fema454_chapter8

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Risk Management Series Designing for EarthquakesA Manual for ArchitectsFEMA 454 / December 200

E!"S#"$% &'"(D"$%S))E*A('A#"+$ A$D RE#R+F"# &, -"(("AM .+(MES1 "$#R+D'#"+$"t is 3iel recogni6e that the most significant seismic risk in this countrresies in our e7isting oler builing stock Much of the countr has enforce

seismic esign for ne3 builings onl recentl8 e9en on the -est oast: seismiccoes enforce in the 1;0s an e9en into the 1;orit of ollar loss frombuilings in earthquakes: although the qualit of structural =erformance affectsthe le9el of that amage Seismic =rotection of nonstructural sstems: both foresign of ne3 builings an for consieration in oler builings: is co9ere inha=ter ;

2 &A?%R+'$D"n e9er oler builing: a host of eficiencies is ientifie as the state of the art of builing esign an builing coes a9ances oe requirements changebecause the risk or the e7=ecte =erformance resulting from the e7isting=ro9isions is eeme unacce=table Deficiencies are commonl ientifie ue toincrease unerstaning of fire an life safet: isable access: ha6arousmaterials: an esign for natural ha6ars #hus: it is not sur=rising that manof the oler builings in this countr are seismicall eficient: an man=resent the risk of life)threatening amage "t is not economicall feasible toseismicall retrofit e9er builing built to coes 3ith no or inaequate seismic=ro9isions: nor is it culturall acce=table to re=lace them all #heserealities create a significant ilemma@ .o3 are the builings that =resent asignificant risk to life safet ientifie .o3 is the e7=ecte =erformance

=reicte for oler builings of high im=ortance to businesses or for thoseneee in emergenc res=onse .o3 can 3e efficientl retrofit those builingsientifie as high risk#he term seismic eficienc is use in this cha=ter as a builing characteristicthat 3ill lea to unacce=table seismic amage Almost all builings: e9en thoseesigne to the latest seismic coes: 3ill suffer earthquake amage gi9en strongenough shaking8 ho3e9er: amage normall consiere acce=table shoul not bee7=ecte in small e9ents 3ith frequent occurrence in a gi9en region: an shoulnot be life threatening Damage ma be >uge unacce=table ue to resulting higheconomic cost to the o3ner or ue to resulting casualties #herefore: conitionsthat create seismic eficiencies can 9ar from o3ner to o3ner: from builing to


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builing: an for ifferent 6ones of seismicit For e7am=le: unbrace:unreinforce brick masonr resiential chimnes are e7tremel 9ulnerable toearthquake shaking an shoul be consiere a eficienc an3here that shakingis =ostulate +n the other han: unreinforce brick masonr 3alls: infillebet3een steel frame structural members: are e7=ecte to be amage onl inmoerate to strong shaking an ma not be consiere a eficienc in lo3erseismic 6ones Seismic eficiencies ientifie in this cha=ter generall 3illcause =remature or une7=ecte amage: often leaing to threats to life safet:

in moerate to strong shaking &uilings in regions of lo3er seismicit thate7=ect Moifie Mercalli "ntensit BMM"C le9els of not more than *"": or =eakgroun accelerations B%AC of less than 010g Bg acceleration of gra9itC: manee s=ecial consieration+f course: e9er builing 3ith com=lete construction is e7isting .o3e9er: the term e7isting builing has been taken to mean those builings in thein9entor that are not of current seismic esign #hese grou=s of builings:some of 3hich ma not be 9er ol: inclue builings 3ith a range of =robable=erformance from colla=se to minimal amage "n this cha=ter: the term e7istingbuiling is use in this conte7t21 hanges in &uiling ractice an Seismic Design Requirements Resulting in&uilings that are urrentl onsiere Seismicall "naequateha=ter < ocuments in etail ho3 builing sstems ha9e e9ol9e in the SanFrancisco &a Area #his e9olution 3as =robabl ri9en more b fire: economic:an construction issues than b a concern for seismic =erformance: at least inthe first se9eral ecaes of the t3entieth centur: but man changes took =laceSimilarl: ha=ter gi9es a brief histor of the e9elo=ment of seismic coesin the 'nite States "t is clear that for man reasons: builing constructionan structural sstems change o9er time "n the time frame of the t3entiethcentur: ue to the ra=i increase in unerstaning of the seismic res=onse ofbuilings an =arallel changes in coe requirements: it shoul be e7=ecte thatman oler builings 3ill no3 be consiere seismicall eficientSeismic coes in this countr i not e9elo= at all until the 1;20s: an atthat time the 3ere use 9oluntaril A manator coe 3as not enforce inalifornia until 1; 'nreinforce masonr B'RMC builings: for e7am=le: a=o=ular builing t=e earl in the t3entieth centur an no3 recogni6e as=erha=s the 3orst seismic =erformer as a class: 3ere not outla3e in the 6ones

of high seismicit until the 1; coe: an continue to be built in much of thecountr 3ith no significant seismic esign =ro9isions until quite recentlFigure )1 sho3s an e7am=le of t=ical 'RM amage #he first moern seismiccoes 3ere not consistentl a==lie until the 1;50s an 1;0s: an then onl inthe kno3n regions of high seismicit +f course: not all builings built beforeseismic coes are ha6arous: but most are e7=ecte to suffer far more amagethan currentl built builingsE9en builings esigne to moern seismic coes ma be susce=tible to high amage le9els an e9en colla=se +ur unerstaning of seismic res=onse has gro3nimmensel since the earl coes: an man builing characteristics that lea to=oor =erformance 3ere allo3e o9er the ears For e7am=le: concrete builings ofall t=es 3ere economical an =o=ular on the -est oast in the 1;50s an 1;0s'nfortunatel: seismic =ro9isions for these builings 3ere inaequate at the

time: an man of these builings require retrofit .ighlights of inaequaciesin =ast builing coes that ha9e: in man cases: create =oor builings aregi9en belo3

hanges "n E7=ecte Shaking "ntensit an hanges in GoningSimilar to a9ancements in structural analsis an the unerstaning of

builing =erformance: enormous a9ancements ha9e been mae in the unerstaningof groun motion: =articularl since the 1;50s an 1;0s #he seismicit Bthatis: the =robabilit of the occurrence of 9arious)si6e earthquakes from eachsourceC of the countr: the likel shaking intensit from those e9ents e=eningon the istance from the source an the local soil conitions: an the e7actnamic nature of the shaking Bthe =attern of accelerations: 9elocities: or


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is=lacementsC are all far better unerstoo #hese a9ancements ha9e causeincreases in seismic esign forces from a factor of 15 in regions 9er nearacti9e faults Bon the -est oastC to a factor of 2 to in a fe3 other areas ofthe countr Beg 'tah8 Mem=his: #ennesseeC #he amage to the first +li9e *ie3.os=ital BFigure )2C: in aition to other issues: 3as a result of inaequate6oning

hanges in Require Strength or DuctilitAs iscusse in ha=ter 4: the require lateral strength of a seismic

sstem is generall trae off 3ith the uctilit Bthe abilit to eforminelasticall normall controlle b the t=e of etailing of the com=onents anconnectionsC of the sstem .igher strength requires lo3er uctilit an 9ice9ersa #he most significant changes in coes reflecting better unerstaning ofminimum requirements for life safet are general increases in both strength anuctilit Man builing t=es esigne uner =re9ious seismic =ro9isions:=articularl in the 1;50s: 1;0s: an 1;


