deco gcoding euroco socodes 2 7: desgsign...
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CO G OCO S 2 S G O O O SDECODING EUROCODES 2 + 7: DESIGN OF FOUNDATIONS
Dr Andrew Bond (Geocentrix)
Outline of talkApril 2010: the death of British Standards?
UK implementation of Eurocodes
Verification of strength: limit states STR and GEOVerification of strength: limit states STR and GEO
Some technical pitfalls
Guidance on use of Eurocodes
APRIL 2010 THE DEATH OF BRITISH STANDARDS?APRIL 2010: THE DEATH OF BRITISH STANDARDS?
British Standards for foundations prior to April 2010
Oct-10 4Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
European design standards for foundations (Eurocodes)
Oct-10 5Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
European specifications for materials (and testing standards)
Oct-10 6Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
European execution standards
Oct-10 7Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
UK IMPLEMENTATION OF EUROCODESUK IMPLEMENTATION OF EUROCODES
BONThe Eurocode family NDANDDHARRIS
(20008)
Oct-10 9Decoding Eurocodes 3+7 ©2010 Geocentrix Ltd and The Steel Construction Institute Ltd
BONRole of Eurocodes in UK practice NDANDDHARRIS
(20008)
Oct-10 10Decoding Eurocodes 3+7 ©2010 Geocentrix Ltd and The Steel Construction Institute Ltd
BSI ‘Published Documents’ to support the Eurocodes
Oct-10 11Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
‘De facto’ UK standards for basement design
Oct-10 12Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
C O O S G S S S G OVERIFICATION OF STRENGTH: LIMIT STATES STR AND GEO
EN Verification of strength 1997‐Verification of strength is expressed in Eurocode 7 by:
d dE R≤ ‐1 §2.4
Ed = design effect of actionsRd = design resistance corresponding to that effect
d d
4.7.1(1
Applies to GEO:“Failure or excessive deformation of the ground, in which the strength
of soil or rock is significant in providing resistance’ 1)Pof soil or rock is significant in providing resistanceEN 1997‐1 §2.4.7.1(1)P
and to STR:…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”significant in providing resistance
EN 1997‐1 §2.4.7.1(1)P
Oct-10 14Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
Application of partial factors and tolerances
dF Fγ=
Actions
Effects of actionsd F repF Fγ=
{ }, ,d E d d dE E F X aγ=Effects of actions
Material properties
kd
XX =
Material properties
dM
Xγ
{ }, ,d d dR F X aR
Resistances
Geometrical parameters { }, ,d d dd
R
Rγ
=d noma a a= ± Δ
Geometrical parameters
15Oct-10 Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
BONVerification of strength for STR (structural design) NDANDDHARRIS
(20008)
Oct-10 16Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
BONVerification of strength for GEO/STR (DA1‐1) † NDANDDHARRIS
(20008)
Oct-10 17Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
BONVerification of strength for GEO/STR (DA1‐2) † NDANDDHARRIS
(20008)
Oct-10 18Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
Partial factors for GEO/STR (DA1): footings, walls, and slopesParameter Symbol Combination 1 Combination 2
A1 M1 R1 A2 M2 R1
Permanent Unfavourable γ 1 35 1 0Permanent action (G)
Unfavourable γG 1.35 1.0
Favourable (γG,fav) 1.0
Variable Unfavourable γQ 1.5 1.3Variable action (Q)
Unfavourable γQ 1.5 1.3
Favourable ‐ (0) (0)
Shearing resistance (tan ϕ) γϕ 1.0 1.25g ( ϕ) γϕEffective cohesion (c’) γcUndrained shear strength (cu) γcu 1.4
Unconfined compressive strength (qu) γquWeight density (γ) γγ 1.0
Bearing resistance (R ) γ 1 0 1 0Bearing resistance (Rv) γRv 1.0 1.0
Sliding resistance (Rh) γRhEarth resistance (Re) γRe
Oct-10 19Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
SOME TECHNICAL DETAILSSOME TECHNICAL DETAILS
EN Design strength of concrete 1992‐Design compressive strength of concrete is:
α γ=cd cc ck cf f ‐1‐1 EXfck = characteristic compressive strength of concrete (from cylinder tests)
γ = partial factor for concrete in compression
γcd cc ck c
XP(3.15
γc = partial factor for concrete in compressionαcc = factor for long term effects on compressive strength and unfavourableeffects resulting from the way the load is applied 5‐3.16Design tensile strength of concrete is:
2 3 ) & TAfctk 0 05 = characteristic tensile strength of concrete (5% fractile value)
2 3,0.05 0.21ctd ct ctk c ct ck cf f fα γ α γ= = ×
BLE3.1
ctk,0.05 g ( )
αct = factor for long‐term effects on tensile strength, etc.
[fck has units of MPa in this expression] 1
Oct-10 21Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
EN Design strength of reinforcing steel 1992‐Design yield strength of reinforcing steel is:
γ=d kf f ‐1‐1 §3
fyk = characteristic yield strength of reinforcing steel
γ = partial factor for reinforcing steel
γyd yk sf f
3.2.7(2
γs = partial factor for reinforcing steel
2)
Oct-10 22Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
EN Factor for long‐term effects on concrete strength 1992‐Document Reinforced concrete Plain/lightly‐reinforced conc.
