Introduction to Structural Timber

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Introduction to Structural Timber Design to the
Eurocodes
Wood for Good CPD seminars 2005
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Timber Design To Limit States
EUROPEAN STANDARDISATION
Eurocodes provide a set of common technical
recommendations a contractual design basis To
reinforce the competitive position of the
European Construction Industry To establish a
common basis for drawing up harmonised technical
specifications
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Overview to European Codes and Standards (1/2)
EN 1990 Eurocode - Basis of structural design
lt Structural safety
EN 1991 Eurocode 1 - Actions on structures
lt Loading
EN 1991-1.1 Densities, self weight and imposed
loads
EN 1991-1.2 Actions on structures exposed to fire
EN 1991-1.3 snow loads
EN 1991-1.4 Wind loads
EN 1991-1.5 Thermal actions
EN 1991-3 Actions induced by cranes and machinery
EN 1991-1.6 Actions during execution
EN 1991-1.7 Accidental actions due to impact and
explosions
EN 1991-2 Traffic loads on bridges
EN 1995 Eurocode 5 - Design of timber structures
lt Design and detailing
EN 1995 -1 -2 General Rules - Structural fire
design
EN 1995 -1 -1 General Rules - General rules and
rules for buildings
EN 1995 -2 Bridges
lt Materials
ENs
lt Durability
ENs
lt Components and assemblies
ENs
lt Metal fasteners connectors and hardware
ENs
ENs
lt Adhesives
EN 1997 Eurocode 7 - Geotechnical data
lt Foundations
EN 1997-1 General rules
EN 1997-2 Design assisted by laboratory testing
EN 1997-3 Design assisted by field testing
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National Annexes to Eurocodes and their Purpose
(1/2)
Examples of Nationally determined parameters are
shown on the next slide
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National Annexes to Eurocodes and their Purpose
(2/2)

• Nationally-determined parameters in EN 1995-1-1
• Assignment of loads to load duration classes
• Assignment of timber constructions to service
  classes
• Partial factors for material properties
• Limiting values for deflections
• Limiting values for vibrations
• Design method for domestic floor vibrations
• Advice on nailed timber-to-timber connections
• Choice of method for design of wall diaphragms
• Mod. Factors for bracing of beam and truss
  systems
• Erection tolerances

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Requirements of a Structure designed to EN 1990
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Durability Examples of Practical Solutions
Exposed untreated oak timber decking.
Capping detail on exposed glulam floor beam.
Steel shoe and concrete pillar isolating round
timber column end grain from the ground.
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Robustness in Structural Design to EN 1990 (1/2)
On one hand robustness relates to
disproportionate collapse concept
Full scale disproportionate collapse testing on a
six storey timber frame building for TF 2000
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Contents of EN 1990
BS EN 1990 2002 Basis of Structural Design
(Eurocode 0)
Section 1 - General Section 2 - Requirements Secti
on 3 - Principles of Limit States Design Section
4 - Basic Variables Section 5 - Structural
Analysis and Design Assisted by
Testing Section 6 - Verification by the Partial
Factor Method Annex A1 - (Normative)
Application for Buildings Annex B - (Informative)
Management of Structural Reliability for
Construction Works Annex C - (Informative)
Basis for Partial Factor Design and Reliability
Analysis Annex D - (Informative) Design
Assisted by Testing
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Contents of EN 1991
BS EN 1991 2002 Actions on Structures
(Eurocode 1)
Part 1 Part 1-1 - General actions - Densities,
self-weight imposed loads for buildings Part
1-2 - General actions - Actions on structure
exposed to fire Part 1-3 - General actions -
Snow loads Part 1-4 - General actions - Wind
actions Part 1-5 - General actions - Thermal
actions Part 1-6 - General actions - Actions
during execution Part 2 Traffic loads on
bridges Part 3 Cranes and machinery Part
4 Actions in silos and tanks
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EN 1995 supporting hENs and Product Specifications
Gluam and the CEN standards arrangements
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Overview to European Codes and Standards

• Scope of Eurocode 5
• Design of buildings and civil engineering work in
  timber i.e. solid timber in sawn or pole form,
  glued laminated timber or wood based panels and
  other structural timber composites such as LVL.
• Only concerned with requirements for mechanical
  resistance, serviceability, durability and fire
  resistance of timber structures.
• In compliance with principles and requirements
  given in EN 1990.

