Implementation of Eurocode 7 in Germany and Consequences for Practical Design

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1 Safety Concepts and Calibration of Partial Factors in European and North American Codes of Practice Workshop Delft University of Technology Implementation of Eurocode 7 in Germany and Consequences for Practical Design Kerstin Lesny University of Duisburg-Essen Institute of Geotechnics

2 Outline History of Geotechnical Design in Germany Implementation of Eurocode 7 New Regulations for Geotechnical Design Consequences for Pratical Design - Examples Conclusions Workshop Delft University of Technology page 2

3 History of Geotechnical Design in Germany Geotechnical design in Germany originally based on a global safety concept with an overall factor of safety η Safety concept defined in DIN 1054 (1976) with reference to various design codes (e.g. DIN 4017 for the bearing resistance) Definition of global factor: η = R/E η min 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 Workshop Delft University of Technology page 3

4 History of Geotechnical Design in Germany Definition of deterministic values of soil parameters (acc. to EAU): 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 the ground, uncertainties during soil sampling and testing e.g. reduction of shear strength paramaters according to E96 of EAU: cal c u c u 1,3 cal c c 1,3 cal tanϕ tanϕ 1,1 EAU: Recommendations of the Committee for Waterfront Structures Workshop Delft University of Technology page 4

5 History of Geotechnical Design in Germany With DIN 1054 (2003) LSD first has been introduced in Germany parallel to the development of Eurocode 7, revised in 2005 Global factor E R η Partial factors E k γ E R k γ R deterministic values R, E (cal R, cal E) characteristic values E k, R k E γ E R γ R E R ( γ γ ) η E R E R = E R η = γ γ Resistance factors γ R derived from global factors assuming typical partial factors for effects of actions γ E! Workshop Delft University of Technology page 5

6 History of Geotechnical Design in Germany Definition of Limit States (in German: Grenzzustände = GZ) GZ 1A Loss of equilibrium without failure of the ground, e.g. uplift, floating, hydraulic heave; partial factors only on actions GZ 1B Failure 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 1C Global failure of the ground, e.g. slope failure; partial factors on actions and on shear strength parameters GZ 2 Displacements and rotations; partial factors are equal to one Workshop Delft University of Technology page 6

7 History of Geotechnical Design in Germany Concept of load cases according to DIN 1054 (1976): LC1: LC2: LC3: Permanent loads and regularly occuring variable loads permanent design conditions plus irregularly occuring variable loads and loads that only occur during construction transient design conditions plus extraordinary loads according to DIN 1054 (2005) Concept of load cases maintained, but they now depend on combinations of actions and safety classes Workshop Delft University of Technology page 7

8 Combinations of actions History of Geotechnical Design in Germany 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 the lifetime of the structure Workshop Delft University of Technology page 8

9 Implementation of Eurocode 7 Original timetable for the implementation of Eurocode 7 in Germany as DIN EN : Kempfert (2009) revised DIN 1054 DIN EN with NA Workshop Delft University of Technology page 9

10 Implementation of Eurocode 7 Eurocode 7 vs. DIN 1054: DIN EN :2009 DIN 1054:2005 not adopted design approaches and informative annexes joint regulations: e.g. limit states, partial factors, geotechnical categories particular German experiences: e.g. acc. base pressures, pile resistances Schuppener & Ruppert (2007) DIN 1054:2005 as the German way to Eurocode 7 designed to maintain the special experiences included in German design codes DIN 1054:2005 had to be completely revised due to overlapping regulations Workshop Delft University of Technology page 10

11 Implementation of Eurocode 7 Current situation Workshop Delft University of Technology page 11

12 Implementation of Eurocode 7 Workshop Delft University of Technology page 12

13 Implementation of Eurocode 7 Normen-Handbuch (Codes Handbook) Summary of the three codes published in May 2011 For a better readability of the three codes! Workshop Delft University of Technology page 13

14 Implementation of Eurocode 7 according to DIN EN : according to DIN 1054: according to DIN EN : Workshop Delft University of Technology page 14

15 Implementation of Eurocode 7 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 projectspecific agreement especially with the approval authorities Workshop Delft University of Technology page 15

16 Implementation of Eurocode 7 Future system of German geotechnical design codes In DIN 1054: reference is made to: Design codes, e.g. DIN 4017 DIN 4019 DIN 4084 Recommendations EAB, EAU, EAP, additionally: Schuppener & Ruppert (2007) Construction codes, e.g. EN 1536 (bored piles) EN (sheet pile walls)... Workshop Delft University of Technology page 16

17 New Regulations for Geotechnical Design Definition of limit states 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 failureof inner failureof the structure, the structure, where thestrengthofconstruction where the strength of construction materials materials for the resistance 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 Kempfert (2009) Workshop Delft University of Technology page 17

18 New Regulations for Geotechnical Design Design Situations Load Cases Design Situation Permanent design situation Transient design situation Accidental design situation Design situation for earthquake Denotation Load case (LC) according to DIN 1054:2005 BS-P LC 1 BS-T LC 2 BS-A LC 3 BS-E LC 3 Workshop Delft University of Technology page 18

