| Bridge cranes is used as special machinery and equipment to support the national economy,and its product quality,bearing capacity,fatigue life and other indicators need to be paid special attention by designers.At present,traditional design methods are used in the design of crane structures,and only qualitatively evaluates in the domestic crane manufacturing industry,the fatigue strength of the structure according to the type of steel,working level and joint form,without carefully considering the cumulative effect of random loads on the fatigue life of the structure during service.The blind pursuit of light weight in the design,unreasonable main girder structure will lead to the life of the mid-span is much shorter than the span end,resulting in uneven distribution of structural life.Often due to premature end of mid-span life,irreparable structural failure of the girder is induced,which often leads to serious safety accidents and resource waste.Therefore,in the design of the crane structure,it is necessary to quantitatively evaluate the fatigue life of the crane structure based on the accurate and reliable service information-load spectrum,taking into account the influence of the two indicators of lightweight and fatigue life on the structural performance,so as to improve the load-bearing performance and safety of use of integral structural within the specified service period.In response to the above problems,a company’s 32t-28.5m bridge crane is taken as the research object of this paper,and research work carried out mainly includes:1)In order to obtain an accurate and reliable crane working load spectrum,an artificial intelligence prediction method of crane load spectrum of "on-site acquisition + machine learning" is proposed.Through the actual measurement of the working load characteristic parameters of the crane in service,the real small sample load spectrum is obtained by statistics,and the step length of beetle is updated by the arctangent function,and the function of judging the "stagnation" link and jumping out of the local optimum is added to improve beetle antennae search algorithm(IBAS),which is used to intelligently selection of kernel function parameters δ and regularization parameters γ in the Least Squares Support Vector Machine(LSSVM)model.The IBAS-LSSVM prediction model is constructed and compared with other prediction models,which proves that the prediction model in this paper has the characteristics of high prediction accuracy and fast convergence speed.Combined with the Latin hypercube sampling technology,the load spectrum is extended and predicted,and a large sample periodic load spectrum that is realistic and representative is obtained,which provides scientific data support for crane fatigue life assessment.2)In view of the problem that it is difficult to accurately quantify the influence of the random loading of cranes on the fatigue life of the structure,a method for evaluating the residual life of dangerous points of crane structures is proposed by using the load information of periodic inspections.According to the periodic working load spectrum of the crane obtained by extension and prediction,based on the load characteristic information,the theoretical calculation is carried out on the metal structure of main girder of the crane,the stress-time history of the dangerous points at different sections of the main girder under the four extreme working conditions is obtained.The equivalent stress spectrum under the corresponding stress ratio is obtained by using the equal life curve and the rain flow counting method,combined with the nominal stress method and the crack propagation theory of linear elastic fracture mechanics,the crack formation and propagation of crane main girder structures are analyzed,so as to obtain the quantitative evaluation results of the full life of each dangerous point on the mid-span and span-end sections of the crane main girder.3)In order to improve the problem of uneven life distribution of the overall structure of the crane main girder and increase the overall service life of the main girder,a method for the equal-life optimization design of crane main girder structure using intelligent optimization algorithm is proposed.Based on the residual life evaluation results of the dangerous point of the crane structure,the section parameters of the main girder structure at the mid-span and at the end of the span are used as design variables,on the basis of the structural bearing capacity constraints,the influence of the structural fatigue life index on the design is considered,the life difference between the two calculated sections at the mid-span and at the end of the span is strictly controlled within 5 years.The improved multi-mirror reflection algorithm is used to find a reasonable combination of design parameters in the design space,in order to obtain the design parameters of the main girder structure that meet the constraints and the optimal lightweight index.In this way,the design purpose of equal life and light weight is achieved,and provide an unique design thinking and reasonable solutions for the equal life design of crane structures.4)In order to verify the load-bearing performance of the optimized main girder structure,a verification method using ANSYS finite element analysis +structural fatigue life evaluation theory is proposed.Through ANSYS Parametric Design Language(APDL),the static analysis of the original main beam structure is carried out,and the results of the strength and stiffness of the finite element analysis and the theoretical calculation were compared,which can verify the rationality and accuracy of the finite element model simplification,element selection and constraint methods of the main girder structure.Based on the design parameters of the optimal main girder structure and the above APDL model processing method,the finite element main girder model is updated,and the static analysis,buckling analysis and modal analysis are carried out to obtain the displacement and stress results of the key position of the main girder.The random load spectrum is regard as a data driver to conduct transient analysis of the main girder structure,the stress-time history of the dangerous point is extracted,and the fatigue life evaluation of the optimal girder structure is completed in combination with the fatigue life evaluation theory,so as to comprehensively verify that the optimal girder structure has stable and reliable load-bearing performance. |
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