A pilot application of EC8-3. - ecpfe.oasp.grecpfe.oasp.gr/sites/default/files/EC8-3 Athens Wkp 2013 (Kappos)_0.pdf · A pilot application of EC8-3. Reflections and comparisons with

Workshop Implementation of the EC 8-3:2005 Assessment and interventions on buildings in earthquake prone areas

A pilot application of EC8-3. Reflections and comparisons with the GCSI

Andreas J Kappos, Professor of Civil Engineering,

City University LondonCity University London

Athens, 12 April 2013


Eurocode 8 – Part 3 Overview

Relatively recent document, intended to be performance- and displacement-based

‘Flexibility’ to accommodate the large variety of situations arising in y g y gpractice and in different countries

Arguably major advantage, also major weakness!..

Logically structured, but (on drafters’ own admission, see Pinto 2011) missing the support from extended use

improvements to be expected from future (and present?) experiencep

Normative part covering only material-independent concepts and rules; verification formulae are in non-mandatory Informative Annexes

Very limited application, mainly in academic/background studies

the GCSI has enjoyed much more extensive application


Performance requirements in EC8 – 3


This presentation

Application of EC8-3 to a realistic building, representative of 1970’s European practice

the ‘SPEAR building’ (designed by Fardis et al.)g ( g y )

Application of all commonly used analysis methods for assessment

Lateral force (elastic) analysis

Multi-modal response spectrum analysis

q-factor approach

Application also of GCSI provisions, wherever different (m-method)

Identification of difficulties in implementing EC8-3

Comparisons with the GCSI

Conclusions and reflections on some issues and future trends


Specimen tested within the frame of the SPEAR project

Key data for the building

3-storey reinforced concrete (R/C) building

Broadly based on Greek codes of 1954 and 1959

deemed representative of 1970’s European practice

Frame structure, no special seismic provisions and detailing

Intentional weak points:

irregular in plan, torsion problem

indirect beam supports

eccentric connections at some joints

Key data for the building (contnd)

BEAM 1

0,25 0,250,25 0,25

BEAM 2

COLUMNS C1-C5 & C7-C9

0,25

4Φ12 10Φ12COLUMN C6

3

C5 C12Φ12 (MONTAGE)

2Φ12

Φ8/0.20

5

Φ8/0.20

2Φ12 (MONTAGE)

2Φ12

C2

Φ12 Φ12 Φ12 Φ12

Eccentric connections

0,25

STIRRUPS Φ8/25 STIRRUPS Φ8/25

0,25

0,75


Building model in ETABSin ETABS

Diploma thesisCh. Anastasiadou,

AUTh 2010


Performance requirements and seismic actions

Significant Damage 10% in 50 years seismic action

Knowledge level: KL3 (full knowledge), not common in actual

buildings (as opposed to Lab specimens)

→ confidence factor: CFKL3=1

Seismic hazard zone: Ι (αg=0.16g) Seismic hazard zone: Ι (αg 0.16g)

Ground conditions: C (dense sand, gravel or stiff clay)

Importance class: ΙΙ (γΙ=1.00)



Multi modal response spectrum analysisElastic response

spectrum

Assessment methods used


q-factor approach

Seismic load combinations:

spectrum

Ex+0.3Ey

Ey+0.3Ex

Assumed stiffnesses: EIef=0.50EIg (EC8 §4.3.1 applies) important difference from GCSI (and ASCE 41-07)! ‘hidden’ in §A3.2.4(5) referring specifically to DL state (not

SD), that if deformations are verified, then EIef=MyLv/3θy


Range of applicability (according to Eurocode 8 – Part 1):

a) period criteria

2 0s

2.4s4TT c

1


No restrictions in Eurocode 8 – Part 1

Additional requirement in EC8–3: ρi = Di / Ci < 2.5 for ductile members

b) Regularity in elevation Additional requirement in EC8–3: ρi = Di / Ci < 2.5 for ductile members

2.0s


q ρi i / i

q= 1.5 for reinforced concrete buildings Verifications based on action effects derived by reduced (1/q) spectrum,

rather than on ρi

Elastic static analysis

q-factor approach


Brittle components/mechanisms

ρi = Di / Ci < 1.0, Di from analysis (VEd)

Flexure and shear verifications

ρi i / i , i y ( Ed)

Ci based on mean values of material strengths (ΜRm)

ρi >1, Di from capacity design

MRd based on mean values of material strengths, modified for CFKL3 and γΜ

)1min( RcMMγM

Ductile components/mechanisms

Verification based on deformations!

