| During the construction and operation of the prestressed concrete structure,the stress of the prestressed tendons will be differently lost.The structure is usually designed according to the existing specifications to calculate the loss of the prestressed tendons in the structure to ensure the normal use of the structure.There are many factors that affect the structural prestress loss,and it is often difficult to achieve accurate calculations.At the same time,the prestress loss of the structure is affected by external loads(such as vibration),These conditions cause the actual prestress loss value of the structure to be greatly deviated from the design value during long-term use,and the design loss estimate is often insufficient.Therefore,it is especially important to monitor the stress state of the prestressed tendon in the structure and evaluate the health of the structure.Based on the idea of influence matrix,this paper establishes the relationship between deformation of prestressed concrete structure and prestress loss,and proposes a method for establishing displacement influence matrix of large span frame structure.Taking the structural deformation and internal force as the early warning indicators,the safety warning threshold of the structure is analyzed.The main research contents and conclusions are as follows:(1)The theoretical calculation methods of prestress loss and the prestress loss detection technology are summarized.The limitations of existing calculation methods and detection techniques are analyzed.The methods of structural security early warning and the calculation method of early warning index thresholds are summarized.(2)The uncertainty of factors affecting prestress loss is analyzed in detail.The relationship between prestress loss and structural deformation of large span structure is established by finite element method.Combined with the idea of influence matrix,a prestress loss identification method based on structural deformation is proposed.(3)For long-span prestressed frame structure,the influence of unit prestress loss on identification results of different prestress loss in structure is analyzed,The influence of prestress loss on deformation observation points in structures is analyzed,The selection method of unit prestress loss and the selection principle of deformation observation points in establishing displacement influence matrix are summarized,A method for establishing displacement influence matrix of frame structures considering concrete shrinkage and creep is presented.(4)The relationship between prestressing loss and bending moment is established by analyzing the load-deformation curve of prestressed concrete flexural members,By introducing the idea of influence matrix,a method for calculating the bending moment of longspan prestressed frame structure based on the identification of prestress loss is established.(5)Taking the mid-span deformation and bending moment values of long-span frame beams as early warning indexes,and combining with the deflection limits in the Code for Design of Concrete Structures,the safety early warning threshold of long-span pre-stressed frame structures is established. |
