Iowa State Capitol Building: The Making of the Golden Dome

The Iowa capitol building’s dome is more than just gold. A dome gets its stability from the arches it's composed of. Steel beams fan out from the peak to form a three dimensional arch system. Lean more about the dome in this special segment from Iowa PBS’s This Old Statehouse project.


Transcript

Narrator: On of the largest gilded domes in the United States is right here in Iowa. Eighty feet in diameter at its base, The state capital’s gold gover dome rises to a height of two-hundred seventy-five feet. Visible for miles, the twenty-three karet main dome beckens both natives and visitors alike to the center of Iowa’s capital city. Something this alluring deserves a closer look.

Scott Allen, Architect: The inner dome is aluminum leaf and it has an amber shellac on it.  It gives an appearance of a gold, but it has more of a rich almost an aged gold appearance.

Narrator: A recently restored banner commemorating the Civil War hovers just below an oil rendition of an Iowa sky. The sky and everything else would come tumbling down if it weren’t for the brick and steel behind the scenes.

Scott Allen, Architect: In order for that brick to be constructed there had to be some fore work that occurred between the two steel beams. When that steel beam was in place and the bricks between those beams were in place, they could then remove that fore work; but until that last piece was put in place like a keystone, it had to remain there until they could move it to the next section.

Narrator: A dome gets its stability from the arches it’s composed of. Like the legs of a giant spider, steel beams fan out from the peak. They and the bricks they support form a three dimensional arch system.

Scott Allen, Architect: All those forces that are coming down vertically and pushing out horizontally on that dome are being taken care of by the buttresses on the drum of the dome. That’s why we have the thick walls on this building.

Narrator: The dome itself is only two brick layers thick, but the walls eventually swell to six feet at the point they meet the buttresses. The combined mass of all that masonry is what helps keep the dome from collapsing

Scott Allen, Architect: We do have some photographs during construction. There’s a beam and a post coming out of the center of both of those structures and then cable coming of the side of those.  From a construction standpoint, they look like they literally lifted up portions of the building from the interior of the building through the center and then placed it on the dome. It was a very extensive process compared to what we have now. We have technology that can lift a beam over the top of the building, but I think back then most of the stones were brought through the building


Excerpt from "This Old Statehouse DVD Special Features," Produced by Iowa PBS, 2001