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Bm CTGTTP & CTT http://ctgttp.org Gao trnh Thit k cu cong v cu cho Ph Lc 2: V d thit k Nt giao thng Bn Lc

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v d 2 Thit k nt giao khc mc bn lc

1.1. Gii php thit k kt cu cu Bn Lc v cu trong nt giao Bn Lc

Cu Bn Lc vt qua sng Vm C ng c s kt cu nhp dm hp lin tc

lin tc 50+90+120+90+50m bng b tng ct thp d ng lc. Vi s ny

cho php to c hnh dng chuyn tip hi ho ca chiu cao dm cho ph hp

vi phn cu dn.

y l cu ln qua sng su, tuy vy do vn nhu cu vn ti m cu cng nh

ton b tuyn ng cao tc c xem xt phn k u t. c cc d n cu

ln thc hin phn k u t nh cu Ph ng qua sng ung, nhng vi cu

Bn Lc li c c th ring v c tng mt ct ngang ti giai on hon thin ln

(39.5m) v li lin quan trc tip ti nt giao lp th ngay u cu. Cc vn t

ra i vi cu ny l c thc s nn phn k hay u t hon thin lun trong giai

on 1 v nu phn k th s phn chia mt ct ngang gia hai giai on nh th

no trong cc phng n xy dng mt bn, hai bn hay gia.

- Phng n u t hon thin: l phng n rt tch cc xt trn quan im k thut nhng vn gp phi l vic s dng cha hp l ngun vn u t v

phi chp nhn mt phn cu s khng c s dng cho ti khi xy dng

xong giai on 2 v iu s dn ti cc cu hi ca d lun x hi.

- Phng n u t phn k: khc phc c nhc im ca phng n u t hon thin nhng li dn ti cc vn phc tp trong x l cng ngh thit

k cng nh thi cng sau ny trong giai on 2.

Cc vn t ra nh vy tng chng n gin xong cng dn ti nhiu tranh

lun da trn cc quan im v k thut, v kinh t v v vic hoch nh chnh

sch, bi v cc quyt nh cu Bn Lc hin ti s c nh hng ln ti cc

cng trnh sau ny. Qua nhiu cuc hp c t chc v cui cng phng n

thit k cu Bn Lc l phn k u t trong giai on 1 xy dng 2 cu hai

bn vi b rng mi cu 12.25m v giai on sau xy dng nt phn cu gia

vi b rng 17.5m. gim bt kh khn cho thi cng giai on sau th ngay t

giai on 1 kt cu phn di ca cu gia cng c u t xy dng vi kt

cu mng ca c 3 cu c ni lin thnh mt khi.


2

8650

2%

81

7200

5000

12250

81

500 3000 2@3750=7500 750 5002 ln xe c gii

tim tuyn giai on hon thin

14775

41800

8650

2%

81

7200

5000

12250

81

50030002@3750=75007505002 ln xe c gii

14775

7501000 750

9000

2%

81

7200

5000

12100

81

500 3000 2@3750=75002 ln xe c gii

14775

41800

2%

81

7200

5000

81

50030002@3750=75002 ln xe c gii

14775

50

1100 2@3750=75002 ln xe c gii

8750 8750 50

11002@3750=75002 ln xe c gii

12100

81

81

2% 2%

khe co gin dckhe co gin dc

Hnh 1. Mt ct ngang cu Bn Lc giai on 1

Hnh 2. Mt ct ngang cu Bn Lc giai on 2 (hon thin)

Nt Bn Lc l nt giao gia ng cao tc Thnh ph H Ch Minh Trung

Lng vi ng tnh l 830.

Nh phn tch trn, kt cu nt giao c dng trumpet kp, trong giai on

1 xy dng phn trumpet lin h vi cu cao trn tuyn cao tc, giai on hon

thin s xy dng nt phn trumpet lin h vi ng tnh l 830. Gii php kt

cu cu trong nt giao phi bo m c mt s vn nh sau:

- To c tnh lin tc ca h cu cao trn chnh tuyn cao tc.

