changes from asce 7-05 to asce 7-10: wind provisions
TRANSCRIPT
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Changes from ASCE 7-05 to ASCE 7-10: Wind Provisions
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ASCE 7-10
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2012 International Building Code
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CHAPTER 6(Wind Loads in ASCE 7-05)
Reserved for Future Provisions
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Chapters 26 - 31Wind Loads
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Reorganization of Wind Provisions
ASCE 7-05: Chapter 6 contained all wind provisions
New:
• 6 new Chapters (Chapters 26-31)
• User Notes added
• Intent is to clarify the applicability of the wind provisions
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Reorganization of Wind Provisions(ASCE 7-05: Dark Gray; ASCE 7-10: Orange)
Method 1 – Envelope Procedure MWFRS, C&C (Simplified Method 2 Low-Rise)
Method 2
All-Heights - Directional Procedure MWFRS, C&C
Low-Rise – Envelope Procedure MWFRS, C&C
Method 3 – Wind Tunnel Procedure
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Chapter 26 – General Requirements
Chapter 27 – MWFRS Directional Procedure Method 2 All-Heights, new simplified version - MWFRS
Chapter 28 – MWFRS Envelope Procedure Method 2 Low-Rise, Method 1 - MWFRS
Chapter 29 – MWFRS Other Structures and
Appurtenances
Chapter 30 – C&C Method 2 Low-Rise, Method 1, Method 2 All-
Heights, new simplified version of Method 2 All-Heights – C&C
Chapter 31 – Wind Tunnel Procedure Method 3
Reorganization of Wind ProvisionsASCE 7-10: Dark Gray; ASCE 7-05: Red)
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Wind Loads
Load factor on W is now 1.0 in Strength Design and 1/1.6 or 0.6 in ASD.
Thus, the design wind speed maps in ASCE 7-10 produce strength-level design wind forces. The mapped design wind speeds are, therefore, higher than in ASCE 7-05.
W SD
0.6W ASD
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Ch 2 Load Combinations with WindStrength Design
2.3.2 Basic Combinations
3. 1.2D + 1.6(Lr or S or R) + (L or 0.8 0.5W )
4. 1.2D + 1.6 1.0W + L + 0.5(Lr or S or R)
6. 0.9D + 1.6 1.0W + 1.6H
Load factor on W in SD load combinations is now 1.0 because mapped design wind speeds will produce strength-level loads
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Ch 2 Load Combinations with WindAllowable Stress Design
2.4.1 Basic Combinations
5. D + H + F + (0.6W or 0.7E)
6a. D + 0.75L + 0.75(0.6W) + 0.75 (Lr or S or R)
7. 0.6D + 0.6W + H
Load factor on W in ASD load combinations is now 0.6 because mapped design wind speeds will produce strength-level loads
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Chapter 26 – General Requirements
• Scoping
• Definitions
• Wind speed map
• Directionality factor
• Exposure
• Gust effect factor
• Topographic effect factor
• Enclosure classification
• Internal pressure coefficient
ASCE 7-10Reorganization of Wind Provisions
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I
Wind Loads
No Importance Factor is used in wind design any more.
