Anastasiadis Gioncu 3rd Hellenic Conf 1998

7/30/2019 Anastasiadis Gioncu 3rd Hellenic Conf 1998

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3, r'!uo il n (A lt /1 l 9i KirA t-(ilftLAna tz4 30.3 orrq.t| 1q 3 tr 3l-3i9

nfluence of Jint Detais n the Lca Ducfiitvf Stee MR FramesAnthims Anastasiadisl . victr Gincul

1Plituhni" Lniersity Timisr ' g00 Timisr , str' Trin Llescu 2 , Romnieywrds: Jint details , Moment resisting frame , Duti1i , Rtatin capacty " DUcRoT computer prgram

AbstractDuring the Nrthridg and b earthquakes , numerous velded stel momnt - resistingrames ( MRFs ) cnnectins failed at the ontat btween beam and clumn. n rder toimprove the behavior f these cnnectins, some new nstrutinal details are proposed :(i)reducing the beam flange crss section area in the prximity of the cnntin ( dg bnecnfiguratin ); (ii) inreasing the onnetins strength supply by stiffening th beam flanges.The rotatinal apacity f these conntins ar siificantly enhanced' Th paper presntsth increasing f local dutility for these new cnstructinal detais, using the DUCTROTomputer prgram.1. ntroductinFor steel moment - resisting frames undr sver earthquakes, it is gnrally assumd in codsthat th input nrgy is absrbed and dissipated primariy by the plasti hinges formed at theends f beams. But th Nrthridge and b earthquakes hav shown that in som nditins, especially in the case f the near - field grund mtins, this cde cnceptin des ntwrk, a widespread brittle damage in the welded nntin curring, withut any sign thatsme plastic defrmatins are prdued in beams. Ther are many als many cases in whichplasti hinges urred in lumns, du to the fat that the interatin beam - flr slab wasunderestimated and the plastic momnt capacities f beams were greater than the columnplasti moment capacities. n the aim to avid ths damage types and to constrain thedeveping the plastic hinges nly in the beams, it is required by desi practice t imprveth onstrutinal details, fr whih a variety f ideas have been proposed.n the paper, the tv slutions afe proposed: the dreasing r incrasing the momentapacity of beam ends. Taking advantage of using the s called .. standard beam ,, and theDUCTRO cmputer prgTam, the increasing of the beam dutility in function ofnstructiona detais, are propsed. The influene f gavitatinal and seismi ads isonsiderd, in the aim to use the atualmoment diagrams.


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2. New constructinal detaisSine after Nrthridge and Kbe the reliability of the welded connectins has lng beenquestiond , it ariss the idea that is better t mve the plasti hinge away from the lumnSurfac, in the field were the welding des nt determinate the nde ductility. There twways t obtain this puses:(i) Weakening the speific beam section near t onnectin by trimming the beam flanges .Th idea was devepd in priniple in the 80,s by umier [1] and was patnted by RBED ,This sution is knwn als as the .. dog bone ,, nfiguratin [2] . The vakening can bebtained by drilled holes, pligonal uts, with nstant reduced setion, urv-d ut withvariable setion, or adjusted cuts, with variable redued setin in funtin f the shapebnding mment [3],[4],[5],[6]. Due to fat that the last one Seams to be the mre adequatefor develping f the arg plastic hinge, it \rill develped in the paper (Fig.1a).(ii) Strengthening the speific bam near t onnectin by adding covering plates, |atera|reinforement plates, vertical ribs [3],[6]. These solutins move th plasti hing away fromth olumn fae , but usually increase the amount of fie1d welding , and may lead t vrydiffiult welding predures in vertial r ver - head psitin. n the paper the slutin withvertical ribs is analyzed ( Fig.1b ).Considring the olmn - beam relation, ther are tlvo MR fram types :(i) Weak beam - strng column (WB-SC), fr which the pastic hinges are formed ony inthe beam ends and at column bases ; (ii) strng beam - weak olumn (SB-WC), whihdevelp a pasti mhanism ony in th weakest storey, the pastic hings being oncentratedat the lumn ends . he mdern cneptions f des considers that nly th WB-SCslutin an ffer a gd ductility . That means that the mment capaity of clumns must begeater than the n offespnding t the beams But the bam mment apacity depnds nthe interaction of steel beam with the reinforced oncrete flor, interation whih is verydiffiult t be quantified . Due t this fat, in many aSeS, the cnditin f gbal mhanismis not satisfied, pasti hinges urring also in clumns n th aim to prevent anunontrlled behavir , sme onstructinal details are prposed: intmlptin of cnnectrsr rinfred nret plate in the field of pasti hinges(Fig 2)3. Rtatin CapacityThe mdern design philsphy is based n the objetive t provide strutures with sufficientductility. S, the aai|abe lcal dutiity, determined at the level f plastic hinges must begreater than the required ductility, btained from the full struture bhavir, ativated by aspeifi earthquake. For this purpose, a methodlogy is detrmined in [7], based on theplasti rtatin apaity of a standard beam, determined by the psitins in actual strutur ofthe pastic hinges and the inflectin points ( Fig.3a ). The rotation capaity, R, is given by(Fig.3b ) R- -! - -L-

