Canterbury Decoding Eurocode 7

Decoding Eurocode 7 – Introduction to Eurocode 7 Institution of Structural Engineers Canterbury Forum 21st February 2008

Geomantix www.geomantix.com

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 Harris MSc DIC MICE CEng FGS Director, Geomantix Ltd Consultant, TGP, Atkins Senior 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 Expert Teaching 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 Feb-08

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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) Feb-08

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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

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] Feb-08

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The wider landscape Overview of EN Eurocodes

3 IS

14

O

EN

36 15

8 68

l ica n n h o ec gat i g t o ti Ge ves stin s in d te ar d an and st

EN

EN

IS

2

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68 14

37

EN

O

1

92 78

O IS

28

3 06

ion s t u ec dard x E an st

EN EN

6 22

12

9

IS

12

15

38

15

2 I

12

SO

47 22

71 12 7 12

EN

E

oc ur

4

1 EN

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9 19

0 EN

1

1 99

62

es d o EN

EN

1

93 19

EN

1

4 99

19

2

5

2

76 24

EN

6 14

19

79 EN

5

99

9 19

8

3 19

EN 1997

96

2

2 99

3

EN

5

13

95

EN

16

9 69 12 9 19 EN 14 EN 5 47 14 EN

O IS EN

5

EN EN

1

31 47

15

13

O IS

22

7 47

7 23

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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

Geotechnical categories GC

Includes…

Design requirements

Design procedure

1

Small and relatively simple structures… with negligible risk

Negligible risk of instability or ground movements Ground conditions known to be straightforward No excavation below water table (or such excavation is straightforward)

Routine design & construction methods

2

Conventional types of structure & foundation with no exceptional risk or difficult soil or loading conditions

Quantitative geotechnical data & analysis to ensure fundamental requirements are satisfied

Routine field & lab testing Routine design & execution

3

Structures or parts of structures not covered above

Include alternative provisions and rules to those in Eurocode 7

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Example risk assessment Category 1 Low height cut slope in London clay

Category 3 Embedded bored pile retaining walls over underground tunnel

Category 2 Embedded retaining wall and bored piles in London clay

Category 3 Underground running tunnels Feb-08

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Limit states EN 1997-1 general rules

Ultimate limit states for strength (STR/GEO)

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

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EQU

UPL

HYD

Loss of static equilibrium

Uplift by vertical forces

Hydraulic failure

Toppling

Buoyancy

Internal erosion

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Limit states for overall stability

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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 Settlement

Differential settlement

Vibration

L

Δh Δh

Deflection

Insufficient pumping

Excessive flow

Δh

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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 Feb-08

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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:

E d ≤ Rd

Ed = design effect of actions Rd = 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 Feb-08

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Obtaining design material properties Test results Derivation Derived values of geotechnical parameters X

Characterization Characteristic value Xk Factorization Design value Xd Feb-08

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Deriving geotechnical parameters

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Characterizing material properties

Derived values of geotechnical parameters X Well-established experience Statistical methods

Standard tables of characteristic values

Cautious estimate

5% fractile

Characteristic value Xk

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Effects of actions Verification of strength

Structural effects are independent of material strength

Conceptually, we may write this as:

E d = E {Fd , ad }

Action

FL γ c bdL2 + M = 4 8

F

Effect

In structural engineering, effects are independent of strength of materials Example: bending moment at midspan of beam is:

deflection

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internal stresses

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Geotechnical effects depend on material strength

E d = E {Fd , X d , ad } Feb-08

Action

q

deflection

Effect

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)H 2 = (1 – sin φ) (γH + q)H (1 + sin φ) Conceptually, we may write this as:

Pa

earth pressure internal stresses

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settlement 37

Resistances Verification of strength

Example: bending resistance of concrete beam is:

f y As ⎞ ⎛ M = As f y d ⎜ 1− ⎟ ⎝ 2fc bd ⎠ Conceptually, we may write this as:

Rd = R {X d , ad }

stress blocks Feb-08

concrete (in compression) concrete (in tension) steel (in tension)

Resistance

In structural engineering, resistance is independent of loading on structure

Material Property

Structural resistance is independent of loading

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strain in cross-section 39

In geotechnical engineering, resistance often depends on selfweight of and loads applied to the ground Example: shear stress mobilized against underside of base depends on self-weight of fill and surcharge:

Material property

Geotechnical resistance depends on loading q

self-weight of fill

Conceptually, we may write this as:

