O Dr Andrew Bond (Geocentrix)

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1 DECODING EUROCODES 2 + 7: DESIGN SG OF FOUNDATIONS O Dr Andrew Bond (Geocentrix)

2 Outline of talk April 2010: the death of British Standards? UK implementation of Eurocodes Verification of strength: limit states STR and GEO Some technical pitfalls Guidance on use of Eurocodes

3 APRIL 2010: THE DEATH OF BRITISH STANDARDS?

8 UK IMPLEMENTATION OF EUROCODES

9 The Eurocode family BON ND AND HARRIS (2008) Oct-10 Decoding Eurocodes Geocentrix Ltd and The Steel Construction Institute Ltd 9

10 Role of Eurocodes in UK practice BON ND AND HARRIS (2008) Oct-10 Decoding Eurocodes Geocentrix Ltd and The Steel Construction Institute Ltd 10

13 VERIFICATION OF STRENGTH: LIMIT STATES S STR AND GEO

14 Verification of strength Verification of strength is expressed in Eurocode 7 by: E d R E d = design effect of actions R d = design resistance corresponding to that effect Applies to GEO: Failure or excessive deformation of the ground, in which the strength of soil or rock is significant in providing resistance d EN (1)P EN (1 1)P and to 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 (1)P Oct-10 Decoding Eurocode Geocentrix Ltd. All rights reserved 14

15 Application of partial factors and tolerances Actions F = γ F d F rep Material properties X = d X γ k M Effects of actions {,, } E = γ E F X a d E d d d Resistances R { F X a } Geometrical parameters,, d d d a = a ±Δa d nom R d = γ R Oct-10 Decoding Eurocode Geocentrix Ltd. All rights reserved 15

19 Partial factors for GEO/STR (DA1): footings, walls, and slopes Parameter Symbol Combination 1 Combination 2 A1 M1 R1 A2 M2 R1 Permanent Unfavourable γ G action (G) Favourable (γ G,fav ) 1.0 Variable Unfavourable γ Q action (Q) Favourable (0) (0) Shearing resistance (tan ϕ) γ ϕ Effective cohesion (c ) Undrained shear strength (c u ) γ cu 1.4 Unconfined compressive strength (q u ) Weight density (γ) γ γ 1.0 γ c γ qu Bearing resistance (R v ) γ Rv Sliding resistance (R h ) Earth resistance (R e ) γ Rh γ Re Oct-10 Decoding Eurocode Geocentrix Ltd. All rights reserved 19

20 SOME TECHNICAL DETAILS

21 Design strength of concrete Design compressive strength of concrete is: f = α f γ cd cc ck c f ck = characteristic compressive strength of concrete (from cylinder tests) γ c = partial factor for concrete in compression α cc = factor for long term effects on compressive strength and unfavourable effects resulting from the way the load is applied Design tensile strength of concrete is: f f f 23 ctd = αct ctk,0.05 γc = 0.21 αct ck γc f ctk, = characteristic tensile strength of concrete (5% fractile value) α ct = factor for long term effects on tensile strength, etc. [f ck has units of MPa in this expression] EN EX XP ( ) & TA BLE 3.1 Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 21

22 Design strength of reinforcing steel Design yield strength of reinforcing steel is: f = f γ yd yk s f yk = characteristic yield strength of reinforcing steel γ s = partial factor for reinforcing steel EN (2 2) Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 22

23 Factor for long term effects on concrete strength Document Reinforced concrete Plain/lightly reinforced conc. Compression Tension Compression Tension α cc α ct α cc,pl α ct,pl EN UK NA (Amd 1) 085flexure/axial otherwise Long vs short term strength Justification for α cc = 0.85 EN & PD Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 23

24 Partial factors for reinforced concrete Limit states Design situation Reinforced concrete Reinforcing and prestressing steel General Piles* γ s γ c Ultimate Persistent k f γ c Transient Accidental Seismic Serviceability *Cast in place piles without permanent casing; k f = Recommended value for situations not explicitly covered by EN 1992 EN & Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 24

25 Bending resistance of singly reinforced beam Verification of bending resistance requires: M Ed M Rd M Ed = design value of applied bending moment effect M Rd = design bending resistance, given by: M Rd A s = area of steel reinforcement fydas = Af s ydd 1 2η fcd bd f yd = design yield ildstrength of reinforcing i steel b= width of cross section; d = its effective depth f cd = design compressive strength of concrete η = 1.0 Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 25

26 Design chats for singly reinforced beams / bd^2fcd K = M / M / bd^ ^2 (MPa) fck = 50 MPa 45 MPa 3 40 MPa 35 MPa 2 30 MPa 1 25 MPa 20 MPa (As / bd) (fyd/fcd) d) As / bd (%) Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 26

27 Differences between design aids Design aids for Eurocode 2 that have appeared to date present N:M interaction diagrams in subtly different ways: Author/Guide Axes Contours TT Designer s Guide Concrete Centre TCC Spreadsheets N M A f vs 2 hf hf hf Ed Ed 2 3 cd hfcd N M vs 2 hf hf Ed Ed 2 3 ck ck s yd hf cd Asfyk hf ck N Ed ( kn ) vs M Ed ( knm ) A s (e.g. 4B32) Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 27

28 Truss model for variable strut inclination method EN (1) Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 28

29 Design charts for shear resistance (MPa) vrd.c % % 1.5% % % 0.75% % 0.5% % 0.15% Effective depth (mm) tance (MPa) Shear resist Truss angle (deg) Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 29

Assumptions used to develop N:M interaction charts Reinforcing bars are (rotationally) symmetrical about the pile centre Aboveneutralaxis axis, concrete andreinforcingbarsprovidecompression

30 Assumptions used to develop N:M interaction charts Reinforcing bars are (rotationally) symmetrical about the pile centre Aboveneutralaxis axis, concrete andreinforcingbarsprovidecompression compression force Below neutral axis, only reinforcing bars provide tension Shape of concrete in compression = segment of circle; must deduct area of steel in compression zone from it Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 30

31 Circular pile (D = 600 mm, c = 75 mm, φ l = 32 mm, φ t = 8 mm) PILE INTERACTION DIAGRAM

32 Feltham (2004), paper in The Structural Engineer d v z β Area of concrete strut 2r s /π Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 32

33 Comparing minimum reinforcement for concrete piles 40 Minimum longitudinal reinforcement for concrete piles A c.en1992,max m 2 30 As (cm^2 2) EN 1536 (bored piles) BD 74/00 (bored piles) EN (driven cast-in-place) EN (micropiles) Minimum for column (EN 1992) Maximum for column (EN 1992) EN 1992 (bored piles) Ac (m^2) Oct-10 Decoding Eurocodes Geocentrix Ltd and Modulus Structural Engineering Ltd 33

34 GUIDANCE ON USE OF EUROCODES

35 Guidance from SCI/BCSA/Corus/Concrete Centre 27 October

38 JACK OFFORD (WITH APOLOGIES TO MUNCH) The Eurocode Scream Oct-10 April the death of British Standards 38

39 FURTHER INFORMATION IS AVAILABLE AT. Eurocode 7 training: Eurocode 7 book: Eurocode 7 blog:

Practical Design to Eurocode 2. The webinar will start at 12.30

Practical Design to Eurocode 2 The webinar will start at 12.30 Course Outline Lecture Date Speaker Title 1 21 Sep Jenny Burridge Introduction, Background and Codes 2 28 Sep Charles Goodchild EC2 Background,