S5-16-Bridge Design w ECs Carvalho 20121002-Ispra

7/29/2019 S5-16-Bridge Design w ECs Carvalho 20121002-Ispra

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Seminar Bridge Design with Eurocodes JRC Ispra, 1-2 October 2012 1

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Seminar Bridge Design with Eurocodes

JRC-Ispra, 1-2 October 2012

rgan ze an suppor e y

European CommissionDG Joint Research Centre

DG Enterprise and Industry

Russian FederationFederal Highway Agency, Ministry of Transport

TC250 Structural Eurocodes


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Seismic design of bridges with Eurocode 8

Eduardo CarvalhoGAPRES SA, Chairman CEN/TC250/SC8


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Eurocode 8 - Design of structures for

earth uake resistance

EN1998-1: General rules, seismic actions and rulesfor buildin s

EN1998-2: Bridges

EN1998-3: Assessment and retrofitting of buildings

- ,

EN1998-5: Foundations, retaining structures andgeo ec n ca aspec s

EN1998-6: Towers, masts and chimneys


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EN1998-2: Bridges

EN1998-2 to be applied in

combination with EN1998-1,-

Eurocodes


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EN1998-2: Bridges NDPs

Introduction (1)

Seismic action (4)

as c requ remen s an comp ance cr er a

Strength verification (4) Analysis (2)

Detailing (5)

Brid es with seismic isolation 4

8 Annexes 2


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EN1998-2: Bridges

A (Informative): Probabilities related to the reference seismic action. Guidance for

the selection of the design seismic action during the construction phase B (Informative): Relationship between displacement ductility and curvature

ductility factors of plastic hinges in concrete piers

C(Informative): Estimation of the effective stiffness of reinforced concreteductile members

D (Informative): Spatial variabilityof earthquake ground motion: Model andmethods of analysis

E(Informative): Probable material properties andplastic hinge deformationcapacities for nonlinear analysis

F(Informative):Added mass of entrained water for immersed piers G(Normative): Calculation ofcapacity design effects

H(Informative): Static non-linear analysis (Pushover)

JJ(Informative): -factors for common isolator types K(Informative): Tests for validation of design properties of sesimic isolator units


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Objectives of EN 1998

In the event of earthquakes:

Human lives are protected

Damage is limited

Structures important for civil protectionremain operational

S ecial structures Nuclear Power Plants, Offshorestructures, Large Dams outside the scope of EN 1998


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Fundamental requirements

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Withstand the design seismic action withoutlocal or

Retain structural integrity andresidual load bearing

capacity after the event (even with considerabledamage)

Flexural yielding of piers allowed. Bridge deck

expected to avoid damage

For ordinary structures this requirement should be met for a

reference seismic action with 10 % probability of exceedance in50 years (recommended value) i.e. with 475 years Return Period


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Fundamental requirements

Withstand a more frequent seismic action withoutdamage (remaining operational without

interruption)

Minor damage only in secondary components(and/or in parts specifically intended to dissipate

energy

action with high probability of occurrence.

No recommended value is given (10 % probability of exceedance in 10 yearsi.e. with 95 years Return Period could be used)


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Intended seismic behaviour

Ductile (D)

Limited ductile/essentially elastic (LD)


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Ductile behaviour

Provide for the formation of an intended

configuration of flexural plastic hinges

The bridge deck shall remain within the elastic range

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significant force plateau at

energy dissipation over at

least 5 inelasticdeformation cycles


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Ductile behaviour

Resistance verifications (forReinforced Concrete in

accordance with Eurocode 2, with some additional rulesfor shear and forSteel Structures in accordance with

Section 6 of EN 1998-1 for dissipative structures)

Capacity design: Shear and joints

Detailing for ductility: Global ductility d

and local

Ductility verification: Deemed to satisfy rules in

ec on


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Limited ductility/Essentially elastic

Deviation from ideal elastic provides some hysteretic

energy dissipation.

Corresponds to a value of the behaviour factorq1,5

Values ofqin the range 1 q1,5are mainly attributedto the inherent margin between design and probable

strength in the seismic design situation (overstrength)


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Reliability differentiation

Target reliability of requirement depending on

consequences of failure

Classify the structures into importance

classes

Assign a higher or lower return periodto

the desi n seismic action

n opera ona erms mu p y e re erence se sm c

action by the importance factor I


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Importance classes for bridges

ass : r ges o cr ca mpor ance or ma n a n ng commun ca ons,

especially in the immediate post-earthquake period; bridges the failure of

which is associated with a large number of probable fatalities and majorbridges where a design life greaterthan normal is required

Class II: General road and railwa brid es avera e im ortance

Class I: Bridges meeting the following conditions simultaneously (less than

the bridge is not critical for communications, and

the adoption of either the reference probability of exceedance, PNCR, inyears or e es gn se sm c ac on, or o e s an ar r ge es gn

life of 50 years is not economically justified.

