K H A O SAT - T H | £ T K £ X A Y DI/NG
NGHIEN CU'U U'NG Xl> C O A NUT GI&A TRONG KHUNG BE TONG C 6 T T H E P DU^OI TAG DONG CCiA TAI TRONG
DONG D A T T H O N G QUA MO HINH THU'C NGHIEM
TS. T R A N C A O THANH NGQC
Trudng Dgi hpc Quoc te, Dgi hpc Quoc Gia Tp. H i Chi Minh Tdm tit: Trong nhOng nim gin diy, nhdm nghidn eO'u thudc trwdng D^i hgc Qudc ti, Dg; hgc Qudc gia Tp.Hd Chi Minh di tiin hinh nghiin c(m sw lim vi$c cOa not giO'a trong khung be tdng cdt thip dwdi tic ddng cua tii trgng ddng dit, mdt vin di dang dwoc iwu tim die bidt t$i Vidt Nam [1-4]. Bii bio niy trinh biy kit qui thi nghi$m cua hai nOt giO'a (NS, LS) trong khung bi tdng cdt thip dwdi tic ddng cOa tii trgng ddng dit. M6 hinh NS dw(?c thiit ki dt/a theo tidu chuin BS [5]. Mdt sd nhw^c diim vi ciu t^o cua md hinh NS tr<mg vide ehju tii trgng ddng dit nhw vide khdng bd tri cdt dai t^i nOt, dwg/c khic phoc trong md hinh LS nhim so sinh tinh hidu qui vdi md hinh NS. Kit qui thi nghi$m cho thiy md hinh LS cd khi ning chiu tii trgng ngang md phdng tii trgng ddng dit tdt hem md hinh NS.
1. M d d l u
Theo thing kd, td Bic chi Nam Vidt Nam cd tit ca 30 khu vyc cd thi phdt sinh ddng dit. Mdc chin ddng ndm trong khodng 5,5 - 6,8 d l Richter. Mdc chin ddng ndy du d l nhd cua bj hu hgi cho tdi phd huy hodn todn. Trong dd hai thdnh phi Idn Id Hd Ndi vd Tp. H i Chi Minh cQng ndm trong hode cdn eac khu vyc ndy. Do dd, nhilu nhd khoa hpc trong vd ngodi nude dd vd dang bdy td mil lo nggi v l hilm hpa ddng dit vd sdng thin d Vi$t Nam.
Ngodi ra, dilu ddng lo nggi nhat Id vide ehua dp dyng tidu chuin khdng chin dli vdi cdc edng trinh xdy dyng, dde bidt tgi cdc thdnh phi Idn. Tuydt dgi da s l cdc edng trinh xdy dyng d nude ta diu chua dp dyng tieu chuin khdng chin. Chi sau khi Hd Ndi vd Tp. H i Chi Minh ehju mdt s l du chin mgnh nhdng ndm gin ddy, mpi ngudi mdi bit diu nghT din.
Theo mdt s l nghidn cdu ddnh gid rui ro ddng dit edc thdnh phi Idn gin ddy: nlu xay ra d|ng dit vdi cudng dd eye dgi theo tinh todn vdp khoang 6,7 dd Richter thi 30% nhd cua se bj phd hOy cOng vdi thidt
hgi v l ngudi khdng thi ludng trudc dupe. Chju tdc ddng ndng nhlt Id nhdng khu ehung eu cQ, bdnh vi$n, trudng hpc,... do khdng dp dyng tieu chuin khang chin. Do dd nghidn edu. ddnh gid tdc ddng eOa dOng dit dli vdi ede edng trinh ddn dyng tgi Vidt Nam Id vo eOng d p bdch vd d n thilt.
