Ket cau go

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Baìi giaíng Kãút cáúu gäù Huyình Minh Sån -------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------- Trang 1 CHÆÅNG MÅÍ ÂÁÖU: ÂAÛI CÆÅNG VÃÖ KÃÚT CÁÚU GÄÙ ξ1. ÂÀÛC ÂIÃØM VAÌ PHAÛM VI SÆÍ DUÛNG Caïc loaûi cäng trçnh xáy dæûng hay bäü pháûn cuía cäng trçnh chëu âæåüc taíi troüng laìm bàòng váût liãûu gäù hay chuí yãúu bàòng váût liãûu gäù goüi laì kãút cáúu gäù. 1.1 Æu, nhæåüc âiãøm cuía kãút cáúu gäù 1. Æu âiãøm: - Nheû, khoeí. Tênh cháút cå hoüc tæång âäúi cao so våïi khäúi læåüng riãng. C= R γ ; C CT3 =3,7. 10 -4 (m -1 ) < C Gäù nhoïm VI =4,3.10 -4 (m -1 ) < C BT 200 = 2,4.10 -3 (m -1 ) - Chëu neïn vaì uäún täút. - Váût liãûu phäø biãún, âëa phæång haû giaï thaình váûn chuyãøn. - Dãù chãú taûo: Cæa, xeí, khoan, baìo, âoïng âinh... - Chäúng xám thæûc cuía mäi træåìng hoaï hoüc täút hån so våïi theïp vaì bã täng. Âa säú axit näöng âäü tháúp åí nhiãût âäü thæåìng khäng laìm gäù hoíng Nhaì maïy eïp hoa quaí, nhaì maïy âæåìng, traûi chàn nuäi... 2. Nhæåüc âiãøm: - Váût liãûu khäng bãön, dãù muûc, mäúi, moüt, chaïy khäng sæí duûng âæåüc trong caïc kãút cáúu vénh cæíu. - Váût liãûu gäù khäng âäöng nháút, khäng âàóng hæåïng. Cuìng mäüt loaûi gäù nhæng cæåìng âäü R coï thãø khaïc nhau tuyì theo nåi moüc, tuyì vë trê trãn thán cáy (gäúc, ngoün), tuyì theo phæång taíi troüng (doüc thán, tiãúp tuyãún, xuyãn tám) khi tênh toaïn láúy hãû säú an toaìn cao. - Coï nhiãöu khuyãút táût (màõt, khe næït, thåï veûo) giaím khaí nàng chëu læûc. - Kêch thæåïc gäù tæû nhiãn haûn chãú (Gäù xeí: 30<b <320; 1< l <8m ). - Váût liãûu ngáûm næåïc, âäü áøm thay âäøi theo nhiãût âäü vaì âäü áøm cuía mäi træåìng. Khi khä co giaîn khäng âãöu theo caïc phæång, dãù cong vãnh, næït neí laìm hoíng liãn kãút. Âãø haûn chãú nhæåüc âiãøm cuía gäù tæû nhiãn, khi sæí duûng cáön xæí lyï âãø gäù khoíi bë muûc, Phaíi sáúy, hong khä gäù træåïc khi sæí duûng, khäng duìng gäù tæåi, gäù quaï âäü áøm qui âënh; choün giaíi phaïp sæí duûng váût liãûu âuïng chäù; tênh toaïn gáön våïi thæûc tãú laìm viãûc cuía kãút cáúu. Hiãûn nay, caïc phæång phaïp chãú biãún gäù hiãûn âaûi âaî caíi thiãûn tênh cháút cuía váût liãûu gäù. Loaûi gäù daïn gäöm nhiãöu låïp gäù moíng daïn laûi våïi nhau, âaî qua xæí lyï hoaï cháút laì loaûi váût liãûu quyï: Nheû, khoeí (chëu læûc täút) bãön, âeûp (khäng bë muûc, mäúi, moüt, khaí nàng chëu læía cao); saín xuáút cäng nghiãûp hoaï (dãù chãú taûo, váûn chuyãøn, thi cäng).

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Ket cau go

Transcript of Ket cau go

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    CHNG M U: AI CNG V KT CU G

    1. C IM VA PHAM VI S DUNG

    Cac loai cng trnh xy dng hay b phn cua cng trnh chu c tai trong lam bng vt liu g hay chu yu bng vt liu g goi la kt cu g.

    1.1 u, nhc im cua kt cu g

    1. u im:

    - Nhe, khoe. Tnh cht c hoc tng i cao so vi khi lng ring.

    C=R ; CCT3=3,7. 10-4 (m-1) < C G nhom VI =4,3.10-4 (m-1) < CBT200= 2,4.10-3 (m-1)

    - Chu nen va un tt. - Vt liu ph bin, a phng ha gia thanh vn chuyn. - D ch tao: Ca, xe, khoan, bao, ong inh... - Chng xm thc cua mi trng hoa hoc tt hn so vi thep va b tng. a s axit nng thp nhit thng khng lam g hong Nha may ep hoa qua, nha may

    ng, trai chn nui...

    2. Nhc im: - Vt liu khng bn, d muc, mi, mot, chay khng s dung c trong cac kt

    cu vnh cu. - Vt liu g khng ng nht, khng ng hng. Cung mt loai g nhng cng

    R co th khac nhau tuy theo ni moc, tuy v tr trn thn cy (gc, ngon), tuy theo phng tai trong (doc thn, tip tuyn, xuyn tm) khi tnh toan ly h s an toan cao.

    - Co nhiu khuyt tt (mt, khe nt, th veo) giam kha nng chu lc.

    - Kch thc g t nhin han ch (G xe: 30

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    2. Pham vi s dung: - Nha dn dung: San, v keo, khung nha, dm mai, xa g, cu phng, lit, cu thang,

    kt cu bao che (ca s, ca i, ca tri)...... - Nha san xut: Nha may, kho tang, chung trai, xng ch bin...

    - Giao thng vn tai: Cu nho, cu tam, cu phao, cu trn ng cp thp... - Thuy li: Cu tau, ca cng, p,... - Thi cng: Dan giao, van khun, cu cng tac, coc van, tng chn...

    cac nc tin tin: G dan c dung rng rai nh cac nha cng nghip ln, cu, b cha cht long, ng ng ( V < 2200m3, d < 1,5 m); ch, nha th, trin lam...

    2. TNH HNH PHAT TRIN VA S DUNG KT CU G VIT NAM

    Cung vi gach a, g la vt liu xy dng chu yu va lu i, at c trnh cao v ngh thut cung nh ky thut (Mt s cng trnh con lu lai nh: Chua Mt Ct (Ha Ni - 1049), chua Keo ( Thai Bnh), chua Ty Phng (Ha Ty)).

    Kt cu g truyn thng cua ta co cac c im: - Hnh thc kt cu chu lc la khung khng gian. cng doc nha ln, vt liu g

    ch chu nen va un, khng chu keo (thch hp vi tnh nng chu lc tt cua g). - Dung sc nng cua nha chu lc x ngang (ct chn khng su)

    - Lin kt: Chu yu la lin kt mng, lin kt cht, chc chn, d thao lp. - Vt liu g c bao v tt nh sn son thp vang, ngm nc, ngm bun, mai

    ua xa ct ht nc ma. - Kch thc: c thng nht hoa tng a phng, c ghi trn cac thc tm

    (rui mc) cua mi nha. - Kin truc: Chi tit trang tr kt hp kheo leo vi b phn chu lc tao nn hnh

    thc nhe nhang, thanh thoat nhng vn chc chn vng vang.

    c im s dung kt cu g cua ta hin nay: - G dung qua t trong cac cng trnh ln. - Hnh thc kt cu ngheo nan. Nguyn nhn: - G nc ta tuy phong phu nhng phc tap, cha c coi trong nghin cu. - Vic bao quan, khai thac, s dung, tai tao g cha hp ly. Hng phat trin: - Khai thac va s dung g hp ly hn Vt liu chnh nng thn va th trn - Cng nghip hoa san xut, ch tao, x ly kt cu g thanh nhiu dang: g dan

    (fane), van san...

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    CHNG I: VT LIU G XY DNG 1. RNG VA G VIT NAM

    1.1 Ngun g:

    Nc ta do iu kin nhit i nn rng phat trin manh va la ngun cung cp g. ( Min Bc: Ty Bc, Vit Bc, Khu Bn; Min Nam:Ty nguyn, Min ng Nam B...)

    G cua ta co c im: - Phong phu, co nhiu loai g qu: inh, lim, trai, lat hoa, mun (Vit Bc); t thit

    (Ngh An); Hu mc, Giang hng (Quang Bnh); king king, trc, mun, cam lai (Nam Trung B)

    - Cht lng xu, h tap. - Tr lng, nng sut khai thac g thp khng u nhu cu san xut.

    1.2 Phn loai g:

    Trong hang ngan loai g cua rng nc ta, s c s dung vao khoang 400 loai.

    1. Theo tp quan: - G qu: Mau sc va vn ep, hng thm, khng b mi, mot, muc ( gu, trc, mun, lat hoa, trai, trm hng...)

    - Thit mc: Nng, cng, tnh cht c hoc cao ( inh, lim, sn, tau, king king...). - Hng sc: Tt, mau hng, nu, o, nng va (m, vang tm, gii, re, si, xoan...

    - G tap: Xu, mau trng, nhe, mm d b su muc ( gao, sung, c...)

    2. Theo quy nh Nha nc

    a.Phn nhom theo TCVN 1072-71; 1077-71 ( v phn nhom g, quy cach, phm cht g)

    - Theo ch tiu ng sut: 6 nhom.

    ng sut (kG/cm2) Nhom

    Nen doc Un keo Keo doc Ct doc

    Vai loai g thng dung

    I 630 1300 1395 125 Xoay, kin kin, lim, sn...

    II 525 - 629 1080 - 1299 1165-1394 105 - 124 Gie, xoan, gii, inh vang...

    III 440 - 524 900 - 1079 970 - 1164 85 - 104 M, qu, bi li, hng may...

    IV 365 - 439 750 - 899 810 - 969 70 - 84 Gie trng, xoan ao...

    V 305 - 364 625 - 749 675 - 809 60 - 69 Xoan mc, trm, thng vang, sng trng...

    VI 304 624 674 59 Sung, gon, nuc nac...

