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- Herausgeber: Wiley-VCH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Timber construction has been one of the most innovative areas of the building industry for several years. The speed with which new products are introduced into practical application is almost breathtaking compared to the other construction materials in the building industry. As a result, timber construction is continuously increasing its market share in commercial buildings and hall structures, and even in multi-storey construction for residential and office buildings. This book provides essential knowledge and skills required for the design, detailing, and construction of timber structures for typical building structures. Special emphasis is placed on the specific features of timber and wood-based materials compared to other construction materials. This concerns the numerous advantages, as e.g. the comparatively low weight, the good workability of the high-performance material and the large variety of assembling technologies, but also the challenges resulting from the material anisotropy and from the susceptibility to natural pests. In each chapter the essential phenomena are explained first and then brought into connection with code regulations. This aims to support the basic understanding of the interrelations and dependencies in timber engineering, which is the fundamental basis of creative engineering.
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Veröffentlichungsjahr: 2024
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Structural Timber Design
Werner Seim
Author:Prof. Dr.-Ing. Werner SeimFachgebiet Bauwerkserhaltung und HolzbauInstitut für Konstruktiven IngenieurbauUniversität KasselKurt-Wolters-Straße 334125 Kassel, Germany
Cover: Airship hangar in Mülheim, Germany, as a timber construction with impressive dimensions (42 × 26 × 92 metres).
Image: Ripkens Wiesenkämper Ingenieure / © Virtua ethic
All books published by Ernst & Sohn are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
Library of Congress Card No.: applied for
British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.
Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.
© 2024 Ernst & Sohn GmbH, Rotherstraße 21, 10245 Berlin, Germany
All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.
Print ISBN: 978-3-433-03404-0
ePDF ISBN: 978-3-433-61158-6
ePub ISBN: 978-3-433-61157-9
oBook ISBN: 978-3-433-61159-3
Cover: Petra Franke, Ernst & Sohn GmbH, Berlin, Germany
List of Fact Sheets
Fact Sheet 1.1
The fibre structure of the wood leads to anisotropic material characteristics of the timber
Fact Sheet 1.2
Ambient conditions (humidity) and load application time influence strength
Fact Sheet 2.1
Design against bending and shear failure
Fact Sheet 2.2
Design against bending buckling (normal forces only)
Fact Sheet 2.3
Serviceability limit state: deformations
Fact Sheet 3.1
Compression perpendicular to the grain
Fact Sheet 3.2
Notches
Fact Sheet 4.1
Design of connections in timber engineering
Fact Sheet 4.2
Shear-loaded dowel-type fasteners |
timber–timber
Fact Sheet 4.3
Shear-loaded dowel-type fasteners |
steel–timber
Fact Sheet 4.4
Connections with screws
Fact Sheet 4.5
Block shear |
steel–timber connections
Fact Sheet 5.1
Shear connectors – general
Fact Sheet 5.2
Shear plate connectors
Fact Sheet 5.3
How to calculate forces on single fasteners – Principle of intersection
Fact Sheet 6.1
Double-tapered beams
Fact Sheet 6.2
Composite beams
Fact Sheet 7.1
Light frame wall element
Fact Sheet 7.2
CLT slab element – distributed load and linear support
Fact Sheet 8.1
Simplified response spectrum method
Fact Sheet 9.1
Durability
Fact Sheet 9.2
Fire protection – effective cross section method
Preface
Timber construction is actually one of the most innovative areas of the building industry. This applies equally to developments in materials, joining and manufacturing technologies, as well as construction site logistics. The speed with which new products are introduced into practical applications is almost breathtaking, especially when compared to the other construction materials in the building industry. Consequently, timber construction is continuously increasing its market share in commercial buildings and hall structures, and even in multi-storey constructions for residential and office buildings. Hardly a month goes by without a new height record being reported, even from countries that have not yet been counted among the classic timber construction nations.