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&uiling coes ha9e long containe =ro9isions to u=ate life)safet features ofbuilings if the occu=anc is significantl increase in number or le9el ofha6ar Btransformation of a 3arehouse to office s=ace: for e7am=leC As earl asthe mi)1;0s: this conce=t starte to be a==lie to seismic sstems Man olerbuilings containe entire structural sstems no longer =ermitte in the coeBeg: 'RM: =oorl reinforce concrete 3allsC: an it quickl became ob9iousthat 1C these com=onents coul not be remo9e: an 2C it 3as im=ractical anuneconomical to re=lace all oler builings #he ne3 coe coul therefore not

be a==lie irectl to oler builings: an s=ecial criteria 3ere neee toenable aa=ti9e reuse 3hile meeting the nee to =rotect life safet of theoccu=ants "n some cases: an entirel ne3 an coe)com=ling lateral sstem 3asinstalle: 3hile lea9ing e7isting: no3 =rohibite: construction in =lace B#his=roceure 3as use in man school builings in alifornia after the Fiel Act3as =asse in 1; u= until the school seismic safet =rogram 3as essentiallcom=lete in the 1;0sC #his =roceure =ro9e 9er costl an isru=ti9e to thebuiling an 3as thought to iscourage both im=ro9e seismic safet an generalree9elo=mentA =hiloso=h quickl e9elo=e suggesting that e7isting builings be treateifferentl from ne3 builings 3ith regar to seismic requirements First:archaic sstems an materials 3oul ha9e to be recogni6e an incor=orate intothe e7=ecte seismic res=onse: an seconl: ue to cost an isru=tion: seismicesign force le9els coul be smaller #he smaller force le9els 3ere rationali6eas =ro9iing minimum life safet: but not the amage control of ne3 builings: atechnicall contro9ersial an un=ro9en conce=t: but =o=ular ommonl e7istingbuilings 3ere then esigne to


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consistent 3ith coe =ractice: but the create t3o ifficult socioeconomic)technical issues that ha9e ne9er been uni9ersall resol9e #he first is theefinition of 3hat le9el of builing rene3al or increase in occu=anc)risktriggers seismic u=graing #he secon is to establish the acce=table le9el ofseismic u=graingMost t=icall: the triggering mechanisms for seismic u=grae are unefine inthe coe an left u= to the local builing official #he 'niform &uiling oe:the =reecessor to the "& in the 3estern states: 3affle on this issue for

ecaes: alternatel inserting 9arious har triggers Beg: 50H of builing9alue s=ent in remoelsC an ambiguous 3oring that ga9e the local builingofficial ultimate =o3er #he use of this mechanism: 3hether 3ell efine inlocal regulation or =lace in the hans of the builing official: ultimatelreflects the local attitue concerning seismic safet Aggressi9e communitiese9elo= easil an commonl triggere criteria: an =assi9e or una3arecommunities require seismic u=grae onl in cases of com=lete reconstruction orha9e =oorl efine: easil negotiate triggers For more s=ecific informationon seismic triggers in coes: see the accom=aning siebar

&o7 1 Seismic #riggers in oesE9ents or actions that require o3ners to seismicall retrofit their builingsare commonl calle triggers For e7am=le: in man communities: if an o3nerincreases the occu=anc risk Bas measure b number of occu=ants: or b use ofthe builingC: the must =erform man life)safet u=graes: incluing seismicones .o3e9er: for =ractical an economic reasons: selom oes this triggerrequire conformance 3ith seismic =ro9ision for ne3 builings: but rather 3ith as=ecial life)safet le9el of seismic =rotection: lo3er than that use for ne3builings#he coe 3ith the longest histor in high)seismic regions: the 'niform &uilingoe B'&C: has long 3affle on this issue &esies the traitional coe life)safet trigger base on clear)cut changes in occu=anc: this coe o9er the earshas inclue =ro9isions using har triggers base on the cost of construction:an soft language that almost com=letel left the ecision to the local builingofficial #he last eition of this coe: the 1;;< '&: basicall allo3e anBnon)occu=anc relateC alteration as long as the seismic ca=acit 3as not mae3orse

#he coes an stanars that 3ill re=lace the '& are base on a feerallfune effort an =ublishe b FEMA as the $E.R ro9isions #hese coesinclue the "nternational &uiling oe B"&C: the $ational Fire rotectionAgenc B$FAC an ASE


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ao=te efiniti9e triggers base on cost of construction: on the =articularbuiling t=e: an on 9arious efinitions of significant structural change%o9ernment: in some cases: has been much more aggressi9e in setting triggers toacti9ate seismic retrofit: =erha=s to create a la3ful nee for funs 3hichother3ise 3oul be ifficult to obtain #he state of alifornia has set aefiniti9e list of seismic triggers for state)o3ne builings@ aC alterationcost e7ceeing 25H of re=lacement cost8 bC change in occu=anc8 cC reuction oflateral loa ca=acit b more than 5H in an stor8 C earthquake amage

reucing lateral loa ca=acit b more than 10H at an stor#he feeral go9ernment like3ise: in R : J$"S#: 2002K: also has efiniti9etriggers@ aC change in occu=anc that increases the builing s im=ortance orle9el of use8 bC alteration cost e7ceeing 50H of re=lacement cost8 cC amage ofan kin that has significantl egrae the lateral sstem8 C eeme to be ahigh seismic risk8 an eC ae to feeral in9entor though =urchase oronation#he regulations an =olicies go9erning an builing: =ri9ate or =ublic: 3hich3ill be significantl altere: shoul be researche in the =lanning stage tounerstan the effecti9e seismic triggers: 3ritten or unerstoo

-hen seismic im=ro9ement is triggere: the most common minimum requirement islife safet consistent 3ith the o9erall coe intent .o3e9er: the use of=erformance)base esign conce=ts to establish equi9alent technical criteria isa recent e9elo=ment an is not et uni9ersall acce=te As inicate in thelast section: the initial res=onse to establishing minimum seismic criteria 3asto use the frame3ork of the coe =ro9isions for ne3 builings 3ith economic antechnical a>ustments as require #hese a>ustments inclue a lo3er lateralforce le9el Ba =ragmatic res=onse to the ifficulties of retrofitC: an s=ecialconsieration for materials an sstems not allo3e b the =ro9isions for ne3builings B'nreinforce masonr: for e7am=le: 3as not onl =rohibite as astructural sstem in 6ones of high seismicit: but also coul not be use in abuiling at allC 'se of a lateral force le9el of urisiction to >urisictionMan local retrofit =ro9isions are grauall being re=lace b nationalguielines an stanars for seismic e9aluation an retrofit Beg ASE 1:

2008 FEMA 5: 2000: etcC "n aition: =erformance base seismic esign isenabling a more irect a==roach to meeting a communit s minimum =erformancestanars although this requires the =olic)makers to ecie 3hat the minimum=erformance stanar shoul be: a ifficult task that crosses social: economic:an technical bounaries"n summar: both the =assi9e triggers for seismic retrofit an the esign or=erformance criteria are often ill)efine an: at best: highl 9ariable bet3een>urisictions Design =rofessionals shoul al3as etermine the go9erning local:state: or feeral regulations or =olicies 3hen esigning alterations or remoelson e7isting builings

Acti9e oe ro9isionsActi9e coe =ro9isions result from =olic ecisions of a >urisiction to reucethe communit seismic risk b requiring seismic u=graing of certain builings

kno3n to be =articularl 9ulnerable to unacce=table amage For the most =art:these =ro9isions are unfune manates: although lo3)interest loan =rograms ha9ebeen e9elo=e in some cases #hese risk reuction =rograms usuall allo3 o3nersa length =erio to =erform the retrofit or to emolish the builings ten earsor more #he stanar for retrofit is also normall inclue in the la3 orregulation an is t=icall =rescri=ti9e: although =erformance)base esigno=tions are becoming more acce=table#3o large)scale e7am=les of acti9e seismic coe =ro9isions 3ere starte b thestate of alifornia #he first 3as a =rogram to reuce the risk from 'RMbuilings #he state legislature: lacking the 9otes to sim=l require mitigationthroughout the state: instea =asse a la3 BS& 54