),1min(

RbiRb,Rddi, M

MγM


• biaxial flexure is reduced to uniaxial one [Eurocode 2 Handbook]

Simplified column check for biaxial flexure (My, Mz, N)

z axis y axis z-axis y-axis

5bM

hM

xi

yi OR 0,2bM

hM

xi

yi Consider both

(i) 0 My

(ii) Mz 0

In all other cases:

if 1b'M

h'M

z

y

b'

Mβh'M z

z 0

if 1b'Mh'M

z

y

0 b'Mβh'

M yz

• the above My, Mz, are compared with corresponding (uniaxial) flexural strengths

z


Flexural verification based on deformations (§A.3.2.1) Existing software packages do not provide chord rotations (θ) as output

how can θ be calculated from given joint rotations?

π+Ry2

Ry2

α12 Ry3

x1,z1

1 23

x1+ux1,z1+uz1

x2,z2 x3,z3

x2+ux2,z2+uz2

x3+ux3,z3+uz3

Ry2

Ry1

α23

chord rotation at end i: where:ijyii R

ziizjjziizjj uzuza

uzuza

arctantan

general case for calculating θ from

joint rotations Ry on plane x-z

xiizjjij

xiizjjij uxxx

auxxx

a

arctantan

Verification: checking of θ against fractions (dependent on PR) of

dc

ywsx f

f

vc

vum h

Lf

100

35,0225.0

el

25.125;01.0max

';01.0max3.0016.0

1


a) For internal beam-column joints:

Critical joint verification: Diagonal compression

) j

b) For external beam-column joints:

jcjd

cdcyds2s1Rdjhd hbηv1ηfVfAAγV

v

Mean values of material strengths, modified for CFKL3 and γΜ

jcjd

cdcyds1Rdjhd hbη

v1ηf80.0VfAγV

Ex+0.3Ey Ey+0.3Ex3

ey

3

ResultsResults: Distribution of ρi = Di/Ci (flexure)

2

store

ελαστική στατικήδυναμική φασματική

2

storey

ελαστική στατικήδυναμική φασματική

Lateral force

Dynamic spectral

Lateral force

Dynamic spectral

10 0.5 1 1.5 2

10.5 1 1.5 2

Lateral force Dynamic response spectrum

minρi = 0.015 minρi = 0.003maxρi = 18.37 maxρi = 11.18


minρi = 0.015 minρi = 0.001maxρi = 7.17 maxρi = 7.49

ρmax/ρmin>>2.5 (ρmin=1.002 for ρ>1) elastic methods not allowed!


Summary of yrequired verifications

Lateral force (m-method) Dynamic response spectrum (m-method)

% of beam failures in flexure (Ex+0.3Ey)

60

80

100

60

80

100

q-approach

0

20

40

1st 2nd 3rd building0

20

40

1st 2nd 3rd building

80

100 ‘θ-method’ (θreq<3/4θu, based on EI 0 50EI )

0

20

40

60

80


on EIef=0.50EIg)

No failures!

60

80

100

60

80

100

% of beam failures in flexure (Ey+0.3Ex)


q-approach

80

100

0

20

40


20

40


‘θ-method’ (θreq<3/4θu)

0

20

40

60

80


No failures!

% of column failures under M, N (Ex+0.3Ey)


60

80

100

60

80

100

q-approach

0

20

40


20

40


80

100

80

100

‘θ-method’

0

20

40

60

80


20

40

60



60

80

100

60

80

100

% of column failures under M, N (Ey+0.3Ex)

q-approach

0

20

40


20

40


80

100

80

100‘θ-method’

0

20

40

60


20

40

60


% of beam shear failures (Ex+0.3Ey) Lateral force Dynamic response spectrum

60

80

100

60

80

100

q-approach

0

20

40


20

40


80

100

0

20

40

60

80


% of ‘failures’Beams in flexure

Comparative results for combination Ex+0.3Ey

% of ‘failures’Columns in flexure

40

60

80

100

lateral force analysis

response spectrum analysis

q-factor approach40

60

80

100



q-factor approach

0

20


20


(lateral force and dynamic analysis based on m-method)

