Application And Research On Reinforced Large-span Structures Strengthened With External Prestressing Tendons

External prestress reinforcement is an active reinforcement method,which can improve the flexural and shear bearing capacity of structures,reduce the deformation and crack width of structural members in normal use,and can be applied to structural members under high stress and strain and difficult to unload.Externally prestressed structure are widely used in bridges,building structures and other fields because of many advantages,especially suitable for large-span structures.At present,the research on external prestressing is mostly based on the research results of unbonded prestressed structures.The influence of the secondary effect is less considered.The "Technical specification for strengthening building structures with external prestressing tendons" and "Code for design of strengthening concrete structure" both propose calculation formulas for the calculation of the ultimate bearing capacity and deflection of concrete members strengthened by external prestressing methods.The effect of the prestressed tendon stress increment and the secondary effect are not considered,and the formula is only applicable to the original concrete member which is a non-prestressed member.This article comprehensively analyzes the research status of domestic and foreign scholars on the reinforcement of long-span concrete members with external prestress,the effects of external rib height,the location and number of steering devices on the increment of prestressed reinforcement,reasonable determination of the prestressed reinforcement stress increment,and how to effectively reduce the impact of secondary effects.In recent years,with the use of a large number of double-T plates on factory roofs,due to factors such as increased roof load and damage during construction and hoisting,the bearing capacity of the double T-plates is insufficient,the crack width and deflection are beyond the specification limits,and the external prestress is the best way to solve such problems.This article takes double T plates with a span of24 m as an example,a double-fold prestressed reinforcement,different rib heights,and different steering block settings.The large-span double T plate prestressed reinforcement simulation loading is carried out by ABAQUS finite element analysis software Test to analyze the influence of rib height,steering position and quantity on the secondary effect,cracking load,ultimate bearing capacity,ultimate deflection,and the cooperative work of internal reinforcement and external prestressed reinforcement,Select the appropriate rib height and steering for subsequent engineering reinforcement,Provide a basis for devices and structural measures to reduce secondary effects.Due to the change in the use function of buildings,many existing buildings need to increase the use space,part of the vertical members are removed,and the span of the transverse members is increased,resulting in insufficient bearing capacity of the transverse members,and the crack width and deflection exceed the specification limits.This article takes the renovation of an existing building as an example,based on the research results of external prestressed double T-plates,the external prestressing method is used to reinforce the transverse members.The calculation method of bearing capacity,refer to the formula algorithm in "Technical specification for strengthening building structures with external prestressing tendons",after the reinforcement is completed,the in-situ loading method is used to check the mechanical performance of the reinforced beam in the normal use stage.