2012.05.09 - asce 7-10 modifications to wind loading requirements

ASCE 7-10: Modifications to Wind

Loading RequirementsLoading Requirements

Jason Ericksen, SE

SE University, May, 2012 www.LearnWithSEU.com

Key Points

� Chapter 6 has been moved to Chapters 26

through 31

� Three new basic wind speed maps replace � Three new basic wind speed maps replace

single map

� Wind Speeds are higher but design loads

are likely unchanged

2

Roadmap

� Reorganization

� Substantive Changes

� New Items� New Items

3

Reorganization

� ASCE 7-05: 3 Methods

� ASCE 7-10: 3 Procedures

4

ASCE 7-05: Methods

� Method 1 - Simplified Procedure

� Method 2 - Analytical Procedure� Low-Rise� Low-Rise

� All heights

� Method 3 - Wind Tunnel Procedure

� IBC 2009: Alternative All-heights

Procedure

5

ASCE 7-10: Procedures

� Directional Procedure

� Envelope Procedure

� Wind Tunnel Procedure� Wind Tunnel Procedure

6

ASCE 7-10 organization

� Chapter 26: General information.

� Chapter 27: Directional procedure for

MWFRS of buildings of all heightsMWFRS of buildings of all heights

� Chapter 28: Envelope procedure for

MWFRS of low-rise buildings

7

ASCE 7-10 organization

� Chapter 29: Directional procedure for

MWFRS of building appurtenances and

other structuresother structures

� Chapter 30: All procedures for

components and cladding

� Chapter 31: Wind tunnel procedure for

MWFRS and components and cladding

8

MWFRS of Enclosed and Partially

Enclosed buildings

ASCE 7-10 ASCE 7-05

Ch 27: Directional Procedure

Part 1: All height Buildings 6.5: Method 2 – Analytical

9


Procedure

6.5.12.2.1: All heights

method

Part 2: Enclosed, Simple

Diaphragm, h ≤ 160 ft

NA

MWFRS of Open buildings

ASCE 7-10 ASCE 7-05

Ch 27: Directional Procedure


10


Procedure

6.5.13: Open Buildings

6.5.13.2: MWFRS

MWFRS of Enclosed and Partially

Enclosed buildings

ASCE 7-10 ASCE 7-05

Ch 28: Envelope Procedure

Part 1: Low-rise with flat, 6.5: Method 2 – Analytical

11

Part 1: Low-rise with flat,

gable, or hip roofs

6.5: Method 2 – Analytical

Procedure

6.5.12.2.2: Low-rise buildings

Part 2: Enclosed, Simple

Diaphragm, Low-rise with

flat, gable, or hips roofs

6.4: Method 1 – Simplified

Procedure

MWFRS of Other Structures and

Building Appurtenances

ASCE 7-10 ASCE 7-05

Chapter 29: Other Structures

and Building Appurtenances


Procedure

12

6.5.14 Solid freestanding

walls and solid signs

6.5.15 Other Structures

Includes Solid Freestanding Walls and Solid Signs

C&C of Enclosed and Partially

Enclosed buildings: Chapter 30

ASCE 7-10 ASCE 7-05

Part 1: Low-rise (Envelope)

or h ≤ 60 ft


Procedure

13

or h ≤ 60 ft Procedure

6.5.12.4.1: Low-rise or h ≤

60 ft

Part 2: Low-rise or h ≤ 60 ft

(Simplified Envelope)

Enclosed with flat, gable (θ ≤

45⁰), hip (θ ≤ 27⁰) roofs

6.4: Method 1 – Simplified

Procedure

6.4.1.2: Low-rise buildings

(same limitations)

C&C of Enclosed and Partially

Enclosed buildings

ASCE 7-10 ASCE 7-05

Part 3: h > 60 ft (Directional) 6.5: Method 2 – Analytical

Procedure

14

Procedure

6.5.12.4.2: h > 60 ft

Part 4: h ≤ 160 ft (Simplified

Directional)

