Bài Giảng Cơ Sở Công Trình Cầu

MC LC BI GING C S CNG TRNH CU

B MN CU HM - CSII H GIAO THNG VN TI - C S II1

MC LCCHNG 1: ................................................................................................................ 8KHI NIM V CC CNG TRNH NHN TO TRN NG .................. 8

1.1. CC LOI CNG TRNH NHN TO TRN NG: ........................................81.1.1. Cu: ........................................................................................................................81.1.2. Cc cng trnh thot nc nh:..............................................................................81.1.3. Tng chn: .........................................................................................................101.1.4. Hm: ....................................................................................................................10

1.2. CC B PHN V CC KCH THC C BN CA CU: ............................131.2.1. Cc b phn ca cng trnh cu:..........................................................................131.2.2. Cc kch thc c bn ca cu: ...........................................................................13

1.3. PHN LOI CU:.....................................................................................................151.3.1. Phn loi theo mc ch s dng: ........................................................................151.3.2. Phn loi theo vt liu lm kt cu nhp: .............................................................151.3.3. Phn loi theo chng ngi vt: ..........................................................................151.3.4. Phn loi theo cao ng xe chy: .................................................................191.3.5. Phn loi theo s tnh hc: ..............................................................................201.3.6. Phn loi theo s cu to: ...............................................................................21

1.4. CC YU CU C BN I VI CU: ...............................................................241.4.1. Yu cu v mt xy dng v khai thc: ...............................................................241.4.2. Yu cu v mt kinh t: .......................................................................................251.4.3. Yu cu v mt m quan: ....................................................................................251.4.4. Yu cu v mt an ninh quc phng: ..................................................................25

1.5. S LC LCH S V XU HNG PHT TRIN NGNH XD CU: ............251.5.1. S lc lch s pht trin ngnh xy dng cu: ..................................................25

1.5.1.1. Cu g: .........................................................................................................251.5.1.2. Cu : ..........................................................................................................251.5.1.3. Cu thp:.......................................................................................................261.5.1.4. Cu btng ct thp:.....................................................................................26

1.5.2. Mt s xu hng pht trin khoa hc k thut trong ngnh xy dng cu: ........291.5.2.1. V vt liu: ...................................................................................................291.5.2.2. V kt cu:....................................................................................................291.5.2.3. V cng ngh thi cng:.................................................................................291.5.2.4. V tnh ton: .................................................................................................29



CHNG 2: .............................................................................................................. 30CC CN C C BN V IU KIN THIT K CU ......................... 30

2.1. CC GIAI ON U T XY DNG V CC BC THIT K: ...............302.1.1. Cc giai on u t xy dng: ...........................................................................30

2.1.1.1. Chun b u t: ...........................................................................................302.1.1.2. Thc hin u t: ..........................................................................................322.1.1.3. Kt thc xy dng a cng trnh vo khai thc s dng: ...........................33

2.1.2. Cc bc thit k: ................................................................................................332.2. TRIT L THIT K: ...............................................................................................34

2.2.1. Phng php thit k theo ng sut cho php: (ASD) ........................................352.2.2. Phng php thit k theo h s ti trng: (LFD) ...............................................352.2.3. Phng php thit k theo trng thi gii hn (LSD): ........................................362.2.4. Phng php thit k theo h s ti trng v sc khng (LRFD): ......................37

2.3. CC TIU CHUN THIT K CU HIN HNH: ..............................................38

CHNG 3: .............................................................................................................. 39THIT K CC PHNG N CU .................................................................... 39

3.1. CC CN C LP PHNG N CU: ................................................................393.1.1. Khi nim chung:.................................................................................................393.1.2. Phn tch cc ti liu khi thit k cc phng n cu: .........................................39

3.1.2.1. Chn v tr cu: .............................................................................................393.1.2.2. Mt ct dc tim cu: .....................................................................................403.1.2.3. Mt ct a cht dc tim cu: .......................................................................403.1.2.4. Cc s liu thy vn: ....................................................................................403.1.2.5. Khu thot nc: .....................................................................................40

3.1.3. Kh gii hn v kh thng thuyn: .....................................................................413.1.3.1. Kh gii hn: ................................................................................................413.1.3.2. Kh thng thuyn: ........................................................................................41

3.2. THNH LP CC PHNG N CU: .................................................................423.2.1. Xc nh tng chiu di kt cu nhp: .................................................................423.2.2. Chn v b tr cc nhp cu: ................................................................................42

3.2.2.1. Xc nh v tr v khu nhp ch: ............................................................423.2.2.2. Chn dng v phn chia kt cu nhp:..........................................................43

3.2.3. Xy dng ng mt cu: ...................................................................................443.2.4. Xy dng ng y kt cu nhp: ......................................................................44



3.2.5. p kt cu nhp vo mt ct sng: .......................................................................443.2.6. Xc nh chiu cao m, tr: .................................................................................44

3.3. XC NH KHI LNG CNG TRNH V TNG MC U T: ...............453.4. THIT K THM M V CNH QUAN:..............................................................453.5. SO SNH LA CHN PHNG N: ....................................................................45

CHNG 4: .............................................................................................................. 46MT CU V NG NGI I ....................................................................... 46

4.1. CU TO MT CU: ..............................................................................................464.1.1. Mt cu t: .........................................................................................................46

4.1.1.1. Mt cu bng btng Atphalt: ......................................................................464.1.1.2. Mt cu bng btng ximng: ......................................................................474.1.1.3. Mt cu bng thp: .......................................................................................48

4.1.2. Mt cu ng st: ..............................................................................................504.1.2.1. Mt cu c mng balt: ............................................................................504.1.2.2. Mt cu trn (t vt t trc tip ln dm): ..................................................514.1.2.3. Mt cu c ray t trc tip ln bn mt cu: ..............................................52

4.2. PHNG NC V THOT NC TRN CU: ..................................................534.2.1. dc phng nc trn cu:...............................................................................53

4.2.1.1. dc dc cu: ............................................................................................534.2.1.2. dc ngang cu: ........................................................................................54

4.2.2. ng thot nc trn cu: .....................................................................................554.2.2.1. Yu cu:........................................................................................................554.2.2.2. Cu to ng thot nc: ...............................................................................554.2.2.3. Nguyn tc b tr ng thot nc: ................................................................57

4.3. KHE CO GIN TRN CU:.....................................................................................584.3.1. Vai tr ca khe co gin: .......................................................................................584.3.2. Yu cu i vi khe co gin: ...............................................................................594.3.3. Cc loi khe co gin:............................................................................................59

4.3.3.1. Khe co gin h: ............................................................................................594.3.3.2. Khe co gin kn: ...........................................................................................604.3.3.3. Khe co gin cao su chu nn:........................................................................604.3.3.4. Khe co gin cao su bn thp:........................................................................614.3.3.5. Khe co gin bn thp trt: ..........................................................................614.3.3.6. Khe co gin rng lc, rng ca: .................................................................62



4.3.3.7. Khe co gin mun: .....................................................................................634.4. MT CU LIN TC NHIT : ..........................................................................64

4.4.1. S cn thit b tr mt cu lin tc nhit : .......................................................644.4.2. Cu to mt cu lin tc nhit : .......................................................................644.4.3. c im lm vic: ..............................................................................................654.4.4. u, nhc im: ..................................................................................................65

4.5. L NGI I V LAN CAN:..................................................................................654.5.1. L ngi i: .........................................................................................................654.5.2. Lan can: ...............................................................................................................66

4.6. NI TIP GIA NG V CU: ........................................................................684.6.1. Yu cu ni tip t ng vo cu: .....................................................................684.6.2. Ni tip gia ng v cu trn ng t :........................................................684.6.3. Ni tip gia ng v cu trn ng st: ........................................................70

CHNG 5: .............................................................................................................. 71KHI NIM CHUNG V M TR CU ............................................................. 71

5.1. KHI NIM CHUNG: ...............................................................................................715.1.1. c im chung: ..................................................................................................715.1.2. M cu: ................................................................................................................715.1.3. Tr cu: ................................................................................................................71

5.2. PHN LOI M TR CU: ....................................................................................725.2.1. Theo s tnh hc: ............................................................................................725.2.2. Theo cng dc cu: .........................................................................................735.2.3. Theo vt liu: .......................................................................................................735.2.4. Theo phng php xy dng: ..............................................................................735.2.5. Theo hnh thc cu to: .......................................................................................73

5.3. NGUYN TC XC NH CC KCH THC CB CA M TR CU: ........735.3.1. V tr ca m tr:..................................................................................................735.3.2. Cao nh mng: ...............................................................................................745.3.3. Cao nh x m m tr: ..................................................................................74

5.3.3.1. Cao nh x m tr: .................................................................................745.3.3.2. Cao nh x m m: ................................................................................75

5.3.4. Kch thc x m m tr trn mt bng:.............................................................75

CHNG 6: .............................................................................................................. 77CU TO M TR CU DM ............................................................................. 77



6.1. CU TO M CU DM:.......................................................................................776.1.1. Vai tr v nhim v ca m cu: .........................................................................77

6.1.1.1. Vai tr ca m cu: ......................................................................................776.1.1.2. Nhim v cc b phn ca m cu:..............................................................77

6.1.2. S pht trin ca cc loi m cu dm: ...............................................................786.1.2.1. M ch nht - quan nim ban u v m cu: .............................................786.1.2.2. M k - mt dng hp l hn ca m ch nht: ..........................................786.1.2.3. M ch U - khot b vt liu trong lng m:...............................................796.1.2.4. M c tng cnh ngang, tng cnh xin - xoay tng cnh m ch U:..806.1.2.5. M ch T, ch thp - khot b vt liu hai bn: ..........................................816.1.2.6. M rng vm dc, vm ngang - khot rng rut ca m: ...........................816.1.2.7. M vi - tng trc v tng cnh c cu to thch hp khi chn vo trongt: .............................................................................................................................826.1.2.8. Cc dng m cu c s chu lc thay i: ...............................................84

6.1.3. Cu to m cu dm ton khi trn ng t: ...................................................856.1.3.1. M ch U: ....................................................................................................856.1.3.2. M vi: .........................................................................................................90

6.2. CU TO TR CU DM: .....................................................................................926.2.1. Cc b phn ca tr cu:......................................................................................92

6.2.1.1. X m tr:.....................................................................................................936.2.1.2. Thn tr: .......................................................................................................936.2.1.3. Mng tr: ......................................................................................................94

6.2.2. Cc loi tr cu: ...................................................................................................946.2.2.1. Phn loi theo phng php thi cng: ..........................................................946.2.2.2. Phn loi theo hnh thc cu to: .................................................................97

6.3. CC DNG KT CU M TR KHC:..............................................................101

CHNG 7: ............................................................................................................ 102C S PHN TCH KT CU CU .................................................................. 102

7.1. KHI NIM V NG X TI TRNG: ..............................................................1027.2. TI TRNG V TC NG: ................................................................................102

7.2.1. Theo 22TCN18-79:............................................................................................1027.2.1.1. Cc trng thi gii hn: ..............................................................................1027.2.1.2. Ti trng: ....................................................................................................1027.2.1.3. T hp ti trng: .........................................................................................104

7.2.2. Theo 22TCN272-05:..........................................................................................105



7.2.2.1. Cc trng thi gii hn: ..............................................................................1057.2.2.2. Ti trng v t hp ti trng:......................................................................105

7.3. CC M HNH PHN TCH KT CU CU: .....................................................1097.3.1. Nguyn tc chung: .............................................................................................1097.3.2. Phng php phn tch kt cu theo m hnh khng gian: ...............................1097.3.3. Phng php phn tch kt cu theo m hnh phng:........................................110

7.4. M HNH BI TON PHNG V CC PHNG PHP TNH TON H SPHN B TI TRNG:.................................................................................................111

7.4.1. Nguyn tc tnh ton:.........................................................................................1117.4.2. Cc nhm phng php tnh ton h s phn b ti trng: ...............................111

