Phn tch nh hng ca cc tham s cu to n trng thi chu lc trong kt cu nhp cu cong BTCT

trn ng t TS. Hong H KS. Nguyn Hu Hng B mn CTGTTP - Trng i hc GTVT

TM Tt : Bi vit gii thiu mt s kt qu nghin cu nh hng ca cc tham s cu to n trng thi chu lc trong kt cu nhp cu cong BTCT trn ng t. Kt qu nghin cu c kh nng h tr cng tc nghin cu, tnh ton thit k cc cng trnh cu cong BTCT trn thc t. SUMMARY: The report introduces the researched results about influence of structural parameters on loaded state of span structure of reinforced concrete curved bridge on otoroad in Vietnam.

1. M u Cng vi qu trnh xy dng v pht

trin t nc ta hin nay, do tc th ha nhanh gy ra tnh trng ch tc giao thng ngy cng c xu th nghim trng nhiu thnh ph v cc khu th.

Mt trong nhng gii php c hiu qu l xy dng cc nt giao ct khng cng mc (nt giao ct lp th). c im ca cc nt giao ct lp th l m bo thng xe an ton v lin tc qua nt, nh m nng cao nng lc thng xe ca tuyn ng.

tin r sang tuyn ng khc hay quay u.Cc nhnh ng r c cu to nh cc

nhp cu cong v cu r nhnh hoc t hp cc lin nhp cu cong, cu cho gc, cu thng ni tip nhau (hnh 2).

Do c im cu to dn n trng thi ni lc, bin dng pht sinh trong kt cu nhp cong rt phc tp. Thc t xy dng v khai thc cc cu cong trn th gii v nc ta cho thy i hi cn nghin cu mt cch y hn v cc cng trnh cu cong c v

Hnh 1: Cu cong nt Nam Chng dng - H ni

Hnh 2: Cu cong trong cc nt giao thng lp th v ng nhiu tng

Nhiu cng trnh cu vt v nt giao lp th c xy dng gn y H ni, Thnh ph H Ch Minh, Hi phng... thc s pht huy hiu qu tt, gp phn lm gim ng k vn nn ch tc giao thng nu trn. Trn hnh 1 gii thiu mt trong nhng nt giao thng lp th c xy dng u tin b nam cu Chng Dng (H ni).

V mt cu to, nt giao thng lp th thuc dng cng trnh phc tp gm tp hp cc tuyn ng, cc cu vt, cc nhp dn cu cn, cu cong, cu r nhnh. Trong kt cu hon chnh ca nt giao thng lp th ngoi cc cu vt dng cho cc tuyn chnh cn c lung ng dnh cho cc phng

mt cu to, m hnh v phng php tnh ton, cng ngh xy dng v c yu cu v mt kin trc, m quan ca cc cng trnh.

Bi vit cp mt s kt qu phn tch nh hng ca cc tham s cu to c bn n s bin i tr s ni lc bin dng trong kt cu nhp cu cong BTCT trn ng t.

2. c im cu to ca kt cu nhp cu cong 2-1. Cc yu cu chung

Do phi tha mn cc ch tiu k thut ca tuyn ng, kt cu nhp cu cong thng c cu to phc tp. Cu c th nm trn ng cong c bn knh khng i, bn

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knh thay i, trn on cong c cc on thng xen gia, ng cong o chiu... Trong trng hp a hnh phc tp cn phi thit k cu cong c dng xon c nh cu dn u cu Thanh tr (H Ni) ang xy dng. Trn hnh 3 gii thiu cc dng ng cong c bn p dng cho qu o tim cc cu cong trn mt bng.

.a b c

.d e f

y Tc khai thc ca ti trng trn cu (v).y Siu cao mt cu phn xe chy trn on

cong (isc). y Bn knh ng cong ng trn cu ( R). y dc dc ( id).

Ngoi ra cn phi quan tm ti cc yu cu v tnh khng, tm nhn di cu, hay chiu di cc on chuyn tip t on cu thng vo cu cong...

