Huge Scale Tests of All-Steel Multi-curve Buckling Restrained Braces

Transcription

1 Hug Scal Tsts of All-Stl Multi-curv Buckling Rstraind Bracs C. S. Tsai Dpartmnt of Civil Enginring, Fng Chia Univrsity, Taichung, Taiwan H. C. Su Dpartmnt of Watr Rsourcs Enginring and Consrvation, Fng Chia Univrsity, Taichung, Taiwan T. C. Chiang Tchnical Managr, Earthquak Proof Systms, Inc., Taichung, Taiwan SUMMARY: In this study, w propos an all-stl BRB calld th multi-curv buckling-rstraind brac (MC-BRB to ovrcom th shortcomings of traditional BRBs that us mortar ncasd in a stl tub. This nw BRB consists of doubl cor plats, ach with multipl nck portions, nlargd sgmnt, latral support lmnts, and constraining lmnts. Th nlargd sgmnt can b connctd to th latral support and constraining lmnts to incras buckling strngth and prvnt th latral support and constraining lmnts from sliding during arthquaks. Th latral support lmnts can b windowd to allow quality control chcks to b prformd and th condition of th cor plat to b monitord aftr an arthquak. A hug-scal componnt tst was carrid out to invstigat th bhavior of th nw BRB. A comparison of th xprimntal rsults and thortical calculations indicat that th all-stl MC-BRB posssss a stabl and prdictabl mchanical bhavior undr cyclic loadings. ywords: Buckling rstraind brac, multi-curv BRB, nrgy dissipation dvic, dampr, structural control. INTRODUCTION Sinc th 97s, thr has bn xtnsiv rsarch into th prvntion of th traditional brac from buckling in rpatd comprssion during an arthquak, which is th sourc of stiffnss and strngth dgradation. Wakabayashi t al. (973 conductd a componnt tst of th buckling-rstraind brac (BRB whil using diffrnt d-bonding matrials btwn th brac and th buckling-rstraint unit to rduc th friction. imura t al. (976 carrid out a componnt tst of th stl brac ncasd in a mortar-filld stl tub subjctd to cyclic loadings. Mochizuki t al. (979 prformd tsts on similar bracs with a layr of shock-absorbing matrial to avoid adhsion btwn th stl and th concrt and to allow transvrs xpansion of th stl cor in comprssion. This typ of brac has bn trmd th unbondd brac bcaus of th layr of unbonding matrial at th stl concrt intrfac. Wada t al. (99 dmonstratd that th BRB could b dsignd as a dampr to dissipat sismic nrgy. A BRB or an unbondd brac basically is composd of thr componnts: th stl cor mmbr, buckling-rstraining part, and d-bonding matrial. Black t al. ( and Mrritt t al. (3 carrid out standard and low-cycl fatigu tsts of BRBs to xamin thir bhavior. Howvr, svral shortcomings nd to b addrssd rgarding traditional BRBs that us mortar ncasd in a stl tub to prvnt th cor plat from buckling. Ths shortcomings includ th complxity of intrfacs btwn adoptd matrials, uncrtain prcision and tim consumption during th manufacturing procsss and difficultis in dtcting th lvl of damag aftr an arthquak has occurrd. As an altrnativ, all-stl buckling-rstraint systms, which do not nd un-bonding matrials, mortar, or complicatd manufacturing intrfacs among diffrnt matrials, hav bn dvlopd to conqur th abovmntiond disadvantags of traditional BRBs (Chn, Tsai t al. 4, 5, 6, 8, 9, Ma t al. 8, Eryasar and Topara. Th stl cor is typically sparatd from th stl buckling-rstraint unit by a small void in th ncssary dirction. All-stl BRBs can also b dmountabl if boltd connctions btwn th stl cor and th buckling-rstraint unit ar usd, thus nabling inspction and monitoring. Tsai t al. (8, 9 proposd a nw typ of

