Transcript THE BUILDING ENVELOPE: Lecture 5

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
ASCE 7-02 METHOD 1: LOW-RISE BUILDING
Commercial Building Data
15’-0”
ASCE 7-02 METHOD 1: LOW-RISE BUILDING
Zone
(Fig. 6-3)
Roof Zone 1
Roof Zone 2
Roof Zone 3
Component
(from bldg.
geometry)
Effective Wind Area1
Roof Joist
30 ft x 30/3 ft = 300 sq ft
Net Pressure
(Fig. 6-3;
V = 130 mph)
psf
+9.8 -27.8
Adj. Fact.
(Table in
Fig. 6-2)2
Design
Pressure
psf
1.21
+11.9
-33.6
Roof Panel
2 ft x 5 ft = 10 sq ft
+12.4 -30.4
1.21
+15.0
-36.8
Roof Joist
30 ft x 30/3 ft = 300 sq ft
+9.8 -33.0
1.21
+11.9
-39.9
Roof Panel
2 ft x 5 ft = 10 sq ft
+12.4 -51.0
1.21
+15.0
-61.7
Roof Joist
30 ft x 30/3 ft = 300 sq ft
+9.8 -33.0
1.21
+11.9
-39.9
Roof Panel
2 ft x 5 ft = 10 sq ft
+12.4 -76.8
1.21
+15.0
-92.9
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
ASCE 7-02 METHOD 2: OFFICE BUILDING
Determine design pressures for windows on a 16-story office
building near Houston, Texas
160
ft
100
ft
200
ft
ASCE 7-02 METHOD 2: OFFICE BUILDING
Building Conditions:
•
•
•
•
•
•
Topography:
Terrain:
Height:
Classification:
Openings
Velocity
Flat
Open; no gravel roofs with 1500 ft
160 ft
Category II
Windows, 10 sq ft in area
120 mph
ASCE 7-02 METHOD 2: OFFICE BUILDING
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 = 1.0
G = gust effects
C = building geometry
ASCE 7-02 METHOD 2: OFFICE BUILDING
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 V2 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 ft
Kz = 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)
ASCE 7-02 METHOD 2: OFFICE BUILDING
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 V2 I
qz = 0.00256 Kz (1.0)(0.85)(120)2(1.0) = 31.3 Kz
and
p = qz (0.9) - qi(-0.18) = qz (0.9) + 7.9
ASCE 7-02 METHOD 2: OFFICE BUILDING
For side and leeward walls (wall corners, Zone 5) p is constant, top to
grade:
GCp = -1.80 for Zone 5 (ASCE 7-02 Fig. 6-17, area = 10 sq ft)
GCpi = +0.18 (positive internal pressure coefficient)
qi = qh = 0.00256(1.39)(1.0)(0.85)(120)2(1.0) = 43.6 psf
and
p = 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 to
grade:
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 psf
and
p = 43.6 (-0.9) - 43.6 (0.18) = -47.1psf (suction pressure)
ASCE 7-02 METHOD 2: OFFICE BUILDING
Component
Windows
(10 sq ft)
z
(ft)
Kz
Design Pressures (psf)
(ASCE 7- Windward Zone 4
Zone 5
02, Table Wall (4&5)
6-3)
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
160
1.39
47.1
-47.1
-86.3
ASCE 7-02 METHOD 3: OFFICE BUILDING
Leighton Cochran will provide a
illustration of design wind speeds for
cladding derived from wind tunnel
studies