Mt vn khc cng i hi quan tm ng mc l do trng thi ni lc bin dng rt phc tp, cc cu cong BTCT c cu to v s b tr ct thp thng v d ng lc khc bit v phc tp hn dn n cu to chi tit khc cng c s bit so vi cc cu trn

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Hnh 3: Cc dng ng cong p dng cho cu cong

Tuy mt s cng trnh cu cong c xy dng nh nt giao thng nam cu Chng Dng (H ni), cu dn vo nh ga sn bay Ni Bi, tuyn cu dn u cu M Thun, cu vt Hong Long (Thanh Ha)... nhng nhn chung kinh nghim thit k v xy dng cc cng trnh cu cong ca ngnh xy dng cu Vit Nam cha tht nhiu.

V mt cu to cng c nhng vn cn quan tm y hn, ngoi mt s nhp cu dng bn cong ti nt giao thng nam Chng Dng, a s cc cng trnh cu cong xy dng nc ta l dng s dng cc sn dm thng t theo ng gp khc, pha trn bn mt cu c ti ch theo ng cong. Gii php trn c u im n gin cu to, gim mc phc tp khu thit k, thun tin thi cng. Tuy nhin cha hon ton tha mn cc yu cu v kin trc. Mt khc khu ca cc nhp cu cong mi p dng trong khong (15 - 20)m cho cc cu bn BTCTDL v (20 - 40) m cho cc cu dng sn dm thng, bn mt cu theo ng cong. Trong tng lai chng ta cn phi xy dng cc cu trn ng cong c hnh dng tha mn yu cu kin trc v chiu di nhp ln hn.

Khc vi cc cu nm trn ng thng, thit k cc cu cong phi quan tm nhiu vn , trong cn c bit ch ti cc yu t hnh hc c trng gm: y Bn knh ca ng cong (R). y m rng phn ng xe chy trn cu

(m).

ng thng thng thng. Hin nay, bn cnh vic tin hnh xy

dng chng ta ang gp rt b sung cc nghin cu, c kt thm kinh nghim cng nh dn hnh thnh cc Tiu chun thit k, cc ch dn c th, ph hp cho thit k v cng ngh xy dng cu cong.

Vn nu trn s c b khuyt v hon thin dn trn c s tp hp cc ni dung nghin cu ca nhng chuyn gia ngnh cu quan tm n vn ny.

2-2. La chn cc tham s cu to trong bi ton thit k cu cong a. Chiu di nhp, s cu.

Trong thc t cc cu cong thng c p dng cho cc cu cn, cu vt ng hay cc nhnh r trong cc nt giao thng lp th.Vic la chn chiu di vt nhp thng da trn cc c s sau y:

Thoa man yeu cau cua tnh khong thong xe pha di cau (hnh 4), do vay chieu dai nhp trc het phai phu hp vi ac iem quy mo be rong cua tuyen ng i pha di cau va chieu dai ket cau nhp co the tnh theo cong thc sau: Lnhp = SLx RL + GPC + 2 xVH + KCAT (1) Trong : - SL: so lan xe cua tuyen ng di cau. - RL: be rong cua 1 lan xe - GPC: be rong cua giai phan cach tren ng- VH: be rong va he - KCAT: khoang cach an toan cua tru (tnh t

mep le ng en mep than tru, thng co the lay t 1 - 2m).

Lnhp: Tong chieu dai cac nhp cau vt.

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Trng hp tuyen di cau khong ln ch dung 1 nhp. Vi trng hp nhieu nhp can m rong va bo tr bo tr tru trung gian giai phan cch (GPC).

Hnh 4 am bao ve tam nhn trong cac nut giao thong lap the. Yeu cau chung la phai am bao cho ngi lai xe nhn thay bien bao hay au ao trong nut t khoang cach t nhat la 180m.

Phai vt qua c nhng vat kien truc cn bo tn bn di cau.

am bao kha nang chu cac loai tai trong tac dung trong giai oan thi cong va khai thac.

