Study On Seismic Behavior Of High Temperature Re-curing Side Joint In Early Age

The beam column joint,as the transmission hub of reinforced concrete(RC)frame structure,is the weak part of the seismic design of the structure.Because the hydration reaction of early age concrete has not been completed,the mechanical properties such as strength and rigidity have not met the design requirements.If the joint is exposed to the high temperature of fire at this time,the seismic performance of the joint will be affected.In order to study the high temperature of the edge joint of early age RC frame in this paper,the seismic performance of the edge joint after re curing was studied as follows:(1)Considering different high temperature age(7d,14 d,21d,28d)and high temperature(100℃,300℃,500℃),the compressive strength and splitting tensile strength of C25 concrete in early age from high temperature to 28 d were studied;the compressive strength and splitting tensile strength of C25 and C30 concrete in early age after high temperature were studied considering the time of re-curing(28d,56d)Research.The results show that under the same high temperature age,the compressive strength and splitting tensile strength of C25 concrete from high temperature re-curing to 28 d in the early age decrease with the increase of high temperature;the compressive strength and splitting tensile strength of C25 and C30 concrete from high temperature re-curing to 28 d and 56 d in the early age increase with the increase of re-curing time,but the increasing range increases with the increase of re-curing time there was a decrease.(2)In this paper,the high temperature tests of RC frame side joints at 100℃,300℃ and 500℃ were carried out at 7 days old,and then maintained to 28 days,and the pseudo static tests were carried out at 100℃,300℃ and500℃ at 28 days old.The influence of different high temperature on the seismic performance(energy dissipation capacity,ductility,etc.)of RC frame side joints was studied.The results show that with the increase of fire temperature,the pinching phenomenon of hysteretic curve became more and more obvious,the cracking load,peak load,initial stiffness gradually decrease,and the energy consumption capacity and ductility gradually deteriorate.(3)The difference of seismic behavior of RC frame side joints between 7-day-old high-temperature-re-curing to 28-day-old and 28-day-old high-temperature was analyzed.The results show that at the same temperature,the seismic performance of the joints after 7-day-old high temperature re curing to 28-day-old was worse than that of the joints after 28-day-old high temperature.After 100℃,300℃ and 500℃,the cracking load value of the joints was reduced by 1.47%,3.82% and 9.51%,the peak load value was reduced by 1.13%,2.14% and 5.74%,and the initial stiffness was reduced by 16.95%,20.13% and 13.51%,respectively.(4)Based on the test results,considering the influence of fire temperature in early age,combined with the existing three fold linear restoring force model,the restoring force model suitable for RC frame side joints after high temperature and re-curing in early age was obtained.There are 76 figures,41 tables and 106 references in this dissertation.