structural design for wind loads: an overview of ... design for wind loads: an overview of...

Structural Design for Wind Loads: An Overview

of Engineering Considerations for Wood

BuildingsLori Koch, PE

Manager, Educational Outreach

American Wood Council

This presentation is protected by US and International

Copyright laws. Reproduction, distribution, display and use

of the presentation without written permission of AWC is

prohibited.

© American Wood Council 2016

Copyright Materials

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“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516.

Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.

This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner ofhandling, using, distributing, or dealing in any material or product.________________________________Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

• This course is intended for structural engineers and building designers seeking an overview of design steps, considerations and detailing best practices related to the wind-resistive design and analysis of non-residential and multi-family wood buildings. Developed in response to the fact that engineering curricula does not typically include a wood design course, it provides an overview of relevant 2012 International Building Code (IBC) provisions and American Wood Council (AWC)-referenced standards, a discussion of common design errors, and guidance related to load path continuity, shear walls, diaphragms, and uplift restraint. Topics covered in detail include:

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• 2012 IBC and AWC-referenced standards applicable to wood-frame wind-resisting systems

• Uplift-resistant design solutions, including combined shear and uplift

• Out-of-plane wall design for wind loads, including tall walls, gable end walls, and tall walls with large openings, as well as deflection criteria for a variety of wall finishes

• Design and stiffness assumptions for rigid, semi-rigid and flexible diaphragms

• Diaphragm deflection and design of components such as chords and collectors

• Shear wall design methods, including segmented, perforated and force transfer around openings

• Design of shear wall components, including holdowns and drag struts

• Multi-story wood-frame design example for high winds, including accommodation of accumulated forces and deflections as well as design and detailing for wood’s interface with concrete podiums and foundations

Course Description

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Upon completion, participants will understand:1. Review applicable building codes and reference standards for the

design of non-residential and multi-family wood-frame wind-

resisting systems.

2. Discuss design and detailing of wood-frame diaphragms, including

flexibility, deflection, boundary fasteners, and chords and collectors.

3. Explore design steps for wood-frame shear walls, including panel

edge nailing, end posts and holdowns, drag struts, and transfer

mechanisms to lower floors and foundations.

4. Examine other wind-related design considerations, such as uplift

and out-of-plane wall forces, and discuss the design and detailing

effects of stacking multiple stories of wood-frame lateral force-

resisting systems.

Objectives

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Outline

• ANSI• NDS• SDPWS• WFCM• Summary• More Info

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ANSI Accreditation

• AWC –ANSI-accredited standards developer• Consensus Body• Wood Design Standards Committee

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Outline


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NDS History

1944

1962

1968

1971

1973

1977

1982

1986

1991

1997

2001

2005

2012

2015

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Governing Codes for Wood Design

2015 NDS referenced in 2015 IBC

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2015 NDS – Primary Change

New Provisions to Address CLT

• Charging Language

• Design Values

• Design Equations

• Product Chapter

• Connection Design

• Fire Design

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2015 NDS Chapter Reorganization

2012 NDS• 1-3 General

• 4-9 Products

• 10-13 Connections

• 14 Shear Walls & Diaphragms

• 15 Special Loading

• 16 Fire

2015 NDS• 1-3 General

• 4-10 Products +CLT

• 11-14 Connections

• Shear Walls & Diaphragms

• 15 Special Loading

• 16 Fire

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NDS 2015 Chapters

1. General Requirements for Building Design

2. Design Values for Structural Members

3. Design Provisions and Equations

4. Sawn Lumber

5. Structural Glued Laminated Timber

6. Round Timber Poles and Piles

7. Prefabricated Wood I-Joists

8. Structural Composite Lumber

9. Wood Structural Panels

10. Cross-Laminated Timber

11. Mechanical Connections

12. Dowel-Type Fasteners

13. Split Ring and Shear Plate Connectors

14. Timber Rivets

15. Special Loading Conditions

16. Fire Design of Wood Members

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1. Sawn Lumber Grading Agencies2. Species Combinations3. Section Properties4. Reference Design Values