(1)


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ovided moment capacityrequired moment caPcitY(gr-avitationat and seismic loads )

br+bz bffiff1n|o_y'_',reqred momenf capacty

provided momenf capacify

_-1 |l' IldI_-4f-1 ,|lhr

bbffi

;l--:-;_:_\--F:.c].-,-ptace of plastic hinge

place of plast[c hnge

place of plastic hinge

place of plastic hinge

,,:

Figure 1. Typical details of the analyzed beam-olumn cornection


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Figure 2. .pical details or beam-flor onnectlons,here ,, is the ultimate pastic rtatin , ,' the rotation coesponding t the first plastichinge , ., . total ultimate rtatin. he rotalin capacity is detenined using a plastimechanism fnned by plastic Zones and yield lines . A cmputer progam DUCRO hasbeen elabrated at CRC irisara [8] fbr detennlnaion f the ducili of lcalmechanism. The available rtatin capait1,, is detennined tiom the reation [7] ,/.. ,) - '' 1._ l\'/ , (2)

local plastic mechanisms

1:a)

Fire 3. Lcal ductilit


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where t,, , are numerial ceffiints introducing the effet yli loading and axialfres, respetivelY * is the partial safety fatr t alw for the same tim uncertainties inthe determining the available rotatin apacity ; a valu f *: 1,5 is prpsd .4. Ductiity f reduced . beam sectinh moving of the plasti hinge away frm the clumn flange is prfrmed by choosingadequate dimensions fr reduced setion . The main geometrial parameters are pfesented inFig.l . The distane from the column f redued setin is sected in aim to avid thedeterioration of material prperties at the heat - affected zne. The distane remlnended inthe literature [4] is sized between 5 - 120 mm , The transitin engths are hsen t avoidth stress nentratins . Th length f redued sectin is determined in a mannr t awthe urring of a single plasti hing . To shrt length impedes the 1brmatin f a argedissipate plastic hinge, while t long length may allws ccurring of tw pastic hingesproduing an unexpted lal beam mehanism , The lengIh of the plastic mehanism isdtermined in [7] as being :

2b t% (3)Fr the variable redued crss-sectin, a medium b value may be used . The rdutin fross-setion from the mment diagram, in whih the both seismi and gravitatina ladsmust be inludedThe dereasing of mment capaity with 5 - |0% is proposd in the aim to ensure that yildocurs in the redued section[4] . So the redued plasti mment capai, fr the t.w ends,Mp.red. t, Mp.red.2, .

M p'red'\'2= (0,9... ,'il''(+_, - *+('_ 91where: is the bam length, Mo,the unrducd plastic mmnt f beam, _ Mo qL2 ' q thevertial gravitational lads . The value is limited to 0'25 because fr smaller values, themaximum moment oufs away frm the olumn fae . The redued moments, in funtin fgravitatinal lads are presented in (Fig.4). The inreasing f rotatin capaciql, R, due to theplastic moment r width reductins is presented in Fig.5,6 . The inreasing is very important,being about 55% . The importance f onsidering the graitational loads results frm theFig.7, the effet being the derasing f rotatinal capaity' Negleting f this efft an be]ead t hs inorret gemetrial paramters and, f urse, to undr estimate thertatin apacity of beam,The importance f cnsidering the gravitatinal loads results frm the Fig.7, the effet beingth decreasing of rtationa apacity. egleting of this effct can be lead t chose inrrectgemetrical parameters and, of cours, to under estimate the rtatin apaity f beam. nthe same time the increasing of gravitatinal lads produces a reducing f rotatin capacity(Fig.8). one can see that the rtation capaity is decrased of abut 25o in case f highvertical lads , Mp / q12: 0,25 - ,30, as mpared with lw vertical lads, p l qL2: ,60 -0.80.

(r,)'n(,1\'uL. =0.61 '1 l ; i\/.,./ \D/

(4)


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aj2

10,90,84,70,60,50,4U'J0,20,1

/ j,25Figure 4. Rduced pasti mments

380xl2x200xi6tF6000 mm ; Lrn=200mmMp / qU =0.3014121ao41z1t .re / !h.t0

0,90,9s 0,920,96

Fire 5. ncreasing of rtatin apaity 380x12x200x16-6000 mm ; Lm=200 mmMp / ql :,30

,!

0'075'04170,0660,033,8

0,0580,025'850,050,0160,9

}/LUg -i'/LI b1/b

Mp.red.1 Mp.red.2+Li / L =0,01 ; Lt/ L=0,0'10+Li / L =0,040 ; Ltl L=0,040Li / L =0,070 ; Lt/ L=0,070+-Li / L =0,10 ; Lt I L=0,10--lX- Li / L =0, 13 ; Lt / L=0,'13-+ Li / L =0,'tG ; Lt / L=0,16

Figure 6. nfluene f geometrial parameters and gravitational oads n rotation capaity.