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    - Theo khi lng th tch: 6 nhom. Cho cac loai g cha co s liu v ng sut

    Nhom Khi lng th tch ( T/m3) Vai loai g thng dung

    I 0,86 Gie vang, gie xam, h b, vai, trm o

    II 0,73 - 0,85 Gie cau, xoan ao, su, trm ha, vang ve

    III 0,62 - 0,72 Bang nu, gie ng, hoa mai, ca l

    IV 0,55 - 0,61 Gie xoan, xoai, xoan ta, sng vang

    V 0,50 - 0,54 Trm i,tram hng, mung lung

    VI 0,49 Gao, sung, nu, vng

    b. Phn nhom theo Ngh nh 10-CP: ( Quy nh tam thi v s dung KCG) 8 nhom: - Nhom I: Co mau sc, b mt, mui hng c bit g quy (trc, gu, trai, mun) - Nhom II: Co tnh cht c hoc cao ( inh, lim, sn , tau, king king, nghin...)

    - Nhom III: Co tnh deo, dai ong tau thuyn ( Cho ch, tch, sang le...) - Nhom IV: Co mau sc va b mt phu hp g cng nghip va mc dn dung ( M,

    vang tm, re, gii...) - Nhom V: Gm cac loai g thuc nhom hng sc ( Gie , thng) - Nhom VI: Gm cac loai g thuc nhom hng sc ( Si, rang rang, bach an...) - Nhom VII, VIII: G tap va xu ( Gao, nuc nac, nong...) khng dung lam KCG.

    c. Phn nhom theo TCXD 44-70 (Quy pham thit k KCG) - Nhom A: Cu kin chu keo chnh - Nhom B: Cu kin chu nen va un - Nhom C: Cu phong, lit, van san, cu kin chu lc phu

    1.3 Quy nh s dung g:

    1. Quy nh s dung g

    Hin vn cha co quy pham thit k KCG ap dung cho TCVN 1072 - 71, TCVN 1076 - 71 ma ch co qui pham thit k KCG ap dung cho ND 10 -CP (4/1960). - Nha lu nm quan trong (nha xng, hi trng...) va cac b phn thng xuyn chu ma nng va tai trong ln (ct cu, dm cu...) c dung g nhom II.

    - Nha ca thng thng dung g nhom V lam kt cu chu lc chnh, con cac kt cu khac ( nha tam, lan trai, coc mong, van khun...) ch c dung g nhom VI, VII.

    Ngh nh 10- CP ra i t nm 1960 n nay khng con phu hp na v tnh hnh cung cp g kho khn nn g nhom 2 th hu nh khng c dung lam nha; kt cu chu lc chnh phai dung nhom VI, kt cu phu dung g nhom VII ( a qua x ly hoa cht ky).

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    2. Quy cach g xy dng:

    a. G xe: Chiu dai g xe t 1 8 m, mi cp 0,25 m - Van: Khi b rng 3 b day: = 10 60 mm; b = 30 320 mm - Hp: Khi b rng < 3 b day: a = 15 320 mm; b = 30 320 mm

    b. G tron: Theo chiu dai L (m) va ng knh D (cm) c chia lam 4 hang:

    Hang ng knh u nho D (cm) Chiu dai L (m)

    I 25 L 2,5

    II 25 1 L < 2,5

    III 10 D < 25 L 2,5

    IV 10 D < 25 1 L < 2,5

    2. S LC V CU TRUC G:

    G Vit Nam hu ht thuc loai cy la rng. G cy la kim ch co khoang10 loai (thng, ngoc am, kim giao, sam,...) G cy la rng co cu truc phc tap hn.

    2.1 Cu truc th ai:

    Ct ngang thn cy bng mt thng ta thy cac lp sau: - Vo cy: 2 lp bao v - Lp g giac (g sng): mau nhat, m, cha cht dinh dng, d muc, mot - Lp g loi (g cht): sm, cng, cha t nc, cng, kho muc,mot. - Tuy: Nm trung tm, mm yu, d muc nat. - Tia loi: Nhng tia nho hng vao tm . - Vong tui: Nhng vong tron ng tm bao quanh tuy (gm 2 lp m (g mun), nhat (g sm), mi vong ng vi 1 nm sinh trng.

    2.2 Cu truc v m: Dung knh hin vi quan sat ta thy: 1. G la rng

    - T bao th g: hnh thoi ni xp nhau theo chiu dai thn cy, chim ti 76% th tch g b phn chnh chu lc cua g. - Mach g: t bao ln hnh ng xp chng ln nhau dn nha.

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    - Tia loi: t bao nm ngang dn nha theo phng ngang. - Nhu t bao: nm quanh mach g gi cht dinh dng.

    2. G la kim:

    Khng co mach g. Ch co quan bao lam nhim vu cua t bao th va mach g va tia loi.

    3. Nhn xet:

    - Cu truc g gm cac th ch xp theo phng doc, co tnh cht xp lp ro rt theo vong tui. G chu lc khoe nht theo phng doc th, kem nht theo phng ngang th (kem vai chuc ln so vi phng doc th) G la vt liu khng ng hng va khng ng nht, tnh cht chu lc khng ging nhau theo cac phng va theo v tr.

    Hnh 1.2 Cu truc g la rng

    - Khi nghin cu tnh cht c hoc cua g phn bit 3 loai mt ct: Mt ct ngang ( thng goc thn cy); Mt ct xuyn tm ( doc theo truc thn cy va xuyn qua tm ); Mt ct tip tuyn ( doc theo truc thn cy va khnh i qua tm ).

    - Cn c theo cac loai mt ct phn bit 3 phng tai trong: Phng doc truc, Phng xuyn tm, Phng tip tuyn

    Hnh 1.3 Cac mt ct g

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    3. TNH CHT C HOC CUA G

    3.1 Anh hng cua thi gian chu lc. Cng lu dai cua g - Cng g phu thuc ro rt vao thi gian tac dung tai trong. Tai trong tac dung trong thi gian ngn th cng cang ln. Khi tai trong t rt nhanh ( t= 0) ta c cng bn tc thi b. Khi tai trong t lu v han ta c cng lu dai ld: La ng sut ln nht ma mu g co th chu c ma khng bao gi b pha hoai.

    + < ld: khng bao gi b g b pha hoai.

    + > ld: sm hay mun g cung b pha hoai.

    Do o xac nh Rtc ta da vao ld:

    ld = ( 0,5 0,6) b = K0 .b (1.1) K0 la h s lu dai

    Rtc = ld = K0. b (1.2)

    3.2. S lam vic cua g khi chu keo

    - Keo doc th mu th tiu chun, ve biu quan h ng sut va bin dang, nhn thy quan h gia - gn nh thng. Pha hoai xay ra t ngt khi bin dang tng i kha nho 0,8% , qui c ly tl = 0,5 b Khi chu keo g lam vic nh vt liu don khng th phn b lai ng sut nn chu anh hng nhiu bi cac yu t khuyt tt va khng ng nht.

    - Cng chu keo khi th nghim cua g kha cao, thng bk = 800 1000 kG/cm2 (g si gai bk =1700kG/cm2). Nhng thc t cng g chu keo giam i nhiu do chu anh hng cac yu t khuyt tt cua g (mt g, th cheo, k n h s K2< 1) hay do kch thc tuyt i cua thanh g ln a n mc khng ng nht cang cao ( k n h s K1 < 1) H s ng nht: K = K1 .K2 Rk = K .R tc (1.3)

    - Cng chu keo ngang th cua g rt nho: ( ) KK RR

    =

    151

    201090 (1.4)

    RK: Cng keo doc th

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    G khng phai la vt liu chu keo tt chu keo phai chon thanh g tt, t khuyt tt.

    3.3 S lam vic cua g khi chu nen: - Nen mu th tiu chun, ve biu nen - , nhn thy: Biu la mt ng cong

    thoai. Phn u thng: tl = 0,5 b. Phn sau cong ro rt, bin dang tng nhanh so vi ng sut. G pha hoai bin dang, tng i khoang 0,6 0,7 % khi chu nen g lam vic nh vt liu deo, ng sut c phn b u trc khi pha hoai nn t chu anh hng bi cac yu t khuyt tt khi chu nen g am bao c cng . Mc du kb = 0,4 bk ( Kb = 300 450 kG/cm2) nhng Rn > RK Nen la hnh thc chu lc phu hp nht vi g.

    3.4 S lam vic cua g khi chu un:

    - Tit din g gm 2 vung keo va nen. Cng chu un cua g vao khoang trung gian gia keo va nen t 700 900 kG/cm2. Anh hng cua khuyt tt cung trung bnh.

    - Khi chu un, g lam vic qua cac giai oan:

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    Khi M con nho: ng sut phap phn b doc chiu cao tit din theo qui lut ng

    thng, biu co dang tam giac: WM

    u = (1.5)

    - Khi M tng ln: ng sut nen tng chm theo ng cong, ng sut keo tng

    nhanh theo ng thng, truc trung hoa lui xung pha di. Khi vung nen xut hin bin dang deo Mu th bt u b pha hoai khi n = nb ( cac th nen b gay). Mu th b pha hoai hoan toan khi k = kb Trong giai oan sau khng th xac nh u theo cng thc bn ma y ch dung cng thc nay theo tnh cht qui c co k anh hng cua hnh dang tit din:

    WmM

    uu = (1.6)

    mu: H s phu thuc hnh dang tit din (theo thc nghim)

    - Mduyn an hi E: c xac nh bi h s goc trong phn ng thng ban u cua biu ng sut - bin dang tc la trong pham vi gii han t l. V phn ng thng ban u cua nen, keo, ung cung xp x nh nhau: G thng Lin X va g nhom V, VI, VII cua ta ly E = 105 kG/cm2

    3.5 S lam vic cua g khi chu ep mt:

    1.Khai nim: Ep mt la s truyn lc t cu kin nay n cu kin khac qua mt

    tip xuc. ng sut ep mt tai mt tip xuc: em

    em FN

    = Rem (1.7)

    N: Lc ep mt Fem: Din tch chu ep mt ( din tch tip xuc)

    - Tuy theo phng tac dung cua lc i vi th g ta co: + Ep mt doc th.

    + Ep mt ngang th. + Ep mt xin th.