2 all-stl BRB calld th multi-curv BRB (MC-BRB that consists of a singl stl cor plat with an nlargd sgmnt in th middl lngth to form a multi-curvd shap for th stl cor, and th buckling-rstraint unit that includs constraining lmnts and latral support lmnts. Twnty fiv buildings in Taiwan and two in China hav implmntd this typ of BRB (Earthquak Proof Systms, Inc.. Zhao t al. ( hav also publishd th follow-up rsarch of th MC-BRB to conclud that th MC-BRB has mor stabl mchanical charactristics than th traditional BRBs and dos not rquir d-bonding matrial (Tsai t al. 9, Zhao t al.. Howvr, thr xist fw, if any, larg-scal tsts, in trms of axial forcs, for all-stl BRBs. To xamin th bhavior of th larg-scal all-stl MC-BRB, componnt tsts of an all-stl MC-BRB dsignd to sustain an axial forc of 4 kn hav bn carrid out in th Matrial Exprimntal Cntr at th Architctur and Building Rsarch Institut, Ministry of th Intrior, Taiwan. Th rsults from th componnt tsts dmonstrat that th all-stl MC-BRB with doubl stl cor plats posssss a stabl bhavior undr cyclic loadings, providing xcllnt inlastic dformation capacity. Furthrmor, th comparisons btwn th xprimntal rsults and numrical rsults calculatd from drivd mathmatical formulations in this study rval that th mchanical bhavior of th all-stl MC-BRB with doubl stl cor plats can b wll prdictd by th proposd formulations.. ALL-STEEL MULTI-CURVE BUCLING RESTRAINED BRACE WITH DOUBLE CORE PLATES As shown in Figurs..9 th all-stl MC-BRB consists of doubl flat stl cor plats, th buckling-rstraint unit, and an insrt plat locatd btwn th two cor plats. Th cross sctions of A-A and B-B of th spcimn ar shown in Figurs.3 and.4. Each stl cor plat has a multi-curvd shap through an nlargd sgmnt, as shown in Figurs.-.5, in th middl lngth of th MC-BRB to construct two nrgy dissipation sgmnts. Figurs.6 and.7 rspctivly show th dtails of th latral support and constraining lmnts. Tabl. shows th dimnsions of th tstd all-stl MC-BRB spcimn. Th stl cor plats of th MC-BRB wr mad of A57 (Grad 5 with a nominal yild strss of 35 kn/cm. Th siz of th nrgy dissipation sgmnt was 85.7 mm in width and 5 mm in thicknss, which rsultd in a nominal yild forc of 5 kn. Two flat stl cor plats lading to th yild forc of kn wr adoptd to avoid wlding at nrgy dissipation sgmnts such as th cruciform cross sction. No ncssary wlding at major portions such as nrgy dissipation sgmnts of th stl cor plat maks th proprtis of th BRB such as th yild forc and yild displacmnt mor prdictabl than thos using cruciform cross sctions that rquir wlding at th nrgy dissipation sgmnts. Th thortical lastic stiffnss of th doubl cor MC-BRB was 653 kn/cm. Th nominal yild displacmnt was 6.5 mm. It should b notd that two flat stl cor plats hav bn adoptd for larg axial loads in this study and that on flat stl cor plat would b sufficint for smallr axial loads. As indicatd in Figurs.3,.4 and.7, th buckling-rstraint unit includd constraining lmnts that can b of any cross-sctional shap, such as that of a rctangular box, a channl, or an I sction, and latral support lmnts to prvnt th stl cor plat from global and local buckling. As indicatd in Figurs.3 and.8, th insrt plat that can b composd of on plat or two plats was locatd in th middl of th cross sction of th MC-BRB to sparat th two flat stl cor plats for asing th connction btwn th MC-BRB and th gusst plat stmmd from th bam and column. Not that th nlargd sgmnts can b wldd to th buckling-rstraint unit to hav highr buckling strngth, and that th connction btwn th latral support lmnts and th insrt plat can b wlding, bolting, or th combination of wlding and bolting to mak th connction compltly or partially dmountabl for chcking and monitoring. Watanab t al. (988 suggstd that th buckling-rstraint unit b proprly dsignd not to rsist any significant axial load and to hav sufficint flxural stiffnss to avoid global buckling of BRBs, which is xprssd as P P cr ysc. 5 (.

