Advanced ASCE 7 – With Significant Changes to the 2010 Edition

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Advanced ASCE 7 Advanced ASCE 7 ––With Significant Changes to the With Significant Changes to the 2010 Edition2010 Edition

presented byT. Eric Stafford

T. Eric Stafford & Associates, LLC

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2007 Florida Codes 2007 Florida Codes –– Base CodesBase Codes

2007 Florida Building Code, Building– Base code: 2006 International Building Code

2007 Florida Building Code, Residential– Base code: 2006 International Residential Code

2007 Florida Building Code, Existing Building– Base code: 2006 International Existing Building

Code

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2007 Florida Codes2007 Florida Codes

Florida-specific amendments from 2001, and 2004 Florida Codes carried forward into the 2007 editionIncludes changes from the 2003 I-Codes to the 2006 I-CodesEffective Date: March 1, 2009

Glitch Amendments/2009 Glitch Amendments/2009 SupplementSupplement

Go into effect March 1, 2009Get amendments from– www.floridabuilding.org– ICC replacement pages– 2007 FBC Building, Code and

Commentary incorporates glitch amendments

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2007 Florida Building Code, 2007 Florida Building Code, BuildingBuilding

Wind Provisions– References ASCE 7-05– Methods for determining wind loads

have been removed in deference to ASCE 7-05

– Retained• Exposure Categories• Protection of Openings• Wind Speed Maps

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Exceptions to ASCE 7 include:– IBHS Guidelines– AF&PA WFCM– FC&PA Guide– TIE/EIA 222

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Design Pressures for Wall Coverings Design Pressures for Wall Coverings and Soffitsand Soffits

Protection of Openings Protection of Openings -- WBDRWBDR

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Wind SpeedsWind Speeds

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Exposure CategoriesExposure Categories

Determination of Exposure Categories is a two step process– Evaluate Surface Roughness Type– Determine Exposure Category based on

type and amount of surface roughnessWind direction and sectors– Exposure of building to be determined

for the two upwind sectors extending 45 degrees either side of selected wind direction.

Surface Roughness CategoriesSurface Roughness Categories

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ASCE 7ASCE 7--0505

Wind Loads

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ASCE 7ASCE 7--0505DefinitionsDefinitions

Hurricane prone region : areas vulnerable to hurricanes; in the US and its territories defined as:1. the US, Atlantic, and Gulf of Mexico

coasts where the basic wind speed is greater than 90 MPH, and

2. Hawaii, Puerto Rico, Guam, Virgin Islands and American Samoa

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ASCE 7ASCE 7--0505DefinitionsDefinitions

Wind borne debris region : areas within hurricane prone regions located:1.Within one mile of the coastal mean

high water line when the basic wind speed is equal to or greater than 110 MPH and in Hawaii, or

2. In areas where the basic wind speed is equal to or greater than 120 MPH

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ASCE 7ASCE 7--0505Transition ZoneTransition Zone

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ASCE 7ASCE 7--0505Exposure CategoriesExposure Categories

MWFRS –– Rigid buildings of all heights – Exposure Category

determined for each wind direction– Low-rise buildings – Exposure Category resulting

in the highest wind loads for any direction for all wind directions

Components and Cladding– Components and cladding design pressures for all

buildings and other structures shall be based on the exposure resulting in the highest wind loads for any direction at the site.

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ASCE 7ASCE 7--05 05 DefinitionDefinition--Enclosure ClassificationEnclosure Classification

Buildings, Open:A building having each wall at least 80% open.

Mathematically, Ao > 0.8Ag where:Ao = Total area of openings in a wall that receives positive external pressure, in sq. ft.

Ag= Gross area of that wall in which Ao is identified, in sq. ft.

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Buildings, Enclosed:

A building that does not comply with the requirements for open or partially enclosed buildings.

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Buildings, Partially Enclosed:If the following two conditions are satisfied:1. Ao > 1.1Aoi 2. Ao > 4 sq. ft or >0.01Ag, whichever is smaller, & Aoi< 0.2Agi

where:Aoi = The sum of the areas of openings in the building envelope (walls & roof) not including Ao, in sq. ft

Agi = The sum of the gross surface areas of the building envelope (walls & roof) not including Ag, in sq. ft

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Positive Internal PressurePositive Internal Pressure

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ASCE 7ASCE 7--0505Wind Borne Debris RegionsWind Borne Debris Regions

Wind borne debris region : areas within hurricane prone regions located:1. Within one mile of the coastal mean

high water line when the basic wind speed is equal to or greater than 110 MPH and in Hawaii, or

2. In areas where the basic wind speed is equal to or greater than 120 MPH

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ASCE 7ASCE 7--0505WindWind--borne Debrisborne Debris

6.6 Method 3 – Wind Tunnel Procedure

6.6.5 Wind Borne Debris. Glazing in buildings in wind-borne debris regions shall be protected in accordance with Section 6.5.9.3.