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>urisictions to e9elo= in9entories of these builings in their area: to notifthe o3ners that their builing 3as consiere ha6arous: an to e9elo= acommunit)3ie ha6ar reuction =lan Although not require to o so: most>urisictions chose as their ha6ar reuction =lan to =ass acti9e coeorinances gi9ing o3ners of the builings ten or so ears to retrofit them +9er10:000 'RM builings ha9e been brought into com=liance 3ith these localorinances: most b retrofit: but some b emolition BSS: 200C#he secon =rogram: create b S& 1;5 in 1;;4 follo3ing the $orthrige

earthquake: ga9e alifornia hos=ital o3ners until 200 to u=grae or re=lacetheir hos=itals to com=l 3ith state la3 go9erning ne3 hos=ital builings #he=rogram s intention is to enable builings to be functional follo3ing anearthquake #his la3 affecte o9er 500 hos=itals an o9er 2:000 builingsB.olmes: 2002C Although com=liance is ongoing: this la3 has been =roblematicue to the high cost an isru=tion associate 3ith retrofitting hos=italbuilings: an the highl 9ariable economic conition of the health sstem as3ell as ini9iual facilities+ther e7am=les inclue local orinances to retrofit tilt)u= builings: lesscontro9ersial because of the clear high 9ulnerabilit an lo3 retrofit cost ofthese builings Similar to in9estigating local regulations regaring triggers:it is also 3ise to etermine if an e7isting builing =lanne for alterations isco9ere b Bor 3ill be co9ere in the foreseeable futureC a requirement toretrofit "t is generall ackno3lege that seismic im=ro9ements are easier toim=lement 3hen one in association 3ith other 3ork on the builing ost)Earthquake oe ro9isionsFollo3ing a amaging earthquake: man builings ma be close =eningetermination of safet an necessar re=airs A lack of clear re=air stanarsan criteria for re)occu=anc has create contro9ers an enie o3ners use oftheir builings after most amaging earthquakes Assuming that the earthquakeitself is the ultimate >uge of seismic acce=tabilit: man communities ma takethe o==ortunit in the =ost)earthquake =erio to require strengthening ofbuilings that are a==arentl seismicall eficient ue to their amage le9el.o3e9er: im=lementation of this theor incor=orating conser9ati9e =olicies thatrequire man retrofits ma ela the economic reco9er of the communit +n theother han: stanars for re=air an/or strengthening 3hich are not conser9ati9ecoul lea to equal or 3orse amage in the ne7t earthquake "t has also been

obser9e that o3ners of historic: rent)controlle: or other3ise economicallcontrolle builings ma ha9e an incenti9e to emolish amage builings to theetriment of the communit at large#raitionall: communities Bbuiling e=artmentsC ha9e use color coes forse9eral or all of the follo3ing categories of builings follo3ing an earthquake@A 'namage8 no action require "f ins=ecte at all: these builings 3ill be%reen)tagge& Damage to a slight e7tent that 3ill onl require re=air of the amage tothe original conition #hese builings 3ill generall be %reen)tagge: but thecategor coul also inclue some ,ello3)tags Damage to a greater e7tent that suggests such seismic 3eaknesses in thebuiling that the o9erall builing shoul be checke for com=liance 3ith minimumseismic stanars #his 3ill often require o9erall retrofit of the builing

#hese builings 3ill generall be Re)tagge: but the categor coul alsoinclue some ,ello3 tags1 BA subcategor of C Damage to an e7tent that the builing creates a=ublic risk that requires immeiate mitigation: either tem=orar shoring oremolition #he ultimate is=osition of these builings ma not be eterminefor se9eral months #hese builings 3ill all be Re)tagge#he most significant categori6ation is the ifferentiation bet3een & an #heifference to an o3ner bet3een being =lace in one categor or the other coulbe an e7=ense on the orer of 0H)50H of the 9alue of the builing: reflectingthe ae cost of retrofit to that of re=air Earthquakes being rare: fe3communities ha9e been force to create these =olicies: but a fe3 ha9e +aklan:


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alifornia: =rior to the (oma rieta earthquake: set a trigger base on the lossof ca=acit cause b the amage "f the amage 3as etermine to ha9e cause aloss of o9er 10H of lateral force ca=acit: then retrofit 3as triggere (osAngeles an other southern alifornia communities affecte b the $orthrigeearthquake use a similar stanar: but the 10H loss 3as a==lie to lines ofseismic resistance rather than the builing as a 3hole #hese coe regulations:although efiniti9e: are =roblematic because of the technical ifficult ofetermining loss of ca=acit: =articularl to the accurac of 1H Ba 1H change

can trigger a retrofitC#he im=ortance of this issue has been magnifie b inter=retation of feeralla3s that creates a tie bet3een reimbursement of the cost of re=air of certainlocal amage to the =re)e7istence an nature of these local amage triggers+3ners an esigners of oler e7isting builings shoul be a3are of suchtriggers that coul affect them shoul the suffer amage from an earthquake "nsome cases: it ma be =ruent for an o3ner to 9oluntaril retrofit a 9ulnerablebuiling to a9oi the =ossibilit of being force to o it in a =ost)earthquakeen9ironment as 3ell as to =ossibl a9oiing a long closure of the builing #.E FEMA R+%RAM #+ RED'E #.E SE"SM" R"S? FR+M E!"S#"$% &'"(D"$%S"n 1;5: the Feeral Emergenc Management Agenc BFEMAC recogni6e that the=rinci=al seismic risk in this countr came from the e7isting builing stock:the ma>orit of 3hich 3as esigne 3ithout aequate seismic =ro9isionsFollo3ing a national 3orksho= that ientifie significant issues an =otentialeucational an guieline =ro>ects that FEMA coul lea: a =rogram 3as launchethat is still ongoing "n aition to =ro9iing eucation an technicalguielines in the area of high)risk e7isting builings: other FEMA =rograms 3erealso significant in enabling communities to unerstan an mitigate theirseismic risk: most notabl the e9elo=ment of the regional loss)estimatingcom=uter =rogram: .AG'S Most of these acti9ities are ocumente as =art of theFEMA ello3 book series Bso kno3n because of its istincti9e ello3 co9ersC: 3ell kno3n to engineers in this countr an: in fact: aroun the 3orl'nfortunatel: these ocuments are less kno3n to architects: although man ofthem contain useful insights into not onl the issues surrouning seismice9aluation an retrofit of e7isting builings: but also into all as=ects ofseismic esign1 FEMA)S=onsore Acti9it for E7isting &uilings

Follo3ing is a summar of selecte FEMA)s=onsore =ro>ects beginning in the late1;0s A full listing is gi9en in FEMA 15: Seismic Rehabilitation of&uilings: Strategic lan 2005

Ra=i *isual ScreeningFEMA 154@ Ra=i *isual Screening of &uilings for otential Seismic

.a6ars: 1;: u=ate 2001A metho to enable an efficient first sorting of selecte builings into

an aequatel life)safe grou= an a secon grou= that 3ill require furthere9aluation #he e9aluation 3as intene to be =erforme on the street in an houror less =er builing #he first task is to assign the builing to a =reefinemoel builing t=e an then ientif aitional characteristics that coulrefine the seismic 9ulnerabilit #he metho has =ro9en useful to efficientlgenerate an a==ro7imate mi7 of builings that 3ill =ro=erl characteri6e a

communit s 9ulnerabilit: but not to efinitel rate ini9iual builings: ue

to the ifficult of ientifing significant features from the street %enerallit is necessar to obtain access to the interior of a builing: or: morecommonl: it is e9en necessar to re9ie3 ra3ings to confientl eliminate olerbuilings as =otentiall ha6arous

E9aluation of E7isting &uilingsFEMA 1


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rehabilitation costs an associate costs such as life)safet u=graes: theAmerican Disabilities Act BADAC: an e9en remoels Although a large amount ofata 3as collecte: there 3as not nearl enough to =o=ulate all combinations ofthe factors $e9ertheless: a metho 3as e9elo=e to use the ata to makeestimates of costs for gi9en situations #he ma>or =roblem 3as that thecoefficient of 9ariation of rehabilitation costs: for an gi9en situation: is9er high ue to high 9ariabilit in the e7tent of seismic eficiencies #heinformation collecte is =robabl most useful to estimate costs for large

numbers of similar builings 3here 9ariations 3ill a9erage out 'se of themetho to accuratel estimate the cost of a single builing is not recommene:although e9en the ranges gi9en coul be useful for architects an engineers notfamiliar 3ith retrofit issues