% of ‘failures’Beams in shear

% of ‘failures’Columns in shear

Comparative results for combination Ex+0.3Ey

40

60

80

100



q-factor approach 40

60

80

100



q-factor approach

0

20


20



Comparative results for combination Ey+0.3Ex

% of ‘failures’Beams in flexure

% of ‘failures’Columns in flexure

100

40

60

80

100




60

80

100



q-factor approach

0

20


20



% of ‘failures’Beams in shear

% of ‘failures’Columns in shear

Comparative results for combination Ey+0.3Ex

100 100

40

60

80




60

80



q-factor approach

0

20


20


% of joints failing in diagonal compression Ex+0.3Ey

Beam-column joint verifications

% of joints failing in diagonal compression Ey+0.3Ex

40

60

80

100



q-factor approach40

60

80

100



q-factor approach

0

20


q-factor approach

0

20


q factor approach

average D/C ratios for columns (Ex+0.3Ey)

Comparisons with the GCSI (θ vs. m method, lateral force)

average D/C ratios for beams (Ex+0.3Ey)

0 5

1.0

1.5

2.0

2.5

3.0

GCSI

EC8-3

0 5

1.0

1.5

2.0

2.5

3.0

GCSI

EC8-3

CGSI (and ASCE 41-06) m-method results in substantially more unfavourable results than EC8-3!

0.0

0.5

1st 2nd 3rd building0.0

0.5


average D/C ratios for columns (Ex+0.3Ey)

Comparisons with the GCSI (θ vs. m method, response spectrum)

average D/C ratios for beams (Ex+0.3Ey)

0 5

1.0

1.5

2.0

GCSI

EC8-30.4

0.6

0.8

1.0

GCSI

EC8-3

again, CGSI (and ASCE 41-06) m-method results in substantially more unfavourable results than EC8-3!

0.0

0.5

1st 2nd 3rd building0.0

0.2


Comparisons with the GCSI (θ vs. m method)

What are the reasons for the discrepancy?

e ifications sho ld be ca ied o t fo stiffnesses compatible ith verifications should be carried out for stiffnesses compatible with θu, θy important, since for old buildings EIef<<0.5EIg (here 0.5EIg was used in all cases, as allowed by §4.3 of EC8-3)

different fractions of allowable deformation are specified by each code (e.g. for SD, θd=3/4θu by EC8-3, =0.5(θu+θy)/γRd by GCSI)

in calculating m approximate LVL/2 is assumed for beams and columns whereas θ corresponds to the exact Lcolumns, whereas θ corresponds to the exact LV

m-factor used to reduce seismic action effects only, θ includes contribution from gravity loads as well

for same EIef and θd, the two procedures give the same outcome only in a cantilever, undeformed under gravity loads


Analysis methods work as expected (same as in the GCSI) Dynamic response spectrum method leads to most favourablefavourable results q-approach leads to most unfavourableunfavourable results

Conclusions and reflections

q pp Realistic structures do not satisfy ρi<2.5 requirement for elastic analysis

(static+dynamic) need for inelastic analysis! (this also true for the GCSI) from GCSI based studies, pushover analysis more favourable results!

Preferable to use procedures prescribed in more detailed and comprehensive codes (like the GCSI)

Existing software packages do not provide chord rotations while θ Existing software packages do not provide chord rotations, while θ method (for flexure) is typically more favourable than m method!

Shear verification (capacity-based) not influenced by analysis method Assessment becomes complicated (and perhaps error-prone) due to

using different material strengths (with/without γM-factors) things equally (actually, a bit more) complex in the GCSI!


Thank you, Thank you, y ,y ,hope I have stirred hope I have stirred some discussion!some discussion!

websites: http://www.city.ac.uk/engineering-maths/staff/professor-andreas-kappos

http://ajkap.weebly.com/english.html

e-mail: [email protected]

Documents

A pilot application of EC8-3. - ecpfe.oasp.grecpfe.oasp.gr/sites/default/files/EC8-3 Athens Wkp 2013 (Kappos)_0.pdf · A pilot application of EC8-3. Reflections and comparisons with