b_belev_fds_eng

8/3/2019 B_BELEV_FDS_ENG

http://slidepdf.com/reader/full/bbelevfdseng 1/44

Dr.Dr. BorislavBorislav BelevBelev

Dept. of Steel and Timber StructuresDept. of Steel and Timber StructuresUACEG, Sofia, BulgariaUACEG, Sofia, Bulgaria

Balkan Seminar on Earthquake Engineering Balkan Seminar on Earthquake Engineering KIIP KIIP - - Sofia Sofia

Sofia, 6 Sofia, 6 - - 7 October 20117 October 2011

Seismic protection of buildingsSeismic protection of buildingswith friction damper systemswith friction damper systems



22Balkan seminar on seismic engineering,Balkan seminar on seismic engineering,

Sofia, 6Sofia, 6--7 October, 20117 October, 2011

Lecture overviewLecture overview

1.1. IntroductionIntroduction

2.2. Capacity design philosophy and its evolutionCapacity design philosophy and its evolution

3.3. Essential definitions and classificationEssential definitions and classification

4.4. Basic concept of passive energy dissipationBasic concept of passive energy dissipation

5.5. Advantages and drawbacks of FDSAdvantages and drawbacks of FDS

6.6. Seismic response of structures with FDSSeismic response of structures with FDS

7.7. Damper configurations and applicationsDamper configurations and applications8.8. Concluding remarksConcluding remarks





IntroductionIntroduction

Capacity Design Philosophy in SeismicCapacity Design Philosophy in Seismic EngineeringEngineering::

Originates from New Zealand (Originates from New Zealand (~ 1970)~ 1970);;

Is also termed “Failure mode control”Is also termed “Failure mode control”

Applicable to all major structural materials and systems;Applicable to all major structural materials and systems;

Is a design approach, not an analysis technique;Is a design approach, not an analysis technique;

Serves as a tool for providing more reliable andServes as a tool for providing more reliable andpredictable seismic response of the structures;predictable seismic response of the structures;

Already embedded in most modern design codes;Already embedded in most modern design codes;Assumes that adequate ductility can be achievedAssumes that adequate ductility can be achievedthrough proper detailing of the potential plastic zonesthrough proper detailing of the potential plastic zones





History of developmentHistory of development





Capacity design principlesCapacity design principles

The structures shall be madeThe structures shall be made insensitiveinsensitive to the uncertainto the uncertain

parameters of ground shakingparameters of ground shakingThe locations of dissipative zones that will experienceThe locations of dissipative zones that will experiencelarge plastic strains should belarge plastic strains should be prepre--selectedselected so that theyso that theydo not endanger the overall stabilitydo not endanger the overall stability

These plastic regions require special detailing in order toThese plastic regions require special detailing in order tomaintain the desired ductile failure mode during amaintain the desired ductile failure mode during aseismic eventseismic event

For maximizing the global ductility, the other (nonFor maximizing the global ductility, the other (non--

dissipative) parts of structuredissipative) parts of structure must be securedmust be secured againstagainstpremature (brittle) failure via adding extra strengthpremature (brittle) failure via adding extra strength





Capacity design principles (contCapacity design principles (cont’’d)d)

Explanation via Prof. Tom Paulay’s chain

Option 1: Brittlelinks weaker

Option 2: Brittlelinks stronger

(Capacity Design)

Brittle links Ductile link Brittle links





The overstrength issueActual resistances at the plastic regions Actual resistances at the plastic regions

well above their nominal/design values well above their nominal/design values

may endanger the global ductility and resistance may endanger the global ductility and resistance

Typical sources ofTypical sources of overstrengthoverstrength::

MaterialMaterial overstrengthoverstrengthStrain hardeningStrain hardening

Strain rate effectsStrain rate effects

Design of members governed by nonDesign of members governed by non--seismicseismiccombinations of loads or noncombinations of loads or non--ULSULS(serviceability) criteria(serviceability) criteria





Approach of the design codesApproach of the design codes

EurocodeEurocode 8, for steel structures:8, for steel structures:

materialmaterial overstrengthoverstrength factorfactor γγovov = [1.25]= [1.25]crosscross--sectionsection overstrengthoverstrength factorfactor ii

systemsystem overstrengthoverstrength factorfactor =min{=min{ii}}

system redundancy insystem redundancy in ee--pp stagestage ααuu / / αα11

typical combination for design actions on nontypical combination for design actions on non--dissipativedissipativemembers: Emembers: Edd == EEd,Gd,G ++ 1.11.1γγovov EEd,Ed,E

strength limit for the dissipative zones:strength limit for the dissipative zones: ffy,maxy,max ≤≤ 1.11.1γγovovffyy

