DliN DAN KHOA HOC C O N G NGHE
MOT SO VAN DE CON ION m LIEN QUAN DEN DANH GIA AN lOAN VE ClfONG DO VA ON DINH IRONG IIEU CHUAN IHIEI KE DAP VOM BE lONG 14ICN 56-88
THS. VU HOANG HUNG, GS. Ll TONG CHUN
Hoc Vien Cdr^g trinh Thuy loi thuy dien - Dgi h o c Ha Hai, Nonn kinh, Trung q u o c TS. N G U Y I N QUANG HUNG: Trudng Ogi h g c Thuy loi
Tdm tit: Cung vdi su phat trien khdng ngUng cua cdng nghe tinh toan thiet ke, tieu chuan thiet ke dap vdm cua tung qudc gia cung cd su thay doi lien tuc de dap Ung yeu cau ngay cang cao ve kinh te va an toan, nd cung phan anh trinh do phat trien dap vdm ctia mdi nudc. Qua vao "Tieu chuan thiet ke dap vdm be tdng va dap be tdng trgng luc EM No. 19" cua My ban hanh nam 1977, "Quy pham thiet ke dap vdm be tdng SL 282 - 2003" cua Trung Qudc ban hanh nam 2003, bai bao da chi ra mgt sd van de cdn tdn tai lien quan den danh gia an toan ve cuang do va on dinh trong "Thiet ke dap be tdng va be tdng cot thep - Tieu chuan thiet ke 14TCN 56-88" cua Viet Nam ban hanh nam 1988.
Tukhda: Dap vdm, quy pham thiet ke, so sanh, to hgp tai trgng, Ung suit cho phep, he sd an toan
1. M d d a u
Oap vdm da trai qua mot qua trinh phat trien hang ngan nam lich sd, td nhung dap vdm ddn gian bang da xay eao vai met den nhifng dap vdm be tdng mdng cong hai chieu eao hang tram met tham chf cao tren 300 met da dUde xay dung. Oe cd nhCfng thanh qua xay dung dap vdm nhU ngay hdm nay dd chinh la sU phat trien khdng ngdng cua cdng nghe tfnh toan thiet ke va tieu chuan thiet ke thdng nha't cua tdng qudc gia. Tieu chuan cua timg qudc gia thay dd'i eung vdi sU phat trien ciia cdng nghe tfnh toan thiet ke lam sao de cong trinh ngay cang an toan va hpp ly ve kinh te, phan anh trinh dp phat trien dap vdm ciia mdi qudc gia. Vi du nhu "Tieu chuan thiet ke dap vdm be tdng va dap be tdng trgng lue EM No.19"[1]
ciia My ban hanh nam 1977 dupe sd dung hien nay da trai qua hai lan thay ddi nam 1953 va nam 1960; "Quy pham thiet ke dap vdm be tdng SL 282 - 2003"[2] eiia Trung Qude ban hanh nam 2003 dupc sda ddi dUa tren "Quy pham thiet ke dap vdm be tdng SD 145 - 85" ban hanh nam 1985. Odi vdi Viet Nam, hien nay van sd dung
"Thiet ke dap be tdng va be tdng
cot thep - Tieu chuan thiet ke 14TCN 56-8d"[3] ban hanh nam 1988 dUa tren Quy pham xay dung ciia Lien Xd va ehUa c6 thay doi gi. c a n c d vao tieu chuan thiet ke dap vdm be tong hien hanh eua My va Trung Qudc, tien hanh so sanh mot vai quy dinh ehu yeu nhu td hpp tai trpng dac biet, phUdng phap phan tieh dng suat, chi tieu khdng che dng suat, dn dinh tdng the va he sd an toan de thay rd mot sd van de cdn tdn tai lien quan den danh gia an toan ve eudng dp va dn dinh khi sCf dung 14TCN 56-88 vao thiet ke dap vdm d Viet nam.