I = 1,3; 1,0 and 0,85


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Importance factor and return period

mos s es e annua ra e o excee ance, agR , o e

reference peak ground acceleration agR may be taken to vary with

a as: H a ~ k a -kwith the value of the ex onent k de endin

on seismicity, but being generally of the order of 3.

If the seismic action is defined in terms of the reference eak

ground acceleration agR, the value of the importance factorI toachieve the same probability of exceedance in TL years as in the

LR ,

computed as: I~ (TLR/TL)1/kence, e mp c re urn per o s or e mpor ance asses are:

Class III: 1.044 years (~ 5% in 50 years)

Class I: 292 years (~15% in 50 years)


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Ground conditions

A - Rock

- ery ense san or grave or very s c a

C- Dense sand or gravel or stiff clay

D - Loose to medium cohesionless soil or soft tofirm cohesive soil

E- Surface alluvium layer C or D, 5 to 20 m thick,

over a much stiffer material

2special ground types S1 and S2requiring special studies

30 m and also by indicative values for NSPT and cu


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Ground conditions.

Groundt Description of stratigraphic profile Parameters

vs,30 (m/s) NSPT(blows/30cm)

cu (kPa)

oc or o er roc - e geoogca

formation, including at most 5 m ofweaker material at the surface.

_ _

B Deposits of very dense sand, gravel, orvery stiff clay, at least several tens of

metres in thickness, characterised by a

360 800 50 250

gradual increase of mechanicalproperties with depth.


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Ground conditions

.

Ground Description of stratigraphic profile Parameters


cu (kPa)

eep epos s o ense or me u -

dense sand, gravel or stiff clay withthickness from several tens to many

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.

D Deposits of loose-to-medium

cohesionless soil (with or without some

180 15 70

so t co esve ayers , or opredominantly soft-to-firm cohesivesoil.


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Ground conditions.

Groundt e

Description of stratigraphic profile Parameters


cu (kPa)

alluvium layer withvs values of type Cor D and thickness varying betweenabout 5 m and 20 m, underlain bystiffer material withvs> 800 m/s.

S1 Deposits consisting, or containing a

la er at least 10mthick of oft

100 _ 10 - 20

clays/silts with a high plasticity index(PI 40) and high water content

n cat ve

,

sensitive clays, or any other soil profilenot included in types A E orS1


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Seismiczonation

Competence of National Authorities

g

acceleration on type A ground)

Corresponds to the reference return periodTNCR

the design ground acceleration (on type A

round a = a .Objective for the future updating of EN1998-1:

Euro ean zonation ma with s ectral values fordifferent

hazard levels (e.g. 100, 500 and 2.500 years)


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Basic representation of the seismic action

Elastic response spectrum

Common sha e for the ULS and DLS verifications

2 orthogonalindependenthorizontalcomponents

Verticalspectrum shape differentfrom thehorizontal spectrum (common for all ground types)

Possible use ofmore than one spectral shape (to

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Account oftopographical effects (EN 1998-5) and spatial

variation of motion (EN1998-2) required in some special cases


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Definition of the horizontal elastic response spectrum(four branches)

0T TB Se(T) =ag . S . (1+T/TB . ( . 2,5 -1))TB T TC e(T) =ag . . . 2,5TC T TD Se(T) =a . S . . 2,5 (TC /T)TD T 4 s Se(T) =ag . S . . 2,5 (TC .TD /T 2)

e e as c response spec rum

ag design ground acceleration on type A ground

B C D corner eriods in the s ectrum NDPsS soilfactor (NDP)

dampingcorrection factor ( = 1 for 5% damping)

Additional information forT > 4 s in Informative Annex in EN 1998-1


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Normalised elastic response spectrum (standard shape)

Control variables

S, B, C, D (NDPs) ( 0,55) dampingcorrection for 5 %Fixed variables

,velocity & displacement

spectral branches acceleration spectral

amplification: 2,5

Different spectral shape forvertical spectrum (spectral

amplification: 3,0)


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Correction for damping 55,0510

1.6

r

1

1.2

1.4

ectionfact

0.6

0.8C

orr

0.2

0.4

0 5 10 15 20 25 30

Viscous damping (%)

To be applied only to elastic spectra


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Elastic response spectrum

Two types of (recommended) spectral shapes

Depending on the characteristics of the most

significant earthquake contributing to the local

T e 1 -Hi h and moderate seismicit re ions

azar :

(Ms > 5,5)

T e 2- Low seismicit re ions 5 5 near fieldearthquakes

of the seismic action


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Recommended parameters for the definition of the

Ground

T eS TB (s) TC (s) TD (s) S TB (s) TC (s) TD (s)

