'9ttt KHOA HOC - CONG NGHE
MO HINH HOA VA PHAN TICH UfNG XU CUA VUNG CHIU Lire CUC 8 0 TRONG KET CAU CAU BE TONG
GS.TS. NGUYEN VIETTRUNG, NCS. LEDAC HI^N, ThS. BUI CONG DO - Khoa COng trinh
Trudng Ogi hgc Giao thong vdn tai
Tdm tat: Phin dau bai bao nay gidi thigu ting quan vi vung chju Iyc cue bd trong kit cau ciu bi tong cung cac phwcmg phap phan tich. Phin chinh cua bai bdo di c$p din cac van di lien quan mo hinh hinh hda va tinh toan vung cue b^ nhw: mo hinh vat lieu, md hinh phin tw huv han, phwang phap lgp.
tieu chuin hdi ty... Tirdd danh gia viec dng dung phin mim Midas FEA trong mO hinh hda va phdn tich wng xt> ctia viing chju Iyc eye bd trong kit cau ciu be tdng.
Abstract: The begin of this article to present an ovetview of the local stress area for concrete bridge structure and the methods of analyzing. The main part of the paper refers to the issues related modeling and computational modeling local stress areas such as material models, finite element modeling. Iteration methods, convergence criteria ... From that assessment applying Midas FEA software for modeling and analyzing the behavior of the local stress areas for concrete bridge structure.
1 . TONG QUAN
Trong qud trinh thi cOng vd khai thdc edc cOng trinh cau be tOng hi$n nay, cde hu hong phdt sinh tgi cdc khu vyc chju Iyc eye bO nhu: vj tri dgt gii tren dam, tm, vj tri cua cdc neo cdp dy dng Iyc, diu dim cdt khac,... chiem mOtty 10 rat p h i biin. Cdc hu hong nay kit hpp vdi cdc tdc nhdn khde se Idm anh hudng nghiem trgng den dO an todn, dO ben va khd nang khai thac eung nhu tuoi thp cua cOng trinh.
ViOc thiit ke chi tiet vung ehju Iyc eye bO nhdm trdnh cdc pha hogi khi cOng trinh Idm viec Id mOt yeu ciu tat yiu. Qud trinh thiet ke phai dya tren cdc phan tieh, tinh todn chi tiet, hpp ly vdi dg chinh xdc cin thiit nhdm mo ta day du ve dng xu eua kit cau be tOng trong vung eye bO-
Vung chju Iyc eye bO (hay cdn gpi la vung D) co t h i dupc hieu la
Hinh 1. Cdc hw hong thyc te
nai md kit cau khong iien tuc v i mdt hinh hgc hodc tTnh hgc. Sy khong lien tyc v i mgt hinh hpe xdy ra khi kit cau eO sy thay doi dot ngOt v i hinh dgng hoge kich thude eua mOt bO phgn. Cdc vj tri cat khae tgi dau dam Super T, vj tri vai ke bdn qua dp la nhung vi dy dien hinh cho dgng khOng lien tue ndy.
Sy khOng lien tyc ve mgt tTnh hgc xuat hien tgi nai co Iyc tgp trung Idn trong mOt phgm vi nho
cua ket edu nhu vj tri tgi neo cap dy dng Iyc hoge cap day vang, edc vj tri tai goiciu.
Crng suat tgp trung Idn, thay doi ca ve hudng vd gid trj. Trang thdi dng suit Id da trye. Vgt ligu lam vigc ro tinh phi tuyin; cdc vit nut xuat hign Idm thay doi trgng thai chju luc eua kit eau.
ThOng thudng viing D dupc gia djnh keo ddi tren mOt khoang bdng chieu eao ciu ki$n ve moi phia tu diim dgt cdc tai trgng t|p
mm
KHOAHOC-CONGNGHE # # # J
trung eua cdc phan lye goi hodc edc vung co mgt cdt hay hudng thay doi dOt ngOt
Cdc phuang phdp p h i bien hiOn nay:
- Phuang phap dam cao.
- Phuang phdp dya tren mo hinh ehong vd gidng.
- Phuang phdp phan tu huu han (PTHH).
Phuang phdp PTHH cho phep mO phong day du tinh chit hinh hpe, trgng thai Idm viec cung nhu cdc dng xu chi tiet eua vung D.
Cde kit qud cua phdn tieh PTHH khOng chi dupe su dung eho thiit ke chi tiet md cOn eO t h i la ea sd cho cdc phuang phdp khac. Vi dy, ede ket qud ve dong dng suit dOng d i de xuat mo hinh he thanh hpp ly trong phuang phdp"chong vd gidng".
Vdi sy phat triin eua khoa hpe mdy tinh, cdc phin mem tinh todn phan tu huu hgn da trd thdnh cong cy khong t h i thiiu cua ede ky su trong vige mO hinh hoa, tinh todn kit cau nOi chung vd vung ehju lye eye bO ndi rieng nhdm dap dng cac ydu ciu ngay cdng khdt khe trong thiit ke hien dgi.
