Tuesday, November 18, 2014

Wind Load - Structural Design

1  Wind load on gabled building
2  Wind load on dome or vault
3  Protected buildings inside a city
4  Exposed tall building inside a city
5  Wind flow around and above exposed building
6  Wind speed amplified by building configuration

Wind channeled between buildings causes a Venturi effect of increased wind speed.  Air movement through buildings causes internal pressure that effects curtain walls and cladding design.  Internal pressure has a balloon-like effect, acting outward if the wind enters primarily on the windward side.  Openings on leeward or side walls cause inward pressure.  In tall buildings with fixed curtain wall the difference between outside wind pressure and interior pressure causes air movement from high pressure to low pressure. 

This causes air infiltration on the windward side and outflow on the leeward side.  In high-rise buildings, warm air moving from lower to upper levels causes pressures at top levels on the leeward face and negative suction on lower levels.  Wind pressure is based on the equation developed by Daniel Bernoulli (1700-1782).   For steady air flow of velocity V, the velocity pressure, q, on a rigid body is

q = pV^2 / 2
p = air density   (air weight divided by the acceleration of gravity g = 32.2 ft/sec2)
Air of 15°C at sea level weighs 0.0765 Ib/ft
3, which yields:
q = 0.00256V^2   (q in psf)

The American National Standards Institute (ANSI) Minimum design loads for buildings and other structures  (ANSI A58.1 - 1982), converted dynamic pressure to velocity pressure qz (psf) at height z as

Wind Load

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