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Wind Importance Factor
Importance Factor No Longer Used
• ASCE 7-05: qz = 0.00256KzKztKdV2I
• ASCE 7-10: qz = 0.00256KzKztKdV2
Basic Wind Speeds: 3 Maps replace need for Importance Factor
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Wind Loads
The Standard includes three design wind speed maps:
A 300-year return period wind speed map for design of Risk Category I structures
A 700-year return period wind speed map for design of Risk Category II structures
A 1700-year return period wind speed map for design of Risk Category III, IV structures
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Occupancy/Risk Categories
Occupancy Category (ASCE 7-05)Risk Category (ASCE 7-10)
Description
I Miscellaneous Occupancy
II Standard Occupancy (not I, III, or IV)
III High Occupancy
IV Essential FacilityHazardous Facility
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NEW WIND SPEED MAPS
Fig. 26.5-1A: Risk Category II
Fig. 26.5-1B: Risk Categories III & IV
Fig. 26.5-1C: Risk Category I
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ASCE 7-10 Chapter 26
ASCE 7-05Chapter 6
New Wind Speed Maps
Risk Category II
Risk Category III+IV
Risk Category I
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ASCE 7-05 Figure 6-1
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ASCE 7-10 Figure 26.5-1A
Risk Category II - 7% probability of exceedance in 50 years, MRI of 700 years
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ASCE 7-10: Figure 26.5-1B
Risk Category III and IV - 3% probability of exceedance in 50 years, MRI of 1700 years
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ASCE 7-10: Figure 26.5-1C
Risk Category I - 15% probability of exceedance in 50 years, MRI of 300 years
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Wind Speed Website
Applied Technology Council
• http://www.atcouncil.org/windspeed/
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Wind Speed Website
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Comparative Wind Pressures forSan Francisco
qz = 0.00256KzKztKdV2I OC I OC II OC III, IV
ASCE 7-05
V, mph 85 85 85
I 0.87 1.00 1.15
25.75 psf 29.59 psf 34.03 psf
RC I RC II RC III, IV
ASCE 7-10
V, mph 100 110 115
25.60 psf 30.98 psf 33.86 psf
-0.58% +4.70% -0.50%
6.1dztz KKK
q
dztz KKK
q
05
1005
qz = 0.00256KzKztKdV2
qz = 0.00256KzKztKdV2I
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Comparative Wind Pressures forChicago
qz = 0.00256KzKztKdV2I OC I OC II OC III, IV
ASCE 7-05
V, mph 90 90 90
I 0.87 1.00 1.15
28.86 psf 33.18 psf 38.15 psf
RC I RC II RC III, IV
ASCE 7-10
V, mph 105 115 120
28.22 psf 33.86 psf 36.86 psf
-2.22% +2.05% -3.38%
6.1dztz KKK
q
dztz KKK
q
05
1005
qz = 0.00256KzKztKdV2
qz = 0.00256KzKztKdV2I
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Risk Category II Comparison
0.74-0.86
0.80-0.93
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Risk Category III and IV Comparison
0.71-0.95
0.79-0.95
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Risk Category I Comparison
1.06-0.97
0.84-1.03
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Section 26.2 Definitions
Changes in the mapped wind speeds necessitated recalibration of some definitions and requirements.
1 map referenced 3 maps referenced
Old wind speed New wind speed
Occupancy Category Risk Category
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Section 26.2 Definitions
HURRICANE PRONE REGIONS: Areas vulnerable to hurricanes; in the United States and its territories defined as
1. The U.S. Atlantic Ocean and Gulf of Mexico coasts where basic wind speed for Risk Category II buildings is greater than 90 115 mph, and
2. Hawaii, Puerto Rico, Guam, Virgin Islands, and American Samoa.
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Section 26.10.3 Protection of Glazed Openings
Glazed openings in Risk Category II, III or IVbuildings located in hurricane-prone regions shall be protected as specified in this Section.
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Section 26.10.3 Protection of Glazed Openings
26.10.3.1 Wind-borne Debris Regions. Glazed openings shall be protected in accordance with 26.10.3.2 in the following locations:
1. Within 1 mile of coastal mean high water line where basic wind speed is equal to or greater than 110 130 mph, or
2. In areas where basic wind speed is equal to or greater than 120 140 mph.
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Section 26.10.3 Protection of Glazed Openings
26.10.3.1 Wind-borne Debris Regions (contd). For Risk Category II buildings and structures and Risk Category III buildings and structures, except health care facilities, wind-borne debris region shall be based on Fig. 26.5-1A. For Risk Category III health care facilities and Risk Category IV buildings and structures, wind-borne debris region shall be based on Fig. 26.5-1B. Risk Categories shall be determined in accordance with Section 1.5.
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Section 26.10.3 Protection of Glazed Openings
For Risk Category II buildings and structures and Risk Category III buildings and structures, except health care facilities
Fig. 26.5-1A
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Section 26.10.3 Protection of Glazed Openings
For Risk Category III health care facilities and Risk Category IV buildings and structures
Fig. 26.5-1B
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Section 26.10.3.2 Protection Requirements for Glazed Openings
ASTM E1886 - 05 Standard Test Method for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials
ASTM E1996 - 09 Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes
EXCEPTION: Other testing methods and/or performance criteria are permitted to be used when approved.
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Section 26.7.2 Surface Roughness Categories
Surface Roughness C: Open terrain with scattered obstructions having heights generally less than 30 ft. This category includes flat open country, andgrasslands, and all water surfaces in hurricane prone regions.