#echnical %uielines for Seismic RehabilitationFEMA 2


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Subsequent to the original e9elo=ment acti9it: .AG'S 3as e7=ane tocreate loss estimates for 3in an floo

"ncremental RehabilitationFEMA ;5: "ncremental Seismic Rehabilitation of School &uilings B?)12C:

200#his is the first in a series of manuals that FEMA B'S De=artment of

.omelan SecuritC intens to e9elo= for 9arious occu=anc t=es incluing: fore7am=le: schools: hos=itals: an office builings #he conce=t is base on the

fact that seismic strengthening acti9ities are more efficientl accom=lishe incon>unction 3ith other 3ork on the builing: an such o==ortunities shoul beientifie an e7=loite e9en if onl =art of a com=lete rehabilitation isaccom=lishe #his is =erha=s most a==licable to ?)12 school builings becauseof their relati9el small si6e an ongoing maintenance =rograms FEMA moelbuiling t=es are again use to categori6e =otential o==ortunities in ifferentconitions As is =ointe out in the manual: this technique has to be a==lie3ith care to a9oi an intermeiate structural conition that is 3orse than theoriginal

2 #he FEMA Moel &uiling #=esMost of these e9elo=ments 3ere =art of the integrate =lan e9elo=e in 1;5As such: FEMA coorinate the =ro>ects an require common terminolog ancross)references#he most successful an 9irtuall stanar)setting effort 3as the creation of aset of moel builing t=es to be use for the characteri6ation of e7istingbuilings #he moel builing t=es are base =rimaril on structural sstemsrather than occu=anc: but ha9e =ro9en e7tremel useful in the o9erall =rogramMoel builing t=es are efine b a combination of the gra9it)loa carringsstem an the lateral)loa carring sstem of the builing $ot e9er builingt=e e9er built in the countr an certainl not the 3orl is re=resente: butthe significant ones are: an the relati9e risks of a communit can 3ell bere=resente b se=arating the local in9entor into these t=es +f course: there3as no attem=t to re=resent e9er moern builing t=e because the are not consiere ha6arous builings .o3e9er: 3ith minor sub)categori6ation that hasoccurre 3ith successi9e ocuments: the ma>orit of builings: ne3 or ol: no3can be assigne a moel builing t=e #he test of the usefulness came 3ith the

successful e9elo=ment of .AG'S using the moel builing t=e because this=rogram neee a reasonabl sim=le metho to characteri6e the seismic9ulnerabilit of in9entories of builings across the countrurrentl: no single FEMA ocument contains a gra=hic an clear escri=tion ofthe moel builing t=es: although engineers can generall etermine the correctcategor &ecause of the ubiquitous FEMA)e9elo=e ocuments: guielines: anstanars regaring e7isting builings: an their common use b engineers: suchescri=tions are inclue here to facilitate communication 3ith architects #het=es are illustrate on =ages )2 through )1 #able ): at the en of thecha=ter: =resents a summar of the =erformance charactoristics an commomrehabilitation techniques4 SE"SM" E*A('A#"+$ +F E!"S#"$% &'"(D"$%S$ot all oler builings are seismicall at risk "f the 3ere: the amage from

se9eral earthquakes in this countr: incluing the 1;


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=arameters are central to =rocesses e9elo=e to ientif builings es=eciall9ulnerable to amage before the earthquake "n fact: the categori6ation ofamage b builing t=e is =rimaril 3hat le to the e9elo=ment of the FEMAMoel &uiling #=es iscusse in Section 2.o3e9er: onl in the most 9ulnerable builing t=es oes amage occur relati9elconsistentl For e7am=le: at higher le9els of shaking: the e7terior 3alls ofunreinforce masonr bearing)3all builings ha9e relati9el consistentl fallena3a from their builings in man earthquakes: e9er since this builing t=e 3as

built in large numbers in the late 1;th centur More recentl: a high=ercentage of =re)$orthrige steel moment)frame builings ha9e recei9e amage to their beam)column connections 3hen sub>ecte to strong shaking E9en inthese cases: the amage is not 100H consistent an certainl not 100H=reictable "n builing t=es 3ith less 9ulnerabilit: the amage has an e9enhigher coefficient of 9ariation Engineers an =olicmakers: therefore: ha9estruggle 3ith methos to reliabl e9aluate e7isting builings for their seismic9ulnerabilitAs iscusse in Section 2: the initial engineering res=onse 3as to >uge olerbuilings b their ca=acit to meet the coe for ne3 builings: but it becamequickl a==arent that this metho 3as o9erl conser9ati9e: because almost e9erbuiling oler than one or t3o coe)change ccles 3oul not com=l an thus beconsiere eficient E9en 3hen lo3er lateral force le9els 3ere use: an the=resence of archaic material 3as not: in itself: consiere a eficienc: manmore builings 3ere foun eficient than 3as e9ience in serious earthquakeamage #hus: =olicmakers ha9e generall been successful in =assing acti9eretrofit =ro9isions Bsee Section 2C onl in the most 9ulnerable builings:such as 'RM an tilt)u=s: 3here amage has been significant an consistent: anini9iual builing e9aluation is not =articularl significant#he e9aluation of e7isting builings t=icall starts 3ith ientification of thebuiling t=e an amaging characteristics of configuration Beg: soft storC#his can be one ra=il an ine7=ensi9el but: e7ce=t for a fe3 9ulnerablebuiling t=es: is unreliable 3hen taken to the ini9iual builing le9elEngineers an coe 3riters ha9e also e9elo=e intermeiate le9els of e9aluationin 3hich more characteristics are ientifie an e9aluate: man b calculation"n the last ecae: more so=histicate methos of analsis an e9aluation ha9ebeen e9elo=e that consier the nonlinear res=onse of most structures to

earthquakes an 9er etaile material an configuration =ro=erties that 3ill9ar from builing to builing41 E7=ecte erformance b &uiling #=eAs =re9iousl mentione: amage le9els after earthquakes are collecte angenerall assigne to bins of common characteristics: most commonl the le9el ofshaking: builing material an t=e: an configuration ombine 3ith numericallateral)force analsis of =rotot=e builings: this information can be anal6estatisticall #he three =rimar =arameters ) builing t=e: shaking le9el:an amage le9el ) are often is=lae together in a amage =robabilit matri7similar to #able )1 #he 9ariabilit of amage is such that for an shakingle9el: as sho3n in the columns: there is normall a =robabilit that somebuilings 3ill be in each amage state #he =robabilities in these tables canbe inter=rete as the =ercentage of a large number of builings e7=ecte to be

in each amage state: or the chances: gi9en the shaking le9el: that anini9iual builing of this t=e 3ith be amage to each le9elStatistical information such as this is use in se9eral 3as@

"entification of clearl 9ulnerable or angerous builings to hel=establish =olicies of mitigationMan e7tremel 9ulnerable builing t=es or com=onents can be ientifie bobser9ation 3ithout statistical analsis: incluing 'RM: soft)stor tuck)uner a=artment builings: the roof)to)3all connection in tilt)u= builings:resiences 3ith cri==le 3all first)floor construction: an connections of =re)$orthrige steel moment)frames #he clearl an more consistentl angerousbuiling t=es ha9e often generate enough communit concern to cause the


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creation of =olicies to mitigate the risks 3ith retrofit For a combination ofreasons: 'RMs an tilt)u=s currentl are the targets of the most acti9emitigation =olicies

Earthquake (oss EstimationRegional earthquake loss estimates ha9e been =erforme for fort or more earsto raise a3areness in the communit about the risks from earthquakes an tofacilitate emergenc =lanning %i9en an a==ro7imate istribution of thebuiling in9entor an a ma= of estimate groun motion from a gi9en earthquake:

amage)=robabilit matrices Bor similar ataC can be use to estimate amagele9els to the builing stock From the amage le9els: economic loss: =otentialcasualties: an business interru=tion in a communit can be estimateStarting in 1;;1: FEMA began a ma>or =rogram to e9elo= a stanar 3a of=erforming such loss estimations to facilitate com=arati9e loss estimates in9arious =arts of the countr #his =rogram resulte in a com=uter =rogram:.AG'S: escribe briefl in Section 1