• Sawn Lumber and Timber

• MSR and MEL

• Decking

• Non-North American Sawn Lumber

• Structural Glued Laminated Timber

• Timber Poles and Piles

NDS 2015 Supplement

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A. Construction and Design Practices

B. Load Duration (ASD Only)

C. Temperature Effects

D. Lateral Stability of Beams

E. Local Stresses in Fastener Groups

F. Design for Creep and Critical Deflection

Applications

G. Effective Column Length

H. Lateral Stability of Columns

I. Yield Limit Equations for Connections

J. Solution of Hankinson Equation

K. Typical Dimensions for Split Ring and Shear

Plate Connectors

L. Typical Dimensions for Standard Hex Bolts,

Hex Lag Screws, Wood Screws, Common,

Box, and Sinker Nails

M. Manufacturing Tolerances for Rivets and Steel

Side Plates for Timber Rivet Connections

N. Appendix for Load and Resistance Factor

Design (LRFD) – Mandatory

NDS 2015 Appendices

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NDS – Chapter 1

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Chapter 1 - Terminology

fb ≤ Fb'

Reference design values (Fb, Ft, Fv, Fc, Fc ,̂ E, Emin)

Adjusted design values (Fb', Ft', Fv', Fc', Fc '̂, E', Emin')

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Chapter 1 – Design Loads

• Reference loads

• Minimum load standards

• ASCE 7 – 10

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NDS – Chapter 2

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Format Conversion Factor KF

RN = φ λ KF RASD

2015 NDS

RN = CDRASDASD

LRFD

RASD reference strengths

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NDS – Chapter 3

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Chapter 3 – CLT Design Equations

New

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Chapter 3 – CLT Design Equations

NDS Commentary – guidance on CP

New 23

NDS – Chapter 4

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Chapter 4 – Lumber

Design values• Visually graded lumber

• MSR / MEL

• Timber

• Decking

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Chapter 4 – Lumber

Lumber adjustment factors

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NDS – Chapter 5, 6, and 7

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NDS – Chapter 8

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Chapter 8 – Structural Composite Lumber

• New products

• Laminated Strand Lumber (LSL)

• Oriented Strand Lumber (OSL)

• ASTM D5456

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NDS – Chapter 9

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Chapter 9 – Wood Structural Panels

Design values – obtain from an approved source• FbS

• FtA

• Fvtv

• Fs

• FcA

• EI

• EA

• Gvtv

• Fc^

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Chapter 9 – Wood Structural Panels

Adjustment factors

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NDS – Chapter 10

New

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What is Cross Laminated Timber (CLT)?

Photos provided by FPInnovations

Chapter 10 – Cross-Laminated Timber

New

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New

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New

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NDS – Chapter 11

Ch 10 Ch 1138

NDS – Chapter 12

Ch 11 Ch 1239

Chapter 12 – Dowel-type Fasteners

New

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NDS – Chapter 13

Ch 12 Ch 1341

NDS – Chapter 14

Ch 13 Ch 1442

NDS – Chapter 15

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Chapter 15 – Special Loading

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NDS – Chapter 16

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…

Chapter 16 – Fire (ASD)

• Fire resistance up to two hours• Columns• Beams • Tension Members• ASD only

• Products• Lumber• Glulam• SCL• Decking• CLT - NEW

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2015 NDS Supplement

• New Southern Pine Design Values

• ALSC approves design values

• June 1, 2013

• AWC compiles them

• NDS Supplement

• More information

• www.spib.org

• www.southernpine.com

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Outline


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Code Acceptance of Standard

• 2015 IBC

• References 2015 SDPWS in Section

2305 for lateral design and

construction

• Chapter 1: Flowchart

• Chapter 2: General Design

Requirements

• Chapter 3: Members and

Connections

• Chapter 4: Lateral Force

Resisting Systems

General Overview

Outline

Chapter 2 – General Requirements

• Terminology

Definitions

• Flexible and Rigid Diaphragm removed

New

Chapter 3 - Members and Connections

• Framing

• Sheathing

• Connections

• Covers out-of-plane wind load resistance of shear walls and

diaphragms


• Framing – walls

• Accounts for composite action

• Strength and Stiffness

• Applies now to EI

• Up to 24” o.c.

