Research On Concrete Microstructure Evolution And The Performance Of RC Beam After High Temperature

With the speed up of urbanization process, the factors which lead to the possibility of fireare increased. The fire caused massive loss of life and property. At present, the concretestructure is one of the main forms of building structure in China. It will last a long time in thefuture. In the decades of service period, the possibility of fire threat to concrete structure is solarge. After fire, reinforced concrete structures are caused unrecoverable damage whichaffecting its working performance. The mechanical properties damage and the damagemechanism and evaluation method of reinforced concrete structure after fire are researched.The purpose is to provide theoretical foundation and scientific basis to establish damageassessment system of reinforced concrete structure after fire in order to adapt to the need ofengineering practice.The damage of concrete microstructure change mechanism after high temperature isresearched. Analysis is according to the microstructure of concrete after fire (X ray diffraction,scanning electron microscope) and ultrasonic test result can determine the temperature rangeof concrete sample, which can provide a basis for temperature field analysis of concrete afterfire. The comparison of temperature determined by microstructure analysis and measured bythermocouple is good agreement. The relationship model of microstructureevolution,temperature history and compressive performance is established preliminary, that isbenefit for the nondestructive evaluation, structural damage detection and the consolidationscheme of concrete structure which suffered from fire or other high temperature process.8simply supported reinforced concrete beams are made on the basis of a practicalproject. Temperature field distribution of section and effects of section size on temperaturefield and effects of different fire damage level on section temperature field of reinforcedconcrete simple-supported beam are researched in fire test. The mid-span deflection, the strainof concrete, steel strain, ultimate bearing capacity are measured in static test ofsimple-supported beam after fire, and section stiffness is calculated. The data ofsimple-supported beam before and after fire is compared, which in order to determine thedamage degree of mechanical properties, such as section stiffness and ultimate bearingcapacity of beam. This can provide the necessary parameters for structure analysis andreinforcement scheme. The width reduction method is used to calculate the stiffness of beamafter fire. The formula which can be used in engineering practice is deduced, the comparisonof calculation results and experimental results is good agreement.The finite element software ABAQUS is used to do numerical simulation analysis ofsection temperature field, the comparison of simulation results and results measured by thethermocouple is good agreement. The heat transfer analysis results are imported into thestatic model of beam, using sequential coupling method to carry on the analysis of mechanicalperformance after fire, the comparison of simulation results and experimental results is goodagreement.