1965

Gateway Arch in St. Louis

Eero Saarinen (1910–1961), Hannskarel Bandel (1925–1993)

Both sides of the Gateway Arch in St. Louis, MO, were built independently, as freestanding towers. Before they were connected, each stood 630 feet (192 meters) in the air with a thin gap separating them. The topmost piece of the arch was 8 feet (2.4 meters) wide, but the sun baked the structure and there was only a 2-foot (0.6 meters) gap due to expansion. The architect who designed the arch, Eero Saarinen, and the engineers, lead by structural engineer Hannskarel Bandel, anticipated this very situation. A huge hydraulic jack sat atop the arch to create one million pounds of gap-widening force. The jack jammed the cavity open and the final piece slid perfectly into place. The alignment had a precision of less than half a millimeter.

The Gateway Arch, completed in 1965, is a world-renowned engineering achievement. No other stainless steel monument in the world is taller. And it’s a timeless beauty—a perfect gleaming curve that could last for millennia and still look just as stunning.

Making the arch strong enough to withstand earthquakes and tornadoes, capacious enough to hold one hundred visitors in the observation deck, and hollow enough to house the strangest elevator in the world are just three of the major challenges engineers faced on this project. The arch starts deep underground in the form of two massive 60-foot-tall (18.3 meters) cast concrete blocks embedded into the limestone bedrock on the site. These blocks weigh 52 million pounds (24 million kg) each. On these engineered foundation blocks, the arch begins with a hollow stainless steel triangle measuring 54 feet (16.5 meters) on each side. The arch tapers smoothly so that the topmost triangle measures 17 feet (5.2 meters) on each side.

Tourists need to get to the observation deck quickly because more than a million a year want to take in the view. How do engineers create an elevator that is vertical at the bottom and horizontal at the top? They make the elevator cars cylindrical like the drum of a clothes dryer and let the cars rotate as they move up the arch to keep the seats horizontal. Every part of this arch is impressive.

SEE ALSO Leaning Tower of Pisa (1372), Elevator (1861), Empire State Building (1931), Burj Khalifa (2010).

Close-up view of the Gateway Arch, the symbolic gateway to the West (although there’s a great deal of Midwest to go before the West is reached).