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    2. Cng ep mt cua g:

    a. Ep mt doc th: Cng tng ng nh nen doc th

    Rem (00) = Rem = Rn (1.8)

    b. Ep mt ngang th:

    - Ban u cac th ep vao nhau trn biu la ng OA. Sau o cac thanh t bao cua g sm b pha hoai, bin dang tng nhanh (AB). Cui cung cac thanh t bao b pha hoai lai ep vao nhau va g lai co th chu c lc (s cng lai). G pha hoai la do bin dang ln qua gii han cho phep. Cng gii han chu ep mt ngang th c cn c vao ng sut ty l tl (im A khi g bin dang nhiu)

    0)90( .0 KR tlem = (1.9)

    K0 : H s lu dai

    - Ep mt ngang th lai c phn thanh: + Ep mt toan b (H.a): Cng nho nht, thc cht la nen ngang th

    + Ep mt 1 phn chiu dai (H.b): Cng tng theo ty l l/lem khi l/lem 3 + Ep mt 1 phn din tch (H.c): Cng ln nht do co s tham gia cac

    phn g xung quanh. Din tch tip xuc cang nho, cng ep mt cang cao.

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    c. Ep mt xin th:

    - Cng phu thuc goc gia phng cua lc va th g:

    ( )

    ( )

    3

    90

    sin110

    +

    =

    em

    em

    emem

    RR

    RR (1.10)

    Rem: Cng ep mt doc th

    Rem(900): Cng ep mt ngang th

    3.6 S lam vic cua g chu trt:

    1. Khai nim: Khi lc trt nm trong mt phng tip xuc 2 cu kin se gy trt.

    ng sut trt tai mt trt: tr

    tb FT

    = Rtbtr (1.11)

    T: Lc trt Ftr: Din tch mt trt

    - Tuy theo v tr lc ct i vi th g, co 04 trng hp chu trt cua g nh sau: + Ct t th.

    + Trt doc th + Tr t ngang th

    + Trt xin th.

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    2. Cng chu trt:

    Rtbtr =

    el

    Rtr

    tr

    +1 (1.12)

    ltr : Chiu dai mt trt e: Canh tay on cua cp lc trt

    - Rtbtr tuy thuc vao s phn b ng sut nn chu anh hng bi cac yu t:

    , + Loai trt: 1 pha hay 2 pha. Trt 2 pha th cng trung bnh cao hn v ng

    sut u hn.

    ==

    phiaphia2:125,0

    1:25,0

    + Ty s ltr/e, cao nht khi ltr/e = 3 4 (nu qua ln th ng sut phn b khng u. Nu qua nho anh hng ni lc boc ngang th g). + Co lc ep vung goc hay khng: Lc ep lam tng kha nng chu trt (v giam ni lc boc).

    a. Ct t th: Kha nng chng ct t th cua g rt ln nn hu nh khng th xay ra v nu co g se b pha hoai bi ep mt hay un trc.

    b. Trt doc th: Vi mu th tiu chun, ng sut trt doc th vao khoang 70 100 kG/cm2 , ln nht so vi cac trng hp khac.

    c. Trt ngang th: Vi mu th tiu chun, ng sut trt ngang th vao khoang 3550 kG/cm2 ,

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    ------------------------------------------------------------------------------------------------------- Trang 13

    d. Trt xin th: (t xay ra)

    ( )

    3

    90

    sin11

    +

    =

    tr

    tr

    trtr

    RR

    RR (1.13)

    V Rtr90 = 0,5 Rtr nn: Rtr = 3sin1+trR (1.14)

    3.7. Cac nhn t anh hng n tnh cht c hoc cua g:

    1. m: %1002

    21

    GGGW = (1.15)

    G1: Trong lng g m G2: Trong lng g sau khi sy kh

    - m cua g thay i theo mi trng xung quanh va anh hng ro rt n cng cua g. Khi m tng t W = 0 n Wmax = 30% ( m bao hoa th ) th tnh cht c ly cua g giam. m thay i 1% th ch tiu c ly thay i 3 5%. Khi W > Wmax th khng con anh hng n cng cua g.

    - nc ta m thng bng cua g la 17 20% nn m tiu chun c qui nh la 18% va cng cua g c quy i v cng tng ng:

    ( )[ ]18118 += Ww (1.16)

    18: Cng m tiu chun 18% : H s iu chnh m tuy thuc loai g = 0,05: nen doc th; = 0,04: un; = 0,035: nen ngang th; = 0,03: trt; = 0,015: keo doc th

    - Khi tnh toan cac kt cu lam vic trong iu kin chu nhiu ma gio th ta ly W% ln hn theo qui pham ng thi E phai nhn vi h s iu kin lam vic:

    + Vi kt cu c che ma nhng v tr khng thoang th ly W = 20% + Vi kt cu khng c che ma nng th ly W = 25%

    2. Nhit : - Khi nhit tng du W nao th cng cua g giam, mun an hi giam nhiu va vong tng. Mt khac, nhit tng, g gian n gy ni ng sut cuc b ln, nu co mt co th ct t th. Kt cu chu nhit > 500C khng dung vt liu g.

    - Khi tnh toan quy i v cng nhit tiu chun c chon la 200C.

    ( )2020 += tT [MN/m2] (1.17)

    : h s iu chnh nhit tuy thuc vao trang thai ng sut = 3,5: nen doc; = 4,5: un; = 4,0: keo doc; = 0,4: trt doc

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    ------------------------------------------------------------------------------------------------------- Trang 14

    3. Khi lng ring: - Noi chung khi cang ln th cng cang cao va cang kho mi, mot, muc, chay.

    4. Cac bnh tt:

    - Mt cy: Ch gc cua canh m t thn ra, cac th b ln veo, mt tnh cht lin tuc (cac th khng trung phng cua lc tac dung) gy nn hin tng tp trung ng sut lam giam kha nng chu lc, gy kho khn trong ch tao. c bit anh hng n cu kin chu keo hay cu kin chu un co mt nm trong vung keo.

    G loai A: Khng cho phep co mt G loai B: Khng cho phep qua 1 mt trn 1m dai

    - Th nghing: Khng nm trung phng truc doc th g, lam giam cng cua g rt nhiu, nht la i vi cac ng sut tac dung doc thanh.

    - Khe nt (thng do co ngot): Lam mt tnh nguyn ven nn kha nng chu lc cua g giam; t anh hng n cng nen doc th; chu yu anh hng n cng nen ngang th va trt; Vt nt vung goc ng sut phap la nguy him nht. Tao khe ng hi nc lam g m, gy muc bn trong anh hng cht lng g.

    - Mi: Mi n g rt nhanh, kho phat hin. - Muc: Do nm, g b bin mau, cu truc b pha hoai, mm, xp, vun nat R giam. - Mot: Do su uc, mt g co l 3mm lam R giam va gy bn. Tc pha hoai

    chm hn mi.

    3.8 Vn bao quan g: - Vt liu g t nhin noi chung khng co kha nng t bao v chng lai s pha hoai

    cua con trung, nm va chong h hai. V vy tng tui tho cng trnh chung ta cn bao quan g. Ngh nh 10CP quy nh moi loai g t nhom VI tr xung phai c x ly trc khi s dung. Ni dung bao quan bao gm vic x ly bng hoa cht cung nh dung cac bin phap ky thut khac.

    1. Phong mi: Pha hoai nhanh, kho phat hin. Bin phap phong mi: Ngn khng cho mi thm nhp vao g, tm thuc vao chn ct chn trong t. Phat hin va dit ca t mi bng hoa cht. Khng mi ly lan t khu vc nay sang khu vc khac.

    2. Phong mot: Su uc g, ao hang, gy bn va giam kha nng chu lc cua g. Bin phap phong tr: Loai tr iu kin sinh trng: Ngm nc cho bt g tri i, sn kn mt g.

    3. Phong ha: Thng gp khi kt cu lam vic trong vung nc mn, nc l. Bin phap phong tr: Thiu g nh ky lam g chay sem thanh lp than mong bn ngoai; dung g cng ( thit mc), deo ( tch); g co nha ( bach an); nguyn lp vo cy; boc kt cu bng kim loai, ng sanh , aming; Dung hoa cht Creozot, CuSO4

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 15

    CHNG II: TNH TOAN CU KIN C BAN

    1 CAC PHNG PHAP TNH TOAN KCG 1.1 Phng phap tnh theo ng sut cho phep:

    max [ ]= kgh (2.1)

    max: ng sut ln nht trong cu kin do tai trong tiu chun sinh ra . [ ]: ng sut cho php cua vt liu.

    gh : Cng gii han cua vt liu. k: H s an toan xet n anh hng tai trong tac dung lu dai, khuyt tt va cac yu t khac.

    - Phng phap nay ch dung 1 h s an toan xet n moi yu t khac, bo qua tnh deo cua vt liu, cha k n iu kin lam vic thc t cua kt cu.

    1.2 Phng phap tnh theo trang thai gii han:

    1.Khai nim: Trang thai gii han (TTGH ) la trang thai luc kt cu bt u khng th tip tuc s dung c na.

    a. Trang thai gii han I (V cng va n nh):

    - iu kin: N S. (2.2)

    N: Ni lc gy ra bi tai trong tnh toan trong cu kin: iciniici nnNPN .... = ici NP . : Ni lc do tai trong tiu chun PIc gy ra trong iu kin bt li nht..

    ni, ni, nci: H s vt tai; h s an toan; h s t hp.

    S: Kha nng chu lc, la ni lc gii han ma cu kin co th chu c, phu thuc vao cac c trng hnh hoc cua tit din va cac c trng c hoc cua vt liu: S = . R. A

    : H s iu kin lam vic. R: Cng tnh toan cua g R=k.Rtc Rtc: Cng tiu chun cua g

    k: H s ng nht; k=k1.k2 A: c trng hnh hoc cua tit din ( F,J,W,S...).

    b. Trang thai gii han II ( V bin dang):

    - iu kin: [ ] (2.3)

    : Bin dang do cac tai trong tiu chun gy ra trong trng hp bt li nht:

    iicinci nP ...=

    i: Bin dang gy bi tai trong n v.

    []: Bin dang cho phep, c qui nh trong tiu chun thit k KCG TCXD 44-70.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 16

    - Phng phap nay dung cac h s ring bit (h s vt tai, h s ng cht, h s iu kin lam vic) cu th va co cn c khoa hoc xet mi trang thai nguy him cua kt cu. V vy, phan anh y u tnh hnh lam vic thc t cua kt cu, tn dung c kha nng chu lc, tit kim vt liu. Do o, phng phap tnh toan theo trang thai gii han ang c ap dung ngay cang rng rai.

    2 CU KIN CHU KEO UNG TM 2.1 Khai nim: Cu kin chu keo ung tm khi lc keo nm doc theo truc cu kin va cac ch

    giam yu (nu co) i xng qua truc cu kin.

