Introduction to Eurocodes March 20051

7/29/2019 Introduction to Eurocodes March 20051

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Introduction to Structural Timber

Design to the Eurocodes

Wood for GoodCPD seminars 2005


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Timber Design To Limit StatesTimber 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 harmonisedtechnical specifications


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Overview to European Codes and Standards (1/2)

EN 1990: Eurocode - Basis of structural design

EN 1991: Eurocode 1 - Actions on structures

EN 1995 -1 -1: General Rules - Generalrules and rules for buildings

< Structural safety

< Loading

EN 1995 -2: Bridges

< Design and detailing

< Materials

< Durability

< Metal fasteners

connectors a

nd hardware

< Components and

assemblies

< Foundations

EN 1997: Eurocode 7 - Geotechnical data

EN 1997-1

General rules

EN 1997-2

Design assisted by laboratory testing

EN 1997-3

Design assisted by field testing

EN 1991-1.1

Densities, selfweight and

imposed loads

EN 1991-1.2 Actions

on structuresexposed to fire

EN 1991-2 Traffic

loads on bridges

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

< Adhesives

EN 1995 -1 -2: General Rules -Structural fire design

EN 1995: Eurocode 5 - Design of timber structures

ENs

ENs

ENs

ENs

ENs


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National Annexes to Eurocodes and their Purpose (1/2)

Examples of Nationally determined parameters are shown on the next slide

UK

Nationa

l

Annex

UK

Nationa

l

Annex

UK

Nationa

l

Annex


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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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- Structural safety

- Serviceability

- Durability

- Robustness

Highest level of reliability taken into account in

timber structures for grandstands

Requirements of a Structure designed to EN 1990


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Steel shoe and concrete

pillar isolating round timber

column end grain from the

ground.

Exposed

untreatedoak timber

decking.

Capping

detail onexposed

glulam floor

beam.

Durability: Examples of Practical Solutions


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Robustness in Structural Design to EN 1990 (1/2)

On one hand robustness relates to disproportionate

collapse concept

Full scale disproportionatecollapse 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 - RequirementsSection 3 - Principles of Limit States Design

Section 4 - Basic Variables

Section 5 - Structural Analysis and Design Assisted

by TestingSection 6 - Verification by the Partial Factor Method

Annex A1 - (Normative) Application for Buildings

Annex B - (Informative) Management of Structural Reliability forConstruction 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 actionsPart 1-6 - General actions - Actions during execution

Part 2 Traffic loads on bridges

Part 3 Cranes and machineryPart 4 Actions in silos and tanks


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EN 1995 supporting hENs and Product Specifications

Gluam and the CEN standards arrangements

Adhesives

EN 301 Testing

En 392

En 408

Woodproperties

EN 350

En 384

Strength

classes

En 1194

Production &dimension

EN 385 EN 386

EN 387 EN 380

11 standards, in 5 groups:


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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

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

Eurocode 5: Design of timber structures

Part 1.1 - General rules and rules for buildings


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NATURE OF EC5

Safety format, basis of design, references to loads, presentation principles,identicalto 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 1.0at 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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PRINCIPLES AND APPLICATION RULES

Principles> Statements, definitions,

requirements

> No alternative

Application rules> Generally recognised, follow principles, satisfy requirements

> Alternatives & extensions acceptable

e.g. for timber in UK within TRADA Guidance Documents


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DIFFERENCE BETWEEN ULS & SLS?DIFFERENCE BETWEEN ULS & SLS?

ULSULS

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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DIFFERENCE BETWEEN ULS & SLS?DIFFERENCE BETWEEN ULS & SLS?

