8.2 Composite Structure,Concrete-filled steel tubular structure,Concrete-filled steel tubular (CFST) was the member which was formed by concrete filled into steel tubular.,Classification,Square double-skin,Square and rectangular,1+12,Circular,Square and rectangle,1+12,Main advantages,Interaction between steel tube and concrete,The occurrence of the local buckling of the steel tube is delayed The strength of concrete is increased due to the confining effect provided from the steel tubular and the strength deterioration is not very severe Drying shrinkage and creep of concrete are much smaller than ordinary reinforced concrete.,Cross-sectional properties,The steel ratio in the CFST cross section is much larger than those in the reinforced concrete and concrete encased steel cross sections. Steel of the CFST section is well plastified under bending since it is located on the outside the section,Construction efficiency,Forms and reinforcing bars are omitted, and concrete casting is done by tremie tube or pump-up method, which lead to savings of manpower and constructional cost and time Constructional site remains clean,Fire resistance Concrete improves the fire resistance performance, and the amount of fire proof material can be reduced or its use can be omitted. Cost performance Because of the merits listed above, a better cost performance is obtained by replacing a steel structure by a CFST structure Ecology Environmental burden can be reduced by omitting the form work, and by reusing steel tubulars and high-quality concrete as recycled aggregates.,Apllication,610 m,Cherry blossom Guarden No. 1 Building, Laiwu,Baihualijing building Jinan,Saige Plaza, Shenzhen (72/292m, 1998）,Yajisha Bridge, Guangzhou,200，344m,Basic performance of CFST,Confining effect on concrete the common opinion is that in a composite column consisting of a concrete-filled hollow steel section, compressive confining stresses on the concrete core are induced by passive confinement provided by the steel tubular. The confining pressure is not constant as is the case for active confinement, and also depends on the lateral deformation of the concrete core under axial load and the stress-strain relationship of the confining steel.,Interaction between the concrete core and the steel tubular,Load transfer mechanisms the investigations for concrete-filled steel tubular show it is of great practical and economic interest not to have any mechanical shear connectors in the interface between the concrete core and the steel tubular. Hence, the load has to be transferred in some way directly over the surfaces of the concrete core and the steel tubular.,Four different mechanisms,Adhesion due to chemical reaction and/or suction forces along the interface, resulting from capillary action during the hydration process. Micro-interlocking between the concrete and the steel due to surface irregularities of the steel tubular. Fraction between the concrete core and the steel tubular due to normal forces. Binding or curvature effect which results from imposing compatible global deformations.,micro-effects adhesion and micro-interlocking macro-effects friction and binding,Micro-effects,Adhesion is an elastic brittle load transfer mechanism that is active mainly at the early stage of loading when the relative displacements are small . The bond mechanism contributes to a typical initial stiff part of the load-deflection relationship obtained from test. Surface irregularities increased the bond strength.,Macro-effects,Friction develops between the concrete core and steel tubular due to normal forces, for instance caused by volumetric increase of the concrete core when subjected to compressive loading. The binding mechanism means that the load is transferred between the concrete core and the steel tubular because they are bounded together by imposing compatible global deformations. Curvature and variations in shape of the steel tubular can be defined as binding mechanisms.,The better compaction could enhance both the effect of micro-effects and macro-effects, resulting in higher bond strength. the ultimate bond strength was not influenced by the concrete strength, the thickness of the tubular, the diameter of the tubular or the length of concrete-tosteel interface.,Connection,CFST column,H-shaped steel beam,6.4mm,1,1,Simple connection,Embeded weldable deformed bars,Interior headed studs,Headed studs on web plate,Cross section continuous through steel tube,Comparison of CFST and Steel systems based on the results of trial designs showed that the structural characteristics of both systems were almost the same, but the total steel consumption of the CFST system for entire building was about 10% less than that of the Steel system, which lead to more advantageous cost performance of the CFST than Steel systems.,1.Describe ingredients used for concrete Interaction between steel tube and concrete Buck