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ASCE 7ASCE 7--05 05 Design ProceduresDesign Procedures

3 Design Procedures

– 6.4 - Method 1 - Simplified Procedure

– 6.5 - Method 2 - Analytical Procedure

– 6.6 - Method 3 - Wind Tunnel Procedure

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ASCE 7ASCE 7--0505Simplified MethodSimplified Method

Refinements to Method 1 – Simplified Method– Exempt from torsional load cases in

Figure 6-10– Added Kzt factor to simplified equations– Add tabular pressures values for 105

mph, 125 mph and 145 mph– Clarified application of Load Cases 1

and 2

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MWFRS Limitations– 1. The building is a simple diaphragm building – 2. Low-rise building– 3. Enclosed building and conforms to wind-borne debris

provisions– 4. The building is regular shaped– 5. The building is not classified as a flexible building– 6. The building does not have response characteristics

making it subject to across wind loading, vortex shedding, instability due to galloping or flutter; and does not have a site location for which channeling effects or buffeting in the wake of upwind obstructions warrant special consideration

– 7. The building has an approximately symmetrical cross section in each direction with roof slopes not exceeding 45 degrees (0.78 rad.).

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Components and Cladding Limitations– 1. Mean roof height less than or equal to 60 ft – 2. Enclosed building and conforms to wind-borne debris

provisions– 3. The building is regular shaped– 4. The building does not have response characteristics

making it subject to across wind loading, vortex shedding, instability due to galloping or flutter; and does not have a site location for which channeling effects or buffeting in the wake of upwind obstructions warrant special consideration

– 5. The building has either a flat roof, a gable roof with roof slopes not exceeding 45 degrees, or a hip roof with roof slopes not exceeding 27 degrees.

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Added new requirement for use of Method 1:

8. The building is exempted from the torsional load cases as indicated in Note 5 of Figure 6-10, or the torsional load cases defined in Note 5 do not control the design of any of the MWFRS’s of the building.

(Commentary gives guidance on determining if the torsional load cases would control the design – flexible

diaphragms, etc.)

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Note 5 of Figure 6-10

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ASCE 7ASCE 7--0505Simplified Method Simplified Method -- MWFRSMWFRS

Simplified design wind pressure, ps, MWFRS

ps = λKztIps30

λ = adjustment factor for height and exposureKzt = topographic factorI = Importance factorps30 = simplified design pressure for h = 30ft,

Exposure Category B

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ASCE 7ASCE 7--0505Simplified Method Simplified Method –– Figure 6Figure 6--22

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Note 4 Figure 6-2Load cases 1 and 2 must be checked for 25°< θ ≤ 45°. Load case 2 at 25° is provided only for interpolation between 25° to 30°.


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Be Aware!– Note 3:

• 3. For the design of the longitudinal MWFRS use θ = 0°, and locate the zone E/F, G/H boundary at the mid-length of the building.

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ASCE 7ASCE 7--0505Simplified Method Simplified Method –– C & CC & C

Simplified design wind pressure, ps, Components and Cladding

pnet = λKztIpnet30

λ = adjustment factor for height and exposureKzt = topographic factorI = Importance factorpnet30 = simplified design pressure for h = 30ft,

Exposure Category B

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ASCE 7-05Simplified Method – C & C

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ASCE 7ASCE 7--0505Method 2: Analytical ProcedureMethod 2: Analytical Procedure

Design Pressure – MWFRS –

Rigid Buildings of All Height:

p = q GCp - qi (GCpi)

Velocity Pressure (6.5.10):

qz = 0.00256KzKztKdV2I

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ASCE 7ASCE 7--05 05 Method 2: Analytical ProcedureMethod 2: Analytical Procedure

Design Pressure – MWFRS – Rigid Buildings of All Height

qi = qh for windward walls, side walls, leeward walls, and roofs of enclosed buildings and for negative pressure evaluation in partially enclosed buildings

qi = qz for positive pressure evaluation in partially enclosed buildings at height z from the ground. Can be conservatively taken as qh

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ASCE 7ASCE 7--0505Method 2: Analytical ProcedureMethod 2: Analytical Procedure