Surface Roughness D: Flat, unobstructed areas and water surfaces outside hurricane prone regions. This category includes smooth mud flats, salt flats, and unbroken ice.
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Section 26.7.2 Surface Roughness Categories
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Section 26.7.2 Surface Roughness Categories
Water surfaces in hurricane-prone regions are moved from Surface Roughness C to Surface Roughness D.
Older research and modeling suggested roughness of ocean approached Surface Roughness C with increase in wind speed.
New research suggests otherwise - roughness of ocean does not continue to increase with increasing wind speed.
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Section 26.9.2 Frequency Determination
In ASCE 7-05, several expressions for computing approximate fundamental frequency , n1, of a building were suggested in C6.5.8.
Some of those expressions are now included within the body of ASCE 7-10
Expressions provide conservative lower-bound estimates of n1, which is needed to distinguish between rigid and flexible buildings.
Low-Rise Buildings, as defined in 26.2, are permitted to be considered rigid.
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Section 26.9.2 Frequency Determination
26.9.2.1. As an alternative to performing an analysis to determine n1, the approximate building natural frequency, na, shall be permitted to be calculated in accordance with 26.9.3 for structural steel, concrete, or masonry buildings meeting the following requirements:
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Section 26.9.2 Frequency Determination
26.9.2.1 May use na for n1 if
1. Building height is less than or equal to 300 ft, and
2. Building height is less than 4 times its effective length, Leff.
(26.9-1)
summations are over height of building wherehi is height above grade of level iLi is building length at level i parallel to wind direction
n
ii
n
iii
eff
h
LhL
1
1
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Section 26.9.3 Approximate Natural Frequency
Structural steel moment-resisting-frame buildings:
na = 22.2/h0.8 (26.9-2)
Concrete moment-resisting-frame buildings:
na = 43.5/h0.9 (26.9-3)
Structural steel and concrete buildings with other lateral-force-resisting system:
na = 75/h (26.9-4)
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Section 26.9.3 Approximate Natural Frequency
Concrete or masonry shear wall buildings
na = 385(Cw)0.5/h (26.9-5)
where
n
i
i
i
i
iBw
Dh
A
h
h
AC
12
2
83.01
100
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Section 26.9.3 Approximate Natural Frequency
h = mean roof height (ft)
n = number of shear walls in building effective in resisting lateral forces in direction under consideration
AB = base area of structure (ft2)
Ai = horizontal cross-section area of shear wall “i” (ft2)
Di = length of shear wall “i” (ft)
hi = height of shear wall “i” (ft)
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ASCE 7-10Reorganization of Wind Provisions
Chapter 27 – MWFRS Directional Procedure
• Part 1 – “Buildings of all heights” method ASCE 7-05 Method 2 All-Heights
• Part 2 – New simplified method for buildings of height less than 160 ft.
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ASCE 7-10 Sections 27.4.7, 28.4.4, 28.6.4 Minimum Design Wind Loads
ASCE 7-05
ASCE 7-10
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Directional Procedure
CLASS 1 BUILDINGSh ≤ 60 ft
0.2 ≤ L/B ≤ 5.0
PART 1Applies to enclosed, partially enclosed, and open buildings
of all heights
CLASS 2 BUILDINGS60 < h ≤ 160 ft0.5 ≤ L/B ≤ 2.0
Chapter 27Directional Procedure for MWFRS
Same as Analytical Method of ASCE 7-05
New simplified procedure in ASCE 7-10
PART 2Applies to enclosed simple diaphragm buildings with
h ≤ 160 ft
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Chapter 27 Directional Procedure for MWFRS – Part 2
ENCLOSED BUILDING: A building that does not comply with the requirements for open or partially enclosed buildings.
Required for the new simplified procedure of Chapter 27 Part 2
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Enclosed Building Example
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Chapter 27 Directional Procedure for MWFRS – Part 2
SIMPLE DIAPHRAGM BUILDING: A building in which both windward and leeward wind loads are transmitted by roof and vertically spanning wall assemblies, through continuous floor and roof diaphragms, to the MWFRS.
Required for the new simplified procedure of Chapter 27 Part 2
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Simple Diaphragm Building
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ASCE 7-10 Chapter 27 Directional Procedure for MWFRS – Part 2 (Both Class 1 & 2)
General Conditions (same as Part 1) per Section 27.1.2:
1. The building is regular-shaped
2. The building does not have response characteristics making it subject to across wind loading, vortex shedding, instability due to galloping or flutter; or does not have a site location for which channeling effects or buffeting in the wake of upwind obstructions warrant special consideration.
