Chng 2 kt cu b tng, b tng ct thp thch: (1) Phi kim tra v bin dng trong trng hp khi chuyn v c th hn ch kh nng lm vic bnh

  • Published on
    11-Feb-2018

  • View
    214

  • Download
    2

Embed Size (px)

Transcript

  • www.

    vnco

    ld.vn

    Chng 2 - Kt cu b tng, b tng ct thp 103 103

    Chng 2

    kt cu b tng, b tng ct thp

    Bin son: GS. TS. Nguyn nh Cng Hiu nh: GS. TS. Nguyn Xun Bo

    2.1. Nguyn tc chung

    Ni dung thit k kt cu b tng, b tng ct thp gm nhng cng vic sau y, ng vi cc bc thit k.

    Bc thit k s b (thit k c s): Chn phng n ( xut, phn tch, so snh, la chn), lp s tng th ca kt cu, chn s b cc kch thc c bn, c tnh khi lng vt liu cn thit.

    Bc thit k k thut: Lp s tnh ton, xc nh ti trng v tc ng, tnh ton ni lc (hoc ng sut), kim tra kh nng chu lc hoc tnh ton ct thp cn thit, kim tra cc iu kin v n nh, bin dng, nt, th hin ln bn v hnh dng, cc mt ct chnh ca kt cu.

    Bc thit k bn v thi cng: Chn v b tr cc loi ct thp, th hin cc chi tit cu to vi hnh dng v kch thc c th, th hin cc chi tit lin kt, lp bng thng k vt liu, gii thch v ghi ch nhng vn c lin quan n vic dng vt liu v thi cng.

    thit k k thut thng chia kt cu b tng v b tng ct thp thy cng thnh hai loi: Kt cu h thanh, bn v kt cu khi ln.

    Tnh ton kt cu h thanh, bn c a v vic xc nh v kim tra ni lc trn cc mt ct ca kt cu. Ty loi ni lc m kim tra vi mt ct thng gc (un, nn, ko), mt ct nghing (ct) hoc mt vnh (xon).

    Tnh ton kt cu khi ln (p trng lc, p vm, tng chng...) hoc cc kt cu c hnh dng c bit (m khng th biu th c bng ni lc cc mt ct) phi tin hnh theo phng php ca c hc mi trng lin tc (hoc l thuyt n hi) m ch yu l xc nh v kim tra ng sut chnh. Vic ny c trnh by trong cc chuyn ring ng vi tng loi kt cu.

    Ni dung chng ny ca s tay khng bao gm ht cc vn thit k nh nu trn y m ch gii hn trong mt s phn c bn v thit k k thut ca kt cu h thanh, bn, khi m c th xc nh ni lc trn cc mt ct ca kt cu.

    Tnh ton kt cu nh va nu c tin hnh theo Tiu chun thit k kt cu b tng v b tng ct thp thy cng TCVN 4116-1985 v cc ti liu lin quan khc.

  • www.

    vnco

    ld.vn

    104 s tay KTTL Phn 1 - c s k thut thy li Tp 2

    Theo TCVN 4116-85 cng nh theo Cc qui nh ch yu v thit k cng trnh thy li TCXDVN 285-2002, kt cu b tng v b tng ct thp thy cng c tnh ton theo phng php trng thi gii hn. Cc vn v yu cu tnh ton ghi trong bng 2-1.

    Bng 2-1. Cc yu cu v tnh ton theo trng thi gii hn

    Thng s, ch tiu Trng thi gii hn th nht Trng thi gii hn th hai

    Vn cn xt Kh nng chu lc iu kin lm vic bnh thng

    Ti trng cn xt Tt c cc t hp ti trng T hp ti trng c bn

    i vi kt cu b tng

    bn, n nh v v tr v hnh dng ca kt cu S hnh thnh khe nt

    Yu

    cu

    tnh

    ton

    i vi kt cu b tng ct thp

    bn, n nh v v tr v hnh dng ca kt cu. bn mi ca kt cu chu ti trng rung ng lp li nhiu ln

    Bin dng (1), m rng khe nt hoc s hnh thnh khe nt (2)

    Ch thch: (1) Phi kim tra v bin dng trong trng hp khi chuyn v c th hn ch kh nng lm vic bnh thng ca kt cu hoc ca thit b t trn n. Tr s gii hn ca bin dng do thit k quy nh xut pht t yu cu lm vic bnh thng ca thit b, my mc. C th khng cn kim tra theo bin dng nu trong khi vn hnh, s dng cc kt cu tng t khng nh c l cng ca cc cu kin m bo cho cng trnh lm vic bnh thng. (2) Phi kim tra v s hnh thnh khe nt trong trng hp iu kin s dng bnh thng ca cng trnh khng cho php hnh thnh khe nt.