7.4.2.1. Nhm 1: Phng php dm + mng dm: .................................................1117.4.2.2. Nhm 2: Phng php thanh thnh mng: ................................................1127.4.2.3. Nhm 3: Phng php bn: ........................................................................1127.4.2.4. Nhm 4: Phng php phn t hu hn: ...................................................112

7.4.3. Phng php tnh ton h s phn b ti trng theo 22TCN272-05:................1127.5. CC PHNG PHP MI TRONG PHN TCH KT CU CU: ..................112

CHNG 8: ............................................................................................................ 113TNH TON M TR CU DM....................................................................... 113

8.1. CC LOI TI TRNG TC DNG LN M TR CU:................................1138.1.1. Ti trng thng xuyn: ....................................................................................1138.1.2. Ti trng tc thi: ..............................................................................................1138.1.3. Tnh ton mt s loi ti trng: .........................................................................113

8.1.3.1. p lc ngang ca t (EH) v p lc t do hot ti (LS): ........................1138.1.3.2. Lc ma st m (DD): ..................................................................................1178.1.3.3. Hot ti xe t (LL): ...................................................................................1178.1.3.4. Lc hm xe (BR): .......................................................................................1188.1.3.5. Lc ma st gi cu (FR): ............................................................................118

8.2. CC MT CT KIM TON V T HP TI TRNG TC DNG LN TRCU DM:......................................................................................................................118

8.2.1. Cc mt ct kim ton: ......................................................................................1188.2.2. T hp ti trng tc dng ln tr cu dm: ........................................................119

8.3. CC MT CT KIM TON V T HP TI TRNG TC DNG LN MCU DM:......................................................................................................................120

8.3.1. Cc mt ct kim ton: ......................................................................................1208.3.2. T hp ti trng tc dng ln m cu dm: .......................................................120



8.3.2.1. Nguyn tc thnh lp t hp ti trng: .......................................................1208.3.2.2. T hp ti trng I: Bt li ra sng. .............................................................1218.3.2.3. T hp ti trng II: Bt li vo b. ............................................................121

8.4. TNH DUYT M TR CU DM: .....................................................................1218.4.1. Tnh duyt theo TTGH cng : .....................................................................121

8.4.1.1. Tnh duyt kh nng chu un: ...................................................................1218.4.1.2. Tnh duyt kh nng chu ct: ....................................................................1238.4.1.3. Kim tra hm lng ct thp ti thiu: ......................................................1238.4.1.4. Kim tra hm lng ct thp ti a: ...........................................................1238.4.1.5. C ly ti a ca ct thp ngang: .................................................................124

8.4.2. Tnh duyt theo TTGH s dng: .......................................................................124

CHNG 9: ............................................................................................................ 125GI CU .................................................................................................................. 125

9.1. KHI NIM CHUNG: .............................................................................................1259.1.1. Vai tr ca gi cu: ............................................................................................1259.1.2. Nguyn tc b tr gi cu:..................................................................................125

9.1.2.1. B tr trn mt chnh: .................................................................................1259.1.2.2. B tr trn mt bng:...................................................................................126

9.2. CU TO GI CU: ..............................................................................................1279.2.1. Gi cu dm BTCT: ..........................................................................................127

9.2.1.1. Gi tip tuyn: ............................................................................................1279.2.1.2. Gi con ln: ................................................................................................1289.2.1.3. Gi chu: ....................................................................................................1299.2.1.4. Gi cao su bn thp: ...................................................................................129

9.2.2. Gi cu dm v dn thp: ..................................................................................130

CHNG 1: KN V CC CTNT TRN NG BI GING C S CNG TRNH CU


CHNG 1:

KHI NIM V CC CNG TRNH NHN TO TRN NG1.1. CC LOI CNG TRNH NHN TO TRN NG:

- Khi nim: L mt kt cu do con ngi xy dng trn ng cho php vt qua ccchng ngi vt m bo giao thng.

- Cng trnh nhn to trn ng ba o gm:

+ Cng trnh vt sng, sui, thung lng,: Cu, hm.

+ Cng trnh chn t: Tng chn .

+ Cng trnh thot nc nh: Cng, ng trn, cu trn.

1.1.1. Cu:

Cu l cng trnh vt qua dng nc, qua thung lng, qua ng, qua cc khu vcsn xut, cc khu thng mi hoc qua khu dn c. Theo tiu chun 22TCN 272-05 th cul mt kt cu bt k vt khu khng di 6m to thnh mt phn ca mt con ng.

Hnh 1.1a: M hnh cng trnh cu.

Hnh 1.1b: Cu Bixby (Hoa k). Hnh 1.1c: Cu Nanpu (Trung Quc)1.1.2. Cc cng trnh thot nc nh:

- ng trn l cng trnh c mt ng nm st cao y sng, vo ma m a ncchy trn qua mt ng nhng xe c vn i li c. C th t cng bn di thotnc. p dng: Cho cc dng chy c lu lng nh, v c l xy ra trong thi gian ngn.

Hnh 1.2a: M hnh ng trn .



Hnh 1.2b: Cng trnh ng trn trong thc t .- Cu trn l cng trnh c thit k dnh mt li thot nc di ng, dng

chy thng qua vi mt lu lng nht nh. Khi v t qu lu lng ny, nc s trn quang. p dng: Cho nhng dng chy c lu lng nh v trung bnh tng i ko ditrong nm.

Hnh 1.3a: M hnh cu trn.

Hnh 1.3b: Cng trnh cu trn trong thc t.

- Cng l cng trnh thot n c ch yu qua cc dng nc nh, c lu lng nh (Q 40 50 m3/s). Quy nh: Chiu dy lp t p trn nh cng 0.5m phn b p lcbnh xe v gim lc xung kch.

Hnh 1.4a: M hnh cng thot nc qua ng.



Hnh 1.4b: Cng trnh cng trong thc t.1.1.3. Tng chn:

Tng chn l cng trnh chn t, c xy dng nhm m bo n nh ca dctaluy nn ng.

Hnh 1.5: Cng trnh tng chn.1.1.4. Hm:

Hm l cng trnh c cao tuyn ng thp hn nhiu so vi mt t t nhin. Tytheo mc ch s dng c cc cng trnh hm sau:

- Hm vt ni: L hm c xy dng xuyn qua ni, c cao tuyn ng thphn nhiu so vi cao mt t t nhin.

Hnh 1.6a: M hnh hm vt ni.



Hnh 1.6b: Hm Hi Vn (Vit Nam).- Hm vt sng, eo bin: Khi vt qua cc sng ln, cc eo bin su, vic xy dng

tr cu kh khn hoc cu qu cao, khi ta c th lm hm.

Hnh 1.7: Hm Th Thim (Vit Nam).- Hm giao thng trong lng t: Trong cc thnh ph ng dn c m bo giao

thng nhanh chng, c th xy dng cc hm cho ngi, xe c hoc tu in i qua.

Hnh 1.8a: M hnh hm giao thng trong lng t.



Hnh 1.8b: Cng trnh hm giao thng trong lng t.

Hnh 1.8c: M hnh xy dng tu in ngm H Ni trong tng lai.- Hm vt ng (hm chui): Ti cc nt giao ta c th xy dng hm chui.

Hnh 1.9: Cng trnh hm vt ng .



1.2. CC B PHN V CC KCH THC C BN CA CU:

1.2.1. Cc b phn ca cng trnh cu:- Cng trnh cu bao gm: Cu, ng dn vo cu, cc cng trnh iu chnh dng chy

v gia c b sng.

- Cu bao gm: Kt cu phn trn v kt cu phn di.

+ Kt cu phn trn: Kt cu nhp.

Tc dng: To ra b mt cho xe chy v cho ngi i b trn cu, m bo xe chym thun v an ton trong qu trnh chuyn ng.

+ Kt cu phn di: M cu, tr cu, nn mng.

Tc dng: kt cu phn trn v truyn ti trng t kt cu phn trn xung tnn. Kt cu phn di thng chim (40 60)% tng gi thnh xy dng cng trnh.

Hnh 1.10: Cc b phn ca cu.- Ngoi ra cn c cc kt cu ph tr khc nh: Lp ph mt cu, lan can, h thng thot

nc, gi cu, khe co gin,

1.2.2. Cc kch thc c bn ca cu:

Lo

Lnh Lnh

Ltt1

Ltt2

Ltt1

Lcau

MNCN MNTTMNTN

H H1

Hkt

Hnh 1.11: Cc kch thc c bn ca cu .- Cc chiu di cu:

+ Khu thot nc di cu (L0): L khong cch tnh t mp trong m bn nyn mp trong ca m bn kia. Khu thot nc di cu c xc nh trn c s tnhton thy vn di cu theo tn sut thit k P%, m bo sau khi xy dng cu khng phtsinh ra hin tng xi chung v xi cc b qu ln hoc khng to nn mc nc dnh quln trc cu.

+ Chiu di nhp (Lnh): L khong cch tnh t u dm bn ny n u dm bn kia.



+ Chiu di nhp tnh ton (Ltt): L chiu di on dm m ti biu mmenkhng i du.

+ Chiu di ton cu (Lcau): L chiu di tnh t ui m bn ny n ui m bn kia.

monhcau LaLL .2Trong :

Lnh: L chiu di ca mt nhp. a: Khe h gia cc u dm. Lmo: Chiu di ca m cu.

- Cc chiu cao thit k cu:

+ Chiu cao t do di cu (H): L khong cch tnh t y KCN n MNCN.

+ Chiu cao kin trc ca cu (Hkt): L khong cch tnh t y KCN n mt ngxe chy.

+ Chiu cao ca cu (H1): L khong cch tnh t mt n g xe chy n MNTN (ivi cu vt qua dng nc) v n mt t t nhin (i vi cu cn).

- Cc mc nc thit k :+ Mc nc cao nht (MNCN): L mc nc ln nht xut hin trn sng ng vi tn

sut l thit k P%. Da vo MNCN xc nh khu cu tnh ton v cao y dm.

+ Mc nc thp nht (MNTN): L mc nc thp nht xut hin trn sng ng vitn sut l thit k P%. Da vo MNTN bit v tr ch lng sng nc su trong macn, cn c vo xc nh v tr cc nhp thng thuyn. Ngoi ra cn xc nh cao nh b mng ca tr gia sng.

Mc nc cao nht v mc nc thp nht c xc nh theo cc s liu quan tr cthy vn v mc nc l, c tnh ton theo tn sut P% quy nh i vi cc cu vng khc nhau.

+ Mc nc thng thuyn (MNTT): L mc nc cao nht cho php tu b i li dicu an ton. Da vo MNTT v chiu cao thng thuyn xc nh cao y dm.

Theo Tiu chun 22TCN18-79, tn sut thit k tnh MNCN, MNTN cho cu va,cu ln l 1%, MNTT l 5%. Hin nay theo Tiu chun 22TCN272-05 khng quy nh.

Xc nh cao y dm:+ y dm ti mi v tr phi cao hn MNCN 0.5m i vi sng ng bng v

1.0m i vi sng min ni c ln cy tri (ng t).+ Ti nhng ni kh cn hoc i vi cu cn, cu vt th cao y dm ti mi v

tr phi cao hn mt t t nhin 1.0m.+ Cao y dm phi cao hn hoc bng MNTT cng vi chiu cao thng thuyn.

+ nh x m ca m tr phi cao hn MNCN ti thiu l 0.25m.



1.3. PHN LOI CU:

1.3.1. Phn loi theo mc ch s dng:Ty theo mc ch s dng, c th phn thnh cc loi cu:

- Cu t: L cng trnh cu cho tt c cc phng tin giao thng trn ng t nh: xeti, xe gn my, xe th s v on ngi b hnh, ...

- Cu ng st: c xy dng dnh ring cho tu ha.

- Cu i b: Phc v dnh ring cho ngi i b.

- Cu thnh ph: L cu cho t, tu in, ngi i b , ...

- Cu chy chung: L cu cho c t, xe la, ngi i b , ...

- Cu c bit: L cc cu phc v cho cc ng dn nc, ng dn kh, ...

1.3.2. Phn loi theo vt liu lm kt cu nhp:

- Cu g.

- Cu .

- Cu b tng.

