| Thanks to the good situation of China’s economic and technological development,the demand for warehousing and logistics industry in China has been growing continuously in recent years.Under the guidance of the concept of " Internet + Efficiency logistics ",how to effectively improve the safety of storage structure has become a hot issue in the industry.As the main product in the logistics warehouse structure,steel storage racks often bear impact loads from cargo when they send or fetch the goods,and their beam-to-column joints are prone to fatigue damage,which leads to the overall instability of steel storage racks.Such accidents will endanger personal safety and lead to property losses.However,the research results on fatigue failure of speedlock connectors of steel storage racks are rare at home and abroad.Especially with the vigorous development of cold chain industry,the fatigue performance of beam-tocolumn joints in storage racks under low temperature environment is particularly concerned.Therefore,the fatigue behavior of speedlock connectors of cold-formed thin-walled steel storage racks under various temperature conditions were studied in this paper,and measures to improve the fatigue life of the connectors are given.It reveals the degradation characteristics of the stiffness of connectors under impact fatigue,and provides experimental data and theoretical support for structural health monitoring and performance evaluation of rack structures in the whole life cycle.Firstly,A experimental scheme of fatigue loading for portal frame is designed to ensure that the actual connection of the storage racks in operation can be simulated.The fatigue experiment of portal frame at normal temperature is carried out by using the impact load spectrum of the goods under various load conditions which is measured on the spot,and the experimental phenomena and the corresponding loading cycles of each stage for speedlock connectors are recorded in real time.By comparing the fatigue experiment phenomena of single cantilever beam at room temperature,the fatigue failure mechanism of speedlock connectors in portal frame is studied.In the whole life cycle of rack structure,besides considering the fatigue life of connectors,it is found that the stiffness of speedlock connectors changes significantly during fatigue experiment.The stiffness characteristics of speedlock connectors in portal frame are obtained by monitoring the displacement of connectors and the mid-span displacement of beams and introducing the calculation method of bending moment at the end of semi-rigid beams.The rationality of the calculation method is verified by monotonic experiment and low cyclic reversed loading experiment.Finally,the stiffness degradation formula of speedlock connectors is deduced according to the change of stiffness during impact fatigue experiment.It provides theoretical support for the safety assessment of racks in service.Then,the accurate and refined finite element model of the portal frame is established,and the stress analysis of the speedlock connectors under various temperature and load conditions is carried out.The result is compared with the phenomena of fatigue experiment,and the validity of the finite element model of the connectors is verified.The stress field results and the strain field results of the finite element analysis are output,and provide model support for the later fatigue life analysis.Finally,the fatigue life of the speedlock connector is calculated by using the whole life analysis method and the crack propagation analysis method.The rationality of the fatigue analysis model is verified by comparing the theoretical fatigue life of connectors with the experimental fatigue life of connectors under normal temperature.Then,the theoretical and experimental values of fatigue life of connectors in the portal frame are compared with those of connectors in the single cantilever beam,and the law of fatigue life of connectors in the two structure forms is summarized.In addition,the parameterized analysis is carried out about the key factors affecting the fatigue life of connectors,such as temperature and load.At the same time,the formula of fatigue life is fitted. |
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