Structural Timber Design to Eurocode 5

555 Pages·2008·5.99 MB·English

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STRUCTURAL TIMBER
DESIGN

to Eurocode 5

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To Margaret and John

Dawn and Romi

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STRUCTURAL TIMBER
DESIGN
to Eurocode 5

Jack Porteous BSc, MSc, DIC, PhD,
CEng, MIStructE, FICE
Director
Jack Porteous Consultancy

Abdy Kermani BSc, MSc, PhD, CEng,
MIStructE, FIWSc
Professor of Timber Engineering
Napier University, Edinburgh

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C⃝ 2007 by Jack Porteous and Abdy Kermani

Blackwell Science Ltd, a Blackwell Publishing company
Editorial Offices:
Blackwell Science Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK
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sought.

First published 2007 by Blackwell Publishing Ltd

ISBN: 978-14051-4638-8

Library of Congress Cataloging-in-Publication Data

Porteous, Jack.
Structural timber design to Eurocode 5 / Jack Porteous & Abdy Kermani.
p. ; cm.
Includes bibliographical references and index.
ISBN-13: 978-1-4051-4638-8 (hardback : alk. paper)
1. Building, Wooden–Standards–Europe.
2. Structural frames–Design and construction–Standards–Europe.
3. Timber–Standards–Europe.
I. Kermani, Abdy.
II. Title.
TA666.P66 2007
694.02′184 – dc22

2007037062

A catalogue record for this title is available from the British Library

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Printed and bound in the United Kingdom
by TJ International Ltd, Padstow, Cornwall

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the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation
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www.blackwellpublishing.com/construction

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Contents

Preface
xi

1. Timber as a Structural Material
1
1.1
Introduction
1
1.2
The structure of timber
2
1.3
Types of timber
3
1.3.1
Softwoods
3
1.3.2
Hardwoods
3
1.4
Natural characteristics of timber
4
1.4.1
Knots
4
1.4.2
Slope of grain
5
1.4.3
Reaction wood
5
1.4.4
Juvenile wood
6
1.4.5
Density and annual ring widths
6
1.4.6
Conversion of timber
7
1.4.7
Seasoning
11
1.4.8
Seasoning defects
11
1.4.9
Cracks and fissures
11
1.4.10
Fungal decay
11
1.5
Strength grading of timber
11
1.5.1
Visual grading
12
1.5.2
Machine grading
12
1.5.3
Strength classes
13
1.6
Section sizes
16
1.7
Engineered wood products (EWPs)
16
1.7.1
Glued-laminated timber (glulam)
18
1.7.2
Plywood
20
1.7.3
Laminated veneer lumber (LVL)
22
1.7.4
Laminated Strand Lumber (LSL), TimberStrand®
22
1.7.5
Parallel Strand Lumber (PSL), Parallam®
25
1.7.6
Oriented Strand Board (OSB)
25
1.7.7
Particleboards and fibre composites
35
1.7.8
Thin webbed joists (I-joists)
37
1.7.9
Thin webbed beams (Box beams)
39
1.7.10
Structural insulated panels (SIPs)
40
1.8
Suspended timber flooring
41
1.9
Adhesive bonding of timber
43
1.10
Preservative treatment for timber
45

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vi
Contents

1.11
Fire safety and resistance
46
1.12
References
48

2. Introduction to Relevant Eurocodes
50
2.1
Eurocodes: General structure
50
2.2
Eurocode 0: Basis of structural design (EC0)
52
2.2.1
Terms and definitions (EC0, 1.5)
52
2.2.2
Basic requirements (EC0, 2.1)
53
2.2.3
Reliability management (EC0, 2.2)
53
2.2.4
Design working life (EC0, 2.3)
54
2.2.5
Durability (EC0, 2.4)
54
2.2.6
Quality management (EC0, 2.5)
55
2.2.7
Principles of limit state design: General (EC0, 3.1)
55
2.2.8
Design situations (EC0, 3.2)
56
2.2.9
Ultimate limit states (EC0, 3.3)
56
2.2.10
Serviceability limit states (EC0, 3.4)
56
2.2.11
Limit states design (EC0, 3.5)
57
2.2.12
Classification of actions (EC0, 4.1.1)
58
2.2.13
Characteristic values of actions (EC0, 4.1.2)
58
2.2.14
Other representative values of variable actions (EC0, 4.1.3)
59
2.2.15
Material and product properties (EC0, 4.2)
60
2.2.16
Structural analysis (EC0, 5.1)
60
2.2.17
Verification by the partial factor method: General (EC0, 6.1)
62
2.2.18
Design values of actions (EC0, 6.3.1)
63
2.2.19
Design values of the effects of actions (EC0, 6.3.2)
63
2.2.20
Design values of material or product properties (EC0, 6.3.3)
64
2.2.21
Factors applied to a design strength at the ULS
68
2.2.22
Design values of geometrical data (EC0, 6.3.4)
68
2.2.23
Design resistance (EC0, 6.3.5)
70
2.2.24
Ultimate limit states (EC0, 6.4.1–6.4.5)
70
2.2.25
Serviceability limit states: General (EC0, 6.5)
74
2.3
Eurocode 5: design of timber structures – Part 1-1: General – Common
rules and rules for buildings (EC5)
76
2.3.1
General matters
76
2.3.2
Serviceability limit states (EC5, 2.2.3)
77
2.3.3
Load duration and moisture influences on strength (EC5, 2.3.2.1)
79
2.3.4
Load duration and moisture influences on deformations (EC5, 2.3.2.2)
80
2.3.5
Stress–strain relations (EC5, 3.1.2)
82
2.3.6
Size and stress distribution effects (EC5, 3.2, 3.3, 3.4 and 6.4.3)
83
2.3.7
System strength (EC5, 6.6)
85
2.4
Symbols
87
2.5
References
92

