Bulletin Cross laminated timber - Bulletin - Cross-laminated timber August 2021 - brettsperrholz.org
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Bulletin – Page 1/10
Cross-laminated timber
August 2021
A campaign by
Studiengemeinschaft Holzleimbau e.V.
Bulletin
Cross laminated timber
August 2021Bulletin – Page 2/10
Cross-laminated timber
August 2021
Table 1
Tolerances at a reference moisture content of 12%
General
Load-bearing cross laminated timber Plate thickness for t ≤ 300 mm ± 2 mm
(X-Lam) components are structurally for t > 300 mm ± 3 mm
designed and meticulously manufactured,
high-quality construction elements.
They are used as large-dimension
plates and diaphragms or as beams Plate widths and openings for b ≤ 3.000 mm ± 2 mm
in service classes 1 or 2 according to for b > 3.000 mm ± 3 mm
DIN EN 1995-1-1: 2010-12.
Cross laminated timber may only be
produced in accordance with a
Plate lengths for ℓ ≤ 3.000 mm ± 3 mm
German technical approval (abZ) of
for 3.000 < ℓ ≤ 10.000 mm ± 4 mm
Deutsches Institut für Bautechnik or a
for ℓ > 10.000 mm ± 5 mm
European technical assessment (ETA).
A list of current German technical
approvals and European technical
assessments can be found at
www.brettsperrholz.org (filed under Lay-up Design
Brettsperrholz / gültige Zulassungen). Cross laminated timber consists of at The design is carried out in accordance
least three orthogonally arranged and with EN 1995-1-1:2010-12 (Eurocode
In the following sections, general
bonded softwood layers. If there are 5-1-1, including its national annex), taking
material-dependent rules are explained
more than three solid-timber layers, into account the requirements of the
which ensure a long service life and the
neighbouring layers may be glued manufacturer‘s technical approval or ETA.
preservation of appearance. Furthermore,
with the grain aligned if permitted
terms important to the determination of Cross laminated timber members may
by the German technical approval or
the quality of cross laminated timber are be designed carrying load along one or
European technical assessment.
explained. two axes. The load-bearing capacity is
The lamellae in each timber layer determined by considering the static
may be arranged along their narrow sides system and load configuration.
either with or without gaps. If arranged The specification of properties will
without gaps, the narrow sides may be not suffice. The cross-sectional
edge bonded. lay-up must instead be stated,
describing the properties of the layers.
Some German technical approvals
and European technical assessments The manufacturers provide design
allow the inclusion of layers of derived aids for conventional systems and load
wood products. The surfaces of distributions.
X-Lam members may have factory-
Since strength and stiffness values vary
applied non-load-bearing layers for
depending on the cross-sectional lay-
aesthetic or building physics reasons.
up and the manufacturer’s production
methods, the design of the load-bearing
Standard dimensions and tolerances
construction and, where applicable, the
Cross laminated timber should be
building physics verification should be
requested with thicknesses starting at
checked when products are exchanged.
60 mm and increasing in 10 mm steps.
The tolerances listed in Table 1 apply. Verification of fire protection is
carried out in reports or assessments
of the manufacturer according to
the requirements of the respective
German technical approvals or
European technical assessments.Bulletin – Page 3/10
Cross-laminated timber
August 2021
Strength class
Further information about Further literature The strength, stiffness, and density
design and construction Detailed design information parameters of cross laminated timber are
can be found in: generally given as the properties of the
General Augustin, M.; Blaß, H.; individual layers in the European technical
The design of plates, diaphragms and Bogensperger, T.; Ebner; Ferk, Heinz J.; assessments or German technical
beams made of a layered orthogonal Fontana, M.; Frangi, A.; Hamm, P.; approvals of the manufacturers. The
material differs from the design of the Jöbstl, R.; Moosbrugger, T.; properties given apply to the direction
linear structural elements commonly Richter, K.; Schickhofer, G.; of the grain of the individual layers.