3 whr P cr is th lastic buckling strngth of th buckling-rstraint unit, and P ysc is th yild forc of th stl cor. If on stl cor plat is adoptd, th lastic stiffnss of th MC-BRB,, in trms of rlativ displacmnt btwn two nds dfining th dformation of th BRB, can b obtaind as follows (Tsai t al. 9: kk k3k 7k8 k k k k k k k k k k k k k k k k k k k k k (. whr EA EA EA 3 7 k ; k3 ; k7 ; L L 3 L7 k E( A A3 ; and L (ln A ln A 3 k 8 8 E( A m L (ln A m A ln A whr L, L, L 3, L 7, and L8 ar th lngths of th nrgy dissipation sgmnt, first transformd sgmnt, brac projction, nlargd sgmnt, and scond transformd sgmnt, rspctivly. A, A 3, and A7 ar th cross-sctional aras of th nrgy dissipation sgmnt, brac projction, and nlargd sgmnt, rspctivly. Am is th largst cross-sctional ara of th scond transformd sgmnt. P is th axial forc of th mmbr, and E is th modulus of lasticity. If on stl cor plat is usd, th rlationship of nodal forcs to nodal displacmnts at both nds of th MC-BRB is givn by F F u u u (.3 BRB u whr th lastic stiffnss of th MC-BRB, BRB, can b xprssd as BRB (.4 whr F and F dnot nodal forcs at both nds of th MC-BRB; and u and u ar nodal displacmnts at both nds of th MC-BRB. Not that if doubl stl cor plats ar usd, th stiffnss drivd abov should b doubld. 3. EXPERIMENTAL RESULTS AND DISCUSSION According to th Rcommndd Provisions for Buckling-Rstraind Bracs (AISC 5, th dsign of bracs shall b basd upon rsults from qualifying cyclic tsts in accordanc with th procdurs and accptanc critria containd in th Provisions Appndix. According to th Rcommndd Provisions (AISC 5, th following loading squnc that includs th standard loading protocol and low-cycl fatigu loading protocol shall b applid to th tst spcimn, whr th dformation is th axial dformation of th cor plat: ( cycls of loading at th dformation corrsponding to by, ( cycls of loading at th dformation corrsponding to.5 bm, (3 cycls of loading at th dformation corrsponding to. bm, (4 cycls of loading at th dformation corrsponding to.5 bm,

4 (5 cycls of loading at th dformation corrsponding to. bm, and (6 Additional complt cycls of loading at th dformation corrsponding to.5 bm as rquird for th Brac Tst Spcimn to achiv a cumulativ inlastic axial dformation of at last tims th yild dformation. by dnots th axial dformation at first significant yild of th spcimn, and bm dpicts th axial dformation of th spcimn at th dsign story drift. Th loading squnc of th 5 AISC Provisions is summarizd in Figur 3.. Th AISC Rcommndd Provision dfins th comprssion strngth adjustmnt factor,, as P T max max (3. whr P max is th maximum comprssiv forc; and T max is th maximum tnsil forc corrsponding to.5 bm. Whil a larg dformation occurs in th longitudinal dirction of a brac, th changs of th crss-sctional ara and th lngth of th mmbr should b takn into considration. In thory, th comprssion strngth adjustmnt factor,, can b approximatly obtaind by th procdurs as follows: Th cross-sctional ara of th nrgy dissipation sgmnt of th BRB undr a larg dformation in comprssion, A com, can b xprssd as A ( com A (3. and th lngth of th nrgy dissipation sgmnt in comprssion, l com, is l com l ( (3.3 whr A and l ar th original cross-sctional ara and original lngth of th nrgy dissipation sgmnt, rspctivly; ν is Poisson s ratio, and ε is th tstd strain of th nrgy dissipation sgmnt. Thrfor, th lasto-plastic stiffnss of th nrgy dissipation sgmnt, com, of th BRB at th tstd strain in comprssion is givn by com E p l A com com E p A ( l ( (3.4 whr E p is th lasto-plastic modulus of th nrgy dissipation sgmnt at th tstd strain. Similarly, th lasto-plastic stiffnss of th nrgy dissipation sgmnt, tn, of th BRB at th tstd strain in tnsion can b obtaind as tn E p l A tn tn E p A ( l ( (3.5 whr A tn and l tn ar th cross-sctional ara and lngth of th nrgy dissipation sgmnt in tnsion at th tstd strain, rspctivly. Thrfor, th ratio of th lasto-plastic stiffnss in comprssion to that in tnsion at th tstd strain, R stiff, is xprssd as