    Trong cc cng trnh thy li cn c th gp cc kt cu b tng ct thp khng

    thuc phm vi ca TCVN 4116. Vi cc kt cu ny (nh, cu, ng hm giao thng...) cn s dng cc tiu chun tng ng.

    Vic thit k kt cu b tng, b tng ct thp thng c tin hnh theo trnh t sau y:

    1. Gii thiu, m t kt cu, s kt cu (mt bng, nhim v, c im...).

    2. Chn kch thc s b.

    3. Xc nh cc loi ti trng, cc tc ng ln kt cu.

    4. Xc nh ni lc do cc ti trng gy ra, t hp ni lc.

    5. Tnh ton hoc kim tra kt cu theo trng thi gii hn th nht.

    6. Tnh ton hoc kim tra kt cu theo trng thi gii hn th hai.

    7. Chn, b tr ct thp, th hin bn v thi cng.

    bc 2 chn s b kch thc ca cc mt ct, bc 5 v 6 s qua tnh ton hoc kim tra m nh gi xem xt kch thc c chn hp l hay cha. Nu kch thc l cha hp l, b qu hoc ln qu, th ty trng hp m xem xt vic thay i kch thc tnh ton li.

  • www.

    vnco

    ld.vn

    Chng 2 - Kt cu b tng, b tng ct thp 105 105

    2.2. S liu c bn 2.2.1. S liu v ti trng

    2.2.1.1. Ti trng tiu chun

    xc nh ti trng tiu chun tc dng ln kt cu cn phi phn tch s lm vic ca n v cn c vo cc s liu thit k.

    Ti trng tiu chun cn c xc nh bng tnh ton theo cc tiu chun hin hnh v trong nhng trng hp c bit, khi cc tiu chun cha c quy nh c th, cn da vo cc kt qu nghin cu l thuyt hoc thc nghim.

    Theo TCXDVN 285-2002 (cc qui nh ch yu v thit k cng trnh thy li), khi thit k cng trnh thy li cn tnh n cc ti trng tc ng sau:

    a. Cc ti trng th-ng xuyn v tm thi (di hn v ngn hn) - Trng lng ca cng trnh v cc thit b c nh t trn v trong cng trnh.

    - p lc nc tc ng trc tip ln b mt cng trnh v nn, p lc nc thm ng vi mc nc ln nht khi xy ra l thit k trong iu kin thit b lc v tiu nc lm vic bnh thng.

    - Trng lng t v p lc bn ca n, p lc ca nham thch.

    - p lc t pht sinh do bin dng nn v kt cu cng trnh, do ti trng bn ngoi khc.

    - p lc bn ct. - Tc dng ca co ngt v t bin.

    - Ti trng gy ra do p lc d ca k rng trong t bo ho nc khi cha c kt hon ton mc nc dng bnh thng trong iu kin thit b lc v tiu nc lm vic bnh thng.

    - Tc ng nhit ln cng trnh v nn trong thi k thi cng v khai thc ca nm c bin dao ng nhit bnh qun thng l trung bnh.

    - Ti trng do tu, thuyn v vt tri (neo buc, va p).

    - Ti trng do cc thit b nng, bc d, vn chuyn v cc my mc, kt cu khc.

    - p lc do sng xc nh theo tc gi ln nht trung bnh nhiu nm. - Ti trng gi.

    - p lc nc va trong thi k khai thc bnh thng. - Ti trng ng sinh ra trong ng dn c p v khng p khi dn mc nc

    dng bnh thng.

    b. Cc ti trng tm thi c bit - Ti trng do ng t hoc n.

    - p lc nc tng ng vi mc nc khi xy ra l kim tra.

  • www.

    vnco

    ld.vn

    106 s tay KTTL Phn 1 - c s k thut thy li Tp 2

    - Ti trng gy ra do p lc d ca k rng trong t bo ho nc khi cha c kt hon ton ng v mc nc kim tra ln nht trong iu kin thit b lc v tiu nc lm vic bnh thng hoc mc nc dng bnh thng nhng thit b lc v tiu nc b hng.

    - p lc nc thm gia tng khi thit b chng thm v tiu nc khng lm vic bnh thng.

    - Tc ng do nhit trong thi k thi cng v khai thc ca nm c bin dao ng nhit bnh qun thng l ln nht.

