TRAO DOI Y KIEN
BAI HOC RUT RA TLT GONG T A G THIET KE VA
m
THAM DINH CAU BAI CHAY
C
hat lupng cdng trinh xay dt/ng ndi ehung phu thude kha nhieu nhan td, d day eh? xin neu mdt sd yeu td Hen quan den van de thie't ke va tham djnh cdng trinh, dua tren co sd thi/e te cua du an cau Bai Chay, vupt ciia Lue thanh phd Ha Long.Cau Bai Chay la mdt trong nhifng edng trinh trpng diem Qude gia, khdng nhifng vi dd la mdt cdng trinh cd nhjp glUa vao loai ky lue, dai nhat the gidi, so vdi nhUng eau ciing loai (Cau day vang mdt mat phing), ma edn la cdng trinh cd nhieu cdng nghe phife tap (mdng gieng c h i n hai ep, dam cd eanh h i n g Idn, bang BTDLTL, due h i n g can bing). Cdng trinh cd y nghTa kinh te, xa hdi quan trpng, nam trong mdt dja ban cd nhieu tiem nang du ljch qude te, dae biet cdng trinh nam g i n khu vi/c dupe edng nhan la Di san the gidi: Vjnh Ha Long.
Khi tie'n hanh k i l m tra hd sa thiet ke ky thuat cua phan c i u chfnh da phat hien thay ngay ca y kien tham dinh thie't ke do Hdi Cau dudng phan bien, cung chua dupc dap ifng d i y dii va phan hdi. Cd ngudi eho ring:
ta edn qua tin tudng vao chat lupng thiet ke ciia tu van Nhat Ban, chua coi trpng nhieu y kie'n eiia cac ehuyen gia cau Viet Nam.
Cau Bai Chay treo mdt dan phang day vang tren mdt thap cao 90m ma ch? cd tie't dien ngang nhu trong thie't ke ky thuat la chua dam bao ve mat dn djnh, vd so vdi 3 cau ciing loai, tUng giff ky lue the gidi trong cae thdi gian 1977, 1987, 1994, lan lupt la cae c i u Brotonne (Phap), c i u Sunshine Skyway (My) va c i u Iroise (Phap), cd nhip giUa ch? dai l i n lupt la 320m,366m va 400m, (cau Bai Chay nhjp giUa dai 435m); nhung kfch thude tru thap eiia nhifng c i u tren vifa thap hon, vUa cd tiet dien tuong ddi du, bao dam dn dinh vdi mpi dieu kien tai trpng tac dung. Mdmen quan tinh cua tru thap c i u Bai Chay lai tuong ddi nhd, dac biet la theo chieu ngang c i u .
Hon nffa, vat lieu xay dt/ng thap tru cau Bai Chay lai chl thiet ke vdi be tdng cap dp ben la 45Mpa (trong khi dd cau Iroise thap tru c i u sif dung loai be tdng cap dp len de'n SOM Pa).
GS.TSKH. NGUYEN TRAM Trudng Dai hpc Kien true Ha Ndi
Ve eau tao chung eua ket c i u nhjp, canh h i n g hai ben c i u rat Idn, dai g i n 5,0m mdi ben (mat c i u rdng 25,30m, han cac c i u khae nhu c i u Brotone ch? rdng 19,20m, edn c i u Iroise rdng 23,10m, hep han c i u Bai Chay mpt chiit, nhung lai bd tri them cae thanh chdng, nen mut hang eh? cdn dai 2,50m mdi ben), do dd thay rang c i n k i l m tra khdng nhffng ve cudng dp ma ca van de dn djnh va dao dpng eua eanh hang trong mpi trang thai chju lire cua cdng trinh.
V l van de truyen tai tU cae day vang xud'ng mat c i u , k i l m tra cho thay ehi tiet cau tao cue bd chd bd tri neo cung ehua that dn, c i n tang cudng them d i m dpc lien tuc d true tim cau.
Cac he giang ngang, tai vj tri neo day vang, eung c i n chii y them ve eau tao, cho dam bao an toan han.
