tpanagiotakos-amsterdam 2008

8/8/2019 TPANAGIOTAKOS-Amsterdam 2008

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Seismic response assessment andSeismic response assessment and

upgrading of a complex of seven RCupgrading of a complex of seven RCbuildings using FRPsbuildings using FRPs

T.B. Panagiotakos, A.J. Kosmopoulos & B. KoliasCivil Engineer, PhD. Civil Engineer, PhD. Civil Engineer

International fib Symposium, May 2008, AmsterdamTailor Made Concrete Structures New Solutions for Our Society

Development & Engineering Consultants S.A.Development & Engineering Consultants S.A.16 Kifissias Ave. 15125 Maroussi

Tel. +30 210 6854801-6 ,fax +30 210 6854800


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Existing (older) buildings in seismic regions:

Typically inadequate (if any) engineered earthquake resistance.

Until recently:

Retrofitting of existing buildings was addressed in an empiric

manner by modern Codes

Part 3 Eurocode 8 (EN 1998-3:2005):

Is the 1stNorm to establish rules & expression for the assessment

of the seismic performance & retrofitting of existing buildings(including the use of FRPs)

Deformation-based approach (for ductile failure modes)

Tools for the engineers upgrade existing structures to meet (ifpossible) the requirements of modern codes for the design of

new buildings.

InternationalInternational fibfib Symposium Amsterdam 2008Symposium Amsterdam 2008 Tailor Made Concrete Structures /Tailor Made Concrete Structures / New Solutions for our SocietyNew Solutions for our Society


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Performance Levels & targets for the retrofitting

Knowledge Levels of available data & confidence factors

Primary & Secondary Elements (for lateral loads) Effect of infill walls

Linear analysis (under restrictions) w/ local ductility

Non-Linear analysis

Force and deformation-based performance checks

Computational tools expressions for the assessment of

structural capacity

EN 199EN 19988--33 Introduces:Introduces:



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EN 1998EN 1998--3 performance levels:3 performance levels:

DesiredDesired performanceperformance duringduring thethe respectiverespective earthquakeearthquake..

InIn termsterms ofof:: Structural damageStructural damage

Protection of the occupants lifeProtection of the occupants life Serviceability after the earthquakeServiceability after the earthquake

DifferentDifferent criteriacriteria forfor structuralstructural // nonnon--structuralstructural elementselements

ServesServes socialsocial && financialfinancial criteriacriteria

ThreeThree performanceperformance levelslevels // designdesign earthquakesearthquakes:: Damage LimitationDamage Limitation Significant DamageSignificant Damage

Near CollapseNear Collapse



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Key modeling aspects:Key modeling aspects:

PrismaticPrismatic 33DD beambeam elements,elements, w/w/ inelasticityinelasticity lumpedlumped atat thethe twotwo endsends..

ElasticElastic stiffnessstiffness takentaken equalequal secantsecant stiffnessstiffness atat yielding,yielding, ((EIEI))effeff,, basedbased onon thethevaluevalue ofof thethe shearshear spanspan atat thethe yieldingyielding end(s)end(s) ofof thethe membermember;; beamsbeams andandcolumnscolumns areare assumedassumed toto yieldyield atat bothboth endsends inin oppositeopposite symmetricsymmetric bendingbending(shear(shear spanspan equalsequals halfhalf thethe clearclear lengthlength ofof thethe elementelement;;

TheThe averageaverage valuevalue ofof ((EIEI))effeff atat thethe twotwo endend sectionssections inin positivepositive oror negativenegativebendingbending isis usedused;;

BeamsBeams supportedsupported onon anotheranother beambeam atat oneone endend yieldingyielding isis assumedassumed toto occuroccuronlyonly atat thethe otherother endend;; thethe shearshear spanspan isis takentaken equalequal toto thethe fullfull clearclear spanspan ofofthethe beambeam..

