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Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Calculation of Wind Loads
According to PR Building
Code 2011
Dr. Ricardo R. López Rodríguez,
Ph.D., P.E.
Professor of Civil Engineering
University of Puerto Rico at
Mayagüez, [email protected]
Earthquake Commission of CIAPR
1
Workshop on Vertical Shelter from Tsunamis
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012 2
Some slides taken and adapted from FEMA presentation
by Adam Reeder, PE, CFM from presentation
Wind Provisions of the 2009 International Building
Code and International Residential Code
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012 3
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
P646 on Wind Loading
4
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Agenda
• Wind effects on structures
• About the PR Building Code
• Wind Load Provisions for Buildings
Definitions and terms used in all Procedures
Alternative Procedures of Analysis
– Simplified
– Analytical (Low rise or high rise)
– Wind Tunnel
• Examples of calculation of horizontal wind pressures
• Cylindrical Structures
5
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Wind effects on structures
6
VIENTO
Rectangular Buildings
The wind generates pressure in windward wall and
suction in leeward wall, lateral walls, and part of the roof.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Internal Pressures
7
There is always some
internal pressure, unless
the building is completely
open. Partially enclosed
buildings have the highest
internal pressures.
It is important for doors and
windows to resist the wind
pressure and impact of
flying objects.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Effect of openings on internal pressure
Windward or leeward opening
8
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Wind effects on structures
9
Multistory Rectangular
Buildings
The wind generates
pressure in windward wall
and suction in leeward wall,
lateral walls, and part of the
roof.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
PR Building Code is Based on
International Codes
10
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Adoption Dates
11
March1, 2011
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
About the International Codes
The First Edition of the I-Codes was released in 2000
Input from five organizations which included:
• Building Officials and Code Administrators International,
Inc. (BOCA),
• International Conference of Building Officials (ICBO)
• Southern Building Code Congress International (SBCCI).
Intended to provide a comprehensive set of codes
New editions on a 3 year cycle
12
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Organization of the IBC
Chapter 1: Administration
Chapter 2: Definitions
Chapter 3: Use and Occupancy Classification
Chapter 5: General Building Heights and Areas
Chapter 6: Types of Construction
Chapter 14: Exterior Walls
Chapter 15: Roof Assemblies and Rooftop Structures
Wind Loads
13
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Organization of the IBC
Chapter 18: Soils and Foundations
Chapter 19: Concrete
Chapter 21: Masonry
Chapter 22: Steel
Chapter 24: Glass and Glazing
Chapter 25: Gypsum Board and Plaster
Chapter 34: Existing Structures
Chapter 35: Referenced Standards
Appendix H: Flood-Resistant Construction
14
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
What Code to Use – ASCE 7-05
15
PR Building Code 2011 refers the user to the International
Building Code 2009.
International Building Code 2009 refers the user to the
ASCE 7-05.
ASCE 7-05 contains the provisions for obtaining wind
pressures expected from hurricanes.
Use the wind pressures to calculate wind loads
Note: There is an ASCE 7-2010 code available. It is not the
currently mandated code for PR.
ASCE 7-2010 wind pressures differ from ASCE 7-05
pressures. (Earthquake loads also differ).
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
What code to use (2)
16
Once loads are obtained using ASCE 7-05, use the design
codes in accordance with the building material
For example, for design of reinforced concrete structures,
the IBC 09 has Chapter 19.
In PR the user is allowed to use ACI 318-08 =
American Concrete Institute Building Code and
Commentary.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Designing for Wind
Loads using the IBC
and ASCE 7-05
The primary source for
wind loads in the IBC
is ASCE 7. The
following is a
summary of important
aspects of ASCE 7-05.