Trong tit d cde togi kit elu cho cdng trinh dan dyng, kit clu khung bd tdng d t thdp dupe su dyng khd phi biln tai Vidt Nam. Trong khung bd tdng cot thdp cua cdc cdng trinh ddn dyng, nOt dim - c$t ddng vai trd vd eOng quan trpng. Cdc khao sdt gin ddy eho thiy, sy hu hgi eua nOt dudi anh hudng cua ddng dit dan din sy syp d l hodn todn cQa d tda nhd. VI thi vide nghidn edu ddnh gid khd ndng ch|u tdi trpng ddng dat cua nOt Id vd cCing d n thilt vd cap bdch. Bdi bdo ndy trinh bdy kit qua thf nghidm cua ndt gida dim - edt trong khung be tong elt thdp dudi tdc ddng cQa tai trpng ddng dit. Mdt trong nhdng khdc bidt cua 2 md hinh ndy Id hdm lupng cit dai 6 not
2. Thi nghidm
Nghidn cdu thyc nghidm trdn dli tupng thyc dem lgi kit qud chinh xdc nhlt tde d$ng cOg til trpng ddng dit dli vdi kit elu xdy dyng. Tuy nhidn do nhilu ylu t l ky thudt vd kinh t l , vide thyc hidn nghidn cdu tren dli tupng thye Id khdng kha thi. Phin Idn cdc nghi§n edu thye nghidm dd dupe thyc hidn thdng qug dc md hinh trong phdng thi nghidm.
Dudi tde dyng cOa tai trpng ngang do ddng 3lt, hd khung bj biln dgng nhu hinh 1. Nghien cdu ndy ehi tdp trung vdo vide thi nghidm vd md hinh sy Idm vide cua nOt gida. Dya vdo sy Idm vi$c cOa khung dudi tde ddng cOa tai trpng ngang nhu hinh 1, mOt nda try trdn, dudi vd mdt nda dim trdi, phai se dupe md hinh trong dli tupng thi nghidm. Dilu kidn bidn ciJa md hinh thi nghidm Id ty do d diu tnj trdn, khdp d diu try dudi vd tya dan a 2 diu dim.
34 T$p chi KHCN X§y dt/ng - so 3/2012'
.[^nMO S A I - THIET KE XAY DyNG
Hinh 1. Biin d$ng cua khung dwdi tic dung cua tai trgng ngang 2.1 M6 hinh thi nghidm
Clu tao cy thi cua dli tup'ng thi nghidm dupe trinh bdy trdn hinh 2 vd bdng 1. Md hinh thi nghidm Q[t^ ddt ten cy thi Id NS vd LS. Md hinh NS dupe lly td md hinh thyc eiia khung nhd 8 ting, dutac thilt k l theo tidu chuin BS [5]. Do thiet k l theo tieu chuin BS [5], Ididng xdt din tai trpng ngang tgi nut ndn khdng cd cit dai ndo d khu vyc nOt gida dam vd edt
efla md hinh NS. Mdt s l nhupc diem trong elu tao cua md hinh NS trong vide ehju tai trpng ngang dupe dieu chinh trong md hinh LS. Cf khu vyc nut gida dim vd edt eOa md hinh LS cd 2 Idp elt dai; md hinh LS khdng cd nli budc tgi vj'trf phia trdn nut; cit dpc Idp dudi vd Idp trdn d dim eua md hinh LS id nhu nhau;
cit dai d dim gin nOt cua md hinh LS dupe tdng cudng.
(a)M6 hinh NS (b) Iwlfl hinh LS Hinh 2. Sa do va cau tao cOa d& twqng thi nghidm 2.2 Cu<mg d$ bd tdng vi thdp
Cudng dO try bd tdng cOa md hinh NS vd LS tgi thdi dilm thi nghidm lln lupl Id 42.5 MPa vd 42.4 MPa.
Thdp trdn cd gai T10 vd T25 vdi gidi hgn chay lln lupl Id 420 MPa, 460 MPa dup-c su dyng Idm d t dpc vd elt dai cOa md hInh.
Bdng 1. Cic thdng sd ca bin cua ddi twiyng thi nghi$m
M6 hinh
NS LS
MPa 42.50 42.40
P
0.14 0.14
1.2 0.84
Lxfo cSt tinh toan,
Pm im
189.00 241.00
T9P chl KHCN XSy dimg - s6 3/2012
K H A O S A T - T H I £ T K £ X A Y D I / N G
2.3 Tai UQng tie dyng
Tai trpng thi nghidm Id y l u t l c o ban-tryc t i l p tde dung Idn d l i t u p n g thi nghidm. Trong thi nghidm ndy, cd 2 logi tdi trpng tde dyng len md hinh thf nghidm (hinh 2): tai trpng ddng vd tai trpng ngang ldp.