EffectiveEffective flangeflange widthwidth ofof TT-- oror LL--beamsbeams onon eithereither sideside ofof thethe beambeam webweb isistakentaken equalequal toto 5050%% ofof thethe minimumminimum ofof beambeam shearshear span,span, distancedistance toto thetheadjacentadjacent parallelparallel beambeam;;

slabslab barsbars parallelparallel toto thethe axisaxis of of aa beambeam areare consideredconsidered fullyfully effectiveeffectivelongitudinallongitudinal reinforcementreinforcement ofof thethe beambeam endend sectionsection;;

ForFor wallswalls onlyonly thethe secantsecant--toto--yieldingyielding stiffnessstiffness ofof thethe basebase sectionsection inin aa storystory isisusedused;; shearshear spanspan isis takentaken asas equalequal toto 5050%% ofof thethe heightheight fromfrom thatthat sectionsection totothethe toptop ofof thethe wallwall..

ModelingModeling assumptionsassumptions havehave beenbeen validatedvalidated byby fullfull--scalescale PsDPsD teststests..



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BasedBased onon ANSRANSR--I,I, developeddeveloped atat thethe UniversityUniversity ofof Patras,Patras, GreeceGreece andandDENCODENCO DevelopmentDevelopment && EngineeringEngineering ConsultantsConsultants inin Athens,Athens, GreeceGreece

LinearLinear elasticelastic analysisanalysis (static(static oror modal)modal) inin 33DD;;

NonlinearNonlinear staticstatic (pushover)(pushover) andand nonlinearnonlinear dynamicdynamic analysisanalysis inin 33DD;;

InIn--planeplane flexibilityflexibility ofof floorfloor diaphragmsdiaphragms;;

EstimationEstimation ofof thethe effectiveeffective (secant)(secant) stiffnessstiffness ofof membersmembers atat yieldingyieldingfromfrom reinforcementreinforcement andand materialmaterial propertiesproperties;;

VerificationVerification ofof ductileductile modesmodes of of membermember behaviourbehaviour inin termsterms of ofdeformationsdeformations (chord(chord--rotationsrotations atat membermember ends)ends) atat thethe threethree LimitLimit StatesStatesforeseenforeseen inin ENEN19981998--33;;

VerificationVerification ofof membersmembers inin shearshear;;

DesignDesign ofof thethe retrofittingretrofitting includingincluding estimationestimation ofof thethe effectiveeffective (secant)(secant);; stiffnessstiffness toto yielding,yielding, flexuralflexural andand shearshear resistanceresistance andand cycliccyclic deformationdeformation

capacitycapacity ofof membersmembers retrofittedretrofitted usingusing RCRC oror FRPFRP jacketsjackets..

Computational tool for the analysisComputational tool for the analysis ANSRuop softwareANSRuop software


DEVELOPMENT & ENGINEERINGCONSULTANTS S.A.


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Assessment of the seismic performance and retrofitting of a Complex of7 RC buildings built in the 1970s to house the Data Processing Centre ofthe Bank of Greece (Data: Knowledge Level 2 according to EN 1998-3)

Typical floor plan view

3D computer model for the analysis



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Non-linear time-history analyses (least conservative; most reliable) Semi-artificial ground motions compatible w/ the Codes elastic 5%-damped spectrum

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Comparison of the response spectra of the semi-artificial groundmotions to the elastic spectrum of the Greek Seismic Code


Non-linear time-history analyses (continued) Semi-artificial ground motions compatible w/ the Codes elastic 5%-damped spectrum


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DemandDemand--toto--CapacityCapacity ratio,ratio, :: comparisoncomparison ofof demand,demand, D,D, totocapacity,capacity, C,C, inin termsterms ofof deformationdeformation (ductile(ductile failurefailure modes)modes)oror forceforce (brittle(brittle failurefailure modes)modes) forfor eacheach structuralstructural elementelement::

Demand, D, from analysisDemand, D, from analysis

Capacity, C from EN 1998Capacity, C from EN 1998--3 expressions3 expressions

Safety factors forSafety factors for:: Material propertiesMaterial properties

Knowledge Level of available dataKnowledge Level of available data

Reliability of structural modelsReliability of structural models

Analysis using probable (mean) values of material propertiesAnalysis using probable (mean) values of material properties