17
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Wind-borne debris region
Portions of hurricane-prone regions
that are within 1 mile of the coastal
mean high water line where the
basic wind speed is 110 mph or
greater; or portions of hurricane-
prone regions where the basic wind
speed is 120 mph or greater
18
Definitions of Wind Related Terms in
the International Codes
Basic wind speed
Three-second gust speed at 33 ft above the ground in Exposure C –
145 mph for Puerto Rico (IBC Figure 1609)
The ASCE 7-1998 had 125 mph for PR.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Main vs Components
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Chapter 6: General Requirements
Basic parameters for determining wind loads:
• Basic wind speed, V, Figure 6-1 (Puerto Rico = 145 mph)
• Wind directionality factor, Kd , Section 6.5.4.4
• Importance Factor, I, Section 6.5.5
• Exposure category, Section 6.5.6
• Topographic factor, Kzt, Section 6.5.7
• Gust Effect Factor, G, Section 6.5.8
• Enclosure classification, Section 6.5.9
• Velocity Pressure, qz, Section 6.5.10
• Pressure coefficients, (GCp), Section 6.5.11
20
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Wind directionality factor, Kd
22
Structure Type Directionality Factor, Kd
Buildings
Main Wind Force Resisting System
Components and Cladding
0.85
0.85
Arched Roofs 0.85
Chimneys, Tanks and Similar Structures
Square
Hexagonal
Round
0.90
0.95
0.95
Solid Freestanding Walls and
Solid Freestanding and Attached Signs 0.85
Open Signs and Lattice Framework 0.85
Trussed Towers
Triangular, square, rectangular
All other cross sections
0.85
0.95
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Occupancy Category
23
I
Low hazard to human life in the event of failure, including but not limited to
• Agricultural facilities
• Certain temporary facilities
• Minor storage facilities
II Not category I, III or IV
III
Substantial hazard to human life in the event of failure, including but not
limited to
• Covered structures for public assembly (>300 occupants)
• Schools (>250 occupants)
• College and other adult-education buildings (>500 occupants)
• Heath care facilities, non-emergency (>50 resident patients)
• Jails and detention facilities
• Any other facility with occupant load >5000
• Public utility facilities not included in Category IV
IV
Essential facilities, including but not limited to
• Hospitals and other health care facilities having surgery or emergency
facilities
• Fire, rescue and police stations
• Emergency shelters and response centers
• Public utility facilities for emergency backup of other Category IV
structures
Definitions of Wind Related Terms in
the International Codes
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Table 6-1 Importance Factor
24
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Surface Roughness – based on topography, vegetation
and structures
25
Category B Terrain with numerous closely spaced obstructions
having the size of single-family dwellings
• Urban areas
• Suburban areas
• Wooded areas
Category C Open terrain with scattered obstructions having heights
generally less than 9144 mm
• Flat open country
• Grasslands
• Water surfaces in hurricane-prone regions
Category D Flat, unobstructed areas
• Smooth mud flats
• Salt flats
Definitions of Wind Related Terms in
the International Codes
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Exposure Category – based on Surface Roughness in the
upwind direction
26
Category B Applies where Surface Roughness category B prevails
in the upwind direction for at least 2,600 ft or 20 times the
building height, whichever is greater
Exception: Where roof height ≤ 30 ft, upwind distance
may be reduced to 1,500 ft.
Category C Not Category B or D
Category D Applies where Surface Roughness category D prevails
in the upwind direction for at least 5,000 ft or 20 times the
building height, whichever is greater
Definitions of Wind Related Terms in
the International Codes
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Exposure Categories
27
Exposure Category B
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Exposure Categories
28
Exposure
Category C
Exposure
Category D
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Exposure category
• Surface Roughness Category B, C or D
• Exposure Category B, C or D
• Wind Direction and Sectors
For each direction at which the wind loads are to be
evaluated, the exposure shall be determined for the two
upwind sectors extending 45° either side of the selected
wind direction.
The exposure resulting in the highest wind loads shall be
used to represent winds from that direction.
7-05 Does not use Exp. D in Hurricane Prone Coasts, 7-10 does
29
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Topographic factor, Kzt
Wind Speed-Up over Hills, Ridges and Escarpments
30
H Height of hill or escarpment relative to the upwind terrain, in meters.
Lh
Distance upwind of crest to where the difference in ground elevation is half the
height of hill or escarpment, in meters.
x Distance (upwind or downwind) from the crest to the building site, in meters.
z Height above ground surface at building site, in meters.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Topographic factor, Kzt
Wind speed-up effects shall be included in the design
when all of the following conditions are met:
31
1
The hill, ridge or escarpment is isolated and unobstructed upwind by other similar topographic
features of comparable height for 100 times the height of the topographic feature (100H) or 2
miles, whichever is less.
