Implementation of Eurocode 7 in Germany and...

Implementation of Eurocode 7 in Germany and Consequences for Practical Design

Kerstin Lesny

University of Duisburg-EssenInstitute of Geotechnics

Safety Concepts and Calibration of Partial Factors in European and North American Codes of Practice

Workshop •••• 30.11 – 01.12. 2011 •••• Delft University of Technology

Outline

History of Geotechnical Design in Germany

Implementation of Eurocode 7

New Regulations for Geotechnical Design

Consequences for Pratical Design - Examples

Conclusions

Workshop • 30.11–01.12. 2011 • Delft University of Technology page 2


� Geotechnical design in Germany originally based on a global safetyconcept with an overall factor of safety η

� Safety concept defined in DIN 1054 (1976) with reference to variousdesign codes (e.g. DIN 4017 for the bearing resistance)

Definition of global factor: η = R/E ≥≥≥≥ ηηηηmin

R, E = deterministic values, named as: cal E, cal R

Global factors:

e.g. bearing resistance failure: η=2,0

e.g. pile bearing capacity: η=2,0

for load case 1

Distinction of three load cases determining the level of safety



� to be derived directly from the results of soil mechanical tests

� basic value is the reduced arithmetic average from n tests

� appropriate additions or deductions to consider the heterogeinity of theground, uncertainties during soil sampling and testing

e.g. reduction of shear strength paramaters according to E96 of EAU:

EAU: Recommendations of the Committee for Waterfront Structures

Definition of deterministic values of soil parameters(acc. to EAU):

3,1c

ccal uu ≤

1,1tantancal ϕ′≤ϕ′3,1

cccal ′≤′



deterministic values R, E (cal R, cal E) ≠ characteristic values Ek , Rk

� With DIN 1054 (2003) LSD first has been introduced in Germany parallel to the development of Eurocode 7, revised in 2005

Resistance factors γR derived from global factors assumingtypical partial factors for effects of actions γE!

η≤ RER

kEk

RE γ≤γ⋅

( ) RERER

ERERERE γ⋅γ=η⇔η≤=γ⋅γ≤⇔γ≤γ⋅

Global factor Partial factors



Definition of Limit States (in German: Grenzzustände = GZ)

GZ 1ALoss of equilibrium without failure of the ground, e.g. uplift, floating, hydraulic heave; partial factors only on actions

GZ 1BFailure of structures or structural components by failure of the structure or the ground, e.g. sliding, bearing resistance failure, failure of piles, retaining structures, etc.; partial factors on characteristic effects of actions and resistances

GZ 1CGlobal failure of the ground, e.g. slope failure; partial factors on actions and on shear strength parameters

GZ 2Displacements and rotations; partial factors are equal to one



Concept of load cases

… according to DIN 1054 (1976):

LC1: Permanent loads and regularly occuring variable loads

permanent design conditions

LC2: plus irregularly occuring variable loads and loads that only occurduring construction

transient design conditions

LC3: plus extraordinary loads

according to DIN 1054 (2005)

Concept of load cases maintained, but they now depend on combinations of actions and safety classes



Combinations of actions

Normal combination CA1: Permanent and variable loads

Rare combination CA2: Rare loads or loads occuring only once

Extraordinary combination CA3: Extraordinary actions occuring at the same time, i.e. catastrophic incidents

Safety classes

Safety class SC1: Normal conditions during the lifetime of the structure

Safety class SC2: Conditions during construction or maintenance of a structure

Safety class SC3: Singular or probably never occuring conditions during thelifetime of the structure



Original timetable for the implementation of Eurocode 7 in Germany as DIN EN 1997-1:

Kempfert (2009)

DIN EN 1997-1 with NA

revised DIN 1054



DIN EN 1997-1:2009

Schuppener & Ruppert (2007)

� DIN 1054:2005 as „the German way“ to Eurocode 7 designed to maintain thespecial experiences included in German design codes

� DIN 1054:2005 had to be completely revised due to overlapping regulations

not adopted design

approaches and

informative annexes

jointregulations:

e.g. limit states,

partial factors,

geotechnicalcategories

particular German

experiences: e.g. acc. base

pressures, pile resis-tances

DIN 1054:2005

Eurocode 7 vs. DIN 1054:2005-01



Current situation



Normen-Handbuch

(Codes Handbook)

Summary of the three codes

published in May 2011

For a better readability of thethree codes!



