Study On The Bearing Capacity Of Early Age RC Columns After High Temperature-recuring

The fire resistance of concrete structure is one of the hot topics in civil engineering research.In the early age of reinforced concrete columns,the degree of hydration has not been completed,and the strength and rigidity have not fully met the design requirements.At this time,after the fire,the bearing performance of the column will be seriously affected.In order to investigate the bearing performance of reinforced concrete columns after high temperaturerecuring in early age.In this paper,the mechanical properties of early age concrete after high temperature-recuring were studied.The bearing capacity of the reinforced concrete column after early age high temperature-recuring was analyzed by the method of experiment and simulation,and the simplified calculation method of the bearing capacity of the reinforced concrete column after early age high temperature-recuring was put forward,and the specific research contents are as follows:Considering the influence of fire age(7d,14 d,21d,28d)and fire temperature(100℃,300℃,500℃),the mechanical properties of C25 concrete after high temperature and after high temperature re-curing to 28 d were analyzed,and the mechanical properties of C25 and C30 concrete after different curing age(28d,56d)were compared.The results show that the compressive strength,splitting tensile strength and elastic modulus of concrete were recovered to a certain extent after early age high temperature re-curing,and the key period of strength recovery was 28 days after fire,and the strength recovery tends to be gentle when the curing time is increased to 56 days.Based on the high temperature tests of 100℃,300℃ and 500℃,the compressive strength and tensile strength of C25 concrete after 700℃ and high temperature-recuring were predicted by using grey prediction theory and python language.The results show that the simulation accuracy of the grey prediction model to the test data was relatively high,and the compressive and tensile strength of the concrete after 700℃ high temperature and high temperaturerecuring determined by the grey theory were consistent with the change trend of the test data in the overall change rule.The strength fitting formulas of early age concrete after high temperature and after high temperature-recuring were given.The correlation index R2 was greater than 0.97,and the fitting result was better.The axial compression tests of reinforced concrete columns were carried out to study the variation of ultimate bearing capacity,axial displacement,failure mode,axial stiffness and ductility with the fire temperature(100℃,300℃,500℃)after 7 day old high temperature and 28 day old high temperature.The results show that,compared with the column exposed to fire for 28 day old,for 7 day old of high temperature-recuring to 28 days,the ultimate bearing capacity of the column was lower than 5.1%,4.7%,12.5%,the axial stiffness was lower than 6.4%,11.3%,26.5%,and the ductility was lower than 2.0%,4.3%,9.3%.According to the test results of mechanical properties of early were reinforced concrete columns after high temperature-recuring,the finite element model was established by using ABAQUS,and the results of finite element calculation were compared with the results of axial compression test of columns,so as to verify the accuracy of finite element simulation,and expand the analysis of the influence of different fire age and fire temperature on the ultimate bearing capacity of columns after high temperature-recuring in early age.Based on the test results and simulation results,the synergy reduction factor γ_d for the early age fired steel and concrete was introduced,and a more accurate formula for calculating the ultimate bearing capacity of the axial compression column after high temperature-recuring at early age was obtained.The calculation results can meet the engineering requirements.There are 80 figures,33 tables and 102 references in this dissertation.