How do you ensure a 324,000-pound dome will fit atop a cathedral? You build it twice.

The chance to help erect a structure like the signature copper dome atop the soaring Holy Name of Jesus Cathedral might come along once in a lucky builder’s life.

Harry L. McKinney helped build it twice.

McKinney, director of virtual design and construction for Clancy & Theys, the general contractor on the cathedral, used three-dimensional design software to “build” the architect’s design for the dome, testing the two-dimensional drawings in virtual form to make sure they would work when crafted of steel and Sheetrock. McKinney was one of the first people in his field to embrace the technology, and was recruited to Clancy & Theys a decade ago.

Baker Glasgow, vice president of construction for the company, said 3D modeling saves time and money on a project by revealing problems when they’re easiest to correct: before materials are purchased and construction is underway.

“Virtual design helps prevent problems in the field,” McKinney said, and reduces surprises.

Builders hate surprises.

“There was one major challenge, McKinney said, when his team began modeling the dome, which rises to a point 171 feet above the ground. While the architect had provided a schematic design for the system of ladders, platforms and catwalks required to give workers access to the dome once it was completed, the construction team needed to use 3D modeling to develop the final design. “It was tricky,” McKinney said, providing access to the lights and sprinkler system in the dome. The hardest ones were the ladders that had to be squeezed in between the dome’s vast vertical windows.

The team built the virtual model out to the finest detail, down to the bolts that fasten the steel framing together into a perfect birdcage.

Armed with the models, builders then put together the real structure. They built it on the ground, using ladders and lifts instead of sky-high scaffolds, while work in the rest of the cathedral building continued uninterrupted. To fit onto the existing construction, four subcontractors had to work to exacting standards, with a margin of error of less than a half-inch.

Parts of the cathedral

 

×

 

Move your cursor over the floor plan for Holy Name of Jesus Cathedral and click to view images and descriptions.

Source: Holy Name of Jesus Cathedral

What took masons decades to do on the cathedrals of Europe in the 1200s was completed by modern tradesmen in 20 months.

When it was finished, the team added temporary steel bracing so the 324,000-pound, 65-foot-tall dome could be lifted into place without buckling. The 162-ton load was hoisted by a crane and set into place. Glasgow said the company had blocked out four hours for the job. It took 30 minutes.

“And it will last,” McKinney said, “for hundreds of years.”

This story was originally published July 26, 2017 at 9:44 AM with the headline "How do you ensure a 324,000-pound dome will fit atop a cathedral? You build it twice.."