IMPLEMENTATION OF THE EC 8.3: ASSESSMENT AND INTERVENTIONS IN EARTHQUAKE PRONE AREAS

PERPETUATE PERformance-based aPproach to Earthquake proTection of cUlturAl heriTage in European and mediterranean countries

Performance based assessment of ancient masonry buildings.

Outcome of the European project PERPETUATE

Sergio LagomarsinoUniversity of Genoa, Italy

[email protected]

IMPLEMENTATION OF THE EC 8.3: ASSESSMENT AND INTERVENTIONS IN EARTHQUAKE PRONE AREAS

Athens - April 12, 2013

PERformance-based aPproach to Earthquake proTection of cUlturAl heriTage in European and

mediterranean countries

Main objectives of the project:Development of European Guidelines for the evaluation

and mitigation of seismic risk to cultural heritage assets.

Both architectonic assets (historic buildings; macroelements) and artistic assets (frescos, stucco-works, statues, pinnacles, battlements, banisters, balconies …) will be considered. Only masonry structures will be considered.

Earthquake protection of cultural heritage

www.perpetuate.eu

The Consortium consists of: - 6 Universities (Genoa, Thessaloniki, Athens, Ljubljana, Bath,

Algiers) - 2 Public/Research Institutions (ENEA, Italy; BRGM, France)- 3 SMEs from Slovenia (ZRMK) and Italy (CENACOLO, PHASE).

Partners

The protection of cultural heritage needs an improvement in methods of analysis and assessment procedures, rather than the development of new intervention techniques.

A reliable assessment procedure is the main tool to respect the principle of “minimum intervention” under the constraint of structural safety.

The displacement-based approach for vulnerability assessment of cultural heritage assets and design of interventions is adopted as standard method of analysis.

Nonlinear models are necessary. Nonlinear static (pushover) analyses are considered as the main tool for the application of the assessment procedure. Nonlinear dynamic analyses are considered as an alternative tool, only for certain types of assets.

If, after a reliable seismic assessment, it comes out the monument is not safe, then its retrofitting is unavoidable, first of all in order to preserve its life along the time and also for the safety of occupants.

Basic principles of PERPETUATE procedure


The outcome of the assessment is the maximum Intensity Measure (e.g. PGA) compatible with the fulfilment of each performance level that has to be considered.

The format of the assessment proposed by PERPETUATE guidelines is deterministic, except for the occurrence of the earthquake, as well as in all codes and recommendations worldwide adopted at present.

However, it is well know many uncertainties, aleatory and epistemic, affect the assessment of an existing masonry building, with reference to: a) the characteristics of seismic input (duration, frequency content, etc.) b) the reliability of mechanical models c) the material parameters d) the incomplete knowledge of the construction

PERPETUATE takes into account probabilistic aspects in some steps of the procedure: acceptance criteria for the definition of PLs sensitivity analysis for drawing the protocol of in-situ investigations and

defining the Confidence Factors


Basic steps of PERPETUATE procedure

Classification of architectonic assets

PERPETUATE considers a classification of architectonic assets which is useful for addressing the choice of proper mechanical models to be adopted for the assessment.

It is functional to model main seismic behaviour of buildings

Classes Description List of assets

AThis class collects architectonic assets with two main bearing structural elements: vertical walls and horizontal floors. If they are properly connected, mutual cooperation between the structural elements allows the building to behave as a box.

A1 palaces, A2 castles, A3 religious houses, A4 caravansaries, A5 madrasas

BThis class collects architectonic assets which are characterized by wide spaces without intermediate floors and few inner walls. Independent damage mechanisms occurs in the different parts of the building, and it is often possible to recognize specific structural macroelements (façade, triumphal arch, apse, dome, transept,…).

B1 churches, B2 mosques, B3 temples, B4 baptisteries, B5 mausoleum, B6 hammam B7 theatres

CThis class collects architectonic assets in which the vertical dimension prevails on the other ones. Since usually, these buildings are characterized by significant slenderness, their seismic response may be assumed as a global flexural behavior.

C1 towers, C2 bell towers, C3 minarets, C4 lighthouses, C5 chimneys

DThis class collects architectonic assets in which the main structural element is an arch or a vault. Both single arches or much more complex constructions based on this basic structural element are included.