SLSSLS

In some instances, exceeding SLS design limitsmay be acceptable (e.g. A rare, reversible effect, such as anevent causing unacceptable vibration levels once every year)

Design assumptions should relate as reasonablyas 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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> Characteristic Values> Characteristic Values

> Partial Coefficients> Partial Coefficients

> Design Values Of Actions> Design Values Of Actions

> Action Combinations> Action Combinations

> Strength Design Values Of> Strength Design Values Of

Materials PropertiesMaterials Properties

> Examples> Examples

Ultimate Limit States DesignUltimate Limit States Design


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CHARACTERISTIC VALUESCHARACTERISTIC VALUES

ActionsPermanent Gk mean

Variable Qk 50 years

Materials

Strengths fk 5 percentile

Stiffness E0,mean mean

E0,05 5 percentile



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PARTIAL COEFFICIENTSPARTIAL 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 increasevalues 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. Theyreduce material properties and member resistances toallow for:

- Uncertainty in material properties

- Design model uncertainty in structural resistance


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PARTIAL COEFFICIENTSPARTIAL COEFFICIENTS

Design Points



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DESIGN VALUES OF ACTIONSDESIGN 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 - EN1990:2002

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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ACTION COMBINATIONSACTION COMBINATIONS

Fundamental design situations - ULS



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ACTION COMBINATIONSACTION COMBINATIONS

Examples (Actual e.g.s

in STEP & TRADA GDs)1 - Self Weight + Snow, Short Term

> Combinationgiving greatest axial force in columns

2 - Self Weight + Wind, Short Term

> Combination requiring anchorage against uplift

3 - Self Weight + Snow + Combination Value of Wind Loading, Short Term

> Combination giving greatest axial force combined with

bending

4 - Self Weight + Wind + Combination Value of Snow Loading, Short Term

> Combination giving greatest moment in columns



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Deriving Design Values of Mechanical

Properties

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;

Conversion factor taking into account

volume and scale effect, effect of moisture

and temperature, any other relevant

parameter.

For Timber and Timber-based Materials correct to EN

1995-1-1:


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Recommended values ofM

EN 1995-1-1 Table 2.2 - Recommended

partial factors for material properties (M)

Fundamental combinations:

Solid timber 1.3

Glued laminated timber 1.25LVL, plywood, OSB 1.2

Other wood-based materials 1.3

Connections 1.3

Punched metal plate fasteners 1.25

Accidental combinations 1


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DESIGN VALUES OF MATERIALS PROPERTIESDESIGN 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

Strength classStandard nam e O rig in

C14 C16 C18 C22 C24

Douglas Fir UK GS SS*

Larch UK GS GS

British P ine UK GS SS

British Spruce UK GS SS


British SoftwoodsTimber graded in accordance with BS 4978


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K Modification Factors

Kmod duration and moisture

kcrit lateral instability beams

kc buckling columns

kdef deformationKser slip

kh depth and width

kls

load sharing



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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 structureswhere 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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SERVICE CLASSESSERVICE 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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Service class 1 Service class 2 Service class 3M.C. ~ 12% M.C. ~ 20% M.C. > 20%

Permanent 0.6 0.6 0.5

Instantaneous 1.1 1.1 0.9

Load duration

Long-term

6 months - 10 years0.7 0.7

0.7

Medium-term1 week - 6 months

Short-term

< 1 week

0.55

0.8 0.8 0.65

0.9 0.9

Values of kmodfor solid timber (from EN 1995-1-1 Table 3.1 Values of kmod)

Values of kmod to EN 1995-1-1 UK National Annex (2/2)


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To check the bending and shear load carrying capacity of

a glulam floor beam.

Part 3 - Illustrated Run Through a Simple

Ultimate Limit State Check


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Strength Modification Factors

Partial safety factor for glulam, M Glulam, service class 1 and short-term loading, kmod

Depth factor, kh

Lateral stability factor, kcrit


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Bending Check (1/2)

M

km,modhcrit

dy,m,fkkkf

=

Design bending resistance according to

EN 1990 Expression (6.3) and EN 1995-1-1 Clause 2.4.3.


