Tensile Test Study On The Reinforced Bar Reinforced By Half-grouting Sleeve At High Temperature

With the advancement of science and technology and the development of society,people pay more attention to energy conservation and environmental protection in buildings.Every year,in environmental pollution,the proportion of waste and waste generated from cast-in-situ structures in construction sites cannot be ignored.In recent years,China is vigorously promoting the process of building assembly.Vigorously promoting prefabricated buildings has been proposed in the "13th Five-Year Plan".The prefabricated building industry is gradually rising,and its unique advantages are also becoming more and more popular in the construction industry.Prefabricated buildings have the advantages of high quality,short construction period,and energy saving.It is precisely because of these advantages that the proportion of prefabricated buildings in the total number of buildings is also increasing.In an assembled structure,whether the components can be reliably and effectively connected is related to the overall safety of the building.In China,the main connection methods of the connection parts between the prefabricated buildings are sleeve connection and grouting anchor connection.Among them,the sleeve grouting connection method has been more and more widely used in actual engineering in recent years.The research on grouting sleeves at home and abroad is still immature,and there are relatively few relevant results.Most of the studies are related to the study of parameters at room temperature,and there are few studies involving grouting sleeves at or after high temperature.Therefore,for grouting sleeves after high temperature The study of the tube is particularly important.In this paper,the tensile properties of the steel bars connected to the semi-grouting sleeve at high temperature are studied.A total of 108 test pieces are designed.Through the pull test of the test pieces,the effects of the anchor length,the thickness of the protective layer,and the temperature on the mechanical properties of the test piece Influence the law,then,based on the bond slip between concrete and steel at room temperature,the temperature variable is introduced,and the ultimate bearing capacity calculation formula between the ultimate tensile force and the temperature and the anchor length is derived.At the same time,the high-temperature post-grouting test pieces were also subjected to bending and compression resistance,and the change rule of strength decrease with increasing temperature was studied.Test and analysis results show:(1)In all the test specimens after high temperature,when the temperature T≤400 ℃,the failure mode of the test specimen is the tensile failure of the steel bar.When T = 600 ℃,the ultimate strength of the steel bar and the adhesion between the grout and the bar The strength of the knots is approximately equal.After being subjected to a high temperature of 800 ° C,the concrete protective layer still has a certain restraining effect on the pull-out of the steel bars.When the anchoring length is145 mm and there is a concrete protective layer,the semi-grouting sleeve connector can still meet the normal working requirements after experiencing a high temperature of800 ° C.(2)After the test specimen is subjected to a high temperature of 600 ° C and below,the ultimate tensile force remains basically unchanged.After the test specimen is subjected to a high temperature of 800 ° C,the ultimate tensile strength of the protected specimen is reduced by 30%.The post-force-displacement curve still has a yield stage.After being subjected to a high temperature of 800 ° C,the yield-displacement curve disappears.(3)As the temperature rises,the flexural strength of the standard test block of grouting material shows a downward trend.The change law is as follows: After subjected to a high temperature of 400 ° C,its flexural strength decreases by about50%,and its temperature resists the flexural strength.The influence is great;its flexural strength decreases relatively smoothly with the increase of temperature,which is basically a linear relationship.When T≤600 ° C,the flexural strength decreases by about 10% for every 100 ° C increase in temperature,at 600 ° C.After that,the effect of temperature on the flexural strength gradually becomes smaller.(4)The strength degradation of grout with temperature changes is similar to that of concrete,and the trend of the compressive strength decline curve is roughly the same.