Pages from Tap chi KHKT Thuy loi &Moi truong so 42-14.pdf

KHOA HC K THUT THY LI V MI TRNG - S 42 (9/2013) 88

PHN TCH TIN CY V AN TON CNG TRNH THY LI VIT NAM

Phm Hng Cng1, Nguyn Lan Hng2, Nguyn Th Huyn Trang2 Tm tt: Tip cn vi tiu chun k thut ca cc nc tin tin v p dng nhng phng php tnh

hin i nng cao chnh xc cho cc quyt nh khi thit k cng nh qun l cht lng cng trnh thy li l mt trong nhng hng nghin cu tch cc trong lnh vc an ton cng trnh Vit Nam hin nay. Ni dung ca bi bo trnh by cch tip cn ca cng trnh thy li vi thit k ngu nhin cp II, ng thi trnh by v d ng dng l thuyt tin cy phn tch an ton ca cng l thin lm r cc vn cn nghin cu. Cc ni dung ca bi bo l nhng kt qu nghin cu mi v l ti liu tham kho hu ch cho cng tc nghin cu, nh gi an ton cho cng trnh thy li.

T kha: An ton cng trnh thy li, cc s c ca cng l thin, tin cy ca cng l thin, phn tch tin cy, thit k ngu nhin.

1. t vn 1 Mi cng trnh l mt h thng kt cu phc tp.

Trong qu trnh lm vic, cc hng mc cng trnh l cc phn t quan trng trong h thng v c lin quan vi nhau theo mt logic. Thc t xy dng v khai thc cng trnh thy li cho thy, khng t h thng cng trnh b s c vi nhiu l do khc nhau, trong c nhng yu t khng c xt n do hn ch ca cc phng php tnh ton nn gy ra nhng tn tht ln i vi sn xut, kinh t, mi trng v con ngi. Cho n nay, Vit Nam, cc h thng cng trnh u mi thy li v ang c thit k theo phng php truyn thng, phng php thit k tt nh. Phng php ny khng nh lng c mc nh hng ca tng thnh phn n an ton chung ca h thng. V vy ngi thit k cng nh ngi qun l cha c cn c chc chn phn tch cc nhn t nh hng n an ton cng trnh, lm c s a ra nhng quyt nh hp l khi thit k cng nh khi vn hnh khai thc cng trnh.

Trn th gii, l thuyt ngu nhin ang c dng tng i ph bin trong nhng nghin cu, tnh ton phn tch an ton h thng nh h thng phng l, h thng cng trnh xy dng... Trong lnh vc cng trnh xy dng, nhiu nc tin tin chu u, M, Nga, Trung Quc vv a ra nhng tiu chun an ton cng trnh theo xc sut an ton cho php hoc tin cy an ton ca cng trnh [2].

Cho n nay, Vit Nam, cc cng trnh cng nh cc h thng thu li v ang c thit k theo phng php truyn thng (tip cn xc sut

1 Vin Khoa hc Thy li 2 Trng i hc Thu li.

cp 0). Trong khi , hng chc nm nay, l thuyt tin cy v tui th cng trnh a vo chng trnh ging dy chnh ca cc trng i hc nh: i Hc Bch Khoa, i Hc Xy Dng, i Hc Thu Li Mt s cc nghin cu mi gn y ng dng l thuyt tin cy trong lnh vc thu li cng mi dng li kt qu nghin cu ca cc lun vn tin s v thc s v cc vn nh: Probabilistic Design of Coastal Flood Defences in Viet Nam - Thit k ngu nhin h thng phng l b bin Vit Nam, [1]; Nghin cu xy dng phng php nh gi cht lng h thng cng trnh thu nng theo l thuyt tin cy trong iu kin Vit Nam, [3]; Phn tch n nh ca mt s tuyn thuc h thng sng Hng v sng Thi Bnh, [3]; Thit k xc sut v phn tch ri ro cho sng ung ng bng chu th sng Hng Vit Nam, [3];Nghin cu n nh mi dc , p, [3]. Kt qu nghin cu gn y ca ti c lp cp nh nc ngh ng dng l thuyt tin cy v phn tch ri ro vo trong nghin cu xc nh tin cy v an ton cho cng trnh xy dng trong iu kin thin tai bt thng, [7]. Hin nay ti Vit Nam cc ti nghin cu v l thuyt tin cy cho lnh vc thy li thng s dng mt s phn mm ca Chu u nh BESTFIT: c lng hp l ti a hm xc sut thng k cho bin ngu nhin t s liu quan trc, VAP: x l bin ngu nhin v gii hm xc sut thng k; Vit Nam c phn mm DTC2007 ca TS. Phm Hng Cng vi ni dung: nh gi cht lng h thng cng trnh thy nng theo l thuyt tin cy. Nh vy trong nghin cu cng nh trong thc t ng dng chng ta cn ang thiu cc phn mm tnh ton cho cc cng trnh cng nh cc h thng cng trnh