2 The hill, ridge or escarpment protrudes above the height of upwind terrain features within a 2 mile
radius in any quadrant by a factor of two or more.
3 The structure is located in the upper one-half of a hill or ridge or near the crest of an escarpment.
4 H/Lh ≥ 0.2.
5 H ≥ 4.5 m for Exposure C and D and H ≥ 18 m for Exposure B.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Topographic factor, Kzt
Wind Speed-Up over Hills, Ridges and Escarpments
Kzt = (1 + K1 K2 K3)2
32
K1
Factor to account for shape of
topographic feature and maximum
speed-up effect.
K2
Factor to account for reduction in
speed-up with distance upwind or
downwind of crest.
K3
Factor to account for reduction in
speed-up with height above local
terrain.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Topographic factor, Kzt
• K1 is determined using the table below
Factor to account for shape of topographic feature and
maximum speed-up effect.
33
Hill Shape
K1/(H/Lh)
Exposure
B C D
2-D Ridges
(or valleys with -
H) 1.30 1.45 1.55
2-D Escarpments 0.75 0.85 0.95
3-D Axisym. Hill 0.95 1.05 1.15
H
Height of hill or
escarpment relative to
the upwind terrain, in
meters.
Lh
Distance upwind of crest
to where the difference
in ground elevation is
half the height of hill or
escarpment, in meters.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Topographic factor, Kzt
• K2 = (1 - )
Factor to account for
reduction in speed-up with
distance upwind or
downwind of crest.
• K3 = e-γz/Lh
Factor to account for
reduction in speed-up with
height above local terrain.
34
hL
|x|
Lh
Distance upwind of crest to where the difference
in ground elevation is half the height of hill or
escarpment, in meters.
x Distance (upwind or downwind) from the crest to
the building site, in meters.
z Height above ground surface at building site, in
meters.
μ Horizontal attenuation factor.
γ Height attenuation factor.
Hill Shape γ
μ
Upwind of
Crest
Downwind
of Crest
2-D Ridges
(or valleys with -
H) 3 1.5 1.5
2-D Escarpments 2.5 1.5 4
3-D Axisym. Hill 4
1.5 1.5
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Topographic factor,
Kzt = (1 + K1 K2 K3)2
35
Notes:
1.Linear interpolation
between values is
permitted.
2.For H/Lh > 0.5,
assume H/Lh = 0.5 for
finding K1 and
substitute 2H for Lh for
finding K2 and K3. 3.Multipliers assume
wind approaches along
the direction of
maximum slope.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Gust Effect Factor, G
• G = 0.85 for rigid buildings and other structures
• G is determined by formula for flexible or dynamically
sensitive buildings or other structures
Flexible: natural frequency < 1
36
Note:
Where combined gust-effect factors and pressure
coefficients (GCp), (GCpi) and (GCpf) are given in figures
and tables, the gust-effect factor shall not be determined
separately.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Enclosure classification
37
Open
Ao ≥ 0.8Ag
Ao = total area of openings in a wall that receives positive
external pressure, in m2
Ag = gross area of that wall in which Ao is identified, in m2
Partially
Enclosed
• Ao > 1.10Aoi AND
• Ao > 0.37 m2 OR Ao > 0.01Ag (whichever is smaller) AND
• Aoi / Agi ≤ 0.20
Aoi = sum of the areas of openings in the building envelope
(walls and roof) not including Ao, in m2
Agi = sum of the gross surface areas of the building envelope
(walls and roof) not including Ag, in m2
Enclosed Not open or partially enclosed.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Velocity pressure qz
Velocity pressure
Factor Kz includes the effect of height
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 and 7-10 – Wind Loads
Internal Pressure Coefficient, (GCpi)
39
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Internal Pressure Coefficient, (GCpi)
40
Enclosure
Classification (GCpi)
Open 0.00
Partially Enclosed +0.55
-0.55
Enclosed +0.18
-0.18
Note:
Plus and minus signs
signify pressures acting
toward and away from
the internal surfaces,
respectively.