PART 2 (Both Class 1 & 2)Applies to enclosed simple diaphragm buildings with
h ≤ 160 ft
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ASCE 7-10 Chapter 27 Directional Procedure for MWFRS – Part 2 Class 1
Additional Condition for Part 2 Class 1 Buildings per Section 27.5.2:
Unless Kzt = 1.0, wind pressures determined from this section shall be multiplied by:
Kzt at each height z as determined from 26.8 or
one value of Kzt for the building calculated at 0.33h.
Alternatively, enter the pressure tables with V√Kztwhere Kzt is determined at 0.33h.
PART 2 CLASS 1 BUILDINGSh ≤ 60 ft
0.2 ≤ L/B ≤ 5.0
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ASCE 7-10 Chapter 27 Directional Procedure for MWFRS – Part 2 Class 2
Additional Conditions for Part 2 Class 2 Buildings per Section 27.5.2:
1. The fundamental natural frequency of building shall not be less 75/h where h is in ft.
2. Unless Kzt = 1.0, wind pressures determined from this section shall be multiplied by:
Kzt at each height z as determined from 26.8 or
one value of Kzt for the building calculated at 0.33h.
Alternatively, enter the pressure tables with V√Kzt where Kzt is determined at 0.33h.
PART 2 CLASS 2 BUILDINGS60 < h ≤ 160 ft0.5 ≤ L/B ≤ 2.0
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Design Steps Parameter Source
1. Determine Basic Wind Speed for appropriate risk category
V (mph) Fig. 26.5-1 Maps
2. Determine exposure category Exp B, C or D Section 26.7
3. Enter table to determine net pressures on walls at top and base of building respectively
ph , p0 (psf) Table 27.6-1
4. Enter table to determine net roof pressures
Pz (psf) Table 27.6-2
5. Determine topographic factor and apply factor to wall and roof pressures (if applicable)
Kzt Section 26.8
Chapter 27 Directional Procedure for MWFRS – Part 2
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V (mph) 110 115 ………… 200
L/Bh (ft)
0.5 or less
1.02.0 or more
0.5 or less
1.02.0 or more
0.5 or less
1.02.0 or more
0.5 or less
1.02.0 or more
160ph
p0
150ph
p0
140ph
p0
15ph
p0
Chapter 27 Directional Procedure for MWFRS – Part 2
Table 27.6-1 for Exposure Categories B, C, and D
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Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution in along-wind direction
h
p0
ph
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Chapter 27 Directional Procedure for MWFRS – Part 2
Pressure (psf) distribution on windward and leeward walls
p0 − pleeward
ph − pleeward
pleeward =
0.38ph for 0.2 ≤ L/B ≤ 1.0
0.27ph for 2.0 ≤ L/B ≤ 5.0
Interpolate for 1.0 < L/B < 2.0
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Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) on parapet
pp = 2.25 ph ph calculated from Table 27.6-1 at top of parapet for L/B = 1.0
Accounts for pressures on windward and leeward surfaces of windward and leeward walls
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Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution on sidewalls
0.54ph for 0.2 ≤ L/B ≤ 1.0
0.64ph for 2.0 ≤ L/B ≤ 5.0
Interpolate for 1.0 < L/B < 2.0
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0.5h
0.5h
h3
4
5
Wind
Flat Roof(θ < 10 deg)
Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution on roof
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θ
1
2
Wind
θ
h Wind
0.5h
0.5h
3
4
554
3
Gable Roof
Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution on roof
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1
2
3
4
5
5 4
3
h 0.5h
0.5h
Wind
1
2
3 4
5
5
4
3
h
0.5h 0.5h
Wind Hip Roof
Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution on roof
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1
h θ
Wind
2
h θ
Wind
Monoslope Roof4
h
Wind
3
5
0.5h 0.5h
Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution on roof
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3 4
Wind
5
h 0.5h
0.5h
θ
1
2
Wind
2
Mansard Roof
Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution on roof
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Chapter 27 Directional Procedure for MWFRS – Part 2
Net pressure (psf) distribution on roof
Roof pressures from Table 27.6-2 for Exposure C
For Exposures B and D, use adjustment factors provided in the footnotes to Table 27.6-2
Where two load cases are shown in the table, both load cases shall be investigated
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V (mph) 110 - 200
h (ft) Roof SlopeLoad Case
Zone
1 2 3 4 5
15 - 160
Flat < 2:12 (9.46 deg)12
3:12 (14.0 deg)12
4:12 (18.4 deg)12
5:12 (22.6 deg)12
6:12 (26.6 deg)12
9:12 (36.9 deg)12
12:12 (45.0 deg)12
Chapter 27 Directional Procedure for MWFRS – Part 2
Table 27.6-2 for Exposure Category C
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Chapter 27 Directional Procedure for MWFRS – Part 2 Conversion from Exposure C to Exposures B and D
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Chapter 27 Directional Procedure for MWFRS – Part 2
Application of wind loadPressures on the windward, leeward and sidewalls, and on roof and parapet are applied simultaneously
h
ph
p0
θ
Wind
L
B
Plan
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The MWFRS’s in each direction shall be designed for the wind load cases defined in Figure 27.4-8.
