Compressive Stiffness of CFDST Columns

Abstract

Columns are more critical in structural frames in earthquake regions, they must exhibit good ductility during an earthquake (Kenji et al. in J Struct Eng 130:180–188, 2004). Based on achievements of CFST columns, this chapter studies the compressive stiffness of CFDST columns. The stiffness is an important property of structural members. The element stiffness matrix is the simple superposition of the material stiffness matrix and geometrical stiffness matrix. The ultimate capacity of columns is influenced by the decrease of column stiffness due to the effect of stability and materials nonlinearity. Expressions of these properties are provided in the AISC 2005 design specification for steel components and American Concrete Institute (ACI) specification for concrete members. However, there is not a unified design code for composite members, and these current design specifications [e.g., AISC Specification in load and resistance factor design specification for structural steel buildings. American Institute of Steel Construction, Chicago, 2005; American Concrete Institute (ACI) (Acceptance criteria for moment frames based on structural testing and commentary. American Certification Institute, Farmington Hills, 2014)] provide different design expressions for CFST components. Herein, the current specification provisions are reviewed and compared. Differences and inconsistencies between these provisions are noted. Axial compression stiffness of CFDST can be obtained by the Unified Theory of CFST, which is testified by a theoretical analysis of method of elasticity.