3. Using Mathcad® for Design Calculations
94
3.1
Introduction
94
3.2
What is Mathcad?
94
3.3
What does Mathcad do?
95
3.3.1
A simple calculation
95

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Contents
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3.3.2
Definitions and variables
95
3.3.3
Entering text
96
3.3.4
Working with units
96
3.3.5
Commonly used Mathcad functions
98
3.4
Summary
100
3.5
References
100

4. Design of Members Subjected to Flexure
101
4.1
Introduction
101
4.2
Design considerations
101
4.3
Design value of the effect of actions
103
4.4
Member Span
103
4.5
Design for Ultimate Limit States (ULS)
104
4.5.1
Bending
104
4.5.2
Shear
115
4.5.3
Bearing (Compression perpendicular to the grain)
119
4.5.4
Torsion
123
4.5.5
Combined shear and torsion
125
4.6
Design for Serviceability Limit States (SLS)
125
4.6.1
Deformation
125
4.6.2
Vibration
129
4.7
References
133
4.8
Examples
133

5. Design of Members and Walls Subjected to Axial or Combined Axial
and Flexural Actions
148
5.1
Introduction
148
5.2
Design considerations
148
5.3
Design of members subjected to axial actions
150
5.3.1
Members subjected to axial compression
150
5.3.2
Members subjected to compression at an angle to the grain
157
5.3.3
Members subjected to axial tension
162
5.4
Members subjected to combined bending and axial loading
163
5.4.1
Where lateral torsional instability due to bending about the major
axis will not occur
163
5.4.2
Lateral torsional instability under the effect of bending about the
major axis
167
5.4.3
Members subjected to combined bending and axial tension
168
5.5
Design of Stud Walls
169
5.5.1
Design of load-bearing walls
169
5.5.2
Out of plane deflection of load-bearing stud walls (and columns)
174
5.6
References
176
5.7
Examples
177

6. Design of Glued Laminated Members
205
6.1
Introduction
205
6.2
Design considerations
205
6.3
General
207

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6.3.1
Horizontal and vertical glued-laminated timber
207
6.3.2
Design methodology
207
6.4
Design of glued-laminated members with tapered, curved or pitched
curved profiles (also applicable to LVL members)
211
6.4.1
Design of single tapered beams
212
6.4.2
Design of double tapered beams, curved and pitched cambered beams
216
6.4.3
Design of double tapered beams, curved and pitched cambered
beams subjected to combined shear and tension perpendicular
to the grain
222
6.5
Finger joints
222
Annex 6.1
Deflection formulae for simply supported tapered and double
tapered beams subjected to a point load at mid-span or to a uniformly
distributed load.
222
Annex 6.2
Graphical representation of factors kℓ and kp used in the derivation
of the bending and radial stresses in the apex zone of double tapered
curved and pitched cambered beams.
225
6.6
References
226
6.7
Examples
227

7. Design of Composite Timber and Wood-Based Sections
248
7.1
Introduction
248
7.2
Design considerations
249
7.3
Design of glued composite sections
249
7.3.1
Glued thin webbed beams
249
7.3.2
Glued thin flanged beams (Stressed skin panels)
260
7.4
References
268
7.5
Examples
268

