Live load, also known as imposed or variable load, refers to the temporary or movable loads that act on a structure during its intended use. Unlike dead loads, live loads are not permanent and can vary in magnitude and location. They represent the loads that a structure experiences from people, furniture, equipment, vehicles, or any other dynamic or transient sources.
Different types of live loads can be categorized based on their characteristics and sources. Here are some examples:
- Occupancy Load: This type of live load is associated with the number of people occupying a building or specific areas within it. The occupancy load depends on the function and intended use of the space. For example, in a commercial building, the occupancy load for a conference room or a theater would be determined by the number of people expected to be present. This load accounts for the weight of people, furniture, and any other movable objects.
- Storage Load: Storage loads are live loads resulting from the storage of materials, goods, or equipment within a structure. It includes the weight of stored items on floors, shelves, and racks. Warehouses, libraries, and retail stores are examples of structures where storage loads are a significant consideration in the design. The type and distribution of stored items influence the magnitude and location of the load.
- Vehicle Load: Vehicle loads are live loads caused by the presence of vehicles or mobile equipment on a structure. This includes the weight of cars, trucks, buses, forklifts, and any other vehicles that might access the structure. Bridges, parking garages, and roadways are examples of structures that must consider the impact of vehicle loads.
- Wind Load: While wind is not a permanent load, it is considered a live load as it is a dynamic force that acts on a structure. Wind loads vary with wind speed, direction, and the shape and orientation of the structure. The magnitude of the wind load depends on the design wind speed specified by local building codes. Structural engineers analyze the wind effects on a building and design it to withstand these loads.
- Snow Load: In regions with cold climates, snow loads are a significant consideration. Snow loads are live loads resulting from the weight of snow accumulated on a structure. The magnitude of the snow load depends on factors such as snowfall rates, snow density, and the design snow load specified in local building codes. Roofs, awnings, and other horizontal surfaces are particularly susceptible to snow loads.
It’s important to note that live loads are not constant and can change over time depending on the occupancy, usage, or environmental conditions. Proper consideration of live loads is crucial in the design and construction of structures to ensure they can safely support the expected loads and maintain structural integrity.