Rd = R {X d , Fd , ad }

Resistance

S = ( γ H + q ) B tanϕ

S shear stress Feb-08

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Introducing reliability into design Verification of strength

Application of partial factors and tolerances Actions

Fd = γ F Frep

Effects of actions

Material properties

Xd =

Xk

γM

Resistances

Geometrical parameters

ad = anom ± Δa Feb-08

E d = γ E E {Fd , X d , ad }

Rd =

R {Fd , X d , ad }

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γR 42

Design Approaches Verification of strength

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…

Design Approach 1 2 3 Combination Combination 2 Actions1 Material Actions or effects Structural actions properties & resistances or effects & material properties Feb-08

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Partial factors Verification of strength

Partial factors for limit states GEO/STR Parameter

Permanent Unfavourable action (G) Favourable Variable Unfavourable action (Q) Favourable Accidental Unfavourable action (A) Favourable Shearing resistance (tan φ) Effective cohesion (c’) Undrained shear strength (cu) Unconfined compressive strength (qu) Weight density (γ) Bearing resistance (Rv) Sliding resistance (Rh) Earth resistance Walls (Re) Slopes Pile resistance Feb-08

Symbol γG

(γG,fav) γQ γA γφ γc γcu γqu γγ γRv γRh γRe

Action factors A1 1.35 1.0 1.5 (0) 1.0 (0)

A2 1.0

Material factors M1 M2

Resistance factors R1

R2

R3

1.0

1.0 1.4 1.1 1.4 1.1 Varies

R4

1.3 (0) 1.0 (0) 1.0

1.25 1.4

1.0

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(1.0)

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Partial factors for limit states GEO/STR (DA1) – footings, walls, and slopes Parameter

Symbol

Permanent action (G)

Unfavourable

Variable action (Q)

γG

Combination 1 M1 R1 A1 1.35

Combination 2 A2 M2 R1 1.0

(γG,fav)

1.0

Unfavourable

γQ

1.5

1.3

Favourable Unfavourable

γA

(0) 1.0

(0) 1.0

Favourable Shearing resistance (tan φ) Effective cohesion (c’) Undrained shear strength (cu) Unconfined compressive strength (qu)

γφ γc γcu γqu

(0)

(0)

Weight density (γ) Bearing resistance (Rv) Sliding resistance (Rh) Earth resistance (Re)

γγ γRv γRh γRe

Accidental action (A)

Feb-08

Favourable

1.25

1.0

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1.4

1.0 1.0

1.0

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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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Partial factors for limit states GEO/STR (DA1) – bridges (from draft amd 1 to NA to BS EN 1990) Parameter Unfavourable

Permanent action (G)

Fav’ble Unfav’ble

Variable action (Q)

Concrete, soil, other materials, creep & shrinkage, non-linear settlement Steel, super-imposed, road surfacing, linear settlement Hydrostatic effects Hydrostatic effects Creep & shrinkage, linear & non-linear settlement All other actions Road traffic & pedestrian

Rail traffic Thermal Wind Favourable Accidental Unfavourable action (A) Favourable Material properties and resistance Feb-08

Sym- Combination 1 A1 M1 R1 bol γG,sup 1.35

Combination 2 A2 M2 R1 1.0

1.20 1.0 1.0 0

1.0 0

γQ,sup

0.95 1.35

1.0 1.15

γA -

??? 1.5 1.7 0 1.0 (0)

??? 1.3 1.5 0 1.0 (0)

γG,inf

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Building s

Buildings 50

Basis of design for stability Verification of stability

Verification of stability Verification of stability is expressed in Eurocode 7 by:

E d ,dst ≤ E d ,stb + Rd

Ed,dst = destabilizing design effect of actions Ed,stb = stabilizing design effect of actions Rd = 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 Feb-08

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Verification of stability for EQU

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factors for limit state EQU for buildings Parameter

Permanent action (G)

Unfavourab le Favourable Variable action (Q) Unfavourab le Favourable Accidental action Unfavourab (A) le Favourable Coeff. of shearing resistance (tan φ) Effective cohesion (c’) Undrained shear strength (cu) Unconfined compressive strength (qu) Weight density (γ) All resistances (R)

Symbol Partial factors on… Actions Material properties 1.1 γG,dst γG,stb γQ,dst

0.9 1.5

-

0 (1.0)

γA,dst γφ

Resistance s

(0)

