Confinement of Concrete Filled Steel Tubular Columns - New Frontiers

Abdelqader Najmi

Abstract


A new type of composite columns consists of tubular sections, filled with concrete has been investigated. Special link connectors are used to join the steel shell with the concrete inside. The method of connecting the two materials brings the level of confinement of concrete in this type of columns to values never reached before. The level of confinement reached surpasses by far the values obtained in spirally reinforced concrete columns when considering ultimate axial load. Concrete strength can be increased by more than 50%. These composite columns attain large axial strains at ultimate load of the order of 2% and more, such strains are well outside the plastic strains of steel and almost (6-10) times the concrete compression crushing strain of 0.3%. The resulting integrity of the cross section goes beyond preventing elastic local buckling of the steel shell; to sustaining the stiffness of the cross section in the plastic zone. Ultimate loads of connected composite concrete columns take place by the plastic buckling of the steel tube, and not by the crushing of concrete.

Keywords


Composite columns, Concrete, Steel, Confinement, U-shaped links.

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