NA

Exception for h < 90 ft and h/l ≤ 1.0 applies to both Ch. 30: Part 3 and

6.5.12

C&C of Open buildings

ASCE 7-10 ASCE 7-05

Part 5: Open Buildings 6.5: Method 2 – Analytical

Procedure


15


6.5.13.3: C&C

Exception for h < 90 ft and h/l ≤ 1.0 applies to both Ch. 30: Part 3 and

6.5.12

C&C of Other Structures

ASCE 7-10 ASCE 7-05

Part 6: Building

Appurtenances and Rooftop

structures and equipment


Procedure

6.5.12.4.4 Parapets

16

structures and equipment 6.5.12.4.4 Parapets

6.5.15.1 Rooftop structures

and equipment for buildings

with h ≤ 60 ft

MWFRS and C&C of Buildings and

Other Structures

ASCE 7-10 ASCE 7-05

Chapter 31: Wind Tunnel

Procedure


Procedure

17

� The requirements have been expanded and

include new limits. (Moved from Commentary)

Reorganization

� Commentary Table C26.1-1

�Cross Reference of Sections between Wind

Provisions of the 2005 and 2010 Editions of Provisions of the 2005 and 2010 Editions of

ASCE 7

�Complete list of cross references for sections,

tables and figures

18

New Editorial Features

� User Notes: Helpful commentary included

within the text

� Table for each procedure with steps.� Table for each procedure with steps.

19

New Editorial Features

Table 28.5-1 Steps to Determine Wind Loads on

MWFRS Simple Diaphragm Low-Rise Buildings

Step 1: Determine risk category of building or other

structure, see Table 1.5-1

Step 2: Determine the basic wind speed, V, for applicable

20

Step 2: Determine the basic wind speed, V, for applicable

risk category, see Fig. 26.5-1 A, B, or C

Step 3: Determine wind load parameters:

�Exposure category B, C, or D, see Section 26.7

�Topographic factor, Kzt, see Section 26.8 and

Fig. 26.8-1

Step 4: Enter figure to determine wind pressures for

h = 30 ft (9.1 m), pS30, see Fig. 28.6-1

Step 5: Enter figure to determine adjustment for building

height and exposure, λ, see Fig.28.6-1

Step 6: Determine adjusted wind pressures, ps, see Eq.

28.6-1

Choosing a Method

� Chapters 27 and 28

� The building is regular shaped building or structure as

defined in Section 26.2

� The building is not dynamically sensitive, or it does � The building is not dynamically sensitive, or it does

not have a site location which warrants special

consideration.

� Chapter 31

� All buildings

21

Choosing a Method

� Chapter 27

�Part 1

� More applicable� More applicable

� If automated, provides more general, less

conservative pressures

�Part 2

� Easier for Hand Calculations

� Conservative

22

Choosing a Method

� Chapter 28

�Part 1

� User note states this method generally yields the � User note states this method generally yields the

lowest wind pressure of all analytical methods

�Part 2

� Easier for Hand Calculations

� Conservative

23

MWFRS: All Heights

24

MWFRS: Low-Rise

25

MWFRS: Low-RiseEnclosed, Simple Diaphragm

26

Components and Cladding:

27

Reorganization: Summary

� Easier way to find all the requirements (if you

are not already familiar with the organization of

ASCE 7-05!).

Changes were made in response to user � Changes were made in response to user

comments

28

Roadmap

� Reorganization



29

Changes

� Importance Factor

� Wind Speed Maps

� Load Combinations� Load Combinations

� Change in Design Loads

� Minimum Loads

� Surface Roughness

30

Importance Factor

� Importance Factor No Longer Used

�ASCE 7-10: qz = 0.00256KzKztKdV2

�ASCE 7-05: qz = 0.00256KzKztKdV2I�ASCE 7-05: qz = 0.00256KzKztKdV I

� Basic Wind Speeds: 3 Maps replace need

for Importance Factor

31

Risk Category

� Risk Category I: Low Risk

� low risk to human life (low occupancy)

� Risk Category II: Typical

� All Others

� Risk Category III: High Risk

� substantial risk to human life (high occupancy or

dangerous materials)

� Risk Category IV: Essential

� Essential facilities (hospitals, etc)

32

Changes


� Wind Speed Maps



� Minimum Loads


33

Wind Speed Maps

� Figure 26.5-1A: Risk Category II

� Figure 26.5-1B: Risk Category III and IV

� Figure 26.5-1B: Risk Category I� Figure 26.5-1B: Risk Category I

� Replace Figure 6-1 (All Occupancy

Categories)

34

Commentary

� “The 2010 edition of ASCE 7 departs from prior

editions by providing wind maps that are directly

applicable for determining pressures for strength

design approaches.”design approaches.”

