To help clear up any confusion when I talk about the “efficiency” or “efficiency score” of the bridges I build. This is a mathematical equation to determine how well a bridge performed.

Simply take the mass that the bridge held, and divide that by the mass of the bridge.

Mass held
________ = Efficiency

Mass of bridge

Some confusion comes up when I weigh the bridge in grams while add weight to the bridge in pounds. These units do not have the same base, and cannot be divided against each other. I usually convert pounds to kilograms (1kg = 2.2 pounds) and then multiply the number of kilograms by 1000 to get grams.

So if my bridge held 54 pounds, I would convert that to kilograms. 54 pounds equals 24.54 kilograms. That equals 24540 grams.

To get the efficiency, I take 24540 and divide that by the mass of the bridge, which was, say, 33 grams. The efficiency score is then 744.

Arch: A structure that is curved and carries weight in a vertical manner primarily by using x-axis compression.

Beam: Horizontal structures that hold a vertical weight while not bending. Girders are multiple beams placed together and are usually the foundation of a truss.

Bridge: A structure used in aiding humans and animals in transportation over gaps, rivers, etc.

Column: The part of a bridge that connects the footing to the bottom of the bridge’s deck.

Deck: The surface of a truss or bridge that people or things drive and walk across.

Fixed Arch: A structure that is permanently in a single area/position.

Footing: The part of a bridge that is under ground level.

Member: A part in a structure, most especially a truss.

Portal: The open ends on a Through Truss, a.k.a the entrance.

Span: The length in between the inner edges of two of the “legs” of a structure.

Strut: A member that is compressive.

Substructure: Bridge parts below deck.

Superstructure: Bridge parts deck and above.

Suspenders: Tension members on the cable from the main cable to the deck of a suspension bridge.

Tie: Tension member of a truss.

Tower: A large frame holding the cables of a suspension bridge.

Truss: A stronger form of a beam or girder made with a web of members.

I hope this helps you build and describe your bridges for your classmates, students, and/or professors. Happy building everybody! If there is any other term that you don’t understand, post a comment and I will attempt to define it for you.

Example of a real pony truss bridge:

Any truss bridge can be a pony truss. But not many are being made anymore (if any?), so chances are small that you will actually see one. Thanks to Historic Bridges of Iowa for this tip.