    2.2 Cng thc tnh: kkth

    RmFN

    = (2.4)

    Fth= Fng- Fgy: Din tch tit din thu hep cua tit din. Fgy : Tng din tch giam yu trn cac tit din trong khoang dai 20cm hay moi giam yu trong pham vi 20cm k trn 1 tit din tranh pha hoai trn ng gay khuc

    Fgy< 0,5Fng: Giam yu i xng Fgy< 0,4Fng: Giam yu khng i xng

    mk: H s iu kin lam vic k n anh hng cua s tp trung ng sut do giam yu lam giam cng chu keo cua g: mk= 0,8: khi co giam yu tit din. mk= 1: khi khng co giam yu tit din.

    Rk: Cng chu keo doc th cua g - Ngoai ra, qui pham con qui nh: []: (2.5)

    []= 150: cu kin chnh chu keo. []= 200: cu kin ging lin kt.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 17

    3. CU KIN CHU NEN UNG TM

    3.1 Khai nim: Cu kin chu nen ung tm khi lc keo nm doc theo truc cu kin va cac ch giam

    yu (nu co) i xng qua truc cu kin. Thng gp ct, thanh chng...

    3.2 Cng thc tnh toan:

    1. iu kin cng :

    nnth

    RmFN

    = (2.6)

    Fth: Din tch tit din thu hep, tnh nh cu kin chu keo.

    mn= 1: Do g co tnh deo khi chu nen nn khng cn xet anh hng cua ng sut tp trung tit din giam yu.

    2. iu kin n nh:

    nntt

    RmFN

    =

    (2.7)

    - Ftt: Din tch tnh toan tit din.

    + Giam yu gia va i xng: Ftt= Fng: Khi Fgy 25% Fng

    Ftt= 4/3Fth: Khi Fgy > 25% Fng

    + Khi giam yu bin va i xng: Ftt=Fth + Khi ch giam yu bin va khng i xng th phai tnh theo nen lch tm

    - : H s un doc: = nb

    th

    (2.8)

    + bn: Gii han bn khi nen doc th + th: ng sut ti han.

    nbngo

    nb

    th

    FlEJ

    12min

    2

    == nb

    E

    2

    2

    =

    t rmin =ngF

    J min : Ban knh quan tnh nho nht cua tit din (2.9)

    minrlo= : manh tit din (2.10)

    lo= .l: Chiu dai tnh toan cua thanh nen

    Trong giai oan an hi: Khi th= 22

    E tl

    tl

    E

    75; kt cu g,

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 18

    ta co: ghn

    E

    = 312 nn: 23100

    = khi > 75 (2.11)

    Ngoai giai oan an hi: Cng thc thc nghim cua .A Cscp:

    = 1- 0,8(/100)2 khi 75 (2.12) Cac tr s co khac so vi lo theo ly thuyt v thc t khng th ngam cht c u g, ch ngam se

    b nen ma bin dang i

    3. iu kin manh:

    [] (2.13) []: Ly theo qui pham:

    + Cng trnh nha ca: [] = 120 cho kt cu chu nen chnh. [] = 150 cho kt cu phu. [] = 200 cho kt cu ging. + Cng trnh cu: []= 100 cho kt cu chu nen chnh. []= 150 cho kt cu ging.

    3.3. Bai toan thc hanh chon tit din cn thit F:

    Chon trc hnh dang tit din (ch nht, tron) va manh (>75 hay 75: nntt

    RmFN

    Ftt nn R

    NRN

    3100

    2

    = (2.14)

    a. Tit din ch nht:

    k = h/b; F = bh = kb2; rmin= FJ / =

    12/b ; Fkl

    bl

    rl ooo

    2

    2

    2

    2

    22 1212 ===

    Thay vao (2.14) Fn

    o

    RkNl

    16 (2.15)

    b. Tit din tron: F= 4

    2d ; J= 64

    4d i2= 416

    2 FdFJ

    == Fl

    il oo

    2

    2

    22 4 ==

    Thay vao (2.14) Fn

    o

    RNl

    75,15 (2.16)

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 19

    2. Cu kin chu lc ngn va khoe: Gia thit 75:

    N = RnF= [1- 0,8(/100)2]RnF= [F- 0,000082F]Rn.

    Hay: F = nR

    N + 0,000082F. (3.13)

    a. Tit din ch nht: Thay vao (3.13) ta c: F =

    nRN + 0,001k 2ol . (3.14)

    b. Tit din tron: Thay vao (3.13) ta c: F =

    nRN + 0,001 2ol . (3.15)

    4. CU KIN CHU UN: 4.1. Khai nim:

    - Tuy theo phng cua tai trong, cu kin chu un c chia ra thanh 02 loai: +Un phng: Tai trong nm trong mt phng cha mt truc quan tnh chnh

    cua tit din. +Un xin: Tai trong khng nm trong mt phng cha truc quan tnh chnh

    nao. - Cac kt cu chu un ph bin: van san, dm san, dm mai, xa g, dm cu ...

    - Khi tnh toan ta gia thit: + G lam vic trong giai oan an hi.

    + ng sut phap phn b u trn chiu cao tit din theo ng thng. + Mun an hi khu vc chu nen va chu keo bng nhau.

    4.2. Tnh toan cu kin chu un phng:

    1. iu kin cng :

    uu RmWM

    = (3.16)

    M: Mmen un tnh toan. Wth: Mmen chng un cua tit din thu hep.

    M va Wth ly trn 1 tit din ni co Mmax hay giam yu ln nht mu: H s iu kin lam vic, phu thuc hnh dang va kch thc cua tit din:

    mu= 1,2: Tit din tron khng co khe, ranh mu= 1,15: Tit din co b 15cm va h/b 3,5. mu= 1,0: Tit din co b 15cm. Ru: Cng chu un tnh toan cua g.

    - Ngoai ra, cn kim tra ng sut tip trong cac trng hp sau: + Dm ngn: l/h 5 ( l: chiu dai dm, h: chiu cao dm).

    + Dm g tit din ch I. + Dm co lc tp trung gn gi.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 20

    trtrng

    ng RmbJSQ

    = max (3.17)

    Sng, Jng: Mmen tnh va mmen quan tnh cua tit din nguyn. b: B rng tit din mt trt. mtr: H s iu kin lam vic. Rtr: Cng trt doc th cua g khi un.

    2. iu kin bin dang:

    lf

    lf (3.18)

    f: vong ln nht do tai trong tiu chun gy ra (bo qua cac giam yu cuc b).

    f =EJ

    lMk tc

    2.. 2 ;

    k=0,208: Dm n, tai phn b u. k=0,167: Dm n gian tai tp trung gia nhp

    l: Nhp cua cu kin, [f/l]: vong tng i cho phep theo quy pham

    [f/l]=1/250: Van san; [f/l]=1/200: San mai, xa g, v keo; [f/l]=1/150: Cu phong, van mai;

    4.3. Tnh toan cu kin chu un xin: - Phn tai trong tac dung thanh cac thanh phn theo phng cac truc chnh x, y:

    + Theo phng x: qx= qcos Mx

    + Theo phng y: qy= qsin My

    1. iu kin cng : - Kim tra ng sut ln nht theo:

    uy

    y

    x

    x RWM

    WM

    += (3.19)

    uy

    x

    x

    y

    x

    x RWW

    MM

    WM

    += 1 (3.20)

    + Tit din ch nht b.h; lx= ly= l:

    tgMM

    kbh

    WW

    x

    y

    y

    x === ; .

    Thay vao (3.20), ta c: Wx u

    x

    RM (1+ ktg) (3.21)

    cu kin lam vic hp ly:

    x= y y

    y

    x

    x

    WM

    WM

    = y

    x

    y

    x

    MM

    WW

    = bh = k=

    tg1 = cotg k= cotg.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 21

    2. iu kin bin dang: f= 22 yx ff + [f] (3.22)

    fx, fy: vong theo phng x va phng y do tai trong tiu chun gy ra.

    Dm n gian tai phn b u: fx,=y

    y

    EJlq 4

    .384

    5 fy =x

    y

    EJlq 4

    .384

    5

    cu kin lam vic hp ly:

    fx= fy yx JJ sincos

    = ghbbh

    JJ

    y

    x cot1212

    3

    3

    == gkbh cot==

    5. CU KIN CHU NEN- UN.

    5.1 Khai nim: La cu kin va chu lc nen doc N, va chu mmen un M, co th do:

    + Lc nen tac dung lch tm. + Tai trong ngang.

    + Cu kin b cong. + Cu kin co ch khuyt khng i xng va chu lc nen doc truc.

    5.2 Tnh toan cu kin chu nen- un: - Xet s tnh toan cua cu kin chu cac thanh phn ni lc:

    + Lc nen doc truc N + Mmen un M do tai trong ngang q + Mmen un phu N.f ( Do N sinh ra khi cu kin b vong )

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 22

    - ng sut ln nht th ngoai cung:

    thth WNfM

    FN +

    += (3.23)

    M: Mmen un do tai trong q gy ra. f: vong ln nht do M va N cung tac dung gy ra.

    Chng minh c thanh chu nen un c tnh theo:

    nu

    n

    thth

    RRR

    WM

    FN

    +=

    (3.24)

    : H s xet n hin tng tng mmen do anh hng cua lc doc N: =1-

    ngnngee FRN

    FN

    NN

    ..1

    .1

    == (3.25)

    TTGH, ng sut th bin at Rn; ch cn quy i thanh phn chu un u

    n

    th RR

    WM

    - Khi > 75: = 1- thN

    N = 1-nng RF

    N3100

    2 (3.26)

    = 1 =0 thanh rt cng, khng cn xet bin dang thanh Thanh chu un thun tuy: = u

    thth

    RWM

    FN

    +

    = 1 Thanh chu nen ung tm : = ntt

    RFN

    .

    - Khi 75: + Nu u < 10%n: Bo qua mmen un va tnh nh cu kin chu nen ung tm theo iu kin n nh. + Nu u < 10%n: Dung (3.26)

    - Khi thit k, phai gia thit trc kch thc tit din, ri tnh ng sut va so sanh vi Rn. Nu cha ung, chon lai tit din va tnh lai ng sut cho ti khi at yu cu. Co th dung nhng cng thc sau:

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------

    Trang 23

    - Nu e= NM > 25cm: W=

    nRM85,0

    (3.27)

    - Nu 1< e= NM < 25cm: W=

    nRN [3,3+ 0,35(l-1)2+

    NM ] (3.28)

    -. Nu e= NM < 1cm: tnh nh thanh chu nen ung tm.

