KHOA HOC-CdNG NGH|
Anh huong cua so luang goi cau 6en ung suat keo trong cot thep theo phuong ngang cua tru re quat be tong cot thep thuong
I TS. NGO C H A U PHirONCThS. HO VINH HA; ThS. NCS. H 6 VI^T LONG Trudng Dgi hoc Giao thdng van tdi - Phdn hieu tgi TP Hd Chi Minh
T O M TAT: D^ng try r^ qu?t be tong cot thep thudng duoc sd dung rpng rai 6 cac cau vu<7t nhip lien tgc o Viet Nam v6i so lupng goi cau thay doi tu 0 2 Pen 4 goi cau. Qua khio sat dgng trg cau nay P cau vuct nut giao khu A, cau vuqii Nguyen Van Lmh, cau Nguyen Van Cu (TP Ho Chi Minh) da thay xuat hien vet nut thang ddng, doc theo than tru trong phgm vi 6 giua tru voi dp md rong vet ndt khac nhau. Cac vet ndt nay la do ung suat keo theo phuong ngang try gay ra. Bai bao trinh bay nghien cuu ve su Snh hudng cua so luong goi cau den ung suat keo theo phuong ngang cua dang tru nay Oe minh hpa, tac g i l tinh toan mpt tru cau dgng r^ quat vPi so lupng goi cau thay doi lan lupt tu 0 2 den 4 goi cau theo hai phuong phap Phuong phap mo hinh ehong giang va phuong phap phan td hQu hen. Ket qu^ cho thay, so lupng goi cau tSng thi ung suat keo trong cot thep theo phuang ngang try gi^m, dong thoi dng suat keo trong cot thep theo phuong ngang try phan bo deu hpn dac chieu dai thanh
T u KHOA: GOI cau, tru cau re quat, phuong phap phan td huu han, mo hinh ehong gi§ng ABSTRACT: Reinforced concrete fan-shaped piers have a widespread application on continuous overpass bridges in Vietnam with the number of bridge bearings varying from two to four bearings. From the observation and investigation of these piers at intersection overpass bridge at zone A, Nguyen Van Linh overpass bridge, Nguyen Van Cu Bridge (Ho Chi Minh City), there were many vertical/axial cracks located at the middle-top of pier cap with a variety of crack width These cracks are caused by transverse-tensile stress The paper presents a study on the effect of the number of bearings to the transverse-tensile stress To illustrate, authors calculated a fan-shaped pier with 0 2 - 4 bearings, in turn, based on two methods
Strut-and-tie model and finite element method.
The results reveal a similar trend that is the more increasing of bearing quantity, the more decreasing of tension stress in steel as well as the more uniform distribution of axial stress in the steel
KEYV/ORDS: Bridge bearings, fan-shaped pier, finite element method, strut-and-tie model
I . O A T V A N D i
Van de nUt doc d tru cau dang re quat be tong cot thep thudng da dUpc quan tam nghien edu tai Viet Nam t u nhdng nam 2006 P tru dan cau Thuan PhUde (Da NSng) cua TS. Nguyen Di^e Thanh vdi De tai cap Bp: Nghien ciili ap dung mp hinh ehong g i l n g trong thiet ke cac ket eau eau be tPng cot thep (DT 064025). Tuy nhien, de tai nly chua duoe nhieu don vj thiet ke biet den va l p dijng pho bien. Tic g i l eung da ed mpt sd nghien cdu ve cic phuong phap ttnh toan den ket cau tru va khIng djnh lai tinh hpp ly l p dung mo hinh chdng giang trong trUdng hpp nay [4].
