KHOA HOC-CdNG NGH|
Anh htfofng cua dang lien ket ngang den mo-men uo'n trong dam ban cau be tong cot thep lap ghep
• TS. NGUYEN DUY TIEN Trudng D§i hgc Giao thdng vdn tdi
• ThS. VLfdNG DiNH T O N G Ban Qudn /ydtfdn 85- B0 GTVT
Tdm tdt: Bdi bdo nghien ctfu dnh hudng eua ede dgng Udn kit ngang din md-men uon idn nhit do hogt tdi sinh ra trong dim ban ciu bd tdng cit thdp lip ghdp khi tinh theo phuong phdp chi din trong Tidu chuan AASHTO LRFD vd phUdng phdp phan tCr hQu hgn (PTHH). Kit qua cho thiy, cdc edng thUc tra bdng tinh h$
si phdn bihogt tdi theo AASHTO LRFD cho kit qua khd thidn vS an toan hon so vdi cdc phUdng phdp tinh bing md hinh PTHH. Viic si? dijng thdm ban be tdng cit thdp di tgi chd ho0e edp dtf tfng Itfe ngang kit htfp vdi dim ngang idm gidm ddng kegid tri md-men uin Idn nhit trong dim bdn so vdi trudng hgp chi sCr dijng khda ching cit giffa cdc dim ban. Trong trudng hgp khdng hgn chi chiiu cao kiin trOc cd the xem xdt kit hgp ed bdn bd tdng cot thdp di tgi chd vd dtf Ung Itfc ngang di tdng cudng phdn bo tai trgng glQa cdc dam ban.
Tii khda: Udn kit ngang, phdn bi tai trgng, ciu dim bdn, bi tdng cit thdp, lip ghdp.
Abstract: This article clarifies the Influence of transverse connection on the maximum bending moment in precast slab girders of concrete bridge due to live loads, calculated according to AASHTO LRFD provisions and by finite element method (FEM). The result comparison shows that the formulas by AASHTO deliver more conservative values than that by using FEM.
The additional cast-in-situ concrete overlay or transverse prestressing through diaphragms reduces the maximum bending moment in slab girders considerably compared to that In the ease of using only shear keys ttetween slab girders.
In case the construction depth is not limited the combination of additional concrete overlay and transverse prestressing to strengthen live load distribution over slab girders could be considered.
Keywords: Transverse connection, load distribution, slab girder bridge, reinforced concrete, precast.
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1. D$t van d l
Clu dim bdn be tong edt thdp lip ghep nhjp gidn ddn dd dupc phdt trien d nhilu nude tidn tiln vdi cdc Uu diem nhu chilu eao kiln true thap, tfnh tham my eao, d l thi edng vd thi edng nhanh, ehi phf duy tu bdo dudng thap, vi vdy dg^c sQ dung rong rdi trong ede khu vue do thj hodc nhQng ndi ydu elu ehilu cao kiln true thip.
Theo clu tgo cd the cd cde dgng eau bdn mdt edt lap ghep hogc lidn hdp vdi bdn bd tdng cdt thep dd tgi ehd. Mat eat ngang dim bdn thudng cd dgng bdn dge, bdn rdng hode dgng hop. Theo phUdng ngang, edc dim bdn ed the dUpc lidn kit vdi nhau bing ede khda ehdng cit, bing bdn be tdng cdt thdp dd tgi chd, cdt thdp dg Qng lgc ngang hode kit hdp edc bidn phdp trdn. Tidu chuan AASHTO LRFD cho phep tfnh todn trgc tiep hd sd phdn bd hogt tai ddi vdi mpt sd dgng eau dim bdn lap ghdp nhu clu dim bdn lidn kit bing khda chdng edt, bang ban be tdng edt thep do tgi chd hogc dg Qng IQc ngang, tuy nhidn dnh hUdng cua dim ngang thudng khdng dupe xdt din.