D1 triumphal arches, D2 aqueducts, D3 bridges, D4 cloisters

EThis class collects massive constructions in which the wide thickness of walls, if compared to other dimensions, doesn’t allow the idealization as plane structural element. Local failure occurs as, for example, the detachment of external leaf.

E1 fortresses, E2 defensive city walls

FThis class collects single isolated architectonic assets, which does not delimit an interior space.

F1 columns, F2 trilithes, F3 obelisks, F4 archaeological ruins

GThis class refers to historical centers, made of ordinary buildings’ aggregates, which assume the relevance of cultural heritage asset as whole in the urban context. The seismic response must consider the interaction among adjacent buildings.


BOX-TYPE STRUCTURES (vertical walls and horizontal floors)


AThis class collects architectonic assets with two main bearing structural elements: vertical walls and horizontal floors. If they are properly connected, mutual cooperation between the structural elements allows the building to behave as a box.

A1 palaces, A2 castles, A3 religious houses, A4 caravansaries, A5 madrasas

A1 Palaces

A2 Castles A3 Religious houses

A4 Caravansaries



BThis class collects architectonic assets which are characterized by wide spaces without intermediate floors and few inner walls. Independent damage mechanisms occurs in the different parts of the building, and it is often possible to recognize specific structural macroelements (façade, triumphal arch, apse, dome, transept,…).

B1 churches, B2 mosques, B3 temples, B4 baptisteries, B5 mausoleum, B6 hammam B7 theatres

B1 Churches B2 Mosques

B6 Hammam

WIDE HALLS WITHOUT INTERMEDIATE FLOORS (macroelements)


SLENDER MASONRY STRUCTURES


CThis class collects architectonic assets in which the vertical dimension prevails on the other ones. Since usually, these buildings are characterized by significant slenderness, their seismic response may be assumed as a global flexural behavior.

C1 towers, C2 bell towers, C3 minarets, C4 lighthouses, C5 chimneys

C1 Towers C2 Bell Towers C3 Minarets C4 Lighthouses


ARCHED AND VAULTED STRUCTURES


DThis class collects architectonic assets in which the main structural element is an arch or a vault. Both single arches or much more complex constructions based on this basic structural element are included.

D1 triumphal arches, D2 aqueducts, D3 bridges, D4 cloisters

D4 CloistersD1 Triumphal arches


MASSIVE MASONRY CONSTRUCTIONS


EThis class collects massive constructions in which the wide thickness of walls, if compared to other dimensions, doesn’t allow the idealization as plane structural element. Local failure occurs as, for example, the detachment of external leaf.

E1 fortresses, E2 defensive city walls

E1 Fortress E2 Defensive city walls


DRY BLOCKS STRUCTURES


F This class collects single isolated architectonic assets, which does not delimit an interior space.

F1 columns, F2 trilithes, F3 obelisks, F4 archaeological ruins

F1 Columns F2 Trilithes F3 Obelisks


AGGREGATED BUILDINGS IN HISTORICAL CENTRES


GThis class refers to historical centers, made of ordinary buildings’ aggregates, which assume the relevance of cultural heritage asset as whole in the urban context. The seismic response must consider the interaction among adjacent buildings.

Navelli, L’Aquila, Italy Skofja Loka, Slovenia


From classification to mechanical models

A B C D E F

CCLM - Continuum Constitutive Laws models

SEM - Structural Element models

DIM – Discrete Interface models

MBM – Macro Block models

ARCHITECTONIC CLASSES

MODELS CLASSES CORRELATION

Classification and modelling

Some types of assets (can be studied by a global 3D model, while in other cases it is necessary to develop more than one model, even of different types. Moreover, the assessment requires taking into accont the possible activation of local mechanisms.