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Procedures for determining wind loads for Main Wind-
Force Resisting System (MWFRS)
41
Procedure Application Location
Simplified Procedure Low-rise buildings Section 6.4
Analytical Procedure
Buildings of all heights
Distinguish low rise and
High-rise
Section 6.5
Wind Tunnel Procedure All buildings and other
structures Section 6.6
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Simplified Procedure
MWFRS and C&C Simplified Procedure (Sec 6.4)
for Enclosed Low-Rise Buildings
• Applicability
Building has simple diaphragm and low-rise (h<60’)
Enclosed and meets WBD requirements
Building not classified as flexible
Building is not subject to the following:
– Across-wind loading
– Vortex shedding
– Instability due to galloping or flutter
– Channeling effects
– Buffeting in the wake of upwind obstructions
Building has a symmetrical cross section
Building exempted from torsional load cases
42
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
MWFRS and C&C Simple Procedure (Sec 6.4)
Enclosed Low-Rise Buildings
ASCE 7-05 – Wind Loads
Step 1 Basic wind speed, V Sec 6.5.4
Step 2 Importance Factor, I Sec 6.5.5
Step 3 Exposure Category Sec 6.5.6
Step 4 Height and Exposure Adjustment, λ Fig 6-2
Step 5 Design pressure at 30 ft ps30 shall be
determined Fig 6-2
Step 6 Topographic amplification factor calculated. Sec 6.5.7
Step 7
Wall and roof pressures calculated. Check
Minimum
Sec 6.4.2.1.1 or
Sec 6.4.2.2.1
43
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Fig 6-2 Simplified Procedure
44
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Simplified Method
Fig 6-2
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Fig 6-2 Simplified Design Wind
pressure ps30
47
p
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
𝒑𝒔 = 𝝺𝑲𝒛𝒕𝑰𝒑𝒔𝟑𝟎
Design pressure, Simplified Procedure
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Analytical Procedure
MWFRS and C&C Analytical Procedure (Sec 6.5) Enclosed, Partially Enclosed and Open Buildings of All Heights
• Applicability
Building is regular-shaped
Building is not subject to the following:
– Across-wind loading
– Vortex shedding
– Instability due to galloping or flutter
– Channeling effects
– Buffeting in the wake of upwind obstructions
49
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
MWFRS and C&C Analytical Procedure (Section 6.5) Enclosed, Partially Enclosed and Open Buildings of All Heights
50
Step 1 Basic wind speed, V, Kd Sec 6.5.4
Step 2 Importance Factor, I Sec 6.5.5
Step 3 Wind load parameters (Exposure and height Kz,
topographic effect, Gust factor, Enclosure)
Sec 6.5.6 thru
6.5.9
Step 4 Internal pressure coefficient, GCpi Sec 6.5.11.1
Step 5 External pressure coefficient, Cp Sec 6.5.11.2 or
6.5.11.3
Step 6 Velocity pressure qz Sec 6.5.10
Step 7 Design Wind Load, F Sec 6.5.12 thru
Sec 6.5.15
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
1. V and Kd (directionality)
2. Importance, I
3. Exposure and height, Kz, Kh
4. Topographic Effect
5. Gust effect G
6. Enclosure
7. Internal pressure GCpi
8. External Pressure Cp
9. Velocity pressure qz
10. Design wind load p
Analytical Method - Procedure
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Exposure Coefficient Kh and Kz
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Internal pressure coefficients
53
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Fig 6-6 Monoslope roof
External wall pressures
54
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Fig 6-6 Cp for Analytical Method
55
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Fig 6-10 Low-Rise Analytical Procedure
56
Wall pressures
Windward: 1, 1E
Leeward: 4, 4E
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Low Rise Force coefficients GCpf
57
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Velocity pressure and wall pressures
Velocity pressure
Wall pressure, analytical method
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Pressures for Analytical Procedure
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
ASCE 7-05 – Wind Loads
Wind Tunnel Procedure (Section 6.6)
• Permitted for any building or structure
• Tests shall meet the following conditions:
Atmospheric boundary layer modeled for wind speed variation
Atmospheric turbulence modeled to match the same scale as
the building model
Modeled building, surrounding building and topography scaled
properly
Modeled building and surrounding area is less than 8 percent
of the test section
Longitudinal pressure gradient accounted for
Reynolds number effects on pressure minimized
Response characteristics consistent with model
60
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Cylindrical Structures
61
ASCE 7-05 does not consider buildings with shapes
different from rectangular or combinations of rectangular.