Bai bdo se nghien cQu dnh hUdng eua cac dgng lidn kit ngang den md-men udn Idn nhit do hogt tdi sinh ra trong dim bdn clu be tdng cdt thdp lip ghdp khi tfnh theo phUdng phdp chl ddn trong Tidu chuin AASHTO LRFD vd bing m6 hinh PTHH nham lam rd hdn hi^u qud phdn bdt^i trpng efla cdc dgng lien kit ngang thudng dung trong cau dam bdn ldp ghep.
2. Cdc dgng lidn kit ngang thUdng dung trong cau d i m bdn b§ tdng lip ghep trdn dUdng 6 td
2.1. Lidn kit bing khda ching cit Khda chdng eat dpc clu liSn kit cdc dim bdn liin k l cho phep truyin lgc eit giuta edc dim.
Khodng cdch giQa cac dam thudng dUdc llp^dly
bang vdt lidu vQa, keo epoxy hode bd tdng edt si?i
(Hinh 2.1). Cd 2 logi khda chdng c i t dUpc sQ dyngehfnh Id khda chdng ban phin khi khe hd theo
ehilu eao giQa hai dam liin k l dUdc lip mdt phin
vd khda ehdng cat todn phin khi khe hd dU(?c lip
todn bd theo ehilu eao dim (Hinh 2.2).
KHOA HOC-CdNGNGHi So 4/2016
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Hinh 2.1: VI dtf m0t cat ngang cau dam ban Idp ghdp iien kit bing khda ching cit
'Mm
Hinh 2.2: Khda chong cat bdn phan (trdi) vd khda chong dt todn phdn (phai)
Dgng lidn kit ndy eo uu dilm la thi cdng dd dang vd nhanh chdng; gidm ttnh tdi nhd khdng sfl dung bdn bd tdng edt thep mdt elu; ehieu cao kiln true thip, kit cau thanh mdnh tdng tfnh thim my cho edng trinh eau. NhUde dilm eua loai k i t cdu nay Id de xdy ra v i t nQt taeh dpc eau tgi vj trf khda ehdng cat do chdnh Ideh dd vdng glQa cdc dim, d i n tdi thim nude qua mdt elu va khe ndi glQa cde dam bdn. Hu hdng cfla khda ehd'ng c i t cung Idm gidm khd nang phdn bd deu hoat tdi.
2.2. Lien kit bing khda ching cit va ban bi tdng cit thdp di tgi cho
Mat eat npang ket eau nhjp logi ndy bao gdm hai thdnh phdn: Dim bdn lip ghdp vd bdn mdt elu do tgi ehd lidn kit vdi dim bdn thdng qua e^t thdp chd {Hinh 2.3). Cdc dam bdn dUdc lien kit vdi nhau bang khda chdng eat tUdng tg nhu trong logi eau d i m bdn dUdc trinh bdy d tren.
Hinh 2.3: VI di^ mgt cat ngang eiu dim bdn tip ghdp iien kit bing khda ching edt vd ban bd tdng Cdt thdp di tgi eho
Bdn mat cau be tdng edt thep dd tgi chd ed tde dyng ngdn nUde tham xudng ben dUdi vd phdn bd lgc deu hdn cho ede dim bdn, Tuy nhien, bdn mdt clu eung Idm tdng trnh tdi bdn thdn vd chilu eao kiln true eua k i t c l u nhjp.
2.3. Lidn kit bing edp dtf tfng itfe ngang Nhd cd lien kit ngang tai ede vj trf glQa nhjp, trdn gdi vd VA nhjp dudi dang edp dg Qng lge edng sau dupe ludn trong ede dng gen d§t sdn, cdc dim bSn dupe lidn k i t vdi nhau thanh mot khdi thdng nhit ('HJn/7 2.4;. Thdng thudng hay sQ dgng cdc bd tao thep xoan 7 sdi eudng dp eao d l cdng dg Ung lge. Khda chdng eit tgi vj tri mdi ndi dpc dupe bo trf g i n hit chilu cao dam (Hinh 2.5).