Low-rise buildings h ≤ 60 ft:

p = qh[(GCpf) - (GCpi)]


qz = 0.00256KzKztKdV2I

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ASCE 7ASCE 7--05 05 Analytical ProcedureAnalytical Procedure

Design Procedure (6.5.3):1. Wind Speed V (Figure 6-1 map)2. Wind Directionality Factor Kd (6.5.4.4, Table 6-4)3. Importance Factor I (6.5.5, Table 6-1)4. For each wind direction:

Exposure Category (6.5.6)Velocity Pressure Exposure Coefficient

Kz, Kh (6.5.6, Table 6-3)

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Directionality factor Kd introduced in 1998– Added to velocity pressure equation

• qz = 0.00256 Kz Kzt Kd V2 I– Separate out effect of wind load factor– Requires adjustment to wind load

factor ( 1.3 → 1.6 )– Table 6-4

Reason: Explicitly identify directionality effect in future editions.

Table 6Table 6--4 Wind Directionality Factor, K4 Wind Directionality Factor, Kdd

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ASCE 7ASCE 7--05 05 Table 6Table 6--1 Importance Factor, I1 Importance Factor, I

ASCE 7ASCE 7--0505Table 6Table 6--3 Velocity 3 Velocity Pressure Exposure Pressure Exposure Coefficients, KCoefficients, Khh and Kand Kzz

Table 6Table 6--2 Terrain Exposure Constants2 Terrain Exposure Constants

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Design Procedure (6.5.3):5. Topographic Factor, Kzt (6.5.7, Figure 6-4)6. Gust Effect Factor G or Gf (6.5.8)7. Enclosure Classification (6.5.9)8. Internal Pressure Coefficient GCpi (6.5.11.1, Figure 6-5)9. External Pressure Coefficients Cp, GCpf (6.5.11.2) or force coefficients Cf (6.5.11.3)

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ASCE 7ASCE 7--05 05 Fig. 6Fig. 6--4 Topographic Factors, K4 Topographic Factors, Kztzt

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ASCE 7ASCE 7--05 05 Fig. 6Fig. 6--4 Topographic Factors, K4 Topographic Factors, Kztzt

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ASCE 7ASCE 7--05056.5.8 Gust Effect Factor, G or G6.5.8 Gust Effect Factor, G or Gff

For rigid structures as defined in Section 6.2, G shall be taken as 0.85 or calculated by Eqs. 6-4, 6-5, 6-6 and 6-7, using Table 6-2.For flexible or dynamically sensitive structures as defined in Section 6.2, Gfshall be calculated by Eqs. 6-8, 6-9, 6-10, 6-11, 6-12, 6-13a, 6-13b and 6-14, using Table 6-2.

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ASCE 7ASCE 7--0505Gust Effect Factor GGust Effect Factor G

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ASCE 7ASCE 7--0505Flexible vs. RigidFlexible vs. Rigid

How to determine if flexible or rigid for wind design?– When to investigate natural frequency:

• H > 4 times least horizontal dimension, or• Reason to believe natural frequency is less

than 1 Hz

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Figure 6Figure 6--55 Internal Pressure Coefficients, GCInternal Pressure Coefficients, GCpipi

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Analytical ProcedureAnalytical ProcedureExternal Pressure CoefficientsExternal Pressure Coefficients

Cp - for main wind force resisting systems -Fig. 6-6

GCpf - for low-rise buildings - Fig. 6-10

GCp - for components & cladding -Fig. 6-11 through 6-17

Cf - Figures 6-18 through 6-23

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Fig. 6Fig. 6--66

External Pressure External Pressure Coefficient, CCoefficient, Cpp for for MWFRS MWFRS –– Rigid Rigid Buildings of All HeightsBuildings of All Heights

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ASCE 7ASCE 7--05 05 Fig. 6Fig. 6--6 6 CCpp for MWFRS: Wallsfor MWFRS: Walls

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ASCE 7ASCE 7--05 05 Fig. 6Fig. 6--66 CCpp for MWFRS: Roofsfor MWFRS: Roofs

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LowLow--rise Buildingsrise BuildingsFig. 6Fig. 6--1010 GGCCpfpf for MWFRS: h for MWFRS: h << 60 ft60 ft


Low-rise Buildings (6.5.12.2.2):

p = qh[GCpf - (GCpi)]


qh = 0.00256KhKztKdV2I

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LowLow--rise Buildingsrise BuildingsFig. 6Fig. 6--1010 GGCCpfpf for MWFRS: h for MWFRS: h << 60 ft60 ft