Tii trong dOng tic dung len cgt do p h i n trpng lupng ban thdn cua e l u kipn vd hogt tai sdn cdc t i n g tren tnjyen x u I n g sau khi dd d u o c tinh toan quy d l i thdnh ede tai trpng tdp trung. Tai trpng ddng ndy tde dung CO djnh vdo trpng tam t i l t didn ngang cua edt.
Trong thi nghidm ndy, gid trj tai trpng ddng tde dyng len cpt Id 0.14 .,4g/J (tuong d u o n g 729 kN vd 725 kN eho md hinh NS vd LS)
Tii trgng ngang i$p: Tai trpng ngang tdc dyng len k i t cau thi nghidm Id tai trpng ddng d i t d u o c quy doi.
Tai trpng ngang trong thi nghiem ndy d u p e ddt tai p h i n d i u tnj trdn. Tai trpng ndy tde dung dao e h i l u
( d l y vd kdo) vd thay doi tdng dan trong qud trinh thi nghidm.
2.4 ciu t^o h$ thong gia tii
Hd thdng gia tii dwng: tai trong ddng d edt dupe tae dung thdng qua kich thOy lye logi 300 kN. Cdc kich thuy lye ndy Id loai kich thdng tdm, dupe dgt phia trdn eua tn,(. L y c tgo ra t d kich truyin tryc tiep vdo tm, phan lyc tgo ra d u p e cdn b i n g bdi 4 thanh vit-me cudng dd eao nhu hinh 3.
H$ thdng gia tii ngang: tai trpng ngang tde dyng len k i t d u thi nghidm thdng qua kieh thuy lye loai 100 kN. Mdt dau d u a e g i n vdo tudng phan lye, dau cdn lgi d u p e n l i vdo p h i n tru tren eua md hinh tfii nghidm nhu hinh 3. Kleh gia tai ndy dupe g i n vdi mijt lye k l didn t u (load cell). Load cell truyen tin hidu vd gid tn iyc trong kich v l mdy tinh thdng qua bd thu nhdn vd chuyen doi tin higu.
Hinh 3, H$ thong gia iai dung va ngang
2.5 Quy trinh thi nghidm gid kha ndng Idm vide d u d i tde dung cua tai trpng Thdng qua hd t h i n g gia tai ddng, tai trpng ddng ngang dao chieu theo chu ky d l i vdi k i t c l u cSng d u d c tdc dyng tdng d i n den khi dd dat d u p e gid trj trinh, d ddy thf nghidm se dupe thyc hidn theo eSch ydu e l u 0.14 A^f^. Gid trj ndy d u p e g i d nguydn trong tdc dyng tai trpng ngang dao c h i l u vdi lich sd tdc s u i t qud trinh thi nghidm. V d i myc dich kiem tra ddnh dyng Idn md hinh thi nghidm nhu hinh 4.
36 Tap chi KHCN Xiy dt/ng - s6 3/2012
K H A o S A T • T H i g T K £ X A Y D I / N G
4
^ 2 Q
« 0
I "' i -2
-3 -4
- 5 • 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ChukJ
Hinh 4. L/ch s d g/a fa/ fnpng ngang (Sa dd tii ngang thay ddi theo chu fry) 2.6 Cic thiit bj do vi thu thap du' ii^u
Do ehuyin vj ngang:
Ddy Id tham so quan trpng d n do vd khong che gid trj trong qud trinh tdc ddng tai trpng ngang theo chu ky. D l do gid trj ndy, mOt d i u do c h u y i n vj LVDT vdi dd ddi do 0 - 300 m m , d d i tgi vj tri nhu hinh 3.
Do gdc xoay vi biin d^ng cit tai cic vj tr! lin ein not vi t^i not:
De xdc djnh gdc xoay t i l t didn ngang hode bien dang e l t cua mdt c l u kidn, mdt cdp dung cy do ehuyin vj dupe s u dyng d l do 3d djch c h u y i n cua 2 dilm khdc nhau trdn eCing mdt t i l t didn khao sdt. T d k i t qua do ndy vd quan hd hinh hpc chOng ta cd t h i d l ddng tinh d u p e gdc xoay hode b i l n dang d t eua d u kidn. So do bo tri t h i l t bi LVDT d l do gdc xoay vd biln dgng e l t tai cdc vj trf fan edn nOt vd tai nOt dupe trinh bdy nhu hinh 5. N h u trinh bdy d hinh ndy, 5 cdp LVDT dupe s u dyng d l do b i l n dgng d t , 6 cdp LVDT dupe s u dyng d l do gdc xoay tgi cdc vj trf khdc nhau cua d i m vd 4 cdp d u p e s d dyng eho try.