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Contents of EN 1995-1-1
Eurocode 5 Design of timber structuresPart 1.1
- General rules and rules for buildings
Section 1 - General Section 2 - Basis of
design Section 3 - Material properties Section
4 - Durability Section 5 - Basis of structural
analysis Section 6 - Ultimate limit states
Section 7 - Serviceability limit states Section
8 - Connections with metal fasteners Section
9 - Components and assemblies Section
10 - Structural detailing and control Annex
A - (Informative) Block Shear and Shear Plug
Failure Annex B - (Informative) Mechanically
jointed beams Annex C - (Informative) Built-up
columns
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Timber Design To Limit States
NATURE OF EC5
Safety format, basis of design, references to
loads, presentation principles, identical to
those for steel, concrete, etc. (via EC0) Safety
format is clear and transparent. Modification
factors are pure principles (e.g. Duration of
load factor is 1.0 at test duration 0.6 for
permanent condition) Fewer fail safe concepts
than in BS 5268 No tables of material
properties, joint strengths etc Significantly
greater empowerment to informed designers (e.g.
harmonised beam-columns in 3D, joint failure
modes transparent, serviceability discretion)
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Timber Design To Limit States
PRINCIPLES AND APPLICATION RULES

• ?Principles
• gt Statements, definitions,
  requirements
• gt No alternative
• Application rules
• gt Generally recognised, follow principles,
  satisfy requirements
• gt Alternatives extensions acceptable e.g.
  for timber in UK within TRADA Guidance Documents

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Timber Design To Limit States
DIFFERENCE BETWEEN ULS SLS? ULS ? ULS
Limits MUST NOT be breached ? Factors of safety
incorporated at various levels to ensure
conservative estimates of structural capacity,
related to the required reliability ? Codified
design limits are relatively inflexible, since
related to material properties design actions
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Timber Design To Limit States
DIFFERENCE BETWEEN ULS SLS? SLS ? In some
instances, exceeding SLS design limits may be
acceptable (e.g. A rare, reversible effect, such
as an event causing unacceptable vibration levels
once every year) ? Design assumptions should
relate as reasonably as possible to the actual
service conditions ? Certain degree of
flexibility in design limits since they relate to
acceptable performance are affected by context
expectation (e.g. Expectations of workshops,
offices homes all markedly different)
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Ultimate Limit States Design
gt Characteristic Values gt Partial
Coefficients gt Design Values Of
Actions gt Action Combinations gt Strength
Design Values Of Materials
Properties gt Examples
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Ultimate Limit States Design
CHARACTERISTIC VALUES Actions Permanent Gk
mean Variable Qk 50 years Materials
Strengths fk 5 percentile Stiffness E0,m
ean mean E0,05 5 percentile
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Ultimate Limit States Design
PARTIAL COEFFICIENTS ?G Permanent
actions ?Q Variable actions ?M Material
properties
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Partial Factors and their Purpose (1/2)

• Partial factors ?F are applied to actions. They
  increase values of actions and effects of actions
  to allow for
• Uncertainty in representative values of actions
• Design model uncertainty in actions and action
  effects

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Partial Factors and their Purpose (2/2)

• Partial factors ?M are applied to material
  properties. They reduce material properties and
  member resistances to allow for
• Uncertainty in material properties
• Design model uncertainty in structural
  resistance

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Ultimate Limit States Design
PARTIAL COEFFICIENTS Design Points
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Ultimate Limit States Design
DESIGN VALUES OF ACTIONS ? Representative
Values ?0 Combination coefficient ?1
Frequent coefficient ?2 Quasi-permanent
coefficient
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Ultimate Limit States Design

• Recommended values of ? factors for buildings -
  EN 19902002
• Building use categories - domestic, residential
  office congregation, shopping storage traffic
• Snow requires reference also to EN 1991-1-3
• Treated more severely in Finland, Iceland,
  Norway, Sweden
• Wind in EN 1991-1-4
• Bridges - different ? factors in relevant parts
  of EN 1990 EN 1991

