Wind Design
TERMINOLOGIES USED
STRUCTURE CATEGORY
Buildings and structures that represent a low hazard to human life in the event of failure
Category I
All buildings not covered by the other 3 categories
Category II
Buildings and other structures containing sufficient quantities of toxic or explosive substances to be dangerous to the public if released....REFINERIES
Buildings or structures where the primary occupancy is one in which more than 300 people congregate in one area
Schools, non-emergency health care facilities, jails, non-essential power stations
Category III
Essential facilities
Category IV
EXPOSURE CATEGORY
The following ground roughness exposure categories are considered and defined in ASCE 7-95 Section 6.5.3.1:
Exposure A: Centers of large cities.
Exposure B: Urban and suburban areas, towns, city outskirts, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single family dwellings or larger.
Exposure C: Open terrain with scattered obstructions having heights generally less than 30 ft (9.1 m).
Exposure D: Flat, unobstructed coastal areas directly exposed to wind blowing over open water; applicable for structures within distance from shoreline of 15OOft or 10 times the structure height.
SHAPE FACTOR (Cf )
GUST RESPONSE FACTOR (G)
IMPORTANCE FACTOR (I)
TOPOGRAPHIC FACTOR (Kzt)
VELOCITY PRESSURE EXPOSURE CO EFFICIENT (Kz)
PROCEDURE FOR CALCULATE DESIGN LONGITUDINAL WIND FORCE (FL):
Step 1:
Calculate projected area of vessel (Af)
Af = 3.142* R2
Step 2:
Find the structure category
Step 3:
Find the exposure category
Step 4:
Determine the following factors
shape factor value for vessel (Cf )
Determine Gust response factor (G)
Importance factor (I)
Topographic factor (Kzt)
Velocity pressure exposure co efficient (Kz)
Step 5:
Calculate velocity pressure at height z above the ground (qz)
qz = 0.00256 X Kz X Kzt X V2 x I
Step 6:
Calculate Design longitudinal wind force (FL)
FL = qz X G X Cf X Af
PROCEDURE FOR CALCULATE DESIGN TRANSVERSE WIND FORCE (FL):
Step 1:
Calculate projected area of vessel (Af)
Af = Le X De
Step 2:
Find the structure category
Step 3:
Find the exposure category
Step 4:
Determine the following factors
shape factor value for vessel (Cf )
Determine Gust response factor (G)
Importance factor (I)
Topographic factor (Kzt)
Velocity pressure exposure co efficient (Kz)
Step 5:
Calculate velocity pressure at height z above the ground (qz)
qz = 0.00256 X Kz X Kzt X V2 x I
Step 6:
Calculate Design longitudinal wind force (FL)
FL = ( qz X G X Cf X Af ) X 0.5
Continue......