Hinh 5. So dd bd tri dung cu do gOc xoay vi bien d^ng dt Tap Chi KHCN XSy dt/ng - s6 3/2012
Do biin d^ng trong cdt thip:
D l k i l m tra dd b i l n dang eua e l t thdp trong qud trinh thf nghidm, edc cam b i l n didn trd (strain gauges) dupe ddn vdo cdc thanh e l t thdp dpc cua d i m vd c$t tdp trung tgi edc vj tri md mdmen u l n dgt gid trj Idn n h l t , ciling vdi mdt s l dupe ddn p cde e l t dai tgi v) tri ndt d i m - edt. Vi tri cOng vdi k i t qua cua vide do bien dgng trong e l t thdp se d u p e trinh bdy chi t i l t d p h i n sau cOa bdi bdo.
2.7 Khi ning tinh toin cua mo hinh thinghi§m Bang 1 tdm t i t cde thdng s l thiet k l cda 2 md hinh thi nghidm. Nhdng thdng s l ndy d u o c tinh d u a vdo cudng dO t h y c t l cija be tdng, cot thdp vd thdng qua tidu chuan ACI-ASCE 352 [6]. Ti s l mdmen gidi hgn chdy gida try vdi d i m eua md hinh NS vd LS l l n lupt Id 1.2 vd 0.84. Lye d t tinh todn d y a theo mdmen gidi hgn chay tai try hode dam (gid trj nao cho lyc d t nhd han) cua mo hinh NS vd LS i l n luot Id 189 kN vd 241 kN.
3. K i t q u d t h i n g h i f m
3.1 Quan h$ lyv cit - chuyen vi ngang Quan hd luc d t - ehuyin vj ngang eua md hinh thi nghidm NS d u p e h i l n thi d hinh 6a. Md hinh NS khdng dgt d u p e kha ndng tinh todn (nominal capacities) trong s u i t qud trinh thf nghiem. Trong d 2 c h i l u d l y vd kdo, lyc d t Idn n h l t d try dgt d u p e Id 133.5 kN tgi dd Idch tang (DR) 2%. Md hinh thi nghi$m NS bi suy giam hon 2 0 % kha ndng chiu lyc d t tgi DR 3.5%. Tgi thdi d i l m ndy md hinh d u p e xem n h u dd bj phd hGy hodn todn.
37
K H A O SAT - THl^T K^ XAY DU'NG
DOI?chtangDR(%)-5 0% -4 OK -3 0% -2.0W -lOM 0 0% 10% D$l?chtangDR(%)
-5 0% .4 0% -3,0% -2.0% - 1 0 % 0 0% 1 0 % 2 0% 3.0% 4 0 » 5.0K
• 16i -13S -lOS -75 .45 -15 15 45 75 105 13S 165
ChuySn vj ngang (mm)
-165 -13S -105 -75 .45 -15 15 45 75 105 135 165
Chuyen vj ngang (mm)
(a) M6 hinh NS (b) Mo hinh LS
Hinh 6. Quan h$ luc cat - chuyen vj ngang cOa md hinh thi nghidm Quan hd lye d t - chuyin vj ngang cua md hinh
thi nghidm LS dyp'c thi hidn d hinh 6b. Trong e l 2 chilu dly vd kdo, lyc elt Idn nhat d try dgt dupe Id 145.0 kN tgi dd Idch ting 2.5%. Md hinh chi dat dupe 60.2% khd ndng tinh todn (241 kN). Ca 2 md hinh khdng dgt kha ndng tinh todn trong suit qud trinh thi nghidm, dilu ndy cho thay d 2 md hinh dilu bj phd hOy tgi nOt trudc khi dim hode edt dat tdi gidi han
deo. Lye d t Idn nhlt eua md hinh LS Idn han 6.7%
so sdnh vdi md hinh thi nghidm NS. Tgi dd Idch ting 4.0%, md hinh LS ehi mit 15% kha ndng ehju tai trpng ngang. Dilu ndy eho thiy vide d i tiln d u tao so vdi thilt k l theo tieu chuin BS [5] dde bidt Id vide bo tri cit dai tgi nut Idm tdng kha ndng ehju tai trpng ngang vd biln dgng deo cua md hinh.