19 New Regulations for Geotechnical Design Design approaches according to DIN : : Design Approach 1 : DA1 is not allowed in Germany according to DIN EN /NA: Design Approach 2: DA2 is applied for the limit states STR and GEO In case of load-dependent resistances the resultant resistance is calculated with characteristic effects of actions: R k = f(e k ) (also named as DA2*) Design Approach 3: DA3 is applied for the limit state GEO in case of global stability or slope stability analyses Workshop Delft University of Technology page 19

20 New Regulations for Geotechnical Design Partial factors for actions according to DIN 1054: abstract: Actions and effects of actions Symbol BS-P (LC1) Design situation 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 Effects of actions from unfavourable variable actions γ G 1,35 (1,35) γ Q 1,50 (1,50) 1,2 (1,20) 1,30 (1,30) 1,1 (1,00) 1,10 (1,00) Black: partial factors acc. to DIN 1054: Red: partial factors acc. to DIN 1054: Workshop Delft University of Technology page 20

21 New Regulations for Geotechnical Design Partial factors for resistances according to DIN 1054: abstract Design situation Resistance Symbol BS-P BS-T (LC1) (LC2) STR and GEO-2: Limit state of failiure according to structures, components and foundation ground Soil resistances Passive earth pressure 1,40 1,30 γ and bearing resistance R,e, γ R,v (1,40) (1,30) 1,10 1,10 Sliding resistance γ R,h BS-A (LC3) 1,20 (1,20) 1,10 (1,10) (1,10) (1,10) Pile resistance from static and dynamic pile load tests 1,10 1,10 1,10 base resistance γ b (1,20) (1,20) (1,20) shaft resistance 1,10 1,10 1,10 γ (pressure) s (1,20) (1,20) (1,20) total resistance (pressure) γ t 1,10 (1,20) 1,10 (1,20) 1,10 (1,20) Black: factors acc. to DIN 1054: Red: factors acc. to DIN 1054: Workshop Delft University of Technology page 21

22 Eurocode 7 Design Examples Example 1 Square pad foundation Characteristic loads: G v,k = 1000 kn G h,k = 0 Q v,k = 750 kn Q h,k = 500 kn γ c = 25 kn/m³ Soil: boulder clay Consequences for Practical Design Examples 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 Workshop Delft University of Technology page 22

23 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 : , Tables A.3.1 to A3.3 Design Approach 2 partial factors according to DIN 1054: , Tables A.2.1 to A2.3 Design method for bearing resistance according to DIN 4017: Workshop Delft University of Technology page 23

24 Consequences for Practical Design Examples Characteristic soil parameters: Undrained conditions: c uk =300 kn/m², φ uk =0 Drained conditions: c k=15 kn/m², φ k =30 Derived as experience values acc. to recommendations in EAU (2004)! DIN EN ISO : on SPT testing does not include any correlations to shear parameters; Various correlations available in the literature have been examined; Finally experience values found to be reasonable Workshop Delft University of Technology page 24

25 Consequences for Practical Design Examples Results of the bearing resistance calculation 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=r d /N d or R k /N k (undrained condition) η=r d /N d or R k /N k (drained condition) 1,014 1,021 1,880 1,014 DIN 1054 (1976): η min = 2,0 (LC1) 1,017 1,027 2,108 1,017 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 Workshop Delft University of Technology page 25

26 Consequences for Practical Design Examples Eurocode 7 Design Examples Example 6 Bored piles, D = 450 mm, a = 2 m Characteristic loads for each pile: G k = 300 kn Q k =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 :2002 Workshop Delft University of Technology page 26

27 Consequences for Practical Design Examples Determination of soil parameters CPT test used for the determination of pile length acc. to DIN 1054: and EAP (2007) Spitzenwiderstand qc[mpa] Linear regression Tiefe z [m] q c (z) =-50,34+2,965*z Workshop Delft University of Technology page 27

28 Consequences for Practical Design Examples 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 depth range: q c = 11,184 MN/m² Table: cone resistance vs. depth from linear regression Tiefe depth z[m] q c [MN/m²] 15,5-4, ,9 16,5-1, ,065 17,5 1, ,03 18,5 4, ,995 19,5 7, ,96 20,5 10, ,925 21,5 13, ,89 22,5 16, ,855 23,5 19, ,82 24,5 22, ,785 25,5 25, ,75 Workshop Delft University of Technology page 28

29 Consequences for Practical Design Examples 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: and EAP (2007) is based on empirical values for the pile resistances; Partial factors can only be applied on resultant resistance (i.e. γ R ), material factors γ M cannot be applied! Workshop Delft University of Technology page 29

30 Consequences for Practical Design Examples Results of the pile analysis: DA1 DA1 Pile length (Comb. 1) (Comb. 2) DA2 DA3 L [m] 17,45-17,25 - η=r d /E d or R k /E k 1,0131 1,0 1,5504 1,0097 Design pile length: ~17,5 m DIN 1054 (1976): η min = 2,0 (LC1)! (= minimum embedment depth in competent layer 2,5m acc. to EAP, 2007) Workshop Delft University of Technology page 30

31 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 Workshop Delft University of Technology page 31