Major drawback: the actual ultimate strength of the Major drawback: the actual ultimate strength of the structure is not known if only linear elastic analysis is structure is not known if only linear elastic analysis is performed performed





Evolution of capacity designEvolution of capacity design

philosophyphilosophy

Structural fuse conceptStructural fuse concept

DamageDamage--tolerant structures (Prof. A. Wada)tolerant structures (Prof. A. Wada)PerformancePerformance--based design with:based design with:

-- Explicit performance objectives for at least twoExplicit performance objectives for at least two

seismic intensity levelsseismic intensity levels-- Direct comparison of seismic demands vs.Direct comparison of seismic demands vs.

capacities via nonlinear analysescapacities via nonlinear analyses

-- Damage limitation not only to structure, butDamage limitation not only to structure, butalso to nonstructural components andalso to nonstructural components andequipmentequipment





Structural fuse concept (SFC)Structural fuse concept (SFC)SFC uses the idea of protecting the electric circuits bySFC uses the idea of protecting the electric circuits byinserting fusesinserting fuses -- sacrificeablesacrificeable and replaceable (relativeand replaceable (relative

cheap) components that limit the damage in extremecheap) components that limit the damage in extremesituations.Thesituations.The fuses are thefuses are the weakestweakest links of the system;links of the system;

Structural fuses have the following functions:Structural fuses have the following functions:

-- dissipate a major part of seismic input energydissipate a major part of seismic input energy

-- keep primary structure deformations in elastic rangekeep primary structure deformations in elastic range-- provide a predictable response of the systemprovide a predictable response of the system

First implementation: the EBFFirst implementation: the EBF--systemsystem

Further developments:Further developments:

BucklingBuckling--restrained braces (BRB)restrained braces (BRB)Rocking systemsRocking systems

Passive energy dissipation systemsPassive energy dissipation systems





EBF link elementsEBF link elements

Plastic link rotation angle (demand) : γp = (L/e) θp

The eccentric brace configuration “amplifies” theThe eccentric brace configuration “amplifies” the interstoreyinterstorey drift:drift:

e.g. for e = 0.2Le.g. for e = 0.2L

γp = 5 θp

“Short” links (e ≤1.6M pl / V pl ) preferred: θp,c = 0.08 Rad (capacity)

Closely spaced web stiffeners to suppress the web shear buckling





BucklingBuckling--restrained braces (BRB)restrained braces (BRB)Also known as “Also known as “UnbondedUnbonded brace”brace”

Symmetrical response in tension and compressionSymmetrical response in tension and compressiondue to avoided bucklingdue to avoided buckling

Enhanced energy dissipating capacityEnhanced energy dissipating capacity

Capacity design approach compulsory due to braceCapacity design approach compulsory due to brace

overstrengthoverstrength (strain hardening)(strain hardening)





Rocking systems (fuses at base)Rocking systems (fuses at base)

(Image from Matt Eatherton et. al paper)






Source:Source: Soong Soong , T.T. and G.F., T.T. and G.F. Dargush Dargush . Passive Energy Dissipation . Passive Energy Dissipation Systems in Structural Engineering. J. Wiley & Sons, 1997.Systems in Structural Engineering. J. Wiley & Sons, 1997.

STRUCTURAL

PROTECTIVE

SYSTEMS

PASSIVE ENERGY

DISSIPATION

SYSTEMS

SEMI-ACTIVE

AND ACTIVE

CONTROL

SEISMIC

(BASE)

ISOLATION





Energy balanceand seismic energy dissipation

Seismic input energy E i = E k + E s + E ξ + E h





Comparison in terms of energyComparison in terms of energy

dissipationdissipationThe structures differ in the way they “manage” andThe structures differ in the way they “manage” and”distribute” the total seismic input energy”distribute” the total seismic input energy E E

i i

Conventional structuresConventional structures::

energy dissipation through cyclic plastic deformationenergy dissipation through cyclic plastic deformation

ductile response means damage and lossesductile response means damage and lossescodecode--based design does not explicitly evaluatebased design does not explicitly evaluate E E h h / / E E

i i

the structure may remain vulnerable to aftershocksthe structure may remain vulnerable to aftershocks

Structures with damping systems:Structures with damping systems:energy dissipation performed byenergy dissipation performed by ““specialized partsspecialized parts””

primary structure/frame has mainly gravity loadprimary structure/frame has mainly gravity loadsupporting function and resupporting function and re--centering functioncentering function






Classification of FEMA 450(Chapter 15: Structures with damping systems)

The damping system (DS) may be external or internal to the structure and may have no shared elements, some shared elements, or all elements in common with the seismic-force-resisting system (SFRS).