8. Design of Built-Up Columns
292
8.1
Introduction
292
8.2
Design considerations
292
8.3
General
293
8.4
Bending stiffness of built-up columns
294
8.4.1
The effective bending stiffness of built-up sections about the
strong (y–y) axis
295
8.4.2
The effective bending stiffness of built-up sections about the
z–z axis
297
8.4.3
Design procedure
299
8.4.4
Built-up sections – spaced columns
303
8.4.5
Built-up sections – latticed columns
308
8.5
Combined axial loading and moment
311
8.6
Effect of creep at the ULS
312
8.7
References
313
8.8
Examples
313

9. Design of Stability Bracing, Floor and Wall Diaphragms
338
9.1
Introduction
338
9.2
Design considerations
338

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Contents
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9.3
Lateral bracing
339
9.3.1
General
339
9.3.2
Bracing of single members (subjected to direct compression) by
local support
341
9.3.3
Bracing of single members (subjected to bending) by local support
344
9.3.4
Bracing for beam, truss or column systems
345
9.4
Floor and roof diaphragms
348
9.4.1
Limitations on the applicability of the method
348
9.4.2
Simplified design procedure
349
9.5
The in-plane racking resistance of timber walls under horizontal and
vertical loading
351
9.5.1
The in-plane racking resistance of timber walls using
Method B in EC5
352
9.6
References
357
9.7
Examples
358

10. Design of Metal Dowel Type Connections
372
10.1
Introduction
372
10.1.1
Metal dowel type fasteners
372
10.2
Design considerations
375
10.3
Failure theory and strength equations for laterally loaded connections
formed using metal dowel fasteners
375
10.3.1
Dowel diameter
382
10.3.2
Characteristic fastener yield moment (My,Rk)
382
10.3.3
Characteristic Embedment strength ( fh)
383
10.3.4
Member thickness, t1 and t2
386
10.3.5
Friction effects and axial withdrawal of the fastener
388
10.3.6
Brittle failure
390
10.4
Multiple dowel fasteners loaded laterally
396
10.4.1
The effective number of fasteners
396
10.4.2
Alternating forces in connections
399
10.5
Design Strength of a laterally loaded metal dowel connection
400
10.5.1
Loaded parallel to the grain
400
10.5.2
Loaded perpendicular to the grain
400
10.6
Examples of the design of connections using metal dowel type fasteners
401
10.7
Multiple shear plane connections
401
10.8
Axial loading of metal dowel connection systems
403
10.8.1
Axially loaded nails
403
10.8.2
Axially loaded bolts
406
10.8.3
Axially loaded dowels
406
10.8.4
Axially loaded screws
406
10.9
Combined laterally and axially loaded metal dowel connections
408
10.10
Lateral stiffness of metal dowel connections at the SLS and ULS
409
10.11
Frame analysis incorporating the effect of lateral movement in metal
dowel fastener connections
415
10.12
References
416
10.13
Examples
417

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Contents

11. Design of Joints with Connectors
452
11.1
Introduction
452
11.2
Design considerations
452
11.3
Toothed-plate connectors
452
11.3.1
Strength behaviour
452
11.4
Ring and shear-plate connectors
459
11.4.1
Strength behaviour
459
11.5
Multiple shear plane connections
465
11.6
Brittle failure due to connection forces at an angle to the grain
466
11.7
Alternating forces in connections
466
11.8
Design strength of a laterally loaded connection
466
11.8.1
Loaded parallel to the grain
466
11.8.2
Loaded perpendicular to the grain
467
11.8.3
Loaded at an angle to the grain
468
11.9
Stiffness behaviour of toothed-plate, ring and shear-plate connectors
468
11.10
Frame analysis incorporating the effect of lateral movement in
connections formed using toothed-plate, split-ring or shear-plate connectors
469
11.11
References
469
11.12
Examples
470

12. Moment Capacity of Connections Formed with Metal Dowel Fasteners
or Connectors
483
12.1
Introduction
483
12.2
Design considerations
483
12.3
The effective number of fasteners in a row in a moment connection
484
12.4
Brittle failure
485
12.5
Moment behaviour in timber connections: rigid model behaviour
485
12.5.1
Assumptions in the connection design procedure
486
12.5.2
Connection design procedure
488
12.5.3
Shear strength and force component checks on connections
subjected to a moment and lateral forces
490
12.6
The analysis of structures with semi-rigid connections
497
12.6.1
The stiffness of semi-rigid moment connections
497
12.6.2
The analysis of beams with semi-rigid end connections
500
12.7
References
503
12.8
Examples
504