    - p lc sng khi xy ra tc gi ln nht thit k.

    - p lc nc va khi t ngt ct ton b ph ti. - Ti trng ng sinh ra trong ng dn c p v khng p, khi dn mc nc

    ln nht thit k.

    - p lc pht sinh trong mi t do mc nc sng, h b h thp t ngt (rt nhanh).

    2.2.1.2. Ti trng tnh ton Ti trng tnh ton ly bng ti trng tiu chun nhn vi h s lch ti n cho

    trong bng 2-2.

    Bng 2-2. H s lch ti n (theo TCVN 4116-85 v TCXDVN 285-2002)

    Tn ti trng v lc tc dng H s lch ti n

    Trng lng bn thn ca cng trnh 1,05 (0,95)

    Trng lng bn thn ca lp o ng hm 1,20 (0,80)

    p lc thng ng do trng lng t 1,1 (0,90)

    p lc bn ca t 1,2

    p lc bn ct 1,2

    p lc (nham thch): - Trng lng ca khi to vm

    - p lc ngang ca

    p lc thy tnh v p lc sng, cng nh p lc nc thm theo ng vin di t ca cng trnh trong cc khp ni v trong cc mt ct tnh ton (p lc y ngc ca nc).

    1,5

    1,2 (0,8)

    1,0

    p lc thy tnh ca nc ngm ln lp o ng hm Cc ti trng do cc my lm vic di t, my bc d, vn chuyn cng nh ti trng do ngi, hng v thit b t trn cng trnh:

    1,1 (0,90)

    - Khi tr s ti trng di 2 kN/m2 1,3

  • www.

    vnco

    ld.vn

    Chng 2 - Kt cu b tng, b tng ct thp 107 107

    Tn ti trng v lc tc dng H s lch ti n

    - Khi tr s ti trng trn 2 kN/m2 1,2

    Ti trng gi 1,3

    Ti trng tu 1,2

    Tc dng do nhit v m 1,1

    Tc dng do ng t 1,0

    Ch thch:

    1. H s lch ti do cc phng tin chuyn ng trn ng st v ng t ly theo tiu chun thit k cu.

    2. Cc h s lch ti ghi trong ngoc n (...) ng vi cc trng hp khi dng gi tr b ca ti trng s dn ti bt li cho s lm vic ca cng trnh.

    3. Khi tnh kt cu theo bn mi v theo trng thi gii hn th hai phi ly h s lch ti bng 1.

    2.2.1.3. T hp ti trng Khi thit k kt cu cng trnh thy phi xt t hp ti trng c bn v t hp ti

    trng c bit.

    a. T hp ti trng c bn bao gm cc ti trng v tc ng: thng xuyn, tm thi di hn, tm thi ngn hn m i tng ang thit k c th phi tip nhn cng mt lc.

    b. T hp ti trng c bit vn bao gm cc ti trng v tc ng xt trong t hp ti trng c bn nhng mt trong chng c thay th bng ti trng (hoc tc ng) tm thi c bit. Khi c lun chng chc chn c th ly hai trong cc ti trng hoc tc ng tm thi c bit kim tra.

    Ngi thit k phi la chn a ra t hp ti trng c bn v t hp ti trng c bit bt li nht c th xy ra trong thi k thi cng v khai thc cng trnh.

    2.2.2. S liu v b tng

    Cn cn c vo nhim v, c im ca cng trnh chn mc thit k ca b tng.

    Vi mi loi kt cu cn quy nh mc theo cng chu nn. Theo tiu chun Nh nc TCVN 6025-1995 (B tng, phn mc theo cng chu nn) th mc c ly theo cng c trng ca mu khi vung cnh 15cm tnh theo n v MPa. Cng c trng ny c tnh ton vi xc sut bo m 95%. Theo tiu chun ngnh 14TCN 63-2003 (B tng thy cng, yu cu k thut) b tng thy cng c cc mc M10; 12,5; 15; 20; 25; 30; 35; 40; 45.

  • www.

    vnco

    ld.vn

    108 s tay KTTL Phn 1 - c s k thut thy li Tp 2

    Ph lc 2-5 cho bit tng quan gia mc theo qui nh c ca TCVN 4116-1985 v theo qui nh ca TCVN 6025-1995 c dng trong chng ny.

    Vi cc kt cu m cht lng c quyt nh bi s lm vic ca b tng chu ko hoc khi khng cho php hnh thnh khe nt th cn quy nh mc theo cng chu ko K: K1; 1,5; 2; 2,5; 3; 3,5.

