Cong trinh Khoa hgc
THIET KE ONG TRON BE TONG COT THEP THEO TIEU CHUAN THIET KE CAU AASHTO LRFD
Bill s u e CHINH Bd mon Cdng trinh GTTP & CTT Tnrdng B(fi hgc Giao thong Van tdi
Tom Idt: Bdi bdo ndy gidi thieu ve cdch tinh hoat tdi tdc dgng tdi cong trinh ngdm dgng ong Iron BTCT. trinh tir tinh lodn cong trinh ngdm dgng ong Iron BTCT theo cdc phuang phdp thiit ke true Hep (Direct Design Method) vd phuang phdp thiit ke gidn tiep (Indirect Design Method) theo AASHTO LRFD 2012. Ngodi ra bdi hdo cdn di cap din mgt so vdn de khi sir dung TCVN 9113:20l2-dng be long cSt thep thoat nudc trong thuc tid Viet Nam.
Summary: This paper introduces how lo calculate effects of live load on reinforced concrete pipe, calculated sequence of Direct Design Method and Indirect Design Method according lo AASHTO LRFD 2012. In addition, the article also mentioned some issues when using TCVN 9113- 2012-Reinforced concrete pipes for water draining in practice in Vietnam
I. GIOI THIEU CHUNG
Ke tiJ nam 2005, Viet Nam da su dung Tieu chuin thi6t ke cSu 22 TCN 272-05 [2] de thilt ke cac cong trinh eau, kft cau vui va vd ham. Cac cong trinh ngam dang ong tron BTCT, mpt dang ket cau vui thi cdng theo phuang phap dao hd, la doi tugng cua 22 TCN 272-05. Ve thuc chat 22 TCN 272-05 dugc bien djch dua tren AASHTO LRFD 1998 [4] ciia Hoa Ky. Viec tinh toan tai trgng va td hpp tai trpng tac dung len ong tron BTCT, tinh toan ngi lyc va tinh duyet ket cau ong trdn BTCT dua tren triet ly eiia phuang phap thiet ke theo he so sue khang va he so tai trpng.
Trong bai nay se gidi thifu ve hoat tai xe tac ddng len cong trinh ngam dang ong tron BTCT theo AASHTO LRFD 2012 [7], cung nhu viec thidt kg 6ng tron BTCT theo phuang phap thiet kf tryc tiep va phuang phap gian tiep.
II. VE TAG DONG CUA HOAT TAI LEN ONG TRON BTCT THEO AASHTO Tac dpng cua boat tai Ifn ong tron BTCT trong cac tifu chuan AASHTO cu vf ca ban dugc dya tren phuang phap trinh bay trong ASCE 15-98 [9] vdi viec su dung cac hoat tai theo quy djnh trong cac tieu chuan AASHTO cG, sau do dupe bo sung dya tren kft qua nghifn cuu cCia ACPA 2011 [8] va dugc cap nhat theo hoat tai xe thilt kl quy dinh trong cac tieu chuin AASHTO LRFD.
2.1. Hoa) tlii thiet ke
Xe thiet k^ trong cac tieu chuin AASHTO cu la HS 20 vdi tai trgng true la 32000 lb (142
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kN) theo ciu hinh xe tai tieu chuin (Normal Truck Configuration) va 24000 lb (107 kN) theo ciu hinh xe tiii thay thi (Alternate Load Configuration).
Xe thiet ke trong AASHTO LRFD la HL 93, ngoai ra con mpt tai trpng lan 640 lb/ft (9,3 kN/m) phan b6 tren chieu rpng lan 10 ft (3m), tai trgng lan nay dugc quy doi thanh tai trpng phan bo 64 lb/foot" (3,06 kN/m^).
2.2^ Tac dpng cua hoat tai len ong tron BTCT
Tac dpng cua hoat tai Ifn 6ng tron BTCT dugc tinh toan theo "kjch ban" bat Igi nhat trong
"3 kjch ban": (i) chi do 1 banh kep cua xe thiet ke; (ii) do 2 banh kep cua 1 xe thay the each nhau 1 khoang la 4ft (120cm) va(3) do 2 banh kep eua 2 xe thay the dgt each nhau 1 khoang la 4ft (120cm). Ngoai ra "kjch ban" bat lgi nhat phu thugc vao: (i) hudng di chuyfn cua xe; (ii) dudng kinh cua ong va (iii) chieu sau dat ong.
