150956631 Engineering Guide Wood for Wood Frame Construction

7/22/2019 150956631 Engineering Guide Wood for Wood Frame Construction

http://slidepdf.com/reader/full/150956631-engineering-guide-wood-for-wood-frame-construction 1/18

Canadian

Wood

Council

Conseil

canadien

du bois

Engineering Guide forWood Frame Construction2009 Edition





Engineering

Guide for

Wood Frame

Construction

2009 Edition

CanadianWoodCouncil

Conseilcanadiendu bois





The Canadian Wood Council (CWC) is the national federation of forest products associations

responsible for development and communication of technical information about the use of

wood products in construction. Ensuring that this information is in tune with technical changesand users’ needs is accomplished through the publication and updating of CWC manuals,

software, technical bulletins and case studies.

The Engineering Guide for Wood Frame Construction has been produced by CWC to provide

guidance to engineers, building designers, building ofcials, builders, and students of these

disciplines, on the structural design of wood elements and connections for wood frame

buildings that:

(a) fall within the scope of Part 9, “Housing and Small Buildings,” of the National Building

Code of Canada, and

(b) due to the size, location or conguration of the building, engineering design is required in

order to augment the prescriptive requirements in Part 9 (See the Foreword for additional

explanation).

This is the third edition of the Guide and it supersedes the previous editions published in 2001

and 2004. The Guide was revised, in this 2009 Edition, in order to conform to changes in the

2010 edition of the National Building Code of Canada.

Article 9.4.1.1 of the 2005 National Building Code of Canada references the “Engineering

Guide for Wood Frame Construction,” published by the Canadian Wood Council as an

example of good engineering practice for the design of Part 9 structural members and their

connections. Design Requirements are provided in Part B of the Guide and Supplementary

Design Tables are provided in Part D of the Guide.

Guidance on the National Building Code of Canada Part 9 prescriptive requirements can be

found in Part C “Supplementary Guidelines on Applicability and Scope” of the Guide.

It is intended that the Guide be used in conjunction with competent engineering design, accu-

rate fabrication and adequate supervision of construction. Every effort has been made to

ensure that the data and information in the Guide are accurate and complete. The CWC does

not, however, assume any responsibility for errors or omissions in the Guide nor for designs or

plans prepared from it.

This edition of the Guide was developed with technical input from a committee of engineers,

builders, building regulators, researchers and industry representatives. The Canadian Wood

Council gratefully acknowledges the contribution of the following people:

Thomas Abbuhl BC Institute of Technology

Michael Bartlett University of Western OntarioDavid Bowick Blackwell Engineering

Steve Boyd Quaile Engineering

Brent Bunting Simpson Strong-Tie Canada Ltd.

Y.H. Chui University of New Brunswick

Steve Copp Steve Copp Construction Ltd.

Bruno DiLenardo National Research Council of Canada,

Canadian Construction Materials Centre

Paul Jaehrlich CertiWood™ Technical Centre

Keith Jansen RCG Developments

Dominique Janssens Consultant

Engineering Guide for Wood Frame Construction V

Preface



Robert Kok Brockport Home Systems Ltd

Kenneth Koo FPInnovations – Forintek Division

Frank Lam University of British ColumbiaChun Ni FPInnovations – Forintek Division

Thor Tandy UNISOL Engineering Ltd.

Cathleen Taraschuk National Research Council of Canada, Canadian Codes Centre

With the permission of Canadian Standards Association, material is reproduced from CSA

Standard CAN/CSA-O86-09, Engineering Design in Wood, which is copyrighted by Canadian

Standards Association, 178 Rexdale Blvd., Toronto, Ontario, M9W 1R3. While use of this

material has been authorized, CSA shall not be responsible for the manner in which the

information is presented, nor for any interpretations thereof.

For additional technical information or to receive more information on CWC design tools,

call this toll-free number 1-800-463-5091 or visit the CWC web site at www.cwc.ca.

