ASCE7 10 Components Cladding Wind Load Provisions

ASCE7‐10Components & CladdingWind Load Provisions

John Hutton, P.E., S.E.Michael Stenstrom, P.E., S.E.

1. Basics of Wind Load Provisions & MWFRS’s

2. Components & Cladding Wind Load Provisions –Roofs & Walls

3. Wind Loads for Signs, Other Structures, Roof –Top Structures, Equipment & Other Special Conditions

4. Wind Tunnel Applications for Buildings

5. Wind Loads on Non‐Standard Buildings

ASCE 7‐10 Wind Webinar Series

• Complete reorganization of wind provisions• Basic Wind Speed Based on Strength Design

–1.0W for LRFD load combinations–0.6W for ASD load combinations

• Separate Maps for Risk Categories – No Importance Factors

• Surface Roughness D again applies along hurricane coastline

• New simplified methods for h<160 ft

Changes in ASCE7‐10

• A. Important Limitations & Definitions

• B. Building Types and the Organization of Chapter 30

• C. Example ProblemsPart 1 ‐ Low‐Rise BuildingsPart 2 ‐ Low‐Rise Buildings (Simplified)Part 3 – Buildings with h > 60 ftPart 4 – Buildings with h <= 160 ft (Simplified) ‐ New

Outline – C&C Loads

Components & CladdingWind Loads

Important Limitations and Definitions

ASCE 7 ‐ 10

• To use the C&C design procedures of ASCE 7‐10, the building must meet the following conditions• The building must be a regular‐shaped building, a building having no unusual geometrical irregularity in spatial form

• The building must not be subject to across wind loading, vortex shedding, galloping, or flutter

Important Limitations

• The site must not be subject to channeling effects or buffeting in the wake of upwind obstructions

• The wind loads for buildings failing to meet these limitations must be determined using wind tunnel procedures or using recognized literature documenting such wind load effects.

Important Limitations

What are Components and Cladding?

Section 26.2 Definitions:C&C: Elements of the building envelope that do not qualify as part of the MWFRS.MWFRS: An assemblage of structural elements assigned to provide support and stability to the overall structure, generally receives wind loading from more than one surface.

Important Definitions

Commentary: Components and Cladding: Cladding receives wind loads directly. Components receive wind loads directly or from cladding and transfer the load to the MWFRS. Examples of components include fasteners, purlins, girts, studs, roof decking, and roof trusses. Components can be part of the MWFRS when they act as shear walls or roof diaphragms, but they may also be loaded as individual components.


Certain components may receive more than one type of wind loading, for example, long‐span roof trusses should be designed for loads associated with MWFRSs (or C&C based on overall tributary area), and individual members of trusses should also be designed for C&C loads (based on member effective areas). Examples of cladding include wall coverings, curtain walls, roof coverings, exterior windows (fixed and operable) and doors, and overhead doors.


• Effective Wind Area – the area used to determine GCp• C&C Elements – the effective wind area is the span length of the element times the spacing to the next element. If the spacing is less than span length/3 one can use the span length/3 which will generate a larger effective area.


• Tributary Area• For C&C elements with tributary area of 700 square feet or less, use the provisions of Chapter 30

• For C&C elements with tributary area greater than 700 square feet, the provisions for MWFRS may be used


Cladding Fasteners – For cladding fasteners, the effective wind area shall not be greater than the area that is tributary to an individual fastener.


• There are two primary procedures used for determining wind loads on buildings ‐Directional Procedure and Envelope Procedure• Directional Procedure – The pressure coefficients use in this procedure are based on past wind tunnel testing of prototypical building models for the corresponding direction of wind


• Envelope Procedure – The pressure coefficients used in this procedure are based on past wind tunnel testing of prototypical building models successively rotated through 360 degrees under the wind loading. The key structural actions (uplift, shear, overturning) are monitored and the maximum effects of all wind directions are used to create an envelope of pseudo‐pressure cases.