- Cu b tng ct thp.

- Cu thp.

1.3.3. Phn loi theo chng ngi vt:- Cu thng thng (vt sng): L cc cng trnh cu c xy dng vt qua cc dng

nc nh: sng, sui, khe su , ...

Hnh 1.12a: M hnh cu thng thng.

Hnh 1.12b: Cng trnh cu thng thng.



- Cu vt (cu qua ng): L cc cng trnh cu c thit k cho cc nt giao nhaukhc mc trn ng t hoc ng st.

Hnh 1.13a: M hnh cu vt ng.

Hnh 1.13b: Cng trnh cu vt ng.- Cu cn: L cc cng trnh cu c xy dng ngay trn mt t lm cu dn vo

cu chnh hoc nng cao tuyn ng ln gii phng khng gian bn di .

Hnh 1.14a: M hnh cu cn.

Hnh 1.14b: Cng trnh cu cn.- Cu cao: L cc cng trnh cu bc qua thung lng khe su, cc tr cu c chiu cao >

2025 m, thm ch n hng trm mt .



Hnh 1.15a: M hnh cu cao.

Hnh 1.15b: Cng trnh cu cao.- Cu phao: L cc cng trnh cu c xy dng bng h ni nhm phc v cho mc

ch qun s hoc phc v giao thng trong mt thi gian ngn.

Hnh 1.16a: M hnh cu phao.

Hnh 1.16b: Cng trnh cu phao.- Cu m: Cu m l cu c 1 hoc 2 nhp s c di ng khi v tr tu b qua li

trong khong thi gian nht nh. C cc loi cu m sau:



+ Cu ct: KCN c th m v 1 pha hoc 2 pha theo gc 700 800 so vi phngnm ngang.

Hnh 1.17a: M hnh cu ct.

Hnh 1.17b: Cng trnh cu ct.+ Cu nng: KCN c nng h theo phng thng ng.

Hnh 1.18a: M hnh cu nng.

Hnh 1.18b: Cng trnh cu nng.



+ Cu quay: KCN quay trn mt bng mt gc 900.

Hnh 1.19a: M hnh cu quay.

Hnh 1.19b: Cng trnh cu quay.1.3.4. Phn loi theo cao ng xe chy:

Ty theo vic b tr cao ng xe chy, c th phn thnh:

- Cu c ng xe chy trn: K hi ng xe chy t trn nh kt cu nhp .

Hnh 1.20: Cu c ng xe chy trn .- Cu c ng xe chy di: Khi ng xe chy b tr dc theo bin di KCN.

Hnh 1.21: Cu c ng xe chy di.



- Cu c ng xe chy gia: K hi ng xe chy b tr gia phm vi ca KCN.

Hnh 1.22: Cu c ng xe chy gia.1.3.5. Phn loi theo s tnh hc:

- S dm gin n:

+ Phn b ni lc: Biu momen chc du (+) v gi tr ln nht ti gia nhp.

+ Phn b vt liu: Vt liu tp trungch yu khu vc gia nhp do ni lc dotnh ti ln, d tr kh nng chu hot ti kmnn kh nng vt nhp thp.

Hnh 1.23. S dm gin n.+ Kh nng vt nhp:

KCN cu dm: L 40m KCN cu dn: L 60m

- S dm mt tha:

Hnh 1.24. S dm mt tha.+ Phn b ni lc: Biu momen xut hin M(-) ti mt ct gi v M(+) ti mt ct

gia nhp.+ Phn b vt liu: Vt liu tp trung ch yu mt ct gi do KCN nh nn kh

nng vt nhp tt hn so vi KCN gin n.- S dm hng - nhp eo:

Hnh 1.25. S dm hng nhp eo.+ KCN c dm eo thng khai thc khng m thun, lc xung kch ln, khe co gin

phi cu to phc tp do hin nay t dng.



- S dm lin tc:

Hnh 1.26. S dm lin tc.+ Gi tr M(-) ti mt ct gi ln hn M(+) mt ct gia nhp do pht huy c

ht kh nng lm vic ca vt liu.+ Kt cu lin tc cn gim c s lng khe co gin trn cu, do m bo m

thun cho xe chy.+ Kh nng vt nhp:

KCN dm thp: L 90m. KCN dn thp: L 120m. KCN dm BTCT DL: L 150m. KCN cu treo, cu dy vng: L 150 450m.

1.3.6. Phn loi theo s cu to:- Cu dm:

+ B phn chu lc ch yu l dm, lm vic chu un.+ Di tc dng ca ti trng thng ng ti gi ch pht sinh phn lc thng ng V.

VV

Hnh 1.27a. M hnh KCN cu dm.

Hnh 1.27b. Cng trnh cu dm.

- Cu vm:+ B phn chu lc ch yu l vm, vm lm vic chu nn v chu un.+ Phn lc gi vm (trong vm khng cht) gm c lc thng ng V, momen un

M v lc y ngang H.



+ Nu c thanh ging chu lc y ngang H th phn lc gi ca vm s ch gmphn lc thng ng V ging nh cu dm. Khi ta c h thng cu dm - vm t hp.

V

V

H

V

H

Hnh 1.28a. M hnh KCN cu vm.

Hnh 1.28b. Cng trnh cu vm.- Cu dn:

+ Kt cu chu lc chnh ca kt cu nhp cu dn l cc mt phng dn, vi cc thanhdn ch chu lc dc trc (ko hoc nn). Chiu cao dn ln nn kh nng chu lc v vtnhp ca kt cu nhp cu dn ln hn so vi kt cu nhp cu dm. Nhc im chnh cakt cu nhp cu dn l cu to v thi cng phc tp.

+ KCN cu dn thng p dng cho cc cu chu ti trng ln nh cu ng st.

Hnh 1.29a: M hnh KCN cu dn.

Hnh 1.29b: Cng trnh cu dn.



- Cu khung:

+ Tr v dm c lin kt cng vinhau chu lc.

+ Phn lc gi gm c phn lc thngng V v lc y ngang H, nu chn khunglin kt khp th s khng c momen M.

V

H

V

H

Hnh 1.30a. M hnh KCN cu khung.

Hnh 1.30b. Cng trnh cu khung.- Cu treo:

+ B phn chu lc ch yu ca cu treo l dy cp hoc dy xch h mt cu (dmhoc dn). Do trn quan im tnh hc, cu treo l h thng t hp gia dy v dm(hoc dn).

+ C th phn cu treo thnh 2 loi:

Cu treo dy vng (gi tt l cu treo).

Cu treo dy xin (cu dy vng).

Cu treo dy xin (cu dy vng): y l kt cu dm cng ta trn cc gi cngl cc gi cu trn m - tr v trn cc gi n hi l cc dy vng. Dy vng neo vo dmcng bin thnh mt h khng c lc y ngang.

Hnh 1.31a: M hnh KCN cu dy vng.



Hnh 1.31b: Cng trnh cu dy vng.

Cu treo dy vng (cu treo): Trong cu treo, dy lm vic ch yu chu ko vti ch neo cp c phn lc thng ng ( lc nh) v phn lc ngang rt ln do trong ktcu nhp cu treo ti v tr m ta phi cu to h neo rt ln v rt phc tp.

H

V

H

V

Hnh 1.32a: M hnh KCN cu treo dy vng.

Hnh 1.32b: Cng trnh cu treo dy vng.1.4. CC YU CU C BN I VI CU :

1.4.1. Yu cu v mt xy dng v khai thc:

- m bo xe chy thun tin, an ton v khng b gim tc trn tuyn ng.- Chiu rng ng xe chy phi ph hp vi lu lng v loi xe tnh ton. Mt cu tt,

bng phng, nhm v thot nc nhanh chng.- S cu, chiu di nhp v chiu di cu phi m bo khu thot nc yu cu,

tu b i li di sng thun li v an ton.- Kt cu cu phi m bo kh nng thi cng, ph hp vi cc cng ngh thi cng. Cu

phi c kt cu hin i, m bo tnh cng nghip ha trong ch to v xy dng. ngthi kt cu phi c bn, cng, n nh ca ton cu v ca tng b phn.



1.4.2. Yu cu v mt kinh t:

- m bo chi ph thit b, vt liu r nht, gim sc lao ng, gim gi thnh xy dngn mc ti a.

- Khi tnh gi thnh ca cng trnh cu, phi xt n gi thnh duy tu, sa cha; ng thiphi tnh n s pht trin ca nn kinh t quc dn khi la chn cc phng n cu.

1.4.3. Yu cu v mt m quan:

Cu phi c hnh dng p, ph hp v i quang cnh a phng c bit l cc cng trnhnm trong thnh ph hoc cc khu danh lam thng cnh, di tch lch s.

1.4.4. Yu cu v mt an ninh quc phng:

Ngoi mc ch giao thng cn phi xt n tnh thit thc cho cc hot ng an ninhquc phng. Khi c chin tranh bt cht xy ra th cc cy cu c th chuyn sang phc vcho cc loi xe c chng ca qun i.

1.5. S LC LCH S V XU HNG PHT TRIN NGNH XY DNG CU :

1.5.1. S lc lch s pht trin ngnh xy dng cu:

1.5.1.1. Cu g:- Cu g l loi cu c xy dng lu i nht.

- G l loi vt liu t nhin tng i tt, tuy nhin khi dng trong xy dng cu thphi chn loi g tt nh lim, g, sn, tu v phi c bin php phng mc.

- Cu g c thi gian s dng ngn, kh nng vt nhp khng ln lm (L 3050m).

- Hin nay ch cn s dng min rng, ng lm nghip v cc cu tm hoc giophc v thi cng.

Hnh 1.33: Cu g.1.5.1.2. Cu :

- c xy dng t hng ngn nm v trc, n ngy nay vn tn ti v s dng c.

- Hu ht cu c xy dng theo dng cu vm ph hp vi tnh cht chu nn ca.

- Cu vm c th vt khu nhp n 100m.



- Cu xy dng kh khn nn t c kh nng xy dng cng nghip ho.

- Hin nay ch p dng cc vng min ni, ni c th khai thc trc tip ti ch hoc lm cc cng trnh kin trc ngh thut nhng danh lam thng cnh.

Hnh 1.34: Cu .1.5.1.3. Cu thp:

- Cu thp xut hin vo na cui ca th k 19.

- Cu kim loi u tin c lm bng gang, tip n l s ra i ca cu treo dy xch.

- vt qua cc sng rt ln vi nhp rt ln, ngi ta dng cu thp.

- u im ni bt ca cu thp l hon ton cng nghip ho ch to v lp rp, d dnglp rp bng phng php hng do d xy dng qua sng su, thung lng su v quasng c nhiu tu b i li.

- Nhc im ca cu thp l g, do tn cng bo dng.

- S ra i v pht trin ca cu vm v cu dy vng ang l bc tin mi ca cuthp.

Hnh 1.35: Cu thp.1.5.1.4. Cu btng ct thp:

- Cui th k 19, trong xy dng cu s dng mt loi vt liu mi l BTCT.

- Trong giai on u, cc cu BTCT thng c dng cu bn, dm v vm c khu nh hn 30m.



- n nhng nm 30 ca th k 20, sau khi k s Freyssinet nghin cu thnh cngBTCT ng sut trc th cu BTCT bt u pht trin mnh m.

- Sau i chin th gii ln th 2, cc kt cu nhp lp ghp, kt cu bn lp ghp bngBTCT DL c s dng hng lot.

- Hin nay, cu BTCT ngy cng c pht trin m ra k nguyn mi trong vic sdng KCN BTCT thay th cho KCN cu thp. Cu BTCT vt c khu n200300m v s hnh thnh cc kt cu lin hp nh dn - dy, dm - dy, chc chn sxut hin nhng cy cu c khu nhp ln hn 400500m.