Ngoai ra, viec k i l m tra edn dupe tht/c hien vdi cac tai kieu lien quan de'n nhffng sd lieu quan t r i e td'c dp gid trong viing Ha Long, cung nhu cac sd lieu lien quan ve thay ddi nhiet dp, dp am va cac he sd tai trpng v.v.. ma t u van thiet ke da sif dung d l tinh toan thie't ke ky thuat c i u Bai Chay.
Hon nffa, vi day la c i u qua b i l n , mdt cdng trinh dac biet quan trpng, tudi thp yeu eau tren 100 nam, xay dung trong mdi trudng k h l c nghiet ve dp an mdn, do dd c i n luu y tinh toan chdng g? cho cdt thep, trong dieu kien ndng am eiia Viet Nam, vdi thdi gian ft nhat cung keo dai tren 100 nam.
Sau khi nhieu cudc hpp vdi tu van thiet ke, true tiep
"ddi thoai - giai trinh" va di de'n yeu c i u la e i n tham tra lai hd so thie't ke ky thuat c i u chfnh.
Ngay 02/4/2004, y kie'n eh? dao eiia Thu tudng Chfnh phii ve k i l m tra lai thie't ke c i u Bai Chay (VB 64/TB.VPCP), ket hpp vdi van ban Chap thuan cua Bd GTVT v l thay ddi sd lieu d i u vao (2193/QD- BGTVT) lien quan den tdc dp gid max tinh toan va eae he sdtai trpng sif dung..., nen Ban quan l y e a e d u an 18 (PMU18) da ed van ban yeu c i u tu van thie't ke Nhat Ban tham tra lai hd so c i u Bai Chay.
Ke't qua sau khi t u van tham tra va tu van thiet ke tinh toan lai mpt each chi tiet da thdng nhat mdt sd
TAP CHI CAU DUONG VIET NAM
TRAO 0 0 1 Y KIEN
dieu ch?nh e i n thiet nhu sau:
- Tang them thep cho ea 3 mdng gieng chim hai ep la 76 tan va bd trf s i p xep lai vj tri cac thanh cdt thep eho hpp ly hon, dua tren ket qua tfnh toan theo phuang phap p h i n tii' hffu han.
- Cap DUL eang ngang mat c i u theo thiet ke cu la 1523 tao, e i n them 193 tao (khoang 18,8 tan) va cd d i l u chinh khoang each tao cap cue bd tai vj trf neo, cho phii hpp vdl ifng s u i t phat sinh.
- Bd trf d i m dpc lien tue sudt chilu dai c i u . U cac thanh chdng cheo d ban day dupc ndi l i l n vdi nhau tao ra mdt khung ngang du truyin luc hcfp ly, tU cac day vang xudng d i m c i u chfnh.
- DUL dpc tai ban eanh tren eiia dam c i u , giam dupc 10 bd cap 12 tao T l 3 d khdi Ko due tren da giao, nhung phai tang them 52 thanh DLTL 32 d cac khdi due hing khac, khi due hang.
- De giam bdt lue gid tae dung len dan day, dudng kinh dng ghen ciia cac bd cap se chpn giam bdt kich thude tu 250-180mm edn 200-150mm.
- Than tru c i u chinh, thep bd tri tang them tU 770 len 778,2 tan (them 8,2 tan thep).
- Be tdng khdi d i m Ko tren dinh tru ciing vdi thap cau phao thiet ke loai be tdng vdi cap dp ben 55Mpa thay cho cap 45Mpa trong thie't ke eu.
- Cac thanh chdng cheo trong Idng d i m , tai 224 vj tri neo day vang, e i n thay the cac dng thep trdn b i n g cac dng thep hinh vudng, cd thanh day 16mm, dien tich g i n gap ddi; ddng thdi thay cae thanh DLTL ....32 bang cap 12 tao T15, vdi luc nen trude gap hai l i n thie't ke eu (1200-1700kN thay eho 666,4kN).
- Rieng hai thap, e i n tang them 165 tan thep dac ehiing ...51 va bd tri them hai Idp cap 12 tao T l 3 (han 50 tan cap DUL). Ddng thdi bd tri them he thd'ng giam chan loai TLD (tuned liquid damper) trong Idng thap.