thy li khc nhau. Hin nay ti Vit Nam, trong tnh ton cng trnh

thy li ang s dng hn hp cc phng php: phng php ng sut cho php, phng php h s an ton v phng php trng thi gii hn cng vi m hnh thit k truyn thng. Theo m hnh thit k ny ti trng v bn tnh ton c mc nh theo cc tiu chun thit k hin hnh trong sut thi gian khai thc ca cng trnh. Nhng thc t cc hm ti trng v bn chu tc ng ca rt nhiu yu t khc nhau v bin i theo quy lut ngu nhin. V vy quan nim v quan h gia ti trng v sc chu ti ca cng trnh trong qu trnh lm vic ca m hnh thit k truyn thng ngy cng tr nn lc hu. Xu hng tin b hin nay l thit k cng trnh theo l thuyt ngu nhin v phn tch tin cy. Mc tip cn vi phng php thit k hin i ny hin c chia ra cc cp khc nhau:

- Tip cn mc xc sut cp 0, thit k truyn thng, s dng phng php h s an ton.

- Tip cn mc xc sut cp I, thit k bn xc sut, s dng phng php nhiu h s an ton (phng php trng thi gii hn).

- Tip cn xc sut cp II v cp III, phng php tip cn ngu nhin.

Mc III, trong cc hm phn b ca cc bin c gi nguyn quy lut phn b v cc tnh ton khng s dng cc phng php gn ng. Cp II, trong s dng cc phng php gn ng bin i lut phn b ca cc ti trng v sc chu ti v cc hm phn b chun, cc tnh ton s dng cc phng php xc sut gn ng.

Bi bo ny trnh by mt s kt qu phn tch an ton ca cng l thin tip cn vi l thuyt ngu nhin cp II lm c s thit lp bi ton phn tch tin cy an ton cho cc cng trnh thy li Vit Nam.

2. Bi ton cp II v tin cy an ton cng trnh.

Vi quan nim cng trnh b mt an ton (xy ra s c), trong trng hp ti trng v cc tc ng (S) vo cng trnh vt qu kh nng chu ti thit k (R), hoc ti trng v tc ng nm trong gii hn thit k nhng sc chu ti ca cng trnh b suy gim, trong tnh ton thit lp c hm tin cy (Z). Z R S (1)

Trong sc chu ti R v ti trng tc dng S l cc hm s ca cc i lng ngu nhin c lut phn phi xc nh. Theo biu thc (1) hm Z c

qui c nh sau: Z < 0 cng trnh khng tha mn iu kin an ton; Z > 0, cng trnh tha mn iu kin an ton; Z = 0 l ranh gii gia vng an ton v vng khng an ton (xem hnh 1).

Hm tin cy Z c th l hm tuyn tnh c cc bin ngu nhin phn phi chun; Z l hm phi tuyn vi cc bin ngu nhin phn phi chun; Z: l hm phi tuyn vi cc bin ngu nhin c lut phn phi bt k

X 2

X 1

Z < 0

Z > 0

Z = 0 Bin gia vng an ton v vng khng an ton

Vng khng an ton

Vng an ton

(R)

(S) Hnh 1: M phng bin s c.

Cc bc tm xc sut ca hm tin cy nh sau

[6]: Thnh lp hm tin cy Z. Bin i cc bin ngu nhin (BNN) ca hm Z

c lut phn phi (PP) bt k v lut phn phi chun. Xc nh k vng ( Xi ) v lch chun ( Xi ) ca cc BNN :

1

ni

Xii

XXn

; (2)

2

1

11

n

Xi ii

X Xn

; (3)

Khai trin Taylor i vi hm Z v s dng 2 biu thc u ca a thc ny. Hm Z c tuyn tnh ha ti im thit k (TK) ban u:

1 2 3, , ,...o o ooX X X X ; (4) trong : oi XiX ; (5)

00 01

.n

ii i

Z XZ Z X X X

X

; (6)

trong : k vng ban u ca hm Z tnh theo (7) v lch chun ban u ca hm Z tnh theo (8)

00 01

.n

Z Xii i

Z XZ X X

X

; (7)


0 21

( . )n

Z Xii i

Z XX

; (8)

Tnh tin cy: Z

Z

; (9)

v xc sut h hng: 0ZP ; (10) Tnh h s nh hng:

Z

Xii

0

i

XXZ

; (11)

Xc nh ta TK mi: * 1 2 3, , ....X X X X ; (12)

trong : . .i Xi i XiX ; (13)

Tnh lp tm im thit k v cc c trng thng k ca hm Z. Qu trnh lp c m t trn s hnh 2, bc lp ch dng li khi im thit k hi t.