5 E p A ( R com l ( ( ( stiff E A ( ( ( tn p l ( (3.6 If ν =.5 (incomprssibl matrial is assumd at larg dformations, thn R stiff is givn by (. 5 ( R stiff 4 8 ( (. 5 ( (3.7 If th nrgy dissipation sgmnt is subjctd to idntical dformations in both tnsion and comprssion without local and global buckling, th thortical comprssion strngth adjustmnt factor,, will b qual to R stiff ; that is, R ( stiff 4 8 (3.8 Th AISC Provisions (5 rquir that th valu of cumulativ inlastic axial dformation capacity, η, for uniaxial tsting of BRBs b at last. As shown in Figur 3., th tsting facility is locatd in th Matrial Exprimntal Cntr at Architctur and Building Rsarch Institut, Ministry of th Intrior, Taiwan. Th loading capacitis of th tst machin ar 3 MN in comprssion and 5 MN in tnsion. Th spcimn was placd vrtically, as shown in Figurs 3. and 3.3. Th load-dformation rsponss of th standard tst of th spcimn ar shown in Figur 3.4. Th axial dformation in Figur 3.4 rprsnts th sum of th displacmnts at both nds of th MC-BRB. Thr xistd a flat in th arly two nonlinar cycls bcaus th strains in ths two cycls wr still within th platau ara of th strss-strain curv of th matrial. Th masurd lastic stiffnss was 668 kn/cm, which was.% highr than th thortical valu of 653 kn/cm calculatd from Eqs. (. and (.4. Th masurd yild forc was 353 kn, which was 3.5% largr than th thortical valu of kn. Th masurd yild displacmnt was 6.3 mm, which was.8% largr than th thortical valu of 6.5 mm. Tabl 3. summarizs th comparison of masurd data and thortical valus calculatd from th mathmatical formulations drivd abov. Th tstd maximum strain in th rgions of nrgy dissipation sgmnts of th spcimn was.6%. Th masurd maximum comprssiv and tnsil forcs at th strain of.6% wr 3934 kn and 573 kn, rspctivly. Th comprssion strngth adjustmnt factor, β, was.8, which was much smallr than th valu (<.3 rquird by th 5 AISC Provisions, and th tnsion strngth adjustmnt factor, ω, which is th ratio of th maximum tnsil forc to th nominal yild forc, was.573 at strain of.6%. Tabl 3. lists th comparison of th masurd comprssion strngth adjustmnt factor, β, and thortical valus calculatd from Eq. (3.8. It can b concludd from th comparison of data in Tabl 3. that th numrical rsults of th comprssion strngth adjustmnt factor calculatd from th proposd mathmatical formulation ar in vry good agrmnt with th xprimntal rsults. Twnty-six cycls of hystrsis loops prsntd in Figur 3.5 giv th rsults of th low-cycl fatigu tst. Th cumulativ inlastic axial dformation capacity, η, rprsnting th ratio of th accumulatd inlastic dformation until failur of th tstd spcimn to th yild dformation, was 567.8, which was much highr than th valu of at last rquird by th 5 AISC Provisions. Figur 3.6 dmonstrats that th xtrior of th MC-BRB had no sign of damag or yilding aftr complt tsting. Figur 3.7 shows ncking and ruptur in on nrgy dissipation sgmnt of th stl cor clos to th transformd sgmnt occurrd during tnsil loading at th last cycl of fatigu tsting. Figurs indicat that thr was no sign of local and global buckling at th stl cor plats, constraining lmnts or latral support lmnts, and no sign of damag at th buckling-rstraint unit. Basd on th xprimntal obsrvations, th wall of th constraining lmnt providd good support to th stl cor without yilding. No slipping btwn th stl cor plats and th buckling-rstraint unit was obsrvd bcaus of th wlding btwn th nlargd sgmnt of th stl cor plat and th buckling-rstraint unit. Ths tst rsults showd xcllnt stabl hystrtic bhavior, satisfactory inlastic axial dformation capacity, and prdictabl