3.2 Biin d^ng cua cot thdp
3000
•g- 2000 -2- ISOO 1 1000
-500
^*' ^""'^'^ \\
- ^ 0 . 0 0 2 5
•—0,005 -.(-0.02 - ^ 0 . 0 2 5
3000
2000 ISOD lOOD SOO 0 -SOO
% ^,^^'^!^xz^^l^\
-<-0.0025 -^0.00J -«-002 -^002S
ri c ^ eim b i ^ difn trd irSn <h. lh£p dpc ldp dudi is dim (mm) V| tri cic eim b i ^ di$n trd trSn c^t th6p dgc ldp dudi d dim
(a)M6 hinh NS (b) Md hinh LS Hinh 7. Biin d^ng cua cdt thep dgc Idp dudi d dim tai vj tri nut Hinh 7 a, b thi hi$n biln dgng cua d t thdp dpc
Idp dudi d dim tgi vj tri nut cho md hinh thi nghidm NS vd LS. Bien dgng elt thdp dpc eCla try tgi vj trf nut eho md hinh thf nghidm NS vd LS dupe trinh bdy d hinh 8a, b. Cdc gid trj ndy dupe thu thdp thdng qua edc cam biln di$n trd dupe gin vdo cot thdp eua md hinh thi nghidm. Hidn tup'ng chay dec xult hidn d elt thdp dim eua md hinh NS tgi dd I$ch ting 2.0%. 6"
nhdng dd Idch ting tilp theo, chdy deo xult hidn ci trong phin d t thdp d nOt. Thdp d try vin d trong miln ddn hli trong suit qua trinh thi nghi$m. Dilu ndy dupe gidi thich do mdmen khdng uln d dim nhd hon try cho md hinh NS (bang 1), do dd tn,i vin nim trong miln ddn hli.
Trgng thdi ehly ddo khdng xult hidn d elt thdp dpc Idp dudi d dim cua md hinh LS trong suit qui
38 T^p Chi KHCN Xiy dijng - s6 3/2012
K H A O S A T • THier KE XAY DU'NG trinh thi nghidm. So vdi mo hinh NS, mo hinh LS difpc thl^t k4 c6 nhl4u cot th^p dpc ldp dual 6 dSm.
Do 66 m6men khing u6n 6- dim cOa mo hinh LS cao hon so vtS-i m6 hinh NS. Momen khing u6n d try nho
hen d4m cho m5 hinh LS (bang 1), do 36 chay deo cot thip dpc & trg l i diAu khOng thi trinh khoi (hinh 7b). Hi$n twqmg chay deo xuat hi^n & cot thep tru cua mo hinh LS t^i 36 l*ch tang 3.0%.
I
1 "tt"
1 200 -8
B .200
1 400
•> « 0 0
W / / L
- • - 0 005 - " - 0 , 0 1
- * - 0 . 0 2 5 ! - • - 0 . 0 3
!
-•-0.005 -"-0.01- « - 0 ^ -•—003
\ N S- / / k
500 1000 1500 2500 MOO 35O0 1500 2000 2500 3000 3500
Bi^dgngfxlO'^
(a) M6 hinh NS
Hinh 8. Biin d^ng cOa cdt thip dgc d tnj t^i vi tri nOt 3.3 Qui trinh hinh thinh vet nui
Khi md hinh NS dupe gia tdi din dd lech tang ± 0.5%, mdt s l v l t ndt do mdmen udn bit diu xult hidn d d dim vd try (hinh 9a). V l t ndt logi ndy xult hidn nhilu hon tgi dam so vdi try do mdmen khdng uln eua dim nhd han cua try (bdng 1). Trong qud
Bionljiig(xlO-^
(b) Md hinh LS
trinh gia tai din dd Idch tang ± 0.75%, vet ndt xien diu tidn xult hidn d vj tri nut. Tgi dd Idch ting 3.5%, khd nhieu vlt nut xidn xult hidn tgi vj tri nOt, dieu ndy ddn din kha ndng ehju tai trpng ngang cua md hinh bj suy giam. Tgi dO Idch ting nay, sy dp vd cua be tdng d nut cung bit diu xult hign.