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B B I JBBBBB B
Hinh 2.5: Vi dtf cau tgo mii ndi bang dtf Ung Itfc ngang cdng sau
Dg Qng ige ngang cdng sau cd tae dgng Idm tang khd ndng phdn bd tdi trpng theo phUdng ngang va giam thilu sp ehdnh leeh dd vdng giQa ede dim. Cdp dp Qng lge thgdng dQde edng sau khi thi cdng khda chdng c i t de han e h i Qng suat keo xud't hidn gdy nen nQt dpc tgi cdc mdi ndi ndy.
Cdc vet nQt dpe cau vd thim nude tgi cac vj trf mdi ndi cd t h i xdy ra trong trudng hdp thilt k l thilu dg Qng lgc ngang cau.
Dgng ket eau nhjp nay thudng ed ket eau thanh mdnh, tfnh thim my eao, thi cdng nhanh, dUdc sQ dgng rdng rdi vd phd bien nhat d nhQng elu cd nhjp vQa vd nhd, thong thudng tU 9m den nhd hdn 35m.
3. lUlo-men udn trong dam bdn Ung vdi cac dgng lien ket ngang khdc nhau
0 l nghidn cQu dnh hUdng eua cde dgng lien kit ngang din md-men udn Idn nhit xuit hidn trong cdc kit eau dam bdn lap ghep 6 trdn trong phan nay mdt kit clu nhjp gidn ddn dien hinh nhu tren Hinh 3.1 vdi ba dgng lien kit ngang nhU & tren
diSdc dua ra phdn tfch. Kit eau nhjp cd chieu ddi L= 30m, mat cit ngang gdm 10 dam bdn, bd trf cdch nhau 1,2m. Mdi dam bdn cd ehilu cao Im, b l ddy sudn 0,15m vd be day cdnh 0,19m. Md-men udn Idn nhit trong dim bdn dQdc tfnh todn theo ch? dan trong Tidu ehuIn /VASHTO LRFD [1] vd bing md hinh PTHH dUdi tde dung cfla hoat tdi HL-93. Kit qud dupc trinh bdy d cde phin tilp theo.
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Hinh 3.1: Mgt cit ngang kit eau nhip dam ban ldp ghdp dugc phan tieh
3.1. Trudng hgp 1 • Ciu dim ban lip ghdp lien kit bing khda ching dt
Hd sd phan bd hogt tdi dupe tinh theo eh? ddn cua Tidu chuin AASHTO LRFD 0. He sd phan bd cho dam trong dUde tfnh theo cdng thQc:
Hinh 2.4: VI dg mdt eat ngang eiu dim ban iip ghdp iidn kit bing Dl/L ngang
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KHOA HOC - C d N G NGHETrong 66:
Z) = 300{n.5-Afj+L4Aft(l-0:2O')
L 30
=>Z) = 3616.46
Hd sd phdn b d cho dam ngodi dUde tfnh theo cdng thQc:
g^^^ = e.g^"' = 1.136 x 0.332 = 0.377 Vdi e = 1.125 + d^/9100 = 1.125 + 100/9100
= 1.136
Md-men udn Idn nhat do hogt tdi sinh ra trong dam bien dUdc xde djnh bang each dgt tdi len dudng dnh hudng md-men giQa nhjp roi nhan vdi he sd phdn bd da tfnh d tren. K i t qud dUdc tdng hpp trong mgc 3.5.
3.2. Trudng hgp 2 - Ciu dim ban iip ghdp lidn kit bang khda ching cit va ban bd tdng cit thdp do tgi chd
Hd s d phdn bd cho hogt tdi dupc tfnh theo edng thQc:
- Trudng hpp chat tdi 1 Idn xe:
Ddm trong:
gH-kl-
Trong dd:
k^25{N,) >1.5
khdo gid tri cfla d g Qng luc theo k i l n nghj cfla Tidu chuan A A S H T O LRFD [1],
SCf dgng phgdng phap dam lidn tye tren gdi , ddn hoi nhu trong [3] tfnh dUdc he s d phan b l hoat tdi Idn nhat ddi vdi d i m trong v d d i m bien la 0,282. Md-men udn Idn nhd't do hogt tai sinh ra trong dam dUpc tdng hpp trong muc 3.5.
