Study On The Behavior Of Concrete-filled Steel Tubular Columns With Recycled Clay Brick Aggregate Under Axial Compression

Given the increasing stock of current construction waste,it has already caused serious threats to China's ecological environment and land resources and has caused an unhealthy phenomenon that cities are besieged by garbage.With the continuous development of China's economic development and urbanization,annual construction waste produced in China is still increasing so that the demand and the consumption for natural aggregates will also increase.A series of problems is urgently needed to be solved.Recycled concrete is one of the effective ways to solve the adverse impact caused by construction waste from the source,and realize the recycling of construction waste resources.However,the recycled concrete has a series of defects,such as the lower strength,which has hindered the promotion and application of recycled aggregates in engineering.Because of its good mechanical properties and seismic performance,the combination of steel pipe and concrete has successfully overcome their shortcomings and complemented each other,making it possible to promote the application of recycled aggregate and recycled concrete in engineering.In this paper,the experimental results and theoretical basis of the previous experiments will be carried out to test the axial performance of concrete-filled steel tubular columns with recycled brick aggregates.This paper mainly studies the following contents:(1)Research on the material properties of recycled brick aggregate concrete.The effects of replacement ratio of recycled brick aggregates and nano-calcium carbonate content on compressive strength are studied by cube compressive strength test.And the tensile strength and other properties of steel are also investigated.(2)Experimental study on the axial performance of concrete-filled steel tubular columns containing recycled brick aggregates.In this paper,the replacement ratio of recycled brick aggregates,nano-calcium carbonate modified material and confinement index are used as variables to test the axial compression performance of four ordinary steel tube concrete and 20 steel tube concrete specimens containing recycled brick aggregates.(3)Analysis of the relationship between load and strain under axial compression of concrete filled with recycled brick aggregates.The load-axial strain relationship,load-transverse strain relationship,strain gauge load in the same direction-averageaxial strain relationship,load-average transverse strain relationship measured by four strain gauges respectively and the full curve of the load-axial strain relationship measured by the self-contained system of the test press are analyzed.(4)In this paper,a total of 637 specimens of the database is established to evaluate specimen axial compression bearing capacity comprehensively by collecting data on round steel tube concrete axial compression test at home and abroad.The effects of concrete strength,yield strength of steel tube,diameter-to-thickness ratio of steel tube,length-to-diameter ratio of steel tube and confinement coefficient on the deviation analysis of GB50936-2014 compared to the database are discussed.(5)The calculation formulas of different theoretical bearing capacity and the classical axial stress-strain relationship of the full-curve constitutive model of recycled concrete-filled steel tubular concrete under axial compression are analyzed.This paper introduces and substitutes experimental data to compare the theoretical load-bearing force calculation formula with the classical axial stress-strain relationship full-curve constitutive model,and uses the experimental data to analyze and fit.Bearing capacity calculation formula and axial stress-strain relationship full curve constitutive model are proposed to be applied to the concrete-filled steel tubular concrete under the axial compression.The main innovations of this paper are to combine recycled red brick aggregate concrete and steel tube to obtain recycled aggregate concrete-filled in steel tube,which provides a new idea for the utilization of construction waste resources.The concrete-filled steel tube column with recycled brick aggregate is a new combined structure with great social,economic and environmental benefits,which is closer to practical engineering.The research results are of great significance to the cost control and technology realization of recycled concrete in practical engineering applications.