au Kl
(a) Mfl hinh NS (b) M6 hinh LS Hinh 9. Vit nut cua mo hinh thi nghiem tai do lech ting ±3 0%
Gilng nhu md hinh NS, v l t ndt do mdmen uln bit diu xult hl$n a ca dim vd try cua md hinh LS trong qud trinh gia tai den dO Idch ting ± 0.5% (hinh 9b). v l t ndt xidn d vj tri nOt xult hidn diu tien tgi dd Idch ting ± 0.75%. Tgi dO Idch ting 4.0%, khd nhilu vlt nut xidn xult hidn tgi vj tri nOt, kha ndng chju tai trpng ngang cOa md hinh bit diu suy gidm. Tuy nhidn do cd d t dai d nOt, tgi thdi dilm ndy md hinh LS ehi T9p chi KHCN Xiy dt/ng - s6 3/2012
suy giam 14% kha ndng chju tai trpng ngang, trong khi dd eOng thdi dilm ndy NS da suy giam trdn 20%
kha ndng chju tai trpng ngang.
4. Kit luan
Sy Idm vide cua nOt gida dudi tdc dyng eua tai trpng ddng dit dd dupe khao sat chi tilt bing phuang phdp thye nghi$m trong bdi bdo ndy. Sau ddy Id m|t
39
K H A O S A T - T H I ^ T Kt X A Y DLfNG
so k i t ludn d y a trdn k i t qua thye nghidm da dupe thye hidn:
D l i vdi md hinh NS d u d c t h i l t k l theo tidu c h u i n BS [5], md hinh m i t tren 20% kha ndng chju tai tgi dd Ipch tang 3.5%; trong khi dd tgi thdi d i l m nay md hinh cai t i l n LS chi m i t 14% kha nang chju tai trpng ngang.
Vide cai t i l n d u tgo so vdi thiet ke theo tieu c h u i n BS [5] dde bi$t Id vide bo tri d t dai tgi nut Idm tdng khd ndng chiu tai cua md hinh, cung nhu tdng kha ndng b i l n dgng trong vCing deo cua md hinh.
Thi nghidm ndy chi khao sdt s y thay d l i ve cau tgo cua md hinh, anh hudng cua cdc tham s l khac nhu tai trpng ddng d n phai d u p e t i l p tue nghien edu thdng qua md hinh thyc nghidm hode tinh todn.
TAI LigU THAM K H A O
,. BING LI, T-C PAN and CAO THANH NGOC TRAN.
"Effects of Axial Compression Load and Eccentricity on Seismic Behavior of Non-seismically Detailed Interior Beam-Wide Column Joints". ASCE Joumal of Structural Engineering, Vol.135, No.7. July 2009.
2. BING LI, CAO THANH NGOC TRAN and T-C PAN.
"EjqDerimental and Numerical Investigations on Seismic Behavior of Lightly Reinforced Concrete Beam-Column Joints'. ASCE Joumal of Stmctural Engineering, Vol.
135, No. 9, September 2009.
3. BING LI and CAO THANH NGOC TRAN. "Seismic Behavior of Non-seismically Detailed Interior Beam-Wide Column and Beam-Wall Connections". ACI Structural Joumal Vol. 106, No. 5, Sept-Oct 2009.
4. BING LI and CAO THANH NGOC TRAN. "Seismic Behavior of Reinforced Concrete Beam-Column Joints witti Vertical Distributed Reinforcemenr. ACI Stmctural Joumal, Vol. 106, No. 6, Nov-Dec 2009.
ii. BS 8110, "Stmctural Use of Concrete, Part 1. Code of Practice for Design and Constniction", Bntish StandanS.
1999.
6. ACI-ASCE Committee 352, "Recommendations for Design of Beam-Column Joints in Monolithic Reinforced Concrete Stmctures". ACI Manual of Concrete Practice, part3,ACI352R-91, 1-21 (1996).
Ngiy nh^n bai: 29/8/2012
4 0 T^p chi KHCN Xay dt/ng - so 3/2012