Sd lupng gdi d tru eau dang re quat ed the la 02 goi nhu cau Nguyen Van CU, 3 goi nhU cau vUcrt nut giao Nguyen Van Linh, cau vupt nut giao khu A hay 4 goi nhi/
dcauThuanPhUdc [1,2,4].
a) - Tru cau Nguyen Van Cu. TP. Ho Chi Minh
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b) - Vl tri vet nut tren dinh tnj Hinh 1.1: Khio sat vet nut tren tru cau 02 gdl
b)- Tnj cau vuot nut giao khu A, TPHoChiMinh Hinh 1.2: Khio sat vet niit tren tru cau 3 gdi CIc cau tren deu cP ket cau nhjp Hen tijc thi eong theo phuong phap dilc phan doan tai eho, hoat t l i thiet ke HL93. Qua khio sit hien trang, mpt so tru eau xay dUng sau nay dViet Nam van xul't hien vet nUt thang dijrng, doe theo than trii do dng suat keo ngang d nhdng vi tri khIc nhau tuy thupe vao so lupng gdi.TrUdng hop 02 goi: Vj tri vet ndt thang ddng, doc theo than tru P gan chinh gida tim try (Hinh 1.1); trUPng hpp 3 goi: Vi tri vet nut thang ddng, doe theo than try d gan ehinh gida cOa goi gida va goi bien (Hinh 1.2).
Hien ehua co nghien cdu nao ve van de so lupng goi cau den nUt dpe t h i n try eau re quat dViet Nam.
Trong dieu kien t h i nghiem khong cho phep, tac gia tien hanh tinh toan try cau re quat be tdng cot thep thudng vdt sd luong goi eau thay doi t d 02 den 4 gdi bang hai phuong phap la mo hinh chdng giang va phan t d hUu han (dung phan mem Abaqus CAE 6.12)
de bude dau gdp phan x l c djnh t i c nhan gay nijt dpe than tru.
2. TfNH T O A N TRU THEO CAC PHUONG P H A P 2.1. So lieu t i n h toan
Bat bao lay cau tao mpt tru cau dang tudng re quat be tong edt thep day 02m, cd be rpng thay ddi theo b i n kinh dudng cong R = 5m r\huHinh2.1. PhIn lUe tai try P
= 30.000 kN. Cot thep chiu keo ngang try gom 3 ludi 14 thanh dudng kinh d = 38mm (A^= 47.609mm2).
m m
Hinh 2.1: Cau tao tru ri quatbd tdng cot thdp thudng 2.2. Tinh toan umg suat keo t r o n g t r u Trong tinh t o l n bo qua I n h hudng cija trong lUpng b i n t h i n phan hang try.
2.2.1. Phuang phdp md hinh ehong gidng 2.2.1.1. Md hinh tinh todn
Trong phuong phap nay, ket eau try dupe mP phPng thanh eae thanh giang T va cac thanh chdng C. Dudi t i e dung ciJa tong p h I n Iue P xudng tru, lue F dUpe xem nhU phan Iue tat tdng gdi, gia tri eua lUc F nay thay doi tuy theo sd luong gdi bd tri tren try. Cac lUc F nay gay ra cac p h I n lUe Rd be tru.
Dua vao cau tao cua try (Hinh 2.2a), dua ra dupc eae so do tinh t o l n duoc minh hpa trong Hinh 2.2b, 2.2e, 2.2d tuong dng vPi eae trudng hpp 2,3 va 4 gdi.
J 8000 ,
75
KHOA H O C - C O N G NGHE
110001 6000 10001
iOQ 1250 I 2500 i 1250 500 1250 I I IZOU I
h=5000
b)-Ma hinh ehong giang cho trij co hai goi ilOOOi 3000 , 3000 ilQOOi
I M " I
c) • t^o hinh chilng giang cho tro cobagoi 110001 2000 I 2000 I 2000 ilOOO,
W T I 'N7T2N8,' TI / N 2
\ Cl \ I Cl / ' /
WR ¥ 7 R|
500 . p25| .1250 I 1250 I 1250 6251
d) - Md hinh ehong giang cho tnj cd bon gdi Hinh 2.2: Bd tri ehung vi md hinh giang chdng cha tru
2.2.1.2. Trinh tutinh todn
- Xac dinh vj tri phIn lUc R each mep than tru 1 khoing x:
-¥ Khi xay dung mP hinh ehong g i l n g , t d di^u kien bien la cac dng suat nen phan bo deu phia dudi be try.
