Study On Practical Methods For Damage Detection Of Steel Structure

The civil engineering structure suffers damage inevitably in the long-term service process. Damage will make the structural resistance weaken and cause some project accidents in the extreme case. Then it will cause great personnel casualties and property losses. Therefore, studying on structural damage identification has significant values. At present, although there are some achievements in damage identification for structures, they couldn't meet the needs of engineering practices. There are two obvious defects in most damage identification method: 1.Current engineering inspection techniques cannot provide accurate and adequate measured data for the application of damage identification 2.Most of damage identification methods lack baseline which judge structural damage and represent structure in good condition. Based on problems mentioned above, three experimental structural damage detection methods are proposed in the paper, and in order to verify the effectivity of the methods proposed, experiments on the steel structure prototype and steel shell are carried out. The main tasks can be summarized as follows:1. It is advanced and summarized three new damage identification methods. These methods are symmetrical signal method, dynamic and static combining method and Musical tone rule method.(1)Symmetrical signal method is a damage identification method based on the basic theory of symmetrical signal. The method based on local detection is applicable to identifying damage in the symmetric member system of structure. The method is of high sensibility, and it can localize the structural damage.(2)Dynamic and static combining method is apply to damage diagnosis involving more beam-type structures which meet the symmetry conditions. It conducts inherently the static detecting method of integral structure. However, based on the correlation between dynamic and static parameters, the effect of complication on static detecting prior to dynamic test can be realized by dynamic and static combining method. So it amplifies the practicality of the static detecting method. Its healthy standard is the allowable deformation of structure in current national code.(3)Musical tone rule method is a damage identification method based on spectrum distribution of structure. This method is applicable to the damage diagnosis of homogeneous and regular structure. The spectrum distribution of regular structure shows the characteristic of clear spectrum and comb-like distribution of peak points. Make an analogy to musical phenomenon, the characteristic is defined as the musical tone rule of structure. The rule is the structural healthy standard for musical tone rule method.Three new methods about damage identification are applied with strict engineering conditions. Without complicated inversion Calculation, these methods have the structural healthy standard of damage identification. The structure parameters used in damage identification possess higher precision in engineering tests, so these methods have good practical engineering prospects.2. A research for the damage-related experiment on a typical beam steel truss structure has been made. An 8-meter-long steel truss structure is designed and built. Through the rotation of members with different section, it could construct many damage conditions. Through the experiment, stiffness, natural frequency, damping, displacement model, and other basic structural parameters of the steel truss structure are obtained. Based on the accuracy and reliability of parameter identification, the stiffness and first step frequency obviously excel the others. And there is a monotonic relation between the change of them and the damage degree of truss. So the stiffness and first step frequency are proposed for the signature of damage detection in the research of structural damage identification.3. The validity of the dynamic static integrated method was verified by the static and dynamic combined experiment of steel truss. Through the members combined, the research constructed twelve truss samples with different damage and acquired the stiffness and first natural frequency of each sample. Then combining the measured results into the dynamic and static parameter general formula of the dynamic static integrated method using unitary normal distribution model, the numerical relation formulas which represent the correlation between the stiffness and first natural frequency were established successfully. All of which have proved the effectivity of this method.4. Symmetrical signal method is verified by experiment. The analytical solution of natural frequencies of a beam with two fixed supports is also obtained. The beam was tested under the single crack damage mode. The test selected several symmetrical members on the steel truss, and carried out dynamic test of four damage conditions. The experiment showed that symmetrical signal method could identify various damages easily. The method has very high sensibility. The test analogue the crack damage in a rock with one anti-torsion spring which neglected weight, and deduced the frequency equation of simply supported beam with one crack. When the boundary of the symmetric member meets the doubly-clamped conditions, the roughly region of damage could be inferred by this equation.5. The validity of musical tone rule method was verified by the damage experiment of three steel shells. The test used three same steel shells. Through the vibration test, the spectral distribution rule of these shells has been obtained. The frequency spectrum of these steel shells without destructive shows the characteristics of clear spectrum and comb-like distribution of peak points. This is in accordance with the feature of musical tone rule. Implementation of the damage identification could only be placed in a coordinate system, and the structural damage can be found easily.6. The project with spatial steel truss structures is diagnosed healthily. The combination of two detecting processes of engineering cases, some problems of health detection in spatial grid structure have been summarized and analyzed. The results of the spatial grid structure detection indicated that static loading method based on structural integral identification can obtain satisfied engineering diagnosis effects. Due to the lack of healthy standard, vibration detecting method is confined in the application of structure Health Diagnosis. Vibration detection for structural vibration analysis is very effective.