This book aims to provide essential knowledge and skills required for the design, detailing and construction of timber structures for typical building structures. Special emphasis is placed on the specific features of timber and wood-based materials compared to other construction materials. This concerns the numerous advantages, such as the comparatively low weight and the good workability of this high-performance material, and the large variety of assembling technologies. However, it also addresses the challenges resulting from the material anisotropy and susceptibility to natural pests. Each chapter begins by explaining the essential phenomena, which are then brought into connection with regulations mainly taken from the different parts of EN 1995. This approach aims to support the basic understanding of the interrelations and dependencies in timber engineering, which forms the fundamental basis of creative engineering.
The individual chapters of the book are structured independently in terms of content. One does not have to work through the book sequentially from beginning to the end, but can start with the topic which seems to be the most interesting one.
The content of the book largely corresponds to the content of the ‘Timber Engineering’ courses offered in the Bachelor’s and Master’s programmes in Civil Engineering at the University of Kassel, and is based on the lecture notes that were compiled there over the years. Carsten Pörtner, Martin Schäfers, Heiko Koch, Lars Eisenhut, Tobias Vogt, Johannes Hummel, Michael Schick, Timo Claus, Sascha Schwendner, Jens Frohnmüller and Giuseppe D’Arenzo have contributed significantly to those classes. Annalena Funke, as student assistant, has taken great care to ensure a good and uniform graphic presentation. I would like to thank them all very much for this.
My special thanks go to Johannes Hummel, who supervised the editing of the lecture notes and co-authored the German version of several chapters of this book.
Kassel, December 2023
Werner Seim
About the Author
Werner Seim is a professor for Timber Engineering and Building Rehabilitation at the University of Kassel, Germany. In addition to his academic role, he is an engineer with more than 35 years of experience in the design and assessment of timber structures. He holds a Civil Engineering Degree from the University of Stuttgart, received his PhD in 1994 from the Karlsruhe Institute for Technology (KIT) and conducted postdoctoral studies in 1998 at the University of California, San Diego (UCSD). His research focuses on bracing systems for high-rise buildings, timber–concrete composites and the assessment and re-use of structures. He is a member of several national and international scientific committees. He has been invited as a Visiting Professor to UBC Vancouver, EPF Lausanne and FCBA Bordeaux. In recognition to his commitment to teaching, he was awarded the Hessian State Prize in 2020. As an engineer, he received a timber construction prize from the state of Baden-Württemberg in 2006.
Symbols and Abbreviations
Latin Upper-case Letters
A
Section area, knottiness
AC
Action combination
A
ef
Effective contact area, effective cross section (steel rod or rebar)
A
k
Characteristic exceptional action
A
net,t
, A
net,v
Net area against tension and shear failure
B
Bending stiffness,
B
=
E
·
I
C
Minimum stiffness of bracing elements
E
cm
Mean modulus of elasticity for concrete
E
mean
, E
05
Mean modulus of elasticity, 5% fractile of modulus of elasticity
E
d
Effects of action, design value
E
d,fi
Effects of action, design values in case of fire
E
k
Effects of action, characteristic value
(
EI
)
ef
Effective stiffness of a composite beam
F
Force
F
90
,
Rd
Capacity against tension perpendicular to the grain
F
ax,Rk
Characteristic axial tensile resistance of a single fastener
F
bs,Rk
Characteristic capacity against block shear
F
v,w,Rd
Design resistance of light frame wall element against horizontal loading
F
c,0,d
Design compression force parallel to the grain
F
tens,k
Characteristic tension capacity of a screw
F
t,90,d
Design tensile force at the crack plane
F
v,Ed