• Minimum Design Wind Pressures – the design wind pressure for C&C shall not be less than a net pressure (including internal pressures) of 16 psf acting in either direction normal to the surface

• (i.e. 10 psf ASD)

General Requirements

• Wind Load Parameters – specified in Chapter 26, General Requirements• V = basic wind speed from one of the three Risk Category wind speed maps, Fig 26.5‐1A, B or C, three second gust speed at 33 feet Exposure Category C

• Kd = wind directionality factor from Table 26.6

Wind Load Parameters

• Exposure Category ‐ Category B, C, or D selected from 26.7.3 based on surface roughness for the exposure resulting in the highest wind loads for any direction on the site(Exposure D now applicable to hurricane‐prone coastal areas)

• Kzt = topographic factor defined in section 26.8 to account for wind speed‐up effect over hills, ridges, and escarpments

• G = Gust effect factor as determined by section 26.9. For the typical rigid building can be taken as 0.85


• Enclosure Classification ‐ used in determining internal pressure coefficient – either enclosed, partially enclosed, or open

• GCpi = internal pressure coefficient including gust factor as determined using Table 26.11‐1


• qz = 0.00256 Kz Kzt Kd V2

• qz = velocity pressure evaluated at any height z• qh = velocity pressure evaluated at the mean roof height,

h• Kz = velocity pressure exposure coefficient defined in

Section 30.3.1 and given in Table 30.3‐1 evaluated at any height z (only used for Part 3, h> 60’ windward pressures and positive internal pressures for partially enclosed buildings)

• Kh = velocity pressure exposure coefficient evaluated at the mean roof height, h (used for low‐rise, roof, leeward and simplified pressures, and can be used for all cases)

Velocity Pressure

Building Types

Building TypesLow Rise Buildings, h < 60’

Part 1 – Analytical• ASEC 7‐05: Method 2 Low‐Rise• Calculated• Envelope Procedure• Enclosed or Partially Enclosed• Lowest Pressures

Part 2 – Simplified• ASEC 7‐05: Method 1 Low‐Rise• Tabulated• Based on Part 1• Enclosed Buildings Only• Flat, Single Gable or Hip Roofs Only

Building TypesBuildings > 60’

Part 3 – Analytical• ASCE 7‐05: Method 2 All‐Heights• > 60’• Calculated• Directional Procedure• Enclosed or Partially Enclosed

Part 4 – Simplified• NEW: Based on Part 3• < 160’• Tabulated• Enclosed Buildings Only• Flat, Monoslope, Gable, Mansard or

Hip Roofs & Parapets Only

Building TypesSpecial Types

Part 5 – Open Buildings• All Heights• Calculated• Directional Procedure• Monoslope, Pitched or Troughed

Roofs

Part 6 – Appurtenances, etc• Calculated• Directional Procedure• Parapets & Roof Overhangs (All

Heights)• Rooftop Structures & Equipment (h

< 60’)

• Building Type Description

• Conditions

• Design Wind Pressure

• Notes

• Step‐by‐step Outline

Building TypesFormat

Part 1: Low‐Rise Buildings Component and Cladding

• Part 1: Low Rise Buildings Component and Cladding

• Per Table 30.4‐1

• Steps to determine C & C Wind Loads

• For this exercise we will assume the following:

• 2 Story Office Building

• Wood Framed, Hip Roof

• 30 Feet Mean Roof Height

• Suburban Location, Flat Ground

Part 1: Low‐Rise Buildings


30 ft 100 ft

34 ft Mean roof height 30 ft

26 ft 15 ft

• Wall studs are 15 feet tall and 16 inches on center (20 square feet tributary)

• ‐‐ use 5 feet wide x 15 feet tall = 75 sq ft for Effective Area for GCp

• Refer to page 243 Definition of Effective Area – Tributary width need not be less than 1/3 span length

• Roof trusses span 30 feet, 2 feet on center (60 square feet tributary area)

• – use 10 feet wide x 30 feet = 300 sq feet for Effective Area for GCp


• Step 1: Determine Risk Category

• Office Building …… Category II

• (Table 1.5‐1 Chapter 1, page 2)

• Step 2: Determine Basic Wind Speed

• ( Figure 26.5‐1A page 247a )

• Wind Speed = 115 mph


• Step 3: Determine Wind Load Parameters

• Kd = 0.85 (Table 26.6 page 250)

• Exposure Category = B (suburban page 251)

