canterbury decoding eurocode 7
TRANSCRIPT
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Decoding Eurocode 7 –Introduction to Eurocode 7
Geomantixwww.geomantix.com
Institution of Structural Engineers
Canterbury Forum 21st February 2008
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Understand, analyse, and assess
Geotechnical engineering is…
“the art of using soils whose properties we do not really understand to form and to support structures we cannot
really analyse, so as to withstand forces which we cannot really assess, in such a way that the public does
not really suspect”
Professor Noel Simons, Inaugural Lecture, University of Surrey
(with apologies to Professor Eric Brown, Imperial College)
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Mr Andrew HarrisMSc DIC MICE CEng FGS
Director, Geomantix LtdConsultant, TGP, AtkinsSenior Lecturer, Kingston University
Eurocode experience• Co-author ‘Decoding Eurocode 7’ (2008), Spon Press • Co-author Chapter 7 PP1990 (Guide to the Structural
Eurocodes), BSI• Trainer for Geocentrix, IStructE/ Professional
Solutions, & Thomas Telford/Eurocode ExpertTeaching experience• Lecturer (1985-2004) and Associate Dean (2000-4) at
Kingston University• Author of CPD courses in geotechnical design & pile
design for Kingston University and IStructE/ Professional Solutions
Consulting• Regional Manager at CL Associates (2004-6)• Design and execution of geotechnical and
contaminated land investigations
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Implementation of Eurocodes
“The structural Eurocodes are a European suite of codes for structural design … developed over … twenty-five
years“By 2010 they will have effectively replaced the current
British Standards as the primary basis for designing buildings and civil engineering structures in the UK
“They [will be] used as an acceptable basis for meeting compliance with UK Building Regulations and the
requirements of other public authorities”
National Strategy for Implementation of the Structural Eurocodes (2004)
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The Eurocode programme
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Connections between main Eurocodes
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Contents of Eurocode 7
Overview of EN Eurocodes
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Contents of EN 1997-1:General rules
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Contents of EN 1997-2: Ground investigation and testing
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Division of responsibilities between Parts 1 & 2 of EN 1997
• EN 1997-1 General rules– General framework for geotechnical design– Definition of ground parameters– Characteristic and design values– General rules for site investigation– Rules for the design of main types of geotechnical structures– Some assumptions on execution procedures
• EN 1997-2 Ground investigation and testing– Detailed rules for site investigations– General test specifications– Derivation of ground properties and geotechnical model of the
site– Examples of calculation methods based on field and laboratory
testing
[ref. EN 1997-2 Figure 1.2]
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The wider landscape
Overview of EN Eurocodes
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EN 14731
EN 15237
EN 1536
EN 1537
EN 1538EN 1206
3
EN 12715
EN 12716
EN 12699
EN 14199
EN 14475
EN 14679
Execution
standards
Geotechnical
investigatio
n
and testin
g
standards
ISO 22476ISO 224
75
ISO 22282
ISO 17892
ISO 14689
ISO 14688
3
2
12
6
12
13EN 19
98
EN 1999
EN 1997
5
5
ISO 22477
13
2
EN 1990
EN 1991
EN 1992
EN 1993 EN 1996
EN 1995
EN 1994
EN Eurocodes
3
2 26
341
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Geotechnical investigation and testing
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Execution of special geotechnical works
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Bringing European standards into national practice
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National Annex completes the Eurocode jigsaw
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Role of Eurocode 7 in UK practice
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Benefits of the Eurocodes
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Of vital importance
‘The Eurocodes will become the Europe wide means of designing Civil and Structural engineering works and so … they are of vital importance to both the design
and construction sectors of the Civil and Building industries’
‘Introduction to Eurocodes’European Commission website (http://ec.europa.eu)
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Geotechnical design
EN 1997-1 general rules