A 1,0 0,15 0,4 2,0 1,0 0,05 0,25 1,2

B 1,2 0,15 0,5 2,0 1,35 0,05 0,25 1,2

C 1,15 0,2 0,6 2,0 1,5 0,1 0,25 1,2

D 1 35 0 2 0 8 2 0 1 8 0 1 0 3 1 2

E 1,4 0,15 0,5 2,0 1,6 0,05 0,25 1,2


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Recommended elastic response spectra

4S 4

5

E

C

D

Se

/ag.S

3Se

/ag

B

C3

A

1

2

1

00 1 2 3 4T(s)

00 1 2 3 4

T(s)

Type 1 -Ms > 5,5 Type 2 -Ms 5,5


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Design spectrum for elastic response analysis(derived from the elastic spectrum)

0T TB Sd(T) =ag . S . (2/3+T/TB . (2,5/q -2/3))TB T TC d(T) =ag . S . 2,5/qTC T TD Sd(T) =a . S . 2,5/ . (TC /T)

. agTD T 4 s Sd(T) =a . S . 2,5/ . (TC .TD /T 2) . ag

Sd( ) design spectrumq behaviour factor

lower boundfactor(NDP recommended value: 0,2)Specific rules forvertical action:

avg = 0,9 . agoravg = 0,45 . ag ; S= 1,0; q 1,5


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Alternative representations of the seismic action

Time history representation (essentially for NL analysis

purposes)

Three simultaneously acting accelerograms

Artificial accelerogramsMatch the elastic response spectrum for 5% damping

ura on compa e w agn u e s sMinimum numberof accelerograms: 3

Recorded or simulated accelerogramsScaledto ag . S


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Spatial variability of the seismic action

Spatial variability shall be considered if one of the

following holds:

More than one ground type occurs in the supports of

The length of continuous deck exceeds Llim = Lg/1,5L - Distance beyond which motion is uncorrelated

Ground Type A B C D E

L (m) 600 500 400 300 500Recommended values

variability and additional information in Annex D


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Modelling - Mass

ass o ermanen oa s an uas -permanen va ues o e

Variable loads (2 Qk)

(For traffic loads: 2= 0,2 in road bridges; 2= 0,3 in railway bridges) Mass ofentrained wateradded to the mass of immersed piers

Procedure for calculation in Informative Annex F

Damping ratio values for elastic analysis :

e e s ee : = ,

Bolted steel: = 0,04

,

Reinforced concrete : = 0,05


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Modelling - Stiffness

or near ana ys s me o s a op e secan exura s ness

at yield (in Limited Ductile bridges the unreduced stiffness of gross concrete

sections may be used)

For Prestressed and Reinforced concrete decks the flexural

stiffness of the gross sections should be used

Reduced torsional stiffness of concrete decks: Open sections: Ignore torsional stiffness

Presstressed box sections: 50% stiffness

Reinforced concrete box sections: 30% stiffness


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Regularity

oca orce re uc on ac or or mem er :

ri = q MEd,i / MRd,i

MEd,i -Maximum value of design

moment at the intended plastic hinge location

from the anal sis

MEd,i -Design flexural resistancewith actual reinforcement

A bridge is considered regularif:

= =

Forirregular bridges the qfactor is reduced:

max m n ,

r ,

Regularity of the bridge conditions the admissible methods of analysis


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Methods of Analysis

near ynam c ana ys s esponse spec rum me o

Significant modes: Sum of effective mass > 0,9 total mass

Combination ofmodes:Square root of the sum of squares (SRSS) or

Complete Quadratic Combination (CQC) for closely spaced

mo es

Combination ofcomponents of seismic action:S uare root of the sum of s uares (SRSS) of each com onent

Fundamental mode method(static forces)

model; Flexible deck model and Individual pier model)

Static nonlinear analysis (pushover analysis)


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Maximum values

of the behaviour

factor q

Valid for

load: k 0,3


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Correction of values of the behaviour factor q

Reduction fornormalised axial loadk

for 0,3 < k 0,6:

r k , , ,

inspection and repair:qr= 0,6 x q 1,0


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Capacity Design

E -

MRd - Design flexural resistance with actual reinforcement

M0

= 0

MRd

- Overstrength moment(for the calculation of shear)

Recommended values:

For concrete members = 1,35

For steel members 0 = 1,25


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Detailing

Confinement of concrete piers

Avoidance of buckling of longitudinal reinforcement

Foundations

ear ngs an se sm c n s


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Seismic Displacements

Seismic displacement: dE = d dEe

Ee sp acemen compu e w e es gn spec rum nc u ng

the q factor)

dam in correction factor

d displacement ductility factor

o = , C d= q

T < T = - 1 T /T + 1 5 4


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Clearances

ruc ura an non-s ruc ura e a ng s ou accommo a e e

displacements in the seismic design situation

Seismic situation displacement: dEd = dE + dG + dT

dE

Seismic displacement

dG Long term displacement (prestress, creep, shrinkage)

T

Quasi permanent combination factor


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Thank you for your attention

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S5-16-Bridge Design w ECs Carvalho 20121002-Ispra