round column spiral ties

[releky]

A round column with close spiral ties can take more ultimate load because the spiral prevents the concrete from shearing outward near ultimate axial load (Pu) and has more resistance to buckling of the longitudinal ties. What would happen if the ties in a square column is made closer too than necessary like every 3 inches apart? How would it behave?

 

[hokie66]

The more ties, the more confinement, so better performance. Concrete filled steel tubes provide even better performance.

 

[FishTheStructure]

As hokie said, spacing ties (or spiral ties) closer together increases the confinement effects which increases the confined concrete strength.

For more information regarding confined concrete I would recommend the article "Theoretical Stress Strain Model for Concrete" by Mander, Priestly, and Park in the "Journal of Structural Engineering" (1988). It is a bit old, and much additional research has been done since then in the area of confined concrete, but I found it a great starting point.

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