found in timber construction. Thiel, A.; Traetta, G.; Uibel, T.:
BSPhandbuch. Various mechanical methods can be
In the past years, numerous reference used to determine the internal forces
Holz-Massivbauweise in Brettsperrholz,
books and booklets containing an and stresses in the layers and the
2nd revised edition, 2010 (only
introduction to the design of cross- deformations of the entire system.
available as download)
laminated timber elements have been System coefficients can be used
published. The following list includes Wallner-Novak, M.; Koppelhuber, J. for the structural verifications of the
some useful publications on this topic. and Pock, K.: individual layers parallel to the grain.
Brettsperrholz Bemessung –
Material parameters Grundlagen für Statik und Cross laminated timber is generally made
The material parameters to use Konstruktion nach Eurocode. of solid-timber layers of strength classes
must be taken from pro Holz Austria, Vienna, Austria, C 24 or T 14 according to DIN EN 338.
– the respective German technical 2013, ISBN 978-3-902320-96-4 The strength and stiffness parameters
approval of the Deutsches lnstitut refer to the solid-timber layers with the
Wallner-Novak, M.; Augustin, M., grain oriented parallel to the direction
für Bautechnik (DIBt) or
Koppelhuber, J. and Pock, K.: of the respective stress. The strength,
– the European technical assessment
Brettsperrholz Bemessung – stiffness, and density parameters
(ETA). To use these parameters
Band II: Anwendungsfälle. for cross laminated timber of strength
for designs executed in Germany,
proHolz Austria, Vienna, Austria, class CL 24 are shown in Table 2.
a manufacturer-specific general
2013, ISBN 978-3-902320-96-4 The manufacturer-specific German
technical approval issued by DIBt
might be required. For fire design, DIN EN 1995-1-2 technical approvals and European
with DIN EN 1995-1-2/NA must also technical assessments do not yet
Design rules be considered. allow the declaration of strength class
The following design rules apply for CL 24 instead of the declaration of the
Structural elements/connections list of individual values.
designs executed in Germany:
A catalogue of structural elements,
– the design rules of the respective The manufacturer-specific individual
including crosslaminated timber
abZ or ETA, possibly with a linked values for solid-timber lamellae of
elements, and relevant building-physics
ETA specific application rules (aBG) strength class C 24 or T 14 can be higher
parameters can be found at www.
– together with than those of strength class CL 24.
dataholz.com.
DIN EN 1995-1-1 (Eurocode 5-1-1) and
The requirements for fire protection Figure 1 assigns the strength and stiffness
DIN EN 1995-1-1/ NA (National Annex).
and necessary design verification parameters listed in Table 2 to the actions.
– Dederich, L. et al:
formats for Germany can be determined
INFORMATIONSDIENST HOLZ,
by using the fire protection navigator
holzbau handbuch,
(www.brandschutznavigator.de). Many
Reihe 3, Teil 5, Folge 2,
manufacturers provide product-specific
Leitdetails für Bauteilanschlüsse in
information.
den Gebäudeklassen 4 und 5
https://informationsdienst-holz.
Software
de/publikationen/leitdetails-fuer-
An extensive software package including
bauteilanschluesse-gebaeudeklasse-
background documentation can be
4-und-5
found at www.cltdesigner.at. Many
– Many manufacturers provide
manufacturers provide productspecific
standard details.
design information.
– Further information can also be found
in design guides of manufacturers of
fasteners and fire protection elements.Bulletin – Page 4/10
Cross-laminated timber
August 2021
Table 2
Minimum values of the strength and stiffness parameters of the solid-timber layers
of cross laminated timber of strength class CL 24 (in N/mm2) and density parameters (in kg/m³)1)
Property 2) Symbol Value
Bending strength 3) For out-of-plane bending moments ƒm,k 24
In plane ƒt,0,k 14
Tensile strength
Out of plane ƒt,90,k 0,12
In plane ƒc,0,k 21
Compressive strength
Out of plane ƒc,90,k 2,50
Longitudinal ƒv,k 3,50
Shear strength 4)
Rolling shear ƒr,k 0,70
In plane E 0,mean 11.000
Young's modulus 5)
Out of plane E 90,mean 370
Out of plane G mean 650
Shear modulus 5) 6)
Rolling shear G r,mean 50
Density ρk 385
1) For verifications using the net cross section.