PrefaceVI



Foreword

Design Requirements

Scope ...................................................................................................................B-3

Denitions and Symbols ......................................................................................B-7

Objectives and Design Requirements ...............................................................B-10

Loads .................................................................................................................B-12

Roof Design .......................................................................................................B-17

Floor Design.......................................................................................................B-23

Wall Design ........................................................................................................B-30

Column Design ..................................................................................................B-35

Diaphragms ........................................................................................................B-36

Shearwalls .........................................................................................................B-47

General Construction Details .............................................................................B-62

Supplementary Guidelines on Applicability and Scope

Supplementary Tables

Load Tables

Gravity Load Tables .............................................................................................D-3

Wind Load Tables ................................................................................................D-9

Seismic Load Tables .........................................................................................D-35

Design Tables

Roof Design Tables ...........................................................................................D-61

Floor Design Tables ...........................................................................................D-73

Wall Design Tables ............................................................................................D-83

Beam and Column Design Tables ...................................................................D-121

Diaphragm Design Tables ...............................................................................D-135

Shearwall Design Tables .................................................................................D-149

Engineering Guide for Wood Frame Construction VII

Table of Contents

Supplementary Guidelines and Tables

A

B

C

D



Wood Frame Construction GuideVIII



Foreword

A

Engineering Guide for Wood Frame Construction



Forward A-2



Engineering Guide for Wood Frame Construction A-3

Foreword

The objective of the Engineering Guide for Wood Frame Construction is to provide acceptable

structural design solutions for wood elements and connections in wood frame buildings that

are 3 stories or less in building height, 600 m2

or less in building area, and roofs, walls andoors are generally constructed using systems of repetitive wood members spaced no more

than 600 mm on centre. These solutions apply to conditions where the element or building

being designed is within the scope of this Guide, and additional information is

provided to supplement the prescriptive wood frame construction requirements in Part 9,

Housing and Small Buildings, of the 2010 edition of the National Building Code of Canada

(NBCC). The provisions and solutions provided in the Guide address structural design

considerations. For design requirements related to other issues such as re, durability,

sound transmission and building envelope refer to the NBCC.

The Design Requirements in Part B of the Guide are based on design calculations that reect

the prescriptive provisions of Part 9 where appropriate, and provide structural solutions for

designs that are beyond the prescriptive solutions in Part 9. Buildings or building elements

beyond the scope of Part 9 and the Guide are designed in accordance with Part 4 of theNBCC. It is recommended that all post-disaster buildings essential to services in the event

of a disaster also be designed in accordance with Part 4 of the NBCC.

The Guide also contains supplementary information to assist in identifying situations, where

engineering analysis is required and structural solutions in the Guide are appropriate.

Structural design provisions are provided in the Design Requirements, Part B, of the Guide.

Supplementary information is included in the sections:

Part C – Supplementary Guidelines on Applicability and Scope, and

Part D – Supplementary Tables

Builders, regulatory authorities and building designers may wish to consult the section on

“Supplementary Guidelines on Applicability and Scope” as a guide to determining whether

a building or element falls outside the assumptions on which the Part 9 prescriptive require-

ments are based.

The Design Requirements and Tables in Parts B and D of the Guide have been written on

the assumption that structural design will be carried out by a Professional Engineer who is

qualied for such design.

PART 9 OF THE NATIONAL BUILDING CODE OF CANADA,

“HOUSING AND SMALL BUILDINGS”

General

Part 9 of the NBCC is a set of primarily prescriptive requirements covering the design of resi-

dential, business, personal service, mercantile and some industrial buildings, 3 stories or lessin building height and 600 m2 or less in building area.

Part 9 and Wood Frame Construction

Part 9 includes prescriptive solutions for wood systems where;

• wall, roof and oor planes are generally comprised of repetitive wood structural members

spaced no more than 600 mm o.c.,

• walls, roofs and oors are clad, sheathed or braced on at least one side,

• clear spans of wood members are limited to 12.2 m, and

• the oor live load does not exceed 2.4 kPa.



The solutions were developed as a simple set of minimum requirements that could be used

without the assistance of an architect or engineer.

The Part 9 requirements for wood frame construction are based on a combination of

calculated designs and solutions based on performance history. There is some overlap

between these two categories; i.e., calculations include performance considerations. In some

circumstances new products are introduced into Part 9 solutions using engineering design.