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Ultimate Limit States Design
ACTION COMBINATIONS Fundamental design
situations - ULS
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Ultimate Limit States Design
ACTION COMBINATIONS Examples (Actual e.g.s in
STEP TRADA GDs) 1 - Self Weight Snow,
Short Term gt Combination giving greatest axial
force in columns 2 - Self Weight Wind, Short
Term gt Combination requiring anchorage against
uplift 3 - Self Weight Snow Combination
Value of Wind Loading, Short Term gt Combination
giving greatest axial force combined with
bending 4 - Self Weight Wind Combination
Value of Snow Loading, Short Term gt Combination
giving greatest moment in columns
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Deriving Design Values of Mechanical Properties
For Timber and Timber-based Materials correct to
EN 1995-1-1
EN 1990 expression (6.3)
Key Xd Design value of a material
property Xk Characteristic value of a material
property ?M Partial factor for material
property h Conversion factor taking into
account volume and scale effect, effect of
moisture and temperature, any other relevant
parameter.
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Recommended values of ?M
EN 1995-1-1 Table 2.2 - Recommended partial
factors for material properties (?M)
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Ultimate Limit States Design
DESIGN VALUES OF MATERIALS PROPERTIES Materials
Properties Solid timber 15 strength
classes C14 - D70 EN338 Glulam 5
strength classes GL20 - GL36 EN1194 Panel
prEN European standards Products for test
methods established products
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Ultimate Limit State Design
DESIGN VALUES OF MATERIALS PROPERTIES British
Softwoods Timber graded in accordance with BS
4978
Extract from BS5268-22002
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Ultimate Limit States Design
DESIGN VALUES OF MATERIALS PROPERTIES K
Modification Factors Kmod duration and
moisture kcrit lateral instability
beams kc buckling columns kdef deformation
Kser slip kh depth and width kls load
sharing
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Ultimate Limit States Design
DESIGN VALUES OF MATERIALS PROPERTIES Service
Classes Service Class 1 Timber in buildings
with heating and protected from damp
conditions - e.g. Internal walls, internal floors
(other than ground floors) and warm
roofs. Service Class 2 Timber in covered
buildings - e.g.Ground floor structures where
no free moisture is present, cold roofs, the
inner leaf of cavity walls and external
single leaf wall with external
cladding. Service Class 3 Timber fully exposed
to the weather - e.g. exposed parts of open
buildings and timber used in marine structures.
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Ultimate Limit States Design
SERVICE CLASSES Service Class 1 Service
Class 2 Service Class 3
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Values of kmod to EN 1995-1-1 UK National Annex
(1/2)
Illustrations to the three Services Classes in EN
1995-1-1
Service class 1
Service class 2
Service class 3
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Values of kmod to EN 1995-1-1 UK National Annex
(2/2)
Values of kmod for solid timber (from EN 1995-1-1
Table 3.1 Values of kmod)
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Part 3 - Illustrated Run Through a Simple
Ultimate Limit State Check
To check the bending and shear load carrying
capacity of a glulam floor beam.
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Geometrical Properties
EN 1995.1.1 Figure 6.1 Member Axes
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Characteristic values of mechanical properties of
Glulam in Strength Class GL28h (homogeneous glued
laminated timber)

• Bending strength fm,k 28 N/mm2,
• Shear strength fv,k 3.2 N/mm2,
• from BS EN 1194 1999 Table 1.

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Strength Modification Factors

• Partial safety factor for glulam, gM
• Glulam, service class 1 and short-term loading,
  kmod
• Depth factor, kh
• Lateral stability factor, kcrit