The torsional load cases in Figure 27.4-8 (Case 2 and Case 4) need not be considered for buildings that meet the requirements for spatial distribution and stiffness of the MWFRS’s provided in new Appendix D.
Chapter 27 Directional Procedure for MWFRS – Part 2
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Chapter 27 Directional Procedure for MWFRS – Part 2
Load Cases
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The MWFRS in each direction needs to be designed for Fig. 27.4-8 wind load cases.
NEW APPENIDX D! The Fig. 27.4-8 Case 2 and 4 torsional load cases need not be considered for buildings that meet the requirements for spatial distribution and stiffness of the MWFRS’s provided in Appendix D.
Chapter 27 Directional Procedure for MWFRS – Part 2
What is Appendix D?BUILDINGS EXEMPTED FROM TORSIONAL
WIND LOAD CASES
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Chapter 27 Directional Procedure for MWFRS – Part 2
Requirements for spatial distribution and stiffness of MWFRS’s in new Appendix D are necessary to ensure that wind torsion does not control design.
In general, the designer should place and proportion vertical elements of the MWFRS in each direction so that center of pressure from wind forces at each story is located at or near center of rigidity of the MWFRS, thereby minimizing inherent torsion from wind on building.
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ASCE 7-10Reorganization of Wind Provisions
Chapter 28 – MWFRS Envelope Procedure
• Part 1 – Low-rise buildings method ASCE 7-05 Method 2 Low-Rise
• Part 2 – Simplified method for simple diaphragm buildings ASCE 7-05 Method 1
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ASCE 7-10Reorganization of Wind Provisions
Chapter 29 – MWFRS Other Structures and Appurtenances
• Signs
• Rooftop structures
• Other structures
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29.4 Solid Freestanding Walls & Solid Signs
The provisions for design wind loads on signs have been revised to clarify the applicability of the requirements for solid attached signs.
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29.4 Solid Freestanding Walls & Solid Signs
29.4 DESIGN WIND LOADS – SOLID FREESTANDING WALLS AND SOLID SIGNS
29.4.1 6.5.14 Design Wind Loads on Solid Freestanding Walls and Solid Freestanding Signs
The design wind force for solid freestanding walls and solid freestanding signs shall be determined by the following formula:
F = qhGCfAs (lb) (N) (29.4-1 6-27)
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29.4 Solid Freestanding Walls & Solid Signs
Where:
qh = the velocity pressure evaluated at height h (defined in Figure 29.4-1 6-20) as determined in accordance with Section 29.3.2 6.5.6.4.1
G = gust-effect factor from Section 26.9 6.5.8
Cf = net force coefficient from Figure 29.4-1 6-20
As = the gross area of the solid freestanding wall or freestanding solid sign, in ft2 (m2)
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29.4 Solid Freestanding Walls & Solid Signs
29.4.2 Solid Attached Signs
The design wind pressure on a solid sign attached to the wall of a building, where the plane of the sign is parallel to and in contact with the plane of the wall, and the sign does not extend beyond the side or top edges of the wall, shall be determined using procedures for wind pressures on walls in accordance with Chapter 30, and setting the internal pressure coefficient (GCpi) equal to 0.
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29.4 Solid Freestanding Walls & Solid Signs
This procedure shall also be applicable to solid signs attached to but not in direct contact with the wall, provided the gap between the sign and wall is no more than 3 ft and the edge of the sign is at least 3 ft in from free edges of the wall, i.e., side and top edges and bottom edges of elevated walls.