Difu lidi phan bo iTQUg baull xe
Hinh I. Cdc "kich bdn " bat lai nhdt ciia hogt tai
78 Tap chi KHOA H O C GIAO THONG VAN TAI So 47 - 08/2015
Cong trinh Khoa hgc
v_>ic?v
J. Jif
or^
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Hinlt 2. Phdn bo dp iuc ciia hoat tdi theo hudng di chuyen 2.3. He so phan bo boat tai tbeo chilu sau (Live Load Distribution Factor-LLDF)
Trong ASCE 15-98 [9] he s6 phan b6 hoat tai theo chigu sau LLDF diri?c lay la 1,75. Ngoai ra dl thien ve an toan con dugfc nhan them he s6 1,15 doi voi dit dip dang hat. Nhirng k6t qua nghien ciru mai nhat v6 LLDF cua Petersen va ddng nghiep da duoc b6 sung trong ACPA 2011 [8] va ducrc dua vao AASHTO LRFD 2012 [7]:
1,15 khiD, <0,60m
LLDF=0,327953.D,+0,95 khi 0,60m <D, < 2,45m ( 0 1,75 khi D,>2,45m
2.4. He so xung Idch (Impact Factor-IM)
Trong ASCE 15-98 [9] khi tinh tac dong cua hoat tai xe khong xet toi he s6 xung kich IM Trong AASHTO LRFD 2012 [7], da dugc di6u chinh va dua vao nhu sau
fO,33(l-D,/0,245) khiH<2,45m
[o khiH>2,45m 2.5. Trinh tir tinh tac dong ciia boat tai 6 to theo AASHTO LRFD 2012
Co thi dua ra trinh tir tlnh tac dgng cua hojt tai theo AASHTO LRFD 2012 [7] nhu sau - Xac dinh chieu sau anh huong cua hoat tai 6 to //,„, (m):
. s , - b LLDF
- Xac djnh dien tich phan bo tai trpng banh xe A,j {m') tren dinh ong j(b+LLDF.H).(a + LLDF.H) k h i H < H „ ,
[(b + s.+LLDF.H).(a + LLDF.H) khi H > H„.
- Xac dinh ap luc tai trgng phan b6 WLL (kN/m") tren dinh clng fLL/A,, khi H<H,„
IM =
H,.,
A,, =
(2)
(3)
(4)
W,, =
2.LL/A,, khi H > H : . (5)
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- Xac dinh chieu dai chat tai difu chinh L,,yov (m)
L,„„ khi H < 0.25 m
LLDF.H khi H > 0.25 m Xac djnh ap luc tai trpng phan b6 WL(kN/m) khai thdc tren dinh cdng
WL=MPF.{l + IM).WLL.min(D,,L,g^^)
(6)
(7) Trong cac cong thuc tren: D, la dudng kinh trong ciia dng, m ; H,ni la chifu sau anh hudng ciia tai trgng banh xe, m; H la chieu sau dat dng, tinh tir mat dat tu nhien tdi dinh ong, m; s„ la khoang each giira cac banh xe liy bing 1,83 m; b la chieu rdng tiep xuc cua ldp xe vdi m^t ducmg liy bang 0,508 m; a la chieu dai tiep xuc cua 16p xe vdi mat dudng liy bang 0,254 cm; LLDF la he s6 phan bo boat tai liy theo cong thu-c(l); LL = L^sjo! LHS2O la tai trong banh xeciiaxeHS20 liy bang 71 kN; MPF la he s3 lan xe liy theo quy djnh cua AASHTO LRFD 2012 [7].
III. PHl/ONG PHAP THIET KE TRUC TIEP VA PHUO'NG PHAP THIET KE GIAN TIEP 3.1. Phutfng phap thiet ke true tiep
Phuang phap thift kf true tiep theo trang thai gidi ban cudng do theo difu 12.10.4.2 cua AASHTO LRFD 2012 [7].
Tai trgng tac dgng len dng trdn BTCT bao gdm:
- Tai trpng dit: phu thugc each lip dat c6ng theo dilu 12.10.2.1 vdi phan bo ap lyc theo tieu chuan HEGER vdi cac hf so phan bo vom ISy theo bang 12.10.2.1-3.
Hinh 3. Phdn bd dp luc HEGER vd cdc hi sd hi?u ung vom
- Trgng lugng cua tmh tai/ehit long trong 6ng: liy theo dilu 12.10.2.1, trgng lugng ciia chit long gay ra ap lyc dit phu hgp vdi phan bo ap lyc theo.tieu chuan HEGER.