Kzt Topo Category = 1 (flat per 26.8.2 last paragraph)

Enclosure Class = Enclosed (office building)

• GCpi = + 0.18 (Table 26.11‐1 page 258)


• Step 4: Determine Velocity Pressure Exposure

• Kh

• Kh = 0.70 per table 30.3‐1 page 317

• Step 5: Determine Velocity Pressure qh

• qh = 0.00256 Kz Kzt Kd (V)2 per equation 30.3‐1 page 316

• qh=0.00256 (0.70)(1)(.85)(115)2

• qh=20.1 psf

•


• Step 6: Determine External Pressure Coefficient GCp

• Walls Per figure 30.4‐1 page 335

• Gcp Zone 4 Zone 5

+ 0.85 + 0.85

• ‐ 0.95 ‐ 1.1


• Step 7: Calculate Wind pressures per EQ 30.4‐1

• p=qh((GCp)± (GCpi))

• Walls

• p=20.1((+0.85) ‐ (± 0.18)) = +13.4 psf, +20.7 psf zone 4 & 5

p=20.1((‐0.95) ‐ (± 0.18)) = ‐ 15.4 psf, ‐22.7 psf zone 4

• p=20.1((‐1.1) ‐ (± 0.18)) = ‐ 18.5 psf, ‐25.7 psf zone 5



100 ft

30 ft a = 10% of least dimension

30x 0.10 = 3 ft Or .4h 0.4 x 30 = 12 ft

Or 4% of largest horizontal dimension

0.04 x 100 = 4 ft controls for ‘a’ dimension

• Hip Roof Per figure 30.4‐2B page 337

• Zone 1 Zone 2 Zone 3

• +0.3 +0.3 +0.3

• ‐0.8 ‐1.2 ‐1.2 *

• * Note: per footnote 7, Zone 3 = Zone 2 for roof slopes less than 25o


• Overhangs Per figure 30.4‐2B (Assume 10 s f )

• Zone 2 Zone 3

• Roof Truss “Tail” ‐2.2 ‐2.5

Use tributary area of affected piece

• Roof Deck ‐2.2 ‐2.2 for 10 sf


• Step 7: Calculate Wind pressures per EQ 30.4‐1 (Continued)

• Hip Roof ‐ Roof Trusses

• Zone 1, 2 & 3

• p=20.1((+0.3) ‐ (±0.18)) = +4.4 psf, +9.7 psf 16 psf minimum governs

• Zone 1

• p=20.1((‐0.8) ‐ (±0.18)) = ‐ 12.4 psf, ‐19.7 psf

• Zone 2 need to apply at discontinuities only

• p=20.1((‐1.2) ‐ (±0.18)) = ‐20.5 psf, ‐27.7 psf

• Zone 3

• p=20.1((‐2.0) ‐ (±0.18)) = ‐36.4 psf, ‐43.8 psf


• Step 7: Calculate Wind pressures per EQ 30.4‐1 (Continued)

• Overhangs Roof Truss “Tails”

• Zone 2 p=20.1(‐2.2) = ‐ 44.2 psf use trib area of tail

• Zone 3 p=20.1(‐2.5) = ‐ 50.3 psf

• Roof Deck at Overhangs

• Zone 2 p=20.1(‐2.2) = ‐ 44.2 psf

• Zone 3 p=20.1(‐3.7) = ‐ 74.4 psf



Zone 2 occurs when wind blows from right

WIND

Higher wind uplift ( zone 2 and 3 ) occurs

when wind crosses roof edge


Roof truss at 2’‐0” on center

Code Zone Diagram

WIND

Load Application Diagram


30 ft

Roof truss at 2’-0” on center

100 ft

Positive Pressure (Downward)

Negative Pressure (upward) Zone 2 can be applied on both sides for simplifying of load cases

Truss Loading Diagrams


Shallow Sloped Roofs (Monosloped or Gable) Gable Roofs � 0 < 70 (~ 1-3/4:12 )

And Monoslope Roofs � 0 < 30 (~ 3/4:12 ) Refer to figure 30.4-5A Footnote #5

Zone 3 Zone 2

Roof Joist @ 5’-0”

WIND

Zone Zzzzzz Zone 1

Positive Pressure (Downward)