Design force applied to the connection; design horizontal force applied to the head of a wall
F
v,Rk
Characteristic lateral resistance per shear plane of a single fastener
Δ
F
v,Rk
Characteristic rope effect contribution to the lateral resistance per shear plane of a single fastener
F
v,α,Rd
Design resistance for shear connector units
F
v
,α,Rd
b
Design resistance of the bolt in a connection with shear plates
F
v
,α,Rd
c
Design resistance of the shear plate
G
mean
, G
05
Mean shear modulus, 5% fractile of shear modulus
G
k
Characteristic self-weight
G
mean
Mean shear modulus
G
R,mean
Mean rolling shear modulus
(
GA
)
ef,xz
Effective shear stiffness for out-of-plane-loaded CLT panels
(
GA
)
ef,xy
Effective shear stiffness for in-plane-loaded CLT panels
H
Altitude above sea level
I
Torsional moment of inertia
I
p
Polar moment of inertia
I
y
, I
z
Moment of inertia related to bending around
y
-axis and
z
-axis
I
ef,x
, I
ef,y
Effective moment of inertia for CLT sections related to stresses in the direction of
x
-axis and
y
-axis
K
ser
, K
u
Slip modulus, stiffness of translational spring
K
ϕ
Stiffness of a rotational spring
LDC
Load duration class
LVL
Laminated veneer lumber
M
Bending moment, shear centre
M
ap,d
Design bending moment at the apex of a double-tapered beam
M
d
Design bending moment
M
D
Torsional moment
M
s
Bending moment at the centre of a group of connectors
M
tor
Torsional moment
M
y,Rk
Characteristic yield moment of a fastener
N
d
Design normal force
N
s
Normal force at the centre of a group of connectors
OSB
Oriented strand board
PGA
Peak ground acceleration
Q
k
Characteristic transient action
Q
k,L
Characteristic action, life load
Q
k,S
Characteristic action, snow
Q
k,W
Characteristic action, wind
R
d
Resistance, design value
R
k
Resistance, characteristic value
S
Centroid, soil amplification factor
S
ap,R
Maximum spectral acceleration
S
e
, S
d
Spectral acceleration, elastic and design value
S
y
Static moment related to bending around the
y
-axis
T
Torsional stiffness, period
ULS
Ultimate limit state
V
Volume
V
d
Design shear force
V
le
, V
re
Shear force at the left and right side resp. of the support
V
red
Reduced shear force at the support area
V
s
Shear force at the centre of a group of connectors
V
z
Shear force in the
z
-direction
W
y
, W
z
Section modulus related to bending around
y
-axis and
z
-axis
W
ap,netto
Section modulus at the apex of a double-tapered beam, if necessary, considering a weakened cross section
W
net
Section modulus of weakened cross section
W
res
Section modulus of residual cross section above or below an opening
Latin Lower-case Letters
a
Length of rectangular opening or diameter of round opening, acceleration
a
1
,
a
2
Spacing parallel and perpendicular to the grain, coefficients for the calculation of the buckling length, protrusion at the contact area
a
3,c
,
a
3,t
Unloaded and loaded end distance parallel to the grain
a
4,c
,
a
4,t
Unloaded and loaded end distance perpendicular to the grain
a
fi
Additional dimensions to reach a certain fire resistance for connections
a
r
Distance of ribs, width of a group of connectors
b
Section width of a member, width of the contact area, length of a wall element
b
fi
Section width after fire exposure
b
net
Net distance between studs of light frame element
b
w
Width of the web of a beam
c
Reduction factor for slender walls, damping constant
d
Diameter of a fastener
d
c
Diameter of a shear connector
d
ef
Charring depth
d
h
Diameter of the head or the washer
d
i
Diameter of knot
i
d
n
Diameter of a nail’s head
d
r
Diameter of a glued-in rod
d
0
Zero strength layer for members under fire exposure
f
Natural frequency
f
ax,k
Characteristic withdrawal strength parameter
f
c,0,d
Design compression strength parallel to the grain
f
c,90,d
Design compression strength perpendicular to the grain
f
c,α,d
Design compression strength at an angle
α
to the grain
f
d,fi
Design strength in case of fire
f
h,k
Characteristic embedment strength
f
h,α,k
Characteristic embedment strength at an angle
α
to the grain
f
head,k
Characteristic head pull-through parameter
f
k
Characteristic strength property