Hnh 1.36: Cu btng ct thp. Lch s pht trin ngnh cu Vit Nam:

- So vi cc nc trn th gii, ngnh xy dng cu Vit Nam vn cn non tr. Trccch mng thng 8, trn cc tuyn ng t ch yu c cc cu BTCT nhp nh t 3 - 20m,kh hp, mt ln xe, ti trng nh thuc cc h thng cu bn, dm gin n, dm hng,khung. Thi k ny cng c mt s cu thp ln vt qua cc sng ln nh cu ung, cuNinh Bnh, cu Lai Vu, cu Long Bin cho ng st v t i chung, , trong cuLong Bin c nhp ln nht gn 130m, chiu di ton cu gn 3km. Trong thi k khngchin chng thc dn Php phn ln cc cu b ph hoi. T sau ha bnh lp li (1954),mt lot cc cu mi trn ng st v t c xy dng. Cu thp c: Cu Hm Rn g(Thanh Ha), cu Lng Ging, cu Vit Tr; cu BTCT thng c: Cu oan V, cu Bng,cu Gi; cu BTCTDUL c: Cu Ph L, cu Ca Tin, nhng cc cu ny n nm1964 - 1972 li b quc M nm bom ph hoi.

- T nm 1975 n nay chng ta xy dnghng lot cc cu mi trn tuyn ng st v t.Sau y l mt s cu in hnh:

+ Cu Thng Long qua sng Hng chong st v t c xy dng xong nm 1982 ,cc nhp chnh l dn thp lin tc, nhp ln nht112m, cu dn l cc nhp dm gin nBTCTDUL nhp 33m, chiu di ton cu 1680m. Hnh 1.37: Cu Thng Long (H Ni) .



+ Cu Chng Dng qua sng Hng (1985), c cc nhp chnh l dn thp, nhpln nht 97.6m, chiu di ton cu 1211m.

+ Cu Quan (Nam nh), nm 1994, nhp chnh l dm thp lin hp bnBTCT, lin tc, c s 42 + 63 + 42 (m).

Hnh 1.38: Cu Chng Dng (H Ni) . Hnh 1.39: Cu Quan (Nam nh ).+ Cu Ph Lng (Hi Dng), nm 1996, cu khung dm BTCTDUL, thi cng

bng phng php c hng, nhp ln nht 102m.

+ Cu Sng Gianh (Qung Bnh), nm 1998, dm lin tc BTCTDUL c nhp lnnht 120m.

Hnh 1.40: Cu Ph Lng (Hi Dng) . Hnh 1.41: Cu Sng Gianh (Qung Bnh).

Hnh 1.42: Cu Hin Lng (Qung Tr). Hnh 1.43: Cu Bnh (Hi Phng).



+ Cu Hong Long (Thanh Ha), cu khung dm BTCTDUL c nhp ln nht130m.

+ Cu Hin Lng (Qung Tr), nm 1999, s 30.75 + (4x42) + 30.75 (m).

+ Hng lot cc cu dy vng c xy dng nh: Cu akrng (Qu ng Tr),cu quay Sng Hn ( Nng), cu M Thun (Vnh Long), cu Bnh (Hi Phng), cu BiChy (Qung Ninh), cu Cn Th,

1.5.2. Mt s xu hng pht trin khoa hc k thut trong ngnh xy dng cu:

1.5.2.1. V vt liu:- Cc loi vt liu c cng cao s sm c s dng rng ri trong xy dng cu: B

tng mc cao, b tng siu do c cng sm, thp cng cao, thp hp kim thp.- gim trng lng bn thn kt cu, y mnh nghin cu s dng cc loi vt liu

nh, hp kim nhm, b tng ct thp hoc si thu tinh,

1.5.2.2. V kt cu:Cc kt cu hp l s c p dng ch yu trong xy dng cu nh:

- Kt cu thp - BTCT lin hp, BTCT DL, - Kt cu c s dng bn trc hng, tit din hnh hp, - Cu dy vng v cu khung dm lin tc BTCT DL,

1.5.2.3. V cng ngh thi cng:- S dng cc phng tin vn chuyn v lao lp c nng lc ln.- p dng nhanh chng cc cng ngh thi cng tin tin nh: c y, c hng, lp

hng, c trn gio di ng,

1.5.2.4. V tnh ton:- Hon thin l thuyt tnh ton vi s gip ca cng ngh tin hc thng qua phn

mm tnh ton chuyn ngnh nh: Midas Civil 2010; RM V8.i 2008; Sap 2000 V15, ...- y mnh nghin cu tnh ton chnh xc kt cu c xt y cc yu t phi tuyn,

khng gian, - Nghin cu cc tc ng ca mi trng n kt cu cu nh: Nhit , gi, bo, ng

t, - Tin hnh th nghim trong phng v th nghim ngoi hin trng so snh v nh

gi s hon chnh ca l thuyt.

CHNG 2: CC CN C CB V K TK CU BI GING C S CNG TRNH CU


CHNG 2:

CC CN C C BN V IU KIN THIT K CU2.1. CC GIAI ON U T XY DNG V CC BC THIT K :

Tham kho Ngh nh s 12/2009/N-CP ngy 10/02/2009 ca Chnh ph.2.1.1. Cc giai on u t xy dng:

Khi nim d n u t (DAT): L mt tp hp cc xut v kh nng, ti chnh, kinht v x hi, lm s s cho vic quyt nh b vn xy dng cng trnh.

nc ta, phn loi theo quy m v tnh cht th DAT xy dng cng trnh c chiathnh cc nhm sau: D n quan trng quc gia do Quc hi xem xt quyt nh v chtrng u t, cc d n cn li c chia thnh 3 nhm A, B, C (i vi cng trnh xydng cu ng c tng mc u t ln hn 1500 t ng thuc nhm A, t 75 t ng n1500 t ng thuc nhm B, di 75 t ng thuc nhm C).

c mt cng trnh xy dng ni chung v cng trnh cu ng ni ring cn tri qua3 giai on: Chun b u t, thc hin u t v kt thc xy dng a cng trnh vo khaithc s dng.

2.1.1.1. Chun b u t:Ni dung cng tc chun b u t gm:

- Lp bo co u t xy dng c ng trnh v xin php u t (ch p dng i vi ccd n quan trng quc gia do Quc hi thng qua ch trng v cho php u t).

- Lp d n u t xy dng cng trnh (i vi cng trnh c tng mc u t xydng di 15 t ng th khng cn qua bc lp d n u t, ch cn lp bo co kinh t -k thut xy dng cng trnh trnh ngi quyt nh u t ph duyt ).

- Thm nh d n quyt nh u t.

a. Ni dung ca bo co u t xy dng cng trnh (bo co ngh in cu tin kh thi)bao gm:

- S cn thit phi u t xy dng cng trnh, cc iu kin thun li v kh khn;ch khai thc v s dng ti nguyn quc gia nu c.

- D kin quy m u t: C ng sut, din tch xy dng; cc hng mc cng trnhthuc d n; d kin v a im xy dng c ng trnh v nhu cu s dng t.

- Phn tch, la chn s b v cng ngh, thng s k thut; cc iu kin cung cp vtt thit b, nguyn liu, nng lng, dch v, h tng k thut; phng n gii phng mt bng, tinh c nu c; cc nh h ng ca d n i vi mi trng sinh thi, phng chng chy n, anninh quc phng.

- Hnh thc u t, xc nh s b tng mc u t, thi hn thc hin d n, phngn huy ng vn theo tin v hiu qu kinh t - x hi ca d n v phn k u t nuc.



b. Xin php u t xy dng cng trnh:- Ch u t c trch nhim gi bo co u t xy dng cng trnh ti B qun l

ngnh. B qun l ngnh l c quan u mi gip th tng chnh ph ly kin ca B,ngnh, a phng lin quan, tng hp v xut kin trnh th tng chnh ph.

- Thi hn ly kin c quy nh nh sau: Trong vng 5 ngy lm vic k t ngynhn c bo co u t xy dng cng trnh, B qun l ngnh phi gi vn bn ly kin n c c B ngnh, a phng c lin quan. Trong vng 30 ngy lm vic k t khinhn c ngh, cc c quan c hi kin phi c vn bn tr li v nhng ni dungthuc phm vi qun l ca mnh. Trong vng 7 ngy sau khi nhn c vn bn tr li theothi hn trn, B qun l ngnh phi lp bo co trnh th tng chnh ph.

c. Ni dung d n u t xy dng cng trnh (bo co nghin cu kh thi) bao gm :D n u t cn phi bao gm 2 phn: Phn thuyt minh d n v phn thit k c s.

- Ni dung phn thuyt minh ca d n:

+ S cn thit v mc tiu u t; nh gi nhu cu th trng, tiu th sn phm i vid n sn xut, kinh doanh; tnh cnh tranh ca sn phm; tc ng x hi i vi a phng,khu vc (nu c); hnh thc u t xy dng cng trnh; a im xy dng, nhu cu s dngt; iu kin cung cp nguyn liu, nhin liu v cc yu t u vo khc.

+ M t v quy m v din tch xy dng cng trnh, cc hng mc cng trnh thuc d n;phn tch la chn phng n k thut, cng ngh v cng sut.

+ Cc gii php thc hin bao gm:

Phng n chung v gii phng mt bng, ti nh c v phng n h tr x ydng h tng k thut nu c.

Cc phng n thit k kin trc i vi cng trnh trong th v cng trnh cyu cu kin trc.

Phng n khai thc d n v s dng lao ng. Phn on thc hin, tin thc hin v hnh thc qun l d n.

+ nh gi tc ng mi trng, cc gii php phng chy, cha chy v cc yu cuv an ninh, quc phng.

+ Tng mc u t ca d n; kh nng thu xp vn, ngun vn v kh nng cp vntheo tin ; phng n hon tr vn i vi d n c yu cu thu hi vn v phn tch nhgi hiu qu kinh t - ti chnh, hiu qu x hi ca d n.

- Ni dung phn thit k c s:

+ Thit k c s l thit k c thc hin trong giai on lp D n u t xy dngcng trnh trn c s phng n thit k c la chn, bo m th hin c cc thng sk thut ch yu ph hp vi cc quy chun, tiu chun c p dng, l cn c trinkhai cc bc thit k tip theo.



Ni dung thit k c s bao gm phn thuyt minh v phn bn v.

+ Phn thuyt minh thit k c s bao gm cc ni dung:

Gii thiu tm tt a im xy dng, phng n thit k; tng mt bng cngtrnh, hoc phng n tuyn cng tr nh i vi cng trnh xy dng theo tuyn; v tr, quy mxy dng cc hng mc cng trnh; vic kt ni gia cc hng mc cng trnh thuc d n vvi h tng k thut ca khu vc.

Phng n cng ngh, dy chuyn cng ngh i vi cng trnh c yu cu cngngh.

Phng n kin trc i vi cng trnh c yu cu kin trc. Phng n kt cu chnh, h thng k thut, h tng k thut ch yu ca cng

trnh.

Phng n bo v mi trng, phng chy, cha c hy theo quy nh ca phplut.

Danh mc cc quy chun, tiu chun ch yu c p dng.+ Phn bn v thit k c s bao gm:

Bn v tng mt bng cng trnh hoc bn v bnh phng n tuyn cngtrnh i vi cng trnh xy dng theo tuyn.

S cng ngh, bn v dy chuyn cng ngh i vi cng tr nh c yu cucng ngh.

Bn v phng n kin trc i vi cng trnh c yu cu kin trc . Bn v phng n kt cu chnh, h thng k thut, h tng k thut ch yu ca

cng trnh, kt ni vi h tng k thut ca khu vc.

d. Ni dung bo co kinh t - k thut xy dng cng trnh bao gm:- Phn thuyt minh ca bo co: Tng t nh phn thuyt minh ca lp d n u t

nhng r rng chi tit hn, c s lp d ton chi tit cho cng trnh.

- Phn thit k bn v thi cng: Bao gm tt c cc bn v tng th v cu to chi titca cng trnh, c s thng k khi lng nhm lp d ton chi tit cho cng trnh.ng thi phn thit k bn v thi cng phi r rng lm cn c cho vic thi cng vhon chnh cng trnh.

e. Thm nh d n q uyt nh u t :Cc bo co trn u phi c thm nh, sau s c cp c thm quyn cp

quyt nh v giy php u t.