Safety and conservation requirements

USE and HUMAN LIFE

BUILDING CONSERVATION

IMMEDIATE OCCUPANCY

LIFE SAFETY

NEAR COLLAPSE

SIGNIFICANT BUT RESTORABLE

DAMAGE

DAMAGE LIMITATION

NO DAMAGEOPERATIONAL

PERFORMANCE LEVELS

ARTISTIC ASSETS

LOSS PREVENTION

RESTORABLE DAMAGE

NEAR INTEGRITY

Performance Levels

EC8 part 3


USE and HUMAN LIFE

BUILDING CONSERVATION

IMMEDIATE OCCUPANCY

LIFE SAFETY

NEAR COLLAPSE

SIGNIFICANT BUT RESTORABLE

DAMAGE

DAMAGE LIMITATION

NO DAMAGEOPERATIONAL1

2

3

4

DAMAGE LEVEL

PERFORMANCE LEVELS

GLO

BA

L S

CA

LE –

WH

OL

E A

SS

ET

ARTISTIC ASSETS

LOSS PREVENTION

RESTORABLE DAMAGE

NEAR INTEGRITY

1

2

3

ST

RU

CT

UR

AL

ELE

ME

NT

–

LOC

AL

SC

ALE

DAMAGE LEVEL

Performance Levels & correlation with damage


Performance and damage Levels & Acceptance Criteria

0

500

1000

1500

2000

2500

0 10 20 30 40

Vtot

[kN]

u [mm]

DLs defined on basis of multicriteriaapproach

DL1 DL2 DL3 DL4

Fragilitycurves

0

0,5

1

0 10 20 30 40

DL1

DL2

DL3

DL4

,

1|

lnd

dds

dds

SPd

sSS

50% of probability ofbeing or exceeding DL3

0

0,5

1

0 10 20 30 40

DL1

DL2

DL3

DL4

d

Probability distribution of DLs

0

0,1

0,2

0,3

0,4

0,5

0 1 2 3 4 5

Damage level

If the acceptance criterion isn’t satisfied , the PL limit threshold may moved back with respect the corresponding DL

Corresponding to Spp=DL3

DL

iP

V

d dDL4dDL3dDL2dDL1

PL3


Performance Levels & corresponding Target Seismic Demand Levels


Performance Levels & corresponding Target Seismic Demand Levels

EC8.3 - 225 years

IMPORTANCE FACTORS

Seismic hazard

A proper definition of the seismic demand is addressed by the information and choices that have been assumed in the first step (Classification).

Intensity Measure (IM): it depends on the Class of the architectonic asset.

Seismic Input can be described by:

1) in case of nonlinear static analyses, an Acceleration-Displacement Response Spectrum (ADRS), completely defined for the specific site of the building under investigation as a function the Intensity Measure (IM);

2) in case of non linear dynamic analyses, a proper set of time-histories, selected from real recorded accelerograms, obtained through numerical models of the seismic source and the propagation to the site or artificially generated, in order to be compatible with a target response spectrum (this last option is questionable).

Seismic hazard

Probabilistic Seismic Hazard Assessment

e.g. PGA & PGD

Seismic hazard

For architectonic assets that require the adoption of an IM representative of the ADRS in the long periods range (e.g. Class F), or more than one IM (Vector-Valued PSHA), the shape of the response spectrum must change, in order to be compatible with the information provided by GMPEs for short a long periods

Seismic hazard

Floor spectra (for the assessment of local mechanisms in the higher levels)

As built information

In this sub-step, geometrical, technological and mechanical features of the asset are analysed in depth, with the aim of defining the structural model of the building and related artistic assets.

Although it is necessary to investigate in detail the construction, in case of ancient masonry buildings it is necessary to consider that:

1) in cultural heritage assets, due to conservation requirements, the impact of investigations should be minimized;

2) in seismic assessment of an existing building epistemic uncertainties due to the incomplete knowledge and reliability of models add up to aleatory uncertainties, in particular related to material parameters.

The approach adopted in PERPETUATE is based on the use of Confidence Factors.