Negative Pressure (upward) Zone 2 can be applied on both sides for simplifying load cases

Truss Loading Diagrams


Stepped Roofs Figure 30.4‐3 page 339

Zone 2

Zone 3 Zone 1 h1 Zone 3 (treat as zone 2 for ‐ GCp)

Zone 2 (treat as zone 1 for ‐ GCp) Zone 1 (treat as zone 1 for –GCp )

b

When h1 ≥ 10 ft b = 1.5 h1 & b < 100 ft (Note b is way out of scale on figure 30.4‐3, it looks like .5 h1 instead of 1.5h1) For area within b distance on low roof, refer to Figure 30.4‐3) use wall values in figure 30.4‐1 for positive values of GCp

• Keys to Remember for Part 1:

• Roof Zones 2 & 3 can be applied immediately adjacent to roof discontinuities based on the direction of the wind force

• Refer to Figure 30.4‐5A for “flat” roofs. Footnote #5 directs user back to Figure 30.4‐2A for monoslopes less than 30

• Do not mix positive and negative wind forces on component loading

• Recommend using wall pressures for roof slopes greater than 450

• Part 1 method may be used for h<90 ft. if the height/width ratio < 1

• This method generally yields the lowest wind pressures


Part 2: Low‐Rise Buildings, h<60 ft(Simplified)Components and Cladding

• Part 2: Low Rise Buildings ( Simplified)

• Component and Cladding

• Per Table 30.5‐1

• For this exercise we will assume the following:

• 2 Story Office Building

• Wood Framed, Hip Roof

• 30 Feet Mean Roof Height

• Suburban Location, Flat Ground

• Roof Slope is 250

Part 2: Low‐Rise Buildings (Simplified)

• Wall studs are 15 feet tall and 16 inches on center (20 square feet tributary)

• ‐‐ use 5 feet wide x 15 feet tall = 75 sq ft for Effective Area for GCp


• Roof trusses span 30 feet, 2 feet on center (60 square feet tributary area)

• – use 10 feet wide x 30 feet = 300 sq feet for Effective Area for GCp


• Part 2: Buildings with h ≤ 60 ft Components and Cladding

• Per Table 30.5‐1 Steps to determine C & C Wind Loads

• The first two steps are exactly the same as in Part 1:• Step 1: Determine Risk Category

– Office Building …… Category II• Step 2: Determine Basic Wind Speed

– Wind Speed = 115 mph• Step 3: Determine Wind Load Parameters (Exp. Cat only)

– Exposure Category = B – (GCPi = +/‐0.18 & Kd = 0.85 already incorporated into tables)

• Step 4: Determine Topographic Factors– Kzt Topo Category = 1 (flat per 26.8.2 last paragraph)


• Use same building as used in Part 1


30 ft 100 ft

34 ft Mean roof height 30 ft

26 ft 15 ft

• Step 5 & 6 : Enter figure 30.5‐1 to determine pressure on walls and roof, p. 346

• pnet = λ Kzt pnet 30 (Eq. 30.5‐1)

λ = 1.0, adjustment factor for bldg height and exposure from fig.30.5‐1

pnet 30 = net design wind pressure for Exposure B, at h = 30 ft.

Kzt = 1.0, topographic factor as defined in Section 26.8 evaluated at 0.33 mean roof height, 0.33h

Note: Figure 30.5‐1 is on page 345, 346 and 347 All figures for this method are called 30.5‐1


Step 5 & 6 : Enter figure 30.5‐1

to determine pressure on walls

and roof, p. 346

•

Part 2: Low‐Rise Bldgs (Simplified)

• Step 5: Enter Figure 30.5‐1 to determine pressure on walls and roof, p

• p = pnet30 for h = 30 ft, Hip Roof Exposure B

•


Zone

1 2 3 4 5

‐19.8 ‐27.8 ‐44.0 ‐22.8 ‐25.8

+16 +16 +16 +20.8 +20.8•p from Part 1

Zone

1 2 3 4 5

‐19.7 ‐27.7 ‐43.8 ‐22.7 ‐25.7

+16 +16 +16 +20.7 +20.7

Part 3: Buildings with h>60 ft Component and Cladding

• Part 3: Buildings with h>60 ft Component and Cladding

• Determine C & C Wind Loads per Table 30.6‐1 Steps

• For this exercise we will assume the following: • 6 Story Office Building with 13 ft floor to floor • Glass Curtain Wall system with vertical mullions at 4 ft on center• Flat Roof framed with bar joists spanning 50 ft at 6’‐8” on center.• 78 Feet Mean Roof Height • Suburban Location, Flat Ground

Part 3: Buildings with h> 60 ft

Part 3: Buildings with h> 60 ftThis image cannot currently be displayed.