Basic types of damper devicesBasic types of damper devices

1. Displacement-dependent

devices (metallic dampers,friction dampers)

2. Velocity-dependent devices(fluid viscous dampers, solid

visco-elastic dampers, etc.)

3. Other types (shape-memoryalloys, self-centering

devices, etc.)





Example: TADAS steel damperExample: TADAS steel damper





Arrangement of TADAS deviceArrangement of TADAS device

Arrangement is identical to that of a vertical link elementin the EBF-system





Expected benefitsExpected benefitsAdded damping (viscous dampers)Added damping (viscous dampers)

Added stiffness and damping (Added stiffness and damping (viscovisco--elastic, metallic, frictionelastic, metallic, frictiondampers)dampers)

As a result, enhanced control of theAs a result, enhanced control of the interstoreyinterstorey driftsdriftsThe capacity design is not abandoned, but the sources ofThe capacity design is not abandoned, but the sources ofoverstrengthoverstrength in the dissipative zones (dampers) are essentiallyin the dissipative zones (dampers) are essentiallyreducedreduced

Seismic response is much more predictable than in conventionalSeismic response is much more predictable than in conventional

structuresstructures------------------------------------------------------------------------------------

In new structures:In new structures:

Enhanced performance (reduced damage)Enhanced performance (reduced damage)

Less stringent detailing for ductilityLess stringent detailing for ductility

In existing structures:In existing structures:

Alternative solution to new shear walls (speedAlternative solution to new shear walls (speed--up retrofit works)up retrofit works)

Correction of irregularitiesCorrection of irregularities

SupressionSupression ofof torsionaltorsional responseresponse



2222Balkan seminar on seismic engineering,Balkan seminar on seismic engineering,Sofia, 6Sofia, 6--7 October, 20117 October, 2011

Friction dampersFriction dampers

Images provided by Damptech A/S., Denmark(www.damptech.com)




Advantages of metallic and frictionAdvantages of metallic and friction

damper devicesdamper devices

Relatively cheapRelatively cheap

Easy maintenanceEasy maintenance

DurabilityDurability

WellWell--defined and predictable response, sodefined and predictable response, so

that the supporting members can be safelythat the supporting members can be safely

designed according to the capacity designdesigned according to the capacity design

rulesrules




Drawbacks of metallic and frictionDrawbacks of metallic and friction

damper devicesdamper devices

Nonlinear response which complicates the analysis

Relatively stiff and thus not very efficient in weakquakes

Relatively small number of working cycles and potentiallow-cycle fatigue problems (metallic dampers)

Possible variation of the coefficient of friction with time

and degradation of contact surfaces (friction dampers)

Reaction to static displacements due to temperatureeffects and long-term deformations (shrinkage, creep)




Parameters governing the seismicParameters governing the seismic

responseresponse

U s U

F s

F

O

K t 1

1

K t

K p

1K f

1K bd

t ss K U F strengthYield =bd f t K K K += f p K K =

f bd K K SR =lock d M F F strengthdamper Normalized ==η




Basic performance indicators:Basic performance indicators:

(a) Response displacements(a) Response displacementsDisplacement reduction, Rd

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Normalized damper strength

R d

El Centro

Taft EW

Cekmece





(b) Response base shear(b) Response base shearBase shear reduction, Rf

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1


R

f El Centro

Taft EW

Cekmece





(c) Energy dissipation capacity(c) Energy dissipation capacityEnergy reduction index, Re

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1


R e

El Centro

Taft EW

Cekmece

Re = (Ei – Eh) / Ei = part of total input energy

not dissipated by the damper




Influence of brace stiffnessInfluence of brace stiffness

Rd for Cekmece NS, PGA=0.35g

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1


R d Kbd

2*Kbd

Rf for Cekmece NS, PGA=0.35g

0

0.5

1

1.5

2

2.5

3

3.5

0 0.2 0.4 0.6 0.8 1


R f Kbd

2*Kbd

As a general rule, the increase of brace stiffness

improves the performance of the damping system




Performance of singlePerformance of single--storey frictionstorey friction--

damped frame (PGA=0.35g)damped frame (PGA=0.35g)Seismic performance index, SPI = f(Rd, Rf, Re)

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1


S P I

El Centro

Taft EW

Cekmece





Shake table testing of frictionShake table testing of friction--dampeddamped

frame in NCREE, Taiwan (2001)frame in NCREE, Taiwan (2001)





