ASCE 7-10 Significant Changes to the Wind Load Provisions

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1 ASCE 7-10 Significant Changes to the Wind Load Provisions William L. Coulbourne, P.E. SECB Applied Technology Council (ATC)

2 Acknowledgements Ron Cook, Univ. of Florida, Wind Load Task Committee Chairman T. Eric Stafford, T. Eric Stafford & Associates Peter Vickery, Applied Research Associates Larry Griffis, Walter P. Moore and Associates ASCE 7 Wind Load Subcommittee NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 2

3 Today s Agenda Classification of buildings Reorganization of wind provisions New wind maps MWFRS and C&C New Simplified Procedure for buildings with h 160 ft. Example problem NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 3

4 ASCE 7-05 Chapter 6 Design Methods Simplified Method (low-rise) Analytical Method Low-rise buildings Buildings of all heights Other Structures Wind Tunnel Procedure All in one chapter Confusing? Yes! NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 4

5 ASCE 7-10 Significant Changes Changes to Building Classification (Chapter 1) Complete reorganization of wind provisions New wind speed maps New wind-borne debris region Re-introduction of Exposure D for water surfaces in hurricane-prone regions Simplified procedure for buildings < 160 ft NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 5

6 Classification of Buildings Use or Occupancy of Buildings and Structures Buildings and other structures that represent a low risk to human life in the event of failure: All buildings and other structures except those listed in Risk Categories I, III, and IV Buildings and other structures, the failure of which could pose a substantial risk to human life. Buildings and other structures, not included in Occupancy Category IV, with potential to cause a substantial economic impact and/or mass disruption of day-to-day civilian life in the event of failure Buildings and other structures not included in Risk Category IV (including, but not limited to, facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, hazardous waste, or explosives) containing toxic or explosive substances where the quantity of the material exceeds a threshold quantity established by the authority having jurisdiction and is sufficient to pose a threat to the public if released. Buildings and other structures designated as essential facilities. Buildings and other structures, the failure of which could pose a substantial hazard to the community. Buildings and other structures (including, but not limited to, facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, or hazardous waste) containing sufficient quantities of highly toxic substances where the quantity exceeds a threshold quantity established by the authority having jurisdiction to be dangerous to the public if released and is sufficient to pose a threat to the public if released. a Buildings and other structures required to maintain the functionality of other Category IV structures. Risk Category I NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 6 II III IV

7 Classification of Buildings Risk Categorization. Buildings and other structures shall be classified, based on the risk to human life, health and welfare associated with their damage or failure by nature of their occupancy or use, according to Table 1-1 for the purposes of applying flood, wind, snow, earthquake, and ice provisions. Each building or other structure shall be assigned to the highest applicable risk category or categories. Minimum design loads for structures shall incorporate the applicable Importance Factors given in Table 1-2, as required by other Sections of this Standard. Assignment of a building or other structure to multiple risk categories based on the type of load condition being evaluated (e.g., wind or seismic) shall be permitted. When the building code or other referenced standard specifies an Occupancy Category, the Risk Category shall not be taken as lower than the Occupancy Category specified therein. NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 7

8 Classification of Buildings Guidance on what types of buildings might fall into each Risk Category is now gone from the body of the standard. Examples are still provided in the Commentary. Elimination of the specific examples of buildings that fall into each category has the benefit that it eliminates the potential for conflict between the standard and locally adopted codes and also provides individual communities and development teams the flexibility to interpret acceptable risk for individual projects. NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 8

9 Reorganization of Wind Provisions New organization (based on the more user-friendly multi-chapter seismic provisions): 6 new Chapters (Chapters 26-31) Flowcharts on how to use in each chapter Intent is to clarify the applicability of the wind provisions NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 9

10 Reorganization of Wind Provisions Chapter 26 General Requirements Chapter 27 MWFRS Directional Procedure Chapter 28 MWFRS Envelope Procedure Chapter 29 MWFRS Other Structures and Appurtenances Chapter 30 Components and Cladding Chapter 31 Wind Tunnel Procedure NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 10