- Thun tin trong vic phn k u t giai on 1 xy dng hai bn.

- X l tt cc cu nhnh c cong ln.

- Tnh kinh t cao.

- Tnh thm m tt.

Bng cc phn tch so snh v nhiu mt trong c cc mt nh nu trn, gii

php kt cu cu cho nt giao nh sau:

- Phn cu trn chnh tuyn cao tc s dng dm Super T cng vi dm cu cao.

- Phn cu nhnh cong s dng dm bn bng b tng ct thp d ng lc thi cng c ti ch trn gio vi chiu di nhp t 24 ti 30m tu theo


3

10000

500 500

1200

2@3500=70001000 1000

i%

cong trn mt bng ca cu. Kt cu thn tr trn b tr 1 gi kt hp vi kt

cu thn tr dng van b tr hai gi ti v tr khe bin dng.

Hnh 3. Mt ct ngang cc cu nhnh A v B

1.2. Vn ng dng cng ngh tin hc trong thit k cu Bn Lc v cu cong trong nt giao Bn Lc

Chng ta c s tr gip c lc ca cng ngh tin hc trong cng vic nhng

khng c l thuc hon ton vo n. Khng phi him cc trng hp ngi s

dng phn mm m khng hiu ht bn cht cc x l tnh ton ca phn mm,

khng qun l c cc kt qu tnh ton, khi mc li khng tm ra c hng

gii quyt,khi cng ngh tin hc s bin chng ta thnh k n l th ng.

Do vy trong khun kh bo co ny, nhm tc gi mun thng qua mt d n c

s dng cng ngh tin hc trong thit k cp ti vic hiu bit v s dng

cng ngh tin hc, bin n thc s tr thnh cng c m khng l thuc hon

ton vo n.

Thit k cu Bn Lc Cu Bn Lc l cu BTCT DL thi cng c hng thit k s dng phn mm

RM2000. Khi tnh ton cn phi nm vng cc kin thc v trnh t cng ngh

xy dng, v m hnh tnh ton, v cc bc tnh ton, v cc c im ca d

ng lc, cc c trng ca b tng, cc phn tch v tnh n hi ca cc lin

kt,

1.2.1.1 Cng ngh xy dng

Trong tnh ton thit k ni chung, iu kin quan trng ban u l phi nm

c cng ngh thi cng v cc iu kin lm vic ca kt cu, t c cc tnh

ton cn thit kim sot c ton b qu trnh lm vic .

Cu Bn Lc thi cng phn on. Trnh t thi cng c th khi qut theo cc giai

on nh sau:

- Thi cng trn gio: kt cu lm vic cha pht sinh ni lc.

- Thi cng hng: kt cu lm vic s tnh nh.

- Thi cng hp long: thc hin vic tng dn lin kt cho kt cu.


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- Thi cng cc hng mc hon thin cu: kt cu lm vic theo s s dng lu di ca qu trnh khai thc.

1.2.1.2 M hnh tnh ton

Kt cu dm hp c th c tnh ton theo s khng gian bng cc phn t

tm hoc tnh ton theo s phng theo phn t thanh.

Vi mi loi m hnh tnh, cn phi c rt nhiu s tnh tng ng vi cc

bc trong trnh t cng ngh. Vi 1 cu thi cng phn on thng phi tri qua

cc dng s : Tnh nh, siu tnh 1 nhp, siu tnh 2 nhp,siu tnh nhiu nhp

tu theo s lng nhp ca cu (S bc siu tnh ph thuc vo kiu lin kt gi).