Formal Economic (oss E9aluations Beg robable Ma7imum (oss or M(CSince consensus loss relationshi=s became a9ailable BA#: 1;5C: a eman hasgro3n to inclue an estimate of seismic loss in ue)iligence stuies one for =urchase of builings: for obtaining loans for =urchase or refinance: or forinsurance =ur=oses An economic loss =arameter: calle robable Ma7imum (oss:has become the stanar measuring stick for these =ur=oses #he M( for abuiling is the =essimistic loss Bthe loss suffere b the 3orst 10H of similarbuilingsC for the 3orst shaking e7=ecte at the site B3hich grauall becameefine as the shaking 3ith a 500)ear return =erio: similar to the coe esigne9entC Although a etaile analsis can be =erforme to obtain a M(: most areestablishe b builing t=e an a fe3 obser9able builing characteristics&ecause of the high 9ariabilit in amage an the relati9el incom=letestatistics a9ailable: M(s are not 9er reliable: =articularl for an ini9iualbuiling

Ra=i E9aluationAs foreseen b FEMA s original =lan for the mitigation of risks from e7istingbuilings: a ra=i e9aluation technique shoul be a9ailable to quickl sort thebuilings into three categories@ ob9iousl ha6arous: ob9iousl acce=table: anuncertain #he intent 3as to s=en less than t3o hours =er builing for thisra=i e9aluation 'ner the =lan: the uncertain grou= 3oul then be e9aluate

b more etaile methos #he results of FEMA s e9elo=ment efforts: FEMA 154BSection 1C is fairl so=histicate but: because of the large amount ofunkno3n builing ata that is inherent in the sstem: for an ini9iualbuiling: is unreliable #he sorting metho is =robabl quite goo forestimating the o9erall 9ulnerabilit of a communit because of the a9eragingeffect 3hen estimating the risk of man builings42 E9aluation of "ni9iual &uilingsEngineers ha9e been seismicall e9aluating e7isting builings for man ears:3hether b com=aring the conitions 3ith those require b the coe for ne3builings: b using some local or builing)s=ecific stanar Beg 'RMsC: or busing their o3n >ugment #hese methos are still use: as 3ell as 9erso=histicate =ro=rietar methos e9elo=e 3ithin =ri9ate offices: but thema>orit of e9aluations are no3 tie in some 3a to the general =roceures of

ASE 1)0: Seismic E9aluation of E7isting &uilings BASE: 200C: that in 200became a national stanar #here are three le9els of e9aluation in thestanar calle tiers: 3hich: not accientall: are similar to the stanar of=ractice =rior to the stanari6ation =rocess #hese le9els of e9aluation arebriefl escribe belo3: as 3ell as similar methos that fall in the samecategories.o3e9er: before beginning a seismic e9aluation: =articularl of a grou= ofbuilings: it is logical to assume that builings built to moern coes mustmeet some acce=table stanar of life safet Due to the large number of olerbuilings: the effort to eliminate some from consieration resulte in se9eral3ell)kno3n milestone ears First it 3as com=liance 3ith the 1;


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&uiling oe B'&C or equi9alent After stu an reconsieration ofrelati9el ma>or changes mae in the 1;


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not e7=ecte to be an e9era tool in the near future: is to simulate themo9ements of the full builings uring an entire earthquake: incluing theconstantl changing =ro=erties of the structural com=onents ue to ieling anamage #he o9erall amage to 9arious com=onents is then accumulate an theglobal amage state thereb surmise4 +ther E9aluation "ssues#here are se9eral other issues associate 3ith seismic e9aluation that shoul berecogni6e +nl three 3ill be iscusse here First is the ata require to

=erform com=etent e9aluations at the 9arious le9els: as iscusse abo9eSecon: it is im=ortant to unerstan the =erformance e7=ectation of the =ass)fail line for 9arious e9aluation methoologies (ast: the reliabilit Bor lackthereofC of the methos an of e9aluation an/or =erformance =reiction ingeneral:shoul be recogni6e Data Require for Seismic E9aluation+b9iousl: for methos e=ening on the FEMA builing t=e: the builing t=emust be kno3n "n fact: there are other similar classifications of builingt=es also use to efine builing =erformance at the broaest le9el 'singata as iscusse in =aragra=h 41: crue e7=ectations of =erformance antherefore com=arati9e e9aluation can be com=lete Most such sstems: ho3e9er:are refine b age: =hsical conition of the builing: configuration: an othermore etaile ata: 3hen a9ailable Most ra=i e9aluation methos: base on builing t=e an 9er basic builing characteristics: o not require structuralra3ings Res=onsible e9aluators 3ill insist on a site 9isit Bin man cases tomake sure the builing is still there: if nothing elseC#he more stanari6e e9aluation methos iscusse in =aragra=h 42essentiall require ra3ings "f etaile structural ra3ings are nota9ailable: sim=le e9aluations of some moel builing t=es B3oo builings:tilt)u=s: an sometimes 'RMC can be =erforme base on laout ra3ings or fromata =re=are from fiel 9isits .o3e9er: 3hen reinforce concrete: reinforcemasonr: or structural steel is a significant =art of the structure: it is mostoften economicall infeasible to re=rouce as)built ra3ings racticall in those cases: 3ith rare e7ce=tions: the builing is euce to be innonconformance an: as a retrofit: a ne3 seismic sstem is introuce to renerthe unkno3ns of the e7isting structure insignificant E9en in those cases:ho3e9er: e7tensi9e fiel 3ork is necessar to =rouce enough structural ata to

create a reasonable set of construction ocuments"f original structural ra3ings are a9ailable that are confirme to bereasonabl accurate from s=ot checks in the fiel: most e9aluation techniquescan be em=loe .o3e9er: material =ro=erties are often not inclue on thera3ings an must be euce from the era of construction Deterioration canalso affect the material =ro=erties of se9eral builing t=es +ften the=otential 9ariabilit in the analsis ue to ifferent =ossible combinations ofmaterial =ro=erties requires in)situ testing of material =ro=erties #hetechniques for this testing are 3ell establishe: but cost an isru=tion totenants are often an issueAs e7=laine in ha=ter : Site E9aluation an Selection : man areas of the countr are ma==e in etail for seismic =arameters relate to esign: althoughsuch =arameters continue to be in9estigate an u=ate -hen 3arrante: site)

s=ecific stuies can be =erforme to obtain timel an locall eri9e ata.o3e9er: other seismic site ha6ars: such as liquefaction: lanslie: an=otential surface fault ru=ture: are less 3ell ma==e an ma require a site)s=ecific stu: if there is reason to sus=ect their =otential at a siteerha=s a less ob9ious im=ortant characteristic of a site is the etail ofa>acent structures articularl in urban settings: a>acent builings oftenha9e inaequate se=aration or are e9en connecte to the builing to bee9aluate Although legal issues aboun 3hen tring to eal 3ith this issue: itis unrealistic to anal6e an e9aluate such a builing as if it 3erefreestaning Formal e9aluation techniques: such as ASE 1: ha9e aressethis issue: at least for builings that are not connecte: b highlighting the


