Minimum design loads for buildings
The structural system of a building is designed to sustain or resist anticipated loads or forces the building may experience during its life in order to provide a reliably safe building structure. Engineers and architects use building codes, which have been developed based on statistical data, to aid designers with the basis of calculating the required loads. However, it cannot be overstated that the building designer must recognize the potential loads and apply them correctly for analysis. Typical loads imposed on a building are vertical loads, such as dead and live loads, and
lateral loads, such as wind and seismic and lateral earth pressures. Building structures experience many other additional loads such as loads due to thermal and hydrostatic forces. We will review these loads and others in more detail in Chapters 2, 3, 4, and 10. However, to understand loads, we want to discuss some of the basics about the loading of buildings. A building’s vertical loading is based on its intended use, the number of occupants and
the type of construction, and which are the building’s dead and live loads, respectively. Dead loads depend on the materials used to construct the building, and live loads are based on the anticipated occupants using the building. Loads are often applied in combination based on their likelihood of occurring simultaneously. Determining the appropriate load to use for structural analysis and design requires knowledge of the long and short duration loads. For example, a warehouse has a much higher ‰oor load than an of‡ce or a residential building because of the weight of the contents of the storage in the warehouse, contributing to its dead load, as compared to that of an of‡ce or a residential building, which generally has more occupants and therefore a higher live load. In this case, the storage is long term and the occupants are transient. Building codes take this into account and consider the appropriate statistical loading to be used in structural calculations. The type of materials and construction will also determine loading by altering the building’s weight or mass. A two-story steel and concrete building, for instance, is likely to be considerably heavier than a wood-framed building of the same size. However, an early circa 1900s masonry building with ‰at-arch ‰oor construction is heavier yet. The materials selected are consequential in determining the dead load of a building. A building’s location will dramatically affect its loading and consequentially its struc-
tural system also. A building located in Buffalo, New York, for instance, will experience much higher snow loads than a building in New York City due to the potential accumulations of lake-effect snowfall in the Great Lakes region of the United States. Similarly, a building located on the West Coast of the United States as compared to a building on the East Coast will experience much higher seismic loading due to a much more active ground motion on the West Coast. Or a building located near the coastline will experience higher
wind forces than a structure inland that is protected by surrounding buildings, trees, and other topographical characteristics. Wind rushing over a building with a gable roof, as shown in Figure 1.1, experiences wind
forces on all surfaces of the structure. Consequently, the building’s primary structural system or main wind force-resisting system is designed to resist these forces. In addition, various loads are applied in combination based on their likelihood of occurring simultaneously. The loads considered for the design of buildings are called minimum design loads and are
in accordance with local and national building codes. The International Building Code (IBC) references the “Minimum Design Loads for Buildings and Other Structures” published by the American Society of Civil Engineers (ASCE) and is the standard for determining applied loads on a building to be used for structural analysis and design.