6 lastic stiffnss, yild displacmnt, yild forc, and comprssion strngth adjustmnt factor that can b calculatd in thory. 4. CONCLUSIONS A larg-scal all-stl multi-curv buckling-rstraind brac (MC-BRB with doubl cor plats was invstigatd xprimntally. Basd on th xprimntal rsults and obsrvations, no sign of global or local buckling was obsrvd, and th buckling-rstraint unit providd good support to th stl cor plats without any damag. Th comparisons btwn tst rsults and thortical calculations rval that th mathmatical formulations drivd in this study can wll prdict th bhavior of th MC-BRB. Exprimntal rsults suggst that no wlding at th major portions of th stl cor plat, such as th nrgy dissipation sgmnts, maks th mchanical bhavior of th BRB mor prdictabl. Wlding th nlargd sgmnt locatd in th middl of th stl cor plat to th buckling-rstraint unit was found to b a suitabl option for prvnting slipping of th buckling-rstraint unit. Satisfactory adjustmnt factors wr obtaind basd on th comparisons of xprimntal rsults with th 5 AISC Provisions. A proprly dsignd all-stl multi-curv buckling-rstraind brac with doubl cor plats possssd stabl mchanical bhavior with xcllnt hystrsis. REFERENCES AISC (5. Sismic provisions for structural stl buildings. Appndix, Part I, AISC. Black, C. J., Makris, N. and Aikn, I. D. (. Componnt tsting, stability analysis and charactrization of buckling-rstraind bracs. Journal of Structural Enginring: ASCE, 3: 6, , USA. Chn, C.C. (. Sismic bhavior and dsign of buckling inhabitd bracs and ductil CBF s. Structural Enginring 5:, 53-78, in Chins. Earthquak Proof Systms, Inc. (,Taichung, Taiwan, Eryasar, M. and Topkara, C. (. An xprimntal study on stl-ncasd buckling-rstraind brac hystrtic damprs. Earthquak Enginring and Structural Dynamics, 39, 56-58, USA. imura,., Yoshizaki,. and Takda, T. (976. Tsts on bracs ncasd by mortar in-filld stl tubs. Summaris of Tchnical Paprs of Annual Mting, Architctural Institut of Japan, 4-4, in Japans. Ma, N., Wu, B., Zhao, J., Li, H., Ou, J. and Yang, W. (8. Full scal tst of all-stl buckling rstraind bracs. Papr No. -8, th 4th World Confrnc on Earthquak Enginring, Bijing, China. Mrritt, S., Uang, C. M. and Bnzoni, G. (3. Subassmblag tsting of corbrac buckling-rstraind bracs. Dpartmnt of Structural Enginring, Structural Systms Projct, Rport No. TR-3/, UC San Digo. Mochizuki, S., Murata, Y., Andou, N. and Takahashi, S. (979. Exprimntal study on buckling of unboundd bracs undr axial forcs: Parts and. Summaris of tchnical paprs of annual mting. Architctural Institut of Japan, 63 66, in Japans. Tsai, C. S., Chiang, T.C., Chn, B. J., Chn, W. S. and Yu, S. H. (4. Componnt tst and mathmatical modling of advancd unbondd brac. Sismic Enginring, Th 4 ASME PVP Confrnc, V. C. Matzn and S. Fujita, ditors, 486:, 3-36, California, U. S. A. Tsai, C. S., Chn, W. S. and Chn,. C. (5. Shaking tabl tst of structur with rinforcd buckling rstraind bracs. Sismic Enginring, Th 5 ASME PVP Confrnc, C. S. Tsai, ditor, Dnvr, 8, 37-3, Colorado, U.S.A. Tsai, C. S., Chn, W. S. and Chn, B. J. (6. Componnt tsts and simulation of advancd buckling rstraind bracs. ASME 6 Prssur Vssls and Piping Confrnc, Vancouvr, Canada, PVP6-ICPVT Tsai, C. S., Chn, W. S. and Lin, Y. C. (8. Full scal shaking tabl tsts of a stl structur with multi-curv buckling rstraind bracs. Papr No , th 4th World Confrnc on Earthquak Enginring, Bijing, China. Tsai, C. S., Lin, Y. C., Chn, W. S. and Su, H. C. (9. Mathmatical modling and full-scal shaking tabl tsts for multi-curv buckling rstraind bracs. Earthquak Enginring and Enginring Vibration 8: 3, Wada, A., Connor, J., awai, H., Iwata, M. and Watanab, A. (99. Damag tolrant structurs. Procding 5th U.S.-Japan Workshop on th Improvmnt of Structural Dsign and Construction Practics, Applid Tchnology Council, ATC-5-4, 7-39, San Digo, CA.