2. CAC VAN DE CAN XEM X^T KHI PHAN TiCH
Nhu da de cgp d phin ting quan, phuang phdp duac lya chpn de su dyng trong phan tieh vung eye bO cua kit ciu be tong cot thep la phuang phdp phan tu huu hgn (PTHH) kit hpp vdi sy xem xet qud trinh lam vigc phi tuyen cua cac v^t liOu khi ehju tai trpng.
De c6 dui^c mO hinh dung ddn va phu hpp vdi sy Idm vigc cua kit ciu so vdi thyc t i can nim ro
ve ly thuyet mo hinh hoa vd phdn tich PTHH ciJng cde nOi dung:
- Cac nghien cdu ve vat ligu vd cac mo htnh vdt ligu trong ket cau be tOng cit thep.
- Cdc nghien cuu ve mo hinh phin tu d i mo ta kit eau be tOng cit thep.
- Cdc phuang phdp su dyng trong phdn tich PTHH phi tuyin cho k i t c i u be tOng cit thep.
Hign nay, eo rat nhieu san pham phin mem cO t h i dupc su dung de mo hinh hda vd tinh todn viJng ehju Iyc eye bO nhu ANSYS, Midas/FEA, ATENA, LUSAS,...
MOi phan mim deu co khd ndng cung nhu uu nhupc diem khac nhau. Do do, vigc lya chgn phan mim can dya trdn bdi todn cy the cung nhu cdc tinh ndng ma phan mem do c6 the ddp ung.
- Dupe phdt trien bdi tap dodn Midas/IT, co dO tin edy cao ve kit qua tinh toan.
- Ho tra tot vigc mo hinh hoa va phdn tich vung cue bO vdi nhiiu cOng cy xuit sdc.
- Moi trudng lam viec than thign, d l su dyng.
- CO ehinh sdch ho trp ngudi dung tot vdi nhiiu hgi thdo mgng, hudng dan chi tiet, ...
- De dang kit noi, trao dii du ligu vdi cac phan mem khac nhu:
MS. Excel, AutoCAD, Midas Civil, Midas Gen,...
3. DNG DUNG MIDAS FEA
Mo hinh hoa hinh hoc Trong FEA, mo hinh hinh hgc dupe tgo thanh tu cdc doi tupng ca ban nhu: diim, dudng, mat, khoi. Cdc cong cy eho phep phat sinh tat ca dang hinh hgc.
Trong thu vign phan tu, Midas FEA ho trp khong chi cac phan td khoi tuyin tinh md ca cae phan tu khoi bae cao vdi ede dgng td dign, Iyc dien, vd ngu dign.
Mo hinh hoa vat lieu FEA h i trp rat nhieu mO hinh vat ligu khde nhau va cho phep tao mo hinh vdt ligu bang each kit hap nhieu mo hinh lai.
- Vdt lieu be tong dupc mo ta dya tren sy kit hpp cua ba mo hinh vdt lieu:
+ Mo hinh vgt ligu ddn hoi tuyin tinh (Linear)
+ MO hinh vdt lieu dan hoi phi tuyen dang da tuyin (Nonlinear- Multilinear Elastic)
+ Mo hinh vdt lieu be tOng (Concrete)
- Vdt lieu eho cot thep dupc mo ta dya tren sy kit hpp eua hai mO hinh vgt ligu;
+ Mo hinh vat lieu ddn hoi tuyen tinh (Linear)
Hinh 2. Mo hinh vgt lieu be tong nen va keo
I S6 7 ndm 2015
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'#### KHOA HOC - CONG NGHE
+ Mo hinh vdt lieu ddn hoi hai lan tuyin tinh - hOa eung dOng hgc (Bilinear Kinematic)
• FEA ho trp mo ta vat ligu theo nhiiu tidu ehuan khac nhau
• FEA cho phep ngudi diJng mO ta dudng eong ung suat - biin dang vdi nhieu kiiu khde nhau vd d i ddng tuy biin.
Mo hinh hoa phan tu* hOu han - Kieu phin tu cho be tOng:
Kieu phin td cho be tOng trong FEA Id phan td khoi. Phin tu nay ddp dng dupc hau hit cae mO hinh ly thuyit da phan tich d cdc phin trudc: cho phep trpn eit thep trong phan tu (mO hinh Smeared cot thep), cho phep xet tdi ung xu deo, tudn theo mO hinh phd hogi nam thong so, cho phep mO td pha hogi nut va vd,...
Phan td ndy co ba dgng chinh;
Iyc dign, ngu dign (hinh nem) vd td diOn, trong dO dgng Iyc dign dupc khuyin nghj dung trong mpi trudng hpp.
- Kieu phan tu eho cot thep;
Trong FEA cho phep mo hinh cot thdp theo mo hinh rdi rac, nhung, hogc phan tdn.