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Geotechnical categories
Include alternative provisions and rules to those in Eurocode 7Structures or parts of structures not covered above
3
Routine field & lab testingRoutine design & execution
Quantitative geotechnical data & analysis to ensure fundamental requirements are satisfied
Conventional types of structure & foundation with no exceptional risk or difficult soil or loading conditions
2
Routine design & construction methods
Negligible risk of instability or ground movementsGround conditions known to be straightforwardNo excavation below water table (or such excavation is straightforward)
Small and relatively simple structures…with negligible risk
1
Design procedureDesign requirementsIncludes…GC
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Example risk assessment
Category 1Low height cut slopein London clay
Category 2Embedded retaining wall and
bored piles in London clayCategory 3Embedded bored pile retainingwalls over underground tunnel
Category 3Underground running tunnels
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Limit states
EN 1997-1 general rules
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Ultimate limit states for strength (STR/GEO)
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Ultimate limit states for stability (EQU/UPL/HYD)
EQULoss of static equilibrium
Toppling Internal erosion
UPL
Buoyancy
Uplift by vertical forces
HYDHydraulic failure
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Limit states for overall stability
Near river/canal/lake/reservoir/sea-shore Near/on natural or man-made slope
Near an excavation or retaining wall Near mine workings/buried structures
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Ultimate limit states for serviceability
L
ΔhΔh
Δh
Settlement Differential settlement Vibration
Deflection Insufficient pumping Excessive flow
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Design by prescriptive measures
• §2.5(2) Design by prescriptive measures may be used where comparable experience makes design calculations unnecessary
• §2.5(1) These [measures] involve conventional and generally conservative rules in the design, and attention to specification and control of materials, workmanship, protection and maintenance procedures
Example (right)• Annex G (informative) – sample
method for deriving presumed bearing resistance for spread foundations on rock
• Information taken from British Standard 8004
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Design by observation or testing
• §2.7(1) When prediction of geotechnical behaviour is difficult, it can be appropriate to apply the approach known as “the observational method”, in which the design is reviewed during construction
• §2.7(2)P The following requirements shall be met before construction is started:– acceptable limits of behaviour shall be established– the range of possible behaviour shall be assessed– a plan of monitoring shall be devised– a plan of contingency actions shall be devised
• §2.6(1)P When the results of load tests or tests on large or small scale models are used to justify a design … the following features shall be considered …:– differences in the ground conditions between the test and the actual
construction– time effects …– scale effects …
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Design by calculation
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Verification of strength
Verification of strength is expressed in Eurocode 7 by:
Ed = design effect of actionsRd = design resistance corresponding to that effect
This requirement applies to limit state GEO:“Failure or excessive deformation of the ground, in which the strength of
soil or rock is significant in providing resistance’EN 1997-1 §2.4.7.1(1)P
…and to ultimate limit state STR“Internal failure or excessive deformation of the structure or structural elements … in which the strength of structural materials is significant in
providing resistance”EN 1997-1 §2.4.7.1(1)P
d dE R≤
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Obtaining design material properties
Derived values of geotechnical parameters X
Characteristic value Xk
Design value Xd
Test results
Derivation
Characterization
Factorization
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Deriving geotechnical parameters
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Characterizing material properties
Derived values of geotechnical parameters X
Characteristic value Xk
Well-established experience
Statistical methodsCautious estimate
Standard tables of characteristic
values
5% fractile
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Effects of actions
Verification of strength