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conitions kno3n to =otentiall =rouce significant amage First: if floors onot align bet3een a>acent builings an =ouning is e7=ecte: the stiff floorfrom one builing coul cause a bearing 3all or column in the a>acent builingto colla=se Seconl: if builings are of significantl ifferent height: theinteraction from =ouning has been obser9e to cause amage See Figure ) erformance +b>ecti9es an Acce=tabilit#raitionall: e9aluation techniques ha9e been targete at etermining if abuiling is aequatel life safe in an earthquake: similar to coe goals for ne3

builings .o3e9er: as iscusse in section 22: a stanar ifferent anless than that use for ne3 builings e9ol9e: but 3as still terme life safet+nl 3ith the e9elo=ment of =erformance)base engineering i e9aluationmethos aime at other =erformance stanars emerge E9en life safet has=ro9en to be amor=hous o9er the ears an often has been efine b thee9aluation technique u >our Seismicall: life safet is a ifficult conce=t:ue to the huge =otential 9ariation in groun motion an the man sources ofamage that coul cause in>ur or eath .o3e9er: the term is 3ell embee in=ublic =olic an continues to =ersist in seismic coes an stanarsFEMA: in s=onsoring the e9elo=ment of FEMA 2ecti9e B&S+C 3as efine #his =erformance ob>ecti9e consistsof t3o requirements@ the builing 3oul =ro9ie life safet for the stanari6ecoe e9ent an: in aition: the builing 3oul not colla=se in the Ma7imumonsiere E9ent BMEC: a 9er rare e9ent no3 efine b coe Since these FEMAocuments are non)manator Bunless locall ao=teC: the &S+ has not become a3iel acce=te stanar Bthe &S+ also inclues manator nonstructural minimumrequirements: 3hich also ma ela its 3ie acce=tanceCha=ter contains a etaile iscussion of =erformance)base engineering: 3hichis gaining acce=tance for e9aluations at an le9el &ut =erformancecharacteri6ation in 9arious forms has been use for some time: =rimaril to set=olic Such =olicies require escri=tions of 9arious =erformance le9els: e9enif the technical abilit to efine or =reict the 9arious le9els often laggebehin #able )2 sho3s se9eral such =erformance escri=tions: man e9elo=eecaes ago: 3hich ha9e been use to set =olic most concentrating on lifesafet #he table is set u= to a==ro7imatel equilibrate le9els of =erformanceacross hori6ontal lines

#he first columns in #able )2 escribe a sstem use b the 'ni9ersit ofalifornia %++D: the best =erformance: is efine as the equi9alent lifesafet as that =ro9ie b the coe for ne3 builings but 3ithout consierationof monetar amage #he ne7t le9el belo3 3as set at the acce=table le9el fore9aluation: 3hile retrofits are require to meet the %++D le9el#he ne7t column: labele DSA : is a Roman numeral sstem e9elo=e b the alifornia Di9ision of the State Architect for use 3ith state)o3ne builingsEach le9el has a escri=tion of amage an =otential results of amageB builing not reocccu=ie for months C but no reference to engineering =arameters #he state use an acce=tance le9el of "*: but set the goal forretrofits to """#he le9els escribe in the ne7t columns come from one of the earl e9elo=mentsof =erformance base earthquake engineering: *ision 2000: e9elo=e b the

Structural Engineers Association of alifornia "t is a relati9elcom=rehensi9e scale using fi9e =rimar escri=tions of amage: each 3ith a=lus an minus : resulting in ten le9els Finall: to inicate a =erha=s more commonl recogni6e stanar of =erformance:are the three occu=anc tagging le9els of Re: ,ello3: an %reen use foremergenc e9aluation immeiatel after amaging earthquakes Reliabilit of Seismic E9aluations#he most significant characteristic in the esign of builings for earthquakesis the 9ariabilit of groun motions $ot onl o magnitues an locations9ar: but also the effects of fault ru=ture: 3a9e =ath: an local site soilscreate a literall infinite set of =ossible time histories of motion Stuies


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ha9e sho3n that time histories 3ithin a common famil of =arameters use foresign Bres=onse s=ectrumC can =rouce significantl ifferent res=onses #his9ariation normall ominates o9er the scatter of results from analsis ore9aluation techniques.o3e9er: coes for ne3 builings can require man limitations of material:lateral sstem: configuration: an height that 3ill reasonabl assure acce=table=erformance: =articularl the =re9ention of colla=se #hese same limitationscan selom be a==lie to e7isting builings: so the 9ariation of actual

=erformance is e7=ecte to be much larger "n aition: the cost of retrofit isoften high: an attem=ts ha9e been mae to a9oi unnecessar conser9atism ine9aluation methoologies "t is =robable: therefore: that a significant numberof builings ma fail to =erform as e9aluate: =erha=s in the range of 10H ormore $o com=rehensi9e stu has been mae to etermine this reliabilit: butongoing =rograms to further e9elo= =erformance)base seismic engineering aree7=ecte to estimate the 9ariabilit of e9aluation results an refine themethos accoringl5 SE"SM" RE.A&"("#A#"+$ +F E!"S#"$% &'"(D"$%S#here are man reasons 3h builings might be seismicall retrofitte: incluingreno9ations that trigger a manator u=grae: a builing sub>ecte to aretroacti9e orinance: or the o3ner sim=l 3anting Bor neeingC im=ro9e=erformance #he reason for the u=grae ma influence the technique anthoroughness of the 3ork: because o3ners face 3ith manator u=grae ma seekout the least e7=ensi9e: but a==ro9able: solution: 3hereas an o3ner neeingbetter =erformance 3ill more likel be 3illing to in9est more for a solutionthat aresses their =articular concerns #here are man other factors thatsha=e a retrofit solution: such as the t=e of eficienc =resent: if thebuiling is occu=ie: an the future use an aesthetic character of thebuiling#he continuing im=ro9ement of analsis techniques an the emergence of=erformance)base esign are also ha9ing a large effect on retrofit schemes: benabling engineers to refine their esigns to aress the s=ecific eficienciesat the esire =erformance le9el "n man cases: ho3e9er: the retrofits arebecoming controlle b the brittleness of e7isting com=onents that must be=rotecte from e7cess eformation 3ith sstems that ma be stronger an/orstiffer than those use for ne3 builings Some oler retrofits: one to

=rescri=ti9e stanars or using no3)outate strengthening elements borro3efrom ne3 builing esigns: ma themsel9es be eficient: e=ening on the esire=erformance Seismic retrofit analsis: techniques: an com=onents: similar tone3 builing technolog: are not static: an a==lications shoul be regularlre9ie3e for continue effecti9eness51 ategories of Rehabilitation Acti9it"n most cases: the =rimar focus for etermining a 9iable retrofit scheme is on9erticall oriente com=onents Beg column: 3alls: braces: etcC because oftheir significance in =ro9iing either lateral stabilit or gra9it)loaresistance Deficiencies in 9ertical elements are cause b e7cessi9e inter)stor eformations that either create unacce=table force or eformation emans.o3e9er: e=ening on the builing t=e: the 3alls an columns ma be aequatefor seismic an gra9it loas: but the builing is inaequatel tie together:

still forming a threat for =artial or com=lete colla=se in an earthquake "t isim=erati9e to ha9e a thorough unerstaning of the e7=ecte seismic res=onse ofthe e7isting builing: an all of its eficiencies to esign an efficientretrofit scheme #here are three basic categories of measures taken to retrofita builing@1C Moification of global beha9ior: usuall ecreasing eformations BriftsC82C Moification of local beha9ior: usuall increasing eformation ca=acit8C onnecti9it: consisting of assuring that ini9iual elements o notbecome etache an fall: assuring a com=lete loa =ath: an assuring that theforce istributions assume b the esigner can occur#he t=es of retrofit measures often balance one another: in that em=loing more


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of one 3ill mean less of another is neee "t is ob9ious that =ro9iing aeglobal stiffness 3ill require less eformation ca=acit for local elements Begini9iual columnsC: but it is often less ob9ious that careful =lacement of ne3lateral elements ma minimi6e a connecti9it issue such as a ia=hragmeficienc "m=ortant connecti9it issues such as 3all)to)floor ties: ho3e9er:are often ine=enent an must be aequatel su==lieMoification of %lobal &eha9iorMoification to global beha9ior normall focuses on eformation: although 3hen

