-Wind pressures are higher on a tall building compared to a short one. -Exposure classification of a site: -Wind speed and pressure in an open field compared to a densely built-up area. -Building sites classified into 3 types, based on roughness of ground ( exposure category ) -B, C, and D. -B: urban, suburban, or wooded area with severally obstructions. -C: terrains with scattered obstructions involving heights less than 30ft. -D: flat, unobstructed ground facing a large body of water. (wind pressures highest here) -Enclosure classification of the building: -Interior of building is always subjected to some internal pressure. -Buildings with large “ballooning” effect are called partially enclosed buildings . -Building not partially enclosed is called an enclosed building. - Most buildings are enclosed. -Partially enclosed building is subjected to greater wind pressure than enclosed. 3.6 Roof Snow Load -Snow load expressed in terms of horizontal projected area of the roof. Factors that Affect Roof Snow Load - Ground snow load at the location. - Roof slope : greater the slope, smaller snow load. - Wind exposure classification of the site (Exposure B, C, D) D = lowest snow load. - Warm roof or cold roof. - Risk category of building's occupancy : above-average risk occupancies are designed for greater snow loads. 3.7 Earthquake Load -Fracturing, or slippages of tectonic plates produce shock wave called seismic motion . -Where the fracture occurs is the fault.
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- Spring '09
- loads, wind pressure