2.1.1.2. Thc hin u t:

- Giao nhn t, chun b mt bng xy dng.



- Tuyn chn t vn xy dng kho st, thit k, gim nh kh nng v cht lngcng trnh.

- Thit k cng trnh:+ i vi cc cng trnh c yu cu k thut cao, c nn mng a cht thy vn phc

tp th phi thc hin thit k theo 2 bc: thit k k thut v thit k thi cng.+ i vi cc cng trnh k thut n gin hoc c thit k mu, x l nn mng

khng phc tp th thc hin 1 bc: thit k k thut thi cng.

- Thm nh, duyt thit k k thut v tng d ton.

- T chc u thu v mua sm thit b v thi cng xy lp.

- Xin giy php xy dng.

- K kt hp ng vi nh thu thc hin d n.

- Thi cng xy lp cng trnh.

- Theo di kim tra vic thc hin cc hp ng.

- Quyt ton vn u t xy dng sau khi hon thnh xy lp a d n vo khai thc.

2.1.1.3. Kt thc xy dng a cng trnh vo khai thc s dng:Ni dung cng vic bao gm:

- Kt thc xy dng.- Bn giao cng trnh.- Bo hnh cng trnh.- Vn hnh d n.

2.1.2. Cc bc thit k:

- Thit k xy dng cng trnh bao gm cc bc: Thit k c s, thit k k thu t, thitk bn v thi cng v cc bc thit k khc theo thng l quc t do ngi quyt nh ut quyt nh khi ph duyt d n.

+ Thit k c s l thit k c thc hin trong giai on lp d n u t xy dngcng trnh trn c s phng n thit k c la chn, bo m th hin c cc thng sk thut ch yu ph hp vi cc quy chun, tiu chun c p dng, l cn c trinkhai cc bc thit k tip theo.

+ Thit k k thut l thit k c thc hin trn c s thit k c s trong d n u txy dng cng trnh c ph duyt, bo m th hin c y cc thng s k thut v vtliu s dng ph hp vi cc quy chun, tiu chun c p dng, l cn c trin kha i bcthit k bn v thi cng.

+ Thit k bn v thi cng l thit k bo m th hin c y cc thng s kthut, vt liu s dng v chi tit cu to ph hp vi cc quy chun, tiu chun c pdng, m bo iu kin trin khai thi cng xy dng cng trnh.



- D n u t xy dng cng trnh c th gm mt hoc nhiu loi cng trnh vi mthoc nhiu cp cng trnh khc nhau. Ty theo quy m, tnh cht ca cng trnh c th, victhit k xy dng cng trnh c thc hin mt bc, hai bc hoc ba bc nh sau:

+ Thit k mt bc l thit k bn v thi cng c p dng i vi cng trnh ch lpBo co kinh t - k thut xy dng cng trnh. Trng hp ny, bc thit k c s, bcthit k k thut v bc thit k bn v thi cng c gp thnh mt bc v gi l thit kbn v thi cng.

i vi trng hp thit k mt bc, c th s dng thit k mu, thit k in hnhdo c quan nh nc c thm quyn ban hnh tri n khai thit k bn v thi cng.

+ Thit k hai bc bao gm bc thit k c s v bc thit k bn v thi cng cp dng i vi cng trnh quy nh phi lp d n tr cc cng trnh c quy nh thit kmt bc, ba bc. Trng hp ny, bc thit k k thut v bc thit k bn v thi cngc gp thnh mt bc v gi l bc thit k bn v thi cng.

+ Thit k ba bc bao gm bc thit k c s, bc thit k k thut v bc thitk bn v thi cng c p dng i vi cng tr nh quy nh phi lp d n. Ty theo mc phc tp ca cng trnh, vic thc hin thit k ba bc do ngi quyt nh u tquyt nh.

Trng hp thc hin thit k hai bc hoc ba bc th thit k bc tip theo phiph hp vi thit k bc trc c ph duyt.

- Ch u t c trch nhim t chc lp thit k xy dng cng trnh, trng hp ch ut c nng lc th c t thit k, trng hp ch u t khng c nng lc th thut chc t vn thit k. Ring i vi trng hp thit k ba bc th nh thu thi cng cth c giao lp thit k bn v thi cng khi c iu kin nng lc theo quy nh.

2.2. TRIT L THIT K:- Trong thit k, cc k s phi kim tra an ton v n nh ca phng n c

chn. Cng tc thit k bao gm vic tnh ton nhm chng minh mi tiu chun tnh tonv cu to u c tha mn.

- Trit l tnh ton thit k l cc quan nim v ng x ca kt cu v s lm vic an tonca n. ng thi xc lp iu kin, phng thc m bo iu kin an ton cho kt cutrong qu trnh khai thc.

- Nguyn tc chung: Khi c ti trng tc ng vo kt cu, n s gy ra mt hiu ngtrong kt cu v hiu ng khng c ln hn kh nng chu lc ca kt cu.

TC NG TRN KT CU KH NNG CHU LC CA KT CUDO TI TRNG GY RA DO BN THN VT LIU

V CU TO CA KT CU

- Quan h ca bt ng thc ny phi c xt trn mi b phn v vt liu ca kt cu.



2.2.1. Phng php thit k theo ng sut cho php: (ASD - Allowance stress design)- Phng trnh c bn: Trong phng php ny, ngi ta nhn nhn ng x ca kt cu

thng qua ng sut ca mt im i din:

max [ ] vi

[ ] ghk

Trong :+ max: ng sut tiu chun (khng h s) ln nht trong b phn kt cu do ti trng

gy ra.+ []: ng sut ln nht cho php xut hin trong b phn kt cu.+ gh: Cng ca vt liu.+ k: H s an ton (k>1).

- c im ca phng php:+ u im:

Tnh ton n gin, cho php tnh ton nhanh chng v tin dng. m bo an ton chu lc cho cc b phn kt cu.

+ Nhc im: Khng p dng c cho vt liu lm vic ngoi gii hn n hi, do khng

tn dng c ht kh nng chu lc ca cc b phn kt cu v gy lng ph vt liu. Khng xt n tnh lm vic thc t ca kt cu. Vic xc nh h s an ton thiu s phn tch c th.

2.2.2. Phng php thit k theo h s ti trng: (LFD - Load factor design)- Phng trnh c bn: Trong phng php ny, s lm vic ca kt cu c nh gi

thng qua mt mt ct i din:

max [ ]S S vi [ ] ghS

Sk

Trong :+ Smax: Ni lc ln nht do ti trng gy ra ti mt ct bt li.+ [S]: Kh nng chu lc ln nht cho php ca mt ct bt li.+Sgh: Kh nng chu lc ln nht ca mt ct.+ k: H s an ton (k>1).

- c im ca phng php:+ u im:

C tnh trc quan, r rng. Ngoi ra LFD cn tin b hn ASD do xt n s lm vic chung ca ton b

mt ct.+ Nhc im:

Cha xt ti s lm vic chung ca cc b phn kt cu.



Vic xc nh h s an ton ch yu da vo kinh nghim.2.2.3. Phng php thit k theo trng thi gii hn (LSD - Limit state design):

- Trng thi gii hn (TTGH) l trng thi m cng trnh b hng hon ton hockhng th s dng bnh thng c na.

- Quy trnh thit k cu cng ca Lin X (c) CH200-62, ban hnh nm 1962, sau nyB Giao thng vn ti nc ta da trn quy trnh ny bin son Quy trnh thit k cucng theo TTGH k hiu 22TCN18-79 nh sau:

+ Phng trnh c bn:

),...,.,.,.(. 02211 FRkRkmNn tctcii Trong :

ni: H s ti trng. Ni: Ni lc trong kt cu do ti trng tiu chun gy ra. : Hm s xc nh mi TTGH ca kt cu. m: H s iu kin lm vic. k1, k2,: H s ng nht vt liu. R1tc, R2tc,: Cng tiu chun ca vt liu. F0: c trng hnh hc ca kt cu.

+ Cc TTGH:

TTGH th nht: L TTGH m kt cu khng cn kh nng chu lc hoc xuthin cc bin dng do ln, nhm m bo v mt chu lc cho cng trnh (v cng , nnh v chu mi).

TTGH th hai: L TTGH m kt cu b pht sinh cc bin dng d qu ln nhdao ng, chuyn v, ln, gy kh khn cho vic s dng bnh thng.

TTGH th ba: L TTGH m tit din kt cu b xut hin cc vt nt ln gy khkhn cho vic s dng bnh thng.

+ Khi tnh ton theo cc TTGH trong 22TCN18-79, thay th cho h s an ton duynht trong phng php ng sut cho php, dng cc h s tnh ton sau:

H s ti trng (n): Xt n nhng sai lch c th xy ra theo chiu hng bt liso vi cc tr s tiu chun ca chng trong cc t hp ti trng v tc ng khc nhau.

H s ng nht (k): Xt kh nng gim thp cng ca vt liu v t so vitr s tiu chun do nhng thay i v tnh cht c hc v tnh khng ng nht ca chng.

H s iu kin lm vic (m): Phn nh s cha ph hp ca tnh ton l thuytvi iu kin lm vic thc t ca kt cu.



2.2.4. Phng php thit k theo h s ti trng v sc khng (LRFD - Load andresistance factor design):

- Phng trnh c bn: Trong thit k, m bo an ton cng trnh th kh nng chulc ca vt liu v tit din (sc khng) phi ln hn ni lc gy ra do ti trng:

rniii RRQ ... Trong :

+ i: H s iu chnh ti trng lin quan n tnh do v tnh d cng nh tm quantrng trong khai thc.

+ i: H s ti trng.

+ Qi: ng lc do ti trng.

+ Rn: Sc khng danh nh.

+ Rr : Sc khng tnh ton.

+ : H s sc khng.

- H s sc khng : i vi mt TTGH no th h s sc khng c s dng xt

n tnh tht thng trong tnh cht ca kt cu, ca vt liu v chnh xc ca ccphng trnh thit k nh gi kh nng chu ti, tnh hung h hng ca cng trnh.

- H s ti trng i: p dng i vi cc loi ti trng, xt n tnh tht thng cacc ti trng v hiu ng ti nh ln ca ti trng, v tr ti, t hp ti trng.

- H s iu chnh ti trng i:

+ i = D.R.I 0.95 i vi cc ti trng dng h s ti trng imax.+ i =

IRD ..1 1.0 i vi cc ti trng dng h s ti trng imin.

Trong :

+ D: do: do ca vt liu rt quan trng cho an ton ca cu. Nu vt liudo, khi mt b phn chu lc qu ti n s phn b ni lc sang b phn khc.

1. D1.05 cho cc cu kin v lin kt khng do.2. D =1.0 cho cc thit k thng thng, theo ng yu cu ca tiu chun thit k.

3. D0.95 cho cc cu kin c dng cc bin php tng thm tnh do.+ R: d tha : d tha c n gha i vi gii hn an ton ca cu. Mt s kt

cu siu tnh c co i l d tha v n c nhiu lin kt hn so vi yu cu cn b ng tnhnh. H cu c mt ng tip t c coi l khng d tha (khng nn dng loi ny).

Trong trng thi gii hn cng (TTGH cng ).

1. R1.05 cho cc b phn khng d tha.2. R=1.0 cho cc mc d tha thng thng.



3. R0.95 cho cc mc d tha c bit.+ I: quan trng:

Dng trong cc TTGH cng v TTGH c bit.

1. I1.05 cho cc cu quan trng.2. I=1.0 cho cc cu in hnh.

3. I0.95 cho cc cu tng i t quan trng.- c im ca phng php:

+ u im:

xt n s khc nhau gia ti trng v sc khng. t c mc an ton tng i ng u i vi cc TTGH khc nhau v

cc loi cu m khng cn n phn tch thng k hoc xc sut phc tp.

L mt phng php thit k thch hp v n nh.+ Nhc im:

Thay i t duy thit k (so vi AASHTO c). Yu cu hiu bit c bn v l thuyt xc sut v thng k. Yu cu c cc s liu thng k y v cc thut ton thit k xc sut c

th chnh l h s sc khng trong tng trng hp ring.