    W, N, M, Rn, l ln lt co n v la cm3, daN, daNm, daN/cm3, m. - Cu kin chu nen un cn c kim tra v n nh khi un ngoai mt phng un

    ( theo phng y-y) nh cu kin chu nen ung tm.

    - Khi tnh lc ct ngang Q va lc trt T, phai xet n mmen un phu do lc nen doc sinh ra v Q va T la cac ham s cua mmen un:

    Q= Qo/ ; T= To/= JSQ0

    Qo, To la lc ct va lc trt ch do tai trong ngang sinh ra. 6. CU KIN CHU KEO- UN.

    6.1 Khai nim: La cu kin va chu lc keo doc N, va chu mmen un M. y, thin v an toan, ta khng xet n mmen phu Nf v no lam giam mmen un do tai trong.

    6.2 Tnh toan cu kin chu keo - un:

    - Kim tra tai tit din co Mmax hay giam yu ln nht:

    ku

    k

    thth

    RRR

    WM

    FN

    += (3.29)

    M: Mmen do tai trong ngang hoc lc tac dung lch tm gy ra, khng xet n vong thanh.

    - Mmen un sinh ra do tac dung lch tm cua lc keo se lam cho ng sut tit din giam yu tng ln rt nhiu. Do o, khi thit k cu kin chu keo lch tm, cn hng cho lc keo vao trong tm tit din a thu hep.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 24

    CHNG III: LIN KT KT CU G

    1. AI CNG V LIN KT

    1.1 Khai nim: - Lin kt la b phn quan trong cua kt cu g co nhng tac dung:Tng chiu dai

    cu kin; M rng tit din; Ni cac cu kin thanh nhng kt cu khac phc tap hn. - Cac loai lin kt: 1. Lin kt mng: Thng dung thanh chu nen (v keo, u tru coc cu,..) 2. Lin kt chm: Dung tng tit din thanh 3. Lin kt cht: Dung ni thanh (hai canh cua v keo) 4. Lin kt dan: y la loai lin kt tin tin, co nhiu trin vong, phu hp vi

    phng hng cng nghip hoa xy dng noi chung va cng nghip ch bin g noi ring. Dung tng tit din thanh (tng b day tit din van ).

    - Ba loai lin kt u co kha nng chu lc thp hn, c goi la lin kt mm. Trong tnh toan phai k n s giam kha nng chu lc o.

    - Lin kt dan thuc loai lin kt cng va khng co giam yu tit din.

    1.2 Cac yu cu c ban i vi lin kt: lin kt lam vic chc chn, cn thoa man cac yu cu: - Cht: Cac mt truyn lc gia cac cu kin phai kht, khng co khe h truyn lc tt va han ch bin dang ban u. Lin kt inh, cht, mng d am bao nht.

    - Deo, dai: Bin dang khi pha hoai ln. Co s phn b lai ng sut trong lin kt va tranh pha hoai t ngt nguy him. Lin kt cht, t u, lin kt kim loai d ap ng nht

    - Phn tan: V g thng co khuyt tt (mt, nt...) nn cn phn tan lin kt han ch anh hng khuyt tt va giam yu i vi lin kt. Dung nhiu lin kt nho tt hn v tranh c lin kt ln ngu nhin trung vao ch khuyt tt.

    - Lin kt mt v tr phai cung cng chu lc ng u ( cung loai, ging nhau) - Tit din giam yu cua cu kin la nho nht. - D ch tao am bao chnh xac, kht, cht; d kim tra, sa cha.

    1.3 Nguyn tc tnh toan lin kt - Cac hnh thc lin kt kt cu g chu yu la chu ep mt ng thi chu trt:

    1. iu kin chu ep mt:

    Nem T = Rem,. Fem ,emem

    em RFN

    (3.1)

    2. iu kin chu trt:

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 25

    Ntr T = Rtbtr,. Ftr ,trtbtr

    tr RFN

    (3.2)

    2. LIN KT MNG

    2.1 c im: - Truyn lc nen trc tip t thanh nay sang thanh khac ma khng qua vt trung gian

    nh tm m, chm, cht...Lin kt mng lam vic chu ep mt va chu trt, thng dung trong mi ni chu nen. - B tr thm cac lin kt phu h tr: Bulng, vong ai, inh a ... t theo cu tao. - u im:

    + Lin kt lu i nht, co nhiu kiu, nhiu loai. + Khng dung kim loai. + Lin kt l ro, d kim tra, d sa cha. + Ch tao khng cn may moc, phu hp hin trng.

    - Nhc : + Tit din b giam yu nhiu, d pha hoai don khi chu trt. + Thu cng, cn th kheo, oi hoi chnh xac, kho ap dung c gii hoa.

    2.2 Mng mt rng: 1. Cu tao:

    Hnh 3.1 Lin kt mng mt rng

    - Truc thanh nen thng goc va i qua trung tm tit din ep mt ab. ( ng sut tai o phn b u hn va thanh canh trn chu nen ung tm; do o, mt tip xuc bc khng lam vic, khng cn bao nhn mt).

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 26

    - Xac nh ung im hi tu cua cac lc. Tai gi dan v keo tam giac: Cn cu tao sao cho cac lc A,Nn, NK ng qui. Phan lc gi ta A. Lc nen thanh canh trn Nn. Lc keo Nk canh di co phng i qua trong tm cua tit din giam yu do ranh gy ra ( phn b ng sut keo tng i u tai tit din giam yu, tranh nguy him cho thanh chu keo. Khi o, phn tit din nguyn th co b lch tm mt t nhng co th bo qua)

    - Chiu su ranh hr: rhcm2 h/3: Mt u dan. rhcm2 h/4 : Mt trung gian. ( cu kin khng b giam yu nhiu qua va mt trt khng

    gn qua loi cy, d gy nguy him khi chu lc).

    - Chiu dai mt trt bd: ltr 10 hr ( phong anh hng cua hin tng xin th n s pha hoai tach do trt gy ra) ltr 1,5 hr ( tranh hin tng tach boc ( ltr 3e)); thng ltr = (1,5 3)h hoc (3 4 )e.

    - B tr bulng an toan theo cu tao b 12mm hay tnh toan: ( phong co s dch chuyn gia cac thanh lin kt hoc hin tng pha hoai lin kt mng khi chu tai,...) Nb = N0 . tg; = 900 - - Theo thc nghim = 310 35 0 ( : goc ma sat)

    2. Tnh toan:

    - iu kin ep mt( tit din ab):

    ,cos.

    emem

    n

    em

    em RF

    NFN

    == (3.3) (mem = 1)

    em

    nr Rb

    Nh

    .cos.

    (3.4)

    3

    90

    sin110

    +

    =

    em

    em

    emem

    RR

    RR ; rem hbF .=

    - iu kin trt ( tit din bd): trtbtr

    trtr RF

    N= (3.5)

    eN

    bR

    Nl

    trtr

    trtr .

    .

    (3.6)

    Ntr = Nk = Nncos;

    el

    RR

    tr

    trtr

    tb

    +=

    1; Ftr = b ltr

    e: lch tm cua lc trt. e = 0,5 h: Khi ranh mng t mt pha..e = 0,25 h: Khi ranh mng t hai pha va chu lc i xng..

    - Kim tra thanh chu keo: kr

    k

    th

    kk Rhhb

    NFN

    8,0)(

    == (3.7) (mK = 0,8)

    2.3 Mng hai rng:

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    - S lam vic cua lin kt mng hai rng cung ging nh lin kt mng 1 rng , nhng do lc nen Nn ln hoc goc nghing cua thanh keo ln cn din tch ep mt ln nn phai dung lin kt mng hai rng

    1. Cu tao: - V nguyn tc, tng t nh lin kt mng mt rng chu y thm cac c im sau:

    - Cac truc thanh cung phai hi tu ung nh trng hp mt rng: lc keo cung i qua trong tm tit din giam yu.

    - nh cua rng th hai nn nm trn ng truc cua thanh chu nen ( ng sut phn b nhiu hn trn cac din tch ep mt). - Cac chiu dai mt trt 'trl , ''trl phai thoa:

    rtr

    rtr

    hlhhlh

    ''10''5,1'10'5,1

    - su cac ranh 'rh , ''rh phai thoa: 'rh 2cm: tranh hin tng tach th do trt gy ra.

    ''rh 'rh + 2cm: hai mt trt t anh hng ln nhau. ''rh h/3: tranh trng hp thanh keo b giam yu nhiu.

    - Mi rng c t mt bulng an toan ( phong hin tng pha hoai gion cua lin kt) - Chu y ch tao phai chnh xac hn.

    2. Tnh toan : a. Chu ep mt ( pha hoai deo ) ( tit din ab) - Din tch ep mt c ly bng tng din tch ep mt. Luc u ng sut khng u,

    sai bin hnh ln phn loai tnh chung 2 rng. - Lc ep mt tac dung ln tng rng ty l din tch ep mt:

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 28

    em

    n

    emem

    emem

    em

    em

    em

    em

    FN

    FFNN

    FN

    FN

    =++

    == ''''''

    ''

    ''

    '

    '

    ( )cos'''''' bhhFFF rrememem

    +=+= (3.8)

    - Kim tra: emem

    n

    em

    emem RF

    NFN

    == (3.9)

    b. Chu trt ( pha hoai don ) ( tit din bd) - Tnh trt cho tng mng ring re. Lc trt mi rng t l vi din tch ep mt.

    em

    emtrtr F

    FNN''

    '' = : lc trt tnh toan i vi rng th nht.

    ''trN = trN = nN cos: lc trt toan b cung la lc trt vi rng th hai (trt sau).

    trtbtr

    trtr RmF

    N '''

    ' = ; trtr blF '' = (3.10)

    trtbtr

    trtr RmF

    N''

    '''' = ; trtr lbF ''.'' = (3.11)

    Chiu dai mt trt:

    'trl

    eN

    bR

    N

    trtr

    tr

    ''

    8,0 (3.12)

    ''trl

    eN

    bR

    N

    trtr

    tr

    15,1

    (3.13)

    H s iu kin lam vic khi tnh 'trl la 0,8. H s iu kin lam vic khi tnh'trl la 1,15

    ( k n s lam vic nng n hn cua rng th nht do cu tao khng chnh xac)

    c. Kim tra thanh chu keo tit din giam yu:

    kr

    k

    th

    kk Rhhb

    NFN

    8,0)( ''

    == (3.14)

    Lin kt mng u dan, cn cu tao g tap va g m: G tap c lin kt vi thanh ngang: B rng bng b rng cua thanh khoet ranh; B day: hr. G m nm di g tap va co khc khp day hr vi g tap.