γc γcu γqu γγ γR

1.25 [1.1] 1.4 [1.2]

1.0 (1.0)

Values underlined provide safety (i.e. are ≠ 1.0) Values in (rounds brackets) are not explicitly given in EN 1997-1 but can be inferred Partial factors = 0 mean that the corresponding action is omitted from design calculations Values in [square brackets] from NA to BS EN 1997-1 Feb-08

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Partial factors for limit state EQU for bridges (from draft amd 1 to NA to BS EN 1990) Parameter

Permanent action (G) Variable action (Q)

Symbol

Unfavourable Favourable Road traffic/ Unfavourable pedestrian Rail traffic Thermal Wind Favourable Accidental Unfavourable action (A) Favourable Material properties Resistances

γG,dst γG,stb γQ,dst

γA,dst γM

Partial factors on… Actions Material properties

Resistances

1.05 0.95 1.35 1.45 1.4 1.5 0 (1.0) (0)

γR

As for buildings (1.0)

Values underlined provide safety (i.e. are ≠ 1.0) Values in (brackets) are not explicitly given in EN 1997-1 but can be inferred Partial factors = 0 mean that the corresponding action is omitted from design calculations Feb-08

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Verification of stability for UPL

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Partial factors for limit state UPL Symbol

Parameter

Permanent action (G)

Unfavourable Favourable Variable action (Q) Unfavourable Favourable Accidental action (A) Unfavourable Favourable Coeff. of shearing resistance (tan φ) Effective cohesion (c’) Undrained shear strength (Cu) Unconfined compressive strength (qu) Weight density (γ) Tensile pile resistance (Rst) Anchorage resistance (Ra)

γG,dst γG,stb γQ,dst γA,dst γφ γc γCu γqu γγ γst γa

Partial factors on… Actions Material properties

Resistances

1.0 [1.1] 0.9 1.5 (0) (1.0) (0) 1.25 1.4 (1.4) (1.0) 1.4 [*] 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 inferred Partial factors = 0 mean that the corresponding action is omitted from design calculations Value in [square brackets] as modified by the NA to BS EN 1997-1; *design as for STR/GEO Feb-08

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Partial factors for limit state EQU for bridges (from draft amd 1 to NA to BS EN 1990) Parameter

Permanent action (G) Variable action (Q)

Symbol

Unfavourable Favourable Road traffic/ Unfavourable pedestrian Rail traffic Thermal Wind Favourable Accidental Unfavourable action (A) Favourable Material properties Resistances

γG,dst γG,stb γQ,dst

γA,dst γM

Partial factors on… Actions Material properties

Resistances

1.05 0.95 1.35 1.45 1.4 1.5 0 (1.0) (0)

γR

As for buildings (1.0)

Values underlined provide safety (i.e. are ≠ 1.0) Values in (brackets) are not explicitly given in EN 1997-1 but can be inferred Partial factors = 0 mean that the corresponding action is omitted from design calculations Feb-08

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Verification of stability for HYD

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Partial factors for limit state HYD Symbol Partial factors on…

Parameter

Actions Permanent action (G) Variable action (Q)

Accidental action (A)

Unfavourab le Favourable

γG,dst

1.35

γG,stb

0.9

Unfavourab le Favourable

γQ,dst

1.5

-

(0)

Unfavourab le Favourable

γA,dst

(1.0)

-

(0)

Weight density (γ)

γγ

All resistances (R)

γR

Material properties

Resistance s

(1.0) (1.0)

Values underlined provide safety (i.e. are ≠ 1.0) Values in (brackets) are not explicitly given in EN 1997-1 but can be inferred Partial factors = 0 mean that the corresponding action is omitted from design calculations Feb-08

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Serviceability limit states Verification of serviceability

Verification of serviceability Verification of serviceability is expressed in Eurocode 7 by:

Ed ≤ Cd 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 1.0 Some guidance on values for Cd is given in Annex H Feb-08

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Verification of SLS

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Geotechnical reports EN 1997-1 general rules

Geotechnical Design Report

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Ground Investigation Report

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Conclusion Overview of EN Eurocodes

Business as usual

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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

• • Feb-08

Authors Andrew Bond (Geocentrix) and Andy Harris (Geomantix) To be published by Spon in hardback, with colour section

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‘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: – – – – – – – – – – –

Feb-08

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 Wilson British Prime Minister (1964-70 and 1974-76)

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