Examples of elements in Part 9 that are explicitly based on calculations include:

• dimension lumber oor joists

• dimension lumber and glulam oor beams

• dimension lumber roof rafters

• dimension lumber roof joists

• dimension lumber ceiling joists

• trusses designed in accordance with TPIC procedures

• dimension lumber lintels, and• anchor bolt connections.

Examples of elements in Part 9 that are based mainly on performance history include:

• notching and drilling limitations

• bearing requirements for rafters, joists and beams

• header joist, and trimmer joist sizes

• hip and valley rafter size and connection

• wall plates

• stud size and spacing, and

• column sizes.

The span tables in Part 9 are based on gravity loads - dead loads, occupancy loads and

balanced snow loads. In addition, elements such as roof rafters and roof trusses that are

designed for gravity loads also withstand lateral loads without being explicitly designed for

that purpose. The gravity loads used in Part 4 are in some cases higher than the gravity loads

used in Part 9 calculations. Some, though not all, of the elements sized by calculation in Part

9 would be larger if they were sized in accordance with Part 4 due to both load

differences and differences in design assumptions. Section 9.4 of the NBCC allows Part 9

structural members and connections to be designed according to Part 4 using the loads and

deection and vibration limits specied in Part 9 or Part 4. Gravity loads in the Guide are

consistent with loads in Part 9 of the NBCC and may be used to design repetitive framing

members and their supporting members.

The NBCC 2010 introduced prescriptive requirements for lateral resistance of Part 9

buildings. The Engineering Guide for Wood Frame Construction species lateral loads andlateral design solutions, and the section on Applicability and Scope includes a framework for

considering where the lateral load provisions in the Guide may be applicable.

Consistent with Part 9, the Engineering Guide for Wood Frame Construction applies to the

design of residential, business, personal service, mercantile and medium or low hazard indus-

trial buildings, 3 stories or less in building height and 600 m2 or less in building area. The

Design Requirements and Tables in Parts B and D of the Guide use an engineering mechan-

ics approach to assess the lateral resistance of a wood frame building, with some simplifying

assumptions for practical purposes. In this approach, the roof systems and oor systems

are assumed to act as diaphragms to transfer the lateral forces to wall systems acting as

shearwalls. Non-structural elements that contribute to the overall building performance are

Forward A-4



disregarded. Only adequately anchored oors, roofs and walls sheathed with structural wood

panels (alone or combined with gypsum board in the same wall or combined with

gypsum board within a storey) are considered in the engineering calculations.

Using this approach, many wood frame buildings based only on the Part 9 prescriptive

requirements would appear to be inadequate for resisting lateral loads; however, perfor -

mance history indicates that this is not the case. The performance history of small wood

frame structures cannot be explained completely by Part 4 structural calculations using

simple 2-dimensional load path assumptions. Traditional wood-frame construction is difcult

to model mathematically due to the many load paths in the indeterminate structural system

and the contributions of “non-structural” elements. Various aspects of building performance

have been investigated experimentally during the past fty years (for example Dorey and

Schriever 1957, Boughton and Reardon, 1982, Boughton, 1988, Ceccotti, 1990, Fischer et

al. 2001, Paevere, 2002, UWO 2002, Doudak, 2005). Most of these studies have focused on

one- and two-story structures on rigid foundations. These reports gave more insight into the

mechanisms of structural deformation including the importance of load sharing among thestructural and “non-structural” elements within the structure:

1. Interior nishes and many types of exterior cladding contribute to the lateral resistance of

the structure. Both the ultimate load capacity and the lateral stiffness are improved by the

addition of architectural components.

2. Non-loadbearing partitions stiffen and strengthen the structure so that the building acts as

a rigid box rather than a series of diaphragms and shearwalls.

3. Other non-structural elements such as stairs, closets and cabinetry also contribute to the

lateral resistance of the building.

4. The performance of wood light frame systems is enhanced by the load sharing and

composite actions. The overturning resistance of a wall is enhanced through “corner

effects” that engage adjacent walls. Roof and oor diaphragms, if adequately connected,

will transfer lateral wind and earthquake loads to all supporting walls, including wallsparallel and perpendicular to the direction of loading that normally may not be considered

in design.

