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
= combined height, exposure and gust factor coefficient.
= pressure coefficient for the structure or portion of structure
= importance factor.
design wind pressure.
qs = wind stagnation pressure at the standard height of 33
feet (10 000 mm).
coefficient varies significantly and highly depends on the roof shape and
the windward or leeward side of the roof.