- Trgng lugng ban than dng tron BTCT: liy theo quy djnh trong phin 3 eiia AASHTO LRFD 2012 [7].
80 Tgp chi KHOA H O C GIAO THONG VAN TAI So 47 - 08/2015
Cong trinh Khoa hoc - Cac hoat tai tac ddng len 6ng trdn BTCT: lay theo quy djnh trong dieu 3.6 phan 3 ciia AASHTO LRFD 2012 [7], chi tilt da trinh bay trong muc 2.
- Phan phan tich npi luc trong ong trdn BTCT: sir dung theo cac phuang phap tinh loan thong dung. Khuyen khich su dung cac phuang phap tinh chinh xac.
- Phan b6 tri cdt thep va tfnh duyft cac trang thai gidi han lay theo quy dinh trong difiu 12.10.4 cua AASHTO LRFD 2012 [7].
3.2. Phuo'ng phap thiet ke gian tiep
Phuang phap thiet kf gian tiep dugc trinh bay trong dilu 12.10.4.3 cua AASHTO LRFD 2012 [7]. V€ thyc chit la xac dinh tai trgng dat va boat tai trfn dng tron BTCT phu hgp vdi cac quy dinh eiia dieu 12.10.2 va so sanh vdi cudng dp nen yfu cau (cdn ggi la tai trpng D hoac D- Load) hay con ggi la cudng dp theo thi nghifm nen 3 canh. Trinh ty nhu sau;
- Tai trpng nen yeu cau len ong tron BTCT theo thi nghiem 3 canh P, dugc xac djnh theo cong thuc sau:
P = D^.D,.L (8) Trong do: D, la dudng kinh trong ciJa ong (m); L la chieu dai dot dng (m); DL la cudng dp
nen yeu eau eua ong theo thi nghiem nen 3 canh (T/m/m).
- Xac djnh cudng do nen yeu ciu DL theo thi nghifm nen 3 canh: Viec xac dmh cudng dg nen yeu cau ciia 6ng tron BTCT theo thi nghifm nen 3 canh dugc tien hanh theo cac budc sau day:
Budc 1: Xac dinh tai trgng dat rai deu len 1 m dai ong. WE, la tai trgng co he s6.
Bude 2: Xac dinh ap lyc do hoat tai rai deu Ifn 1 m dai dng, WLL, la tai trgng co he so.
Bude 3 Lua chgn loai hinh lap dat dng, thudng su dung loai hinh lap dat la loai 1.
Budc 4: Xac dinh hf so nfn, gom 2 gia tri. he so nen doi vdi vdi tai trpng dat B|e va he so nen d6i vdi hoat tai Bfi,L. He sd nfn ddi vdi tai trpng dat B^ dupc lay theo bang 1. He so nen doi vdi hoat tai Bfl.L dugc lay theo bang 2. Can chu y nfu dudng kinh D, cua dng BTCT khac vdi cac gia trj d bang 1 va bang 2, cac gia tri he sd nfn doi vdi tai trpng dat B^ va hf so nen doi vdi ho^t tai BfLL duge xac djnh bang each npi suy.
Bdng I. He sS nin ddi vdi ldi trgng ddt (AASHTO LRFD 2012 [7]) Duong kinh
trong ong D; (m) 0.3 0.6 0.9 1.8 3.6
Loai hinh l i p dat ong trdn BTCT Lo^i 1
4.4 4 2 4.0 3.8 3.6
Loai 2 3.2 3.0 2.9 2.8 2.8
Loai 3 2.5 2.4 2.3 2.2 2.2
Loai 4 1.7 1.7 1.7 1.7 1.7
T9P chi KHOA HQC GIAO THONG VAN TAI 86 47-08/2015
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Bang 2. He so nin doi vdi hnar tni rAASHTO LRFD 2012 fff) Chieu cao
0 5 1.0 1.5 2.0 2.5 3.0 3 5 4 0
BirftTig k(nh IronE 6ne trdn BTCT. D: <m) 0.3
2 2 2 2 2 2 2.2 2.2 2.2 2.2 2 2
0.6 1 7 2 2 2 2 2.2 2 2 2 2 2.2 2 2
0.9 14 1 7 2 1 2 2 2 2 2 2 2 2 2 2
1.2 13 1 5 1.8 2.0 2.2 2.2 2 2 2 2
1.5 1 3 1 4 15 1 8 2 0 2 2 2 2 2,2
1.8 1 1 1.3 1.4 1.5 1.8 2,2 2 2 2 2
2.1 t 1 1 3 1.4 1.5 1.7 1-8 1-9 2-1
2.4 1.1 1.3 1.3 1.4 1.5 1.7 1 8 1 9
2.7 1 1 1 1 1 3 14 14 1,5 1 7 1 8
3.0 1 1 1 1 1 3 1 3 1.4 1 5 1-5 i.7
3.6 1.1 1.1 l.t 1 3 13 14 1 4 1 5
Budc 5: Xac dinh hf so an toan, FS, dugc lay bang 1, ung vdi vifc xac djnh eudng dp ciia cong khi xuat hien vet nut den 0.3mm.