Approach used by codes Main drawbacks

i. Usually the reaching of a certain knowledge level implies an almost homogeneous degree of accuracy to be reached on all the different knowledge aspects (material, geometry, constructive details).

ii. The confidence factor is conventionally applied only to the parameter which is assumed to mainly affect the structural response. This parameter (or set of parameters) is proposed by codes a priori: usually, in fact, it coincides with strength mechanical parameters (only some codes – such as the ASCE/SEI 41-06 – proposes to apply it to the drift values, only in case of deformed controlled modes).

iii. The value of the confidence factor is conventionally proposed by codes only as a function of the reached knowledge level.

i. Since in general different parameters may differently (more or less significantly) affect the structural behaviour, it seems more reasonable to allows a calibration of the improvement of knowledge required as a function of the degree of sensitivity of the response. In some cases, a lower level of knowledge has been accepted because no remarkable building details have been analysed notwithstanding these abovementioned information could not be so relevant in terms of seismic safety.

ii. In general, as a function of the structure examined, this conventional assumption could not be the best one.

iii. The actual variability of from time to time examined parameters which may affect the response of the building is not considered.


The idea is that investigation program should be based on a preliminary sensitivity analysis aimed to:

1) identify the main parameters to be investigated;2) define proper Confidence Factors (CFs), to be used for the assessment

in order to take into account uncertainties.

The identification of main parameters influencing the structural response of the asset allows to finalize the investigation to few important points (thus reducing costs and time) and to reduce the number of destructive tests.

The calibration of CFs on the basis of sensitivity analyses instead of a-priori assumptions (as usually done for standard buildings) provides more reliable models and results.

As built information: sensitivity analysis


Notes on steps d) related to the execution of sensititvity analysis

Examples of sensitivity analyses results

0

50

100

150

200

250

300

0 0,5 1 1,5 2 2,5

F* (k

N)

d* (cm)

mean values

drift -

drift +

0

50

100

150

200

250

300

0 0,5 1 1,5 2 2,5

F* (k

N)

d* (cm)

mechanical parameters +

mean values

mechalical parameters -0

50

100

150

200

250

300

0 0,5 1 1,5 2 2,5

F* (k

N)

d* (cm)

mean values

masses -

masses +

SENSITIVITY TO DRIFT

SENSITIVITY TO MECHANICAL PARAMTERS SENSITIVITY TO MASSES


Sensitivity to epistemic uncertainties

Performance Level

Sensitivity to random variables


In sensitivity analyses both statistical uncertainties, treated by proper random variables, and epistemic uncertainties, treated by a logic tree approach, are considered.

Y1 Y2Coupling effectiveness of piers Shear floor stiffness

A – presence oftension-only rods at

floor level

B – presence of beamelements at floor level

A – rigid floor

B – flexible floor

A – rigid floor

B – flexible floor

YAA

YAB

YBA

YBB

On Y1 : High sensitivity class + KL3

According to information achieved model B has been

adopted

On Y2 : High sensitivity class + KL2

A subjective probability hasbeen assigned to each model in

order to combine the results

wY1_A=0wY1_B=1

wY2_A=0.7wY2_B=0.3

wYAA =0

wYAB = 0

wYBA = 0.7

wYBB = 0.3


Steps of the proposed procedure:

a) Achievement of a “basic” knowledge level to preliminarly identify the suitable model (or models) to be adopted for the seismic assessment.

b) Identification of all parameters or set of parameters (in case of parameters dependent on each other) affecting the model.

c) For each parameter, identification of the more rational range of variation.

d) Execution of the sensitivity analysis onto selected parameters in order to evaluate how much each one really affects the seismic behaviour of the examined building. Non linear static analysis is assumed as the standard one.

e) Attribution of a “sensitivity class” (low, medium or high), on the basis of the post processing of results provided from the sensitivity analysis, for each parameter.

f) Plan of the investigation and testing by using the results obtained from steps d) and e).

g) Execution of investigations and tests;

h) Definition of the confidence factor, possible updating of the mean value of parameters (on the basis of tests/investigations results) and final definition of parameters to be used in models for the seismic assessment.

Notes on steps h) related to the definition of confidence factor

According to the common approaches based on the use of confidence factor , it seems reasonable to apply CF to the “main parameter” which affect the structural seismic response.In the case of PERPETUATE procedure, it is possible choosing the “main parameter” among those associated to a high sensitivity class and not conventionally a priori. Regarding the value to be adopted for CF it has to take into account :

i. the actual variability of the parameter which will be applied to (by considering the related fk value);

ii. the “remaining” uncertainties associated to the incomplete knowledge process (since it could be not possible to reach the maximum knowledge level on all parameters ).