11 Reorganization of Wind Provisions Chapter 26 General Requirements Scoping Definitions Wind speed map Exposure Gust factor Topographic factor NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 11

12 MWRFS Directional Procedure Buildings of all heights (old Figure 6-6, new Figure ) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 12

13 MWFRS Directional Procedure A procedure for determining wind loads on buildings and other structures for specific wind directions, in which the external pressure coefficients utilized are based on past wind tunnel testing of prototypical building models for the corresponding direction of wind. NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 13

14 MWRFS Envelope Procedure Buildings 60 ft (old Figure 6-10, new Figure ) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 14

15 MWFRS Envelope Procedure A procedure for determining wind load cases on buildings, in which pseudo external pressure coefficients are derived from past wind tunnel testing of prototypical building models successively rotated through 360 degrees, such that the pseudo pressure cases produce key structural actions (uplift, horizontal shear, bending moments, etc.) that envelop their maximum values among all possible wind directions. NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 15

16 Reorganization of Wind Provisions Chapter 27 MWFRS Directional Procedure Part 1: Buildings of all heights method Part 2: New simplified method for simple diaphragm buildings 160 ft NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 16

17 Reorganization of Wind Provisions Chapter 28 MWFRS Envelope Procedure Part 1: Low-rise ( 60 ft) buildings method Part 2: Simplified method for low-rise ( 60 ft) simple diaphragm buildings NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 17

18 Reorganization of Wind Provisions Chapter 29 MWFRS Other Structures and Appurtenances Signs Rooftop structures Other structures NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 18

19 Reorganization of Wind Provisions Chapter 30 Components and Cladding 1. Envelope method for h 60 ft 2. Simplified method for h 60 ft 3. Directional method for h > 60 ft 4. Simplified method for h 160 ft 5. Analytical method for open buildings of all heights 6. Building appurtenances and roof top structures NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 19

20 Reorganization of Wind Provisions Chapter 31 Wind Tunnel Procedure NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 20

21 New Wind Speed Maps New data and data analysis indicate current ASCE 7 hurricane wind speeds are generally conservative Introduction of ultimate wind speed maps LRFD Wind Load Factor = 1.0 ASD Wind Load Factor = 0.6 Specific maps for each building category NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 21

22 Facts About the ASCE 7-05 Wind Speed Map In most of the non-hurricane US mainland, the mapped values represented a 50-year mean recurrence interval In hurricane regions, the mapped values varied from 50 to 100 years along the hurricane coastline Wind speeds along the hurricane coastline had been adjusted upward so that when incorporated with the wind LF, produce a wind load having a consistent hazard level with the interior US (700 MRI) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 22

23 Wind Speed vs MRI ASCE 7-05 V(T)/V50 = (LF) Non-Hurricane V(T)/V(50)= ln(12T) Hurricane V(T)/V(50)=0.167ln(12T) 0.97 x x MRI T For Non-Hurr V map = 50 Yr MRI For Hurr, V map = 500 yr/(1.5) = ; 97 MRI NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 23

24 3.50 Wind Pressure vs MRI ASCE 7-05 P(T)/P50 = LF Hurricane Non-Hurricane Non Hurr: V map = 50 yr MRI Hurr: V map = 97 yr MRI MRI T NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 24

25 P(T)/P50 = LF Wind Pressure vs MRI ASCE Hurricane Non-Hurricane With I=1.15 Map V for hurr. (> 50 yr) MRI T NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 25

26 Why Change the Map? Current hybrid pseudo MRI Map confusing Designers, students, clients Most Users Don t Know LF =1.6: 700 yr MRI ultimate wind speed Importance Factor of 1.15: 1700 yr MRI Update for new hurricane model Provide 3 Maps: 300 yr (Cat 1), 700 yr (Cat 2) 1700 yr (Cat 3,4) Eliminate Wind Importance Factors NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 26