2. To hpp tai t r p n g dac biet To hpp tai trpng trong tieu chuan thiet ke dap vdm eua eae qude gia la khdng gidng nhau.
14TCN 56-88 va SL282-2003 chi phan hai nhdm td hpp tai trpng la td hdp tai trpng cd ban va to hdp tai trpng dac biet. EM No.19 phan thanh ba nhdm to hgp tai trgng la to hgp tai trgng binh thudng, to hgp tai trgng khdng binh thudng va td hdp tai trpng cue doan. Cac trudng hdp tai trpng trong cac to hdp tai trpng eung khac nhau.
Dudi day chi xin neu mot van de ve tai trpng dpng dat trong td hpp tai trpng dae biet hay td hdp tai
trpng cue dean.
Khi thiet ke dap vdm d Trung qudc, tai trpng ddng dat dupe tfnh toan dUa vao "Quy pham thiet ke khang chan cdng trinh thCiy cdng SL203-97"[4]. Dap vdm chi thiet ke vdi ddng dat cap 6, 7, 8, 9 va cdng trinh cap 1,2,3. Odi vdi dpng dat cap 6 ed the khdng can tfnh toan khang chan, vdi dpng da't cao hdn cap 9 hoac dap vdm eao hdn 250m can phai tien hanh nghien edu them. Tfnh tdan hieu dng tac dung dia chan dap vdm sd dung phUdng phap dpng lUc hoac phUdng phap md phdng tTnh lUc.
Ddi vdi dap vdm ed yeu eau thiet ke khang chan tha'p dudi cap 8 ma edng trinh tha'p hon 70m cd the sCf dung phUdng phap md phdng tTnh lUe de tfnh toan, Khi sd dung phUdng phap ddng luc tfnh toan hieu ifng tac dung dia chan dap vdm can sd dung phuong phap phd phan Cmg ehdng chat dao dpng, ddi vdi dap vdm dac biet ed the diing phuong phap phan tich lich sd - thdi gian tien hanh tfnh toan bd sung. Dap vdm be tdng nen ddng thdi xem xet tac dung dia chan theo hudng ngang thuan ddng chay va vudng gdc vdi ddng chay. Odi vdi dap vdm mdng eong hai chieu cap 1, 2 hinh thdc dac
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MOT SO VAN OE CON TON TAI IIFN QUAN DEN DANH GIA AN TOAN..
biet nhu khdng ddi xdng, bung rong...eung vdi ddng dat thiet ke cap 8, 9 can nghien eCfu tac dung dia chan hudng thing dCfng. Gia tde dja chan thiet ke phuong ngang tUdng Cmg vdi cap dpng da't 7, 8, 9 lan lUpt la O.lg, 0.2g va 0.4g (g=9.81m/s'). Gia tde dia chan thiet ke theo phUdng ddng bang 2/3 theo phuong ngang. Gia tri Idn nhat phd phan Cmg thiet ke ddi vdi dap vdm bang 2.50. Gia trj gidi han dudi phd phan Cmg thiet ke khdng nhd hdn 20% gia tri Idn nhat. Khi dap vdm chju td hdp tai trpng dac biet ed tai trpng dpng dat, Cfng suat dap vdm v i n d trong giai doan dan hdi tuyen tfnh.
Trong EM No.19, khi tfnh toan dpng da't, phuong phap phd phan dng hoSe gia tde ljeh sd - thdi gian deu dupc xem xet sd dung.
PhUdng phap phan tfch dUa tren phUdng phap phan td hOru han dpng lue dan hdi tuyen tinh va xem xet tac dung tUdng hd dap - nude - nen [5]. To hpp tai trpng cue ddan bao gdm tai trpng ddng dat Idn nha't ed kha nang xuat hien. Khi chju td hpp tai trpng nay cho phep dap bi ndt, he sd an toan Cmg suat nen lay la 1.0 hay ndi each khac Cmg suat nen Idn nhat cd the dat den cUdng dp khang nen cua be tdng. Cmg suat dap d vao trang thai phi tuyen tinh, eho phep dap bj pha hoai d mdc dp tuong dd'i nhung khdng cho phep vd dap.