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Structural effects are independent of material strength
In structural engineering, effects are independent of strength of materials
Example: bending moment at mid-span of beam is:
Conceptually, we may write this as:
{ },d d dE E F a=
2
4 8cbdLFL
Mγ
= +
internal stressesdeflection
Act
ion
Effe
ct
F
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Geotechnical effects depend on material strength
In geotechnical engineering, effects often depend on the strength of materials
Example: internal stresses in and deflection/settlement of retaining wall all depend on earth pressure:
Pa = Ka (γH + q)H2
= (1 – sin φ) (γH + q)H(1 + sin φ)
Conceptually, we may write this as:{ }, ,d d d dE E F X a=
Pa
q
earth pressure
settlement
deflection
Act
ion
Effe
ct
internal stresses
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Resistances
Verification of strength
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Structural resistance is independent of loading
In structural engineering, resistance is independent of loading on structure
Example: bending resistance of concrete beam is:
Conceptually, we may write this as:
{ },d d dR R X a=
12y s
s yc
f AM A f d
f bd
⎛ ⎞= −⎜ ⎟
⎝ ⎠
concrete(in tension)
concrete(in compression)
steel(in tension)
Mat
eria
l Pro
pert
y
strain in cross-sectionstress blocks
Res
ista
nce
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Geotechnical resistance depends on loading
In geotechnical engineering, resistance often depends on self-weight of and loads applied to the ground
Example: shear stress mobilized against underside of base depends on self-weight of fill and surcharge:
Conceptually, we may write this as:
{ }, ,d d d dR R X F a=
( ) tanS H q Bγ ϕ= +
S
q
shear stress
self-weightof fill
Mat
eria
l pro
per
tyR
esis
tan
ce
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Introducing reliability into design
Verification of strength
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Application of partial factors and tolerances
d F repF Fγ=
kd
M
XX
γ=
{ }, ,d E d d dE E F X aγ=
{ }, ,d d dd
R
R F X aR
γ=
Actions
Resistances
Effects of actions
Material properties
d noma a a= ± Δ
Geometrical parameters
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Design Approaches
Verification of strength
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Design Approaches for STR/GEO
• §2.4.7.3.4.1(1)P The manner in which equations [above] are applied shall be determined using one of three Design Approaches
– Design Approaches apply ONLY to STR and GEO limit states– Each nation can choose which one (or more) to allow
• UK National Annex, NA.4 …only Design Approach 1 is to be used in the UK
• In simplest terms, the design approaches apply factors to the following…
Structural actions or effects& material properties
Actions or effects& resistances
Material properties
ActionsCombination
2Combination
1
321Design Approach
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Partial factors
Verification of strength
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Partial factors for limit states GEO/STR
SlopesWalls
(1.0)
R4
VariesPile resistance1.11.4γReEarth resistance
(Re)
1.11.4
1.0
1.4
Material factors
1.0
M1
(0)1.0(0)1.3
(0)1.0(0)1.51.0
1.35A1
Action factors
1.0A2
1.25
M2
γRhSliding resistance (Rh)
γcEffective cohesion (c’)γcuUndrained shear strength (cu)
1.01.0γRvBearing resistance (Rv)γγWeight density (γ)
γquUnconfined compressive strength (qu)
γφShearing resistance (tan φ)
Sym-bol
-FavourableγAUnfavourableAccidental
action (A)
-FavourableγQUnfavourableVariable
action (Q)
(γG,fav)FavourableγGUnfavourablePermanent
action (G)
R3R2R1
Resistance factorsParameter
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Partial factors for limit states GEO/STR (DA1)– footings, walls, and slopes
γReEarth resistance (Re)
1.0
1.4
(0)
1.0(0)
1.5
1.01.35A1
Combination 1
1.0
M1
1.0
R1
γRhSliding resistance (Rh)
γcEffective cohesion (c’)γcuUndrained shear strength (cu)
1.0γRvBearing resistance (Rv)γγWeight density (γ)
γquUnconfined compressive strength (qu)
1.25γφShearing resistance (tan φ)
Symbol
(0)-Favourable
1.0γAUnfavourableAccidental action (A)
(0)-Favourable
1.3γQUnfavourableVariable action (Q)
(γG,fav)Favourable1.0γGUnfavourablePermanent
action (G)
R1M2A2Combination 2Parameter
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Verification of strength for GEO/STR (DA1-1)
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Verification of strength for GEO/STR (DA1-2)
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BuildingsBuildings
00Creep & shrinkage, linear & non-linear settlementAll other actions
Hydrostatic effects 1.01.0Hydrostatic effects
1.0
1.0
WindThermal 1.31.5Rail trafficRoad traffic & pedestrian 1.151.35
Unfav’ble
??????