f
k1,k
, f
k2,k
Characteristic bond shear strength
f
d
Design strength
f
m,k
Characteristic bending strength
f
t,0,k
Characteristic tension strength parallel to the grain
f
t,90,k
Characteristic tension strength perpendicular to the grain
f
v,k
Characteristic shear strength
f
v,90,k
Characteristic rolling shear strength
f
u,k
Characteristic tension strength of steel
h
Section height of a member, length of a column, height of a wall element
h
A
Height of a member at the support
h
ap
Height of a beam at apex
h
c
Height of a shear connector
h
e
Distance from the loaded edge to the location where the full connection force is transmitted, embedment depth of a shear connector
h
ef
Effective member height or depth
h
f
Height of the flange of a beam
h
i
Distance of a row of fasteners from the unstressed edge
h
fi
Section height after fire exposure
h
w
Height of the web of a beam
i
Radius of inertia
i
m
Radius of inertia for torsional buckling
k
Spring stiffness
k
1
,
k
2
,
k
3
Prefactors for shear connectors to consider density, member thickness and edge distance
k
1
,
k
2
,
k
3
, k
4
Prefactors for beams to calculate increased bending stresses
k
5
,
k
6
,
k
7
, k
4
Prefactors for beams to calculate stresses perp. to grain
k
α,c
Prefactor to consider force–grain direction for shear connectors
k
c
Buckling coefficient
k
c,90
Stress spreading factor for compression perpendicular to grain
k
90
Modification factor for embedment strength
k
cr
Modification factor for shear
k
crit
Torsional buckling reduction factor
k
def
Deformation factor
k
dis
Factor accounting for effects of the stress distribution in the apex zone
k
l
Factor for the increased bending stresses in the apex zone
k
m,α
Factor accounting for the stress combination at the tapered edge
k
mod
Modification factor accounting for load duration and moisture content
k
pl
Factor to consider plate buckling und unintended stresses for the sheathing of light frame elements
k
v
Adjustment factor for shear strength
k
r
Strength reduction factor for the effects of bending of laminations during production
k
R
Factor for the calculation of rolling shear stresses for out-of-plane-loaded CLT panels with single loads
l
Member length or span
l
A
Length of the contact area
l
a
Bond length or effective penetration length of reinforcing element
l
ef
Effective length of the contact area, buckling length, torsional buckling length, penetration length of the screw
l
k
Length of cantilever
l
r
Width of external reinforcing panel
l
v,
i
, l
t,
i
Length of shear- and tension-loaded areas in block shear
l
v
End grain distance
m
Mass
m
0
Mass of the oven-dried wood sample
m
u
Mass of the moist wood sample
n
Number of fasteners (in a row), number of structural elements
n
ef
Effective number of fasteners
n
sp
Number of shear planes of a single fastener
n
x,
n
z
Number of fasteners in local
x
- and
z
-directions
p
Linear distributed load
q
Linear distributed load from transient action, behaviour factor of the structure
r
in
Inner radius of the curvature
s
Span of compression members, spacing of connectors, distance of single walls from the centroid of the bracing system
t
Thickness of single board lamella, thickness of sheathing, time of fire exposure
t
1
,
t
2
Thickness of side member, thickness of side or middle member, penetration length
t
ef
Effective penetration length of a fastener
t
pen
Penetration length of nails and staples
t
r
Thickness of external reinforcing panel
t
v
Notch depth
u
Wood moisture, displacement
v
Deformation, velocity
w
Deformation
w
c
Precamber unloaded
w
creep
Creep deformation
w
fin
Final deformation
w
inst
Elastic deformation
w
net
,
fin
Final deformation minus precamber
z
i
Distance between the axis of single layer
i
and the effective centroid of the composite section
Greek Upper-case Letters
Δ
Difference sign
Ω
Overdesign factor
Greek Lower-case Letters
α
Angle between the direction of acting stresses and the grain direction, coefficient for the calculation of the buckling length, angle at the tapered edge of a beam
β
Angle, buckling length coefficient, relation between embedment strength values for two different materials
