Low-rise Buildings - Wind Engineering - Lecture Slides, Slides of Environmental Law and Policy

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• Low-rise buildings : enclosed structures less than 50 feet (15 metres) in height
  • Immersed within aerodynamic roughness - high turbulence, shelter effects are important
  • Sustain most damage in severe wind storms
  • Extensive research on wind loads in 1970’s, 1980’s and 1990’s - wind tunnel and full scale
  • Wind loads on roofs are very important
  • Internal pressures are important - especially for dominant openings
  • Resonant effects are negligible

• Full scale studies
• Aylesbury Experimental Building, U.K. 1970-
  • Variable pitch roof (adjustable between 5 and 45 degrees)
  • Use for an international comparative wind tunnel experiment

• Full scale studies
• Texas Tech Field Experiment , U.S. 1987- now
  • Flat roof. Can be rotated on turntable.
  • High quality data on fluctuating local and area-averaged pressures

• General flow characteristics (0o^ to wall):

(movie by Shimizu Corporation, Tokyo, Japan)

• General flow characteristics (45o^ to wall):

(movie by Shimizu Corporation, Tokyo, Japan)

• General flow characteristics :

Four values of pressure coefficients :

2 a h

0 p ρ U 2

1 C  pp 2 a h

0 p ρ U 2

1 Cˆ^  pˆp 2 a h

0 p ρ U 2

1 C  p^ p 2 a h

2 p Cp ρ U 2

1

p C σ

   

Time

Cp (t)

C^ ˆp

Cp

C (^) p

Cp



• Mean pressure coefficients on pitched roofs :

5 o^ roof pitch :

5  roof pitch

wind tunnel

Cp = 1.

h/d = 0.

h/d = 1.

No separation at ridge. Higher negative pressures for greater h/d.

• Mean pressure coefficients on pitched roofs :

18 o^ roof pitch :

Pressure on windward face is less negative at lower h/d’s.

wind tunnel

Cp = 1.

h/d = 0.

h/d = 0.

h/d = 1.

18 

• Mean pressure coefficients on pitched roofs :

30 o^ roof pitch :

Positive pressure on upwind face of roof for lower h/d’s. Uniform negative pressure on downwind roof.

wind tunnel

Cp = 1.

h/d = 0.

h/d = 0.

h/d = 1.

30 

• Fluctuating and peak pressures at corners of roofs :

High negative pressure peaks (‘spikes’) near corners - associated with formation of conical vortices

0 3 6 9 12 15 Time (minutes)

Cp

2 0

• Fluctuating and peak pressures at corners of roofs :

Formation of conical vortices

30-60o

• Cladding loads on pitched roofs :

Largest minimum pressure coefficients for any wind direction :

-2.

-2.

-1.

-2. -1.

-5 -

-2 - 15 O

20 o

30 o

Gable end has highest minimum pressure coefficients

• Structural loads :

Calculate peak structural loads and effective static load distributions :

Instantaneous load around frame will vary in magnitude and distribution

Codes and standards give simplified uniform distributions on surfaces