A girder is a large, strong beam used to support the weight of a building, bridge, or other structure. Girders are typically made of steel or concrete and form the skeleton that holds everything up. When you see construction workers high above the ground walking on thick metal beams, those are often girders.

In a bridge, girders span from one support column to another, carrying the weight of the road deck and all the vehicles crossing it. In a skyscraper, girders form a framework that supports each floor. They're engineered to handle enormous weight without bending or breaking.

Engineers carefully calculate how thick and long girders need to be, based on the weight they'll carry.