� “The update maps are based on a new and

more complete analysis of hurricane

characteristics performed over the last ten

years.”

35

ASCE 7-05: Figure 6-1

36

ASCE 7-10: Figure 26.5-1A

37Risk Category II - 7% probability of exceedance in 50 years, MRI of 700 years

ASCE 7-10: Figure 26.5-1B

38Risk Category III and IV- 3% probability of exceedance in 50 years, MRI of 1700

years

ASCE 7-10: Figure 26.5-1C

39Risk Category I- 15% probability of exceedance in 50 years, MRI of 300 years

Wind Speed Website

� Applied Technology Council

�http://www.atcouncil.org/windspeed/

87

Wind Speed Website

88Wilmington, NC

Hurricane Prone Regions

� ASCE 7-05 (Section 6.2)

�The U.S. Atlantic Ocean and Gulf of Mexico

coasts where the basic wind speed is greater coasts where the basic wind speed is greater

than 90 mph and

�Hawaii, Puerto Rica, Guam, Virgin Islands,

and American Samoa

89

Hurricane Prone Regions


�The U.S. Atlantic Ocean and Gulf of Mexico

coasts where the basic wind speed for Risk coasts where the basic wind speed for Risk

Category II buildings is greater than 115 mph

and

�Hawaii, Puerto Rica, Guam, Virgin Islands,

and American Samoa

90

Wind-borne Debris Regions


�Within 1 mile of the coastal mean high water

line where the basic wind speed is equal to or line where the basic wind speed is equal to or

greater than 110 mph and in Hawaii, or

� In areas where the basic wind speed is equal

to or greater than 120 mph

91


� ASCE 7-10 (Section 26.10.3.1)

�Within 1 mile of the coastal mean high water

line where the basic wind speed is equal to or line where the basic wind speed is equal to or

greater than 130 mph and in Hawaii, or

� In areas where the basic wind speed is equal

to or greater than 140 mph

92


� ASCE 7-10 (Section 26.10.3.1)

�Wind Speed based on:

Risk Category All but health care Health care

93

Risk Category All but health care Health care

I NA NA

II Fig. 26.5-1A Fig. 26.5-1A

III Fig. 26.5-1A Fig. 26.5-1B

IV Fig. 26.5-1B Fig. 26.5-1B

Changes


� Wind Speed Maps



� Minimum Loads


40

Changes

� Wind is now calculated at ‘strength’ level

� Load combination factors for LRFD and

ASD have changed (again)ASD have changed (again)

41

Commentary

“The decision to move to multiple-strength design maps in

conjunction with a wind load factor of 1.0… relied on

several factors important to an accurate wind

specification:specification:

i. strength design ... brings wind loading approach in

line with seismic loads…

ii. Multiple maps remove inconsistencies in the use of

importance factors that actually should vary with

location and between hurricane-prone and

nonhurricane-prone regions…

42

Commentary

“The decision to move to multiple-strength design maps in

conjunction with a wind load factor of 1.0… relied on

several factors important to an accurate wind

specification:specification:

iii. The new maps establish uniformity in the return

period for the design basis winds, and they more

clearly convey that information.

iv. The new maps, by providing wind speed directly,

more clearly inform owners and their consultants

about the storm intensities for which designs are

performed.”