2.3. CC TIU CHUN THIT K CU HIN HNH:Mi mt d n u phi tun th theo cc quy trnh thit k, hin nay nc ta tn ti song

hnh hai quy trnh thit k:

+ Quy trnh tnh ton thit k cu cng theo cc trng thi gii hn do B GTVT banhnh nm 1979:

22TCN 18 - 79

+ Quy trnh theo h s ti trng v sc khng (Quy trnh AASHTO 98):

22TCN 272 - 05

CHNG 3: THIT K CC PHNG N CU BI GING C S CNG TRNH CU


CHNG 3:

THIT K CC PHNG N CU3.1. CC CN C LP PHNG N CU :

3.1.1. Khi nim chung:Vic thit k v la chn phng n cu l mt bi ton tng th nhiu mt: K thut

cng ngh, quy hoch, mi trng, kinh t. Cc phng n cu nu ra phi tha mn yucu k thut, kinh t, cng ngh thi cng, iu kin khai thc duy tu bo dng, nghaquc phng v yu cu m quan.

Trong thit k, ngi ta phi thnh lp nhiu phng n, sau tnh ton c th tngphng n v nh gi chng t la chn ra phng n ti u nht.

3.1.2. Phn tch cc ti liu khi thit k cc phng n cu:

3.1.2.1. Chn v tr cu:- Cu nh (L100m): Tuyn ng ph thuc vo cu. Nh vy vic kho st, la chnv tr cu l rt quan trng nhm chn c v tr xy dng cu hp l nht sau c thnn tuyn theo v tr cu chn.

- Cu trung (L=25100m): Phi xem xt c hai kh nng cu theo tuyn hoc tuyn theocu, sau so snh phn tch xem phng n no c li hn th la chn v trin khai xydng.

Trong thc t, khi thnh lp phng n cu th ta phi a ra rt nhiu cc phng n vtr cu khc nhau sau so snh cc phng n trn nhiu phng din:

- V mt k thut: So snh theo cc iu kin a hnh, a cht, thy vn, thi cng vb tr cng trng,

V tr cu nn trnh t ti cc v tr sau:+ Cu i qua a hnh thp, a cht hai u cu yu dn n vic x l ln phc tp

v gp rt nhiu kh khn.

+ Khng t cu gn cc cn c qun s, sn bay hoc nhng ni yu cu phi mbo an ninh c bit.

+ Khng nn t cu cho vi dng chy.

- V mt quy hoch: Phi so snh v vic pht trin cc vng ln cn trong tng lai,v tr cu theo quan im b tr kin trc tng th ca khu vc v theo quan im qucphng.

- V mt kinh t: Phi so snh theo gi thnh (thi cng v khai thc), so snh v githnh vn doanh cc phng n tuyn do cc v tr cu khc nhau gy nn.



V tr cu c lin quan cht ch n vic chn phng n kt cu nn sau khi phntch chn c phng n cu tt nht mi tin hnh thit k c c phng n kt cu ng viv tr cu mt cch c th.

3.1.2.2. Mt ct dc tim cu:Da vo mt ct dc tim cu cho php xc nh v tr ca m tr, trnh t tr vo ch

su nht, phn b cc nhp thng thuyn, xc nh dc dc cu (mt chiu ha y hai chiu).

3.1.2.3. Mt ct a cht dc tim cu:Cn c vo tnh hnh a cht dc ng tim cu, s b xc nh cc loi mng cu, ng

thi xc nh cc phng n kt cu nhp (tnh nh hay siu tnh).

- Nu tr cao, a cht xu, tnh hnh thi cng phc tp, gi thnh tr s t, khi nnlm cc kt cu nhp di.

- Nu a cht tt, tng t cng nm khng su, iu kin thi cng d dng th c thdng cc kt cu nhp siu tnh, cc loi kt cu nhp c lc y ngang.

3.1.2.4. Cc s liu thy vn:- Mc nc thp nht (MNTN) :

+ Cho bit v tr su nht ca lng sng trong ma cn. Cn c vo nhng v tr b tr cc nhp thng thuyn theo b rng ca sng. Tuy nhin, nhng con sng d b xil cn tnh n kh nng di chuyn cc khu v c su theo thi gian v nh vy lung lch tu b qua li cng phi dch chuyn theo b rng ngang sng.

+ Xc nh cao nh b mng ca tr t trong nc: C th t b mng st vimt t hoc cng c th t b mng ni trn mt t. Trong tr ng hp t b mng niln trn mt t, th cao nh b mng thng thng ly thp hn MNTN ti thiu l0.5m. V tr nh mng nh vy s lm gim khi lng xy v gim thu hp dng chy,ng thi cn m bo vn m quan cho cng trnh cu.

- Cn c vo MNCN xc nh chiu di tnh ton ca khu thot nc, ng thixc nh cao nh x m m, tr v cao y KCN:

+ nh x m m, tr phi cao hn MNCN ti thiu l 0.25m.

+ y dm khng c v phm tnh khng thng thuyn hoc thng xe di cu vy dm ti mi v tr phi cao hn MNCN ti thiu l 0.5m i vi sng ng bng v 1mi vi sng min ni c ln cy tri (ng t).

+ Ti nhng ni kh cn hoc i vi cu cn, cu vt th cao y dm phi caohn mt t t n hin 1m.

- Cn c vo MNTT v chiu cao thng thuyn xc nh cao y KCN.

3.1.2.5. Khu thot nc :T khu thot nc (L0) s nh ra chiu di ton b cu.



3.1.3. Kh gii hn v kh thng thuyn:

3.1.3.1. Kh gii hn:- Kh gii hn thng xe trn cu (thng gi tt l kh gii hn) l khong khng gian

c ginh ring cho giao thng trn cu m khng mt kt cu hay b phn kt cu noc vi phm khong khng gian m bo an ton giao thng.

- Kh gii hn trn cu ng t: i vi cu ng t th kh gii hn ly theo cctiu chun thit k ng tng ng do B Giao thng vn ti ban hnh. Ni chung chiurng mt cu thng gm cc phn sau:

+ Phn xe chy c th l: 4, 6, 7, 8, 9, 10.5, (m).

+ Phn l ngi i b c th l: 0.5, 1, 1.5, 2, (m).

+ Phn lan can, dy bo v, dy phn cch.

- Kh gii hn trn cu ng st: Ly theo kch thc nh hnh v i vi kh ray1000mm v kh ray 1435mm. (mc 2.3.3.4 trong 22TCN272-05).

Hnh 3.1a: Trn ng st kh 1000mm Hnh 3.1b: Trn ng st kh 1435mmTrong :

+ ng nt lin ____: Cho cc cng trnh vt pha trn ng st dng sc ko hinc v izen.

+ ng nt t -------: Cho cc cng trnh vt pha trn ng st dng sc koin xoay chiu.

+ S trong ngoc n dng khi c kh khn v chiu cao .

3.1.3.2. Kh thng thuyn:- Kh thng thuyn l khong khng gian c dnh cho giao thng ng thy di

gm cu m khng mt kt cu hay b phn kt cu no c vi phm vo khong khnggian m bo an ton cho giao thng ng thy.

- Kh thng thuyn c dng hnh ch nht vi kch thc B tt x Htt



Hnh 3.2: Kh thng thuyn.- Kh thng thuyn cn theo nhng quy nh ca nhim v thit k v quy nh ring ty

thuc vo cp k thut ng thy ni a, tc l cn c vo cp thng thuyn ca sng.Ph hp vi quy nh thit k kh gii hn di cu trn sng thng thuyn v nhng yucu ch yu v v tr cu.

Bng: Kh thng thuyn (bng 2.3.3.1.1 trong 22TCN272-05).

Cp

sng

Khu B tt Tnh khng

Htt (m)

Tnh khngdy inSng Knh

I 80 50 10 12II 60 40 9 11III 50 30 7 9IV 40 25 6 (5) 8V 25 20 3.5 8VI 15 10 2.5 8

3.2. THNH LP CC PHNG N CU:Cn c vo cc s liu kho st, ta dng c mt ct sng ti v tr xy dng cu.

Trn mt ct ngang c y cc s liu thit k: cc mc nc thit k, cc l khoan acht, khu thot nc (nu c).

3.2.1. Xc nh tng chiu di kt cu nhp:- Trng hp c khu thot nc L 0 (trn c s tnh ton thy vn):

+ Dng khu thot nc trn mt ct sng.

+ Xc nh v tr t m d kin: V tr hai m cn t sao cho khng c php viphm vo khu thot nc di cu L0.

+ Tng chiu di kt cu nhp c tnh t mp m ny n mp m bn kia.

- Trng hp khng c khu thot nc L0: i vi sng nh thuc vng trung du vmin ni, dng chy hp v r rt, b dc ng: dng phng n nc ngp n u th lmcu n , v tr hai m cn t sao cho khng c php vi phm vo mp ca MNCN.Tng chiu di kt cu nhp cng c tnh t mp m ny n mp m bn kia.

3.2.2. Chn v b tr cc nhp cu:

3.2.2.1. Xc nh v tr v khu nhp ch:

- Nhp ch l nhp thng thuyn hoc l nhp c khu ln nht.



- Nhp ch c t ti v tr ch lng sng nc su nht trong ma cn (c xc nhcn c vo MNTN).

- Dng kh thng thuyn vo v tr nhp ch ta s xc nh c khu nhp ch. Khu nhp ch khng c vi phm vo b rng thng thuyn.

- Trong s cu phi b tr t nht mt nhp thng thuyn (i vi sng thng thuyn).i vi trng hp lng sng c a cht khng n nh c th dch chuyn lng sng theomt ct ngang sng th phi b tr cc nhp thng thuyn d phng.

3.2.2.2. Chn dng v phn chia kt cu nhp:- Cn c vo khu nhp ch cn thit xc nh trn chn dng KCN chnh s

dng:

+ KCN gin n: Cu dm BTCT, lin hp thp - BTCT, dn thp hoc cu vm.

+ KCN lin tc: Cu dm lin tc lin hp thp - BTCT, cu dm BTCT thi cng theophng php c y, c hng, cu treo dy vng hoc dy vng,

- Sau ta la chn dng KCN dn (nu c) sao cho ph hp vi KCN chnh: Thng sdng KCN dm gin n c chiu di bng nhau c thit k nh hnh bng thp hocBTCT.

- Cn c vo dng KCN nhp chnh, KCN dn, v tr hai m v cn c vo c im camt ct sng tin hnh phn chia nhp:

+ i vi KCN gin n th la chn chiu di KCN sau tnh c s nhp cnthit. Thng thng ta chn s nhp l trnh vic t tr v tr gia sng v gia khthng thuyn.

+ i vi KCN lin tc th ty dng KCN s dng m ta chn s nhp v t l phnchia nhp khc nhau (thng dng lm KCN chnh).

Cc chiu di nhp tham kho:i vi cc KCN cu nh hoc cu dn th nn dng cc KCN gin n nh hnh:

- Cu BTCT thng: L=9, 12, 15, 18m.

- Cu BTCT DL:

+ Cu dm I, T: L=21, 24.54, 28, 30, 33m.

+ Cu dm Super T: L=38, 40m.

- Cu dm thp lin hp bn BTCT: L=21, 24, 28, 30, 33m.

- Cu dm thp ng sut trc Prebeam L=3842m.

i vi cc KCN cu trung v cu ln th chiu di nhp ph thuc nhiu vo loi kt cuv cng ngh thi cng:

- Cu dm thp lin hp bn BTCT: L90m.

- Cu dm BTCT DL thi cng theo phng php c hng: L150m.



- Cu dn thp: L150m.

- Cu treo: L=150450m.

3.2.3. Xy dng ng mt cu:- Cn c vo cc cp thit k ca tuyn ng ta xc nh cc yu t c trng hnh hc

c bn ca tuyn nh: dc dc id, bn knh ng cong ng, + dc dc:

i vi cu c 1 nhp gin n c th ly id=0%. i vi cu nh nhp gin n c th ly id=12%. i vi cu trung v ln (dm lin tc v nhp dn gin n) c th ly id5%. Hai nhp k nhau dc khng c chnh qua 2% xe chy m thun.