Hai hoa ve mat kien truc, phu hp vi trnh o cong nghe xay dng hien tai. b. Chiu rng cu v phn m rng phn ng xe chy trn cu

Theo tieu chuan 22TCN-273-01[1], o rong cua 1 lan xe tieu chuan la boi so cua 0.25m va thng thay oi t 3.0m en 3.75m. Vi nhng cau c xay dng trong o th , be rong lan xe (cha tnh phan m rong ng cong) co the tham khao cac gia tr bang 1.

c. Ban knh cong Tuy theo toc o thiet ke, ac iem a hnh va

giai phap thi cong ma la chon ban knh cong cau cho phu hp. Tuy vay, ban knh cong phai tha mn yeu cau cua ban knh toi thieu theo Tiu chun thit k [1].

)fi(127

vR (2) maxsc

2min +=

Trong o: v: van toc thiet ke (km/h) isc : o sieu cao tnh theo % f : he so ma sat ngang cua mat ng. Gia tr f tham khao bang 3. Tr so ban knh cong toi thieu tnh theo cong

thc (2) ap dung cho cac cau cong tren cac tuyen giao thong, tai cac nut giao lap the, toc o thiet ke (v) co the lay bang 0.7 gia tr toc o thiet ke cua xe trc khi vao nut, theo o ban knh toi thieu cua cac cau cong trong nut cung giami. ieu nay se lam giam bt kho khan ve mat bang xay dng cac nut giao lap the.

Ngoai tr nhng cau nhanh re, cac cau chnh nen u tien thiet ke vi ban knh cong ln:

+ Vi toc o thiet ke t 6080 km/h, dung ban knh R=505000m.

+ Vi toc o thiet ke t 8090 km/h, dung ban knh R=10005000m.

+ Vi toc o thiet ke t 90110 km/h, dung ban knh R=20005000m

+ Vi toc o thiet ke t 110120 km/h, dung

Bang 1: Be rong cau khi cau xay dng trong thanh pho

Toc o thiet ke (km/h) 40 50 60 70 80 90 100 Be rong lan (m) 3.00 3.50 3.50 3.50 3.75 3.75 3.75 Be rong mat cau 2 lan(m) 6.00 7.00 7.00 7.00 7.50 7.50 7.50 Be rong mat cau 4 lan(m) 12.0 14.0 14.0 14.0 15.0 15.0 15.0

Be rong mat cau cong lay bang be rong mat cau thang (bang 1) cong them phan m rong phan xe chay tren ng cong. Tuy vay, trong cac trng hp khi xac nh be rong mat cau can phai tham khao them ve s phu hp vi quy mo mat cat ngang cua toan tuyen.

o m rong mat cau cho cho 2 lan xe, chieu rong phan xe chay K = 7.0 m tren ng cong phu thuoc ban knh cong va toc o thiet ke theo [1] ghi trong bang 2.

ban knh R=30005000m Vi nhng cau co toc o thiet ke nho hoac

tai cac nhanh re th ban knh cong thiet ke co the giam ti mc toi thieu.

3. nh hng ca cc tham s cu to n s bin i ni lc v chuyn v ca kt cu nhp cu cong. Theo kt qu nghin cu ca G.S Gibsman [3]. Ni lc trong kt cu nhp cu cong ph

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thuc vo cc tham s c bn sau y: 1. S kt cu (s lng nhp lin tc).

2. Dng ng cong (cong lin tc hay cc ng cong c cc on thng ni gia). 3. iu kin lin kt ti gi (s gi kim

do mt bng xy dng cht hp v yu cu vn tc phng tin khng ln v vy thng chn bn knh rt nh, trng hp c bit c th phi s dng Rmin=10m. ph hp vi iu kin chu lc cn chn t l

2)/( RL , cho cc chiu di nhp L 20m. Bang 2: Phan m rong mat cau trong trng hp co 2 lan xe (kho 7m)