3.4. Xdc dmh md-men uon Idn nhit trong dim ban bing phdn tich md hinh PTHH
SQ dgng p h i n m i m Midas/Civil d l md hinh hda ket cau va xdc djnh md-men udn Idn nhat trong d i m ban trong 3 trudng hdp neu trdn. Cac khda ehdng cat dUdc md hinh dudi dgng edc lidn k i t dan hdi elastic link (Hinh 3.2). Bdn be tdng cot thep dd tgi cho vd dam bdn lap ghep dupc coi la hen k i t cQng vdi nhau (Hinh 3.3). Dg Qng lgc ngang dQpe md hinh bang cae phan tfl cap dg Qng lgc nam trong d i m ngang theo phUdng ngang cau (Hinh 3.4). Ket qud tfnh todn md-men udn Idn nhit trong d i m bdn trong 3 trudng hdp dUdc tdng hpp trong mgc 3.5.
e = l 1 2 5 + — ^ 9100
- Trudng hpp c h i t tdi 2 Idn xe hoae n h i l u hdn:
Dam trong:
D i m bien:
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Hinh 3.2: Md hinh lien kit ngang trudng hgp 1 bing phin mem Midas/Civil
Hinh 3.3: Md hinh iidn kit ngang trudng hgp 2 bing phan mem MIdas/Clvil
TQdng tg nhu d tren ttnh ra dUdc he sd phan bd Idn n h i t eho d i m trong vd dam bien i i n Igpt Id 0,274 va 0,31. Md-men udn Idn nhat do hogt tdi sinh ra trong d i m bien dupe tdng hpp trong mye 3.5 3.3. Trudng hgp 3 - Ciu dim ban lap ghdp lidn kit bing cdp dtf Ung Itfc trong dim ngang
De ddm bdo todn bp k i t cau nhip dupc lien k i t vdi nhau thdnh mot khdi thdng nhat thdng qua cdp d g Qng lgc ddt trong d i m ngang cd t h i tham
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Hinh 3.4: Md hinh lidn kit ngang trudng h<fp 3 bing phin mem Midas/Civil
KHOA H O C - C O N G N G H I
3.5. Ting hgp vd nhgn xdt
K e t q u d tfnh t o d n m d - m e n udn ldn nhat trong d i m b d n trong 3 t r u d n g hpp ndu trdn theo chT d i n cfla T i d u ehuan A A S H T O LRFD vd bang m d hinh PTHH dUdc trinh bay n h g trong edc bdng 5 dudi.
So sdnh ede ket q u d tfnh todn ed t h i t h i y : - C h d n h ideh m d - m e n udn tfnh dupc theo hai phUdng p h d p thay ddi tdy theo trudng hpp lidn k i t ngang x e m xet {Bdng 3.1). TrUdng hop 1 ed s g chdnh lech Idn n h i t (14,6%) vd trudng hdp 3 cd s g ehdnh leeh n h d nhat (1,2%). D i l u ndy the hidn ede eong thQc tfnh hd s d phdn b d hogt tdi theo A A S H T O L R F D k h d thidn v l an todn hdn so v d i phuong phdp phan tfch bang md hinh P T H H .
- A n h h u d n g efla c d c logi lidn k i t ngang d e n gid trj m d - m e n udn Idn nhat trong d i m ban Id ro rdt (Bing 3.2). TUdng Qng vdi hai phQdng phdp tfnh theo eh? d d n efla A A S H T O LRFD v d bang md hinh P T H H , vide sii d g n g thdm bdn be tdng edt thep d d tgi ehd da lam gidm gid trj md-men udn Idn nhd't x u d n g tUdng Qng Id 17,5% vd 11,7%.
