Research On Damage Identification Of Reinforced Concrete Beams Based On Multi-modal Parameter Fusion

After the completion of bridge structures,various damages will inevitably occur as the service life progresses.These damages to bridge structures has laid a critical hidden safety hazard to the normal operation of road traffic.The problem of damage identification of bridge structures has always been a hot issue that many domestic and foreign researchers focus on in their studies.The damage can be detected in time by monitoring changes in the modal characteristic parameters of the bridge structure.Based on engineering vibration theory and experimental modal analysis theory,this dissertation takes highway bridge-beam structure,the most important structural form,as the research object,and with the combination of numerical simulation and experiment,conducts researches on the principles and methodology of damage identification for reinforced concrete bridge structures that are able to meet the actual inspection requirements of projects.The main research work and research results of this dissertation are as follows:1.A method for structural damage identification based on strain response direct obtain of strain mode is studied.In this method,the strain mode of the structure is directly determined from the strain response amplitude and phase information by analyzing the strain response raw data information.It has the advantages of simple modal experiment process and small calculation workload.(1)Comparing the experimental results of the displacement mode and strain mode parameters of the simply-supported steel beam,it is shown in this research that the modal parameters such as frequency,shape and damping of strain mode can be directly obtained from the strain response information.This method can be used to identify structural strain modal parameters.(2)The strain mode damage identification of simply-supported steel beams with double preset damage experimental results show that the natural mode frequency of the structure is not sensitive to damage.In the strain mode shape,mutation occurs in the damage position of the non-vibration type joint of the simply supported steel beam experi-mental specimen.The amount of mutation increases with the degree of damage increased,by which the preset damage location is accurately identified.2.The finite element model of pre-damaged reinforced concrete beam was established by finite element numerical simulation.The internal relationships and mutual influence mechanisms between modal parameters such as frequency,displacement mode,curvature mode and strain mode of reinforced concrete beam under different damage conditions has been studied.The sensitivity of each modal parameter to structural damage and its general variation with the degree of damage of different structures have been studied.The results show that the natural frequency and displacement mode of reinforced concrete beams are not sensitive to damage,that the natural frequency of the whole body decreases with the increase of damage,and that the curvature mode and strain mode of reinforced concrete beams are very sensitive to structural damage: there are sharp mutations in the damage position of non-vibration type nodes,which accurately reflect the difference between the preset damage position and the damage amount.In the case of the same amount of structural damage,the amplitude of the high-order curvature mode and the strain mode shape is much larger than the low-order mode,which means higher sensitivity to structural damage.3.The modal parameter identification and damage identification of pre-damaged reinforced concrete beams based on frequency domain decomposition under environmental excitation have been studied.The comparison with the results of finite element numerical simulation shows that the structural modal parameter identification method based on frequency domain decomposition can effectively identify the displacement modal parameters of reinforced concrete beam when the excitation input is in a non-straight spectrum.This method can be used for modal parameter identification of reinforced concrete bridge structure under environmental excitation.4.The structural modal parameter identification and damage identification based on the combination of frequency domain decomposition and strain mode are carried out.(1)The identification results of strain modal parameters of reinforced concrete beams under random excitation experiment show that the strain modal parameter identification method based on frequency domain decomposition can better identify the strain modal parameters of reinforced concrete beams under strong noise background.This method can be used for modal parameter identification of reinforced concrete bridge structure under environmental excitation.(2)The damage identification study of pre-damaged reinforced concrete beams under random excitation shows that the strain mode shape has obvious mutations in the damage position of the non-vibration type nodes,and according to this,the preset damage position can be accurately identified.High-order strain mode shape is more sensitive to structural damage of reinforced concrete beam with the same amount of damage.There is a certain linear relationship between the damage amount and the strain mode mutation of reinforced concrete beam.This method can be used for damage identification of reinforced concrete bridge structure under environmental excitation.5.The relationship between strain mode mutation coefficient and structural damage degree is established.The damage identification experiment of double pre-damaged steel beam and pre-damaged reinforced concrete beam show that there is a certain linear relationship between the degree of structural damage and the strain mode shape mutation.In the actual bridge engineering structure damage identification,if the structural damage criterion is established in advance,the damage degree of the structure can be judged according to the strain mode shape mutation.The results of this dissertation can not only determine the location of structural damage,but also achieve structural damage assessment.It has certain guiding significance for the damage identification of actual reinforced concrete bridge structure.It has important application value for rational analysis and evaluation of the health status of reinforced concrete bridge structure and avoiding the occurrence of catastrophic major traffic accidents.