27 New Hurricane Model Summary New intensity model includes ocean mixing to limit hurricane intensity (defined by central pressure) New statistical model for Holland B parameter (yields lower wind speeds than 2000 model) New filling (storm weakening after landfall) model New wind field model 100,000 year simulation vs. 20,000 in the old map Map developed using 2851 pts vs. 208 in the old map NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 27

28 New Wind Speed Maps Specific maps for each building category Category II buildings 700 year return period wind speed Category III and IV buildings 1700 year return period wind speeds Category I buildings 300 year return period wind speeds Importance Factor no longer required Serviceability maps (10, 25, 50 and 100 year) to be included in Appendix C Find wind NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 28

29 Site-Specific Wind Speed Example Location: New Orleans, LA NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 29

30 700 Year RP Winds 115(51) 110(49) 130(58) 140(63) 120(54) 115(51) 115(51) 140(63) 150(67) 150(67) 140(63) 130(58) 120(54) 110(49) 160(72) 170(76) 140(63) 150(67) 160(72) 170(76) 110(49) 115(51) 150(67) 120(54) 130(58) 140(63) 180(80) 180(80) 160(72) 160(72) 120(54) 130(58) 140(63) 150(67) Special Wind Region Location Vmph (m/s) Guam 195 (87) Virgin Islands 165 (74) American Samoa 160 (72) Hawaii Special Wind Region Statewide 150(67) 160(72) 170(76) Puerto Rico Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category. 2. Linear interpolation between contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions. 5. Wind speeds correspond to approximately a 7% probability of exceedance in 50 years (Annual Exceedance Probability = , MRI = 700 Years). NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 30

31 New V 700 / 1.6 vs. ASCE NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 31

32 1700 Year RP Winds 120(54) 115(52) 130(58) 140(63) 150(67) 120(54) 160(72) 120(54) 150(67) 160(72) 160(72) 150(67) 140(63) 130(58) 120(54) 115(51) 170(76) 180(80) 150(67) 160(72) 170(76) 180(80) 190(85) 115(51) 120(54) 120(54) 160(72) 130(58) 140(63) 150(67) 200(89) 200(89) 165(74) 165(74) 130(58) 140(63) 150(67) Special Wind Region Location Vmph (m/s) Guam 210 (94) Virgin Islands 175 (78) American Samoa 170 (76) Hawaii Special Wind Region Statewide 160(72) 170(76) 180(80) Puerto Rico Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category. 2. Linear interpolation between contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions. 5. Wind speeds correspond to approximately a 3% probability of exceedance in 50 years (Annual Exceedance Probability = , MRI = 1700 Years). NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 32

33 300 Year RP Winds 105(47) 100(45) 110(49) 120(54) 130(58) 105(47) 140(63) 105(47) 130(58) 140(63) 140(63) 130(58) 120(54) 110(49) 105(47) 130(58) 140(63) 150(67) 150(67) 160(72) 150(67) 150(67) 105(47) 110(49) 120(54) 130(58) 140(63) 105(47) 110(49) 140(63) Location Vmph (m/s) Guam 180 (80) Virgin Islands 150 (67) American Samoa 150 (67) Hawaii Special Wind Region Statewide 140(63) 150(67) 160(72) Puerto Rico Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category. 2. Linear interpolation between contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions. 5. Wind speeds correspond to approximately a 15% probability of exceedance in 50 years (Annual Exceedance Probability = , MRI = 300 Years). NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions (54) 130(58) Speical Wind Region 170(76) 170(76)

34 Wind speeds at selected locations Location ASCE 7-05 Exposure C V 700 / 1.6 Exposure C Exposure D Bar Harbor, Maine Boston, MA Hyannis, MA New Port, RI Southampton, NY Atlantic City, NJ Wrightsville Beach, NC Folly Beach, SC Miami Beach Clearwater, FL Panama City, FL Biloxi, MS Galveston, TX Port Aransas, TX Hawaii Guam NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 34

