Comparative Strength Analyses of Concrete-Encased Steel Composite Columns

Comparisons of strengths determined from 150 physical tests of rectangular composite steel–concrete columns available in the published literature with the strengths calculated from selected computational procedures are conducted. The computational procedures compared in this study include ACI 318-02, American Institute of Steel Construction–load and resistance factor design, and Eurocode 4. The physical tests used for comparisons were conducted on composite columns in which steel shapes are encased in concrete. The columns were braced and pinned at both ends and subjected to short-term loads, producing pure axial force, axial force combined with symmetrical single-curvature bending, or pure bending. The study included only those columns for which the complete information required for analysis was available from the published physical test data and for which the compressive strength of normal-density concrete ranged from approximately 17–56 MPa $(2\text{,}500-8\text{,}100\mathrm{psi})$. Major variables include the concrete strength, the end eccentricity ratio, the slenderness ratio, the structural steel index, and the transverse reinforcement (tie/hoop) volumetric ratio. The comparative study provides a critical review of the reliability of the computational methods examined. A recommendation for improving the ACI 318-02 procedure is also presented.