# Roik and Bergmann 1993

Two methods for the analysis and design of composite columns were presented in some detail. The first method covered a simplified method of analyzing and designing composite columns under compression, bending, and shear, as specified by Eurocode 4. Following the commentary on this code were a number of examples for both steel-reinforced concrete columns and concrete-filled steel tubes. The second method presented was an incremental method of analysis structured for computer calculation. In conclusion, experimental results compiled from different sources were compared graphically to the presented methods and showed accurate correlation.

## Analytical and Design Formulation

The authors cite a number of formulas from the Eurocode. Limiting ratios of section depth to thickness were specified to prevent local buckling of the steel shell. For rectangular sections:

and for circular sections:

The value of the yield strength, f_{y}, in these equation is in metric, with units of MPa. The resistance to axial force is specified by:

where the 1.1 and 1.5 are safety reduction factors. The factor of 0.85 usually applied to the concrete strength is omitted because the steel encasement provides confinement effects and the protects the concrete from environmental effects. A presentation of combined moment-axial load calculations based on plastic stress blocks and the computation of the neutral axis location is detailed for composite sections (both CFT and SRC).

## References

Roik, K. and Bergmann, R. (1992). “Composite Columns,” Constructional Steel Design: An International Guide, Dowling, P. J., Harding, J. E., and Bjorhovde, R. (eds.), Elsevier Science Publishers Ltd., London and New York, 1992.