according toDIN 1054:2010-12

according toDIN EN 1997-1:2009-09

according toDIN EN 1997-1:2009-09



Deadline for implementation

For the ultimate implementation of the new codes a deadline regulation has been established:

Estimated date: 1st of July 2012

This means:

� DIN 1054:2005 will be withdrawn

� new codes (most probably a set of Eurocodes 0 to 5, 7-1 and 9 with their NA) officially will be approved and introduced by the building authorities

� new codes may already be used before the deadline based on a project-specific agreement especially with the approval authorities



Schuppener & Ruppert (2007)

2010-12

Future system of German geotechnical design codes

In DIN 1054:2010-12 reference is made to:

� Design codes, e.g.

DIN 4017 DIN 4019 DIN 4084

� Recommendations

EAB, EAU, EAP, …

additionally:

� Construction codes, e.g.

EN 1536 (bored piles)EN 12063 (sheet pile walls)

.

.

.



Kempfert (2009)

inner failure of the structure , where

the strength of construction materials for the resistance

Limit state

loss of equilibrium of the structure or of the foundation ground, where the strengths of the resistance are not decisive

loss of equilibrium of the structure or the foundation ground due to uplift or by the effect of other vertical forces

Hydraulic failure, inner erosion and piping in the ground, caused by flow gradient

inner failure of the structure , where the strength of construction

materials for the resistance

inner failure of the structure , where the strength of construction materials for the resistance

fail or very large deformation of the structure, where the strength of the foundation ground according to the resistance is not decisive

Definition of limit states


Design Situations Load Cases


Design Situation

DenotationLoad case (LC) according to

DIN 1054:2005

Permanent design situation

BS-P LC 1

Transient design situation

BS-T LC 2

Accidental designsituation

BS-A LC 3

Design situationfor earthquake

BS-E LC 3



Design approaches according to DIN 1997-1:2009-09:

� Design Approach 1 :

DA1 is not allowed in Germany according to DIN EN 1997-1/NA:2010-12

� Design Approach 2:

DA2 is applied for the limit states STR and GEO

In case of load-dependent resistances the resultant resistance is calculatedwith characteristic effects of actions: Rk = f(Ek) (also named as DA2*)

� Design Approach 3:

DA3 is applied for the limit state GEO in case of global stability or slopestability analyses



Partial factors for actions

according to DIN 1054:2010-12 – abstract:

Actions and effects of actions

Symbol

Design situation

BS-P (LC1)

BS-T (LC2)

BS-A (LC3)

STR and GEO-2: Limit state of failure of structures, structural components and the ground

Effects of actions from permanent actions, general

γG1,35

(1,35)1,2

(1,20)1,1

(1,00)

Effects of actions from unfavourable variable actions

γQ1,50

(1,50)1,30

(1,30)1,10

(1,00)

Black: partial factors acc. to DIN 1054:2010-12

Red: partial factors acc. to DIN 1054:2005-01



Partial factors for resistances

according to DIN 1054:2010-12 - abstract

Black: factors acc. toDIN 1054:2010-12

Red: factors acc. toDIN 1054:2005-01

Resistance SymbolDesign situation

BS-P (LC1)

BS-T (LC2)

BS-A (LC3)

STR and GEO-2: Limit state of failiure according to structures, components and foundation ground

Soil resistances

Passive earth pressure and bearing resistance

γR,e, γR,v1,40

(1,40)1,30

(1,30)1,20

(1,20)

Sliding resistance γR,h1,10

(1,10)1,10

(1,10)1,10

(1,10)

Pile resistance from static and dynamic pile load tests

base resistance γb1,10

(1,20)1,10

(1,20)1,10

(1,20)

shaft resistance(pressure)

γs1,10

(1,20)1,10

(1,20)1,10

(1,20)

total resistance(pressure)

γt1,10

(1,20)1,10

(1,20)1,10

(1,20)


Eurocode 7 Design Examples – Example 1

Square pad foundation

Characteristic loads:Gv,k = 1000 kNGh,k = 0Qv,k = 750 kNQh,k = 500 kNγc = 25 kN/m³

Soil: boulder clay

Details:five SPT tests, water contents and index tests bulk weight density: 21.4 kN/m³ ground water level 1.0 m below ground level

Consequences for Practical Design – Examples


Comparison of design approaches with German design within DA2

Specific features in the calculation:

� Design Approach 1 (combination 1 and 2) and 3

partial factors according to DIN EN 1997-1:2009-09, Tables A.3.1 to A3.3

� Design Approach 2

partial factors according to DIN 1054:2010-12, Tables A.2.1 to A2.3

� Design method for bearing resistance according to DIN 4017:2006-03



Characteristic soil parameters:

Undrained conditions: cuk=300 kN/m², φuk=0°

Drained conditions: c´k=15 kN/m², φ’k=30°

Derived as experience values acc. to recommendations in EAU (2004)!