esigning to =rescri=ti9e stanars: this ma take the form of aing strength+9erall seismic eformation eman can be reuce b aing stiffness in theform of shear 3alls or brace frames Aition of moment frames is normallineffecti9e in aing stiffness $e3 elements ma be ae or create from acom=osite of ne3 an ol com=onents E7am=les of such com=osites incluefilling in o=enings of 3alls an using e7isting columns for chor members forne3 shear 3alls or brace framesarticular groun motions ha9e a 9er s=ecific eformation eman on structures3ith 9arious =erios: as iscusse in ha=ter 4 %i9en an equal =erio of9ibration: this eformation 3ill occur: 3hether istribute o9er the height ofthe builing or concentrate at one floor "f one or more inter)stor riftsare unacce=table: it ma be =ossible to reistribute stiffness 9erticall toobtain a more e9en istribution of rift A soft or 3eak stor is an e7tremee7am=le of such a =roblem Such stories are usuall eliminate b aingstrength an stiffness in such a 3a as to more closel balance the stiffness ofeach le9el: an thus e9enl s=rea the eformation eman o9er the height of thestructureSeismic isolation is the su=reme e7am=le of the conce=t of reistribution ofeformation Essentiall all eformation is shifte to bearings: =lace at theisolation le9el: that are s=ecificall esigne for such res=onse #he bearingslimit the res=onse of the su=erstructure: 3hich can be esigne to remainessentiall unamage for this ma7imum loa #he feasibilit of =ro9iingisolation bearings that limit su=erstructure accelerations to lo3 le9els notonl facilitates esign of su=erstructures to remain nearl elastic: but also=ro9ies a controlle en9ironment for esign of nonstructural sstems ancontents%lobal eformations can also be controlle b the aition of =assi9e energ

issi=ation e9ices: or am=ers: to the structure Although effecti9e atcontrolling eformations: large local forces ma be generate at the am=ersthat must be transferre from the e9ice to structure an founation: an theisru=ti9e effect of these elements on the interior of the builing is noifferent than a rigi brace Moification of (ocal &eha9iorRather than =ro9iing retrofit measures that affect the entire structure:eficiencies also can be eliminate at the local com=onent le9el #his can beone b enhancing the e7isting shear or moment strength of an element: or sim=lb altering the element in a 3a that allo3s aitional eformation 3ithoutcom=romising 9ertical)loa carring ca=acit%i9en that in most cases: that certain com=onents of the structure 3ill ielBie: become inelasticC: some ieling sequences are almost al3as benign@

beams ieling before columns: bracing members ieling before connections: anbening ieling before shear failure in columns an 3alls #hese relationshi=scan be etermine b analsis an controlle b local retrofit in a 9ariet of3as olumns in frames an connections in braces can be strengthene: an theshear ca=acit of columns an 3alls can be enhance to be stronger than theshear that can be eli9ereoncrete columns can be 3ra==e 3ith steel: concrete: or other materials to=ro9ie confinement an shear strength oncrete an masonr 3alls can belaere 3ith reinforce concrete: =late steel: an other materials om=ositesof glass or carbon fibers an e=o7 are becoming =o=ular to enhance shearstrength an confinement in columns: an to =ro9ie strengthening to 3alls


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Another metho to =rotect against the colla=se risk =ose b e7cess rift is to=ro9ie a su==lementar gra9it su==ort sstem for elements that might beunreliable at e7=ecte high)eformation le9els For e7am=le: su==lementarsu==ort for concentrate 3all)su==orte loas is a requirement in aliforniastanars for retrofit of unreinforce masonr builings "n se9eral cases:su==lementar su==ort has also been use in concrete builings(astl: eformation ca=acit can be enhance locall b uncou=ling brittleelements from the eforming structure: or b remo9ing them com=letel E7am=les

of this =roceure inclue =lacement of 9ertical sa3 cuts in unreinforce masonr3alls to change their beha9ior from shear failure to a more acce=table rockingmoe: an to create slots bet3een s=anrel beams an columns to =re9ent thecolumn from acting as a short column =rone to shear failure onnecti9itonnecti9it eficiencies are 3ithin the loa =ath@ 3all out)of)=lane connectionto ia=hragms8 connection of ia=hragm to 9ertical lateral force)resistingelements8 connection of 9ertical elements to founation8 connection offounation to soil A com=lete loa =ath of some minimum strength is al3asrequire: so connecti9it eficiencies are usuall a matter of egree Abuiling 3ith a com=lete but relati9el 3eak or brittle loa =ath might be acaniate for retrofit b seismic isolation to sim=l kee= the loa belo3 thebrittle range#he onl location in the connecti9it loa =ath at 3hich ieling is generallallo3e is the founation/structure interface Allo3ing no mo9ement at thislocation is e7=ensi9e an often counter=roucti9e: as fi7e founations transferlarger seismic emans to the su=erstructure Most recentl e9elo=e retrofitguielines are attem=ting to =ro9ie sim=lifie guiance to the esigner on ho3to eal 3ith this ifficult issue an minimi6e founation costs52 once=tual Design of a Retrofit Scheme for an "ni9iual &uiling#here are man s=ecific methos of inter9ention a9ailable to retrofit esigners:as =re9iousl iscusse #he selection of the s=ecific t=e of element orsstem is e=enent on local cost: a9ailabilit: an suitabilit for thestructure in question An sstem use to resist lateral loa in ne3 builingscan also be use for retrofit "t is thus an e7tensi9e task to e9elo=guielines for such selection "n aition: as in the esign of a ne3 builing:there is usuall a choice of 3here to locate elements: although it is generall

more restricti9e in e7isting builings .o3e9er: in the en: there arenonseismic issues associate 3ith each builing or =ro>ect that most oftencontrol the s=ecific scheme to be use#he solution chosen for retrofit is almost al3as ictate b builing user)oriente issues rather than b merel satisfing technical emans #here arefi9e basic issues that are al3as of concern to builing o3ners or users@seismic =erformance: construction cost: isru=tion to the builing users uringconstruction Boften translating to a costC: long)term affect on builing s=ace=lanning: an aesthetics: incluing consieration of historic =reser9ationAll of these characteristics are al3as consiere: but an im=ortance 3ille9entuall be =ut on each of them: either consciousl or subconsciousl: anthese 3eighting factors in9ariabl 3ill etermine the scheme chosen

Seismic =erformance

rior to the em=hasis on =erformance)base esign: =ercei9e qualitati9eifferences bet3een the =robable =erformance of ifference schemes 3ere use toassist in choosing a scheme $o3: s=ecific =erformance ob>ecti9es are often set=rior to beginning e9elo=ment of schemes +b>ecti9es that require a 9erlimite amount of amage or continue occu=anc 3ill se9erel limit the retrofit methos that can be use an ma control the other four issues

onstruction costonstruction cost is al3as im=ortant an is balance against one or more

other consierations eeme significant .o3e9er: sometimes other economicconsierations: such as the cost of isru=tion to builing users: or the 9alueof contents to be seismicall =rotecte: can be orers of magnitue larger than


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construction costs: thus lessening its im=ortanceDisru=tion to the builing users uring constructionRetrofits are often one at the time of ma>or builing remoels: an this

issue is minimi6e .o3e9er: in cases 3here the builing is =artiall orcom=letel occu=ie: this =arameter commonl becomes ominant an controls theesign

(ong)term effect on builing s=ace =lanning#his characteristic is often >uge less im=ortant that the other four an

is therefore usuall sacrifice to satisf other goals "n man cases: the=lanning fle7ibilit is onl subtl change .o3e9er: it can be significant inbuiling occu=ancies that nee o=en s=aces: such as retail s=aces an =arkinggarages

Aesthetics"n historic builings: consierations of =reser9ation of historic fabric

usuall control the esign "n man cases: e9en =erformance ob>ecti9es arecontrolle b guielines im=ose b =reser9ation "n non historic builings:aesthetics is commonl state as a criterion: but in the en is oftensacrifice: =articularl in fa9or of minimi6ing cost an isru=tion to tenants#hese =arameters can merel be recogni6e as significant influences on theretrofit scheme or can be use formall to com=are schemes For e7am=le: acom=arison matri7 can be e9elo=e b scoring alternati9e schemes in eachcategor an then a==ling a 3eighting factor euce from the o3ner s nees toeach categorFigure ); escribes the e9olution of a retrofit scheme base on se9eral changesin the o3ner s 3eighting of these fi9e characteristics5 +ther Rehabilitation "ssues "naequate recognition of isru=tion to occu=ants"t is unfortunatel common for the e7tent of interior construction anisru=tion to be unerestimate "n man cases: occu=ants 3ho 3ere originallscheule to remain in =lace are tem=oraril mo9e at a significant increase incost of the =ro>ect or the 3ork is require to be one in off)hours: also a=remium cost Figures )10 an )11 inicate the le9el of constructionintensit often require in retrofitSimilarl: e7terior solutions: 3here strengthening elements are =lace on the outsie of the builing are often more isru=ti9e an noisier than antici=ate

an often require collector members to be =lace on each floor 3ithin thebuiling Figure )12 sho3s the result of an e7terior retrofit of aing to3erson the outsie of a builing that: in fact: i not cause a single lost a ofoccu=anc .igh)strength steel ros 3ere e=o7ie into hori6ontal cores: rillet3ent feet into the e7isting concrete beams to form the neee collectorsollateral require 3orkAs =re9iousl mentione: retrofit 3ork is often =erforme in con>unction 3ithother remoeling or u=graing acti9ities in a builing Such 3ork normalltriggers other manator im=ro9ements to the builing: such as ADA com=liance orlife safet u=ating all of 3hich a cost to the =ro>ect .o3e9er: e9en 3henseismic retrofit is unertaken b itself: the costs of ADA com=liance: remo9alof isturbe ha6arous material: an =ossibl life safet u=graes must beconsiere