Notes on steps h) related to the definition of confidence factor

It is necessary to increase the knowledge level for parameters that have a higher sensitivity class.

Sensitivity ClassKnowledge level Low Medium High

KL1 0.3 0.6 1KL2 0 0.3 0.6KL3 0 0 0

Hence CF is computed as:

)(1

)(1

max

max

bf

afFC

c

c

where fc corresponds to fk associated to the k-th parameter assumed as reference as “main

parameter” that affects the seismic response.

Measure of the sensitivity of the structural performance

at k- th parameter

1,3

,1,31,3,1

PL

kPLPLk a

aa

Measure of the sensitivity of the structural performance

at n- th factors


Modelling and verification procedures

Verification procedures adopted:

METHODS OF ANALYSIS AND ASSESSMENT PROCEDURES

Pushover analyses and Capacity Spectrum MethodSTANDARD METHOD

Nonlinear dynamic analysis (IDA)MORE ACCURATE METHOD – APPLICABLE WITH A REASONABLE COMPUTATIONAL EFFORT ONLY FOR SOME CLASSES

Linear elastic analysis and assessment based on behaviour factor (q)ONLY IN CASE OF VERY COMPLEX ASSETS


ASSESSMENT PROCEDURES AND ARCHITECTONIC ASSET CLASSES

Homogeneous and coherent criteria are adopted for the development of the assessment procedures which have to be applied to the different classes of assets defined in D4 (from A to F)

In particular three main cases may be identified:

1) Asset composed by a single macroelement;

2) Complex assets described by a single capacity curve;

3) Complex assets described by a N capacity curves

Case 1) Case 2) Case 3)


ASSESSMENT PROCEDURES AND ARCHITECTONIC ASSET CLASSES

Case Procedure

Architectonic Asset Class

APrevailing in-plane

response

BPrevailing

out-of-plane response

CMonodimens

ional masonry elements

DArched

subject to in-plane

response

EMassive structure

FBlocky

structures subjected to overturning

Asset composed by a single macroelement

- X X - X

Complex assets described by a single capacity curve

Standard Possible -

Complex assets described by N capacity curve

Rare Standard -

A B C D E F


SUMMARY OF THE PROCEDURE:

1. Pushover analysis

2. Definition of PLs on the pushover curve

3. Capacity curve – Equivalent SDOF

4. Seismic demand and hazard curve (Intensity Measure - IM)

5. Computation of the maximum IM value (IMPLi) compatible with the given perfomance level (PLi)

6. Comparison of IMPLi with the corresponding target value IM*PLi

7. Use of seismic assessment outcome for the rehabilitation decisions

Assets composed by a single macroelement

1. PUSHOVER ANALYSIS

NON LINEAR KINEMATIC ANALYSIS

MACRO BLOCK MODELS (MBM)

Seismic forces proportional to masses applied in each block

NON LINEAR STATIC ANALYSIS

CONTINUUM CONSTITUTIVE LAWS MODELS (CCLM)

AND STRUCTURAL ELEMENT MODELS (SEM)

Seismic forces proportional to the first mode

CLASS C

F and D CLASSES


2. Definition of PLs on the pushover curve

NON LINEAR KINEMATIC ANALYSISMBM models

F and D classes

NON LINEAR STATIC ANALYSISCCLM and SEM models

C class


m*

h*

3. Capacity curve – Equivalent SDOF

NON LINEAR KINEMATIC ANALYSISMBM models

It is assumed as a fundamental shape the block displacements of the kinematism

NON LINEAR STATIC ANALYSISCCLM and SEM models

It is based on the fundamental modal shape

ay=Vy /m*G

m*

h*

d=u/G

*i i

2 2i i i i

m mΓ= =

m m

i

N


4. Seismic demand and hazard curve (Intensity Measure - IM)

Seismic demand is an Acceleration Displacement Response Spectra (ADRS).It may be defined (for a given soil condition):o by a set of parameters (PGA, TC, TB, F0, …..) and analytical functions;o by a set of values (T, Sa)

An Intensity Measure (IM) has to be defined as representative for the Probabilistic Seismic Hazard Assessment (PSHA)

