Study On Mechanical Properties Of Beams Strengthened By External Prestressing Of Three Web Member

At present,the external prestress reinforcement technology has unique advantages over other reinforcement methods in the common reinforcement methods of integrated concrete structures.However,there are still some defects,such as complex anchorage treatment,may destroy the original structure of the column,plate.In order to solve these problems,this paper puts forward the external prestress reinforcement technology of three web member.The main research contents and conclusions are as follows:(1)In this paper,a new type of steering device and the application method of prestress are presented.The equations of extrinsic cables and the expressions of the internal forces of each segment are derived,and the elongation of 1/4 of the web on both sides of the external cable is 3/4 of that of the midspan web;The relationship between the increment of cable length and the elongation increment of midspan web member,the mathematical expression of the increment of cable length and the load of web member are obtained and verified by the finite element software ABAQUS.The results show that the internal force of the cable at both ends is greater than that of the inner cable;the relationship between the cable length and the incremental load of the web is compared with the simulation results.It is found that the two are basically linear,and when the load step is small,the theory The value is basically consistent with the analog value.When the loading step is smaller,the simulation result is closer to the theory.(2)Considering the concentrated load and uniform load of the externally prestressed reinforced beams of the three webs,the calculation formula of the external cable stress increment in the elastic stage is derived from the geometric relationship before and after the external beam deformation.According to the theory that the linear relationship between the external cable stress increment and the mid-span deflection in the elastic stage and the bearing capacity limit state of the reinforced beam is further extended to the calculation formula of the external cable stress increment in the limit state of the bearing capacity.(3)The finite element software ABAQUS is used to simulate the reinforced beams,and the four failure stages of the reinforced beams are obtained.The influence of different cable cross-sectional area,initial stress and cable sag on the reinforced beams is studied.The conclusions show that the external cable stress increment has a linear relationship with the mid-span deflection,which is consistent with the conclusion of Ⅲ Chapter.The externally prestressed reinforced beams of the three webs can improve the stress performance of the beam.With the increase of three influencing factors,the cracking load and ultimate load of the reinforced beams are increased.In the construction design,the cable sag is close to the beam height,and the small cross section and high initial stress of the external cable should be avoided.