Parabolic arches

A parabolic arch is an arch shaped like a parabola. Such arches are used in bridges, cathedrals, and elsewhere in architecture and engineering.

While a parabolic arch may resemble a catenary arch, a parabola is a quadratic function while a catenary is the hyperbolic cosine, cosh(x), a sum of two exponential functions.

Unlike a catenary arch, the parabolic arch employs the principle that when weight is uniformly applied above, the internal compression (see line of thrust) resulting from that weight will follow a parabolic curve. Of all arch types, the parabolic arch produces the most thrust at the base. Also, it can span the widest area. It is commonly used in bridge design, where long spans are needed.

When an arch carries a uniformly distributed vertical load, the correct shape is a parabola. When an arch carries only its own weight, the best shape is a catenary.

Parabola (red) graphed against a catenary (blue), view to simulate an arch.

Parabola (red) graphed against a catenary (blue), view to simulate an arch. Zoomed out.

A hen's egg can be fairly well described as two different paraboloids connected by part of an ellipse.

A few examples of parabolic arches.:

Oscar Niemeyer used parabolic arches, and Antoni Gaudí was another well known architect who used both parabolic and catenary arches.

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