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Solid Attached Sign with Small Gap Showing Limitations on Use of Component & Cladding Loads for Signs on Walls
29.4 Solid Freestanding Walls & Solid Signs
This is a SOLID SIGN
Elevation Cross-Section
3 ft
Exterior Wall
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29.5.1, 30.11Rooftop Structures & Equipment
Design wind force for rooftop structures and equipment for buildings with h ≤ 60 ft has been revised and now also includes a vertical component.
New section has been added for determining component and cladding loads on rooftop structures and equipment for buildings with h ≤ 60 ft.
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29.5.1, 30.11Rooftop Structures & Equipment
29.5.1 6.5.15.1 Rooftop Structures and Equipment for Buildings with h ≤ 60 ft
The lateral force Fh, on rooftop structures and equipment with Af less than (0.1Bh) located on buildings with a mean roof height, h ≤ 60 ft shall be determined from Eq. 29.5-2 6-28. increased by a factor of 1.9. The factor shall be permitted to be reduced linearly from 1.9 to 1.0 as the value of Af is increased from (0.1Bh) to (Bh).
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29.5.1, 30.11Rooftop Structures & Equipment
Fh = qh (GCr) Af (lb) (29.5-2)
where:
GCr = 1.9 for rooftop structures and equipment with Af less than (0.1Bh). GCr shall be permitted to be reduced linearly from 1.9 to 1.0 as the value of Af is increased from (0.1Bh) to (Bh)
qh = velocity pressure evaluated at mean roof height of building
Af = vertical projected area of rooftop structure or equipment on plane normal to direction of wind, ft2
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Af
h
ELEVATION
B
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29.5.1, 30.11Rooftop Structures & EquipmentThe vertical uplift force, Fv, on rooftop structures and
equipment shall be determined from Eq. 29.5-3:
Fv = qh (GCr) Ar (29.5-3)
where:
GCr = 1.5 for rooftop structures and equipment with Ar less than (0.1BL). GCr shall be permitted to be reduced linearly from 1.5 to 1.0 as the value of Ar is increased from (0.1BL) to (BL).
qh = velocity pressure evaluated at mean roof height of building
Ar = horizontal projected area of roof top structure or equipment, ft2
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ArL
WIN
D
PLAN
B
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29.5.1, 30.11Rooftop Structures & Equipment
Rooftop Equipment MWFRS Loads
Horizontal Projected Area of Equipment, Ar
Vertical Projected Area, Af
Fv = qh (GCr)Ar
Fh = qh(GCr)Af
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29.5.1, 30.11Rooftop Structures & Equipment
30.11 ROOFTOP STRUCTURES AND EQUIPMENT FOR BUILDINGS WITH h ≤ 60 ft
The components and cladding pressure on each wall of the rooftop structure shall be equal to the lateral force determined in accordance with Section 29.5.1 divided by the respective wall surface area of the rooftop structure and shall be considered to act inward and outward.
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29.5.1, 30.11Rooftop Structures & Equipment
The components and cladding pressure on the roof shall be equal to the vertical uplift force determined in accordance with Section 29.5.1 divided by the horizontal projected area of the roof of the rooftop structure and shall be considered to act in the upward direction.
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29.5.1, 30.11Rooftop Structures & Equipment
Rooftop Equipment Component & Cladding Loads
(Design for Positive & Negative Pressures)
p = Fv /Ar
p = Fh /Af
(Design for Positive & Negative Pressures)
p = Fh /Af Rooftop Equipment
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BREAK!
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Question and Answer Session
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ASCE 7-10Reorganization of Wind Provisions
Chapter 30 – C&C
• Part 1 – Analytical method for h ≤ 60 ftASCE 7-05 Method 2 Low-Rise C&C
• Part 2 – Simplified method for h ≤ 60 ftASCE 7-05 Method 1 C&C
• Part 3 – Analytical method for h > 60 ftASCE 7-05 Method 2 All-Heights C&C
• Part 4 – New Simplified method for h ≤ 160 ft
• Part 5 – Analytical method for free roofs
• Part 6 – Building appurtenances
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Chapter 30 Components and Cladding
Part 4 applies to enclosed buildings having a mean roof height h ≤ 160 ft having flat roofs, gable roofs, hip roofs, monoslope roofs and mansard roofs. Wind pressures are determined directly from a table.