2) See Figure 1.
3) For in-plane bending moments, such as those present in the design of columns and cantilevering panels, the characteristic value
of the in-plane edgewise bending strength ƒm,edge,k is required. This value is generally not found in the German technical approval or
European technical assessment. According to FprEN 16351:2020, a value of ƒm,edge,k = 20,5 N/mm2 may be used.
Any information supplied by the manufacturer must be taken into account.
4) For the verification of the shear strength of the entire cross section or the torsion strength of the glued intersection areas of the lamellae of
neighbouring solid-timber layers, further parameters are necessary which generally cannot be declared, based on the German technical approval
or European technical assessment. According to FprEN 16351:2020, the shear strength of the entire cross section can be assumed as ƒv,xy,k or
ƒv,yx,k = 5,50 N/mm2. The torsion strength of the intersection areas is given as ƒtor,node,k = 2,5 N/mm2.
Any information supplied by the manufacturer must be taken into account.
5) The 5% quantiles of the Young’s and shear moduli may be assumed to be 5/6 of the mean values: E05 = Emean · 5/6 and G05 = Gmean · 5/6
6) The in-plane shear modulus may be assumed to be Gxy = 250 N/mm2. This parameter is generally not found in the German technical approval
or European technical assessment. Any information by the manufacturer must be taken into account.Bulletin – Page 5/10
Cross-laminated timber
August 2021
Parameters for the verification
Action of the layers parallel to the grain
F F ƒm
ƒv and ƒr
E0
F/2 F/2 F/2 F/2
G and Gr
F F ƒm, edge
ƒv,xy and ƒtor,node
E0
F/2 F/2 F/2 F/2 Gxy
ƒt,0
F F F F Et,0
F
ƒt,90
E90
F
F
ƒc,0
F F Ec,0
F
F
ƒc,90
Ec,90
F
Figure 1
The strength and stiffness parameters listed in Table 2 assigned to actionsBulletin – Page 6/10
Cross-laminated timber
August 2021
Tension perpendicular to the grain
Tension perpendicular to the grain
(tension perpendicular to the plane < CE-mark pursuant to
Directive 93/68/EEC
of the panel) must be sustained by
orthogonal reinforcement, e.g. by
self-drilling fully threaded screws. 4321 < Number of the notified body
< Name and address or
Holes, notches, cut-outs, sign of the manufacturer
Manufacturer XY
bore holes, and cuts executed on-site,
and additional loads XX < Last two digits of the year in which
the CE-mark was first applied
Execution of holes, notches, bore holes,
NB – xyz
and cuts, as well as changes to the < Number of declaration of performance
static system and additional loads,
must be discussed with the designer ETA xx/yyyy < Number of the ETA
of the structure.
