47.5 MB - The Whole Building Design Guide

The Saffir-Simpson Hurricane Scale is basedon measurements of sustained wind speedsin hurricanes; these measurements aretaken over open water. The wind speedsdescribed in the Saffir-Simpson HurricaneScale are used to prepare storm responseactions and are not intended to be usedfor building design. Design wind loads onbuildings should be determined using thebasic wind speeds given in ASCE 7.Hurricane: This is a system of spiraling winds converging withincreasing speed toward the storm’s center (the eye of the hurricane).Hurricanes form over warm ocean waters. The diameterof the storm varies and can be between 50 and 600 miles. A hurricane’sforward movement (translational speed) can vary betweenapproximately 5 miles per hour (mph) tomore than 25 mph. Besides being capableof delivering extremely strong winds for severalhours and moderately strong winds for aday or more, many hurricanes also bring veryheavy rainfall. Hurricanes also occasionallyspawn tornadoes. The Saffir-Simpson HurricaneScale (see Table 3-1) categorizes theintensity of hurricanes. The five-step scaleranges from Category 1 (the weakest) to Category5 (the strongest). Hurricane-proneregions are defined in Section 3.1.3.Of all the storm types, hurricanes have thegreatest potential for devastating a large geographical area and,hence, affect the greatest number of people. The terms “hurricane,”“cyclone,” and “typhoon” describe the same type of storm.The term used depends on the region of the world where thestorm occurs. See Figure 3-1 for hurricane-prone regions.Table 3-1: Saffir-Simpson Hurricane ScaleStrength Sustained Wind Speed (mph)* Gust Wind Speed (mph)** Pressure (millibar)Category 1 74-95 89-116 >980Category 2 96-110 117-134 965-979Category 3 111-130 135-159 945-964Category 4 131-155 160-189 920-944Category 5 >155 >189