In case of more IM Vector-valued PSHA In general, the Peak Ground Acceleration (PGA) is assumed as IM

The IM varies with the return period (TR) (that is with the annual probability of occurrence

By a set of valuesBy a set of parameters and analytical functions


5. Maximum IM value (IMPLi) compatible with the given perfomance level (PLi)

PERPETUATE procedure needs, for each PLi, the evaluation of IMPLi: to this end, it is sufficient to define the damping coefficient (xPLi) and period (TPLi)

Use of Capacity Spectrum Method (overdamped spectra)Through cyclic pushover Through analitycal laws

proposed in literature

equ el β

1ξ =ξ +α 1-

μ

Law calibrated on experimental campaigns on full scale masonry building (S2 Project)


5. Maximum IM value (IMPLi) compatible with the given perfomance level (PLi)

Sa

Sd

*0ddPLi

TPLi

Sd0 (T,x)

Sd (T, IM ,x)

1

IMPLi


6. Comparison of IMPLi with the corresponding target value IM*PLi

By using the hazard curve the return period TR,PLi corresponding to IMPLi may be evaluated

The assessment consists in the comparison of TR,Pli with T*R,Pli . It is positive if TR,Pli > T*R,Pli .

IMPLi

lRPLi T RPLi


7. Use of seismic assessment outcome for the rehabilitation decisions

Evaluation of the nominal life VN

Hazard levels are usually defined for probabilities of exceedance in 50 years

If VN > 50 years the seismic performance of the architectonic asset is adequate!

If VN < 50 years rehabilitation decisions have to be taken!

It is an useful parameter to define the priority list of interventions in case of assessment of a group of buildings.

This approach is correct from a conceptual point of view only if a time dependent hazard is available.


1. PUSHOVER ANALYSIS

CONTINUUM CONSTITUTIVE LAWS MODELS (CCLM)

B class

NON LINEAR STATIC ANALYSIS

STRUCTURAL ELEMENT MODELS (SEM)

A class

Complex assets described by a single capacity curve

Within the context of equivalent frame approach, multilinear constitutive laws for masonry panels on phenomenological base have been formulated and implemented in TREMURI Program (Lagomarsino et al. 2007, ask to: [email protected])

Seismic analysis of 3D complex models -

floor modelled as ortotropic membrane

Rigid nodesSpandrelsPiers

0

0,2

0,4

0,6

0,8

1

0 0,5 1 1,5 2 2,5 3

0

0,2

0,4

0,6

0,8

1

0 0,5 1

DL3

DL4

DL3

DL4

DL5

dE,5

dE [%]dE [%]

V/V

u

V/V

uDL5

dE,4 dE,5dE,4dE,3dE,3

E,3 Vu

E,4 Vu E,3 Vu

-80

-60

-40

-20

0

20

40

60

80

-20 -15 -10 -5 0 5 10 15 20

V [k

N]

U [mm]-100

-80

-60

-40

-20

0

20

40

60

80

100

-8 -6 -4 -2 0 2 4 6 8

V [k

N]

U [mm]

Multilinear laws for single masonry panels

Able to reproduce different hysteretic behaviours

Mechanical models for the assessment

Multicriteria definition of Performance Levels

Complex assets described by a many capacity curves

TERRITORIAL SCALE

• different scales (single asset or group of buildings in town) • conditions (seismic prevention or reconstruction after an earthquake)

Casbah of Algiers

Bovec Region & Ljubljana City Centre

Earthquake 1976, 1998, 2004

Earthquake 1895

Historical centre of Rhodes

Application of PBA to case studies

SINGLE ASSET SCALENeoclassical School Hassan Bey’s MansionArsenal de Milly

GR

EE

CE

AL

GIE

RS

Great Mosque


SINGLE ASSET SCALE

ITA

LY

Santa Maria Paganica Church St.Pardo CathedralArdinghelli Palace

SL

OV

EN

IA

Koljzei Palace


www.perpetuate.eu

IMPLEMENTATION OF THE EC 8.3: ASSESSMENT AND INTERVENTIONS IN EARTHQUAKE PRONE AREAS

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