43

Load Combinations: ASD

ASCE 7-05

D+1.0W

D+1.0W+0.75L+0.5Lr

ASCE 7-10

D+0.6W

D+0.75(0.6W)+0.75L+0.5Lr

44

D+1.0W+0.75L+0.5Lr

0.6D+1.0W

Lr = (Lr or S or R)

D+0.75(0.6W)+0.75L+0.5Lr

0.6D+0.6W

Lr = (Lr or S or R)

Load Combinations: LRFD

ASCE 7-05

1.2D+1.6Lr+0.8W

1.2D+1.6W+1.0L+0.5Lr

ASCE 7-10

1.2D+1.6Lr+0.5W

1.2D+1.0W+1.0L+0.5Lr1.2D+1.6W+1.0L+0.5Lr

0.9D+1.6W

Lr = (Lr or S or R)

1.2D+1.0W+1.0L+0.5Lr

0.9D+1.0W

Lr = (Lr or S or R)

45

Changes


� Wind Speed Maps



� Minimum Loads


46

Design Loads

� The velocity pressure in ASCE 7-10 is

based on the equation

qz = 0.00256KzKztKdV2qz = 0.00256KzKztKdV2

� While in ASCE 7-05 it is:

qz = 0.00256KzKztKdIV2

47

Design Loads

� To get equal factored design wind

pressures in both methods, the wind

speeds in ASCE 7-10, V10, will be related speeds in ASCE 7-10, V10, will be related

to the mapped wind speed from ASCE 7-

05, V05, in the following manner (assuming

KzKztKd is equal in both) :

(fw_05)x(I)x(V05)2 = (fw_10)x(V10)

2

48

Design Loads

� Conversion equation

w_050510 f

fIVV ×=

fw_05 = load factor on wind in ASCE 7-05

fw_10 = load factor on wind in ASCE 7-10

49

w_100510 fIVV ×=

Design Loads

� Conversion equation

6.1IVV 0510 ×=

fw_05 = 1.6

fw_10 = 1.0

50

6.1IVV 0510 ×=

Design Loads

� Commentary Table C26.5-6 includes

comparison of “equivalent” wind speeds

for category IIfor category II

� ASCE 7 -05 (3 second gust),

� ASCE 7-10 (3 second gust), and

� ASCE 7-93 (fastest mile)

51

V05 Calculated V10 Actual V10 Pressure Ratio

85 107.5 110 1.05

90 113.8 115 1.02

Risk II Comparison

I = 1.00

90 113.8 115 1.02

100 126.5

110 139.1

120 151.8

130 164.4

140 177.1

150 189.7 52

Risk Category II Comparison

53


Harlingen, TX

135/147 => 0.74

New Iberia, LA

111/136 => 0.94

Panama City, FL

128/134 => 0.68

54

Miami, FL

143/168 => 0.86


Wilmington, NC

130/145 => 0.78

55

Charleston, SC

130/147 => 0.80


Boston, MA

105/128 => 0.93

56

Virginia Beach, VA

114/122 => 0.72


85 115.3 115 1.00

90 122.1 120 0.97

Risk III + IV ComparisonI = 1.15

90 122.1 120 0.97

100 135.6

110 149.2

120 162.8

130 176.3

140 189.9

150 203.5 57

Risk Cat. III and IV Comparison

58


Harlingen, TX

135/154 => 0.71

New Iberia, LA

111/147 => 0.95

Panama City, FL

128/144 => 0.69

59

Miami, FL

143/180 => 0.86


Wilmington, NC

130/154 => 0.76

60

Charleston, SC

130/157 => 0.79


Boston, MA

105/139 => 0.95

61

Virginia Beach, VA

114/132 => 0.73


85 100.3 100 0.99

90 106.2 105 0.98

Risk I ComparisonI = 0.87 (0.77 V05 > 100)*

90 106.2 105 0.98

100 118

110* 122.1

120* 133.2

130* 144.3

140* 155.4

150* 166.5 62

Risk Category I Comparison

63


Harlingen, TX

120/137 => 1.06

New Iberia, LA

111/126 => 1.05

Panama City, FL

128/123 => 0.75

64

Miami, FL

143/156 => 0.97


Wilmington, NC

130/134 => 0.86

65

Charleston, SC

130/132 => 0.84


Boston, MA

105/118 => 1.03

66

Virginia Beach, VA

114/114 => 0.81

Changes


� Wind Speed Maps



� Minimum Loads


67

ASCE 7-05: Minimum Loads

68

ASCE 7-10: Minimum Loads

69

Changes


� Wind Speed Maps



� Minimum Loads


70

ASCE 7-10 26.7.2

� Surface Roughness C: Open terrain with

scattered obstructions having heights generally

less than 30 ft. This category includes flat open

country and grasslands, and all water surfaces country and grasslands, 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.