Viee sQ d g n g cdp d g Qng lgc ngang k i t hpp vdi d i m ngang lam gidm dupe md-men udn Idn n h i t tUdng Qng Id 2 4 , 9 % vd 1 3 , 1 % so v d i trgdng hdp ehi s f l d y n g khda ehdng cat giQa cde d i m bdn.
- Vide si!f dgng them bdn be tdng edt thdp dd tgi c h d Idm tang lien k i t ngang giQa cac d i m bdn vd gidm dUdc ddng ke md-men udn Idn n h i t do hogt tdi trong d i m ban, tuy nhidn Igi Idm tdng e h i l u eao k i l n true eua k i t e i u nhip Idn (khodng 15cm) vd t d n g tTnh tdi ket e l u nhjp. Vide sQ dgng d g Qng ngang k i t hpp vdi d i m ngang cung lam gidm dupe d a n g k l md-men udn Idn nhat trong d i m b d n , d d n g thdi khdng Idm tdng ddng ke e h i l u eao k i l n true v d tTnh tdi ket cau nhjp.
Bang 3.1. Kit qua tinh md-men uin Idn nhit trong dim ban theo haiphudng phdp
So 4/2016
A A S H T O LRFD v d bang md hinh P T H H . Ket q u d cho thay, edc cdng thQc tfnh hd s d phan b d hogt tdi theo A A S H T O LRFD khd thien v l an todn hdn so vdi phuong phap phan tfch bang md hinh P T H H . Vide sQ dgng t h e m ban bd tdng cdt thep d d tgi chd hogc cdp d g Qng lgc ngang k i t h p p vdi d i m ngang Idm gidm dang ke gia trj m d - m e n udn ldn nhd't so vdi trUdng hpp ch? sQ dgng k h d a ehdng edt giQa cac d i m b d n . Trong trudng hdp khdng han c h l chieu cao kien true cd the xem xet k i t hdp ed bdn be tdng cdt thdp d d tai ehd v a d u Qng lge ngang de tdng CQdng phdn b d tdi trpng glQa ede dam ban •
T a i l i g u t h a m k h d o
[1]. AASHTO LRFD Bridge Design Specifications, Si unit, 2007.
[2]. National Cooperative Highway Research Program (NCHRP) Synthesis 393 (2009), Adjacent Precast Concrete Box Beam Bridges:
Connection Details, Transportation Research Board, Washington, D.C,
[3]. Nguyen Viet Trung, Hoang H a , Nguydn Ngpc Long (2011), Ciu be tdng cot thdp, N X B . GTVT, H d Ndi.
N g a y n h d n b a i : 7/3/2016 N g a y c h i ' p n h d n d a n g : 28/3/2016 NgUdi p h d n b i d n : T S . B i j i T i e n T h a n h
T S . N g o V a n lUlinh
Pbmnig phdp linh T r u i n g h f p 1 A A S H T O L R F D 1 l l 5 a k N m
P T H H 98J kNm Chenh Ifcb giOa 2 , 14 h°'
phinms phap 1
T n r i m g hifp 2
367 kNm 8.6%
TririruB l i W 3 864 kNm S541eim 1.2%
Bang 3.2. Chdnh Igch md-men uin Idn nhit trong dim ban Ung vdi edc trudng hgp
PhuoDg p h i p linh A A S H T O L R F D Chfiih I M i giam PTHH C h m h l M h g i u n
T n i d n g h n > l 1150 kNm 0 983 kNm
0
Tnrdng bifp 2 949 kNm
17.SM 867 kNm
117%
T n r t n g h g p S 864 kNm
24.9%
SS4kNffl 13.1%
4 . K i t l u $ n
Bdi bdo da so sdnh md-men udn Idn n h i t do hogt tdi sinh ra trong d i m ban bd tdng l i p g h d p khi tfnh todn theo eh? d i n cfla Tidu e h u I n
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