| The promotion of recycled aggregate concrete is conducive to the resource utilization and sustainable development of construction waste,and recycled aggregate concrete has the characteristics of low strength and elastic modulus,and unstable performance.The introduction of steel tube constraints can enhance the bearing capacity of components and improve the application level of recycled aggregate concrete.However,steel tube recycled aggregate concrete is prone to steel tube buckling failure.In this paper,fiber-reinforced polymer/plastic(FRP)is used to confine the concrete core,which helps reduce the buckling of the steel tube and improve the bearing capacity and ductility of the member.Because FRP has good corrosion resistance,isolates chloride ions to corrode steel,and small-diameter FRP tubes have a strong constraining effect,multiple small-diameter FRP are used to confine sea sand concrete to improve the bearing capacity of specimens,effectively utilize abundant sea sand resources,and reduce river The environmental and ecological problems caused by over-exploitation of sand have good geographical advantages in offshore engineering applications.In this study,the steel tube-constrained recycled aggregate concrete was combined with multiple small-diameter FRP-constrained sea sand concrete,and a new type of composite column member was proposed: Recycled Aggregate Concrete Filled Steel Tubular Columns with built-in multi-tube sea sand concrete cores.with Multiple FRP Tubes Confined SSC Core,referred to as a new type of multi-tube composite column),the composite column is composed of outer steel tubes,several inner glass fiber-reinforced polymers(Glass-fiber-reinforced polymer,referred to as GFRP)constrained seawater concrete core and filling between the inner and outer tubes Constructed of recycled aggregate concrete.In order to understand the compressive performance of this type of composite column and promote the application and development of energy-saving and environmentally friendly materials in new components,this paper adopts a comprehensive method of experimental research,theoretical derivation and finite element analysis to carry out research.In the study,10 composite columns and 1 steel tube recycled aggregate concrete column were firstly subjected to axial compression tests,and the results were determined by the presence or absence of built-in GFRP tubes,the arrangement of GFRP tubes,the ratio of diameter to thickness of GFRP tubes,the strength of recycled aggregate concrete,the strength of sea sand concrete and the shape of steel tubes.As the main research parameters,the failure mode and loaddisplacement curve and load-strain curve of the specimen are obtained;the influence of relevant parameters is analyzed.Then,the new multi-tubular composite column is theoretically analyzed,and the bearing capacity design method is quantitatively described.Finally,the ABAQUS finite element is used to carry out the simulation calculation of the axial compression force of the composite column in the whole process,and the extended parameter analysis is carried out.The results of the study are as follows:(1)The load-displacement curve of the new multi-tube composite cylinder is divided into four stages,namely the elastic stage,the elastic-plastic stage,the descending stage and the stable development stage;the new multi-tube composite square column has only three stages,compared with the cylinder The specimen lacks a stable development stage.(2)The GFRP tube arrangement has a significant impact on the bearing capacity of the specimen.The GFRP tube specimen with a larger FRP content in the core area has better bearing capacity,because the FRP at the center limits the expansion of the concrete at the center,making the surrounding area smaller.The diameter FRP tube can play a good restraint effect;the loaddisplacement descending section of the new multi-tube composite column is different from the traditional composite column,and the new multi-tube composite column is stepped down;the strength of recycled aggregate concrete and sea sand concrete can be improved.The peak load of the specimen,in which increasing the SSC strength can better strengthen the bearing performance of the specimen,and also has a better initial stiffness.(3)According to the existing bearing capacity calculation formula,on this basis,using the test data,the corresponding correction coefficient is proposed for the steel tube restraint coefficient and the FRP restraint coefficient,and a new bearing capacity formula is obtained.Data validation shows that the formula has good applicability.(4)The ABAQUS finite element simulation is basically consistent with the loaddisplacement curve obtained from the test.Increasing the thickness of the steel tube and the FRP tube can effectively improve the bearing capacity of the specimen,but when the thickness of the FRP tube is greater than 4 mm,the ductility of the specimen will be gradually weakened. |
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