1.2.1.3 Lin kt ni t

Lin kt ni t thng l cc vn rt nhy cm trong tnh ton kt cu v n

nh hng ln ti kt qu ni lc kt cu cu, c bit l i vi kt cu phn

di. Lin kt ni t thng l cc lin kt n hi (spring). Vic xc nh chnh

xc cc thng s ny ngoi vic am hiu v kt cu cn phi c kin thc tt v

a k thut v nn mng.

1.2.1.4 Mt s tc ng v ng x ca kt cu trong qu trnh thi cng

- Tc ng ca trng lng bn thn: i vi kt cu cu thi cng phn on s dng phng php c hng th trng lng ca bn thn b tng cng

phi c phn bit gia tc ng khi b tng cn t (cha c cng ) v

khi b tng c cng ko d ng lc v tr thnh kt cu chu lc. Cn

phn tch k c tnh ny c th a cc s liu chnh xc vo m hnh ti

trng tnh ton.

- Tc ng ca xe c: Xe c cn c gi l h gio vn khun di ng c cc khi b tng dm. Trng lng xe c thng thng t 50 ti 120

tn tu theo kch c khi c ca mi cu. Tc ng ca xe v tr c dm

gm trng lng theo phng thng ng v m men do lch tm ti u dm

hng. Khi xe di chuyn s to ra mt ngu lc tc ng ln kt cu.

- Tc ng ca vic tho d h gio v cc lin kt tm: H gio v cc lin kt tm u c chung mt nguyn l l c s dng v cng lm

vic vi kt cu trong mt giai on thi cng no v khi ht nhim v s

c tho b. Do vy trong qu trnh lm vic chng c tip nhn v tch

lu mt phn ni lc. Khi tho b chng, cc ni lc ny s tr thnh ngoi

lc v tc ng trc tip ln kt cu theo chiu ngc li.


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1.2.1.5 nh hng ca nhit

Trong qu trnh thi cng, khi s kt cu l tnh nh th tc dng ca nhit

gy ra chuyn v cho kt cu m khng pht sinh ni lc. Khi kt cu tr thnh

siu tnh th ngoi vic gy chuyn v, nhit cn gy ni lc ln trong kt cu.

nh hng ca nhit c xem xt di hai dng l: Nhit thay i u dc theo kt cu (Uniform temperature) v Chnh lch nhit theo hai phng

trn mt ct ngang kt cu (Gradient temperature). Cng thc chung bin dng do

nhit bng tch ca h s bin dng nhit v tr s nhit chnh lch.

Trng hp nhit thay i u do c coi l phn b u trn mt ct nn

trong kt cu ch pht sinh bin dng dc trc.

Trng hp nhit thay i trn mt n v theo chiu cao hoc chiu ngang

mt ct (gradient nhit ) s pht sinh bin dng un trn mt ct dm.

1.2.1.6 nh hng ca t bin co ngt

Kt cu cu b tng ct thp d ng lc thi cng phn on theo phng php

c hng cn bng vn t bin v co ngt c xem xt i vi mi giai on

thi cng cng nh hon thin cu.

nh hng ca t bin v co ngt ph thuc vo cc yu t bao gm:

- Cc c trng vt liu, mt ct ngang, mi trng (nhit , m).

- Trng thi ng sut trong kt cu.

- Thi im t ti tnh t bin.

ng bin do t bin v co ngt l cc tr s c lp, tuy nhin do tnh cht tng t nn thng c xem xt cng nhau.

ng x ca kt cu do t bin c gi thit l tuyn tnh, do vy ng bin do t bin l hm tuyn tnh ca ng bin n hi vi h s t bin l . iu ny bo m mt ct ngang vn phng khi chu lc.

c

cccc E

.