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H 380x12x200x16-oo::. -- :1-:"0 ---'1614121fr84z00,0750,0410.75

0,0660,0330,8'05,0160,9

/L/Lbt /b

0'580,0250,85U1

i--a-Mseismi..FMg+s ( Mp /qL2 =),3)

Figure 7. nfluene f lading System on rtation apaity

380x12x200x16.- 6000 mmLm =200 mm161412't086

Ii.-r-i+'0i6 : Lt ,:0,05;b2ltrO'7 ; b1/b:,9Li-4'a25 : Lt ,{-:,058;b2iF0,65 ; h1/b:0,85-,(*Li{.033 l Lt /L=,66;b2r0,6 ; b1,ib=O,82U (o^ -. . (o. ..-oooop/qL

(o

Figure 8. nflunc f $avitatinalloads5. Ductility of strengthened beam sectinhe dimensins f strengthened beam are presented in Fig.1b. Fr this setin the plastihinge ocurs at the distane of dl3 frm the edge of reinforced nnetion[6]. Fordetermining the required strengthened sectin, it iS recmmended t consider different Strainhardning ffets fr beam and Strengthned setins. The over strength f reinfored beamcan b f rder 20-30% [7], while for the strengthened setin may be nly 5-10%. S, theplastic mment capaity f strengthened sctin must be:

-{-Unreduced setion

--x-- Li{,O 1o ., Lr lL:o,o1 5;b2l1r0,55 , b1/b


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(s)

where the oeffiient onsiders the ffect of strain hardening, t is recmmended that :0,75-a'65. The influene f this cffiient is presented in (Fig.9).1,8,,|

^11)1

0,80,60,4'z

0

380x12x200xl6;6000 mma

2ri-05_066

Np/qL,

Figure 9. Effect f stain hardeningt is very learly that the effet is t inrease the required strengthning . The influenc fribs lngth and pasti hinges position on the rtation apacity is presnted in Fig.10, one cansee that the increasing f distane between lumn fac and plasti hinges give rise to anincreasing of rtation capacity f order 8%. The influene f gravitatina frces n thertatin apaity is presented in Fig' 11, fr different rib lengths'

I 380xl2x200x16;6000mmMp / ql{},3

FLp=;--i+p=Lr+d/30,16 ,025Lr /L

0,25 0,8,7,6,5'4

,09,5

98,5

e7q

Figure 10. nfluene f rib length n rtatin apacity


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H 380x12x200x16=6000 mm

i-.tsLr l,4'03-{-Lr /L {.04_-*_Lrl, {'0650,5

rp /q}

Fig' 11 nfluence of gravitatinal loads on the rotation capacity6. CncusionsTh veakening r strengthening of beam ends, in the aim to mve away th formatin ofpastic hinges frm coumn faes, is in the same time a very god solution t inreasing thelocal ductility of beams. he weakening of cross Stion seems to be the mst adequatesolution, the inreasing of rotation apaity being highst than for strengthening solution. Thesecond sution an be effective when the weding material have suff,tcient toughness andthe rveding is xeuted \/ith high quaity. t is very important t consider in analysis theinfluene of gravitational lads, therwise the above mentined effect f weakenins orstrngthning bing questionabe.References

Plumier, A, ,1996' Reduced beam section; a safety oncept for structures in seismicZones, uetin Stiintific, Seri Construct, rchitectur, m 41(55), Fas.2, 46-60.wankiw, N. R., Carter, Ch. J., 1996, he dgbone: a ne\ry.idea to chew on, MclernSteel (|'nstructin,36, N 4' |8-23.Chen, S. J., Chu, J.M. , Chu, . L., |997 ,Dynami behaviours of steel frames withbeam flanges shaved arund onnection, J.Constr.Seel Res.,42, N1, 49-70.Chen, S. J., Yeh, C. H., Chu, J.M. ' |996'Ductie steel beam-to-column connctinsfr seismic resistane, J,Struct. ng.' 122' 1 1, 1292-|297 .Popov, E' P', Bondet, M., Stepanov, L., t996' ppliction of Dgnes forimproement f seismic behiour f steel cnnectin^s, , Report UCB/EERC 96-05,University of California, Berkeley, U.S.A.Bruneau, M., Uang., C, M,, Whittaker, A, 1998, Ductile Design f Steel Structures,McGraw-Fill, ew York.Ginu, V., etcu, D',1997, Availabe rotatin apaity of wide flange beams andbeam column, Part 1, Thoretical approahes,Part 2, Exprimenta and Numerialtests, J.Cnst. Seel Res.,43, N -3, 161-217,29-244Petcu, D., Gincu,.' |996, DUCTR)T 96, Guide for SerS, CERC Timisoara ' Ro.

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Anastasiadis Gioncu 3rd Hellenic Conf 1998