35 ASCE 7-10 Strength Design Load Combinations 1.4D 1.2D + 1.6L + 0.5(L r or S or R) 1.2D + 1.6(L r or S or R) + (L or 0.5W) 1.2D + 1.0W + L + 0.5(L r or S or R) 1.2D + 1.0E + L + 0.2S 0.9D+ 1.0W 0.9D + 1.0E NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 35

36 ASCE 7-10 Allowable Stress Design Load Combinations D D + L D + (L r or S or R ) D L (L r or S or R) D + (0.6W or 0.7E) D L (0.6W) (L r or S or R) D L (0.7 E) S 0.6D + 0.6W 0.6D + 0.7E NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 36

37 Windborne Debris Region Current Standard V > 120 or 110 within one mile of coast Exact Mapping (new 700 year map) =152~ =139~140 New Standard V > 140 or 130 within one mile of coast Results in less area within WBD Region than the existing standard NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 37

38 NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 38

39 NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 39 39

40 Reintroduction of Exposure D in Hurricane- Prone Regions Older research and modeling suggested roughness of ocean approached Exposure C with increase in wind speed Hence ASCE 7-98, -02, and -05 classified water surfaces in hurricaneprone regions as Exposure C NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 40

41 Reintroduction of Exposure D in Hurricane- Prone Regions New research suggests hurricane coastline matches the exposure description for Exposure D Roughness of ocean does not continue to increase with increasing wind speed. NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 41

42 Exposure D Gust Wind Speed Ratio (Marine/Land) Vickery et al. (2000a) Vickery et al. (2008a), RMW=20 km Vickery et al. (2008a), RMW=40 km Vickery et al. (2008a), RMW=80 km Mean Wind Speed at 10m Over Water (m/sec) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 42

43 Summary of Wind Maps Use individual maps for structures with different life-safety concerns rather than using Importance Factors A 1.0 load factor for LRFD (same as Seismic) A 0.6 load factor for ASD design The result is consistent with the intent of ASCE 7-98 and better represents life-safety objectives Exposure D must be used on hurricane coastlines Serviceability wind load maps are in Appendix C NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 43

44 New Simplified Procedure Applicable to buildings less than or equal to 160 ft in height Simple diaphragm buildings Frequency limitations and torsional limitations Tabular loads for MWFRS and Components and Cladding NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 44

45 Simplified Wind Design - MWFRS Chapter 27 - Part 2 Simple diaphragm buildings Enclosed building (GCpi = + or 0.18) h 160 feet Flat, monoslope, mansard roofs, gable roofs Based on ASCE 7-10 Figure Part 1 Traditional Directional Approach NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 45

46 Simple Diaphragm Building Building - with vertically spanning wall systems in which both windward and leeward wind loads are transmitted through floor and roof diaphragms (rigid or flexible) to the same MWFRS NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 46

47 Simple Diaphragm Building Main Wind Force Resisting System (MWFRS) rigid or flexible floor diaphragms Vertically spanning walls NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 47

48 Simplified 160 ft Method Two Classes of Buildings Class 1: Simple diaphragm building h 60 ft 0.2 L/B 5.0 K zt = 1.0 or calculated B L h NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 48

49 Assumptions Class 1 Bldgs Rigid or flexible diaphragm enclosed buildings h 60 ft. 0.2 L/B 5.0 (interpolate between) No topographic effects (K zt = 1) or calculate Symmetric placement MWFRS MWFRS placed so that torsion does not control (guidance provided) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 49

50 Simplified 160 ft Method Two Classes of Buildings Class 2: Simple diaphragm building 60 h 160 ft 0.5 L/B 2.0 K zt = 1.0 or calculated B L h NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 50

51 Assumptions Class 2 Bldgs Rigid or flexible diaphragm enclosed buildings h = ft. Period T = h/75 seconds (upper bound) Damping = 1.5% (lower bound) L/B = , 2.0 (interpolate between) No topographic effects (K zt = 1) or calculate Symmetric placement MWFRS elements MWFRS placed so that torsion does not control (guidance provided) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 51