6 Viet nam mdt thdi gian dai trudc day khi thiet ke khang chan cdng trinh xay dung phd bien la ap dung tieu chuan CH8 1 1 - 7 - 8 1 cua Lien Xd. Hien nay dang sir dung TCXDVN 375:2006 "Thiet ke cdng trinh chiu ddng dat"[6] bien soan dua tren cd sd Tieu chuan Chau Au Eurocode 8 cd bo sung hoac thay the cac phan mang tfnh dae thii Viet Nam. Trong tieu chuan khdng quy djnh rd rang thiet ke khang chan cho cdng trinh thuy dac biet la cdng trinh dap vdm, vi vay van can phai tham khao tieu chuan thiet ke khang chan dap vdm eua nudc ngoai khi
chua cd mdt tieu chuan thiet ke khang cha'n rieng.
Do chenh lech yeu cau tinh trang lam viec dap vdm khi chju tai trpng ddng dat cua cac qudc gia la rat khac nhau, viec tham khao tieu chuan thiet ke khang chain dap vdm cua nude ngoai can phai nghien cCfu lUa chpn cho phu hdp vdi dac thii Viet nam.
3. Phi/dng phap phan tich ufng suat
14TCN 56-88 quy dinh viec xae dinh trang thai dng suit bien dang phai dugc thdng qua tinh toan va nghien cCfu thuc nghiem tren md hinh. Odi vdi dap cap I va II cao hdn 60m, cung nhu ddi vdi cac dap cd chieu cao nhd hdn 60m trong dieu kien dja chat edng trinh dac biet phdc tap va cd ap dung nhifng ke't eau mdi ehUa dUdc kiem nghiem qua khai thac, thi bat bude phai tien hanh nghien cCfu thue nghiem. Viec tfnh toan trang thai Cmg suat - bien dang eua dap vdm va vdm trpng life can dupc tien hanh cd xet den trinh tU thi edng dap, sU dd be tdng vao cac khdp ndi de lam cho dap thanh lien khdi va tich nude vao ho ehda bang each sCf dung nhiJmg phUOng phap tfnh toan chinh xae (phuong phap giai toan dien cac dam - cdng son, phuong phap phan tiir hiJru han v.v...). Khi tinh toan dap cap III va IV, cung nhu khi tinh toan sd bd dap thudc tat ca cac cap, eho phep sCf dung nhirng phUdng phap ddn gian (phUdng phap vdm - edng son trung tam, ly thuyet vd mdng v.v...). Trong khi dd EM No. 19 quy dmh ket qua phan tich Cfng suat dap vdm dupc lay khi sd dung phUdng phap thd tai (Trial Load Method) hoSc he thdng phan mem phan tich Cmg suat dap vdm ADSAS (Arch Dam Stress Analysis System) cua Bureau of Reclamation. Trong quy pham thiet ke dap vdm cua Trung Qudc SL 282 - 2003 da chi rd phan tfch Cmg suat dap vdm dUa tren ket qua tinh toan phUdng phap phan tai dam vdm va phUdng phap phan td hCfu han.
Dap vdm cap 1, 2 va dap vom cao hoSc dap vdm phdc tap, ngoai silr dung phuong phap phan tai dam vdm v i n nen sCr dung tinh toan phUdng phap phan td hiiu han. Khi can thiet nen tien hanh thi nghiem md hinh ket cau.
Hien nay phUdng phap chii yeu diing de phan tich Cmg suat dap vdm cd phUdng phap nhieu dam vdm, phuong phap phan tCf hCru han va phuong phap thi nghiem md hinh ke't cau. TrUdc day phUdng phap nhieu dam vom duoc sCf dung nhieu nha't, nhi/ng vdi sU phat trien cua phUdng phap phan td hufu han va phan mem mo phdng sd tren may tinh dien tCf, phUdng phap nhieu dam vdm va phuong phap thi nghiem md hinh ket eau ngay cang it sCf dung.
