Theoretical Analysis And Experimental Study On Damage Identification Of Reinforced Concrete Beams Based On Curvature Modes

Reinforced concrete beams are the most basic bearing components in engineering structures such as buildings,bridges and roads,and have a wide range of applications.In our country,civil engineering structures need to serve a long time and take complex loads,damage will occur inevitably on the surface or even inside the structure.In view of these problems,if damage can not be found in time and we do not take early measures,huge losses will be caused undoubtedly.For this reason,scholars have proposed a variety of damage identification methods.Due to the continuous improvement of basic theory,the rapid development of computer technology and detection methods,the damage identification method based on vibration information has been widely used in practical engineering structures.Firstly,the damage identification method based on vibration information obtains the basic modal parameters(damping ratio,frequency,mode shape)of the structure through testing.Because the displacement modal is not particularly sensitive to damage,therefore,displacement modal analysis is difficult to be applied,however,curvature modal damage parameters can greatly improve the sensitivity of damage detection.Therefore,the research on damage identification of reinforced concrete beams based on curvature modal method has very broad application prospects.Based on this topic,the main research contents in this paper are as follows:(1)Based on the vibration differential equation of Euler-Bernoulli beam,the theoretical basis of damage identification using curvature modes is deduced,and two methods of obtaining curvature modes are introduced.(2)The separated solid model of simple-supported reinforced concrete beam is established by ANSYS,and the modal analysis of beam structures under different damage conditions is carried out.identification parameters based on curvature modal such as absolute difference of curvature modal,mode ratio of curvature modal,instantaneous curvature modal damage factor,average curvature modal damage factor are compared.After processing the data,we found that:a.The curvature mode and absolute difference of curvature mode can accurately identify the damage location,but the mode ratio of curvature modal is prone to misjudge the damage location.b.Instantaneous curvature modal damage factor can be used to make an early judgment of whether the structure is damaged or not.Average curvature modal damage factor can reflect the relative relationship between the damage degree.c.The curvature modal curve of intact structure is still needed to identify the damage location,otherwise the damage identification of non-uniform structure is liable to cause misjudgment.d.When the damage is located at the modal nodes,the change of curvature modes may vary slightly because of the order of the selected modes.This problem can be solved by choosing different modal orders which do not overlap the damage location or by placing sensors on the side of the modal nodes rather than exactly on the modal nodes.(3)The theory of modal parameter identification is introduced,which lays a theoretical foundation for modal test.(4)Taking a simply supported reinforced concrete beam as the test object,the modal tests of the test beam before and after damage are carried out by arranging acceleration sensors.The test process,including the manufacture of the test beam,the material property test,the test instrument,the arrangement of the test points and the damage simulation are introduced in detail.The first two order of frequencies and normalized mode shapes of the test beam are obtained through experiments.The analysis of the frequencies shows that the natural frequency of the beam decreases with the occurrence of damage,and the more damage the beam has,the greater the frequency decreases.After obtaining the curvature mode by processing the normalized mode shapes,the damage identification of the beam structure is carried out.The results show that the curvature mode can accurately locate the damage of the reinforced concrete beam structure,which lays a foundation for the application of curvature mode to damage identification in practical engineering structures.In addition,in the process of modal test,some empirical methods for the simulation of simply supported test beams and the curvature modal solution of non-uniform measuring points are proposed,which can be used for reference in the follow-up study.