LSU Building Envelope Lecture 5 - Wind 10-03

8/13/2019 LSU Building Envelope Lecture 5 - Wind 10-03

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THE BUILDING ENVELOPE: Lecture 5

Analysis of Wind Loads:

ASCE 7-02 Method 1: Simplified

ASCE 7-02 Method 2: Analytical

ASCE 7-02 Method 3: Wind Tunnel


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ASCE 7-02 METHOD 1: LOW-RISE BUILDING

Zone(Fig. 6-3)

Component(from bldg.geometry)

Effective Wind Area1 Net Pressure(Fig. 6-3;

V = 130 mph)psf

Adj. Fact.(Table inFig. 6-2)2

DesignPressure

psf

Roof Joist 30 ft x 30/3 ft = 300 sq ft +9.8 -27.8 1.21 +11.9 -33.6Roof Zone 1

Roof Panel 2 ft x 5 ft = 10 sq ft +12.4 -30.4 1.21 +15.0 -36.8





Wall Zone 4 Window 10 sq ft +30.4 -33.0 1.21 +36.8 -39.9

Wall Zone 5 Window 10 sq ft +30.4 -40.7 1.21 +36.8 -49.3


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ASCE 7-02 METHOD 2: OFFICE BUILDING

Determine design pressures for windows on a 16-story office

building near Houston, Texas

200

ft100

ft

160

ft


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Building Conditions: Topography: Flat

Terrain: Open; no gravel roofs with 1500 ft Height: 160 ft

Classification: Category II

Openings Windows, 10 sq ft in area

Velocity 120 mph


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Factors affecting wind pressure:

Kz= terrain factor at elevation z

Kzt= topography factor = 1.0

Kd = directionality factor = 0.85

V = design wind velocity = 120 mph

I = importance factor = 1.0G = gust effects

C = building geometry


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p = q(GCp) qi(GCpi) (psf) (from ASCE 7-02, Section 6.5.12.4.2)

where: q= 0.00256 Kz Kzt Kd V2 I

for windward wall: q = qz= 0.00256 Kz Kzt Kd V

2

I (q varies with z)for side and leeward walls: q = qh= 0.00256 Kh Kzt Kd V2 I (q at h)

qi = internal dynamic pressure = qh= velocity pressure at h = 160 ftKz= terrain factor at elevation z (K varies with z; ASCE 7-02, Table 6-3)Kh= terrain factor at top of building = 1.39 at 160 ft (Table 6-3, Exp. C)Kzt= topography factor = 1.0 for flat topography (ASCE 7-02, Sec. 6.5.7)

Kd = directionality factor = 0.85 for buildings (ASCE 7-02, Sec. 6.5.4.4)V = design wind velocity = 120 mph (from local building code)I = importance factor = 1.0 for Building Classification II (office) (ASCE

7-02, Table 6-1)


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For windward wall windows p varies with elevation z:

GCp= +0.9 (positive from ASCE 7-02, Fig. 6-17)GCpi = -0.18 (internal pressure coefficient, ASCE 7-02, Fig. 6-5,enclosed)qz= 0.00256 Kz Kzt Kd V

2 Iqz= 0.00256 Kz (1.0)(0.85)(120)

2(1.0) = 31.3 Kzandp = qz (0.9) - qi(-0.18) = qz (0.9) + 7.9


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For side and leeward walls (wall corners, Zone 5) p is constant, top tograde:

GCp= -1.80 for Zone 5 (ASCE 7-02 Fig. 6-17, area = 10 sq ft)GC

pi= +0.18 (positive internal pressure coefficient)

qi = qh= 0.00256(1.39)(1.0)(0.85)(120)2(1.0) = 43.6 psf

andp = 43.6 (-1.80) - 43.6 (0.18) = -86.3 psf (suction pressure)

For side and leeward walls (wall interior; Zone 4) p is constant, top tograde:

GCp= -0.9 for Zone (ASCE 7-02 Fig. 6-17, area = 10 sq ft)GCpi= 0.18 (internal pressure coefficient (ASCE 7-02, Fig. 6-5,enclosed)qi = qh= 0.00256(1.39)(1.0)(0.85)(120)

2(1.0) = 43.6 psfandp = 43.6 (-0.9) - 43.6 (0.18) = -47.1psf (suction pressure)


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Design Pressures (psf)Component z(ft)

Kz(ASCE 7-02, Table

6-3)

WindwardWall (4&5)

Zone 4 Zone 5

15 0.85 31.8 -47.1 -86.3

30 0.98 35.5 -47.1 -86.3

50 1.09 38.6 -47.1 -86.3

80 1.21 42.0 -47.1 -86.3

120 1.31 44.8 -47.1 -86.3

Windows(10 sq ft)

160 1.39 47.1 -47.1 -86.3


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Leighton Cochran will provide a

illustration of design wind speeds for

cladding derived from wind tunnel

studies

Documents

LSU Building Envelope Lecture 5 - Wind 10-03