Extension of 1.15 repetitive member factor, Cr

New


• Uplift Resisting Systems

New


3.4 Uplift Force Resisting

Systems

New

Chapter 4 – Anchorage of Concrete or Masonry Walls

• 4.1.5.1 Anchorage of

Concrete or Masonry

Walls to Diaphragm

• SDC C, D, E, or F

New

Chapter 4 – Anchorage of Concrete or Masonry Walls

• Pre-fabricated roof sections

lifted into place

• Safety, cost, speed

• Two common types• All wood• Hybrid

Chapter 4 – Nominal Design Value

Revised

Chapter 4 – Nominal Design Value

• Diaphragm Configuration Figures

• Direction with respect to load of• Continuous panel joints• Framing members

• Independent of panel orientation

Revised

Chapter 4 – Horizontal Distribution

Revised

4.2.5 Horizontal Distribution of Shear• Idealized as Flexible

• ASCE 12.3.1.1, or

• DDIAPHRAGM > 2 x DSHEARWALLS

• tributary area

• Idealized as Rigid

• ASCE 12.3.1.2, or

• DDIAPHRAGM < 2 x DSHEARWALLS

• relative lateral stiffness of vertical LFRS• Semi-rigid – complex analysis or “envelope” (NEW)

Chapter 4 - Lateral Force-Resisting Systems

• Torsional Irregularity

• Rigid or Semi-rigid• Torsionally Irregular

• Story Drift DA max > 1.2 DB & C Average


Revised

4.2.5.1 Torsional Irregularity• SDC A – Exempt• Rigid or Semi-rigid• WSP diaphragms L/W < 1.5:1• Diagonal Lumber (single or double layer) L/W < 1:1• ΔA max < ASCE 7 allowable story drift

Chapter 4 – Open Front Diaphragms

Revised


Revised

4.2.5.2 Open Front Structures• Not Torsionally Irregular

• WSP diaphragms L’/W’ < 1.5:1• Diagonal Lumber (single or double layer) L’/W’ < 1:1

• Torsionally Irregular• > 1-story L’/W’ < 0.67:1• 1-story L’/W’ < 1:1


Revised

4.2.5.2 Open Front Structures• Load parallel to opening - model as semi-rigid or rigid

D A max < ASCE 7 allowable story drift

• L’ < 35’

Exception: Cantilever < 6’ beyond nearest vertical LFRS need not

comply to 4.2.5.2.


Revised

4.2.5.2.1 Open Front Structures – 1 story

• L’ < 25’

• L’/W’ < 1:1

• Idealized as rigid - distribution of torsional shear

20’

40’

Chapter 4 – High Load Diaphragms

Revised

Blocked Diaphragm Configuration Figures

• Direction with respect to load of

• Continuous panel joints

• Framing members

• Independent of panel orientation

Chapter 4 – High Load Diaphragms

4.2.7.1.2 High Load Blocked Diaphragms4. The depth of framing members and blocking into which the

nail penetrates shall be 3" nominal or greater.

4. 5. The width of the nailed face of framing members and

blocking at boundaries and adjoining panel edges shall be 3"

nominal or greater. The width of the nailed face not located

at boundaries or adjoining panel edges shall be 2" nominal or

greater.


• Wood Shear Walls


Structural Fiberboard Shear Walls

NEW

Chapter 4 – Design Value Format

• Nominal design values tabulated for

shear walls

• ASD

• reduction factor (2.0)

• LRFD

• resistance factor f(0.80)


4.3.3.4 Shears Walls in a Line:

same materials and construction

4.3.3.4.1 - Individual full height shear walls

provide all same deflection, dswException:

• WSP h/bs > 2:1 vs x 2bs/h

• Fiberboard h/bs > 1:1 vs x (0.1 + 0.9bs/h)

• Shear distribution proportional to capacities

• Shear capacity reduction not combined with

aspect ratio adjustment (4.3.4.2)

2:1 3:1 3½:1

1.00 0.67 0.57

2:1 unless vs = 2(bs/h)

