How does external post-tensioning improve the seismic performance of concrete columns?

External post-tensioning improves the seismic performance of concrete columns primarily by increasing their confinement and axial load-carrying capacity, which enhances their ductility and resistance to buckling. Post-tensioning involves applying a compressive force to the concrete column by tensioning high-strength steel tendons or bars placed outside the column section and anchored to it. This compressive force counteracts the tensile stresses that develop in the concrete during an earthquake, reducing cracking and improving the concrete's ability to withstand deformation. The increased confinement provided by the post-tensioning tendons also enhances the concrete's compressive strength and ductility, allowing it to undergo larger deformations before failure. Furthermore, the axial compression from post-tensioning increases the column's resistance to buckling under combined axial and lateral loads, improving its stability and preventing premature collapse. In summary, external post-tensioning enhances the overall strength, ductility, and stability of concrete columns, making them more resistant to seismic forces.