Analyses And Reliability Evaluation On Fatigue Life Of Existing Industrial Steel Structure Buildings

Because of light quality and good anti-seismic performance,steel structure is widely applied to industrial building for industrial production activities.Steel structure industrial plant is the most common forms.Due to fatigue load in term of service,the fatigue failure always occurs in the stress concentration area,especially the weld,containing congenital defects,which lead to the initiation and evolution of micro cracks,under service load.Then cracks appear and extend further,finally the structure function fails.In order to study the local fatigue failure in steel structure industrial building,a multi-scale modeling strategy is set up in this paper.In case of the steel main workshop of tube billet continuous casting,a multi-scale finite element model containing vulnerable parts is set up.The failure process in vulnerable parts from damage accumulation to crack propagation is simulated and analyzed,Based on different theories,fatigue life is evaluated.Considering the randomness of crack propagation,the reliability of structural key components is calculated and analyzed.The main research and conclusions of this paper are listed as following:1)In order to study the law of local fatigue failure in steel structure industrialbuilding,a multi-scale modeling strategy for the fatigue life analysis ofexisting industrial building steel structures is established in this paper.In caseof the steel main workshop of tube billet continuous casting,a multi-scalefinite element model containing vulnerable parts and service load modelbased on vertical load of crane are developed,and verify the accuracy of themodels are verified.The results show that the relative error between themaximum lower deflection of the multi-scale finite element simulation andthe actual test results is 3.9%,and the relative error between the stressintensity factor and the corresponding analytical solution obtained by thefinite element numerical simulation is 4.3%.This indicates that the finiteelement model is credible.2)In case of the steel main workshop of tube billet continuous casting,based ondifferent damage criterion,multi-scale simulation and analysis are carried outfor fatigue damage accumulation of vulnerable parts in structural keycomponents at the early stage of service.The calculation results of Lemaitrehigh cycle fatigue damage criterion show that the damage cumulative curveis relatively slow in the early stage.When the damage cumulative value isover 0.4,the cumulative damage rate is obviously increased.Based on linearMiner fatigue damage criterion,the engineering evaluation result isconservative.3)In case of the steel main plant of tube billet continuous casting,crackpropagation of vulnerable parts is simulated and analyzed,and the fatigue lifeof existing steel structure industrial building is evaluated.The expression ofequivalent stress intensity factor can be given to study crack propagationunder variable amplitude load.When the crack depth is greater than 5 mm,the crack propagates faster.The crack propagation rate of the primary part ismuch larger than that of other parts at the same cycle,and the remaining lifeis relatively small.The existence of the cracks in the primary parts has agreater impact on the fatigue performance deterioration of other parts.4)An evaluation strategy is built for life reliability analysis of existing steelstructure industrial building.In case of the steel main workshop of tube billetcontinuous casting,the ultimate state equation is developed for the crackpropagation analysis of the steel crane beam,and the reliability index underyears is calculated by Monte Carlo method.The results show vulnerable localreliability index decreases and rate is getting slower and slower as the term ofservice goes by.The reliability index of the connecting area between pluggedplate and sealing plate is the most serious part,which should be paid moreattention in engineering inspection to make sure whether the cracks appear.