Bude 6: Xac dinh cudng dp ciia ong, DL
"w, W,
—L + — h . Bf. Bo.
D,
[?]
(9)Vdi: WE - tai trpng dat Ifn ong, xac dinh theo budc 1, T/m; WL - hogt tai tac dung len 6ng, xac dinh theo budc 2, T/m; 6^ - he so nen doi vdi tai trpng dat, xac dinh theo budc 3; BfLL - he s6 nen doi vdi boat tai, xac djnh theo budc 4; FS - he so an toan; D - dudng kinh trong ciia 6ng, m.
Hifn nay d Viet Nam, viec thiSt ke ong trdn BTCT theo AASHTO LRFD 98 [2] chu yku dya tren phuang phap thiet ke true tiep. Cac thiet ke cho cac ong tron BTCT cd dudng kinh trong tu 0,3m den 2,0m su dung cdt thep keo ngupi theo cac cong nghe quay ly tam va cac cong nghe tien tien khac (cdng nghe rung ep vdi ten thuang mai BiDi® eua Hoa Ky, cong nghf Souveran va Jumbo cua CHLB D u e . ) do tac gia va cdng su eung cip da &\sac dua vao san xuat dai tra tai Cong ty TNHH Hung Vuang, Cong ty TNHH Cudng Thuan, Cdng ty C6 phin ciu kifn be tong Nhan Trach 2, Cdng ty C6 phin diu tu va Xay dyng Tien Giang...
IV. VE CAC TIEU CHUAN THIET KE CONG TRON THOAT NUOG CJ VIET NAM D6i vdi 6ng tron BTCT thoat nudc, Bg Xay dung ban hanh TCXDVN 372-2006 Ong BTCT thoat nudc vao nam 2006 va nam 2012 dugc chuyen doi thanh TCVN 9113:2012 [3].
Trong tieu chuan TCVN 9113:2012 chu yeu dua ra cac quy djnh v6 ciu t?o, v6 mdi ndi, cong tac nghiem thu..., ma khong dua ra cac chi din vi tinh toan thiSt kg. Kha nang ehju tai cua 6ng cong BTCT dugc danh gia thong qua phuong phap ep ba cgnh. Theo kha nang ehju tai, 6ng BTCT dupc phan lam ba cip chiu tai ca ban: cip T, cip TC va cip C theo quy djnh ciia cac tifu chuin hifn hanh Phu thupc cip chiu tai, 6ng BTCT phai dat dugc ba loai lyc sau:
- Lyc khong nut (tai trpng khong nut) la lyc ep quy dinh cho moi loai 6ng BTCT vdi mpt cip chiu tai xac dinh dugc duy tri it nhit trong mgt phiit ma khdng xuat hifn vet nut;
- Lyc lam viec (tai trgng lam vifc) la luc ep dupe sii dung trong tinh toan thigt VA. Lyc ep quy dinh dupe duy tri it nhat trong mpt phut ma khong xuit hien vet nut hogc xuit hien vSt mit nho CO chieu sau khong Idn han 2 mm hoac be rpng vft mit khdng Idn ban 0,25mm;
- Luc cue dai (tai trpng eye dai hay tai trgng pha hoai) la Iuc ep t6i da ma 6ng BTCT dat dugc;
Ba loai lyc ep neu tren cho tirng cip tai trpng iing vdi m6i loai dudng kinh danh dinh dupc cho d bang 2.4 trong [3].