• Curtain Wall mullions are 13 feet tall and 48 inches on center (52 square feet tributary)


• ‐‐ use 4’‐4” wide x 13 feet tall = 56 sq ft for Effective Area for GCp

• Roof joists span 50 feet at 6’‐8” on center (333 square feet tributary area)

• – use 16’‐8” wide x 50 feet = 833 sq feet for Effective Area for GCp


• Step 1: Determine Risk Category

• Office Building …… Category II

• (Table 1.5‐1 Chapter 1, page 2)

• Step 2: Determine Basic Wind Speed

• ( Figure 26.5‐1A page 247b )

• Wind Speed = 115 mph


• Step 3: Determine Wind Load Parameters

• Kd = 0.85 (Table 26.6 page 250)

• Exposure Category = B (suburban page 251)

Kzt Topo Category = 1 (flat per 26.8.2 last paragraph)

Enclosure Class = Enclosed (office building)

• GCpi = +/‐ 0.18 (Table 26.11‐1 page 258)


• Step 4: Determine Velocity Pressure Exposure

• Kz or Kh

• Kh = 0.92 per table 30.3‐1 page 317

• Kz = varies with height from 0.70 to 0.92 per table 30.3‐1 page 317

•


• Step 5: Determine Velocity Pressure qh and qz

• qh is determined at the mean roof height

• qh = 0.00256 Kh Kzt Kd (V)2 per equation 30.3‐1 page 316

• qh=0.00256 (0.92)(1)(.85)(115)2

• qh=26.5 psf

• qz is determined at the height of the element being considered

• qz = 0.00256 Kz Kzt Kd (V)2 per equation 30.3‐1 page 316

• qz=0.00256 (Kz)(1)(.85)(115)2 = (Kz)28.8 psf

• qh=varies from 20.1 psf in the lower 15 ft to 26.5 psf at the top

•


• Step 6: Determine External Pressure Coefficient GCp

• Per figure 30.6‐1 page 348

• Roof Walls Joists Mullions

• 833 sq ft 56 sq ft

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

+ 0.8 + 0.8

‐ 0.9 ‐ 1.6 ‐ 2.3 ‐ 0.85 ‐ 1.55


• Step 7: Calculate Wall Mullion Wind pressures per EQ 30.6‐1

• p=q(GCp)‐qi (GCpi)

• Windward Walls q=qz which varies from bottom to top

• p=qz(+0.8) – 26.5(± 0.18) zone 4 & 5

for the following selected heights (40’, 60’, 78’)

@40’ p=21.9(+0.8) – 26.5(± 0.18) = 22.3 psf

@60’ p=24.5(+0.8) – 26.5(± 0.18) = 24.4 psf

@78’ p=26.5(+0.8) – 26.5(± 0.18) = 26.0 psf


• Step 7: Calculate Wall Mullion Wind pressures per EQ 30.6‐1


• Leeward Walls q=qh which is constant from bottom to top

• p=qh(GCp) – 26.5(± 0.18) zone 4 & 5

p=26.5(‐0.85) – 26.5(± 0.18) = ‐ 27.3 psf zone 4

• p=26.5(‐1.55) – 26.5(± 0.18) = ‐ 45.8 psf zone 5



• Step 7: Calculate Roof Joist Wind pressures per EQ 30.6‐1


• Roof q=qh evaluated at mean roof height

• p=26.5(GCp) – 26.5(± 0.18) zone 1, 2, & 3

p=26.5(‐0.9) – 26.5(± 0.18) = ‐ 28.6 psf zone 1

p=26.5 (‐1.6) – 26.5(± 0.18) = ‐ 47.2 psf zone 2

p=26.5 (‐2.3) – 26.5(± 0.18) = ‐ 65.7 psf zone 3

p=16 psf minimum positive pressure all zones



• Keys to Remember for Part 3: • Use Figure 30.6‐1 for walls & flat roofs, <10 degrees • For Roof slopes >10 degrees, use Part 1 Figures for GCp• Use Fig 30.4‐7 for dome roofs• See Fig 27.4‐3, footnote 4, for arched roofs