52 Why is Building Period Important? Related to mass and stiffness of building Stiffness affects drift and motion perception Mass affects wind forces Mass affects seismic forces Mass affects motion perception Period affects Gust Effect Factor, thus pressure p Buildings with high periods interact more with the wind Note: Higher Period T is conservative (opposite from seismic!) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 52

53 Wall Pressures NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 53

54 Internal pressure GC pi Affects M, V, uplift in one story rigid frame buildings Cancels out in simple diaphragm buildings NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 54

55 Wind Pressure Equation p qg f C p q i GC p - General Equation (27.4-2) p qg f C p - For simple diaphragm buildings p z G f q z C pw q h C pl - windward, leeward walls NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 55

56 Wind Pressure Vs Height ASCE p = 1.04p 160 Height (ft) h=160 ft. V=120 MPH Exposure C T=h/75 Damping=1% ASCE 7-05 Exact Simplified 20 0 p Pressure (psf) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 56

57 Wind Load Equations Pressure (psf): p z = p 0 (1 - z / h) + (z / h) p h z p z p h Table values p 0 Story Shear (pounds): v z = 0.5(h - z) [(p 0 (1 - z / h) + p h (1 + z / h)] z v z Overturning Moment (ft.-pounds): m z = 1/3 (h - z) 2 [0.5p 0 (1 z / h) + p h ( z / h)] z m z NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 57

58 Tabularized Wall Pressures NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 58

59 Story Shear Vs Height Exact vs Simplified Height (ft) Story Shear (pounds) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 59

60 Story Moment Vs Height Exact vs Simplified Height (ft) Moment (foot-pounds) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 60

61 Roof Pressures - MWFRS Roof Pressure Zones Roof Shapes: Flat Gable Hip Monoslope Mansard NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 61

62 Height h (ft) Roof Slope Roof Zone V (MPH) Exposure B,C,D Tables NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 62 Pressure (psf) (Two load cases for sloped roofs)

63 Example Problem Building is 100 ft. tall with flat roof The wind speed from ASCE 7-05 was 140 mph Ocean exposure Category II enclosed building Dimensions are B = 40 ft. and L = 200 ft. Determine pressures at 100 ft. using All heights method of ASCE 7-05, ASCE 7-10, and the Simplified Method for buildings less than 160 ft. from ASCE 7-10 NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 63

64 Comparative Results Engineering Standard Windward Wall (psf) Roof Edge Zone (psf) ASCE 7-05 Exposure C ASCE 7-10 Exposure D Simplified Exposure D NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 64

65 Components and Cladding Chapter 30 Part 4 p h = q h [(G C p ) (GC pi )] = q h (GC p ) net GC pi values for enclosed buildings are taken as +(-) GC p values : Flat roofs Fig for zones 1-3 Gable roofs, mansard roofs Fig A, B, C for zones 1-3 Hip roofs Fig B for zones 1-3 Monoslope roofs Fig A, B for zones 1-3 Wall zones 4 and 5 for all cases from Fig Table pressures based on h and q h NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 65

66 Component and Cladding Wall and Roof Zones NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 66

67 Component and Cladding Pressures Height h (ft) Roof Shape Load Case Zone Exposure C Effective Wind Area = 10 sf V (mph) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 67

68 Exposure Amplification Factor Roof and Wall Pressures - Components and Cladding Exposure Amplification Factor Building height h (ft) B/C Exp. Ampl. Factor h (ft) B/C D/C D/C Multiplier to Table pressures Exp B, D Ratio Exposure B/C, D/C NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 68

69 Reduction Factors - Effective Wind Area 1.1 Reduction Factors Effective Wind Area Roof type/case A B 0.9 C 0.9 Reduction Factor 0.8 D E Effective Wind Area (sf) NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 69

70 Other Changes 30 items approved by the Wind Load Subcommittee Examples: Improved roughness definitions and examples Revisions to low-rise envelope method Guidelines on wind-tunnel testing Reduced minimum load on projected area of roof etc, etc. NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 70

71 Questions? NCSEA Webinar ASCE 7-10 Changes in Wind Load Provisions 71

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