In the design of buildings, loads caused by gravity, wind, and earthquake must be considered by the structural designer. Gravity loads, both dead and live, are always present but somewhat variable and hard to forecast because of lack of knowledge about extremes and are considered to be the most important loads. Wind load is less easy to predict and is subject to wide variation, including the extremes caused by hurricanes and tornados. Earthquake loads, also subject to extremes, are infrequent at any given location. How-ever, the designer recognizes that all three of these load effects must be provided for in the design.

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