Vdt dng suat nen dupe xlc dinh theo eong thdc (1). Di/a vao moi quan he nay xlc dinh dUpc g i l trj eua x, dupc the hien P Sdng 2./.
b.(x + f} b.y 0)
VPi2x-i-(n^.,-l)y^h
Trong dd: n, = so lupng goi. Gia tri b, h, x, y dugc the hten trong Hinh 2.2.
- Xac dinh npi lUc tinh toan trong c^c thanh gilng T:
-H d thd tren eCia try xuat hi&n Ung suat keo nen viec xlc dinh dupe vi tri eae thanh keo T la trpng tam cQa cot thep d u djnh bd tri. Vi trf elc nut nam ngay dUdI vj tri dat cac li^e F va nam ngay tren vj tri cac phIn lUc R. Cac thanh nen dupc xac dmh theo hudng ddng lUe nen chly ti!/cac goi cau ve phia be try va giij'a eae phIn lUc d be [3,4].
-I- Npi Iue tinh toan trong cae thanh giang T dUOc tinh b i n g each xem xet dieu kien eIn b i n g cCia cic nut theo cong thUc (2):
tgiW) --T L H (2)
Trong do: H - Khoing each theo phUOng ddng t d nilt N| (dudi t l i t i c dung) den nut N^ - Chieu cao vung ehiu luc cue bp,H = 3.5m.
L - Khoing clch theo phUOng ngang nut N, (dudi tai tae dyng) den nijt N^, L - 0.5-fx.
- Xlc dinh Ung suat keo trong cot thep thong qua not luc tinh toan trong thanh gilng T theo eong thUc (3):
/ = T/A^ (3)
2.2.1.3. Ket qua tinh todn
Dua tren dieu kien dng suat nen phIn bo deu, xlc cHnh dupc g i l tri v l vj tri cua elc phIn lUc R ducri tie dung eOa tong phIn lUe P = 30,000kN, dupe the hien trong Bdng 2.1
Bing 2.1. Cii tri va vj tri ciia phin lucR TrUoing
hop 2 goi 3 goi 4 goi
y (ra)
2.5 1.667
1.25 X (m) 1.25 0.833 0.625
(kN) 15000 10000 7500
( B i ^ 15000 10000 7500 Vdi vi tri cic phIn luc R da xae djnh, diia vao dieu kien can bang eua elc niit, xlc dinh dupe npi lUc trong thanh giang T, t d dP xac djnh dupc Ung suat trong thanh cot thep (Bdng 2.2).
Bing 2.2. Ung suat trong cot thep, fs Trudng
hcrp H (m) 2 goi 3.5 3 goi 3.5 4 goi 3.5 L (m) 1.75 1.333 1.125
T IkN) 7500 3809.52 2410.71
As (mm^) 47609 47609 47609
fs (Mpa) 157.53 80.02 50.64 2.2.2. Phuang phdp phan tCrhUu han 2.2.2.1. Md hinh tinh todn
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Bing 2.3. Cie thdng sdvat lieu vat I. "^^^"9
\ti„ li'orng rieng I kN/m' Be tPng
Thep
Cudng Mpa
30
Md-dun Hgso dan hoi poat Mpa I xong 19000 0.3
Phan liic gdi d ele trudng hop 2 gdi, 3 goi, 4 gdi lan lupt la (F = 30000/2)kN, (F = 30000/3)kN, {F = 30000/4)kN.
Tru duoc mp phong t d cle phan ti:f dang khdi S ndt (C3D8R), cot thep mp phong t d phan t d thanh (T3D2) cP kich thude ludi la 200mm (Hinh 2.3).