Toc o thiet ke (km/h) Ban knh cong (m) 50 60 70 80 90 100 110 120

1500 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 1000 0.0 0.0 0.1 0.1 0.1 0.1 0.2 0.2 750 0.0 0.0 0.1 0.1 0.1 0.2 0.3 0.3 500 0.2 0.3 0.3 0.4 0.4 0.5 0.5 400 0.3 0.3 0.4 0.4 0.5 0.5 300 0.3 0.4 0.4 0.5 0.5 250 0.4 0.5 0.5 0.6 200 0.6 0.7 0.8 150 0.7 0.8 140 0.7 0.8 130 0.7 0.8 120 0.7 0.8 110 0.7 100 0.8 90 0.8 80 1.0 70 1.1

Bang 3: He so ma sat ngang cua mat ng Toc o thiet ke (km/h) 40 50 60 70 80 90 100 110 120

He so ma sat ngang 0.17 0.16 0.15 0.14 0.14 0.13 0.12 0.11 0.09

ch xon trn m, tr). 4. T l chiu di nhp so vi bn knh cong L/R. 5. T l gia cng chng un v cng chng xon ca kt cu nhp EJ/GJx

Hai tham s bn knh cong (R) v chiu di nhp (L) quyt nh cong ca kt cu t nh hng trc tip n trng thi ni lc v bin dng trong kt cu nhp. Trn bng 4 gii thiu v d kt qu nghin cu ng nh hng ni lc bin dng cho cu cong mt nhp theo [3].

Kt qu trn bng 4 cho thy t s L/ R nh hng rt ln ti ni lc trong kt cu nhp cu cong. c bit ch khi t l ny bng 3 ni lc tng mt cch t bin.

Trn thc t, thit k cu cong thuc lp bi ton kh c khu cu to v tnh ton. Trong thnh ph v cc khu th,

Do yu cu cng ngh cng nh xt ti kt cu nn mng cng trnh thng thng chiu di cc nhp trong mt cu c chn bng nhau. Nh vy vic iu chnh ng cong tim cu trn mt bng s ty thuc vo s bin i bn knh cong. Trn bng 5 l kt qu tnh ton th nghim cho kt cu nhp cong c chiu di L =25m, bn knh cong thay i t 20- 70m.

Bng 6 l kt qu kho st cho trng hp bn knh cong khng i R = 20 m trong khi tham s chiu di nhp thay i t 20 -30m.

mt kha cnh khc ca vn , trong iu kin t l L / R c chn hp l v khng i, s bin thin ni lc v vng khi chiu di nhp v bn knh thay i cng cho thy yu cu cn nghin cu y hn.

Trn bng 7 gii thiu mt s kt qu kho st bc u cho khong nhp trung bnh t 20 - 40 m khi bn knh cong thay i tng ng nhm c nh t l L /R.

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Bng 4: Dm cong mt nhp c b tr gi chng xon hai u nhp

Tung ng nh hng khi P=1 t ti cc v tr Mt ct

xGJEJ

RL

0 L/8 L/4 3L/8 L/2 5L/8 3L/4 7L/8 L

G/T chun nhn vo tung

ng nh hng m men un do lc n v di ng theo tim dm 0.0 0.00 0.09 0.19 0.16 0.12 0.09 0.06 0.03 0.00

1.0 0.00 0.10 0.20 0.17 0.14 0.11 0.07 0.03 0.00 1.5 0.00 0.11 0.22 0.20 0.17 0.13 0.09 0.04 0.00 2.0 0.00 0.14 0.26 0.25 0.22 0.18 0.13 0.06 0.00 2.5 0.00 0.20 0.37 0.39 0.37 0.32 0.23 0.12 0.00

L/4

0.1-10.0

3.0 0.00 0.67 1.25 1.54 1.61 1.45 1.10 0.59 0.00

L

0.0 0.00 0.06 012 0.19 0.25 0.19 012 0.06 0.00 1.0 0.00 0.07 0.14 0.21 0.27 0.21 0.14 0.07 0.00 1.5 0.00 0.08 0.17 0.24 0.31 0.24 0.17 0.08 0.00 2.0 0.00 0.11 0.22 0.32 0.39 0.32 0.22 0.11 0.00 2.5 0.00 0.12 0.37 0.51 0.60 0.51 0.37 0.12 0.00