The only guidance for cylindrical structures is in the
section on Other Structures (Sec 6.5.15).
The total lateral load is calculated from equation 6-28
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Other Structures
62
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Fig 6-21 – Other Structures Coeff. Cf
63
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012 64
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Example
65
Rectangular building
Plan dimensions 70’ x 70’
Height = 60’
Plan View
70’
70’
Elevation
24’
12’
12’
12’
Story
Heights
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using simplified procedure
66
V = 145 mph from Fig 6-1
I = 1.15 from table 6-1 and occupation Cat IV (or III)
Exposure Category = C
λ = 1.62 from Fig 6-2 with h=60’ and Exp C
Width of special zone A = 2a
• a < 0.10 (B) = 0.10 (70) = 7’
• a < 0.4 (h) = 0.4 (60) = 24’
• Select the smallest = 7’ but not less than
• a > .04 (B) = .04 (70) = 2.8’
• a > 3’,
•Select a = 3’, 2a = 6’
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using simplified procedure
67
Width of zone A = 6
Width of zone C = 70 – 2(6) = 58’
assuming zone A on both corners simultaneously
Horizontal pressures from Fig and roof angle ϴ = 0
Ps30 = 33.4 psf in zone A
Ps30 = 22.1 psf in zone C
Topographic factor Kzt =1 for flat terrain
Pressures 𝒑𝒔 = 𝝺𝑲𝒛𝒕𝑰𝒑𝒔𝟑𝟎
• psA = 1.62(1)(1.15)(33.4) = 62.2 psf
• psC = 1.62(1)(1.15)(22.1) = 41.2 psf
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Fig 6-2 Simplified Design Wind
pressure ps30
68
p
PA = 33.4 psf PC = 22.1 psf
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using simplified procedure
69
Apply uniform pressures in corresponding areas.
Use tributary wall area for each story level
Level Height,
ft
PsA,
psf
Width
A, ft
PsC,
psf
Width
C, ft
Force
Kips
1 30 62.2 12 41.2 58 94.1
2 12 62.2 12 41.2 58 37.6
3 12 62.2 12 41.2 58 37.6
4 6 62.2 12 41.2 58 18.8
Total 188.1
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
1. V and Kd (directionality)
2. Importance, I
3. Exposure and height, Kz, Kh
4. Topographic Effect
5. Gust effect G
6. Enclosure
7. Internal pressure GCpi
8. External Pressure Cp
9. Velocity pressure qz
10. Design wind load p
Analytical Method - Procedure
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using analytical procedure
71
V = 145 mph from Fig 6-1
Kd = 0.85 from Table 6-4
I = 1.15 from table 6-1 and occupation Cat IV (or III)
Exposure Category = C
For Low-rise buildings use Fig 6-10 and q = qh
• Select a = 3’, 2a = 6’
• Select values of GCpf for zones 1, 1E, 4, 4E
• GCpf1 = 0.40, GCpf1E = 0.61
• GCpf4 = -0.29, GCpf4E = -0.43
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using analytical procedure
Low-rise buildings
72
Kzt = 1
G = 0.85 for rigid structures, T< 1sec
Enclosure classification = enclosed
Internal pressure coefficients Fig 6-5
GCpi = ± 0.18
Kz = Kh = 1.13 from Table 6-3 and h=60’
Velocity pressure coefficient,
qz = qh = 0.00256(1.13)(1)(0.85)(145^2)(1.15) = 59.5 psf
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using analytical procedure
Low-rise buildings
73
Design pressures
Use q = qh
Windward
p1 = 59.5(0.40 + 0.18) = 34.5 psf
p1E = 59.5(0.61 + 0.18) = 47.0 psf
Leeward
p4 = 59.5(-0.29 + 0.18) = -6.5 psf
p4E = 59.5(-0.43 + 0.18) = -14.9 psf
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using analytical procedure
Low-rise buildings
74
Forces per level, calculated adding the windward and
leeward pressures because they act in the same
direction.