Cross laminated timber of Class CL24
< Intended purpose and identifying
Marking as load-bearing element code of the product type
in buildings and timber structures
Cross laminated timber components
comply with the requirements of the
building authorities. Components Strength, stiffness and density properties < Mandated properties
manufactured in accordance with to be listed as individual values
a German technical approval
Embedmendt strength,
bear the German conformity mark
kmod and kdef according to EN 1995-1-1
(Ü-Zeichen) (see Figure 2);
those manufactured in accordance Tolerances
with a European technical assessment for widths and thicknesses up to xx mm ± yy mm
carry the CE-mark (see Figure 3). for widths and thicknesses > xx mm ± zz mm
MC ≤ 12%
Hersteller α = 5 x 10-6/K
Z-9.1-xxx
DC 5
Brett- SC 1 oder 2
sperrholz
Area: xxxxx
Finger joints: yyyyy
Bildzeichen der
Zertifizierungsstelle Glue line integrity test: passed
D-s2, d0
Figure 2 Fire resistance according to Table xx
Example of an Ü-Zeichen (Ü mark) of Annex yy of ETA xxxx/yyy
E1
μ = xx (dry); μ = yy (moist)
Soft body impact resistance test: passed
R = xx dB
L´n,w = XX dB
α = xx for yy Hz to zz Hz;
α = ss for tt Hz to uu Hz
λ = 0, 12 W/(m/K)
Figure 3
C ≤ X m3 / [h·m3/(h Pa) n ] Example of a CE-mark for
cross laminated timber
cp = 1.600 J/(kg/K) according to an ETA based on
EAD 130005-00-0304 (manu-
facturer-specific text in bold)Bulletin – Page 7/10
Cross-laminated timber
August 2021
Wood preservation and wood species Cracking
Structural protection of wood should Moisture is absorbed mainly by the outer
take precedence over preservative layers of cross laminated timber. The
treatment. Preservative treatment of wood moisture content must gradually approach
is uncommon and also not required as the moisture expected during later use.
per DIN 68800: cross laminated timber is
As is the case with all structural solid-
manufactured from kiln-dried timber
timber products, the cracks appearing
and only used for service classes (SC) 1
due to the moisture content of the
and 2. An attack by wood-destroying
material progressing towards the
fungi is unlikely due to the expected
equilibrium moisture content of the
moisture content of the timber being
product at its final location are product-
less than 20% (u < 20%). Pursuant to
specific and cannot be avoided.
DIN 68800-1: 2011-10, adequate durability
against insect attack may be assumed
Transport and assembly
in SC 1 and SC 2, irrespective of species.
Cross laminated timber components
Cross laminated timber is generally should be transported and installed
manufactured from spruce; however, other only by experienced, suitably equipped
types of softwood may also be used. and trained specialist companies. The
following should be taken into account:
Surface qualities – The members must be protected from
Cross laminated timber components can moisture and dirt during transport
be manufactured with varying surface and until installation. To prevent
qualities. Three surface qualities are discolouration and rust marks, the
defined in Table 3 (see Page 8). Other, components must be covered when in
manufacturer-specific definitions of the vicinity of steel being welded or cut.
surface quality also exist. The following – Transport packaging must be removed
general criteria apply: soon after delivery to reduce the risk
– Additionally, for example for knot sizes, of condensation, which leads to blue
grading requirements apply. stains or mildew.
– Glue lines and finger joints are – Members must be stored at an
not defects, since they are specific adequate distance from the ground,
to the product. covered with tarpaulins, and secured
– Wood-based panels are generally against toppling.
butt-joined. – Adequately dimensioned lifting gear
– Additional treatment of the surface, and slings must be used for lifting.
such as sanding, brushing, or profiling, – Cross laminated timber members
can be arranged. must be accurately aligned.
– The desired surface texture of the Components must be supported
member must be contractually agreed temporarily if necessary.
on and specified in the tender. – Installed members must be kept
– The surfaces of a cross laminated covered until the final weather Figure 4 – 6
timber member may be supplied with protection is in place. Application examples of cross laminated timber
different surface qualities. – To prevent rust marks on the timber
– Unless otherwise agreed, industrial members, corrosion protection must be
quality is provided. applied to steel parts before installation.