Khi tit ea cac thiit lap tren da dupc kit thuc, cong tdc chia ludi PTHH dupc tiin hdnh. Co 2 kiiu chia ludi chinh PTHH cO t h i dupc sd dyng trong FEA:
- Chia ty dOng, FEA se can cd vdo kich thude cua phan tu 6e ty dOng chia ludi PTHH. Vdi each chia ndy, hau nhu cdc mien hinh hgc deu cO t h i dupc rdi rgc hOa thdnh cOng. Tuy nhien, neu sd dyng mO hinh phan tu khoi thi nhieu khd ndng trong ludi PTHH dupc tgo thdnh se chda mOt ti Ig Idn ede phin tu tu dign.
Hinh 3. Mo hinh phin twiuc dien bgc cao
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Hinh 4. Phan chia phan tCrhOu h^n
Hinh 5. Phin tw tiip xuc dgng dwdng
- Chia theo phdn hogeh cija ngudl dung: Vdi each chia ndy, ngudi dung se thiit lgp cac khoang chia tren bien hlnh hpe; sau do, FEA se cdn eu ede khoang chia vd kieu phan tu chpn (vi du lue dign) d i tiin hanh chia ludi PTHH.
Phan td tiep xuc
- Phan tu tiep xuc dupc su dyng de mo hinh lien kit giua cot thep va be tong hodc giua cde phan be tOng tai vet ndt
- Co 3 logi phan tu tiip xuc la:
Nut, Dudng, vd Mat- Mo hinh hoa tai trong
- FEA ho trp hau hit cdc dang tdi trpng nham mo ta cac tai trgng tac dOng tgi vung chju Iyc cgc bO theo thyc te chju Iyc.
Md hinh dieu kien bien FEA ho trp mO hinh lidn kit da dang rit da dang cho phdp mfl td tot cdc lien kit cO the ed trong viJng chju lye eye bp:
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So 7 nam 2015 IKHOA HOC - C C N G N G H ^ # # # # #
• Rdng buOc nut
• Rang buOc da diem
• Khoang lidn kit dau dam
• Khoang lien kit tai nut ban
• Giai phdng lidn kit tgi nut phan tu
• Dieu kign bien truyen nhigt
• Dieu kign bien tiep xuc Cac tieu chi deo - pha hoai Midas FEA ho trp*
FEA ho trp rit nhieu tieu chi ddo va tieu chi pha hogi.
- Tresca - Von-Mises - Mohr-Coulomb - Rankine - Drucker-Prager Mo hinh vet nut cua bg tong
• D'ng xu nut cua be tOng dupe t h i hign qua mO hinh "vet ndt vdi bien dgng ting hpp": day Id mOt mo hinh dng xd nut dupc Midas de xuit trdn ea sd mo hinh vet nut phdn tan.
• ViOc xem xet dng xu sau nut dya tren mo hinh vit ndt c i djnh hoge v i t ndt xoay tuy theo cdc tryc tham chiiu cua vet nut.
Cac phan tich trong FEA
• Phan tinh tTnh tuyen tinh
• Phan tich theo giai dogn thi cong
• Phan tich hinh thai
• Phan tieh i n djnh tuyin tinh
• Phdn tich ngdn hgn/dai hgn/
pho phan ung.
• Phdn tieh phi tuyen vgt ligu/
hinh hpe
• Phdn tich tiip xuc mgt phi tuyin
• Phdn tieh xdt tdi cit thep/ cpc
• Phan tich ndt trong be tOng
• Phdn tieh nhi^t
I S6 7 nam 2015
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Mohr-Caultimb
Hinh 6. Mat deo theo ti§u chi Drucker- Prager
(a) fixed crack model (b) rotating crack model
Hinh 7. Md hinh vit nirt
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Hinh 8. Mo hinh c6t thep neo cap DlfL c^u dam
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t t t l l KHOA HOC - C O N G N G H $
. Phan tich hi?u ipng tiep xOc lien quan den tieu chuan hoi tg: s6 gian trong cao bu*c phan t i * cung bu'dc tai, so bydc l^p, tieu chuan co the duwc thu'c hien dS^ dang
• Phan tich moi ^^ 1^^. j g ^ pf,gj„ „ ^ chuyen vj, nhSm thoa man yeu cSu ket qua
• Midas FEA cho phep nguiri hoae tieu chuan ve nang lu'png. ciia nguwi diing.
diing thilt lap diy du cac dang • Vl#c thiit IJp cac ket qua trung
Mot so ket qua phan tich
VI du thif nh4t thu'c hien mo hinh hoa va phan tich ifng suat cgc bg cho bo ph$n neo cap dg' m g ig.c clu dSm diic hing can b^ng. Cac thong s6 c6t thep thuwng du'cfc ma hinh diy du de xac dmh vung nui.
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Hinh 9. Sien d^ng - ifng suat - Nut vung neo cap cau dam
Vi du thif hai m6 hlnh hda va phan tich viing neo cap cau day vang vo'i day du cot thep thu'ong.
Hinh 11 Bien dang - U'ng suat - Nirt vung neo cap ciu day vang
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(Xem tiep trang 1S)
So 7 nam 201SI
