Comparative study of strength design methods for rectangular reinforced concrete and composite steel-concrete columns

Abstract

A comparative study of available design methods in predicting the ultimate strength determined from physical tests of rectangular normal-density concrete columns was undertaken. The physical tests included in the study involve reinforced concrete and encased composite (steel-concrete) columns. The design methods compared include ACI 318-95 (Building 1995) which is very similar to CSA A23.3 (Design 1984), the AISC-LRFD Specifications (1994), Eurocode 2 (Design 1992), and Eurocode 4 (Design 1994). The results of a finite element modelling (FEM) procedure were also compared by using a commercially available nonlinear FEM software (ABAQUS 1994a, 1994b). The columns used for comparison in this study were braced and pin-ended and were constructed using normal strength concrete with a specified compressive strength between 2500 and 8250 psi. The columns were subjected to short-term loads producing pure axial force, combined axial force and single or double curvature bending, or pure bending. Major variables included the concrete strength, the end eccentricity ratio, the slenderness ratio, the reinforcing steel index, the structural steel index and the tie/hoop volumetric ratio. A total of 398 reinforced concrete and 221 composite steel-concrete columns were taken from the literature that formed the basis for a comparative study of different design methods. This comparative study provided an insight for the variability and related statistics of the design methods examined. No further tests were conducted for this study. Most of the design methods were affected to some degree by some or all of the major variables studied. Recommendations for improving the ACI 318-95 and the AISC-LRFD procedures are presented.