    Vi cc kt cu c yu cu chng thm cn quy nh thm mc theo tnh chng thm.

    Cng tiu chun v cng tnh ton ca b tng c cho trong bng 2-3.

    Bng 2-3. Cng ca b tng

    Cng tiu chun (MPa) Cng tnh ton (MPa) Mc thit k ca b tng nng

    (theo TCVN 6025-1995) Nn dc trc Rtcn Ko dc trc R

    tck Nn dc trc Rn Ko dc trc Rk

    M 10 8,4 0,9 5,6 0,60

    M 12,5 10,5 1,0 7,0 0,67

    M 15 12,6 1,12 8,4 0,75

    M 20 16,5 1,36 11,0 0,90

    M 25 19,5 1,56 13,0 1,00

    M 30 24,0 1,74 16,0 1,16

    M 35 28,5 1,90 19,0 1,26

    M 40 32,8 2,05 21,5 1,36

    M 45 36,7 2,20 24,5 1,46

    K 1 - 0,78 - 0,60

    K 1,5 - 1,17 - 0,90

    K 2 - 1,56 - 1,20

    K 2,5 - 1,95 - 1,50

    K 3 - 2,35 - 1,80

    K 3,5 - 2,70 - 2,10

    Khi tnh ton theo trng thi gii hn th nht cn nhn cng tnh ton ca b tng vi h s iu kin lm vic mb cho bng 2-4.

  • www.

    vnco

    ld.vn

    Chng 2 - Kt cu b tng, b tng ct thp 109 109

    Bng 2-4. H s iu kin lm vic mb

    H s iu kin lm vic ca b tng Cc yu t to nn s cn thit phi a h s iu kin lm vic

    K hiu Tr s

    1. T hp c bit i vi kt cu b tng mb1 1,10

    2. Ti trng lp li nhiu ln (kim tra v bn mi) mb2 Xem bng 2.5

    3. Kt cu b tng ct thp kiu bn vi chiu dy: mb3

    - Ln hn hoc bng 60cm 1,15

    - Nh hn 60 cm 1,0

    4. Kt cu b tng mb4 0,9

    Ch thch: - Khi c mt s yu t tc dng ng thi th ly tch ca cc h s iu kin lm vic tng ng tnh ton.

    - Khi khng c cc yu t to nn s cn thit nh trn th khng cn a h s iu kin lm vic mb hoc cng nh ly mb = 1.

    Bng 2-5. H s iu kin lm vic mb2

    H s mb2 khi ti trng lp li nhiu ln, ng vi h s khng i xng ca chu k b bng Trng thi m

    ca b tng 0 - 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8

    m t nhin 0,65 0,70 0,75 0,80 0,85 0,90 0,95 1,0

    Bo ho nc 0,45 0,50 0,60 0,70 0,80 0,85 0,95 1,0

    Mun n hi ban u ca b tng Eb c cho bng 2-6.

    H s bin dng ngang ca b tng = 0,15.

    Mun trt ca b tng G ly bng 0,4 Eb

  • www.

    vnco

    ld.vn

    110 s tay KTTL Phn 1 - c s k thut thy li Tp 2

    Bng 2-6. Mun n hi ban u ca b tng nng

    Mun n hi ban u ca b tng nng Eb (MPa) ng vi mc thit k

    iu kin ng cng ca b tng M10 M12,5 M15 M20 M25 M30 M35 M40 M45

    ng cng t nhin 19.800 22.000 23.600 27.200 30.000 32.300 34.200 35.800 37.200

    Khi x l nhit trong iu kin

    p lc khng kh 17.800 19.700 21.300 24.500 27.000 29.000 30.800 32.200 33.500

    2.2.3. S liu v ct thp

    Ct thp dng cho kt cu b tng ct thp thy cng phi ph hp vi tiu chun Nh nc v thp ct b tng.

    Cng tiu chun v cng tnh ton ca cc ct thp theo TCVN c cho trong bng 2-7.

    Bng 2-7. Cng ca ct thp

    Cng tnh ton v ko (MPa) Loi (nhm)

    ct thp

    Cng tiu chun

    R tca (MPa) Tnh ton ct thp dc Ra

    Tnh ton ct thp ngang Ra

    Theo TCVN 1651-1985

    Ct trn nhm CI 240 200 160

    Ct c g CII 300 260 208

    Ct c g CIII 400 340 270

    Ct c g CIV 600 480 360

    Theo TCVN 6285-1997

    Loi RB300 300 260 208

    RB400 400 340 270

    RB400W 400 340 270

    RB500 500 400 300

    RB500W 500 400 300

    Ch thch: Cng tnh ton v nn ca ct thp Ran ly nh sau: - Khi Ra 400 MPa ly Ran = Ra - Khi Ra > 400 MPa ly Ran = 400MPa. Cc loi thp RB400W, RB500W, CI, CII l thp d hn, loi RB300, RB400, RB500 l thp kh hn.

