Research On Reliability Analysis And Residual Life Prediction Method Of Concrete Beam After Fire

With the rapid economic development in recent years,the number of high-rise buildings in China is increasing.Because of its convenient construction and wide application,concrete rectangular beam often becomes the first choice of high-rise building beam component.However,the frequent occurrence of building fire accidents makes the problem of concrete beam fire damage urgently need to be studied and solved.A large number of studies have shown that fire can cause damage to concrete beams,threaten their service safety,and affect the reliability and residual life of structural members.In this paper,the concrete beam as the research object,through the study of its temperature field after fire and obtained the required data of reliability and residual life,and then carried out the reliability analysis and residual life prediction of concrete beam after fire.The main research contents of this paper are as follows:(1)The research on fire resistance,temperature field,reliability and residual life of concrete and steel bar under high temperature at home and abroad in recent years is discussed.(2)The ISO-834 standard temperature rise curve is selected as the fire condition,and the thermodynamic parameters and calculation formulas of concrete and steel bar are obtained from a large number of tests and examples,so as to provide reliable material thermodynamic basis and calculation formulas for the temperature field simulation,reliability analysis and residual life prediction with the finite element software ABAQUS.(3)The temperature field model of concrete beam under fire is established through the finite element software ABAQUS.The influence of concrete beam temperature field distribution is analyzed from three aspects namely,the thickness of concrete beam protective layer,the ratio of stirrup reinforcement and the time of fire.Through the analysis,it can be seen that the increase of the thickness of the concrete protective layer has a slowing effect on the heating of the structure and the diffusion of the high temperature area in the section,the reinforcement ratio has little effect on the distribution of the temperature field,and the increase of the fire time will significantly accelerate the spread of the high temperature area in the temperature field.(4)The reliability of concrete structural components mainly includes the uncertainty of structural analysis,basic functional requirements,limit state equation,and failure probability,etc.By studying the reliability,the failure criterion of structural durability is determined and the limit state equation of the structure is established.The failure probability was calculated by combining the data obtained from the temperature field,the.Monte Carlo calculation program developed by MATLAB software and the limit state equation,and the reliability index and the remaining life result were obtained:The concrete beam with concrete strength of C40 and protective layer thickness of 35mm is subjected to fire for 3 hours,and the remaining life of the beam is about 13 years and 7 years respectively under the use requirements of the general building and important building components.The reliability of the beam that can continue to serve for 10 years is 0.2.By analyzing the results of reliability and residual life under different working conditions,it can be concluded that the concrete grade and the thickness of concrete protective layer have a significant influence on the reliability and residual life of concrete rectangular beams after fire,whether it is the requirements of general building members or important building members.Finally,the practical results based on the case and the Monte Carlo method are used to verify the feasibility of the calculation.