    2.4 Mng g tron:

    1. Cu tao:

    - Khac vi g hp, moi ch, cac mt tip xuc vi nhau u ct vat tao phng

    - Cac lc co th ng quy vao truc cua cac thanh v thanh di c vat ca mt trn va mt di nn trong tm cua tit din giam yu cung gn trung trn truc thanh.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    - Trong lin kt mng u dan, phai cu tao g tap va g gi m di mng.

    - G tap co b rng bng b rng thanh khoet ranh va co b day hr ( s inh lin kt g tap vi thanh ngang c tnh vi lc trt bng thanh phn nm ngang cua lc tnh bulng an toan ).

    - G m di g tap , g gi m phai co khc khp vi g tap su t nht la 2 cm .

    2. Tnh toan:

    - Din tch ep mt cua lin kt: Fem = cosvinphnF ; ( 3.15)

    Fvinphn = 0,71b.hr; (3.16) b = 2 )( rr hdh

    - Din tch mt trt: Ftr = b.ltr (3.17)

    2.5 Mt s lin kt mng khac: - Khi cn lin kt hai thanh chu nen hoc khi lin kt mt thanh chu nen va mt thanh chu keo thng qua gi m bng g, co th dung mng ty u n gian: + Din tch ty u c kim tra theo iu kin ep mt. + Gi m co tac dung nh mt vt trung gian truyn ni lc t thanh nay sang thanh khac. Do o, ban thn gi cung phai u cng khng b bin dang khi lam nhim vu truyn lc.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    3. LlN KT CHM

    3.1 ai cng v lin kt chm : 1. Cac loai chm: - Lin kt chm dung tng tit din cu kin. Hnh thc: Chm g ch nht, chm

    thep, dang tron hoc hnh hp. - Tuy tng trng hp, ta co th dung chm doc, chm ngang, chm nghing.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    Hnh 3.8 Cac loai chm g

    a.Chm doc: Th chm cung phng vi th thanh g, do o chm b ep mt va trt doc theo th g:

    b. Chm ngang: Th chm vung goc vi th cua thanh g; c lam theo dang nm ong t 2 pha co th ep rt cht vao 2 thanh g ( vat canh cheo i=1/61/10), co sc cng ln so vi cac loai chm khac nhng chu lc kem v phai chu ep mt va trt ngang th.

    c. Chm nghing: Th chm tao vi th cua thanh g mt goc tng i nho: Trong ban thn chm khng xay ra trt; phn phn t nm gia cac chm co lc nen, chm ch chu ep mt nghing th do o kha nng chng trt tt hn. Chm nghing lam vic theo mt phng nn phu hp khi lc trt gia cac phn t khng i du.

    d. Chm cach: Chm doc va chm nghing co th t theo kiu chm cach. Hai thanh g co khe h tng cng tit din va thng thoang. Luc nay, phai gia cng bng bulng ngn can s xoay cua chm. ng knh bulng xit 12mm.

    2. iu kin cu tao: - B su ranh uc hr cua 1 phn t trong lin kt:

    + 2cm hr h/5: g hp. + 3cm hr d/4: g tron. h,d: chiu cao tit din thanh g hp va ng knh thanh g tron.

    - Chiu dai chm: lch 5hr ( chm khoi trt ) - Khoang cach gia cac chm: S lch ( g trong pham vi gia cac chm khng b trt ) - Cac mt tip xuc cua chm ch tao phng, khi lp phai kht cht khng gy ra

    pha hoai gion do ng sut cuc b. - Bulng xit c tnh theo lc y ngang cua chm. BL 12 mm

    3.2 Tnh toan lin kt chm: 1. S lam vic cua lin kt chm : - Chm va g c ban: Lam vic theo cac iu kin chu ep mt va chu trt. - Bulng xit: Chu keo.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    Hnh 3.9 Tnh toan lin kt chm

    2. Kha nng chu lc cua lin kt chm:

    a. Kha nng chu lc cua chm:

    a1. Theo kha nng chu ep mt: Bo qua v g chm thng tt hn g c ban

    a2. Theo kha nng chu trt cua thn chm: Ttr.ch= TBchtrR ,. Ftr.chmtr.ch (3.18) Ftr.ch: Din tch mt trt cua chm: Ftr.ch= blch.

    el

    RR

    ch

    chtrTBchtr

    +=

    1

    ,.,.

    = 0,125: do chu trt hai pha. e= hr: Chm sat. e= hr+ So: Chm cach.

    mtr.ch: H s iu kin lam vic Ch co mt chm: mtr.ch= 1. Co nhiu chm: mtr.ch= 0,9 chm ngang; mtr.ch= 0,8 chm doc.

    b. Kha nng chu lc cua g c ban:

    b1. Theo kha nng chu ep mt u chm:

    Tem= Rem,Fem (3.19)

    Fem: din tch ep mt cua u chm: Fem= bhr. b2. Theo kha nng chu trt cua phn cu kin nm gia cac chm:

    Ttr.CK= TBtrR .Ftr.CK.mtr.CK. (3.20)

    Ftr.CK: Din tch mt trt cua phn cu kin nm gia hai chm ln cn: Ftr.CK= bS.

    '1

    ..

    eS

    RR CKtrTBCKtr

    +=

    = 0,25: do chu trt mt pha. e= hr/2. mtr.CK: H s iu kin lam vic mtr.CK= 0,8 chm ngang

    mtr.CK= 0,7 chm doc.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 33

    c. Kha nng chu lc cua 1 chm trong lin kt:

    T= min(Ttr,ch; Tem,ch; Ttr,CK) (3.21)

    3. Tnh bulng xit: - Di tac dung mmen T.e, chm xoay tao ra phan lc Qch. Qch.lch= T.hr Qch

    =T.hr/lch lam tach cac th g ra , chng lai lc tach ta dung bulng xit.

    Te= Qchlch Qch= Te/lch. (3.22)

    T: Kha nng chu lc cua 1 chm. e: Khoang cach gia 2 lc trt. e= hr ( chm khng cach); e = hr +S0 ( chm cach)

    T Qch tnh bulng xit chu keo, chng lai vic tach cac phn t do Qch.

    4. LlN KT CHT 4.1 ai cng v lin kt cht

    1. Khai nim: - Cht la nhng loai thanh tron hoc tm nho dung ni dai cac thanh g hoc lam

    tng tit din cua cac thanh ghep, chng lai lc trt xay ra gia cac phn t ghep khi chu ngoai lc tac dung.

    - Kha nng chu lc cua lin kt tt v dai , deo , phn tan. - Ch tao n gian; Lin kt l ro d kim tra. - Chu chn ng kem ( cn phai co bulng xen ke ). - D co bin dang ban u ln do ch tao khng chnh xac.

    2. Phn loai: - Thng co hai loai cht:

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 34

    + Cht tru: Co th bng thep tron (bulng, inh, vt,...) hoc bng g, tre cht deo. Cac loai cht nay co ng knh >12mm.

    + Cht ban: Thng lam bng cac loai g tt, deo.

    3. S lam vic cua cht:

    - Khi lam vic, cht chu un, bin dang va cac phn t g b ep mt. V vy kha nng chu lc cua lin kt cht co th xut phat t iu kin chu un cua ban thn cht ( thng th hin qua kha nng chng ct ) hoc t iu kin chu ep mt cua phn t g. Ngoai ra, nu cht lam bng g hoc tre th phai xet thm s pha hoai cua cht do ep mt.

    - Hnh thc lin kt co th i xng hay khng i xng va tuy s lng cac phn t c lin kt ta phn bit lin kt cht co mt hai hay nhiu mt ct

    Vic tng ng knh cua cht qua ln cng khi un cua cht ln th lin kt co th pha hoai don do hin tng trt hoc tach mt phng gia cac l cht dung cht cng qua cha chc a tt .

    4.2 Lin kt cht tru:

    1. S lam vic cua cht tru: - nghin cu s lam vic cua cht, coi cht nh dm trn nn an hi chu tai

    trong do phan lc t cac phn t g khi cht bin dang gy ra. Bin i cac phn biu tam giac thanh nhng lc tp trung T1,T2 t tai trong tm biu . T o ta c biu M va Q. S pha hoai thng xay ra sau khi hnh thanh khp deo tai v tr Mmax.

    2. Kha nng chu lc cua lin kt:

    a.Theo iu kin ep mt phn t bin:

    aemT = ka a.d (3.23)

    b. Theo iu kin ep mt phn t gia:

    cemT = kc c.d (3.24)

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 35

    c. Theo iu kin chu un cua cht:

    Tu= K1d2+ K2a2 K3d2 (3.25)

    a, c: B day cua phn t bin va phn t gia, cm. Khi hai phn t co b day khac nhau th a, c ln lt la b day phn t co b day be va phn t co b day ln. d: ng knh cua cht, cm. ka, kc, k1, k2, k3: Tra bang.

    Kha nng chu lc (N) cua mt mt ct cht.

    S chu lc cua lin kt.

    iu kin tnh toan. inh Cht thep Cht g

    Lin kt i xng. Ep mt cua phn t bin aemT Ep mt cua phn t gia cemT

    80ad 50cd

    80ad 50cd

    50ad 30cd

    Lin kt khng i xng.

    Ep mt cua phn t bin aemT Ep mt cua phn t gia cemT

    80ad 35cd

    80ad 35cd

    50ad 20cd

    Lin kt i xng va khng i xng.

    Un thn cht Tu. 250d2+ a2 400d2.

    180d2+ 2a2 250d2.

    45d2+ 2a2 65d2.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 36

    - Khi lc tac dung hp mt goc vi phng th g cua lin kt, cac tr s tnh theo cac cng thc trn phai nhn vi h s iu chnh k khi tnh theo ep mt va vi k khi tnh theo un. (k: tra bang)

    i vi cht thep co ng knh (cm) Goc 1,2 1,6 2 2,4

    i vi cht g

    30 60 90

    0,95 0,75 0,70

    0,9 0,7 0,6

    0,90 0,65 0,55

    0,9 0,6 0,5

    1,0 0,8 0,7

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    - Kha nng chu lc T cua mt mt ct cht la tr nho nht cua 3 tr s: T = min (Tema,Temc, Tu) (3.26)

    3.Tnh s cht trong lin kt:

    - S lng mt ct cn thit nc cua lin kt: nc= TN (3.27)

    - S lng cht cn thit cua lin kt: nch= nnc =

    nTN (3.28)

    N: lc tac dung vao lin kt. n: s lng mt ct tnh toan trn mt cht.