+ Thng thng t ton b cu hoc mt phn ca cu nm trn ng cong ng cbn knh R=300012000m. Thng thng ly R=50006000m.

- Cn c vo tng chiu di KCN tnh t mp m bn ny n mp m bn kia xcnh trn th ta c th xc nh c ng mt cu c th bao gm c phn on thng von cong trn hoc c th ch c phn ng cong trn.

- Thng thng vi KCN gin n, th ta t KCN trn ng thng m khng cn b trtrn ng cong trn n gin trong thi cng. Nu s nhp chn th ta c th b tr cu c dc v hai pha t nh tr gia, cn n u s nhp l th ta c th t nhp gia c dcdc id=0% v cc nhp bin c dc dc i d=12% v hai pha.

3.2.4. Xy dng ng y kt cu nhp:- Cn c vo dng KCN v chiu di nhp la chn, xc nh s b chiu cao dm

theo cng thc kinh nghim hoc theo KCN nh hnh sn.

- Dng ng y KCN theo chiu cao dm s b la chn.

3.2.5. p kt cu nhp vo mt ct sng:Di chuyn KCN dng xung mt ct sng theo phng thng ng sao cho m bo

ng thi cc yu cu:

- y KCN ti mi v tr phi cao hn MNCN ti thiu 0.5m i vi sng ng bng v1.0m i vi sng min ni c ln, cy tri (ng t).

- Cao nh x m m tr phi ln hn MNCN ti thiu l 0.25m . Khi cao yKCN c xc nh thng qua cao nh x m m tr, chiu cao gi v k gi.

- KCN nhp thng thuyn khng c php vi phm kh thng thuyn.

3.2.6. Xc nh chiu cao m, tr:- Xc nh chiu cao m: Cn c vo cao ca y KCN ti v tr m cu ta xc nh li

chnh xc loi m, chiu cao v cc kch thc ca m m bo m c th c KCNm vn tha mn c cc yu cu i vi v tr ca m.

- Xc nh chiu cao tr:



+ Cn c vo y KCN, chiu cao gi v k gi ta xc nh c cao ca nhx m tr. ng thi cao nh x m tr phi cao hn MNCN ti thiu l 0.25m.

+ Cn c vo MNTN, xc nh cao nh b tr ( trnh by trn).

+ T ta xc nh c chiu cao tr.

3.3. XC NH KHI LNG CNG TRNH V TNG MC U T :

3.4. THIT K THM M V CNH QUAN:

3.5. SO SNH LA CHN PHNG N:- Phn tch tng mc u t ca mi phng n c xt n cc yu t:

+ Thi gian hon vn.

+ Chi ph duy tu, bo dng.

+ Vn u t ban u xy dng cng trnh.

- Thng k ton b khi lng vt liu:

+ Ct, , si,

+ Xi mng, ct thp

+ gio, vn khun v cc thit b phc v thi cng khc,

- So snh cc phng n v mt cng ngh ch to v thi cng:

+ Nn chn nhng phng n c bin php c kim chng v c th tin hnhthc hin thnh tho.

+ u tin nhng phng n thi cng hin c trong nc.

+ u tin nhng phng n c cng ngh thi cng mi cho dng kt cu mi.

- So snh cc phng n v m quan, kin trc v m bo yu cu v an ninh, qucphng.

- So snh cc phng n v cng tc duy tu, bo dng v thay th khi cn thit.

CHNG 4: MT CU V NG NGI I BI GING C S CNG TRNH CU


CHNG 4:

MT CU V NG NGI I4.1. CU TO MT CU:

4.1.1. Mt cu t:Mt cu t l b phn tip xc trc tip vi bnh xe ca hot ti nn phi p ng cc

yu cu nh:

- m bo cng .

- t b mi mn, bng phng xe chy m thun, khng gy xung kch.

- Thot nc nhanh.

- Trng lng bn thn nh gim tnh ti.

Lp ph mt cu

2% 2%

Hnh 4.1: Mt cu t.4.1.1.1. Mt cu bng btng Atphalt:a. Cu to:

2%

5010

30lp btng asphalt dy 5cmlp btng bo v dy 3cmlp phng nc dy 1cmlp mui luyn dy 9cm (ti tim cu)

Hnh 4.2: Mt cu btng atphalt.- Lp mui luyn (lp va m):

+ Lm bng va xi mng cp fc=1824Mpa (mc 150200 theo 22TCN18-79).

+ Chiu dy =11.5cm (ti v tr st g chn lan can) ri tng dn theo dc ngangv pha trc i xng gia mt ct ngang nhp.

+ Tc dng: To bng phng hoc dc ngang cu.

- Lp phng nc:



+ Gm mt lp nha ng nng, mt lp vi th tm nha v trn cng ph tip mtlp nha nng.

+ Chiu dy =11.5cm.+ Tc dng: Bo v bn mt cu khi b ngm nc.

- Lp btng bo v:

+ Lm bng btng cp fc24Mpa (mc200 theo 22TCN18-79). tng tc dngca lp bo v v bn ca lp ny, thng t li ct thp c =34mm vi li5x5cm hoc 10x10cm.

+ Chiu dy =34cm.+ Tc dng: Chu p lc cc b t bnh xe truyn xung v phn u xung bn mt

cu.

- Lp btng asphalt:

+ Lm t hn hp bng nha ri nng hoc ri m.

+ Chiu dy =57cm.+ Tc dng: To ra mt ng m thun cho xe chy, hn ch lc xung kch truyn

xung bn mt cu.

b. u, nhc im v phm vi p dng:

- Mt cu bng btng Atphalt c kh nng chng thm tt, thi cng nhanh.

- To ra mt ng m thun cho xe chy , hn ch lc xung kch truyn xung bnbtng mt cu v hn ch ting n.

- Gi thnh r hn mt cu bng btng xi mng.

- Tui th thp khong 10 20 nm v nhanh b hao mn do tng chi ph duy tu bodng.

- Hin nay mt cu bng btng atphalt ang c p dng ph bin.

4.1.1.2. Mt cu bng btng ximng:a. Cu to:

lp btng xi mng mc 300 dy 8cm tli ct thp d6, bc ct thp 10x10cmlp phng nc dy 1cmlp mui luyn dy 9cm (ti tim cu)

1080

2%

Hnh 4.3: Mt cu btng ximng .



- Lp mui luyn (lp va m): Ging trn.

- Lp phng nc: Ging trn.

- Lp btng ct thp:

+ Cu to bng btng cp fc30Mpa (mc300 theo 22TCN18-79).+ Chiu dy =68cm.+ Li ct thp =68mm, bc 10x10cm.+ Tc dng: Chu p lc cc b t bnh xe truyn xung v phn u xung bn

btng mt cu. ng thi to ra mt ng cho xe chy.

b. u, nhc im v phm vi p dng:

- Mt cu btng ximng c tui th khong 5060 nm (cao hn mt cu bng btngAtphalt) v t b hao mn do gim chi ph duy tu bo dng.

- Mt cu bng BTXM c kh nng chng thm tt.

- Mt ng khng m thun cho xe chy, gy ra lc xung kch v ting n ln khi c xechy qua cu.

- Gi thnh t hn mt cu bng btng Atphalt.

- Hin nay mt cu bng BTXM t c p dng.

4.1.1.3. Mt cu bng thp:Trong cu thp, gim tnh ti mt cu c th cu to mt cu bng thp.

a. Mt cu bng thp bn trc hng:

Cu to:

Hnh 4.4: Mt cu bn thp trc hng.- Bn thp:

+ Chiu dy =1224mm.- Sn tng cng dc v ngang:

+ Lm t cc di thp bn hnh nh vo mt di ca tm thp.

+ Cc sn tng cng b tr ng hoc nghing.



+ Ti ch giao nhau gia sn dc v ngang th sn ngang thng c khot l cho sn dc c lin tc.

Cu to sn dc:+ Khong cch gia cc sn dc thng t 3050cm.

+ Dng mt ct h: Cu to t thp bn, thp hnh I, L, [ hoc T ngc. Dngmt ct h c cu to n gin, tuy nhin kh nng tng cng cng chng xon cho bnthp mt cu km.

Hnh 4.5: Dng sn dc c mt ct h.+ Dng mt ct kn: Cu to t thp bn c hn thnh cc tit din ch V, U

hoc hnh bn nguyt. Loi mt ct ny c kh nng tng cng cng chng xon vchu un cho bn thp tt hn so vi mt ct h.

Hnh 4.6: Dng sn dc c mt ct kn.

Cu to sn ngang:+ C tc dng lin kt cc dm ch hoc cc mt phng dn ch, ng thi h

thng sn dc v bn mt cu.

+ Sn ngang thng c cu to t cc dm nh hnh hoc dm t hp cdng mt ct ch I hoc [.

+ Khong cch gia cc sn ngang thng t 24m.

- Li ct thp:

+ Lm t cc thanh ct thp ng knh 6mm vi bc ct thp 1015cm.

+ Tc dng: cho lp btng asphalt hoc btng ximng dnh kt tt vi tmthp mt cu.



- Lp ph btng asphalt hoc btng ximng:

+ Chiu dy =57cm. u, nhc im:

- Kt cu mt cu kiu ny tham gia chu lc cng dm ch nh l mt b phn cadm ch.

- Khng cn cu to lp phng nc v cc tm thp dng lm mt cu l loi thpkhng g.

- Loi mt cu ny p ng tt yu cu v s dng nh bng phng, nhm, ngthi khng cn thit n h thng thot nc.

- Cu bn trc hng c trng lng bn thn nh nn n c bit thch hp vi ccnhp di khi t s momen do tnh ti v hot ti ln.

- Gi thnh loi mt cu ny cao hn so vi cc loi mt cu khc.

- Kt cu bn trc hng c th p dng cho bn mt cu hoc cho c dm ch trongtrng hp dm hp.

b. Mt cu bng thp dng sn mt co:Ngoi ra, cn c kiu mt cu bng thp lm di dng sn mt co rng c trng lng

rt nh. Loi mt cu ny p ng tt cc yu c u v s dng nh bng phng, nhmng thi li khng cn thit n h thng thot nc nhng c nhc im l t tin.

4.1.2. Mt cu ng st:

Mt cu ng st c 3 loi chnh: Mt cu c mng dm (balt), mt cu c t vt ttrc tip ln dm v mt cu c ray t trc tip ln bn mt cu (khng c t vt v balt).

4.1.2.1. Mt cu c mng balt:

a. Cu to:

200 200

14353500

Mng dm balt

T vt g

Ray chnhRay ph

400

200

Hnh 4.7: Mt cu ng st c mng balt.



- Ray t trn t vt, di t vt l balt.

- Bn mt cu BTCT thng c dng lng mng cha dm.

- Chiu rng lng mng ln hn 3400mm vi kh ng ray 1435 v ln hn 2600mmvi kh ng ray 1000.

- Khong cch gia ray chnh v ray ph a=2024cm.

- Chiu dy lp balt di t vt h20cm.

b. u, nhc im:- Loi mt cu c mng dm to ra s ng nht v cng gia ng v cu nn

m bo tu chy m thun, hn ch ti a lc xung kch.

- Trong trng hp cu t trn ng cong bng th loi mt cu ny cho php to csiu cao bng cch thay i chiu dy ca lp dm.

- Nhc m chnh ca loi mt cu ny l lm tng tnh ti mt cu v tng chiu caokin trc ca cu nn hin nay t s dng (c bit l trong cu dn thp).

4.1.2.2. Mt cu trn (t vt t trc tip ln dm):

a. Cu to:

300

200

200300 200

1435

T vt g

G g200x160

Ray chnhRay ph

Hnh 4.8a: M hnh mt cu trn c t vt t trc tip ln dm .- T vt:

+ Di L=3m.

+ C tit din ngang t nht l 20x24cm (cho kh 1435) v 20x22cm (cho kh 1000).

+ Khong cch gia cc t vt l 1015cm.

- Thanh g dc (g g):

+ Tit din 20x16cm.