L/2

0.1-10.0

3.0 0.00 0.86 1.61 2.13 2.35 2.13 1.61 0.86 0.00

L

ng nh hng m men xon do lc n v di ng theo tim dm 0.0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.0 0.00 -0.04 -0.06 -0.07 -0.07 -0.06 -0.04 -0.02 0.00 1.5 0.00 -0.06 -0.10 -0.12 -0.12 -0.11 -0.08 -0.04 0.00 2.0 0.00 -0.10 -0.17 -0.21 -0.21 -0.19 -0.14 -0.07 0.00 2.5 0.00 -0.20 -0.34 -0.42 -0.43 -0.39 -0.29 -0.16 0.00

Gi L=0

0.1-10.0

3.0 0.00 -0.88 -1.59 -2.04 -2.19 -2.01 -1.53 -0.82 0.00

L

0.0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.0 0.00 -0.02 -0.03 -0.05 -0.05 -0.05 -0.03 -0.02 0.00 1.5 0.00 -0.03 -0.06 -0.08 -0.09 -0.08 -0.06 -0.03 0.00 2.0 0.00 -0.05 -0.11 -0.14 -0.16 -0.14 -0.11 -0.06 0.00 2.5 0.00 -0.11 -0.29 -0.29 -0.31 -0.29 -0.29 -0.12 0.00

L/ 4

0.1-10.0

3.0 0.00 -0.58 -1.09 -1.44 -1.56 -1.43 -1.09 -0.59 0.00

L

ng nh hng vng khi P =1 di ng dc tim dm 0.0 0.00 -0.76 -1.43 -1.90 -2.08 -1.90 -1.43 -0.76 0.00 1.0 0.00 -0.96 -1.80 -2.38 -2.60 -2.38 -1.80 -0.96 0.00 1.5 0.00 -1.33 -2.47 -3.26 -3.55 -3.26 -2.47 -1.33 0.00 2.0 0.00 -2.29 -4.25 -5.59 -6.07 -5.59 -4.25 -2.29 0.00

0.01EJ

L3

2.5 0.00 -0.62 -1.15 -1.50 -1.63 -1.50 -1.15 -0.62 0.00 0.1 L3/ EJ

0.1

3.0 0.00 -1.10 -2.04 -2.67 -2.89 -2.67 -2.04 -1.10 0.00 1.0 L3/ EJ0.0 0.00 -0.76 -1.43 -1.90 -2.08 -1.90 -1.43 -0.76 0.00 1.0 0.00 -1.93 -3.60 - 4.74 -5.15 - 4.74 -3.60 -1.93 0.00

0.01L3/EJ

1.5 0.00 -0.43 -0.80 -1.04 -1.13 -1.04 -0.80 -0.43 0.00 2.0 0.00 -1.12 -2.07 - 2.71 -2.94 - 2.71 -2.07 -1.12 0.00

0.3 L3/EJ

2.5 0.00 -0.43 -0.79 -1.03 -1.12 -1.03 -0.79 -0.43 0.00 1.0 L3/ EJ

L/ 2

10

3.0 0.00 -1.02 -1.89 -2.47 -2.68 -2.47 -1.89 -1.02 0.00 10. L3/ EJ

Bng 5 : Kt qu tnh ton th nghim cho kt cu nhp cong c chiu di L=25, bn knh cong thay i t 20 70m

L(m) 25 25 25 25 25 25 25 25 25 25 25 R(m) 20 25 30 35 40 45 50 55 60 65 70 L/R 1.25 1.00 0.833 0.714 0.625 0. 556 0. 500 0. 455 0. 417 0. 385 0. 357