Compression Tension Compression Tension ‐1‐1 §3
αcc αct αcc,pl αct,pl
EN 1992‐1‐1 1.0 1.0 0.8 0.8
UK NA (Amd 1) 0 85 flexure/axial 1 0 0 6 0 8
3.1.6 &
UK NA (Amd 1) 0.85 flexure/axial1.0 otherwise
1.0 0.6 0.8
& PD
66
Long‐ vs short‐term strength Justification for αcc = 0.85
687
Oct-10 23Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
EN Partial factors for reinforced concrete 1992‐Limit states Design
situationReinforced concrete Reinforcing and pre‐
stressing steel
General Piles* γ ‐1‐1 §2
General Piles γsγc kfγc
Ultimate Persistent 1.5 1.65 1.15 2.4.2.4
Transient 1.5 1.65 1.15
Accidental 1.2 1.32 1.0 4 & 2.4
Seismic 1.0† 1.0† 1.0†
Serviceability 1.0 1.0 1.0
*Cast in place piles without permanent casing; k = 1 1
4.2.5
Cast‐in‐place piles without permanent casing; kf = 1.1†Recommended value for situations not explicitly covered by EN 1992
Oct-10 24Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
Bending resistance of singly‐reinforced beamVerification of bending resistance requires:
≤Ed RdM M
MEd = design value of applied bending moment effect
MRd = design bending resistance given by:
Ed Rd
MRd = design bending resistance, given by:
⎛ ⎞= −⎜ ⎟
⎝ ⎠1
2yd s
Rd s yd
f AM A f d
f bd
As = area of steel reinforcement
f d i i ld h f i f i l
η⎜ ⎟⎝ ⎠2d s yd
cdf bd
fyd = design yield strength of reinforcing steel
b = width of cross‐section; d = its effective depth
f d = design compressive strength of concretefcd design compressive strength of concrete
η = 1.0
Oct-10 25Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
Design chats for singly‐reinforced beams
0 24
0.26
0.28
0.3
7
8
9
0.16
0.18
0.2
0.22
0.24
/ bd^
2fcd
5
6
7
^2 (M
Pa)
0 06
0.08
0.1
0.12
0.14
K =
M /
2
3
4 fck = 50 MPa45 MPa40 MPa35 MPa30 MP
M /
bd^
0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32 0.36
0.02
0.04
0.06
( / bd) (f d/f d)0 0.5 1 1.5 2 2.5 3 3.5 4
1
30 MPa25 MPa20 MPa
(As / bd) (fyd/fcd) As / bd (%)
Oct-10 26Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
Differences between design aidsDesign 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
2 3Ed EdN Mvs
h f h f 2s ydA f
h fConcrete Centre
2 3Ed EdN Mvs
2 3cd cdh f h f
s ykA f
2cdh f
TCC Spreadsheets
2 3ck ck
vsh f h f 2
ckh f
( ) vs ( )Ed EdN kN M kNm (e.g. 4B32)sA( ) ( )Ed Ed ( g )s
Oct-10 27Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
EN Truss model for variable strut inclination method 1992‐‐1‐1 §66.2.3(11)
Oct-10 28Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
Design charts for shear resistance
0 8
0.9
1
7
8
7
821.8
0 5
0.6
0.7
0.8
2%1 75% (M
Pa)
4
5
6
4
5
6
tanc
e (M
Pa)
0 2
0.3
0.4
0.5 1.75%1.5%1.25%1.0%0.75%0 5%
vRd.
c
2
3
4
2
3
4
Shea
r res
ist
0 200 400 600 800 1000 1200 1400 1600
0.1
0.2 0.5%0.25%0.15%
20 25 30 35 40 45
1 1
Truss angle (deg)Effective depth (mm)
g ( g)
Oct-10 29Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
Assumptions used to develop N:M interaction charts
Reinforcing bars are (rotationally) symmetrical about the pile centre
Above neutral axis concrete and reinforcing bars provide compression forceAbove neutral axis, concrete and reinforcing bars provide 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 30Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
PILECircular pile (D = 600 mm, c = 75 mm, φl = 32 mm, φt = 8 mm) EINTERAA
CTIONDIAGRAA
M
Feltham (2004), paper in The Structural Engineer
dv z βArea of concrete strut
2rs/π
Oct-10 32Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
Comparing minimum reinforcement for concrete piles
40Minimum longitudinal reinforcement for concrete piles
Ac.EN1992,max
30
m2
30
2)
20
As
(cm
^2
10
EN 1536 (bored piles)BD 74/00 (bored piles)EN 14199 (driven cast-in-place)EN 14199 (micropiles)
0 0 25 0 5 0 75 1 1 25 1 5
Minimum for column (EN 1992)Maximum for column (EN 1992)EN 1992 (bored piles)
0 0.25 0.5 0.75 1 1.25 1.5
Ac (m^2)
Oct-10 33Decoding Eurocodes 2+7 ©2010 Geocentrix Ltd and Modulus Structural Engineering Ltd
GUIDANCE ON USE OF EUROCODESGUIDANCE ON USE OF EUROCODES
Guidance from SCI/BCSA/Corus/Concrete Centre
27 October 2010http://www.steel-ncci.co.uk/
WWDesigners’ Guides, ‘Decoding’ book and blog WW.EU
RROCO
DEE7.CO
M
Oct-10 36Decoding the Structural Eurocodes ©2005-10 Geocentrix Ltd. All rights reserved
WW‘Decoding’ training courses from Geocentrix WW.GEOO
CENTRIX.CO.UU
K/TRAINING
Oct-10 37Decoding Eurocode 7 ©2005-10 Geocentrix Ltd. All rights reserved
JAC‘The Eurocode Scream’ K
OFFOO
RD(W
IITHAPOO
LOGIESS
TOM
UNCH)
38Oct-10 April 2010 - the death of British Standards
FURTHER INFORMATION IS AVAILABLE AT ….
Eurocode 7 training: www.geocentrix.co.uk
Eurocode 7 book: www.decodingeurocode7.com
Eurocode 7 blog: www.eurocode7.com