Cyclone wind loads
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WIND LOADS DURING A CYCLONE

Wind loads during a cyclone, named a Hurricane in the Caribbean, or a cyclone, named a Typhoon in the seas of Asia,  are enormous and can be devastating.  A mature Hurricane or Typhoon consists of bands of thunderclouds. Hurricanes (only occurring at the Northern Hemisphere) spiral in counter clockwise direction around the center (eye) of the storm. Typhoons (only occurring at the Southern Hemisphere) rotate in clock wise direction. The wind speeds are highest in the eye. The whole storm can consist of hundreds of thunderstorms and measure up to 1000 kilometers in diameter. To qualify as a Hurricane or Typhoon, a storm must produce winds of over 33 meters per second (193 Mph or 119 Km/h).

The wind loads in the Hurricane or Typhoon belt depend on the Saffir-Simpson scale in which category such storm is assigned. A category 5 storm may well reach a devastating wind speed of 155 Mph (252 km/h). In accordance with the IBC 2006, the highest basic wind speed may occur at the Southern Hemisphere (Typhoon) measuring 170 Mph (276 Km/h). The Hurricanes in the Caribbean storm belt are mostly assigned to a maximum of a category 4 storm with a maximum speed of 145 Mph (235 Km/h). The Hawaiian islands  are assigned to category 2 with a maximum wind speed of 105 Mph. Recent scientific studies, however, reveal that the Hurricane and Typhoon wind forces will increase considerably during the next decennium due to global warming. In consequence and as per the scientific prediction we have arbitrarily increased the standard IBC wind loads with 10% for extra safety.

The formula for the determination of the basic wind load is given by P = Ce Cq qs Iw        

 Where:

Ce =     combined height, exposure and gust factor coefficient.

Cq =     pressure coefficient for the structure or portion of structure under consideration.

I=    importance factor.

P  =     design wind pressure.

         q=    wind stagnation pressure at the standard height of 33 feet (10 000 mm).

The Cq coefficient varies significantly and highly depends on the roof shape and the windward or leeward side of the roof.

 

 

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Last modified: September 20, 2013
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