What should be the shape of the pillars or columns in buildings and bridges?

The shape of a pillar or column in buildings and bridges should be designed to distribute the load effectively.
As shown in the figure,a pillar with a distributed shape at the ends (as in figure $b$) is more efficient than a simple cylindrical pillar (as in figure $a$).
$A$ pillar with a distributed shape at the ends provides a larger surface area for contact,which helps in distributing the load over a wider area,thereby reducing the stress (force per unit area) and increasing the load-bearing capacity of the structure.
Conversely,a pillar with rounded or narrow ends supports less load because the stress concentration is higher at the contact points.