Mu(T.m) 190.9 179.88 173.88 171.35 169.41 168.10 167.18 166.50 165.99 165.60 165.29(T/m2) 143.18 134.91 130.40 128.51 127.06 126.08 125.39 124.88 124.49 124.20 123.97Mx(T.m) 69.67 52.30 42.01 35.48 30.67 27.04 23.30 21.90 20.01 18.42 17.07 (T/m2) 28.37 21.30 17.11 14.45 12.49 11.01 9.68 8.67 8.15 7.50 6.95

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Bng 6: Kt qu kho st cho trng hp bn knh cong khng i R=50m, trong khi tham s chiu di nhp thay i t 20 - 30m

L(m) 20 21 22 23 24 25 26 27 28 29 30 R(m) 50 50 50 50 50 50 50 50 50 50 50 L/R 0.400 0.420 0.440 0.460 0.480 0.500 0.520 0.540 0.560 0.580 0.600

Mu(T.m) 124.24 131.97 139.85 149.38 157.64 167.11 176.64 185.81 195.16 204.51 215.26

(T/m2) 145.59 140.27 135.44 132.37 128.29 125.33 122.48 119.48 116.69 113.99 112.11Mx(T.m) 14.47 16.20 17.93 19.66 21.39 24.32 27.25 30.18 33.11 36.04 45.82

(T/m2) 9.03 9.17 9.25 9.28 9.68 9.71 10.06 10.33 10.54 10.70 12.71Bng 7 : Kt qu kho st cho trng hp chiu di nhp t 20 - 40m, khi bn knh cong

thay i tng ng nhm c nh t l L/R = 0.5 L(m) 20 25 30 35 40

R(m) 40 50 60 70 80

Mu(T.m) 125.25 167.18 213.09 286.20 363.83

(T/m2) 183.47 125.39 92.50 135.17 115.11Mx(T.m) 18.05 24.19 35.63 48.17 60.39

(T/m2) 11.83 9.85 10.07 14.41 13.83

Ghi ch : Trong cc bng 5,6 v 7 - Kt cu bn gin n, chiu cao h = 1m, rng B= 8m - Mu, : M men un, ng sut ln nht xut hin trn kt cu do on xe H30. - Mx, : M men xon, ng sut tip ln nht xut hin trn kt cu do on xe H30.

4. Kt lun 1. La chn cu to hp l l mt trong

nhng ni dung phc tp v c ngha quan trng trong bi ton thit k cu cong. Mc kh khn cn tng thm trong trng hp mt bng xy dng cht hp nh trong cc nt giao thng lp th hay trong th.

2. Kt qu phn tch trong cc bng 4, 5 v 6 cho thy r t l L / R c tc ng rt nhy cm vi trng thi ng sut bin dng trong kt cu. Kt hp vi cc kt qu nghin cu trong [2], [3], [4] v[5] cho thy nn chn t k L/ R 2.

3. Trong trng hp a hnh cht hp khng ch bn knh cong nh c th la chn mt trong hai gii php: - Chn nhp nh c dc t l L / R

ph hp. - S dng ng cong c bn knh thay

i lin tc ci thin trng thi ni lc, bin dng trong h.

4. Kt qu nghin cu cng cho thy u im ni tri ca vic s dng mt ct ngang

hnh hp gim t l EJ/GJx trong cu to cc kt cu nhp cu cong.

Ti liu tham kho

[1]. Tiu chun thit k cu 22 TCN-272-01. B GTVT, 2001. [2]. M.E. GIBSMAN: Proektirovanie Transpornk Xooruzenyi - Transport- Moskva, 1980. (Ting Nga). [3]. M.E. GIBSMAN: Tablys dlia raxtrieta proletnkh stroenyi Transpornk Xooruzenyi - Transport- Moskva, 1985. (Ting Nga). [4]. Hiroshi Nakai, Chai Hong Yoo: Analysis and design of curved steel Bridges. McGraw- Hill. New Yrok, 1988. [5]. E.C. Hambly Feng, FICE: Bridge deck behaviour- E&FN SPON, London, 1991. [6]. Dng vn hip: Nghin cu tng quan v thit k v cng ngh xy dng cu cong. Lun vn Thc s k thut, i hc GTVT, H ni, 11-2002

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