Load Spectrum And Life Analysis Of Metal Structure Of General Bridge Cranes

As our country vigorously promotes the construction of infrastructure,efforts toward the goal of industrial power,lifting machinery in the process of the role of more prominent.At present,a large number of cranes are widely used in the construction of national economy.However,due to different manufacturing accuracy,different working conditions,and different maintenance and repair capabilities,even the life of the same batch of lifting machinery will be different.Every year,there are crane accidents at home and abroad,causing irreparable damage to human life and property,among which bridge crane in large special equipment casualties accident rate is the largest.According to a large number of previous cases,the most common form of failure of bridge cranes is fatigue failure.It is the initiation and development of crack that finally leads to the occurrence of fracture.For a bridge crane,when the crack of its main beam metal structure develops to a critical crack,it often represents the end of its entire working life.Effective and reliable evaluation of the life of the lifting machinery can timely find the safety problems of the crane,strengthen or replace it,and exert the maximum economic benefits of the crane.And the crane is scrapped in time to avoid the occurrence of safety accidents,which has guiding significance for crane design,manufacturing,actual use and maintenance.Although there are many methods for crane life assessment at this stage,few studies have been done to evaluate crane life using damage mechanics and load spectrum.Compared with other life prediction methods,continuous damage mechanics（CDM）has a reliable mechanical basis and physical significance.It can more accurately evaluate the life before macrocracks appear.This phase is called the early life of the material.The statistics and processing of load spectrum play an important role in the calculation of damage accumulation,and provide a basis for equipment life assessment.This subject first performed static tensile and fatigue tests on Q235B steel to the material of the metal structure of the main bridge crane.Fatigue tests of Q235B steel under stress control at room temperature using different stress amplitudes（220～300MPa）,and the relationship between the maximum stress and the life was fitted by the test data.Based on the theory of continuous damage mechanics,initial damage parameter₀ and damage indexin the damage model have been established through linearity of combining lg（1-）and lg(1-/₁))under double-logarithmic coordinate axis.Thus,a model of Q235B steel damage degradation at room temperature was established.According to the actual general bridge crane model,based on the strength,horizontal stiffness and vertical stiffness of the main beam of the universal bridge crane,a bridge crane model was constructed and the danger point was determined.Collect the lifting times and lifting loads of a bridge crane in a certain factory in a month.Through the established finite element model,the dangerous point stress corresponding to each load is simulated.The data was processed by rain current counting method and compiled into stress spectrum.According to the compiled stress spectrum and the established damage model,early life of the metal structure of the main bridge crane is estimated to be 26.1 years.