Hmh 2 3 Mo hinh tru sau khi duoe ehia ludi 2.2.2.2. Ket qud phdn tich
Ket qua phan tieh Ung xdcua tru b i n g phan mem phan t d hQu h, i i .4,2.5 vd 2.6 va Bdng.
Hinh 2.4: lfng suat trong ed't thep chiu keo vdi tru cd hai gdi f^= 1.219 X 10^ (N/nf)
Hmh 2 6 Ung suat trong cot thep chiu keo vai tru co bon goi f^ = 3 11Bx10'(N/mr)
Bing 2.4. Bing tdng hap kit qui tinh toan dng suit kio trong edt thep theo phuong phap phan t&hOu han
ddng phan mem Abaqus CAB 6.12 Tri/dng hop
2 goi 3 gdi 4 goi
O^ng suat trong th^p, fs (Mpa) 121.9 Mpa 91.6 Mpa 31.2 Mpa Nhdn xet:
Dua vao ket q u i tinh toan, ca hai phuong phap mo hinh chdng g i l n g v l phuong p h I p phan tCf hufu han deu the hien ehung mot xu hudng, do la khi so lUpng gdi tren try tang thi Ung suat keo trong cot thep eang g i l m (Hinh2.7).
Bieu do irng suat trong cot thep chm keo
Hinh 2.7: Ung suat keo trong edt thep theo phuong phip md hinh ehong giing va phuong phip phan tuhiju han Lfng sua't keo trong cot thep phan bo doe theo chieu dai thanh deu hon khi tang sd luong gdi (Hinh 2.4, 2.5,2.6).
Vj tri dng suat keo Idn nhat trong edt thep d gida try ddi vdi truPng hpp 2 goi (Hinh 2.4), P chinh giQa cua goi gida va cae goi bien (Hinh 2.5, 2.6). fiieu nay phu hpp vdi vi tri vet ndt thang ddng, dpe try khio sat P cac tru eau thUetefH;n/i/ /, 1.2).
3. K^T LUAN
Ket q u i tinh toan trong vi dy bang hai phuong p h i p mo hinh he thanh va phuong phap phan Xd hUu han deu cho thay sd lupng goi eau anh huPng den dng suat keo trong tru re quat be tPng cot thep thUPng, ma cy the so lupng goi eau eang tang thi Ung suat keo trong cot thep phuong ngang tru gilm.
So luong goi eau eang nhieu thi Ung suat keo trong 77
KHOA H O C - C O N G N G H |
cot thep eang phIn bd deu hOn doc chieu dai thanh.
Dieu nay lam tang hieu q u i khi bd tri cot thep giong nhau theo phuong ngang cau.
Tai lieu tham khSo
[1]. Cdng tyTNHHTuvan thiet ke BR (2017), Ketqud khdo sdt cdc cau vUat nut giao khu A, cdu nut giao QL lA - Nguyen Vdn Linh, cdu Nguyen Vdn CU.
[2]. CPng ty TU van thiet ke Cau Idn - Ham (2008), Ho sa thiet ke'bdn ve thi cdng eau nut giao QL 1A - Nguyen Vdn Linh.
[3]. Nguyen Duy Tien, NgP Van Minh (2016), P/iUOng phdp mo hinh he thanh trong thiet ke ket edu cdu be tdng cot thep. NXB. Xay dung.
[4]. Nguyen DUc Thanh {2006}, Md hinh he thanh trong thiet ke ket cdu cdu be tong cot thep, De tai cap Bp, Ma sd: DT064025.
[5]. Nguyen Xuan LUu (2010), Phuang phdp phdn fu"
huU hpn, NXB. GTVT.
Ngay nhSn bai: 29/9/2018 Ngdych^p nhin ddng: 8/10/2018 NgiTcri phdn bi^n: TS. Ngo Van Minh
TS.LeB^Anh