TK: l im nm trn ng bin gia vng an ton v vng khng an ton m ti mt phn phi xc sut ca hm tin cy Z l ln nht. S dng kt qu TK cui cng ( hi t) tnh cc c trng thng k ca hm Z, t xc nh c xc sut xy ra s c 0ZP .

3. ng dng l thuyt tin cy nh gi n nh cho mt hnh thc cng trnh thy li: cng l thin.

3.1 Gii thiu v cng l thin. Cng l thin l mt loi cng trnh thy li c

s dng ph bin trong cc h thng ti, tiu, phng l, ngn triuCng thng c chiu rng kh ln, nn c chia ra thnh cc khoang. Cc cng c xy dng hoc chun b xy dng nc ta c chiu rng khoang t mt vi mt n hng chc mt. Cc cng ly nc, ti, tiu hoc cng iu tit trong h thng knh c chiu rng khoang thng t 1m n 10m. Cc cng xy dng trn sng lm nhim v iu tit dng chy, nht l cc cng ngn mn c xy dng gn ca sng nh cng im, cng Tho Long, cng Nghi Quang..., mt s cng ang c thit k trong h thng chng ngp thnh ph H Ch Minh nh: cng Th B, cng Mng Chui..., phi tha mn iu kin giao thng thy nn chiu rng mi khoang ca cc cng ny c thit k t 30m n 60m. Chiu su ct nc cc cng xy dng trn h thng ti

tiu khong t 1m n 10m, cc cng xy dng trn sng khong t 5m n 15m. So vi ct nc cc p to thnh h cha th cc cng h chu ct nc thp hn, v vy khi phn loi theo ct nc cng h cn c gi l cng trnh ct nc thp.

Cc b phn ca cng lin kt vi nhau thnh mt h thng kt cu. Trong thc t, cng l thin c xy dng c trn nn v nn t. Cng chu tc ng ca nhiu ti trng, trong cc ti trng t mi trng nc v cc ti trng pht sinh t mi trng nn l cc ti trng c din bin phc tp. Cng nh mt s cc cng trnh dng nc khc, s lm vic ca cng h l qu trnh tng tc gia ba mi trng nc, nn v cng. nh gi an ton ca cng l xt s cn bng gia sc chu ti v ti trng tc dng, trong cc yu t to nn sc chu ti v ti trng bao gm c cc yu t tt nh v yu t ngu nhin. Mc chnh xc ca cc kt lun v an ton ca cng ph thuc rt nhiu vo mc xt n tnh ngu nhin ca cc yu t to thnh sc chu ti v ti trng ca cc phng php c la chn tnh ton.

3.2 Cc c ch ph hoi ca cng l thin Cng l thin b s c c th xut pht t mt

nguyn nhn hoc nhiu nguyn nhn mc ni vi nhau. Cc kt qu phn tch c hc v cc nghin cu tng kt trong thc tin a cc quy nh v c ch ph hoi in hnh v cc iu kin m bo an ton cho cng vo trong cc tiu chun k thut thit k cng l thin. Trn c s phn tch c im lm vic ca cng v da theo tiu chun thit k cng l thin hin hnh c th thit lp c s cy s c nh hnh 3.

Mt n nhdng chy

Mt n nhtng th

Mt n nhkt cu

Cc sc khc

Cng btrt

Cng blt

Cng by ni

hoc

hochochochoc

hoc hoc hoc

Cng bln

S c cng l thin

hoc

Nn cngkhng khnng chu ti

Hnh 2: S cy s c ca cng l thin 3.3. Hm tin cy ca cc c ch ph hoi C rt nhiu nguyn nhn dn n s c cng l

thin nhng trong bi bo ny tc gi ch cp n 3 nguyn nhn lm mt n nh tng th cng v xy dng hm tin cy cho 3 c ch ph hoi ny: cng b trt, cng b lt, nn cng khng kh nng chu ti.


(1) Cng b trt phng Cng c th b trt phng qua mt tip gip gia

phn chn khay ca y cng v t nn. Hm tin cy ca c ch trt phng nh sau:

1 ct gtZ F F Trong :

ctF : tng cc lc chng trt; gtF : tng cc lc gy trt.