14TCN 56-88 da ra ddi each day da hdn 20 nSm, khi dd cdng nghe tfnh toan md phong tren may tinh chUa phat trien, viec nghien cCfu thuc nghiem tren md hinh vat ly la can thiet. NhUng vdi thdi diem hien nay, md phdng chan thuc cong trinh tren may tfnh da dat den mCfc dp hoan thien va cd dp tin cay cao, phuong phap thf nghiem mo hinh ke't cau chi nen sCf dung khi tfnh toan kiem tra eho nhCfng cdng trinh trpng yeu.
4. Chi tieu khong che umg s u i t va he so an toan
Trong EM No. 19 quy djnh ro rang chi tieu khdng che Cmg sua't keo, nen va he sd an toan cUdng dp khang nen ddi vdi timg to hdp tai trpng nhung khdng phu thuoc vao cap cdng trinh. Trong SL 282- 2003 ngoai quy djnh rd rang Cfng suat keo cho phep khi sCf dung cac phUdng phap phan tich Cmg suait khac nhau, he sd an toan khang nen cung thay ddi tuy thudc vao cap cdng trinh va td hpp tai trpng.
Cdn trong 14TCN 46-88 dap vdm ditgc thiet ke theo trang thai gidi han vdi nhieu he so va ifng suit eho phep khdng quy djnh rd rang.
Hinh dang, kich thudc, ngay tudi eua mau thf nghiem be tong khi xae djnh chi tieu cudng do khang nen cua be tdng cua cac
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MOT SO VAN DE CON ION TAI UEN QUAN OEN DANH GIA AH TOAN..
qudc gia deu khdng thong nha't. Trong SL 282-2003 quy djnh cudng dp khang nen cue han eua be tdng ehi'nh la cUdng dp khdi lap phUPng 15em d 90 ngay tudi vdi suat bad dam 80%. Trong EM No.19 quy djnh cudng dp nen cua be tdng dupe lay td mau thf nghiem tru trdn dudng kfnh 45cm, cao 90cm d 365 ngay tudi. Dd'i vdi Viet Nam, eUdng dp nen eiia be tdng thuy cdng dupe xae djnh tren mau chuan hinh lap phUdng ec kfch thudc 150x150x150 mm dupe bao dudng trong dieu kien tieu chuan d tudi 28 ngay [7].
5. On djnh tri/dt tong the va he so an toan
Trdng 14TCN 56-88 khdng quy djnh rd rang phUdng phap xae djnh he sd an tdan dn dinh ddi vdi eae cap edng trinh, tde la cd xet den lue dfnh ke't tren mat pha hoai hay khdng. He sd an toan dn dinh trong EM No. 19 cd xet den ma sat va lUc dfnh ke't tren mat pha hoai nhung khdng phu thude vao cap cdng trinh. Trong Quy pham SL 282 - 2003 quy dinh rd rang he sd an toan va phuong phap xae dinh nd dd'i vdi cac cap cdng trinh. Bang 1 so sanh he sd an toan dn dinh trong tieu chuan thiet ke dap vdm eiia 3 qudc gia.
Bang 1: So sanh he sd an toan dn djnh trong tieu chuan thiet ke dap vom eua 3 qudc gia
Quoc gia
Viet Nam My
Trung Quoc
To hop tai trong co ban Cap 1
>1.39*
3.0 3.50
Cap 2
>1.33*
3.0 3.25
Cap 3
>1.28*
3.0 3.00
To hop tai trong dac biet Cap 1
>1.125*
2.0 3.00
Cap 2
>1.08*
2 0 2 7 5
Cap 3
>1.035*
2.0 2 5 0 Ghi chii: Gia tri h§ sd an toan lay Idn han nhi/ng khong qua 15%[8]
Td bang 1 ed the tha'y rang he sd an toan ehdng trUdt eiia dap vom dupc quy djnh trong 14TCN 56-88 la qua nhd so vdi he sd an toan quy dmh trong EM No. 19 va SL 282-2003. He soan toan nay chi phii hpp vdi he sd an toan chdng trUpt dap be tdng trpng lUe, vdi dap vdm thi can phai nghien cdu them.