82 Tap chi iCHOA H O C GIAO THONG VAN TAI So 47 - 08/2015
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V. NHAN XET VA KIEN NGHI
Dua tren cac kfit qua nghien cuu ly thuyit va thyc nghifm dugc thyc hien trong nhirng nam gan day, cac phuang phap tinh tac dgng ciia boat tai len ong tron BTCT da co nhieu thay doi ca ban. Cae kien nghj ve hf sd phan bo tai trgng theo chieu sau, hf so xung kich. . da dugc cap nhat trong cac tieu chuan thiit ke ctia Hoa Ky, nhit la trong AASHTO LRFD 2012.
Cac nghien cuu va kinh nghifm thuc If d Hoa Ky va cac nude da chi ra ring, cae kft qua nhan dugc khi ap dyng phuang phap thift kf true tiep va phuang phap thiet ke gian tiip co thi khac nhau va van co nhiing sai khac so vdi kit qua thi nghiem thuc tf Mot trong nhung ly do la mo hinh tinh van chua phan anh day du thyc te lam viec cua ong tron BTCT
Tai Vift Nam hifn nay dang su dyng TCVN 9113:2012 [3] di thiit ki cong iron BTCT thoat nudc Vi thuc chit TCXDVN 372-2006 va duge bien dich dua tren BS 5911-1001988 ciia Vucmg quie Anh [10] (hien nay da dugc thay thi bing BS EN 1916:2002 [11]). Mpt diim can chii y them la'khi su dung tifu chuan BS 5911-100:1988 phai su dyng kit hap vdi cac hudng din ciia H.M.S.O 1986 [12] va H.M.S.O 1983 [13]. Trong khi dd TCVN 9113:2012 chua lam ro van de nay va khong co hudng dan cu the. Nhirng ket qua thi nghifm ep 3 canh cac 6ng tron BTCT thiit ki theo cac tieu ehuin 22 TCN 18-79 va 22 TCN 272-05 diu cho eac kit qua chua thuc sy thoa dang theo cac quy djnh cua TCVN 9113:2012. Day la van de can dugc quan tam nghien cuu trong thai gian tdi.
Ngay nhan bai lan dan: 21/5/2015 Ngay nhan bai sua: 2/6/2015 Ngay chap nhan dang bai: 11/6/2015
Tai lieu tham khao
[i]. Tieu chuan nganh (1979), 22 TCN 18-79 Quy trinh thiet k i ciu c5ng theo trang thai giai han, Bo GTVT, HaNpi, 1979.
[2]. Tieu chuin nganh (2005), 22 TCN 272-05 Tieu chuin thiet kg ciu. Bo GTVT, H^ Noi, 2005.
[3]. Tieu chuin quic gia (2012), TCVN 9113:2012 Ong be tong cit thep thoat nudc. Ha N6i, 2012.
[4]. AASHTO (1998), AASHTO LRFD Bridge Design Specifications, 2th Edition, American Association of • State Highway and Transportation Officials. Washington, D.C, 1998.
[5]. AASHTO (2007), AASHTO LRFD Bridge Design Specifications, 4th Edition, American Association of State Highway and Transportation Officials, Washington, D.C, 2007.
[6] AASHTO (2010), AASHTO LRFD Bridge Design Specifications, 5th Edition, American Association of State Highway and Transportation Officials, Washington, D.C, 2010.
[7]. AASHTO (2012), AASHTO LRFD Bridge Design Specifications, 6th Edition, American Association of State Highway and Transportation Officials, Washington, D.C, 2012.
[8]. ACPA (2011), Concrete Pipe Design Manual, American Concrete Pipe Association, 201!.
[9]. ASCE (2000), Standard Practice for Direct Design of Buried Precast Concrete Pipe Using Standard Installations (15-98), American Society of Civil Engineers, 2000.
[10]. BS 5911-100:1988 Precast concrete pipes, finings and ancillary products. Specification for unremforced and reinforced pipes and fittings with flexible joints, British Standards institution, London, 1988.
[11]. BS EN 1916:2002 Concrete pipes and fittings, unreinforced, steel fibre and reinforced, British Standards Institution, London, 2002.
[12]. Young O C O'Reilly M. P and Brennan G. (1986), Simplified tables of external loads on buried pipelines. Transport and Road Research Laboratory. London, H.M.S.O, 1986.
[13]. Young O. C O'Reilly M. P (1983), A guide lo design loadings for buried rigid pipe. Transport and Road Research Laboratory. London, H M.S.O, 1983*
Phan bifn: Nguyen Duy Tien; Oao Duy Lam
Tap chl KHOA HOC GIAO THONG VAN TAI S6 4 7 - 08/2015 8 3