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Shear Check

M

kv,mod

dv,

fkf

=

Design shear resistance according to

EN 1990 Expression (6.3) and EN 1995-1-1 Clause 2.4.3.

dy,m,dy,m,f

EN 1995-1-1 Expression (6.13)


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> Deformation Principles> Deformation Principles

> MOE & Shear> MOE & ShearModuliModuli

> Combinations Of> Combinations Of

ActionsActions

> Components Of> Components Of

DeflectionDeflection

> Final Deflection> Final Deflection

> Deflection Limits> Deflection Limits

> Examples> Examples

Serviceability Limit StatesServiceability Limit States


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DEFORMATION PRINCIPLESDEFORMATION PRINCIPLES



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MOE & SMMOE & SM

TO CALCULATE DEFORMATIONSTO CALCULATE DEFORMATIONS



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COMBINATION OF ACTIONSCOMBINATION OF ACTIONS

Representative Values0 Combination coefficient

1 Frequent coefficient

2 Quasi-permanent coefficient



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S SS i bilit Li it St t


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Irreversible Limit States

CharacteristicorRare combination


S i bilit Li it St tS i bilit Li it St t


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Reversible Limit States

Frequentcombination




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Quasi-permanent combination

When checking the long term effects of SLS i.e. creep in the case of timber

structures




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COMPONENTS OF DEFLECTIONCOMPONENTS OF DEFLECTION

Deformations may occur due to one or combinations of the

following effects:

> Instantaneous elastic deflection

> Time dependent deflections, i.e. creep

> Shrinkage & related movements due to

moisture fluctuations in member

> Slip in mechanically fastened joints (relative

movement between members under load)> Initial deformations - e.g. pre-cambered

beams


S i bilit Li it St tServiceability Limit States


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unet = net deflection

uinst = instantaneous net

deflection

ufin = final net deflection

= uinst(1 + kdef)




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FINAL DEFLECTIONFINAL DEFLECTION

ufin = uinst(1 + kdef)

Values of kdef

Material / Load duration Service class / kdef

Solid timber & Glulam 1 2 3Permanent 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



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DEFLECTION LIMITSDEFLECTION LIMITS

Appearance

Reversible or Irreversible Limit States

> Excessive sagging of floors / ceilings - e.g. reversibleeffect due to temporary crowd gathering in a room,

irreversible effect due to installation of permanent fixturesfor change of use

> Possible damage to finishes- e.g. cracking of ceilings

> Visual effects causing concern to occupants- e.g. gaps

appearing under non structural partitions




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Function

Irreversible Limit States

> Damage to finishes & fixtures

> May encompass functioning of non structural parts,plant & equipment



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Comfort

Reversible Limit States

> Nuisance

> Discomfort - e.g. vibration related problems : the bouncyfloor

> May involve secondary effects - e.g. rattling furniture,VDU screen wobble,

etc due to vibrations



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EXAMPLES OF DEFLECTION LIMITSEXAMPLES 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 + ucreepFinal glass etc. at end of design life L/250

Reversible: vibration of u1,d + u2,d min

Instantaneous domestic timber joisted floors (14 mm, L/333)

Final Reversible:appearance of roofs and ceilings u1,d + u2,d + ucreep L/150




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EXAMPLES OF DEFLECTION LIMITSEXAMPLES 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/300buildings

Whole height u2,d he/500

Irreversible Horizontal deflections u1,d + u2,d + ucreep he/650final - t.frame + masonry caused by vertical

actions




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HORIZONTAL DEFLECTION LIMITSHORIZONTAL DEFLECTION LIMITS

Portal Frames

Medium Rise Timber Frame




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Examples


Portal Frame Structure

Irreversible instantaneous

he /300+ masonry

he /200, no masonry



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Pre-cambered Bridge Truss

Reversible final (appearance)

u1 + u2 + ucreep acceptable

pre-camber

after 50yrs.


Examples



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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

TRADA software - flitch beam designer


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TRADA software flitch beam designer

PII 304 Eurocode Actions Pre-ProcessorPII 304 Eurocode Actions Pre-Processor


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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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Project primary output: The Actions Pre-Processorsoftware

Software assisting in defining and calculating designvalues of actions to Eurocode suite.

Target users:

Trained structural / civil engineers who intend toacquire a thorough knowledge of Eurocodes 0, 1 and 5principles or have already received some dedicatedTRADA CPD training.

CPD lecturers



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Input window of the software:



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Output screen 1: Actions summary



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Output screen 2: Critical load cases



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Output screen 3: All load cases



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The Actions Pre-Processor can be downloadedon 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 furtherinformation on Eurocodes

Software: Software: http://www.trada.co.uk/software

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