  • www.

    vnco

    ld.vn

    Chng 2 - Kt cu b tng, b tng ct thp 111 111

    Khi tnh ton theo trng thi gii hn th nht cn nhn cng tnh ton ca ct thp vi h s ma cho trong bng 2-8.

    Bng 2-8. H s iu kin lm vic ma

    Cc yu t to nn s cn thit phi a h s iu kin lm vic ca ct thp vo cng thc tnh ton K hiu Tr s

    - Ti trng lp li nhiu ln ma1 Xem cng

    thc (*)

    - Cu kin b tng ct thp c s thanh ct thp chu lc mt ct ngang

    t hn 10 ma2 1,1

    T 10 tr ln 1,15

    - Kt cu b tng ct thp kt hp vi kt cu thp. ma3 0,8

    Ch thch: Khi khng c cc yu t nu trn th khng cn a h s ma vo cng thc, hoc cng nh ly ma = 1.

    H s iu kin lm vic khi kim tra v mi ma1 c xc nh theo cng thc sau:

    o ha1

    o ha

    1,8 k k km

    k k k1 1

    1,8

    =

    (*)

    trong : ko - H s nhm ct thp, bng 2-9;

    k - H s ng knh ct thp, bng 2-10;

    kh - H s kiu mi hn, bng 2-11;

    a = a mina max

    - h s khng i xng ca chu k;

    a min, a max - ng sut nh nht v ln nht trong ct thp chu ko, tnh ti cng mt im, khi ti trng thay i (xem mc 2.6.2).

    Khi theo cng thc trn tnh c ma1 > 1 th khng cn kim tra ct thp v mi.

    Bng 2-9. H s ko

    Nhm (loi) ct thp CI CII, RB300 CIII, RB400

    ko 0,44 0,32 0,28

  • www.

    vnco

    ld.vn

    112 s tay KTTL Phn 1 - c s k thut thy li Tp 2

    Bng 2-10. H s k

    ng knh ct thp (mm) 20 30 40 60

    k 1,0 0,9 0,85 0,8

    Vi cc ng knh trung gian ly k theo ni suy.

    Bng 2-11. H s kh

    Loi lin k hn ca ct thp thanh kh

    1. Hn i u tip xc:

    - C nh sch bng c kh 1,0

    - Khng nh sch bng c kh 0,8

    2. Hn i u bng phng php hn mng (h quang) khi mng thp c chiu di l:

    l 5 ng knh ca thanh thp b 0,8

    l = 1,5 n 3 ng knh thanh thp b. 0,6

    3. Hn i u vi hai thanh kp i xng 0,55

    M un n hi ca ct thp Ea ly nh sau:

    - Vi ct thp CI, CII, RB300: E =210.000 MPa.

    - Vi ct thp CIII, CIV, RB400, RB500: Ea=200.000 MPa.

    H s tnh i t ct thp ra b tng tng ng l na = a

    b

    E

    E

    trong l h s n hi ca b tng. Gi tr ca na cho bng 2-12.

    Bng 2-12. H s tnh i na

    Mc thit k ca b tng M15 M20 M25 M30 M35 M40 M45

    na 25 23 20 18 15 12 10

  • www.

    vnco

    ld.vn

    Chng 2 - Kt cu b tng, b tng ct thp 113 113

    2.2.4. S liu v kt cu

    tnh ton kt cu b tng v b tng ct thp thy cng cn dng h s bo m kn v h s t hp ti trng cho cc bng 2-13 v 2-14.

    Bng 2-13. H s bo m kn

    Cp cng trnh Cp I Cp II Cp III v IV

    kn 1,25 1,20 1,15

    Bng 2-14. H s t hp ti trng nc

    Cc t hp ti trng nc

    T hp ti trng c bn

    T hp ti trng c bit

    T hp ti trng thi k thi cng v sa cha

    1,00

    0,90

    0,95

    2.3. Tnh ton bn kt cu b tng 2.3.1. Nguyn tc chung

    bn ca kt cu b tng c tnh ton, kim tra theo mt ct thng gc vi trc.

    Ty thuc vo iu k...

Recommended

View more >