Bridge Crane Based On Cloud Modelevidence Theory Metal Structure Safety Evaluation

The mechanical properties of the metal structure of the crane will degrade in the long-term use process,which will reduce the safety of the crane,cause safety accidents,and cause great economic losses and even casualties.The safety problem of bridge crane has complicated mechanism and many influences,and each evaluation index has certain fuzziness and randomness in the evaluation process.Considering the safety factors existing in the safety evaluation of bridge crane structure,the safety evaluation index system of bridge crane metal structure is established,and the on-site inspection scheme is given.The evaluation index of bridge crane is analyzed by finite element analysis method and fatigue crack propagation life theory.Linear weighting method is used to combine the weights of entropy weight method and Dematel method,which are brought into the multi-stage evaluation method of metal structure of bridge crane based on cloud model theory and D-S evidence theory,and the safety evaluation of bridge crane is studied.The main work completed in this paper is as follows:(1)By analyzing the factors affecting the safety of metal structure of bridge crane,considering strength,stiffness,local stability,fatigue,crack and other factors,seven safety evaluation indexes of strength,stiffness,fatigue life,local warpage of web,horizontal deflection of upper flange plate,vertical deflection of web and inspection cycle are determined.The safety evaluation index system of the bridge crane is established,which takes the safety evaluation index of the bridge crane as the bottom index layer,two main girders as the middle subsystem layer and the metal structure of the bridge crane as the system layer.(2)Finite element software was used for static analysis to obtain the measured values of the five evaluation indexes of the bridge crane,including strength,stiffness,local warpage of the web,horizontal deflection of the upper flange and vertical deflection of the web.Based on vibration theory,the simplified bridge crane system,wire rope,cars and goods for the two degree of freedom model,using the finite element modal superposition method for bridge crane girder of time-stress of the dangerous point of course,and through the rain flow count method for data processing,the time-the process of the stress of random stress into variable amplitude stress.Based on the fatigue crack propagation life theory,the variable amplitude stress data obtained by rainflow counting method is converted into equivalent stress,and then the fatigue life is calculated by using Paris formula.(3)Aiming at the problems of fuzziness and randomness existing in the safety evaluation process of metal structure of bridge crane,the safety evaluation method is studied.Firstly,the weights of safety evaluation indexes of bridge cranes are constructed by using the linear combination of entropy weight method and Dematel method.Then,with the help of cloud model theory,the cloud model membership degree of each main girder in subsystem layer is calculated,and the basic distribution probability of main girder is constructed according to probability transformation formula.Finally,the D-S evidence theory is used to fuse the basic distribution probabilities of the main girders and obtain the safety grade probabilities of the metal structure of the bridge crane.An engineering example is given to verify the correctness of the method,which provides a set of effective safety evaluation methods for metal structure of bridge crane for special inspection department.