54 E7am=les"t is im=ossible to inclue e7am=les that sho3 the full range of structuralelements an configurations use in seismic retrofit #here are efinitel=atterns: usuall ri9en b economics or a9oiance of isru=tion to occu=ants:but e=ening on the =articular mi7 of o3ner requirements: as iscusse inSection 52: thoughtful architects an engineers 3ill al3as come u= 3ith ane3 solutionhotogra=hs of retrofit builings: although often interesting: selom can tellthe full stor of the e9elo=ment of the scheme: an if the ma>orit of retrofitelements are insie or hien: tell almost nothing Some =hotos are sho3n here:but are not intene to emonstrate the full range of builings that ha9e


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successfull unergone seismic retrofit or the full range of solutions toini9iual =roblems "n aition: ue to limite s=ace: onl one or t3o =ointsare mae 3ith each =hoto: rather than a full case stu SE"A( "SS'ES -"#. ."S#+R" &'"(D"$%SSeismic e9aluation an retrofit of historic builings generate com=le7 =ublic=olic issues for 3hich fe3 general rules can be ientifie Restoration: orreno9ations of large an im=ortant historic builings usuall ha9e consierable=ublic an >urisictional o9ersight: in aition to em=loing an e7=erience

esign team that inclues a s=ecial historic =reser9ation consultant #hecontrol an o9ersight for less im=ortant builings that ha9e historic status atsome le9el: or that ma qualif for such status: are highl 9ariable Designersare cautione to locall in9estigate a==ro9al =roceures for alterations on suchbuilings as 3ell as seismic requirement: for them1 S=ecial Seismic onsierations"t has been recogni6e in most areas of high seismicit that local =ublic =olicconcerning seismic retrofit triggers must inclue s=ecial consierations forhistoric builings As iscusse in Section 2: initial seismic safetcriteria for e7isting builings 3ere focuse on requirements for ne3 builings:3hich 3ere marginall a==ro=riate for most oler builings: but com=letelina==ro=riate for historic builings S=ecial allo3ances 3ere therefore createfor archaic materials that 3ere not allo3e in ne3 builings: an the o9erallseismic u=grae le9el 3as lo3ere to reuce 3ork that coul com=romise historicintegrit an fabric #hese kins of technical criteria issues ha9e beensome3hat mitigate b the com=letion of FEMA 5 an the emergence of=erformance)base earthquake engineering: because consieration of archaicmaterials an fine)tuning of =erformance le9els are no3 =art of the normalle7icon2 ommon "ssues of #raeoffsMan builings in this countr that qualif for historic status are note7ce=tionall ol an can be mae commerciall 9iable #he changes that areneee for successful aa=ti9e reuse 3ill often conflict 3ith strict=reser9ation guielines: an com=romises are neee in both irections toachie9e a successful =ro>ect that: in the en: coul sa9e the builing fromcontinuing eca an make it more accessible to the =ublic #hese traeoffsoccur in man areas of esign: but seismic u=graing 3ork often requires

inter9entions that are not neee for an other reason #hese inter9entionsoften fall uner historic =reser9ation guielines that call for clearifferentiation of ne3 structural com=onents: or that iscourage recreation ofhistoric com=onents that are remo9e As =re9iousl inicate: there are norules for these conitions: an the most a==ro=riate solution for each case mustbe etermine ini9iuallAnother common conflict is bet3een current =reser9ation of historic fabric anfuture =reser9ation of the builing ue to the chosen seismic =erformance le9el#=icall: a better target =erformance in the future: =ossibl =re9entingunreco9erable amage: requires more seismic reno9ation 3ork no3 Most historic=reser9ation coes allo3 lo3er e7=ecte seismic =erformance to reuceconstruction 3ork an minimi6e amage (ike man seismic =olicies: there ha9enot been enough earthquakes 3ith seismicall amage historic builings to test

this general =hiloso=h "n an e9er)gro3ing number of cases of im=ortantbuilings: this ilemma has been aresse using seismic isolation 3hich breucing loaing to the su=erstructure: reuces require construction 3ork analso reuces e7=ecte amage in future earthquakes #=icall: ho3e9er:installing isolation into an e7isting builing is e7=ensi9e an ma require asignificant =ublic subsi to make 9iable Se9eral high)=rofile cit hallbuilings such as San Francisco: +aklan: &erkele Bafter the 1;; (oma rietaearthquakeC: an (os Angeles Bafter the 1;;4 $orthrige earthquakeC ha9e beenisolate: 3ith FEMA assistance as =art of =ost earthquake amage re=airs E7am=les of .istorical &uilings#he follo3ing illustrations sho3 sam=les of seismic retrofit of historic


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builings 3ith brief escri=ti9e notes om=lete iscussion of the =reser9ationissues an rehabilitation techniques of each case 3oul be e7tensi9e an cannotbe inclue here< onclusion#able ) summari6es common seismic eficiencies stemming from 9arious site anconfiguration characteristics as 3ell as those that might be e7=ecte in eachFEMA moel builing t=e See Section 2 for a iscussion of seismiceficienc as use in this cha=ter an this table Also inclue in #able )

are retrofit measures that are often use for each situation

References

1 References from #e7tAmerican Societ of i9il Engineers BASEC: Seismic E9aluation of E7isting&uilings: ASE 1)0: 200A==lie #echnolog ouncil BA#C: Earthquake Damage E9aluation Data foralifornia: A# 1: 1;5alifornia Seismic Safet ommission BSSC: Status of the 'nreinforce Masonr&uiling (a3: 200 Re=ort to the (egislature: SS 200)0: 200Feeral Emergenc Management Agenc BFEMAC: restanar an ommentar for theSeismic Rehabilitation of &uilings: FEMA 5: 2000.olmes: -illiam #: &ackgroun an .istor of the alifornia .os=ital SeismicSafet rogram: roceeings: Se9enth $ational onference on EarthquakeEngineering: &oston: 2002: Earthquake Engineering Research "nstitute.oo9er: nthia A: Seismic Retrofit olicies@ An E9aluation of (ocal racticesin Gone 4 an #heir A==lication to Gone : 1;;2: Earthquake Engineering Research"nstitute$ational "nstitute of Stanars an #echnolog B$"S#C: Stanars of SeismicSafet for E7isting Feerall +3ne or (ease &uilings: "SS R : 2002' S De=artment of "nterior B"nterior aC: #he Secretar of the "nterior sStanars for Rehabilitation: De=artment of "nterior Regulations: FR


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E7tremel interesting from a histor stan=oint: this book "nclues iscussionof seismolog: geotechnical engineering: structural engineering: coes: an lossestimation: an e7cellent histor an a9ailable ata on earthquakes u= to 1;2

.olmes: -illiam #: Risk Assessment an Retrofit of E7isting &uilings:roceeings #3el9e -orl onference on Earthquake Engineering: Aucklan: $e3Gealan: 2000#his =a=er contains a more technicall oriente escri=tion of the methos of

FEMA 5 an strategies for esign of retrofit sstems

JEn of ha=ter K

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