� DIN EN ISO 22476-3:2005-04 on SPT testing does not include anycorrelations to shear parameters;

� Various correlations available in the literature have been examined;

� Finally experience values found to be reasonable


Results of the bearing resistance calculation

� Undrained conditions:Pad width acc. to DA2 2 minimally larger (2,89 m) than acc. to DA1 and DA3

� Drained conditions:Pad width acc. to DA2 much larger (4,69 m) than acc. to DA1 and DA3

Pad width DA1(Comb. 1) DA1(Comb. 2) DA2 DA3

B [m] (Undrained condition)

2,53 2,63 2,89 2,53

B [m] (Drained condition)

3,44 3,45 4,69 3,44

η=Rd/Nd or Rk/Nk

(undrained condition)1,014 1,021 1,880 1,014

η=Rd/Nd or Rk/Nk

(drained condition)1,017 1,027 2,108 1,017


DIN 1054 (1976):

ηηηηmin = 2,0 (LC1)


Eurocode 7 Design Examples – Example 6

Bored piles, D = 450 mm, a = 2 m

Characteristic loads for each pile:

Gk = 300 kN

Qk =150 kN

Soil:

Pleistocene fine and medium sand

covered by Holocene layers of loose sand,

soft clay, and peat

Details:

1 CPT at a distance of 5m from the boring

performed and evaluated acc. to DIN 4094-1:2002



Determination of soil parameters

CPT test used for the determination of pile length acc. to DIN 1054:2010-12and EAP (2007)

qc(z) =-50,34+2,965*z

0 4 8 12 16 20

Spitzenwiderstand qc[MPa]

-30

-20

-10

0

Tie

fe z

[m]


Linear regression


Soil layers between 0 and ~15 m assumed to be not bearing

Design pile length below ~15 m

Average value of cone resistance for this depthrange:

qc = 11,184 MN/m²

Table: cone resistance vs. depth from linear regression



Tiefe z[m] qc [MN/m²]

15,5 -4,382516 -2,9

16,5 -1,417517 0,065

17,5 1,547518 3,03

18,5 4,512519 5,995

19,5 7,477520 8,96

20,5 10,442521 11,925

21,5 13,407522 14,89

22,5 16,372523 17,855

23,5 19,337524 20,82

24,5 22,302525 23,785

25,5 25,267526 26,75

depth z[m]

Comparison of design approaches with German design within DA2

Specific features in the calculation:

� Calculation according to DA1 (Combination 1) and DA2

� DA1 (Combination 2) and DA3 were not included in this calculation:

The applied calculation model acc. to DIN 1054:2010-12 and EAP (2007) is based on empirical values for the pile resistances;

Partial factors can only be applied on resultant resistance (i.e. γR),material factors γM cannot be applied!



Results of the pile analysis:

Design pile length: ~17,5 m

(= minimum embedment depth in competent layer 2,5m acc. to EAP, 2007)

Pile lengthDA1

(Comb. 1)DA1

(Comb. 2) DA2 DA3

L [m] 17,45 - 17,25 -

η=Rd/Ed or Rk/Ek 1,0131 1,0 1,5504 1,0097


DIN 1054 (1976):

ηηηηmin = 2,0 (LC1)!


Conclusions

Implementation of LSD by Eurocode 7 represented a radical change in the German design philosophy which was based on a long-term experience and which was commonly justified to be very reliable

Engineers had to adjust to the new concept of limit states and partial factors and the new terminology with the introduction of DIN 1054:2003/2005 parallel to the Eurocode (“the German way”)

With the deadline of July 2012 DIN 1054:2005 can no longer be used and engineers again need to adjust to changes accompanied by the implementation of Eurocode 7

In the future three codes (EC7 and its NA plus a revised DIN 1054) are to be used in geotechnical design besides other design and construction codes

The safety level included in these codes is not based on probabilistic calculations, but has been derived from the former global safety concept – i.e. the actual reliability remains unknown


Implementation of Eurocode 7 in Germany and...

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