What the heck is an Orthotropic Deck and why is it so awesome?

Anyone working in engineering knows that their industry is constantly changing and molding to meet the innovative needs of consumers. In the heavy construction and civil engineering industry, equipment and material move on the demands of safety and cost. The result is usually creative and (sometimes) odd-looking.

A fairly new bridge building method requires the use of something called an orthotropic deck. Before you close out of this page thinking, “this is too technical for me”, consider an object you use everyday but take for granted. A piece of cardboard. Ever wonder why some cardboard is shaped like this?

corrugated-cardboard-packaging

Notice the “U” shaped pieces inside the slab? That’s an engineering technique making the structure orthotropic, or as Wikipedia would like to define it –

An orthotropic material has three mutually orthogonal twofold axes of rotational symmetry so that its material properties are, in general, different along each axis.

What makes this kind of structure so difficult to bend (and why it’s used in lots of packaging) is because of that precise U-shaped orthotropic design. The ribbed shape makes it easy to bend horizontally, but difficult to bend longitudinally. You can even try this at home. Take a flat piece of paper and apply weight to it over a hollow surface. Naturally, it’s going to bend or rip. But trip ribbing the paper like you see in the photo above by folding it in a U-shape and suddenly it can hold a lot more weight.

Bridges today are using the same method to carry the weight on their decks. Orthotropic decks are engineered to contain these rib-like structures under a flat surface longitudinally. This design is far more cost effective than pouring tons of concrete and reinforcing concrete slabs with even more steel (rebar). Instead, orthotropic decks are fairly hollow on the inside and make bridge decks lighter – meaning there is less tension on bridge suspensions, too. Here’s what an orthotropic deck on a bridge looks like in fabrication:

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Notice how the bottom of the deck looks incredibly similar to the cardboard photo above? When fabrication is complete and the deck panel is ready to be placed on the bridge, it usually looks something like this:

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Lots of bridges today use orthotropic decks. The Golden Gate Bridge (California), Millau Viaduct (France), and Akashi Kaikyō Bridge (Japan) are some of the most famous structures using orthotropic decks. In the New York City area, the Verrazano and Wittpenn bridges are also getting orthotropic upgrades.

If you want to learn more about orthotropic bridge decks, click here or read this academic article on the science behind it here.