REVISED

Section 4.3.3.2

• Nails 6" panel edge spacing

• Up to 2:1 aspect ratio

• 16' height limit

• Based on cyclic testing

• Shear capacity reduction

Chapter 4 - Unblocked Shear Walls

ubCv

Chapter 4 - Unblocked Shear Walls

Deflection (4.3.2.2)

• Less stiffness

• Deflection amplified

by Cub


Wood Shear Walls

Footnotes moved to text and revised to reflect recent testing

Chapter 4 – Aspect Ratios & Capacity Adjustments

Revised

4.3.4.2 – Shear Wall Aspect Ratio Factors

• h/bs > 2:1 WSP

• vs x (1.25 – 0.125h/bs)

• h/bs > 1:1 Struct. Fiberboard

• vs x (1.09 – 0.09h/bs)

2:1 3:1 3½:1

1.00 0.875 0.813

2:1 unless vs = (1.25 – 0.125(h/bs))

Chapter 4 – Aspect Ratios & Capacity Adjustments

Revised

4.3.4.3 – Perforated Shear

Walls • h/bs > 3.5:1 Not considered

• h/bs > 2:1 Li = L (2bs/h)

• Aspect Ratio Factors (4.3.4.2) do not

apply

• Shear distribution exceptions (4.3.3.4.1)

do not apply

What’s Missing for CLT?

Lateral Design!• ASCE 7 Minimum Design Loads for

Buildings and Other Structures• Response Modification Coefficient, R• CLT not recognized system in ASCE 7

Table 12.2-1

• Options

• Performance-based design

• Demonstrate equivalence to existing

ASCE 7 system

• ASCE 7-10, FEMA P695, and FEMA P795

Quantification of Building Seismic

Performance Factors; Component

Equivalency Methodology

• CLT floors with traditional shear walls78

Outline

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WFCM and IRC/IBC

• 2001 WFCM → 2003, 2006, 2009 IRC/IBC• 2012 WFCM → 2012 IRC/IBC• 2015 WFCM → 2015 IRC/IBC

WFCM and IRC

• R301.1.1 Alternative Provisions• WFCM permitted

• R301.2.1.1 Wind Design• For bldgs. where wind design is

required or > 110 mph use one or more of the following:

• WFCM

• ICC 600 (newly referenced)

• ASCE 7

• IBC

WFCM and IBC

• Chapter 16 – Determination of Wind Loads Section of IBC (1609.1.1)• Wind loads in accordance with ASCE 7• Exception: residential structures per

WFCM

• Not used for structures on hills, ridges, or

escarpments

• Chapter 23 – Wood design• 2301.2 & 2309 conventional

construction

2015 IBC

2015 IBC

• Applications• Single-story• Slab-on-grade• L and W < 80’

• Examples• Restaurants• Office Buildings

• Design• Lateral• Gravity

WFCM

• Chapter 1: General• Chapter 2: Engineered Design• Chapter 3: Prescriptive Design• General outline Chapters 2-3

• Connections• Floor systems• Wall systems• Roof systems

• Supplement

Chapter 1: General

• Mean roof height < 33 ft• < 3 stories• Building length/width < 80 ft• Loads – ASCE 7-10• 0-70 psf ground snow load• 110-195 mph wind speed• 700 yr. return, 3-sec gust, Exp. B, C, D

• Seismic Design Categories• A, B, C, D0, D1, D2

• Loads and load path

• Continuous

• Continuity created by

connections

• Always ends in supporting soil

• Building has hundreds of load

paths

Chapter 2: Engineered

Source: FEMA

Chapter 2: Engineered

• Suction loads

Chapter 3: Prescriptive

• Segmented shear walls - wind

2015 WFCM Changes

• Rafters/Ceiling Joists – Brittle Finishes

New

2015 WFCM Changes

• Header Spans Supporting Roof and Ceiling New

Availability

• www.awc.org• PDF versions• Free view-only

• Buy a printable PDF

• Summer 2015• Commentary

• Printed version

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• This concludes The American Institute of Architects Continuing Education Systems Course

Questions?

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[email protected]

www.awc.org

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