04/15/2026
Right here in our own backyard stands one of the most remarkable structural engineering feats in American history β the Gateway Arch in St. Louis, Missouri.
At 630 feet tall, it's the tallest arch in the world, and building it required solving a puzzle that had never been solved before.
The Arch is a catenary curve, which is the natural shape a hanging chain makes when suspended from two ends. Architect Eero Saarinen chose this form because it's structurally ideal, the shape distributes weight efficiently down to the foundation. The legs are hollow, triangular stainless steel tubes that get smaller as they rise, going from 54 feet wide at the base to just 17 feet at the top.
Here's the incredible part: the two legs were built simultaneously from the ground up on opposite sides of the arch β with no connection between them until the very last piece, the keystone section, was set in place on October 28, 1965. The margin of error for the two legs to align perfectly at the top? Just 1/64th of an inch.
But on the morning of the final placement, there was a problem. A warm day had caused the south leg to expand from the heat, closing the gap at the top by several inches, not enough room to fit the keystone. Workers had to grab fire hoses and spray down the south leg to cool the steel and make it contract just enough. It worked, and the keystone slid into place.
It took precision surveying, advanced structural calculations, and an engineering team that refused to accept "close enough."
As an engineering firm right here in Missouri, stories like this one remind us why we love what we do.