– At roof perimeter, use the external pressure coefficients in Fig. 30.42 A, B and C with θ based on spring‐line slope

– for remaining roof areas, use MWFRS external pressure coefficients multiplied by 0.87.


Part 4: Buildings with h<160 ftComponents and Cladding

• Assume the same building used in Part 3: Buildings >60ft• 78 Feet Mean Roof Height, flat roof

Part 4: Buildings with h<160 ft

• Part 4: Buildings with h>160 ft Components and Cladding

• Per Table 30.7‐1 Steps to determine C & C Wind Loads

• The first two steps are exactly the same as in Part 3:• Step 1: Determine Risk Category

– Office Building …… Category II• Step 2: Determine Basic Wind Speed

– Wind Speed = 115 mph• Step 3: Determine Wind Load Parameters (Exp. Cat only)

– Exposure Category = B – (GCPi = +/‐0.18 & Kd = 0.85 already incorporated into tables)

• Step 5: Determine Topographic Factors

– Kzt Topo Category = 1 (flat per 26.8.2 last paragraph)


• Step 4: Enter Table 30.7‐2 to determine pressure on walls and roof, p

• p = ptable (EAF)(RF)Kzt (Eq. 30.7‐1)

ptable = Tabulated Pressure for Exp C, 10 ft2 from Table 30.7‐2

RF = Effective Area Reduction Factor from Table 30.7‐2EAF = Exposure Adjustment Factor from Table 30.7‐2Kzt = 1

•



• p = ptable for h = 78 ft, Flat Roof

•



• p = ptable for h = 78 ft, Flat Roof

•


Zone

1 2 3 4 5

‐54.6 ‐85.7 ‐116.8 ‐37.3 ‐68.4NA NA NA 37.5 37.5


• EAF = 0.766 (Exposure B, Mean Roof Ht. = 78’)– Use linear interpolation as permitted for Kz– Part 4 uses Kh for all pressures. EAF values could be calculated for alternate heights for windward pressures, but since leeward pressures are larger anyway, this is not typically needed.

•




Roof Joists Curtain Wall

Effective Area = 833 ft^2

Effective Area = 56 ft^2



RF, Reduction FactorsFor Effective Wind Areas

Roof Joists Curtain Wall

Effective Area = 833 ft^2 Effective Area = 56 ft^2

SignPressure

Zone

1 2 3 4 5

Minus D D D C E

Plus NA NA NA D D

Minus .7 .7 .7 .91 .82

Plus .87 .87



Part 4: p = ptable (EAF)(RF)Kzt (psf)Roof Joists Curtain Wall

Zone

1 2 3 4 5

‐29.3 ‐46.0 ‐62.6 ‐26.0 ‐43.0

16.0* 16.0* 16.0* 24.9 24.9

Part 3, h>60 ft: p

‐28.6 ‐47.2 ‐65.7 ‐27.3 ‐45.8

16.0* 16.0* 16.0* 26.0 26.0

•Note that the simplified method is not always the most conservative.


a is not defined in Part 4, however, use zone dimensions as in Part 3:



• Keys to Remember for Part 4:• Quick solution for Exposure C , 10 sf effective wind area• Must be modified for Exposure B or D • Must be modified for effective wind areas > 10sf• May be used for all heights < 160ft• Not always the most conservative method – look for errata

• General Keys to Remember for Components & Cladding:

• ASCE 7‐10 wind loads are strength method (0.6 W for ASD)• Use effective areas to establish GCp• Recommend using wall pressures for roof slopes > 450

• May use 0.42W (=.6*.7) for IBC deflection limits (10 year winds)


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ASCE7 10 Components Cladding Wind Load Provisions