Study On Flexural Behavior Of The Composite Beams With U-shaped Steel Encased Recycled Concrete Section

In recent years,the construction industry has been rapid development.Concrete as the largest amount of building materials,consumption is increasing.The development and application of recycled concrete can not only ease the occupancy of natural resources by concrete and ensure the sustainable development of human society,but also be of great significance to the recycling of resources and environmental protection as a green and healthy concrete.The section steel-recycled concrete beam is a new type of structural system.It not only has the advantages of large rigidity and high bearing capacity of steel-concrete structure,good ductility,good seismic and disaster prevention properties,but also has the advantages of environmental protection of recycled concrete,recyclable advantage.In order to meet the new requirements of modern building structure and promote the application of steel-reinforced concrete structure in practical engineering,a new type of outsourced U-steel-recycled concrete composite beam is proposed and systematically studied.In this paper,the research status of recycled concrete and steel-recycled concrete are introduced firstly.Secondly,the mechanical properties of recycled concrete are analyzed and studied in detail.Then the analysis model of outsourced U-shaped steel-concrete composite beam and the recycled concrete constitutive model have been verified accurately.The effects of recycled aggregate replacement ratio,recycled concrete strength,the thickness of steel plate,the number of angle steel and other eight parameters on the flexural properties of U-steel-recycled concrete composite beams were analyzed by ABAQUS finite element software.Finally,in the plastic design theory the formula of flexural capacity of U-section steel-recycled concrete composite beam outsourcing is deduced.At the same time,the formula of deflection of composite beam is deduced by deduction stiffness method.The research results are as follows:(1)With the increase of the replacement ratio of recycled aggregate,the ultimate bearing capacity and mid-span deflection of composite beams show a slow downward trend.The recycled concrete composite beams are more prone to brittle failure than ordinary concrete composite beams.(2)The strength of recycled concrete can not only improve the ultimate bearing capacity of composite beams,but also make the composite beams have better ductility.(3)Although the increase of U-shaped rigidity,floor thickness and recycled concrete flange thickness can improve the ultimate bearing capacity of composite beam,it is more likely to cause brittle failure of composite beam.(4)When the number of angle-shear connectors reaches more than 15,the composite beam is a complete shear connection.(5)The reinforcement strength and the U-shaped just-bottom setting pegs have little effect on the ultimate bearing capacity of composite beams.(6)The calculation method of the flexural capacity of outsourcing U-steel-recycled concrete composite beam can be used to predict the flexural capacity of the composite beam.