7 Wakabayashi, M., Nakamura, T., ashibara, A., Morizono, T. and Yokoyama, H. (973. Exprimntal study of lasto-plastic proprtis of prcast concrt wall panls with built-in insulating bracs. Summaris of Tchnical Paprs of Annual Mting, Architctural Institut of Japan, Structural Enginring Sction : 4-44, in Japans. Watanab, A., Hitomi, Y., Saki, E., Wada, A. and Fujimoto, M. (988. Proprtis of brac ncasd in buckling-rstraining concrt and stl tub. Procdings of th 9th World Confrnc on Earthquak Enginrin: IV, Tokyo. Zhao, J., Wu, B. and Ou, J. (. A novl typ of angl stl buckling-rstraind brac: cyclic bhavior and failur mchanism. Earthquak Enginring and Structural Dynamics, 4, 83-. Tabl.. Dimnsions of All-Stl BRB (unit: mm Lw L L L3 L4 L5 L6 L7 B B B B3 B4 B5 b b b b b4 H H R tz tw tc t Ls ts Hs g N N B6 Lg tw L Tabl 3.. Comparison of Masurd and Thortical Paramtrs Itms Masurd Data Thortical Valus Errors Elastic Stiffnss (kn/cm % Yild Forc (kn % Yild Displacmnt (mm % Tabl3.. Comparison of Masurd and Thortical Comprssion Strngth Adjustmnt Factors (β Strain (% Masurd β Thortical β Errors % % % B A L8 L8 C B A C Figur.. All-Stl Multi-Curv Buckling Rstraind Brac with Doubl Cors (Cross sctions ar shown in Figurs.3 and.4 Enrgy Brac Dissipation Projction Sgmnt (L3 (L (L First Transformd Sgmnt Enlargd Sgmnt (L7 (L8 Scond Transformd Sgmnt Enrgy Dissipation Brac Sgmnt Projction (L (L3 (L8 (L Scond First Transformd Transformd Sgmnt Sgmnt Figur.. Dtails of Each of Doubl Flat Stl Cor Plats of th MC-BRB

8 ts Insrt Plat tw Constraining Elmnt (Typ. tw H tw H H H tw Stl Cor Plat Latral Support Elmnt (Typ. A - A B - B Figur.3. Dtails of Sction A-A Figur.4. Dtails of Sction B-B Lw B4 L3 L L L8 L L7 L8 L L L R R R R B3 (N-@46 Ls B5 B H (N-@5 Figur.5. Dimnsions of th Flat Stl Cor Plat with Stiffnr at Both Ends L6 B tw H tw Figur.6. Dtails of th Latral Support Elmnt (rfrring to Figurs. and.3 Figur.7. Dtails of th Constraining Elmnt (rfrring to Figurs. and.3 L3 L Hs Figur.8. Dtails of th Insrt Plat Figur.9. Dtails of th Stiffnr of Sction C-C

9 Standard Loading Tst Low-Cycl Fatigu Tst Figur 3.. Loading Squnc According to AISC Provisions (5 Figur 3.. Tst St-Up of th All-Stl MC-BRB Figur 3.3. Pictur for th Bottom End of th All-Stl MC-BRB Bfor Tsting Axial Load-Dformation Curv Axial Load-Dformation Curv Axial Load (N Axial Dformation (mm Figur 3.4. Hystrtic Loops of th Standard Tst of th All-Stl MC-BRB Axial Load (N Axial Dformation (mm Figur 3.5. Hystrtic Loops of th Low Cycl Fatigu Tst of All-Stl MC-BRB

10 Figur 3.6. Pictur for th Bottom End of th All-Stl MC-BRB Aftr Tsting Figur 3.7. Ncking and Ruptur at th Bottom End of th Right Enrgy Dissipation Sgmnt of th Stl Cor During Tnsil Loading Figur 3.8. Opn-up Viw of th Bottom End of th Lft Enrgy Dissipation Sgmnt of th All-Stl BRB Aftr Tsting Figur 3.9. Opn-up Viw of th Top End of th Lft Enrgy Dissipation Sgmnt Aftr Tsting Figur 3.. Opn-up Viw of th Top End of th Right Enrgy Dissipation Sgmnt Aftr Tsting