| Abstract | High-strength concrete (HSC) columns can achieve a ductile behaviour when sufficiently confined by high-strength lateral steel reinforcement. The full potential of high-strength steel, however, may not be achieved in lightly confined HSC columns, since the stress in the confining steel may not reach the expected yield stress usually assumed in design. Different approaches that determine the actual stress in the confining steel at peak stress of confined concrete for prismatic or cylindrical columns have been developed, namely (i) an iterative approach, and (ii) a direct approach assuming an equivalent circular column concept. In order to eliminate some of the complexities and assumptions used in these models, a new direct and simple approach is proposed. It is based on the compatibility of strains and equilibrium of forces in the column cross-section, and on actual deformations measured in the confining steel of 50 large-scale HSC columns made with widely different concrete strengths, steel yield stresses and confinement pressures. The proposed model shows that the effective stress in the confining steel does not exceed 400 MPa in lightly confined HSC columns. In this case, the use of high-strength steel for the confining reinforcement is not necessary. On the other hand, in sufficiently confined HSC columns, much higher lateral stresses can be achieved if high-strength steel is used with yield stresses up to 800 MPa, ensuring a very ductile load-carrying behaviour. Predictions of the peak stress and peak strain of 50 large-scale confined HSC columns showed a very good agreement with the experimental results. |
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