Experimental resultsExperimental resultsInterstoreyInterstorey drift comparison for El Centro 0.30g testdrift comparison for El Centro 0.30g test

71.114.350.1Third

76.119.079.2Second

78.417.480.4First

With FDDsW/O FDDs

Reduction (%)Interstorey drifts (mm)

Storey

71.114.350.1Third

76.119.079.2Second

78.417.480.4First

With FDDsW/O FDDs

Reduction (%)Interstorey drifts (mm)

Storey

After all the 14 tests (After all the 14 tests (PGA=0.05g to 0.30g)PGA=0.05g to 0.30g) no damage occurredno damage occurred

to the dampers, bracing bars, frame members and connectionsto the dampers, bracing bars, frame members and connections

The fullThe full--scale testing at NCREE proved the excellent capacity ofscale testing at NCREE proved the excellent capacity of

the proposed damping system to significantly reduce earthquakethe proposed damping system to significantly reduce earthquake--

induced building vibrationsinduced building vibrations

The seismic performance can be predicted reasonably well byThe seismic performance can be predicted reasonably well by

nonnon--linear time history analysis with DRAINlinear time history analysis with DRAIN--2DX2DX and SAP2000and SAP2000





DamperDamper configrationsconfigrations with singlewith single

frictional hingefrictional hinge

Typical range of slip capacity from 10 to 200 kN





Large capacity dampersLarge capacity dampers

Range of slip capacity: from 200 to 5000 kN





Possible arrangements in buildingsPossible arrangements in buildings





Example of applicationExample of application

Seismic protection of industrial facilitySeismic protection of industrial facility

Design PGA=0.24g, I=1.0, Soil type=B (stiff soil)Design PGA=0.24g, I=1.0, Soil type=B (stiff soil)

Seismic weight W=7800Seismic weight W=7800 kNkN

Design objective: To reduce the base shear to levelsDesign objective: To reduce the base shear to levelsbelow 1100below 1100 kNkN, for which the existing supporting RC, for which the existing supporting RC--

structure was originally designedstructure was originally designedConventional design of the steel structure as CBFConventional design of the steel structure as CBFsystem with chevron braces was inappropriate due tosystem with chevron braces was inappropriate due tohigher base shear levelhigher base shear level

Design solution: use friction dampers with slip capacityDesign solution: use friction dampers with slip capacityof 50of 50--6060 kNkN per device (total slip capacity per directionper device (total slip capacity per direction ~~600600 kNkN) to protect the foundations) to protect the foundations





Typical FDD arrangement in XTypical FDD arrangement in X--directiondirection

31





Check of the energy dissipatingCheck of the energy dissipating

capacitycapacity





Under construction…Under construction…





Potential for seismic retrofitPotential for seismic retrofit

Friction dampers in two additional stories erected

over an existing residential building in Greece





The European standardThe European standardEN 15129:2009 AntiEN 15129:2009 Anti--seismic devicesseismic devices

Contents:Contents:

ForewordForeword11.. ScopeScope22.. Normative referencesNormative references33.. Terms, definitions, symbols and abbreviationsTerms, definitions, symbols and abbreviations44.. General design rulesGeneral design rules55.. Rigid connection devicesRigid connection devices66.. Displacement Dependent DevicesDisplacement Dependent Devices77.. Velocity Dependent DevicesVelocity Dependent Devices88.. IsolatorsIsolators99.. Combinations of DevicesCombinations of Devices1010.. Evaluation of conformityEvaluation of conformity

1111.. InstallationInstallation1212.. InIn--service inspectionservice inspection





Concluding remarksConcluding remarksThe passive energy dissipation systems are now aThe passive energy dissipation systems are now amature and reliable technology for seismic protectionmature and reliable technology for seismic protection

The metallic and friction dampers offer many advantagesThe metallic and friction dampers offer many advantagesover the conventional ductilityover the conventional ductility--based seismic designbased seismic design

The analysis and design of such displacementThe analysis and design of such displacement--

dependent damping systems require increased effortsdependent damping systems require increased effortsand time but could be really rewardingand time but could be really rewarding

Addition of new chapter toAddition of new chapter to EurocodeEurocode 8 similar to Chapter8 similar to Chapter1010 ““Base IsolationBase Isolation”” would facilitate the broaderwould facilitate the broader

application of damping systems in the earthquakeapplication of damping systems in the earthquake--proneproneEuropean countries.European countries.





Thank you for your attention !Thank you for your attention !

b_belev_fds_eng

Documents