There are large, short pillars that extend up through the roof. They look like they would be strong enough to support the additional weight since the building was designed for it. The economics of adding to the building is another matter.
While we're on that subject, and in the interest of promoting thread drift, I remember when the OneOK building was announced it had 60 stories, then was cut back to the present thirty back when Cities Service was building it. This would be sometime in late 1980 or early 1981, and I think the decision to downsize was made after construction began. Does anyone know if the building's structure would support the additional 30 stories per the original design?
"Originally designed to be 52 stories, and then reduced to 37, the plans were modified to the present height of 17 floors after the building was sold during construction"
"ONEOK bought the Cities Service Company (later renamed Citgo) in August, 1982" The "OneOK building" is actually the Cities Service Company building... under construction when OneOK bought them...
I do know that enough granite was ordered to complete the 37-floor version of the building.
Here's some OneOK granite on S Lewis
http://goo.gl/maps/jsab