    4.B tr cht tru : - Sau khi bit s lng cht tru nch, tin hanh b tr cht theo iu kin cu tao

    am bao kha nng chng tach, trt doc th va kha nng ep mt cac l cht, cung nh chu y n s giam yu tit din do cac l cht gy ra.

    - Co th b tr cht theo hai cach: thng hang hoc sole. Kiu vung , c ,hoc thng hang .

    5. B tr inh: - Khoang cach S1 gia cac inh theo chiu doc th phu thuc ng knh inh , b

    day cua phn t lin kt va phai phong hin tng tach hoc nt doc khi ong inh - Cac cach b tr inh :

    + B tr thng hang; + B tr kiu c; + B tr kiu xin ngang.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    4.3 LIn kt cht ban: 1. Cu tao:

    - Cht ban thng lam cac loai g tt ,deo , a c x ly ky ,co tac dung lam tng tdin theo chiu cao , chng trt tt ,tnh s lng cht ban phai da vao lc ct Q

    - ng dung: Nhng thanh ghep cht ban co th ghep t 2 hoc 3 phn t (thng phn t co tit din hnh vung); va thng c dung dm (cu kin t hp chu un), thanh canh trn cua dan vom tam giac (cu kin chu nen un).

    2. Tnh toan: a.Theo iu kin ep mt cua cht ban:

    Tb,em= 140lbbb. (3.29) b.Theo iu kin un cua cht ban:

    Tb,u = 630bbb. (3.30) lb, bb, b: ln lt la chiu dai, b rng va b day cht ban, tnh theo cm.

    c. Kha nng chu lc T(N) cua mt cht ban : La gia tr nho nht trong 2 tr s trn: T = min ( Tb,em; Tb,u) (N) (3.31)

    - Chon kch thc cht ban sao cho u kha nng chu lc va hai kha nng trn chnh lch nhau khng qua 10%: l= 4,5b S lng cht.

    3. B tr cht ban: - Khoang cach S gia hai truc cht ban: S 2lb= 9b.Do vic ch tao cht ban co th khng chnh xac, nn chiu su ranh t cht hr phai ly theo: hr= l.b/2+ 0,1cm.

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 39

    5. LlN KT CHU KEO Lin kt chu keo bao gm cac loai : inh va vt chu lc nh , inh a ,ai , ban

    thep, bulng xit, thanh cng,...

    5.1. inh va vt: - Chng trt nh cht. - Chu lc nh do ma sat gia inh

    va g ( trong nhng trng hp khoan trc khi ong inh hoc cu kin chu tai trong ng th khng k n kha nng chu nho nht - Kha nng chu nh la do co lc ma sat gia inh va g.

    - Kha nng chu lc tnh toan cua inh chu nh: T= Rnhdl1 (3.32)

    Rnh: cng tnh toan cua inh khi tnh nh. Rnh= 30 N/cm2: g sy kh t nhin. Rnh= 10 N/cm2: g ti. d: ng knh inh. Nu d 0,6cm, ly d= 0,5cm tnh toan.(Khng nn dung inh co d> 0,6cm). l1: chiu dai tnh toan cua phn inh b ngam; l1 10d; l1 2a (a4d: b day van)

    - inh chu lc nh c b tr nh inh chu lc trt. - Vt: Nn vn vao nhng l khoan sn ng knh nho hn ng knh vt 12mm. - Kha nng chu lc cua vt ngang th g: T= Rnhdl1 (3.33)

    Rnh= 100N/cm2. d: ng knh phn vt khng co ren. l1: dai phn vt co rng.

    5.2. Bulng xit va thanh cng: - Bulng xit va thanh cng thng dung treo, chu lc x trong cac lin kt

    chm, dung lam neo, cac b phn chu keo cua dan, thanh cng cua vom... Bulng co 1 u ren , thanh cng co 2 u ren

    - Cng thc kim tra: kkth

    RmFN

    = (3.34)

    Rk: Cng tnh toan chu keo. mk= 1: Tit din khng b giam yu; mk= 0,8: Tit din b giam yu

    - Longen: Dung tranh hin tng ep mt cho g ,kch thc Longen ly theo

    iu kin ep mt : 90,2 emem RaN

    = a90,emR

    N (3.35)

    a: Canh cua long en. Rem,90: Cng tnh toan ep mt cua g di long en.

    5.3. inh a: - ng knh t 1218mm, c t theo cu tao nhng mt co lin kt mng.

    Thng c dung nhng kt cu bng g hp hoc g tron, khng dung g van.

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    6. LIN KT DAN.

    6.1 c im : - Lin kt dan la loai lin kt tin tin , phu hp tnh cht cng nghip hoa xy dng

    - Lin kt dan c dung rng rai tao thanh g dan nh g dan mong t lang (Fane) mi lp day 1mm , g dan c day t 34 cm. Hnh thc tit din dung lin kt dan kha phong phu: ch I, ch nht, ch nht rng,hnh hp...

    - Khi ch bin g, ta co th loai tr cac khuyt tt, ngm tm g va sp xp hp ly cac lp van theo cht lng tng ng vi yu cu chu lc nn nng cao c tnh cht, cng cua g cung nh cua cu kin lin kt dan.

    - c im : +Dang kt cu va hnh thc tit din ln, phong phu. +Tit din khng b giam yu , phng ep. +Tn dung c g xu ,ngn. +Cng xng hoa cao +Phu thuc keo dan, ch tao phc tap, gia thanh cao.

    - Tnh toan: Lin kt dan loai lin kt cng va khng co tit din giam yu. Tnh toan nh cu kin tit din nguyn va b sung thm phn kim tra trt gia cac lp dan

    6.2 Keo dan : - Keo dan la dang vt cht th deo co th chuyn sang th cng va co th lin kt

    cac phn t em dan. Keo dan bao gm nha va cht ong rn + Nha : phnon phoocmanhit ,rzoocxi phoocmanhit + Cht ong rn : ru , dung dch axit oxalic - Cac hnh thc dan : - Yu cu ky thut dan: Thc hin dan g trong nha may thoa man cac yu cu : + Ch tao mi ni chnh xac. + Th keo trc. + Ep sau khi dan vi ap lc 35 kg/cm2 i vi thanh thng va 7 10 kg/cm2 i vi

    thanh cong + Nhit va m thoa man yu cu dan ( m trong b nh cua g dung dan la

    18 20% tranh hin tng g hut nc keo)

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    CHNG V: CU KIN T HP

    1. KHAI NIM CHUNG V CU KIN T HP 1.1 Khai nim cu kin t hp (CKTH) - Cu kin t hp la cu kin do nhng thanh g nguyn ghep lai vi nhau (bng lin

    kt chm , cht , keo dan ..) co tit din ln, khc phuc kch thc thin nhin han ch. - c dung rng rai trong xy dng: Cu kin chu un (dm ), chu nen (cac thanh

    dan ), chu nen-un (ct chu nen lch tm , vom ,cac thanh canh dan chu tai cuc b ).

    1.2. S lam vic: 1. Cu kin t hp chu un:

    - Khao sat dm t hp t hai thanh g hp co cung chiu dai, cung tit din ngang va cung chu tai trong nh nhau:

    - Dm lin kt cng (lin kt dan):Lam vic nh dm tit din nguyn, chiu cao gp i. - Dm khng lin kt:Lam vic nh 2 dm c lp, co s trt tng i gia 2 dm. - Dm lin kt mm (lin kt cht, chm,...): Lam vic trung gian gia hai loai trn.

    - Nhn xet: + f = fc< fm< fo. + max = maxc< maxm< maxo. + J= Jc> Jm> Jo. + W= Wc> Wm> Wo.

    c, m, o la cac ch s biu th tnh cht cac dm lin kt cng, lin kt mm va khng lin kt. Do o, khi tnh cu kin t hp lin kt mm phai nhn thm h s iu chnh: + Jm= (fc/fm)Jc= kjJc= kjJ. (4.1) + Wm= (maxc/ maxm)Wc= kWWc= kWW. (4.2) kj, kw (

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

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    2. Cu kin t hp chu nen va nen un: - Khi chu nen hay nen un, cu kin t hp lin kt mm cung co kha nng lam vic trung gian gia cu kin khng lin kt va cu kin nguyn (cu kin lin kt cng). Va khi tnh toan, ta cung dung cac h s ki va kw i sang cac cu kin nguyn. - manh m cua cu kin t hp c suy ra t manh c cua cu kin nguyn:

    m= t= cim

    i

    o

    m

    o

    kF

    Jk

    l

    FJl

    1== (4.3)

    - Nhn xet : + Cu kin t hp lin kt dan lam vic nh cu kin nguyn la CKTH lin kt cng + Cu kin t hp lin kt chm hay cht lam vic yu hn v lin kt co bin dang va

    goi la CKTH lin kt mm + Khi tnh cu kin t hp lin kt mm th tnh nh cu kin nguyn nhng phai

    nhn thm vi cac h s iu chnh ( K n tnh mm cua lin kt ) - Trng hp thanh t hp lin kt mm chu nen va nen un ta cung dung cac h s Kj ,Kw i ra tdin cu kin nguyn . manh cung i ra manh tng ng t 2. TNH TOAN CU KIN T HP CHU UN.

    2.1. Theo cng :

    uuWm

    RmWk

    MWM

    == (4.4)

    kw : H s iu chnh phu thuc loai lin kt , s lp ghep va chiu dai nhp tra bang 2.1

    2.2. Theo cng:

    lf

    lf (4.5)

    Khi tnh f ly Jm= kjJ vi kj c tra bang.

