Institution of Structural Engineers Canterbury Forum 21st ...geocentrix.typepad.com/.../files/canterbury_decoding_eurocode_7.pdf · Decoding Eurocode 7 – Introduction to Eurocode

Decoding Eurocode 7 –Introduction to Eurocode 7

Geomantixwww.geomantix.com

Institution of Structural Engineers

Canterbury Forum 21st February 2008

Feb-08 Decoding Eurocode 7 ©2005-8 Geocentrix Ltd. All rights reserved 2

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)


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


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)


The Eurocode programme


Connections between main Eurocodes

Contents of Eurocode 7

Overview of EN Eurocodes


Contents of EN 1997-1:General rules


Contents of EN 1997-2: Ground investigation and testing


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]

The wider landscape



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


Geotechnical investigation and testing


Execution of special geotechnical works


Bringing European standards into national practice


National Annex completes the Eurocode jigsaw


Role of Eurocode 7 in UK practice


Benefits of the Eurocodes


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)

Geotechnical design

EN 1997-1 general rules


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


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

Limit states



Ultimate limit states for strength (STR/GEO)


Ultimate limit states for stability (EQU/UPL/HYD)

EQULoss of static equilibrium

Toppling Internal erosion

UPL

Buoyancy

Uplift by vertical forces

HYDHydraulic failure


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


Ultimate limit states for serviceability

L

ΔhΔh

Δh

Settlement Differential settlement Vibration

Deflection Insufficient pumping Excessive flow


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


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 …


Design by calculation


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≤


Obtaining design material properties

Derived values of geotechnical parameters X

Characteristic value Xk

Design value Xd

Test results

Derivation

Characterization

Factorization


Deriving geotechnical parameters


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

Effects of actions



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


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

Resistances



Structural resistance is independent of loading

In structural engineering, resistance is independent of loading on structure

Example: bending resistance of concrete beam is:


{ },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


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:


{ }, ,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

Introducing reliability into design



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

Design Approaches



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

Partial factors



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


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)


1.0γRvBearing resistance (Rv)γγWeight density (γ)


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


Verification of strength for GEO/STR (DA1-1)


Verification of strength for GEO/STR (DA1-2)


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)

Basis of design for stability

Verification of stability


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≤ +


Verification of stability for EQU


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)


γγWeight density (γ)


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


Resistances

Material properties

ActionsPartial factors on…Parameter

factors for limit state EQU for buildings


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



Verification of stability for UPL


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)




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


(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)




Verification of stability for HYD


Partial factors for limit state HYD


(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


Resistances

Material properties


Serviceability limit states

Verification of serviceability


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≤


Verification of SLS

Geotechnical reports



Geotechnical Design Report


Ground Investigation Report

Conclusion



Business as usual


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


‘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


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)

Decoding Eurocode 7

www.eurocode7.com

Documents

Institution of Structural Engineers Canterbury Forum 21st ...geocentrix.typepad.com/.../files/canterbury_decoding_eurocode_7.pdf · Decoding Eurocode 7 – Introduction to Eurocode