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Chapter 30 Components and Cladding
General Requirements:
30.2.2 Minimum Design Wind Pressures. The design wind pressure for C&C of buildings shall not be less than a net pressure of 16 lb/ft2 acting in either direction normal to surface.
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Chapter 30 Components and Cladding– Part 4
Design Step Parameter Source
1. Determine Basic Wind Speed for appropriate risk category
V (mph) Fig. 26.5-1 Maps
2. Determine exposure category Exp B, C or D Section 26.7
3. Enter table to determine net pressures on walls and roof for Exposure C
ptable (psf) Table 30.7-2
4. For Exposures B and D, use adjustment factors
ptable (psf)Notes to Table
30.7-2
5. Determine topographic factor and apply factor to wall and roof pressures (if applicable)
Kzt Section 26.8
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V (mph) 110 - 200
h (ft) Roof FormLoad Case
Zone
1 2 3 4 5
15 - 160
Flat Roof1
2
Gable RoofMansard Roof
1
2
Hip Roof1
2
Monoslope Roof1
2
Chapter 30 Components and Cladding– Part 4
Table 30.7-2 for Exposure Category C
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Chapter 30 Components and Cladding– Part 4 Conversion from Exposure C to Exposures B and D
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2
3
1
2a
a
a 2a
a
44
5
22
33
2
55
3
Flat roof (θ < 10)
Chapter 30 Components and Cladding– Part 4
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Chapter 30 Components and Cladding– Part 4
3
2
5
4
1
2 2
3
4
3
5
2a a
2a
2a
4a
a
Monoslope roof
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Chapter 30 Components and Cladding– Part 4
Gable roof
3
4
5
1
4 3
2
2
a a
a
3
3
1
3
2
5
2
3
5
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1
23
4
5
2
4
3
a a
a
a
3
3
5
1
2
Chapter 30 Components and Cladding– Part 4
Hip roof
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Chapter 30 Components and Cladding– Part 4
1
4
5
2 4
a
a a
3
5 3 5
1
2
3
Mansard roof
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Chapter 30 Components and Cladding– Part 4
Pressures shown in Table 30.7-2 are based on an effective wind area of 10 ft2. Reductions in wind pressure for larger effective wind areas may be taken based on reduction multipliers shown in notes to table.
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Chapter 30 Components and Cladding– Part 4
0.5
0.6
0.7
0.8
0.9
1
1.1
1 10 100 1000
Re
du
ctio
n F
acto
r
Effective Wind Area (sf)
20 50 200 500
0.8
0.7
0.6
1.0
0.9
A
B
C
D
E
Reduction Factor Based on Effective Wind Area
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Chapter 30 Components and Cladding– Part 4
Pressure (psf) on parapet:
p1 = Positive wall pressure for Zone 4 or 5, as applicable, computed at top of parapet
p2 = Negative roof pressure for Zone 2 or 3, as applicable
p1 p2
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Chapter 30 Components and Cladding– Part 4
Pressure (psf) on parapet:
p3 = Positive wall pressure for Zone 4 or 5, as applicable, computed at top of parapet
p4 = Negative wall pressure for Zone 4 or 5, as applicable, computed at top of parapet
p4 p3
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SKGA Wind Simple Computer Program
Uses the new simplified directional (all-heights) procedure in ASCE 7-10.
Calculates MWFRS and C&C design pressures on walls, roofs, roof overhangs, and parapets.
Applies the effective area reduction factor for C&C pressures.
Provides the design wind pressures for each applicable zone of the building in clear and concise tables.
Documents the calculations in clear and attractive reports.
And more…..
http://skghoshassociates.com/wind-simple
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30.10.1 Roof Overhangs
The determination and application of wind loads on roof overhangs has been revised to provide a more accurate description of how the loads are to be applied.
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30.10.1 Roof Overhangs
6.5.11.4.2 Components and Cladding. For all buildings, roof overhangs shall be designed for pressures determined from pressure coefficients given in Figs. 6-11B,C,D.
