Research On Crack Damage Identification Of Beam Structures Based On Pattern Recognition Technology

The operation environment of bridge structures is complicated and changeable,so it is hard to avoid the aging of materials,partial cracking and overall damage in the service process.Therefore,identifying the damage of bridge structures effectively and monitoring the operation status of the bridge timely are of great significance to the security of people’s lives and development of national economy.Damage identification depends on accurate finite element model,so it is very important to obtain a finite element model that can reflect the actual static and dynamic characteristics of structures through model modification.Natural frequency is used widely in the damage identification of bridge structures for the following three reasons.First,natural frequency is the global quantity that can reflect the whole vibration characteristics of structures.Second,natural frequency is sensitive to the change of structural stiffness.Third,the measurement of natural frequency is simple and accurate.In this paper,a pattern recognition technique for crack damage of beam structures based on model correction method and natural frequency is studied by combining theoretical derivation,numerical simulation and experimental verification.To verify the feasibility of this technique,numerical simulations and pattern recognition experiments of cantilever beam and simply supported beam are carried out.The main contents of the paper are as follows.Firstly,in order to obtain the finite element model that can reflect the actual static and dynamic characteristics of structures,the sensitivity order of the correction parameters should be determined by the finite element model modification theory which based on the sensitivity analysis method.Then modify the finite element model of beam structures by using the parameters from high sensitivity to low sensitivity until the model is well modified.And a numerical example of cantilever beam structure is given to verify the effectiveness of the proposed method.Then,based on the relation between the energy of structures and the modal parameters of structures,the relation between the stiffness and the natural frequency is deduced.Based on the above relations,the paper concludes that the ratio of the relative change of natural frequency of any adjacent order of beam structure is only related to the square ratio of curvature modes of the corresponding order,and has nothing to do with the factor of stiffness change.The eigenvector is constructed by using the ratio of the relative change of multi-order natural frequency.In this way,the pattern recognition technology is applied successfully to the identification of crack damage in beam structures finally.In order to verify the effectiveness of the pattern recognition technique for crack damage of beam structures based on model correction method and natural frequency,numerical simulations and pattern recognition experiments are carried out for the cantilever beam and simply supported beam.From the above discussion,it can be seen that the steps of using this technology to identify the crack damage of beam structures are as follows.Establishing the initial finite element model.→ Calculating the initial frequency of the model.→ Finding the natural frequency of the undamaged structure.→ Modifying the finite element model.→ Calculating the frequency after the model modification.→ Testing the natural frequency of the damaged structure.→ Comparing and analyzing the measured results and calculated results.→ Identifying the damage location and degree of beam structures.Finally,error analysis is made on the results of the experiment of cantilever beam and simply supported beam,and the main reasons that affect the determination of damage location and the assessment of damage degree are as follows.First,unit division precision is not enough.Second,the model cannot be corrected absolutely.Third,cutting depth is difficult to grasp accurately.Among them,the precision of unit division affects mainly the accurate identification of damage location,but has a little influence on the assessment of damage degree.The effect of model modification has a great influence on the result of damage identification,which requires attention in the damage identification work of engineering structures.The cutting depth only affects the verification effect of the pattern recognition experiments in this paper,not the experiments of engineering structures.