8 Load Cases

LowLow--rise buildingsrise buildings

Note!– Figure 6-10 revised in ASCE 7-10 to

clarify location of end zones

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ASCE 7ASCE 7--0505Fig. 6Fig. 6--1010 GGCCpfpf for MWFRS: h for MWFRS: h << 60 ft60 ft

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ASCE 7ASCE 7--05 05 Torsion Torsion –– LowLow--rise Buildings Fig. 6rise Buildings Fig. 6--1010Note 5 of Figure 6-10

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ASCE 7ASCE 7--05 05 Torsion Torsion –– LowLow--rise Buildings Fig. 6rise Buildings Fig. 6--1010

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ASCE 7ASCE 7--0505Basic Wind Speeds Using Climatic DataBasic Wind Speeds Using Climatic Data

New language clarifying that basic wind speeds obtained from regional climatic data may be less than Figure 6-1

6.5.4.2 Estimation of Basic Wind Speeds from Regional Climatic Data In areas outside hurricane prone regions, regional climatic data shall only be used in lieu of the basic wind speeds given in Fig. 6-1 when: (1) approved extreme-value statistical-analysis procedures have been employed in reducing the data; and (2) the length of record, sampling error, averaging time, anemometer height, data quality, and terrain exposure of the anemometer have been taken into account. Reduction in basic wind speed below that of Figure 6-1 shall be permitted.

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ASCE 7ASCE 7--1010

Available May 2010Most comprehensive update to wind load provisions since ASCE 7-98Approved at Code Development Hearings for inclusion in 2012 IBC and 2012 IRC

ASCE 7ASCE 7--1010

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ASCE 7ASCE 7--1010Wind ProvisionsWind Provisions

Topics Discussed– Reorganization– New wind speed maps– Exposure Categories

– Wind-borne Debris– Roof Overhangs– Minimum Design Wind Loads– Simplified methods for MWFRS and C&C

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ASCE 7ASCE 7--1010ReorganizationReorganization

ASCE 7-05: Chapter 6 contains all wind provisionsASCE 7-10:– 6 new Chapters (Chapters 26-31)– Step by step design procedure provided

at the beginning of each method– Intent is to clarify the applicability of the

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ASCE 7ASCE 7--1010ReorganizationReorganizationChapter 26 – General Requirements– Scoping– Definitions– Wind speed map– Exposure– Gust factor– Topographic factor

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Chapter 27 – MWFRS Directional Procedure– Buildings of all heights method– New simplified method for buildings

with h ≤ 160 ftChapter 28 – MWFRS Envelope Procedure– Low-rise buildings method– Simplified method for simple diaphragm

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Chapter 29 – MWFRS Other Structures and Appurtenances– Signs– Rooftop structures– Other structures

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Chapter 30 – Components and Cladding– Analytical method for h ≤ 60 ft– Simplified method for h ≤ 60 ft– Analytical method for h > 60 ft– Simplified method for h ≤ 160 ft– Analytical method for free roofs– Building appurtenances

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Chapter 31 – Wind Tunnel Procedure

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Each chapter further subdivided into Parts for exampleChapter 27 Part 1

Chapter 27 Part 2

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How to find provisions in ASCE 7-10 using ASCE 7-05 as the basis.Significant Changes to Wind Load Provisions contains a crosswalk table.

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Excerpt


Each method/part also is provided with a tabular step-by-step design procedure

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ASCE 7ASCE 7--1010Chapter 26: General RequirementsChapter 26: General Requirements

Basic wind speed, V, see Figure 26.5-1A, B or CWind directionality factor, Kd , see Section 26.6Exposure category, see Section 26.7Topographic factor, Kzt, see Section 26.8Gust Effect Factor, see Section 26.9Enclosure classification, see Section 26.10Internal pressure coefficient, (GCpi), see Section 26-11

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ASCE 7ASCE 7--1010Basic Wind SpeedsBasic Wind Speeds

Basic wind speeds haven’t changed at all since ASCE 7-983-sec gust wind speeds introduced in ASCE 7-95 to replace fastest-mile wind speedsMinor adjustments between ASCE 7-95 and ASCE 7-98

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3 new maps– Risk Category II (Occupancy Category)

– 700 yr MRI– Risk category III and IV – 1700 yr MRI– Risk Category I – 300 yr MRI

Strength design-based or “Ultimate”wind speeds

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In most of the non-hurricane US mainland, the mapped values are exactly a 50 year mean recurrence interval

In hurricane regions, the mapped values vary from 50 to 100 years along the hurricane coastline

Wind speeds along the hurricane coastline have 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)


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Implications– Net wind loads are decreasing

New data suggests ASCE 7-05 wind speeds are conservative

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Comparison of (VComparison of (V700700//√√1.6) to ASCE 71.6) to ASCE 7--05 Wind Speeds05 Wind Speeds

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120130150

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Strength Design Load Factor = 1.0Allowable Stress Design – multiply W x 0.6Use of different maps for different Risk Categories negates the need for Importance Factors– “I” deleted from wind chapters

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Converting from Vasd to Vult

Vasd = Vult√0.6

Where:Vasd = allowable stress design wind speed applicable to

methods specified in Exceptions 1 through 5 of Section 1609.1.1

Vult = strength design wind speeds determined from Figures 1609A, 1609B, or 1609C.