6. Ket luan
Qua cac sc sanh tren tha'y rang cdn nhieu van de can phai nghien cdu trUde khi tfnh toan thiet ke dap vdm be tdng dae biet la van de khdng che img sua't va lUa chpn he sd an toan. Viec ap dung tieu chua'n 14TCN 56-88 de thiet ke dap vdm la ehUa that phii hop.
Viet nam chUa cd nhieu kinh nghiem xay dUng dap vdm, tham khao tieu chua'n thiet ke eua cac nude tien tien la viec lam can thiet trong thdi budi hien nay khi chua ed mdt tieu chuan mdi eho thiet ke dap vdm.Q
Tai lieu tham khao:
1 Bo Thuy loi, Nudc Cpng hoa Xa hoi Chu nghTa Viet Nam. Thiet ke dap be tong va be tong cot thep - Tieu chuan thiet ke 14TCN 56-88, 1988.
2 United States department of the interior - Bureau of Reclamation.
Design Criteria for Concrete Arch and Gravity Dams, 1977.
3. PR. China. Design specification for concrete arch dams SL282-2003, 2003.
4 PR.China. Specifications for seismic design of hydraulic structures SL203-97. 1997.
5. U.S. Army Corps of Engineers. Arch Dam Design EM1110-2-2201, 1994.
6 Tieu chuan xay durig Viet Nam. Thiet ke edng trinh chiu ddng dat TCXDVN 375-2006. 2006.
7. Bd NN v^ PTNT Nudc Cdng hoa xa hpi chu nghTa Viet nam. 776u chuSn ng^nh
14 TON 63-2001. Be tdng thuy cdng - Yeu cau ky thuat, 2001.
8. Tieu chuan xay dung Viet nam. Cong trinh thuy Igi - Cac quy dinh chu yeu ve thiet ke TCXDVN 285:2002. 2002.
9. Li Zhan-mei. Design allowable stress of arch dam in China companng with that in American, Guizhou water power, 2002, Vol.16 No.1, pp85-87.
10. Dong Fu-pin, Zhu Bo-fang, Shen Zhi-liang, Ge Nan. A survey of high arch dam stresses in the world, Journal of China Institute of Water Resources and Hydropower Research, 2003, Vol.1 No.4, pp292-299.
COMPARISON OF VIETNAMESE CONCRETE ARCH DAM DESIGN STAN- DARDS WITH AMERICANS AND CHI- NESE IN SOME BASIC CRITERION
VU HOANG HUNG*, Ll TONGCHUN, NGUYEN QUANG HUNG 'College of Water conservancy and Hydropower Engineering, Hohai University, Nanjing, China
Postal address: no.1 Xikang Road, Nanjing, China. Postal code: 210098
Email: [email protected] Abstract: In company with the devel- opment of design technology, arch con- crete dam design standard of each nation needs regular edit and update to meet the higher and higher requirements in econo- my and safety. This is also show the devel- opmental grade of each nation in arch dam construction technology. Based on "The American Design Criteria for Concrete Arch and Gravity Dam EM No. W issued In
1977, "The Chinese Design specification for concrete arch dams SL 282-2003"
launched in 2003 and 'The Design Code for Concrete and Reinforced Concrete Dams - Vietnamese Design Standard
14TCN 56-88"published in 1988, the paper concentrates on analyzing and comparing some of the major regulations such as load combination, the stress analysis methods, criteria for controling stress, analyzing sta- bility ana the safety factors to distinguish the difference between the mentioned standards.
Keywords: arch dam, design critena, comparison, load combination, allowable stress, safety factor
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