H s t bin l thng s rt quan trng trong tnh ton t bin, n l hm ca nhiu thng s gm thi gian, c trng vt liu, c trng mt ct ngang, iu

kin kh hu khu vc xy dng cng trnh. Cc m hnh tnh ton t bin trong

cc quy trnh khc nhau chnh l vic xem xt cc dng hm khc nhau v quan

h ca h s t bin vi cc thng s k trn.

ng bin ca kt cu do co ngt l hm ca thi gian v c c trng bi h s co ngt cs. ng bin do co ngt c gi thit bng hng s trn mt ct ngang,


6

do vy iu kin mt ct ngang vn phng c bo m. Cc m hnh tnh ton

cho co ngt cng c dng tng t nh tnh ton cho t bin.

Cc thng s v vt liu thng s dng trong tnh ton t bin v co ngt:

- M un n hi b tng: y l thng s ph thuc vo thi gian. Mt s m hnh tnh h s t bin yu cu tr s ny (v d nh quy trnh 22TCN 18-79)

nhng cng c nhiu m hnh tnh khng yu cu (v d nh cc tiu chun

22TCN272-01, CEB-FIP, AASHTO, BS5400).

- c chc ca b tng ti khi b tng: thng thng c chia lm 3 cp tu theo t l nc/xi mng l thp, trung bnh hay cao. Thng s ny

c s dng trong cc m hnh ca CEB78 hay OE4750. Vi cc m hnh

nh CEB90, BS5400 hay AASHTO khng dng thng s ny.

- ng cng ca xi mng: Thng s ny ph thuc vo tnh cht ca xi mng v c chia lm 3 cp l ng cng nhanh, ng cng va v nhanh v

xi mng cng cao ng cng nhanh. Thng s ny dng trong m hnh

CEB90, DIN1045, nhng li khng s dng trong CEB78, BS5400 hay

AASHTO.

Cc thng s v mi trng thng s dng trong tnh ton t bin v co ngt:

- m: m s dng cho tnh ton t bin v co ngt l m tng i trung bnh bnh qun nm ca mi trng khu vc xy dng. Thng thng

c th p dng bng hng s cho tt c cc cu kin, tuy nhin cng c th p

dng khc nhau cho cc phn t nm trong cc mi trng khc nhau nh

trong khng kh, trong t hay trong nc.

- Nhit : Nhit c s dng l nhit trung bnh bnh qun nm ca khu vc xy dng.

Thng s v thi gian trong tnh ton t bin v co ngt:

Yu t thi gian i vi t bin v co ngt l rt quan trng, trong tnh ton cn

quan tm ti cc mc thi gian nh sau:

- Thi im bt u b tng.

- Thi im b tng ng cng hon ton sn sng tip nhn ti trng.

- Thi im t ti v tnh ton t bin.

Mt s m hnh t bin v co ngt cho php tnh ton thi im bt u t bin

v co ngt l khc nhau.

Thng s v ti trng trong tnh ton t bin:


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nh hng ca t bin c tnh ton vi cc ti trng tc dng lu di trn kt cu.

1.2.1.7 Ni lc s cp v th cp i vi cc tc ng t bin v d ng lc

Trong tnh ton kt cu siu tnh cn i vi cc tc ng nh t bin hay d ng

lc cn phn bit hai khi nim ni lc s cp v ni lc th cp. Nguyn l

chung c th hiu ni lc s cp l ni lc sinh ra ngay trong phn t kt cu chu

tc ng trc tip ca cc yu t (t bin, d ng lc) cn ni lc th cp sinh ra

trn ton kt cu do cc phn lc trong cc lin kt bin sinh ra do cc tc ng

k trn to thnh. Hay c th hiu mt cch n gin hn l cc tc ng sinh ra

ni lc s cp trn phn t m n tc ng ng thi gy bin dng cho phn t

. Do bin dng ny b kim ch bi cc lin kt bin nn gy ra ni lc trong

cc lin kt bin . Ni lc trong cc lin kt bin s ging nh ngoi lc tc

ng tr li kt cu v sinh ra ni lc th cp.

