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

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

APRIL 2010: THE DEATH OF BRITISH STANDARDS?

UK IMPLEMENTATION OF EUROCODES

The Eurocode family BON ND AND HARRIS (2008) Oct-10 Decoding Eurocodes 3+7 2010 Geocentrix Ltd and The Steel Construction Institute Ltd 9

Role of Eurocodes in UK practice BON ND AND HARRIS (2008) Oct-10 Decoding Eurocodes 3+7 2010 Geocentrix Ltd and The Steel Construction Institute Ltd 10

VERIFICATION OF STRENGTH: LIMIT STATES S STR AND GEO

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 1997 1 2.4.7.1(1)P EN 1997 1 2.4 4.7.1(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 1997 1 2.4.7.1(1)P Oct-10 Decoding Eurocode 7 2005-10 Geocentrix Ltd. All rights reserved 14

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 7 2005-10 Geocentrix Ltd. All rights reserved 15

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 135 1.35 10 1.0 action (G) Favourable (γ G,fav ) 1.0 Variable Unfavourable γ Q 1.5 1.3 action (Q) Favourable (0) (0) Shearing resistance (tan ϕ) γ ϕ 1.0 1.25 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 1.0 1.0 Sliding resistance (R h ) Earth resistance (R e ) γ Rh γ Re Oct-10 Decoding Eurocode 7 2005-10 Geocentrix Ltd. All rights reserved 19

SOME TECHNICAL DETAILS

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,0.05 05 = 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 1992 1 1 EX XP (3.15 5 3.16 ) & TA BLE 3.1 Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 21

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 1992 1 1 3 3.2.7(2 2) Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 22

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 1992 1 1 1.0 1.0 0.8 0.8 UK NA (Amd 1) 085flexure/axial 0.85 10 1.0 06 0.6 08 0.8 1.0 otherwise Long vs short term strength Justification for α cc = 0.85 EN 1992 1 1 3 3.1.6 & PD 66 687 Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 23

Partial factors for reinforced concrete Limit states Design situation Reinforced concrete Reinforcing and prestressing steel General Piles* γ s γ c Ultimate Persistent 1.5 1.65 1.15 k f γ c Transient 1.5 1.65 1.15 Accidental 1.2 1.32 1.0 Seismic 1.0 1.0 1.0 Serviceability 1.0 1.0 1.0 *Cast in place piles without permanent casing; k f = 11 1.1 Recommended value for situations not explicitly covered by EN 1992 EN 1992 1 1 2 2.4.2.4 4 & 2.4 4.2.5 Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 24

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 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 25

Design chats for singly reinforced beams 0.3 9 0.28 0.26 8 / bd^2fcd K = M / 024 0.24 0.22 0.2 0.18 0.16 0.14 0.12 0.1 0.08 006 0.06 0.04 0.02 M / bd^ ^2 (MPa) 7 6 5 4 fck = 50 MPa 45 MPa 3 40 MPa 35 MPa 2 30 MPa 1 25 MPa 20 MPa 0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32 0.36 (As / bd) (fyd/fcd) d) 0 0.5 1 1.5 2 2.5 3 3.5 4 As / bd (%) Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 26

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 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 27

Truss model for variable strut inclination method EN 1992 1 1 6.2.3(1) Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 28

Design charts for shear resistance 1 0.9 08 0.8 8 7 21.8 8 7 (MPa) vrd.c 0.7 0.6 2% 05 0.5 1.75% 1.5% 0.4 1.25% 0.3 1.0% 0.75% 02 0.2 05% 0.5% 0.1 0.25% 0.15% 0 200 400 600 800 1000 1200 1400 1600 Effective depth (mm) tance (MPa) Shear resist 6 6 5 5 4 4 3 3 2 2 1 1 20 25 30 35 40 45 Truss angle (deg) Oct-10 Decoding Eurocodes 2+7 2010 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 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 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 30

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

Feltham (2004), paper in The Structural Engineer d v z β Area of concrete strut 2r s /π Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 32

Comparing minimum reinforcement for concrete piles 40 Minimum longitudinal reinforcement for concrete piles A c.en1992,max m 2 30 As (cm^2 2) 20 10 EN 1536 (bored piles) BD 74/00 (bored piles) EN 14199 (driven cast-in-place) EN 14199 (micropiles) Minimum for column (EN 1992) Maximum for column (EN 1992) EN 1992 (bored piles) 0 025 0.25 05 0.5 075 0.75 1 125 1.25 15 1.5 Ac (m^2) Oct-10 Decoding Eurocodes 2+7 2010 Geocentrix Ltd and Modulus Structural Engineering Ltd 33

GUIDANCE ON USE OF EUROCODES

Guidance from SCI/BCSA/Corus/Concrete Centre 27 October 2010 http://www.steel-ncci.co.uk/

JACK OFFORD (WITH APOLOGIES TO MUNCH) The Eurocode Scream Oct-10 April 2010 - the death of British Standards 38

FURTHER INFORMATION IS AVAILABLE AT. Eurocode 7 training: www.geocentrix.co.uk Eurocode 7 book: www.decodingeurocode7.com Eurocode 7 blog: www.eurocode7.com