Steel, super-imposed, road surfacing, linear settlement
Concrete, soil, other materials, creep & shrinkage, non-linear settlement
0.95
1.20
Permanent action (G)
(0)1.00
1.7
1.35A1
Combination 1M1 R1
Material properties and resistance
Sym-bol
(0)-Favourable1.0γAUnfavourableAccidental
action (A)
0-Favourable1.5
γQ,supVariable action (Q)
γG,inf
Fav’ble
1.0
γG,sup
Unfavourable
R1M2A2Combination 2Parameter
Partial factors for limit states GEO/STR (DA1)– bridges (from draft amd 1 to NA to BS EN 1990)
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Basis of design for stability
Verification of stability
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Verification of stability
Verification of stability is expressed in Eurocode 7 by:
Ed,dst = destabilizing design effect of actionsEd,stb = stabilizing design effect of actionsRd = any additional design resistance that stabilizes the structures
This requirement applies to limit state EQU:“Loss of equilibrium of the structure or the ground, considered as a rigid body, in
which the strengths of structural materials and the ground are insignificant in providing resistance”
EN 1997-1 §2.4.7.1(1)P
…and to ultimate limit state UPL:“Loss of equilibrium of the structure or the ground, due to uplift by water pressure
(buoyancy) or other vertical actions”EN 1997-1 §2.4.7.1(1)P
, ,d dst d stb dE E R≤ +
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Verification of stability for EQU
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Values underlined provide safety (i.e. are ≠ 1.0)Values in (rounds brackets) are not explicitly given in EN 1997-1 but can be inferredPartial factors = 0 mean that the corresponding action is omitted from design calculationsValues in [square brackets] from NA to BS EN 1997-1
(1.0)1.0
1.4 [1.2]
γRAll resistances (R)
γcEffective cohesion (c’)γcuUndrained shear strength (cu)
γγWeight density (γ)
γquUnconfined compressive strength (qu)
1.25 [1.1]γφCoeff. of shearing resistance (tan φ)
Symbol
(0)-Favourable
(1.0)γA,dstUnfavourable
Accidental action (A)
0-Favourable
1.5γQ,dstUnfavourable
Variable action (Q)0.9γG,stbFavourable
1.1γG,dstUnfavourable
Permanent action (G)
Resistances
Material properties
ActionsPartial factors on…Parameter
factors for limit state EQU for buildings
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Partial factors for limit state EQU for bridges (from draft amd 1 to NA to BS EN 1990)
Wind
Rail trafficThermal
Road traffic/pedestrian
1.41.45
1.5
Values underlined provide safety (i.e. are ≠ 1.0)Values in (brackets) are not explicitly given in EN 1997-1 but can be inferredPartial factors = 0 mean that the corresponding action is omitted from design calculations
(1.0)γRResistances
As for buildings
γMMaterial properties
Symbol
(0)-Favourable(1.0)γA,dstUnfavourableAccidental
action (A)
0-Favourable
1.35γQ,dstUn-favourable
Variable action (Q)
0.95γG,stbFavourable1.05γG,dstUnfavourablePermanent
action (G)
ResistancesMaterial properties
ActionsPartial factors on…Parameter
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Verification of stability for UPL
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Partial factors for limit state UPL
1.4 [*]Values underlined provide safety (i.e. are ≠ 1.0)Values in (round brackets) are not explicitly given in EN 1997-1 but can be inferredPartial factors = 0 mean that the corresponding action is omitted from design calculationsValue in [square brackets] as modified by the NA to BS EN 1997-1; *design as for STR/GEO
1.4 [*](1.0)
1.4(1.4)
γaAnchorage resistance (Ra)
γcEffective cohesion (c’)γCuUndrained shear strength (Cu)
γstTensile pile resistance (Rst)γγWeight density (γ)γquUnconfined compressive strength (qu)
1.25γφCoeff. of shearing resistance (tan φ)
Symbol
(0)-Favourable(1.0)γA,dstUnfavourableAccidental action (A)(0)-Favourable1.5γQ,dstUnfavourableVariable action (Q)0.9γG,stbFavourable
1.0 [1.1]γG,dstUnfavourablePermanent action (G)
ResistancesMaterial properties