Cc lc chng trt v gy trt c xc nh trn c s phn tch tt c cc lc tc dng ln bn y cng.

Cng lm vic an ton khi 1

1 0 fZP P

Trong 1fP xc sut s c cho php ca c ch mt n nh trt phng.

(2) Cng b lt Trong qu trnh lm vic cng b c th b lt

quanh mt trc chn mng h lu. Hm tin cy ca c ch lt nh sau:

2 cl glZ M M Trong : clM ; glM : tng mmen chng

lt v gy lt ly vi trc chn mng h lu. Cng lm vic an ton khi

22 0 fZP P

Trong 2fP xc sut s c cho php ca c ch mt n nh lt.

(3) Nn cng khng kh nng chu ti ng sut ln nht m cng phi chu thng xut

hin ti chn mng thng lu hoc h lu ca cng. Khi ng sut trung bnh ti chn mng vt qu kh nng chu ti ca nn cng th nn cng b ph hoi.

3TC

TBZ R Trong :

TCR : sc chu ti ca t nn; TB : ng sut trung bnh ca mng cng.

Nn cng kh nng chu ti khi

3

3 0 fZP P

Trong 3fP xc sut s c cho php ca c ch mt n nh: nn cng khng kh nng chu ti.

3.4 Xc sut s c ca cng l thin S cy s c ca cng l thin nh hnh 3,

cc c ch s c xy ra l c lp v c quan h vi nhau trong mt h thng ni tip. Hm tin cy Z c tnh ton cp II nn xc sut s c ca

cng l CfP c tnh theo cng thc bin rng:

3

1

max 0 0i C if i f f ii

P Z P P Z

Trong : 0if iP Z : xc sut s c ca c ch th i.

3.5 V d tnh tin cy ca cng l thin Nam n.

lm r cc vn trnh by trn, trong phn ny trnh by v d bng s vi cc s liu thu thp c cng l thin Nam n tnh Ngh An. Cc tnh ton c thc hin theo ba phng php: h s an ton, trng thi gii hn (TTGH) v l thuyt tin cy (LTTC).

3.5.1 Gii thiu mt phng n tham kho trong thit k cng l thin Nam n (phng n cha x l nn)

Cng thuc loi cng trnh cp II c xy dng b t sng Lam thuc a bn x Xun Ho huyn Nam n, tnh Ngh An. y l cng ly nc l thin c lu lng thit k Qtk = 27,64 m3/s, cng gm 3 khoang mi khoang rng 5m ng m bng ca van phng, thn cng di 28,0m, pha sau van c tng ngc cao 9,45m. Trn nh cng c b tr cu giao thng, cu cng tc, cu th phai v cc thit b chuyn dng khc.

3.5.2 Cc s liu tnh ton. - Trng hp tnh ton: Chnh lch mc nc

thng h lu ln nht, cng ng. - S dng phn mm BESTFIT tm lut phn

phi xc sut thc nghim v cc c trng thng k , ca cc BNN nh bng 1.

Bng 1: Cc BNN s dng trong tnh ton

Tn cc BNNK hiu

n viLut phn phi ca cc BNN

Dung trng kh ca t nn k KN/m3Phn Phi

chun18,5 0,92

Gc ma st trong ca t nn Phn Phi

chun18 0,88

Lc dnh n v ca t nn C KN/m2Phn Phi

chun12,51 0,88

Dung trng ca b tng bt KN/m3Phn Phi

chun25 1,19

3.5.3 Cc tham s cho php theo tiu chun

Eurocode v tiu chun Vit Nam


3.5.4 Kt qu tnh ton - Tnh ton n nh cc c ch s

c theo 3 phng php khc nhau: h s an ton, trng thi gii hn v phng php tnh theo tin cy. S dng phn mm VAP (Variables Processor): tnh ton xc sut s c ca cc c ch ph hoi theo phng php tnh theo tin cy. Kt qu nh bng 3.

K hiu: (1): Cng b trt phng; (2): Cng b lt; (3): Nn cng khng kh nng chu ti.

3.5.5. nh gi kt qu Kt qu tnh theo tiu chun hin

hnh ca Vit Nam, trong s dng phng php h s an ton v phng php trng thi gii hn cho kt qu tha mn cc iu kin n nh.

Kt qu tnh theo phng php thit k ngu nhin: xc sut ly tiu chun an ton theo Eurocode th phng n thit k nu s hnh 3 khng m bo iu kin n nh.