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ASCE 7ASCE 7--1010Surface Roughness C and DSurface Roughness C and D

Older research and modeling suggested roughness increased with increase in wind speedHence ASCE 7-98, -02, and -05 classified water surfaces in hurricane-prone regions as Exposure CNew research suggests otherwiseRoughness of ocean does not continue to increase with increasing wind speed.

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Sea surface drag coefficient reaches a maximum at wind speeds of nearly 70 mphSome evidence that sea surface drag coefficient actually decreases at higher wind speeds reflecting a “frothing” or smoothingUse of Surface Roughness D now required for all water surfaces in Hurricane Prone Regions

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ASCE 7ASCE 7--1010Enclosure ClassificationEnclosure Classification

Protection of Glazed Openings– Wind-borne debris region triggered by

wind speed– New wind speeds necessitate

recalibration of the trigger.

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ASCE 7ASCE 7--1010Protection of Glazed OpeningsProtection of Glazed Openings

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Cont.

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ASCE 7ASCE 7--1010Minimum Design Wind LoadsMinimum Design Wind Loads

ASCE 7-05 requires minimum wind load to not be less than 10 psf multiplied by the vertical projection of buildingParticular impact on low-rise buildingsOften over-rides lateral design provisions from the analytical proceduresCan require same lateral resistance in low wind areas as in the highest hurricane-prone regions for many buildings

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Minimum wind load on vertical projection of roof reduced to half the minimum lateral load on wall

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Higher numbers due to ultimate wind speeds– 16 psf x 0.6 = 9.6 psf = 10 psf– 8 psf x 0.6 = 4.8 psf = 5 psf

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New simplified methodApplies to – Enclosed building– Simple diaphragm building– h ≤ 160 ft– Class 1 or Class 2 building

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ASCE 7ASCE 7--1010Chapter 27 Chapter 27 –– MWFRS Directional ProcedureMWFRS Directional Procedure

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ASCE 7ASCE 7--1010Chapter 27 Chapter 27 ––MWFRS Directional MWFRS Directional ProcedureProcedure

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Roof loads are tabulated for all wind speeds at various mean roof heights for Exposure Category CNote 1 provides conversion factors for Exposure Categories B or D

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Simplified method also addresses parapets and roof overhangsTorsional Load Cases have to be considered unless requirements of Appendix D are met

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Key Changes to GCp– Eliminated phrase “Direction of MWFRS

Being Designed”– Corrected the application of the End

Zones (Zone 2a) on the roof– Reintroduced Load Case B

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ASCE 7ASCE 7--1010Chapter 28 MWFRS Envelope ProcedureChapter 28 MWFRS Envelope Procedure

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Minimum Design Wind Loads

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Minimum Design Wind Loads

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ASCE 7ASCE 7--1010Roof OverhangsRoof Overhangs

Effects on MWFRS– Section (Directional Procedure)– Section (Envelope Procedure)

Design as Component and Cladding– Section 30.10

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ASCE 7ASCE 7--1010Roof Overhangs Roof Overhangs -- MWFRSMWFRS

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ASCE 7ASCE 7--1010Roof Overhangs Roof Overhangs --MWFRSMWFRS

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ASCE 7ASCE 7--1010Roof Overhangs Roof Overhangs –– Components and CladdingComponents and Cladding

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ASCE 7ASCE 7--1010Roof Overhangs Roof Overhangs –– Components and CladdingComponents and Cladding

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ASCE 7ASCE 7--1010Chapter 30 Chapter 30 –– Components and CladdingComponents and Cladding

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Old analytical method for h ≤ 60 ft

Old simplified method (Method 1) for h ≤ 60 ft


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Old analytical method for h > 60 ft

New simplified method for h ≤ 160 ft

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ASCE 7ASCE 7--1010Chapter 30 Chapter 30 –– Simplified h Simplified h ≤≤ 160 ft160 ft

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Documents

Advanced ASCE 7 – With Significant Changes to the 2010 Edition