– See also Page 9.Bulletin – Page 8/10
Cross-laminated timber
August 2021
Table 3
Surface qualities of the visible area (surface layer made of solid-timber lamellae)
of cross laminated timber at a moisture content of 12%
Surface quality Surface quality Surface quality
Criterion (non-visible quality) (industrial quality) (room quality)
Wood species Addition of One species; One species;
other species possible spruce/fir are deemed spruce/fir are deemed
one wood type one wood type
Surface Smoothed, without Planed or sanded Planed or sanded
further surface treatment
Gap width 1) Maximum 6 mm Maximum 4 mm Maximum 2 mm
Knots No restrictions Fixed knots permitted; Fixed knots permitted;
black and missing knots over 30 mm black and missing knots over 15 mm
mean diameter must be patched mean diameter must be patched
Pitch pockets1 1) Permitted Permitted Up to 5 mm × 50 mm or
equivalent area permitted;
larger areas must be patched
Discolouration 1) No restrictions Up to 20% of the surface area Up to 5% of the surface area
Insect attack Worm grooves up to Ø 2 mm Not permitted Not permitted
permitted
Ingrown bark Permitted Permitted Isolated occurrence permitted
Pith Permitted Permitted Isolated occurrence permitted
Cracks 1) Criteria according to Criteria according to Criteria according to
strength grading strength grading strength grading
1) Condition upon deliveryBulletin – Page 9/10
Cross-laminated timber
August 2021
Important notes for working
with cross laminated timber (X-Lam) Figure 7
1 Transport and delivery 2 Fastening and lifting by crane
– The loading sequence should be
discussed with the manufacturer – Operation only by trained staff.
if necessary. – Heed accident prevention
– During transport, the members must regulations.
be protected from moisture and dirt. – Use suitably dimensioned lifting
– Keep driveways clear to allow traffic. gear and slings according to the
– If elements are stored on the installation instructions.
building site, the ground must be – Before use, check lifting gear,
dry and have adequate load-bearing slings, and attachment points for
capacity. damage.
3 Storage at building site 4 Components during installation
– Use timber spacers.
– When stacking members horizontally,
align timber spacers vertically.
– Secure stored members
against toppling. Install in accordance with
– Remove packaging to prevent installation instructions.
condensation. – Avoid detrimental absorption
– Provide adequate ground clearance of moisture.
and tarpaulins to protect – Keep members covered until
members from rain, water spray, the final weather protection
and rising damp. is in place.
– For extended storage, use – Prevent soiling and protect
additional timber spacers to members by covering them
prevent creep deformations. if necessary.
5 Protection of installed members 6 Modifications on-site
7 8 9
4 5 6
Avoid staining by covering visible 1 2 3
surfaces
– Ensure adequate ventilation to
prevent discolouration due to moisture
Notches (1),
absorption during construction (e.g. due 3
to screeding or rendering). holes (2), and
– Dry components which have additional loads (3)
1
absorbed moisture as soon as
possible, but very carefully. – The effect of opening holes and 2
– Tarpaulins should be attached recessing on-site on load-carrying
in a way that prevents water capacities must be discussed
accumulation and limits capillary in advance with the site engineer.
absorption of water in gaps. – The capacity for carrying additional
– Heed accident prevention regulations. static loads must be verified.Bulletin – Page 10/12 Cross-laminated timber May 2021 Notes: ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................
Bulletin – Page 11/12 Cross-laminated timber May 2021 Notes: ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................
Bulletin – Page 10/10
Cross-laminated timber
August 2021
A campaign by
Studiengemeinschaft Holzleimbau e.V.
Picture credits:
Cover picture, rear page, and Figure 6:
Stora Enso, Ybbs
Figure 4: Lignotrend, Weilheim-Bannholz /
Studiengemeinschaft Holzleimbau e.V. Herlet, Köln
Heinz-Fangman-Str. 2 Figure 5: Züblin Timber, Aichach
D-42287 Wuppertal Figure 7: Studiengemeinschaft Holzleimbau
+49 (0)202 · 76 97 27 33 Fax
1st edition: Juni 2013
www.ingenieurholzbau.de 2nd edition: August 2016
www.brettschichtholz.de 3rd edition: January 2021
info@brettschichtholz.de 4th edition: August 2021You can also read