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30.10.1 Roof Overhangs
30.10 ROOF OVERHANGS
The design wind pressure for roof overhangs of enclosed and partially enclosed buildings of all heights, except enclosed buildings with h ≤ 160 ft. for which the provisions of Part 4 are used, shall be determined from the following equation:
p = qh[(GCp) – (GCpi)] (lb/ft2) (30.10-1)
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30.10.1 Roof Overhangs
where
qh = velocity pressure from Section 30.3.2 evaluated at mean roof height h using exposure defined in Section 26.7.3
(GCp) = external pressure coefficients for overhangs given in Figures 30.4-2A to 30.4-2C (flat roofs, gable roofs, and hip roofs), including contributions from top and bottom surfaces of overhang. The external pressure coefficient for the covering on the underside of the roof overhang is the same as the external pressure coefficient on the adjacent wall surface, adjusted for effective wind area, determined from Figure 30.4-1 or Figure 30.6-1 as applicable
(GCpi) = internal pressure coefficient given in Table 26.11-1
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30.10.1 Roof Overhangs
The steps required for the determination of wind loads on components and cladding of roof overhangs is shown in Table 30.10-1.
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30.10.1 Roof Overhangs
Roof Overhang C & C
Top Surface Pressure = Pressure Calculated using GCp for overhangs in Figures 30.4-2A to 30.4-2C minus bottom surface pressure calculated below
Bottom Surface Pressure = Pressure Calculated using GCp for walls from Figures 30.4-1 or 30.6-1 as applicable based on the effective wind area of the soffit
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ASCE 7-10Reorganization of Wind Provisions
Chapter 31 – Wind Tunnel Procedure
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31.4.3 Limitations on Loads
Lower limits on loads determined from wind tunnel testing are relocated from the Commentary directly into the standard.
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31.4.3 Limitations on Loads
Loads for the MWFRS determined by wind tunnel testing shall be limited such that the overall principal loads in the x and y directions are not less than 80 percent of those that would be obtained from Part 1 of Chapter 27 or Part 1 of Chapter 28.
The overall principal load shall be based on overturning moment for flexible buildings and base shear for other buildings.
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31.4.3 Limitations on Loads
Pressures for C&C determined by wind tunnel testing shall be limited to not less than 80 percent of those calculated for Zone 4 for walls and Zone 1 for roofs using the procedure of Chapter 30.
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31.4.3 Limitations on Loads
The limiting values of 80 percent may be reduced to 50 percent for the MWFRS and 65 percent for C&C if either of the following conditions applies:
1. There were no specific influential buildings or objects within the detailed proximity model.
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31.4.3 Limitations on Loads
2010 Standard (contd.)
2. Loads and pressures from supplemental tests for all significant wind directions in which specific influential buildings or objects are replaced by the roughness representative of the adjacent roughness condition, but not rougher than exposure B, are included in the test results.
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ASCE 7-10Reorganization of Wind Provisions
Appendix C – Serviceability Considerations
C. SERVICEABILITY CONSIDERATIONS
This appendix is not a mandatory part of the Standard but provides guidance for design for serviceability. . ..
C.1.2 Drift of Walls and Frames. Lateral deflection or drift of structures and deformation of horizontal diaphragms and bracing systems due to wind effects shall not impair serviceability of structure.
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ASCE 7-10Reorganization of Wind Provisions
Commentary to Appendix C – Serviceability Considerations
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Commentary to Appendix C
Use of the nominal (700-year mean recurrence interval (MRI) or 1,700-year MRI) wind load in checking serviceability is excessively conservative. The following load combination can be used to check short-term effects:
D + 0.5L + 0.7Wa (CC-3)
in which Wa is wind load based on serviceability wind speeds in Figs. CC-1 through CC-4.
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Figure CC-1 10-Year MRI 3-sec Gust Wind Speed in mph (m/s) at 33 ft (10m) above Ground in Exposure C
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Figure CC-2 25-Year MRI 3-sec Gust Wind Speed in mph (m/s) at 33 ft (10m) above Ground in Exposure C
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Figure CC-3 50-Year MRI 3-sec Gust Wind Speed in mph (m/s) at 33 ft (10m) above Ground in Exposure C
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Figure CC-4 100-Year MRI 3-sec Gust Wind Speed in mph (m/s) at 33 ft (10m) above Ground in Exposure C
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ASCE 7-10New Appendix
Appendix D – Buildings Exempted from Torsional Wind Load Cases
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Closing Comments
Impact of Changes
Need for Changes
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Question and Answer Session
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Chicago Main Office334 East Colfax Street, Unit EPalatine, IL 60067Phone: (847) 991-2700Fax: (847) 991-2702Email: [email protected]
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