71

ASCE 7-10 26.7.2

� Surface Roughness C: Open terrain with

scattered obstructions having heights generally

less than 30 ft. This category includes flat open

country and grasslands.country and grasslands.

� Surface Roughness D: Flat, unobstructed areas

and water surfaces. This category includes

smooth mud flats, salt flats, and unbroken ice.

72

ASCE 7-10 26.7.2

� Coastal buildings may go from Exposure C to

Exposure Category D in ASCE 7-10

� Calculated velocity pressure may increase 15%-

20% for buildings 60 ft and less. 20% for buildings 60 ft and less.

� The percentage increase decreases as the building

gets taller to a minimum of about 10%.

73

Kz Comparison: Table 27.3-1

z C D D/C

0-15 0.85 1.03 1.21

20 0.9 1.08 1.20

30 0.98 1.16 1.1830 0.98 1.16 1.18

40 1.04 1.22 1.17

50 1.09 1.27 1.16

60 1.14 1.31 1.15

90 1.24 1.41 1.14

120 1.32 1.48 1.12

180 1.43 1.59 1.11

300 1.59 1.73 1.09

500 1.78 1.9 1.0774

Substantive Changes Summary

� No importance factor

� 3 Maps replace one

� Strength factors decreased� Strength factors decreased

� Design pressures generally unchanged

�Decreased in hurricane regions

95

Roadmap

� Reorganization



75

New Simplified Directional

Procedure

� Obtain pressures directly from a table

� Total shear and overturning compare very

wellwell

76

Serviceability

� Appendix C – Serviceability Considerations

� NOT MANDATORY

� Commentary contains wind speed maps for:� Commentary contains wind speed maps for:

� 10-year MRI

� 25-year MRI

� 50-year MRI

� 100-year MRI

77

New Appendix D

“Buildings Exempted from Torsional Wind

Load Cases “

�D1.1 One and Two Stories�D1.1 One and Two Stories

�D1.2 Controlled by Seismic Design

�D1.3 Torsionally Regular

�D1.4 Flexible Diaphragms

�D1.5 Chapter 27: Part 2 Exemptions

78

New Natural Frequency

Calculation� For steel and concrete buildings

� Eliminates need for structural analysis

� Limitations� Limitations

�h ≤ 300 ft

�h ≤ 4xLeff

79

IBC Adoption� ICC Website

http://www.iccsafe.org/gr/pages/adoptions.

aspx

80

IBC Adoption� State or Jurisdiction List with Year

81

Key Points

� Chapter 6 has been moved to Chapters 26

through 31

� Three new basic wind speed maps replace � Three new basic wind speed maps replace

single map

� Wind Speeds are higher but design loads

are likely unchanged

82

Questions or Comments

Jason R. Ericksen, SE

[email protected]

Linkedin Profile

http://www.linkedin.com/in/jasonericksen

83

Questions or Comments

[email protected]

http://www.linkedin.com/in/jasonericksen

IBC Adoption:

http://www.iccsafe.org/gr/pages/adoptions.

aspx

Wind Speeds:

http://www.atcouncil.org/windspeed/84

ASCE 7-10: Modifications to Wind

Loading Requirements

By Jason Ericksen, SE

SE University, Month, Year www.LearnWithSEU.com

Loading Requirements

2012.05.09 - asce 7-10 modifications to wind loading requirements

Documents

simplified procedure

analytical procedure6

methods method

lowrise envelope

enclosed buildingsasce

analytical procedure13or

heights chapter

height buildings