Although to a large extent the structural stability of Part 9 buildings relies on these non-structural

elements, to date, this action has not been quantied in a systematic manner suitable for use in

structural design.

The numerous wood frame buildings throughout Canada and elsewhere represent countless

“prototypes” subject to eld-testing over many decades. However, some wood frame buildings

covered by Part 9 differ sufciently from the norm that they cannot be counted on to demon -

strate similar performance if their design is based only on the prescriptive provisions of Part 9.

WOOD FRAME CONSTRUCTION – PART 9 AND THE GUIDE

The Part 9 structural requirements for wood frame construction are derived from a com-

bination of calculated designs and solutions based on performance history. In the Guide,

calculations are used to develop structural requirements. The Guide calculations use:

• Gravity loads based on Section 9.4 of the NBCC

• Wind and earthquake loads from Part 4 of the NBCC, and

• Resistances for lumber members, sheathing, I-joists, structural composite lumber, shearwalls,

diaphragms and connections based on CSA Standard O86, Engineering Design in Wood with

some modications.

Lateral Design




Performance of wood frame construction under high wind loads

The wind design provisions in the National Building Code of Canada and the Engineering

Guide for Wood Frame Construction are intended to simulate peak gusts in storms havinga 1 in 50 probability of occurring every year. Studying the damage from hurricane force

winds in other parts of the world provides insight into how wood frame construction behaves

under high wind loads. Similar forms of damage have been reported in wood frame houses

exposed to the direct paths of tornadoes. (Allen, 1984; Allen 1986; Dagliesh and Allen, 1994)

The damage to housing in hurricanes and tornadoes shows that:

1. Sheathing attachment, gable end details and attachment of roof framing to walls are criti-

cal. (Douglas, 1992; Keith and Rose, 1992; Shefeld, 1993; Wolfe, Riba and Triche, 1993)

2. When it occurs, structural damage is usually related to the roof system. Damage to walls

and foundations are rarer. (Crandell, Gibson, Laatsch, Nowak and vanOvereem, 1993)

3. Major damage occurs at gradient wind speeds of 70 m/s or greater and minor damage

occurs at gradient wind speeds below 50 m/s (Sparks and Bhinderwala, 1993).

Neither the National Building Code nor this guide is intended to provide design solutions

against the direct force of tornadoes. Based on observations made in Canadian tornadoes,

the Structural Commentaries to the National Building Code state, “It is generally not

economical to design buildings for tornadoes beyond what is currently required by NBCC

Subsection 4.1.7 because of the low risk of loss to individual owners. It is, however, impor-

tant to provide key construction details for the safety of building occupants….anchorage

of home oors, is essentially covered by NBCC Article 9.23.6.1 for normal housing with

permanent foundations.” (Canadian Commission on Building and Fire Codes, 2010)

Performance of wood frame construction under earthquake loads

Canada has not experienced an earthquake that has caused widespread damage to wood

frame buildings. The damage from the 1989 earthquake in the San Francisco area was stud-

ied by Canadian researchers (Rainer, Jablonski, Law and Allen, 1990), leading to the following

observations concerning the performance of wood frame construction:

1. Foundation walls weak in racking resistance—such as cripple-stud walls—led to failure

of buildings.

2. Openings for doors in the ground oor of multiple storey buildings created “weak storeys”

which led to damage of the buildings.

3. Most of the serious structural failures that occurred to residential construction were due

to deciencies prohibited by California building codes and reected in the 1985 Uniform

Building Code (UBC).

The authors concluded: “Nominal lateral resistance in the UBC is achieved by specifying

minimum percentages of shear panels in the walls.”

Similar observations were made following the 1994 Northridge earthquake in California (NAHB

Research Center, 1994; American Forest and Paper Association, 1994). Structural damage

to wood frame construction in this earthquake was attributed to site conditions or non-confor -

mance with building codes.

Forward A-6



In a survey of wood frame building construction from around the world (Rainer and

Karacabeyli, 1999) the authors concluded that, “…despite some specic shortcomings

and resultant failures, wood frame construction has performed exceedingly well, bothfrom the perspective of life safety and incidence of damage.”