Hnh 4: Biu m men s cp khi ko d ng lc hp long nhp k bin

Hnh 5: Biu m men th cp khi ko d ng lc hp long nhp k bin

Hnh 6: Biu m men tng cng khi ko d ng lc hp long nhp k bin


8

rq

N

Q

M M+dM

N+dN

Q+dQ

r

d

ds

t

I

Thit k cu cong trong nt giao Bn Lc Gii quyt bi ton cu cong ta phi hiu v bn cht ca thanh cong chu lc.

Thanh cong c phn lm hai loi l thanh c cong ln khi t l gia bn

knh cong ca trc (R) v chiu cao mt ct (h) nh hn 10, ngc li l thanh c

cong b. Vi thanh c cong b th c th s dng cc cng thc ca thanh

thng tnh ng sut m sai s khng ng k. Nt giao Bn Lc gm c 4

nhnh cu cong trong 2 nhnh A v B thuc loi c cong ln cn hai nhnh

C v D c cong nh.

i vi kt cu dm cu cong b tng ct thp d ng lc cn phn bit hai loi

lc tc dng l: cc lc loi 1 nm trong mt phng vung gc vi mt phng

cha trc thanh cong v d nh trng lng bn thn, trng lng hoi ti v cc

lc loi 2 nm trong mt phng cha trc thanh cong nh lc hm, lc ko d

ng lc, lc ly tm. Xt v c bn cc lc loi 1 gy ni lc trong kt cu khng

khc nhiu so vi thanh thng ngoi vic lm tng hiu ng xon hay gy cc lc

ly tm i vi ti trng di ng trong khi cc lc loi 2 li gy cc trng thi

ng sut phc tp trong thanh cong. Cc biu thc di y th hin quan h vi

phn gia ni lc v ngoi lc ca thanh cong khi xt mt phn t thanh cong bn

knh r c chiu di ds v chu lc bt k q v t nm trong mt phng cha trc

thanh

rQt

dsdN

;

rNq

dsdQ

;

Qds

dM .

Hnh 7: Quan h ni lc v ngoi lc thanh cong

Ngoi ra phn tch ng sut php trn mt ct ngang thanh cong chu cc lc loi

2 cho cc kt lun nh sau:

- Thanh cong chu ko (nn) dc trc, ng sut php phn b u trn mt ct ngang v thanh cong khng ch c bin dng dc trc mt ct cn b quay.

- Thanh cong chu un thun tu th ng sut php phn b trn mt ct ngang theo dng ng hypecbol c hai ng tim cn, mt ng i qua tm cong

v vung gc vi mt ct cn mt ng nm song song vi mt ct v ct

mt ct mt khong M/Fa (xem hnh v di y).


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Hnh 8: ng sut php trn mt ct ngang thanh cong chu un thun tu

R rng vic xem xt bi ton thanh cong l rt phc tp v ch c thc hin

nhanh chng bng my tnh.

Cc cu cong trong cc nhnh ca nt giao Bn Lc c tnh ton bng phn

mm RM2000.

Mc lc 1.1. Gii php thit k kt cu cu Bn Lc v cu trong nt giao

Bn Lc .................................................................................................................... 1

1.2. Vn ng dng cng ngh tin hc trong thit k cu Bn Lc v cu cong trong nt giao Bn Lc ............................................ 3

1.2.1 Thit k cu Bn Lc ......................................................................................... 3

1.2.1.1 Cng ngh xy dng ......................................................................................... 3

1.2.1.2 M hnh tnh ton .............................................................................................. 4

1.2.1.3 Lin kt ni t ................................................................................................. 4

1.2.1.4 Mt s tc ng v ng x ca kt cu trong qu trnh thi cng ...................... 4

1.2.1.5 nh hng ca nhit .................................................................................... 5

1.2.1.6 nh hng ca t bin co ngt ......................................................................... 5

1.2.1.7 Ni lc s cp v th cp i vi cc tc ng t bin v d ng lc ............... 7

1.2.2 Thit k cu cong trong nt giao Bn Lc ........................................................ 8

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