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Bending Check (1/2)
Design bending resistance according to EN 1990
Expression (6.3) and EN 1995-1-1 Clause 2.4.3.
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Bending Check (2/2)
EN 1995-1-1 Expression (6.11), and km , factor
considering redistribution of bending stresses in
a cross section, is inapplicable with single-axis
bending.
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Shear Check
Design shear resistance according to EN 1990
Expression (6.3) and EN 1995-1-1 Clause 2.4.3.
EN 1995-1-1 Expression (6.13)
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Serviceability Limit States
gt Deformation Principles gt MOE Shear
Moduli gt Combinations Of
Actions gt Components Of
Deflection gt Final Deflection gt Deflection
Limits gt Examples
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Serviceability Limit States
DEFORMATION PRINCIPLES
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Serviceability Limit States
MOE SM TO CALCULATE DEFORMATIONS
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Serviceability Limit States
COMBINATION OF ACTIONS ? Representative
Values ?0 Combination coefficient ?1
Frequent coefficient ?2 Quasi-permanent
coefficient
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Serviceability Limit States
COMBINATION OF ACTIONS
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Serviceability Limit States
COMBINATION OF ACTIONS Irreversible Limit
States Characteristic or Rare combination
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Serviceability Limit States
COMBINATION OF ACTIONS Reversible Limit
States Frequent combination
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Serviceability Limit States
COMBINATION OF ACTIONS Quasi-permanent
combination When checking the long term effects
of SLS i.e. creep in the case of timber structures
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Serviceability Limit States
COMPONENTS OF DEFLECTION Deformations may occur
due to one or combinations of the following
effects gt Instantaneous elastic
deflection gt Time dependent deflections, i.e.
creep gt Shrinkage related movements due to
moisture fluctuations in member gt Slip in
mechanically fastened joints (relative
movement between members under
load) gt Initial deformations - e.g.
pre-cambered beams
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Serviceability Limit States
COMPONENTS OF DEFLECTION
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Serviceability Limit States
COMPONENTS OF DEFLECTION unet net
deflection uinst instantaneous net
deflection ufin final net deflection
uinst(1 kdef)
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Serviceability Limit States
FINAL DEFLECTION ufin uinst(1 kdef) Values
of kdef Material / Load duration Service class
/ kdef Solid timber Glulam 1 2 3 Permanent
0.8 0.8 2.0 Long term 0.5 0.5 1.5 Medium
term 0.25 0.25 0.75 Short term 0 0 0.3
Extract Only
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Serviceability Limit States
DEFLECTION LIMITS Appearance Reversible or
Irreversible Limit States gt Excessive sagging
of floors / ceilings - e.g. reversible effect
due to temporary crowd gathering in a room,
irreversible effect due to installation of
permanent fixtures for change of use gt
Possible damage to finishes - e.g. cracking of
ceilings gt Visual effects causing concern to
occupants - e.g. gaps appearing under non
structural partitions
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Serviceability Limit States
DEFLECTION LIMITS Function Irreversible Limit
States gt Damage to finishes fixtures gt
May encompass functioning of non structural
parts, plant equipment
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Serviceability Limit States
DEFLECTION LIMITS Comfort Reversible Limit
States gt Nuisance gt Discomfort - e.g.
vibration related problems the bouncy
floor gt May involve secondary effects -
e.g. rattling furniture, VDU screen
wobble, etc due to vibrations
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Serviceability Limit States
EXAMPLES OF DEFLECTION LIMITS Recommended
Vertical Deflection Limits Limit State Example
of use Recommended limits Irreversible
cracking of plasterboard, Instantaneous glass
etc. following installation u2,d ?
L/350 Irreversible cracking of
plasterboard, u1,d u2,d ucreep
Final glass etc. at end of design life
?L/250 Reversible vibration of u1,d
u2,d ? minInstantaneous domestic timber joisted
floors (14 mm, L/333) Final Reversibleappear
ance of roofs and ceilings u1,d u2,d ucreep
? L/150
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Serviceability Limit States
EXAMPLES OF DEFLECTION LIMITS Recommended
Horizontal Deflections Limit State Example of
use Recommended limits Irreversible Portal
frames etc. with masonry u2,d ?
he/300 Instantaneous Portal frames
etc. without masonry u2,d ? he/200
Multi-storey Per storey u2,d ?
he/300 buildings Whole height u2,d ?
he/500 Irreversible Horizontal
deflections u1,d u2,d ucreep ? he/650 final
- t.frame masonry caused by vertical actions
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Serviceability Limit States
HORIZONTAL DEFLECTION LIMITS Portal
Frames Medium Rise Timber Frame
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Serviceability Limit States
DEFLECTION LIMITS Examples
Portal Frame Structure Irreversible
instantaneous ? he /300 masonry
he /200, no masonry
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Serviceability Limit States
DEFLECTION LIMITS Examples
Pre-cambered Bridge Truss Reversible final
(appearance) u1 u2 ucreep
? acceptable pre-camber after 50yrs.
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TRADA software - timber sizer
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TRADA software - joints designer
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TRADA software - joints designer
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TRADA software - flitch beam designer
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TRADA software - flitch beam designer
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PII 304 Eurocode Actions Pre-Processor

• PII 304 project will
• enable designers to perform safe economical
  interpretation and application of Eurocodes 0, 1
  and 5.
• improve better current current practice design
  via software and downloadable supporting
  information.

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PII 304 Eurocode Actions Pre-Processor

• Project primary output The Actions Pre-Processor
  software
• Software assisting in defining and calculating
  design values of actions to Eurocode suite.
• Target users
• Trained structural / civil engineers who intend
  to acquire a thorough knowledge of Eurocodes 0, 1
  and 5 principles or have already received some
  dedicated TRADA CPD training.
• CPD lecturers

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PII 304 Eurocode Actions Pre-Processor

• Input window of the software

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PII 304 Eurocode Actions Pre-Processor

• Output screen 1 Actions summary

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PII 304 Eurocode Actions Pre-Processor

• Output screen 2 Critical load cases

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PII 304 Eurocode Actions Pre-Processor

• Output screen 3 All load cases

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PII 304 Eurocode Actions Pre-Processor

• The Actions Pre-Processor can be downloaded on
  TRADA website
• http//research.ttlchiltern.co.uk/pii304/index.htm
  
• Further information on TRADA website
• Eurocode 5 Design Guidance
• Eurocode 5 Design Examples
• Worked examples illustrating the software
  potential.
• Timber Design Knowledge provide further
  information on Eurocodes
• Software
• Software http//www.trada.co.uk/software

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