Is the Gateway Arch a Parabola?

The Gateway Arch, or Gateway to the West, is part of the Jefferson National Expansion Memorial in St. Louis, Missouri.

Built as a monument to the westward expansion of the United States, the arch has become the iconic image of St. Louis. It typifies "the pioneer spirit of the men and women who won the West, and those of a latter day to strive on other frontiers". At 630 feet (192 m), it is the tallest man-made monument in the United States, and Missouri's tallest accessible building. Located on the west bank of the Mississippi River.

Why do they use the parabola shape for bridges ?

The arch helps transfer force to the outside of the bridge so that the abutments can support it.

Comparing our parabola to the photo, we can see (especially near the waterline at the bottom) the shape of the arch is not really a parabola at all. The designer of the Gateway Arch, Eero Saarinen, knew that a parabola was not the best shape for such an arch. An arch shape that is often used is the catenary. The Gateway Arch is also the largest architectural structure designed as a weighted or flattened catenary arch.

So, the Gateway Arch is not a parabola. It is a catenary arch!!!