Hnh 3: S cng Nam n dng trong tnh ton

Bng 2: Cc gi tr cho php theo tiu chun Vit Nam v Eurocode

Tiu chun Vit Nam. Xc sut s c cho php theo tiu chun Eurocode. Phng php h s an ton Phng php TTGH

CfP

1fP

2fP

3fP [Kt] [Kl]

.n ct

k nKm

.n clk nK

m

1.10-3 6.10-4 3.10-4 1.10-4 1,2 1,2 1,2 1,2

Bng 3: Kt qu tnh ton n nh cng theo 3 phng php Cc phng php tnh ton: Cc c

ch s c H s an ton TTGH LTTC

(1) Kt = 1,69 Kt = 1,57 P(Z1


chun Eurocode ca Chu u cao hn so vi tiu chun Vit Nam. Tuy nhin cc kt qu trn ch l tham kho v tin cy v cc ti liu dng trong tnh ton mt mc nht nh. S tnh l s ca phng n tham kho, mt s sai s ngu nhin cha c y ti liu thng k cn phi gi nh.

Nghin cu ng dng v pht trin cc phng php tnh ton hin i v tip cn vi cc tiu

chun k thut ca cc nc tin tin l mt trong nhng hng tch cc hin nay trong lnh vc an ton cng trnh nc ta. Tuy nhin pht trin c l thuyt ny nc ta cn phi tin hnh mt s nghin cu nh: lu tr d liu trong xy dng v trong quan trc, xy dng cc phn mm chuyn dng cho cc bi ton cng trnh cng nh h thng cng trnh

TI LIU THAM KHO 1. Mai Van Cong. Probabilistic design of coastal flood defences in Vietnam. Sieca Repro, the Netherlands

(2010). ISBN: 978-90-9025648-1, 249p. 2. Mai Vn Cng. Thit k cng trnh theo l thuyt ngu nhin v phn tch tin cy. Gio trnh 2005. 3. Phm Hng Cng. Nghin cu xy dng phng php nh gi cht lng h thng cng trnh thu

nng theo l thuyt tin cy trong iu kin Vit Nam. Lun n tin s k thut, 2009. 4. Nguyn Lan Hng, Nguyn Vn Mo, Mai Vn Cng. Application of probabilistic reliability analysis

in dam safety in Vietnam. ICEC 2012, Proceedings of the fourth International Conference on Estuaries and Coasts, volume 2.

5. Nguyn Lan Hng, Nguyn Vn Mo, Mai Vn Cng. Nghin cu ng dng l thuyt tin cy v phn tch ri ro nh gi mc m bo an ton cho h thng cng trnh thy li ly nc bng h cha trong iu kin Vit Nam. Tp ch KHKTTL v MT s c bit, 20/11/2011.

6. Nguyn Lan Hng, Nguyn Vn Mo, Mai Vn Cng. Phn tch tin cy an ton ca p t. Tp ch KHKTTL v MT s 39, thng 12 nm 2012.

7. Nguyn Vn Mo. L thuyt tin cy trong thit k cng trnh thu cng. Bi ging cao hc. i hc Thu Li 2000.

8. Nguyn Vn Mo & nnk. Nghin cu c s khoa hc v cc gii php k thut m bo an ton cng trnh xy dng trong iu kin thin tai bt thng Min Trung. ti cp Nh Nc. H Ni 2009.- 2011

9. TCXDVN 285-2002. 10. EN 1990:2002. Eurocode - Basis of structural design. 11. Trnh Bn L Ha Xng, Thit k cng, Nh xut bn nng nghip 12. Gio trnh thy cng, tp 1, 2 Trng i hc thy li, Nh xut bn Xy Dng, nm 2004.

Summary

RELIABILITY ANALYSIS OF HYDRAULIC STRUCTURE SAFETY IN VIETNAM Approaching to the technical standards of developed countries and applying the modern methods of

calculation to improve the accuracy of the design decisions as well as to manage the quality of hydraulic structure is one of the advanced research directions in the field of hydraulic structure Safety in Vietnam today. The main content of this paper is to analyze the probability of hydraulic structure safety according to the stochastic theory - level II, and application examples presented theoretical analysis of the reliability and safety sluices to clarify the issues to research organizations. This paper includes the results of the last studies and can be considered to be the reference for research in the field of hydraulic structure safety.

Keywords: hydraulic structure safety, failures sluice, reliability of sluice, reliability analysis ,probabilistic design.

Ngi phn bin: PGS. TS. Nguyn Quang Hng BBT nhn bi: 21/7/2013 Phn bin xong: 23/8/2013

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