Lateral Resistance in the Guide

The section on “Applicability and Scope,” provides guidelines that are additional to the Part 9

prescriptive requirements of the NBCC. The detailed design information in the Guide can be

used where a full lateral design to resist wind and earthquake loads is considered necessary.

In the Design Requirements, lateral design for wind and earthquake loads includes the design

of fully detailed roof and oor diaphragms supported on shearwalls.

Gravity Loads

The prescriptive requirements in Part 9 are limited to buildings with occupancy loads of

2.4 kPa and the oor joist, lintel and oor beam span tables in Part 9 apply only to residentialloads of 1.9 kPa even though Part 9 may apply to occupancies which have specied live oor

loads up to 2.4 kPa. Sometimes only a small portion of a building will have higher loads and

engineering may be required to address an element supporting a combination of loads. The

Guide provides design solutions for small wood frame buildings with occupancy loads up to

2.4 kPa.

Snow loads in the Guide are calculated in accordance with Part 9 or, where required, Part 4 of

the NBCC. The dead loads in the Guide reect actual construction and are provided for oors

with normal weight nishes and concrete toppings.

New Materials

Increasingly, wood frame buildings incorporate engineered, proprietary wood products such as

wood I-joists, oor trusses, laminated veneer lumber, parallel strand lumber, laminated strandlumber and proprietary wood framed roof and wall systems and their connections. Builders,

designers and building ofcials have sought guidance in using these products

with Part 9 requirements. One of the objectives of the Engineering Guide for Wood Frame

Construction is to clarify load requirements for engineered wood products used in small wood

buildings.

The Guide may be used with proprietary wood products that are manufactured in accordance

with a quality assurance program supervised by an independent third-party certication

organization with design values developed in accordance with Clauses 13 and 14 of CSA

Standard O86 and are designed and installed in accordance with the manufacturer’s material

evaluation report.

Design of Individual Elements

Studs

NBCC Part 9 stud provisions are limited to stud lengths of 4.2 m for interior studs and 3.6 m

for exterior studs. In some situations, such as entrances and gable end walls, longer studs are

used.

The stud design procedures and stud tables in the Engineering Guide for Wood Frame

Construction have been developed using wind load data and considering the composite action

of wall elements.




Beams, headers and lintels supporting point loads

Part 9 provides beam, header and lintel tables for built-up wood members supporting uniformloads. The Guide provides design solutions for built-up wood members supporting point loads.

Column design

Part 9 prescriptive requirements for columns are limited to columns supporting 2 oors, a

maximum tributary width of 5 m and a maximum of 2.4 kPa occupancy load. The Guide

section on “Applicability and Scope,” provides guidance on limits to the Part 9 prescriptive

requirements and the “Design Requirements” provide column design solutions for a broad

range of loads and sizes.

Roof rafters

Part 9 rafter spans are limited to rafters tied at the eave. The Guide provides rafter design for

rafters with raised ties. In addition, the Guide provides structural design solutions for hip andvalley rafters.

Floor members

The Guide may be used to design oor support members supporting non-residential oor

loads. In addition, the Guide may be used for designing header and trimmer joists for open-

ings larger than allowed with the prescriptive requirements of Part 9.

Forward A-8



REFERENCES

Allen, D.E. 1984. Tornado Damage at Blue Sea Lake and Nicabong, Quebec, July 1984. Building ResearchNote 222. Division of Building Research. National Research Council of Canada. Ottawa, Canada.

Allen, D.E. 1986. Tornado Damage in the Barrie/Orangeville Area, Ontario, May 1985. Building Research

Note 240. Institute for Research in Construction. National Research Council of Canada. Ottawa, Canada.

American Forest and Paper Association, 1994. The Northridge Earthquake – A Preliminary Report. American

Wood Council. Washington DC

Boughton, G. N. and Reardon, G. F. (1982) “Simulated wind test on a house: Part 1 -Description” Tech. Rep.

No. 12, James Cook Cyclone Testing station, Townsville, Queensland, Australia.

