What Forces Are Exerted on a Bridge?
- Sometimes called a "probabilistic load" or an "imposed load," this refers to the vehicles, animals or humans crossing or expected to be crossing the bridge. This helps determine how a bridge should be constructed, both in materials and engineering design. For example, many short, stout, wooden pier bridges can be crossed by light vehicles, but not 18-wheelers, because that bridge design has a low live load capacity.
- The dead load, also called the "construction load" or "permanent load," is the weight of the bridge itself. The forces of gravity are counteracted by the supports of the bridge, whether by arches, piers, cantilevers or suspension cables, and this force determines how long and wide a bridge can extend. Maintenance is required to mitigate the effects of wear and settling of the materials.
- A dynamic load, sometimes called a "displacement load," refers to extreme loads caused by extenuating circumstances, such as high winds from a storm, earthquakes, huge waves and unexpected impacts. Many huge bridges are designed with these in mind, like suspension bridges, which can resist very high winds and earthquakes.
- The environmental load refers to constant exposure to the elements in the environment, such as heat, wind, erosion, rust and stress. Many road construction materials expand and contract due to the heat and humidity, causing cracks, pits and potholes in the road surface. The supporting materials of a bridge may be susceptible to erosion and rust; this is the reason the Golden Gate Bridge is frequently repainted.
