame model with only reinforced beams,the strengthening columns and joints can not improve the bearing capacity of frame beams more than that of reinforced beams.2)The increase of stress cable sag and section area and the increase of ring stirrup section area can improve the reinforcement effect,and cable sag has a more significant effect on the reinforcement effect.3)Under the external load,the deformation of fully reinforced frame beams is smaller than that of unreinforced frame beams,which delays the yield time of the steel bars and stirrups of the frame beams,which can improve the flexural bearing capacity of the frame beams.