Study On The Bearing Performance Of Prefabricated Reinforced Concrete Beams With Docking Connections After Fire

Prefabricated buildings are more and more widely used in the field of capital construction.When the building structure is subjected to fire,its material performance will be seriously degraded,resulting in the reduction of its bearing performance.Therefore,the research on the deterioration mechanism of the bearing performance of the building structure affected by fire is a research hotspot in the field of disaster prevention and reduction,and the research on the fire resistance of a large number of fabricated building structures has more important practical significance.In addition to bearing static load,building structures will also bear cyclic load in some specific environments.The research on the deterioration mechanism and evaluation method of bearing performance of building structures under the coupling effect of fire high temperature and cyclic load has important theoretical significance and practical value.This thesis mainly takes the fabricated reinforced concrete beam as the research object,and studies its fatigue performance under static and cyclic load after fire and high temperature.The test pieces of butt assembled reinforced concrete simply supported beams with prefabricated parts at both ends and connected by grouting sleeve reinforcement in the middle of the span are designed to simulate the performance of this kind of prefabricated connection joints of reinforced concrete beams,and the comparative test of static bending performance after fire and high temperature is carried out.On this basis,the theoretical and numerical simulation analysis of static and fatigue performance of prefabricated reinforced concrete beams under fire is carried out,and the basic law of bearing performance degradation is analyzed and summarized.The main research contents and results are as follows:（1）Two types of grouting sleeve reinforcement connectors were made,tensile tests were carried out,the yield strength and ultimate strength of the sleeve connectors were measured,and the failure modes of each group of sleeves were observed and analyzed.The test results show that the two types of grouting sleeve connectors have broken the connecting reinforcement outside the sleeve,and there is no sleeve cracking or scraping plow pull-out failure of the reinforcement.The tensile strength of the grouting sleeve connectors is greater than the standard value of the tensile strength of the connecting reinforcement.（2）Two fabricated reinforced concrete test beams were tested for fire temperature rise,and the effect of fire time on the section temperature of fabricated reinforced concrete test beams was studied.The results of temperature rise test show that the variation law of section temperature time curve of each fabricated reinforced concrete test beam under different fire time is basically similar;At the same heating time,the temperature of the measuring point inside the test beam section is related to the distance from the fire surface,and there is an obvious temperature gradient;When the furnace temperature curve has a peak value,the peak value of the temperature at the measuring point of the test beam section will lag behind.（3）The bending performance tests of the above two prefabricated reinforced concrete test beams with different fire action time and one comparison test beam at room temperature under static load are carried out,and the effects of different fire action time on the deflection,steel and concrete strain,load-bearing capacity,crack development and failure mode of prefabricated reinforced concrete beams are analyzed.The test results show that the normal section of the test beams has been damaged by bending,the mating joint surface of the test beams has no obvious cracking,and the reinforcement has not been broken or pulled out at the connection of the grouting sleeve,that is,there is no obvious sign of weakness in the connection between the connection joint and the precast part;With the increase of fire time,the flexural stiffness and bearing capacity of fabricated reinforced concrete test beams gradually decrease,and the crack development is more obvious.Compared with the cracking moment of the comparison test beam at room temperature,the cracking moment of the test beam with fire time of 60 min is reduced by 12.5%,and the cracking moment of the test beam with fire time of 120 min is reduced by25%;Compared with the comparison test beam at room temperature,the ultimate bending moment of the test beam with fire time of 60 min is reduced by 7%,and the ultimate bending moment of the test beam with fire time of 120 min is reduced by 12%.（4）On the basis of experimental research and referring to the research results of existing relevant literature,the degradation law of the residual flexural capacity of prefabricated reinforced concrete beams subjected to high temperature fire is analyzed.On this basis,the calculation and prediction method of the residual bearing capacity of prefabricated reinforced concrete beams under fatigue load after high temperature fire is proposed.This method is used to analyze the residual bearing capacity of the test beams under fatigue load,The results show that under the same fatigue life ratio,the fatigue residual bearing capacity of the test beam decreases gradually with the increase of heating time.Therefore,the high temperature effect of fire has an obvious adverse effect on the fatigue resistance of fabricated reinforced concrete beams.（5）On the basis of the above experimental research,the finite element simulation analysis of the whole process of static loading is carried out for the fabricated reinforced concrete test beam,and the simulation analysis results are compared with the test measured results.The results show that the simulation analysis results are in good agreement with the test measured results.（6）Using Fe safe fatigue analysis software,the fatigue performance of three fabricated reinforced concrete test beams subjected to fire for 60 min and 120 min at room temperature is analyzed under cyclic load.The analysis results show that the fatigue damage of the test beam is mainly concentrated in the top area of the mid span beam and extends from the mid span to both sides;Under the same stress ratio,the fatigue life of the test beam decreases significantly with the increase of fire time.