Level Height
, ft
Ps1E+
4E, psf
Width
E, ft
Ps1+4,
psf
Width ,
ft
Force
Kips
1 30 61.9 12 41.0 58 93.6
2 12 61.9 12 41.0 58 37.5
3 12 61.9 12 41.0 58 37.5
4 6 61.9 12 41.0 58 18.7
Total 187.3
Workshop on Vertical Shelter from Tsunamis
CIAPR June 18-20 2012
Solution using analytical procedure
75
For comparison the solution was obtained neglecting the
low-rise classification
V = 145 mph from Fig 6-1
Kd = 0.85 from Table 6-4
I = 1.15 from table 6-1 and occupation Cat IV (or III)
Exposure Category = C
Kzt = 1
G = 0.85 for rigid structures, T< 1sec
Enclosure classification = enclosed
Internal pressure coefficients Fig 6-5, GCpi = ± 0.18
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Solution using analytical procedure
76
Obtain Kz from from Table 6-3 and z = level height
Velocity pressure coefficient,
Height, z, ft Kz qz, psf
24 0.94 45.5
36 1.01 53.1
48 1.08 56.8
60 1.13 59.5
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Solution using analytical procedure
77
Design pressures. No special regions, but pressure varies
with height
Use q = qz for windward pressures
Use q = qh for leeward pressures
Use qi = qh
Shape factors Cp = 0.8 windward, Cp = -0.5 leeward,
obtained from Fig 6-6
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Solution using analytical procedure
78
Forces per level
Level Z qz,
psf
Windw
qzGCp
Internal
qhGCpi
Leew
qhGCp
Windw
p Leew
p
Total
p
Area,
sqft
Force
kips
1 24 45.5 30.9 -10.7 -25.3 41.6 14.6 56.2 70x30 118.0
2 36 53.1 36.1 -10.7 -25.3 46.8 14.6 61.4 70x12 51.6
3 48 56.8 38.6 -10.7 -25.3 49.3 14.6 63.9 70x12 53.7
4 60 59.5 40.5 -10.7 -25.3 51.2 14.6 65.8 70x6 27.6
Total 250.9
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Solution for Cylindrical Plan Building
79
The code does not propose a solution for cylindrical
buildings.
Assuming a building with D = 70’, and height = 60’
Using z = h/2 = 60/2 = 30’
Kz = 0.98
qz = 0.00256(0.98)(0.85)(145^2)(1.15) = 51.6 psf
D√qz = 70√51.6 = 503 > 2.5
For h/D = 60/70 = 0.86 ≈ 1
Assuming moderately smooth surface
Cf = 0.5
F = 51.6(0.85)(0.5)(70x60) = 92 kips
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Solution for Cylindrical Plan Building
80
Or assuming rough surface
Cf = 0.8
F = 51.6(0.85)(0.8)(70x60) = 147 kips
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Summary of examples
81
Calculated Base Shear Forces
Procedure Calculated Base
Shear Force, kips
% Difference
from Simplified
Procedure
Simplified 188.1 0
Analytical, Low-
rise
187.3 -0.4
Analytical 250.9 33.4
Cylindrical, other
structures, note
plan area is not the
same
92 for smooth
surface,
147 for rough
surface
-51.1
-21.9
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ASCE 7-10 – Wind Loads
Basic wind speed, V, mph (m/s)
82
Figure 26.5-1A: Basic Wind Speeds for
Occupancy Category II Buildings and
Other Structures
Figure 26.5-1B: Basic Wind Speeds for
Occupancy Category III and IV Buildings
and Other Structures
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ASCE 7-05 to ASCE 7-10 Wind Speeds
ASCE 7-05 uses an approximate 500-year return period
wind speed divided by the square root of the expect load
factor of 1.5. (This was approximately the 100-year wind
speed) – this was later multiplied by an importance factor
ASCE 7-10 uses maps per occupancy category (risk
category)
• Risk Category II (700 year)
• Risk Category III and IV (1700 year)
• No importance factor
Converting from ASCE 7-05 to ASCE 7-10
83
The preferred conversion of wind speeds is the
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Questions?
84
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Impacts of Wind Provisions on
Building Components
Load Paths and Connectors
Roof Systems
Windows, Doors and Openings
Wall Systems
Foundations
85