Boughton, G. N. (1988) “Full scale structural testing of houses under cyclonic wind loads” Proceedings of the

1988 International Conference on Timber Engineering, Seattle, WA, Vol. 1, 82-88.

Canadian Commission on Building and Fire Codes, 2005. National Building Code of Canada. National

Research Council of Canada. Ottawa, Canada

Canadian Commission on Building and Fire Codes, 2005. User’s Guide - NBCC 2005 Structural

Commentaries. National Research Council of Canada. Ottawa, Canada

Ceccotti, A. (Ed.) 1990. Structural Behavior of Timber Constructions in Seismic Zones, Commission of the

European Communities and Florence University, Dipartimento di Ingegneria Civille, Florence University, Italy,

427 pp.

Crandell, J.H., M.T. Gibson, E.M. Laatsch, M.S. Nowak and J.A. vanOvereem. 1993. Statistically-Based

Evaluation of Homes Damaged by Hurricanes Andrew and Iniki. Hurricanes of 1992: Lessons Learned and

Implications for the Future. American Society of Civil Engineers. New York, New York.

Dalgliesh, W.A. and D.E. Allen, 1994. Tornado Damage in Aylmer, Quebec on August 4, 1994. Internal ReportNo. 669. National Research Council of Canada. Ottawa, Canada.

Dorey, D. B. and Schriever, W. R. (1957) “Structural test on a house under simulated wind and snow loads.”

Special tech. Pub. No. 210. American Society for Testing and Materials, Philadelphia, PA.

Doudak, G., 2005. Field Determination and Modeling of Load Paths in Wood Light-Frame Structures, PhD

thesis, McGill University, Montreal, QC.

Douglas, B.K., 1992, Hurricane Andrew, Part 2 Wood Building Analysis and Recommendations. A Special

Report of the National Forest Products Association

Fischer, D., Filiatrault, A., Folz, B., Uang, C-M., and Seible, F. (2001) “Shake Table Tests of a Two-Story

Wood-fame House. CUREE Publication No. W-06. CUREE, Richmond, CA.

International Conference of Building Ofcials, 1994. Uniform Building Code. International Conference of

Building Ofcials. Whittier, California.

Keith, E.L. and J.D. Rose, 1992. Hurricane Andrew – Structural Performance of Buildings in Southern Florida

(August 24, 1992). APA Report T92-21. American Plywood Association. Tacoma, Washington.

Paevere, P. (2002) “Full-scale Testing, Modeling and Analysis of Light-Frame Structures Under Lateral

Loading”, Ph.D. Thesis, Department of Civil and Environmental Engineering, University of Melbourne, Australia.

Rainer, J.H., A.M. Jablonski, K.T. Law and D.E. Allen, 1990. Earthquake Damage in the San Francisco Area

and Projection to Greater Vancouver. Canada Mortgage and Housing Corporation. Ottawa, Canada.




NAHB Research Center, 1994. Assessment of Damage to Residential Buildings Caused by the Northridge

Earthquake. U.S. Department of Housing and Urban Development, Ofce of Policy Development and

Research.

Rainer, J.H. and E. Karacabeyli, 1999. Performance of Wood frame Building Construction in Earthquakes.

Forintek Canada Corp, Special Publication SP 40. Vancouver, Canada

Shefeld, J.W. 1993. A Survey of Building Performance in Hurricane Iniki and Typhoon Omar. Hurricanes

of 1992: Lessons Learned and Implications for the Future. American Society of Civil Engineers. New York,

New York.

Sparks, P.R. and S.A. Bhinderwala, 1993. Relationship Between Residential Insurance Losses and Wind

Conditions in Hurricane Andrew. Hurricanes of 1992: Lessons Learned and Implications for the Future.

American Society of Civil Engineers. New York, New York.

UWO. 2002. “Mitigating housing losses in extreme natural events”, Proceedings of Workshop,

2 & 3 December 2002, Toronto, University of Western Ontario, ON, Canada (on CD).

Wolfe, R.W., R.M. Riba and M. Triche. 1993. Wind Resistance of Conventional Light-Frame Buildings.

Hurricanes of 1992: Lessons Learned and Implications for the Future. American Society of Civil Engineers.

New York, New York.

Forward A-10

Documents

150956631 Engineering Guide Wood for Wood Frame Construction