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Fatigue Deterioration Analysis And Lifetime Reliability Assessment Of Reinforced-concrete Industrial Building Structures

Posted on:2019-05-18Degree:MasterType:Thesis
Country:ChinaCandidate:Y M TangFull Text:PDF
GTID:2382330596460619Subject:Solid mechanics
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A large number of reinforced-concrete industrial buildings,which were constructed in the last century in China,have been in service for nearly 40 years.Nowadays they face severe safety challenges,while collapse accidents occur from time to time.Therefore,to enhance service performance,the diagnosis and treatment of existing industrial buildings is urgently required.At present,the structure diagnosis and performance improvement of existing reinforced-concrete industrial buildings are faced with new scientific problems.First,the existing fatigue life assessment of structure is concentrated in the design and construction phase,and it is impossible to consider a large number of defects in existing structures.In addition,the damage evolution and fatigue performance degradation of industrial buildings is a nonlinear process,especially in the middle or even later stages of the process.However,it brings greater error that existing fatigue life assessment generally adopts a linear accumulation method for the fatigue assessment of existing industrial buildings.In order to solve the above problems,based on fatigue performance degradation analysis,a life reliability assessment method for existing reinforced-concrete building structures is developed,providing new analysis theories and calculation methods for fatigue life evaluation.The main work and research results of the thesis are as follows:1.According to the on-site inspection results of reinforced-concrete industrial plant that has been in use for many years,the continuous damage mechanics theory was introduced to characterize the defects of the defects.For the damage evolution characteristics of concrete materials under different operating loads of reinforced-concrete industrial buildings,three damage constitutive models of concrete were selected and their parameters were determined.They are: plastic damage model for calculating dynamic effects,elastic damage model for calculating structural cumulative damage when overloaded,and high-cycle fatigue damage accumulation model for calculating structural fatigue damage evolution and fatigue performance degradation process.2.The concrete damage is introduced into the deterioration analysis of the reinforcedconcrete industrial building structure,while a multi-level simulation method is established.Firstly,through stress analysis of structural level model,the dangerous parts of the key components are identified,and based on this,a detailed analysis model of component level is established.Then the existing damages are introduced into the detailed analysis model,and the impact of damage evolution caused by the existing defects on structural performance degradation is analyzed under overload.For the simulation of crane load,the concentrated wheel load is equivalent to the distributed load acting in the local area,and the dynamic response coefficient obtained by numerical calculation is 1.06.3.Based on the continuous damage mechanics of high-cycle fatigue damage evolution model of concrete tension-compression difference,a general method for the fatigue damage accumulation of reinforced-concrete industrial building structures is developed,which is applied to the fatigue performance deterioration analysis under different cumulative rates of damage by programing UMAT subroutines.Taking an industrial plant for instance,the updating process of the fatigue cycle block was simulated.Then,fatigue damage evolution process for the key components under equal-amplitude load,variable-amplitude load and sudden load was obtained,respectively,and the influence of existing defects were analyzed.The results show: the fatigue damage evolution process of the structure under the variable amplitude load is obviously accelerated,while the fatigue life is greatly reduced;In addition,the existing defects have the effect of aggravating the fatigue performance of the structure,which increases as the years of service continuing;The overload phenomenon aggravates the damage evolution of the structure,and its effect is more obvious under the long-term service the structure.4.Based on the detailed component level model and the fatigue life formula of concrete,the response surface method is applied to determine the explicit analytical expression of limit state equation.Then,the fatigue life reliability index of key components is calculated,while the curve of structural reliability index under different service ages is obtained.At the same time,the influence of the existing damage and load frequency on the fatigue life reliability index of the structure is discussed.
Keywords/Search Tags:reinforced-concrete industrial building structure, fatigue damage evolution, existing defects, numerical simulation, reliability
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