- V l chilu day Idp be tdng bao ve cdt thep. Vi yeu c i u thiet ke lai vdi dff lieu d i u vao mdi (sau khi cd ket qua thi nghiem m i u thif tai Vien khoa hpe cdng nghe xay di/ng va tai cdng trudng), da lay nhu sau:
+ Ddi vdi thap: Idp bao ve tang tdi 44mm;
+ Ddi vdi d i m : tir 35 len 45 mm (ban day va sudn d i m ) , neu khdng dii, phai quet Idp son epdxy bao ve;
+ Ddi vdi tru v i n de Idp bao ve day 5mm;
+ Ddi vdi ban canh tren, Idp cdt thep tren ciing, vi da ed Idp ao dudng bao ve thi van d l Idp nay day
35mm nhu thiet k e e u .
Kit luan:
Qua Du an c i u Bai Chay ehung tdi thay c i n rtJt ra nhUng bai hpe:
1. Tu van thiet ke mac dii hp da cd kinh nghiem lau n§m va da cd b l day ljch siJ" trong thiet ke nhung cdng trinh dae biet. Nhung tht/c chat "tu van" la tinh toan va danh gia eua nhung eon ngudi eu t h l , trong tUng thdi gian cu the, ed nhung t i l m luc va the manh khac nhau.
Vi vay, Chii d i u tu (Ban quan ly duan) phai tuan thii cac quy djnh ciia phap luat ve xay dung. Od la phai td chUe lay cac phan bien ddc lap. Nhung ddi vdi nhung cdng trinh dac biet, c i n td ehUe bao dam tht/c su liy dupc nhung y kien khaeh quan va cd chat lupng cua cae chuyen gia d i u nganh ve ITnh vt/c khoa hpe ky thuat cu the. Tranh hien tupng kilu phan bien kilm tra thiet ke lien danh, vUa da bdng vUa thdi cdi, vdi nhung nhan xet phan bien xudi chieu ciia ciing lien danh, hoac eung khdng nen lay y kien chdp nhoang, chieu le trong thdi gian qua ngin. Hoac ch? dimg d giai doan l i y y kien cua nhung ngudi lam edng tac quan ly cao cap.
2. Neu xet thay c i n thiet thi phai td ehUe hdi thao ve cae v i n de edn gay tranh cai, chua di den thd'ng nhat. Hdi thao ed t h l dudi hinh thUe hdi nghj tham ke md rdng, trong dd phan bien ddc lap la cac chuyen gia, nhifng nha khoa hpc chuyen sau ve mdt sd ITnh vt/e dang van edn tdn tai, vudng mac.
3. Thdng sd d i u vao c i n dupc khao sat ky ludng hon, cang chfnh xac eang tdt, dae biet chii trpng den sd lieu dja chat, d i l u kien thdi tiet thiiy van eua dja ban edng trinh. Neu khdng dii sd lieu d i n den edn nghi ngd dp chinh xac ciia ket qua tfnh toan - thie't ke thi e i n phai yeu c i u Chii d i u tu t h l hop ddng vdi tu van thiet ke khao sat bd sung.
4. Cudi eiing c i n n h i n manh them : viec ra soat lai thie't ke, tham tra mpi mat lien quan, nhilu t i n g , nhieu Idp, la mdt viee cue ky quan trpng, nhat la ddi vdi cac cdng trinh trpng d i l m Qudc gia.
Nhan tien day, cOng xin de nghj tdi cac c i p ed lien quan: nhung phan bien cd gia tri, nhung y kien de xuat lam thay ddi phuang an thiet ke, hoac edng nghe thi cdng, mang lai nhieu lpi fch eho du an ve mat kinh te, ky thuat hoac an toan... nen chang e i n dupc xem xet khen thudng dung mUc, nhu mdt sang kien, mdt d l xuat, ap dung cai tien, mang lai hieu qua cho du an •
TAP CHi CAU DLTdNG VIET NAM