Appendix A: Weights of Building Materials
528

Appendix B: Related British Standards for Timber Engineering in Buildings
530

Appendix C: Outline of Draft Amendment A1 to EN 1995-1-1
532

Index
536

The Example Worksheets Disks Order Form
542

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Preface

As a natural material, timber is unique, innovative and easy to handle. It is sustainable,
environmentally friendly, can be readily recycled, and as sawn sections or quality-
controlledengineeredproducts,timberhasalargepotentialmarketforuseasastructural
and building material. However, the existing civil and structural engineering curricula
neglect, to a large extent, the importance of timber as a viable engineering material and
as a consequence relatively few textbooks provide information on the design of timber
structures. Also, most books have tended to concentrate on designs in accordance with
BS 5268, a permissible stress-based design, with limited information on designs to
Eurocode 5, which is based on a limit states design philosophy.
BS 5268 is to be replaced by Eurocode 5 in the very near future and all timber designs
in the United Kingdom will have to be carried out in accordance with this code. This
book is based solely on the use of Eurocode 5: Design of Structures. Part 1-1: General –
Common Rules and Rules for Building, referred to as EC5 in the book, and incorporates
the requirements of the associated UK National Annex. There is a pressing need for
practising engineers as well as specialist contractors, postgraduate and undergraduate
students of civil and structural engineering courses to become familiar with the design
rules in EC5 and this book offers a detailed explanation and guide to the use of the code.
It provides comprehensive information and a step-by-step approach to the design of
elements, connections and structures using numerous worked examples and encourages
the use of computers to carry out design calculations.
Chapter 1 introduces the nature and inherent characteristics of timber and gives an
overview of timber and its engineered products as structural and building materials,
and includes design-related information on the strength and stiffness properties re-
quired for design in accordance with the requirements of EC5. In Chapter 2 the design
philosophy used in Eurocodes is explained. It includes information on the relevance
of the requirements of Eurocode 0 to EC5 as well as the significance of the effects of
moisture content, load duration, creep behaviour and size factors etc., in the design
process.
Chapter 3 gives an overview of Mathcad®, a computer software package used to
carry out mathematical calculations, and details its simplicity and the advantages that
it provides when used for design calculations. The software is commonly used in design
offices and universities and the aim is to encourage readers to use computing as a tool to
increase their understanding of how design solutions vary in response to a change in one
or more of the variables and how alternative design options can be easily investigated.
The design of basic elements is explained and illustrated in Chapters 4 and 5 whilst
the design of more specialised elements such as glued-laminated straight, tapered and
curved beams and columns, thin webbed and thin flanged beams and built-up columns
is covered in Chapters 6–8 using numerous worked examples.

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xii
Preface

In Chapter 9, the lateral stability requirements of timber structures are addressed, and
the design of stability bracing and the racking resistance of floor and wall diaphragms
using the rules in EC5 are explained.
The design of connections using metal dowel type fasteners is covered in Chapter
10. It includes an overview of the theory used for connection design together with
a comprehensive coverage of the lateral and axial strength requirements of nailed,
screwed and bolted joints. The lateral stiffness behaviour of these types of connections
is also covered in Chapter 10 as well as the design of connections with multiple shear
planes. Several step-by-step worked examples are provided to illustrate the design
methods explained in this chapter.
Chapter 11 covers the strength and stiffness behaviour of connectors such as toothed
plates, split-rings and shear plates. In Chapter 12, the design of rigid and semi-rigid
connections subjected to combined moment and lateral forces is addressed with ex-
amples showing the significant effect on joint and member behaviour when semi-rigid
behaviour is included in the design process.
At the time of publication of the book a Draft Amendment A1 to EC5 is being
processed. An outline of the proposed changes being considered is given in Appendix
C and where an amendment will result in a change to the design procedure described
in the book, reference is made to the draft proposal in the text.
All design examples given in this book are produced in the form of worksheet files
and are available on a CD to run under Mathcad Version 11, or higher. Details are
given at the back of the book (see page 542). The examples are fully self-explanatory
and well annotated and the authors are confident that the readers, whether practising
design engineers, course instructors or students, will find them extremely useful to
produce design solutions or prepare course handouts. In particular, the worksheets
will allow design engineers to undertake sensitivity analyses to arrive at the most
suitable/economic solution(s) very quickly.
To prevent any confusion between the numbering system used in the book and that
used in the Eurocodes, where reference is made in the text to a specific section, item
number, or table in a Eurocode and/or its accompanying UKNA, it is given in italics.
For example 6.4.2 refers to item 6.4.2 of EC5 whereas 6.4.2 refers to Section 6.4.2 in
Chapter 6 of the book.
Permission to reproduce extracts from British Standards is granted by BSI. British
Standards can be obtained from BSI Customer Services, 389 Chiswick High Road,
London W4 4AL. Tel: [phone]. email: