Study On Prestress Loss Identification Of Concrete Simply Supported Beams

During the long-term service of prestressed concrete bridges,the relaxation of prestressed tendons and the shrinkage,creep and damage of concrete lead to different degrees of loss of prestress,which affects the safety and normal operation of the bridge.Some bridges even have serious safety accidents due to the excessive loss of prestress,which has caused irreparable losses to the national economy.Identifying the prestress loss of the bridge and determining the residual effective prestress value is the focus of bridge health monitoring,and it is also an important index to evaluate the health status of the bridge.Dynamic testing method has been widely concerned because of its nondestructive and convenient characteristics.However,the inconsistency between the modal analysis results of the numerical model,which is the basis for evaluating the prestress loss,and the experimental results affects the application of this method in practical engineering.This is also the focus of this study,the main work is as follows:(1)It is found that the modal parameters of prestressed concrete structure obtained from laboratory tests are quite different from the results of numerical model,which hinders the application of prestress loss identification method in practical engineering.(2)The natural frequency of prestressed steel beam and prestressed concrete beam is compared and analyzed.it is found that the natural frequency of the former decreases with the increase of prestress,while that of the latter decreases.The finite element simulation and theoretical calculation show that the prestress makes the structure produce geometric nonlinearity and material nonlinearity,and the dynamic characteristics of concrete are greatly affected by material nonlinearity.The modal parameters of the numerical model of prestressed concrete established by homogeneous constant elastic modulus are not in accordance with the practice.(3)Based on the material nonlinearity,the constitutive relation of concrete material is developed by UMAT,and the prestressed structure model is improved based on this,and the results are compared with the results of previous dynamic tests.It is found that the improved prestress model can better reflect the relationship between prestress and structural modal frequency,and can be used to identify the prestress loss of concrete beams.(4)The prestressed concrete model is established by considering geometric nonlinearity,material nonlinearity and initial damage of concrete,and the prestress loss is identified based on this model.The dynamic characteristics of prestressed concrete beams are affected by geometric nonlinearity and material nonlinearity,when the prestress level is low,the material nonlinearity plays a control role;when the prestress level is high,the geometric nonlinearity plays a control role.(5)The research results are summarized,and the prospect of further research is put forward..