C

D!P

Assessment of the seismic performanceAssessment of the seismic performance



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Significant Damage (SD) performance level

D/C ratios of beams end-chord rotations (flexure)

D/C ratios of columns end-chord rotations (flexure)

Near Collapse (NC) performance level

D/C ratios of beams end-chord rotations (flexure)

D/C ratios of columns end-chord rotations (flexure)

D/C ratios of beams in terms of shear force

D/C ratios of columns in terms of shear force

Results from nonResults from non--linear timelinear time--history analyseshistory analyses::



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Results of non-linear time-history analyses D/C ratios of beams end-chord rotations (Significant Damage Performance Level)


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Results of non-linear time-history analyses D/C ratios of beams end-chord rotations (Near Collapse Performance Level)


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Results of non-linear time-history analyses D/C ratios of columns end-chord rotations (Significant Damage Performance Level)



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Results of non-linear time-history analyses D/C ratios of columns end-chord rotations (Near Collapse Performance Level)



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Results of non-linear time-history analyses D/C ratios of beams in terms of shear force



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Results of non-linear time-history analyses D/C ratios of columns in terms of shear force



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Building top displacements and interstory drift values werewithin acceptable limits;

Numerous columns (mainly at the upper floors) and a significantnumber of beams exhibit shear deficiencies;

A few columns exhibit deficiencies in flexure and ductility.

Evaluation of the analyses resultsEvaluation of the analyses results


Retrofitting strategyRetrofitting strategy

Retrofitting w/ RC jackets or overlays presents several problems

and disadvantages (time, cost, aesthetic) The seismic upgrading was implemented by means of externally

bonded Fiber Reinforced Polymer (FRP) sheets.

Target of the retrofitting: Seismic performance that complieswith Near Collapse Performance Level according to EN 1998-3.


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Retrofitting with FRP sheetsRetrofitting with FRP sheets

Retrofitting for the increase of shear capacity:

For each element which is foreseen to be subjected to a shear force beyond its shear capacity,this excess shear is calculated (Vmax,anal VR)

Choice of retrofitting material : GFRP sheets

Direct dimensioning of the retrofitting (number of FRP layers) for the excess shear force

according to EN 1998-3 .4.4.2, taking into account the possibility of failure of the RC-FRPinterface before maximum strain of the FRP is reached (debonding)

Confinement and increase of deformation capacity

(retrofitting against ductile failure modes):

Choice of retrofitting material : GFRP sheets

Dimensioning: for each element that is foreseen to fail in flexure, a number of FRP layers isassumed for the increase (through confinement, A.4.4.3) of the ultimate end-chord rotation, u(A.3.2.2.) so as to prevent failure

Calculation of the new value ofu and check for the adequacy of the selected number of FRP

layers



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Retrofitting of columns for increase of flexural deformation capacity Layers of GFRP sheets



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Retrofitting of beams for increase of shear capacity Layers of GFRP sheets



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Retrofitting of columns for increase of shear capacity Layers of GFRP sheets



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Schematic view of the retrofitting (Office buildings)



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A complex of 7 RC buildings (built in the 1970s) was upgradedseismically to withstand the design earthquake (according to theGreek Seismic code)

Evaluation of the buildings and design of the retrofitting wereaccording to EN1998-3

Externally bonded Fiber Reinforced Polymers (FRPs) were used:cost-effective way of improving the seismic performance withoutmodifying dynamic response

ConclusionsConclusions



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Seismic response assessment and upgrading of a complex ofSeismic response assessment and upgrading of a complex ofseven RC buildings using FRPsseven RC buildings using FRPs

T.B. Panagiotakos, A.J. Kosmopoulos & B. Kolias

Civil Engineer, PhD. Civil Engineer, PhD. Civil Engineer

International fib Symposium, May 2008, AmsterdamTailor Made Concrete Structures New Solutions for Our Society

Development & Engineering Consultants S.A.Development & Engineering Consultants S.A.

16 Kifissias Ave. 15125 MaroussiTel. +30 210 6854801-6 ,fax +30 210 6854800

Thank you!Thank you!

tpanagiotakos-amsterdam 2008

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