Deformation-based Identification Method For Prestress Loss Of Truss Structures

Prestressed concrete structures will have some prestress loss during construction and the process of use.However,the existing theoretical calculation method does not consider prestress loss caused by vibration and other factors,resulting in the underestimate of the design value of prestress loss,and causing structural damage or destruction.There is a certain relationship between the deformation of the structural members and the loss of prestress;this paper takes the prestressed concrete truss structure of a high-speed rail station house as the research object,and based on the principle of the influence matrix,proposes the method of recognizing the loss of prestress loss based on the displacement influence matrix method.The main research content and conclusions are as follows:(1)The calculation methods and measurement methods of the existing prestress losses are reviewed,and the limitations of current calculation theory and measurement methods are summarized.(2)A method for establishing the displacement influence matrix considering the shrinkage and creep of concrete was proposed.In this method,the variation of the truss deflection caused by the loss of prestress is obtained by finite element analysis,and the relationship between the prestress loss of the prestressed steel and the displacement value of the observation point of the truss deflection is established.Finally,The prestress loss is calculated according to the principle of minimum optimization.(3)The selection position of displacement observation point is determined for the common prestressed triangular truss structure.The results show that the displacement of observation points is more sensitive to the prestress loss in the 1/4 span and 3/4 span of the truss structure,which is suitable for this kind of truss.The influence of the unit prestress loss on the accuracy of matrix recognition is analyzed.The results show that the prestress loss identification error is the minimum when the unit prestress loss is between 30% and 50% of the prestress.Considering the influence of concrete shrinkage creep,the displacement observation time interval is determined.(4)Finally,the accuracy of this method is verified by studying the large span prestressed concrete truss roof of a high-speed railway station in Qian-Yu line.