A box girder is a type of structural beam that has a hollow rectangular or square cross-section. It is commonly used in bridges and buildings due to its high strength-to-weight ratio, allowing it to support heavy loads while minimizing material use. The design helps distribute forces evenly, making it an efficient choice for various construction applications. Box girders can be made from different materials, including steel, concrete, or a combination of both. They are often used in cantilever and suspension bridges, where their structural integrity is crucial for safety and stability. Their versatility makes them a popular choice in modern engineering.