+ G g khc su 2cm ti nhng ch p vo t vt v lin kt vi t vt bng bulng.

+ Khong cch gia mp ray chnh v g g vo khong 3040cm.

+ Tc dng: Gi cho cc t vt khng b x lch i, ng thi cng c tnh cht nhmt ray bo v t pha bn ng oi.

- Ray ph:

+ Khong cch gia mp trong ca ray chnh v ray ph l 2024cm.

+ Ray ph thng c cng s hiu vi ray chnh hoc c s hiu nh hn.



+ Ray ph c b tr trong phm vi trn cu v on ng u cu c chiu diL10 v c un ni chp li vi nhau nhm mc ch dn hng cho bnh xe i vo lnggia ray chnh v ray ph.

+ Tc dng: phng trng hp xy ra trt bnh th bnh xe khng ln i qu xang ray.

b. u, nhc im:

- Mt cu loi ny c cu to n gin, gim c tnh ti mt cu v chiu cao kin trcca cu nn c p dng kh ph bin.

- Nhc im chnh l kh m bo s ng nht v cng gia ng trn cu vngoi cu nn thng gy ra lc xung kch v ting n ln khi c tu.

- Kh to c siu cao khi cu t trn ng cong bng.

Hnh 4.8b: Mt cu trn c t vt t trc tip ln dm .4.1.2.3. Mt cu c ray t trc tip ln bn mt cu:a. Cu to:

Bn thp 10mm

m g

Bn btng mt cu Bn thp 30mm

Bulng

Rng enBn m

m cao su

Thp gc

m thp

Hnh 4.9a: M hnh mt cu c ray t trc tip ln bn mt cu.- Ray c lin kt trc tip vi bn btng mt cu.

- Di ray c bn m cao su v bn m thp, dng bulng hoc cc lin kt ray, cth dng thp gc thay ray ph.

- Tc tu chy cng cao, cp ti trng cng ln th cu to ca lin kt ny cng ph ctp.



Hnh 4.9b: Mt cu c ray t trc tip ln bn mt cu.b. u, nhc im :

- Do khng c mng dm v t vt nn kiu mt cu ny gim chiu cao kin trc vtnh ti ca kt cu nhp, tit kim vt liu v chi ph duy tu sa cha mng dm t vt.

- Hnh dng dm cu btng n gin, d thi cng v b c g mng dm.

- Nhc im l cu to lin kt ray cng phc tp khi tc chy tu cng nhanh.

- m thun khi tu ra vo cu km hn so vi mt cu c mng dm.

- i vi cu c ng st v t i chung th kiu mt cu ny kh thch hp.

4.2. PHNG NC V THOT NC TRN CU :

4.2.1. dc phng nc trn cu:

4.2.1.1. dc dc cu:a. Vai tr:

- Nhm m bo thot nc theo phng dc cu.

- Gim chiu di ton cu v chiu cao nn ng p u cu , t gim gi thnh xydng.

- To hnh dng kin trc.

b. Ch dn thit k dc dc:- dc dc c chn cn c vo cp thit k ca tuyn ng (Tiu chun thit k

ng t TCVN4054-2005). dc dc cng ln, thot nc cng nhanh tuy vy dcdc qu ln s c th lm thay i s lm vic ca cng trnh v gy ra nhng kh khn choxe chy.

- Thng thng m bo m thun cho xe chy v trnh gy phc tp trong qu trnhthi cng kt cu nhp, ngi ta b tr dc dc ca cu id=15%.



Cp thit k ng

(ng bng)Vn tc thit k (Km/h) idmax(%) Rdmin(m)

VI 30 9 400V 40 7 700IV 60 6 2500III 80 5 4000II 100 4 6000I 120 3 11000

c. Cch to dc dc:- i vi cu nh v trung (L100m) th dc dc c to bng cch thay i cao

nh tr hoc thay i chiu cao k gi. Cng c th lm dc dc mt chiu hoc dc dc bng khng.

3300033000330006000 33000 33000

2% 2% 0% 0% 2%6000

2%

Hnh 4.10a: dc dc cu i xng v hai pha .

2%2% 2%

Hnh 4.10b: dc dc cu v mt pha.- i vi cu ln (L>100m) th ta c th b tr ton b cu hoc hoc mt phn chiu di

cu nm trn ng cong ng c bn knh R d=300012000m ng vi cp ng .

4.2.1.2. dc ngang cu:a. Vai tr:

- Nhm m bo thot nc theo phng ngang cu.

b. Ch dn thit k v dc ngang:- dc ngang c la chn cn c vo cp thit k ca tuyn ng.

- Thng thng m bo thot nc th ta ch cn b tr dc ngang i n=1.52%.

- Trong trng hp cu nm trn ng cong bng th to siu cao ta c th b tr cu c dc ngang in=56%.

- ng ngi i trn cu thng lm dc ngang i n=11.5% v pha tim cu.



Hnh 4.11a: To dc ngang cu.c. Cch to dc ngang:

- dc ngang c to bng cch thay i chiu dy lp va m (lp mui luyn) hocthay i chiu cao k gi theo phng ngang cu.

- i vi mt cu bng BTCT ti ch th dc ngang c to ngay trong qu trnh btng.

2%2%

Hnh 4.11b: dc ngang c to ngay trong qu trnh thi cng .4.2.2. ng thot nc trn cu:

4.2.2.1. Yu cu:- Cn b tr ng thot nc sao cho ma thot nhanh v khng thm vo mt ngoi ca

cu hoc chy ln nn ng chui di cu.

- ng thot nc phi m bo thot ht nc ng trn mt cu v d thay th, dn dpkhi cn thit.

- Nu thit k khng hp l v thi cng sai st s dn n gim tui th ca cu do vngBTCT ln cn ng thot nc b h hng.

4.2.2.2. Cu to ng thot nc:- Cc ng thot nc c th cu to bng gang c, nha PVC hoc tn un thnh dng

ng trn.

- ng knh ng 15cm.- Ming ng phi c np y chn rc.

- u di phi nh ra khi b mt btng bn mt cu a10cm trnh nc khngchy tt vo bn btng.



ng thot ncng thot nc

Tim ng thot nc

B tng cnh dm

B tng ht nh M400

np chn rc

ng thot nc

Hnh 4.12a: Cu to ng thot nc bng gang c.1/2 mt ct ti gi 1/2 mt ct gia nhp

12000

500 11000 500



ng ni

l tho ncnp chn rc

250

10152001515

10

300

250

15 10

1510

198

212

250

140

7

216

202

77

250

1515

3015

20

60230022082700

575 250

10

152525

8.9

226

18023 23

276

2330

2030

2020

3030

2030

176

196

Hnh 4.12b: Cu to ng thot nc PVC.4.2.2.3. Nguyn tc b tr ng thot nc :

- Din tch ng:

+ Trn cu ng t: C 1m2 b mt hng ma ca cu phi b tr 1cm2 din tch lthot nc.

+ Trn cu ng st: C 1m2 b mt hng ma ca cu phi b tr 4cm2 din tch lthot nc.

- Khong cch gia cc ng:

+ Khong cch gia cc ng d15m.

+ Nu dc dc cu id



+ Khong cch t tim ng n mp va (mp chn lan can) t 2040cm.

ng thot nc

Hnh 4.13: B tr ng thot nc.- Trong nhng trng hp nhy cm v mi trng, khng th x nc trc tip t mt

ng xung sng pha di cn xem xt gii php dn nc theo ng ng dc gn pha di kt cu nhp v x vo ni ph hp trn mt t t nhin.

Hnh 4.14: Gii php dn ng thot nc cu.4.3. KHE CO GIN TRN CU:

4.3.1. Vai tr ca khe co gin:- Cng trnh cu chu nh hng di lu ca hon cnh t nhin nh: gi thi, mt tri

chiu vo, chnh lch nhit gia ngy v m. c bit l kt cu nhp di tc ng canng lnh sinh ra ni lc ca bin dng co ngt, t bin do pht sinh ra cc bin dng.Khi s co gin khng u v lp i lp li lu ngy khin cho kt cu b nt.



- Ngoi ra di tc ng ca cc lc ngang theo phng dc cu th kt cu nhp c schuyn v: chuyn v xoay v chuyn v tnh tin. Nu khng m bo cho u kt cu nhpc c cc chuyn v ny th cng s dn n hin tng nt v xut hin ni lc ph trongdm.

=> cn thit phi b tr khe co gin trn cu nhm mc ch: m bo cho u kt cunhp c th chuyn v t do di tc dng ca hot ti, thay i nhit , t bin v co ngtca btng.

4.3.2. Yu cu i v i khe co gin:- m bo bn, c tui th tng i cao hn ch chi ph duy tu bo dng v

thay th.

- m bo cho xe chy m thun, hn ch lc xung kch v ting n khi c xe chy.

- m bo kn v thot nc tt, chng r r nc v cc mnh vn gch ca lngng.

- Khe co gin phi c cu to n gin, d thi cng, d kim tra v thay th, sa cha khicn thit.

4.3.3. Cc loi khe co gin:

4.3.3.1. Khe co gin h:

a. Phm vi s dng:

i vi cc cu c chiu di nhp nh L15m vi cc chuyn v nh =12cm th ta cth s dng khe co gin h.

b. Cu to:- Khe co gin ch gm cc thanh thp gc ti u dm tng cng cng cho u

dm v m bo cho nc khng thm vo btng dm.

- Pha di b tr mng hng nc bng cao su nc khng chy xung gi cu v xm m, tr.

Hnh 4.15: Khe co gin h.c. u, nhc im:

Khe co gin loi ny c cu to rt n gin, thc cht l cc chi tit c b tr ch m bo thot nc. Nhc im chnh l khng kn nc, rt d b ng rc lm tc khe cogin. ng thi gy ra ting n khi c xe chy.



4.3.3.2. Khe co gin kn:a. Phm vi s dng:

p dng cho cc chuyn v = 23cm.b. Cu to:

- C tng phng nc lin tc cn tng btng bo h gin on qua khe.

- Khe c b phn co gin bng ng thau hoc tn trng km.

- Lp nha matt nha: Tng n hi 2 u dm dn ra mt c ch t do.

Hnh 4.16: Khe co gin kn.c. u, nhc im:

- Xe chy m thun.

- Ch to phc tp hn khe co gin h.

4.3.3.3. Khe co gin cao su chu nn:a. Phm vi s dng:

Khe co gin loi ny cng ch nn p dng cho cc chuyn v nh = 12cm vi chiudi nhp L 15m.b. Cu to:

- Nhc im chnh ca khe co gin h l khng kn nc ng thi gy ra ting n lnkhi c xe chy. khc phc nhc im trn th ta s dng tm cao su chu nn c tp cht vo khe h gia hai u dm.

- B mt cao su c t thp hn 5mm so vi mt cu trnh h hng do xe c.

Hnh 4.17: Khe co gin cao su chu nn.



c. u, nhc im:

Tm cao su va c tc dng to ra s co gin n hi cho u d m, chng thm nc vahn ch c lc xung kch cng nh ting n khi c xe chy.

4.3.3.4. Khe co gin cao su bn thp:

a. Phm vi s dng:

c s dng ph bin nc ta hin nay. p dng cho cc chuyn v =1.52cm vicc nhp nhp cu L=1530m.

b. Cu to:- Khe co gin gm 1 khi cao su c cch rnh dc tng bin dng, cc bn thp c

chiu dy 68mm nm trong tm cao su c tc dng lm tng cng chu nn v chu unca tm.

- Cc tm cao su c ghp ni di bng keo. Cc tm ny c t qua khe h gia haiu dm v neo vo bn btng mt cu bng cc bulng neo t chm.

- Cc bulng neo c lin kt hn vi cc thanh ct thp ch t sn trong kt cu nhp.

Ct thp nh v 16Ct thp ch 20

Va khng co ngt

Tm cao su

Bu lng neo 20

Lp ph mt cu

Hnh 4.18: Khe co gin cao su bn thp.c. u, nhc im:

Khe co gin cao su bn thp m bo xe chy m thun, hn ch c lc xung kc

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