ActionsPartial factors on…Parameter
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Feb-08 Decoding Eurocode 7 ©2005-8 Geocentrix Ltd. All rights reserved 58
Partial factors for limit state EQU for bridges (from draft amd 1 to NA to BS EN 1990)
Wind
Rail trafficThermal
Road traffic/pedestrian
1.41.45
1.5
Values underlined provide safety (i.e. are ≠ 1.0)Values in (brackets) are not explicitly given in EN 1997-1 but can be inferredPartial factors = 0 mean that the corresponding action is omitted from design calculations
(1.0)γRResistances
As for buildings
γMMaterial properties
Symbol
(0)-Favourable(1.0)γA,dstUnfavourableAccidental
action (A)
0-Favourable
1.35γQ,dstUn-favourable
Variable action (Q)
0.95γG,stbFavourable1.05γG,dstUnfavourablePermanent
action (G)
ResistancesMaterial properties
ActionsPartial factors on…Parameter
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Verification of stability for HYD
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Partial factors for limit state HYD
Values underlined provide safety (i.e. are ≠ 1.0)Values in (brackets) are not explicitly given in EN 1997-1 but can be inferredPartial factors = 0 mean that the corresponding action is omitted from design calculations
(1.0)(1.0)
γRAll resistances (R)γγWeight density (γ)
Symbol
(0)-Favourable
(1.0)γA,dstUnfavourable
Accidental action (A)
(0)-Favourable
1.5γQ,dstUnfavourable
Variable action (Q)0.9γG,stbFavourable
1.35γG,dstUnfavourable
Permanent action (G)
Resistances
Material properties
ActionsPartial factors on…Parameter
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Serviceability limit states
Verification of serviceability
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Verification of serviceability
Verification of serviceability is expressed in Eurocode 7 by:
Ed = design effect of actions (e.g. displacement, distortion)Cd = limiting design value of the effect of actions
Serviceability limit states are defined as:“States that correspond to conditions beyond which specified service requirements for a structure or structural member are no
longer met”EN 1990 §1.5.2.14
Partial factors should normally be taken as 1.0Some guidance on values for Cd is given in Annex H
d dE C≤
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Verification of SLS
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Geotechnical reports
EN 1997-1 general rules
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Geotechnical Design Report
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Ground Investigation Report
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Conclusion
Overview of EN Eurocodes
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Business as usual
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Feb-08 Decoding Eurocode 7 ©2005-8 Geocentrix Ltd. All rights reserved 69
Decoding Eurocode 7
• Book due middle 2008• Key features
– Covers Eurocode 7 Parts 1 and 2, plus relevant parts of other Eurocodes
– Also covers associated execution and testing standards
– Explains key principles– Illustrates application rules with
real-life case studies– Material extensively tested on
training courses over 5 years• Authors Andrew Bond
(Geocentrix) and Andy Harris (Geomantix)
• To be published by Spon in hardback, with colour section
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Feb-08 Decoding Eurocode 7 ©2005-8 Geocentrix Ltd. All rights reserved 70
‘Decoding the Eurocodes’ blog
• Web log (blog) started May 2006
• Address: www.eurocode7.com• Aim to post articles at least
once a month, on following subjects:
– BGA– Books– BSI– Eurocode 3– Eurocode 7– ICE– IStructE– Seminars– Singapore– Structural Eurocodes– Training courses
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Don’t be the architect of decay
‘He who rejects change is the architect of decay’
Harold WilsonBritish Prime Minister (1964-70 and 1974-76)
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Decoding Eurocode 7
www.eurocode7.com