β
c
Imperfection factor
β
n
Design charring rate
γ
Angle
γ
i
Factor for efficiency of mechanical connections in composite beams
γ
G
Partial safety factor for persistent action
γ
Q
Partial safety factor for transient action
γ
m
Partial safety factor for a material property
γ
ov
Overstrength factor
λ
Slenderness for lateral flexural buckling
λ
rel,m
Relative slenderness for lateral torsional buckling
ζ
Lehr’s damping factor
σ
c,0,d
Design compression stress parallel to the grain
σ
c,90,d
Design compression stress perpendicular to the grain
σ
c,α,d
Design compression stress at an angle α to the grain (0° > α > 90°)
σ
t,0,d
Design tension stress parallel to the grain
σ
t,90,d
Design tension stress perpendicular to the grain
σ
m,d
Design bending stress
σ
m,α,d
Design bending stress at an angle to the grain in plane
λ
rel,c
Relative slenderness ratio for lateral flexural buckling
λ
rel,m
Relative slenderness ratio for lateral torsional buckling
τ
ef
Shear stress in the adhesively bonded area
τ
d
Design shear stress
τ
xz
, τ
xy
Shear stresses from bending
τ
zy
,
τ
v,90
Rolling shear stresses
τ
v,tor
Rolling shear stresses for in-plane loaded CLT panels
ψ
0
,
ψ
1
,
ψ
2
Combination factors for actions
ρ
k
, ρ
m
Characteristic density, mean density
ω
u
Equilibrium moisture content
ϑ
Angle
1Timber as a Structural Material
In this chapter, the most important physical properties of wood are described with regard to its use as a construction material. These include fibre structure, irregularities and moisture absorption and release. Timber and wood-based materials used in construction are introduced and their mechanical properties are presented.
With regard to the manifold topics of wood physics and wood chemistry, selected literature for further reading is recommended and listed.
1.1 Building with Timber: Advantages and Challenges
Alongside masonry using natural stones, timber construction is one of the oldest building methods known to humankind. Until the industrial production of steel profiles, timber was the only building material available for beam-type building components subjected to normal forces and bending moments. In the course of history, carpenters developed a multitude of applications for this comparatively easy-to-handle material. Timber has been used for roof constructions, timbered-framed buildings, bridges, ships and much more. Wood is locally available in most regions of the northern hemisphere and can be transported from the forest via the sawmill to the construction site in a short span of time. Timber is the only natural growing material that is widely used for building constructions and other load-bearing structures. Wood has excellent potential for optimised cascade use, as depicted schematically in Figure 1.1.
Figure 1.1 Cascade use of wood in the construction sector.
Source: VHI Verband der deutschen Holzwerkstoffindustrie (Association of the German Wood-based Materials Industry).
In Europe, approximately 35% of the land area is forested. Finland tops the list with over 70%, while Ireland with 10%, is among the countries with sparse forests. Monaco is the only country without any forests. Forests store significant amounts of CO2 through photosynthesis. Burning or rotting of wood releases as much CO2 as was absorbed from the atmosphere during its growth. When wood is used as a construction material in buildings or other structures, the CO2 remains sequestered for the entire lifespan of the building. The management of forests follows the principle of sustainability: only as much wood is harvested per year as will regrow during that time. Wood, as a natural material, can be destroyed by fungi or insects under certain conditions. Thus, the service life of wooden structures depends significantly on the construction details and the selected preservation method. The fact that wooden buildings can last several hundred years with the right construction and care is evidenced by the numerous mediaeval roof constructions and half-timbered houses that have been preserved throughout Europe, some dating back more than 800 years.