    2.3. Tnh s vt lin kt: - S lng vt lin kt trn mi mach ghep phu thuc vao lc trt trn mach ghep khi dm b un. Lc trt o trn mi n v chiu dai cua mach ghep la:

    T1= ng

    ng

    JQS

    (4.6)

    Q: Lc ct ngang tit din dm cn xet. Sng, Jng:Mmen tnh va mmen quan tnh cua phn tit din nguyn i vi truc trung hoa

    - Tng s lc trt trn mi dm:

    Tl/2= dxJQSl

    ng

    ng

    2/

    0

    (4.7)

    Dm n gian, tit din khng i, chu tai trong phn b u hoc cac tai trong i xng khac:

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 43

    Tl/2= ng

    ngl

    ng

    ngl

    ng

    ng

    JSM

    MJS

    dxQJS max2/

    0

    2/

    0

    == (4.8)

    Goi [T] la kha nng chu lc cua mt vt lin kt. Ta co:

    - B tr sao cho cac vt lin kt chu lc u nhau va do o khoang cach gia chung la khoang cach trong tm phn din tch bng nhau cua biu lc trt.

    - S vt lin kt trn mi mach ghep cua na dm la:

    n ][2/

    TTl (4.9)

    Tuy nhin n gian cho vic cu tao, ta tm cach b tr sao cho cac vt lin kt cach u nhau. Nu ly s vt lin kt n tnh c (4.9) b tr cach u nhau, cac vt lin kt gi ta se chu tai qua ln. Ta tm cng thc khac (4.9):

    Dm n gian chu tai trong phn b u: biu lc trt la hnh ch nht ADEC co S(ADEC)= S(ABC)= Tl/2. (AB=2AD). Nhng do tnh mm cua lin kt, biu lc trc co dang ng cosin HC vi AH> AD. Do o, cac vt lin kt gi khng b vt tai nhiu th s lng vt lin kt c tnh tng ng vi din tch hnh ch nht AHGC trong o AH bng

    tung ng cosin: Do S(AHGC) / S(AHC)=

    lAH

    lAH

    2 1,5: nn s vt lin kt cn thit la:

    nTJSM

    ng

    ngmax5,1 (4.10)

    Vi b tr nay d ch tao, dung nhiu trong kt cu nha ca. Trng hp dm chu tai trong nng nh dm cu co cach b tr khac.

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    2.4. vng cu tao:

    fo= o

    g

    hnl

    2

    , cm. (4.11)

    l: nhp dm, cm. ho: khoang cach truc hai thanh ngoai cung cua dm t hp, cm. ng: s mach ghep. : x dch tnh toan mach ghep:

    Cac loai cht: = 0,2 cm; Cac loai cac loai chm khng co khe h gia cac thanh ghep: = 0,3 cm. Cac loai cac loai chm co khe h gia cac thanh ghep: = 0,4 cm.

    3 TNH TOAN CU KIN T HP CHU NEN UNG TM CKTH chu nen ung tm thng gm: - Thanh co tit din bo (h.a) - Thanh co nhng ming m ngn (h.b) - Thanh co nhng ming m dai (h.c,d)

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    3.1 Thanh co tit din bo :

    Cu kin gm nhiu thanh dai bng nhau, ghep sat lai va cung tham gia chu lc.

    1. Theo phng x-x: (vung goc vi mach ghep) - Lam vic nh cu kin nguyn.

    - Cng thc kim tra: nttx

    RF

    N=

    (4.12)

    2. Theo phng y-y: (song song vi mach ghep) - S lam vic chu anh hng cua tnh mm cua lin kt.

    - Cng thc kim tra: ntty

    RF

    N=

    (4.13)

    y c xac nh theo manh tnh i t:

    t= ( ) 212 +yy

    ng

    ng

    o

    FJl

    ,1 (4.14)

    manh tnh i cua thanh t hp khng ln hn manh bnh qun cua cac nhanh J1,ng: Tng mmen quan tnh cua tit din nguyn cua cac nhanh /v truc ban thn song song vi

    y-y (truc 1-1). Fng: Din tch tit din nguyn cua thanh t hp.

    y=

    bhbh

    lo12/3

    : manh cua thanh t hp vi truc y-y khng xet n tnh mm cua lin kt.

    1: manh cua ring tng nhanh vi truc ban thn 1-1 (song song vi mach ghep), tnh theo

    chiu dai tnh toan l1: 1=

    bcbc

    l

    12/31 . Khi l1< 7c: ly 1= 0.

    - Y: H s manh tnh i cua thanh t hp co xet n tnh mm cua lin kt:

    co

    gy nl

    bhnk

    21+= (4.15)

    k: h s xet n tnh mm cua lin kt, phu thuc ng knh inh hoc cht. ng: s mach ghep tnh toan trong thanh t hp. nc: s mt ct tnh toan cua cac vt lin kt trong mi mach ghep trn chiu dai 1m

    cua thanh t hp. - Nu co cac mach ghep co s mt ct khng ging nhau th ly tr s bnh qun. - Nu trn mach ghep dung hai loai vt lin kt khac nhau th s mt ct tnh toan

    cua vt lin kt mach ghep c tnh theo: nc= nc+ nck/k.

    (nc; k) va (nc; k) ln lt la s mt ct va h s cho loai vt lin kt th nht va th hai.

    3.2. Thanh co nhng ming m ngn: - Gm 2 hay nhiu nhanh cach nhau bng nhng ming m ngn, ch lam mmen quan tnh toan tit din thanh tng (do a vt liu ra xa TTH) ch khng tham gia chu lc.

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    1. Theo phng x-x: (vung goc vi mach ghep) - Tnh nh thanh nguyn, khng k cac ming m.

    2. Theo phng y-y: (song song vi mach ghep) - Tnh toan tng t nh /v thanh co tit din bo. Trong o:

    - Khi tnh manh tnh i t, mmen quan tnh va din tch tit din tnh y ,khng xet n tit din cac ming m. - Chiu dai tnh toan l1 phai chon sao cho manh cua nhanh nho hn manh cua toan b thanh t hp: 1= l1/i1 yy l1 yyi1 .

    3.2. Thanh co nhng thanh m dai toan khi:

    - Nhng thanh m nay co th t bn trong hoc p bn trong . Nhng thanh m nay ch lam tng cng toan thanh, khng trc tip chu lc nen nhng tham gia chu lc un doc khi thanh ngang n nh.

    1. Theo phng x-x: (vung goc vi mach ghep) - Do tnh mm cua lin kt nn cac ming m khng hoan toan tham gia chu lc.

    - Jx c tnh theo cng thc gn ung sau: Jx= Jct+ 0,5Jo (4.16) Jct va Jo la mmen quan tnh cua tit din cua cac nhanh trc tip chu lc va cua cac ming m.

    - Ban knh quan tnh vi truc x-x: rx= cl

    x

    FJ

    Fcl la din tch tit din cac nhanh trc tip chu lc.

    2. Theo phng y-y: (song song vi mach ghep) - manh tnh i vn tnh nh thanh co tit din bo ngha nhng chu y: Khi tnh

    mmen quan tnh th k ca ming m nhng khi tnh din tch tit din th ch k cac nhanh trc tip chu lc.

    4 TNH TOAN CKTH CHU NEN - UN 4.1 Trong mt phng un: - Tnh nh thanh nguyn chu nen- un:

    nu

    n

    thth

    RRR

    WM

    FN

    +=

    (4.17)

    Xet n tnh mm cua lin kt, ta a h s kw vao mmenchng un - i vi thanh t hp co nhng ming m ngn, khi chiu dai tnh toan cua nhanh

    ln hn 7 ln b day c cua no, ta phai kim tra thm n nh cua nhanh co ng sut ln nht (tc nhanh ngoai cung) theo cng thc:

    nngng

    RWM

    FN

    1 += (4.18)

    1: H s un doc cua ring nhanh ngoai cung. Fng, Wng: Din tch va mmen chng un cua tit din nguyn cua thanh t hp.

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    - S vt lin kt n mach ghep trn na chiu dai tnh toan cua thanh chu nen- un phai chu c lc trt do mmen un cua ngoai lc va do mmen un phu cua lc doc truc sinh ra va c xac nh theo cng thc:

    TJ

    MSn

    ng

    ng

    5,1 (4.19)

    T: kha nng chu lc tnh toan cua mi lin kt .

    - Khi M/Wng 10%N/Fng: tnh nh thanh chu nen ung tm, khng cn xet n mmen un.

    4.2 Ngoai mt phng un: - Tnh nh thanh chu nen ung tm ( bo qua mmen un ).

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    CHNG V: KT CU G CHU LC

    1. AI CNG V KT CU G CHU LC 1.1 Cac s kt cu g chu lc: - Kt cu chu lc bng g la loai kt cu c tao thanh t nhng thanh g c ban

    (van, g hp, g tron) ghep lai vi nhau bng cac loai lin kt. - Theo hnh thc kt cu co : + Kt cu phng: Lam vic trong mt phng cua no.

    + Kt cu khng gian: Lam vic theo phng bt ky.

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    - Theo s tnh, kt cu phng c chia ra: + Dm: Dm van ghep; Dm dan keo; Dm g dan, nhp thng thng 6 12

    m, co th n 15m. + Vom: Kt cu co lc x ngang, 2 khp, 3 khp (loai 1 khp va khng khp

    khng nn dung v kho thc hin ngm cng chn vom).Vom co dang tam giac hoc vong cung, nhp 12 24m.

    + Dan: Kt cu g nhp ln ph bin va la loai kt cu rng co nhiu dang khac nhau. Nhp ln nht ti 24 m.

    Dm, vom, dan ch chu tai trong ng. + Khung: Kt cu gm co keo ln ct, chu moi tai trong ln nha, am bao

    cng ngang cua nha.

    1.2. La chon s kt cu: 1. Yu cu s dung:

    - Gm cac vn : Khng gian nha, cng cn thit cua nha xng, kha nng chu lc cua kt cu, nhit va m cua khng kh, hi hoa hoc n mon kim loai (thng gi, chiu sang) tao iu kin s dung tt. kinh t nhp nha nn chon: L 10 m: dm; L 20m: dan; L > 20m : vom rng hay khung rng.

    2. Yu cu kin truc: - Hnh dang kt cu phai thch hp vi vt liu lp, phu hp vi kin truc, iu kin thng gio chiu sang, kt cu l hoc che kn.

    3. iu kin ch tao va nguyn vt liu: - Nu ch tao trong nha may th nn ap dung cac loai kt cu hin ai, kt cu hn hp thep g, kt cu g dan. - Nu ch tao hin trng th nn chon hnh thc kt cu n gian lam bng g hp, g van vi kt mng, chm, cht thng thng. Nu co thep th co th lam kt cu hn hp thep, g, trong o cac cu kin chu keo lam bng thep.

    chon giai phap kt cu hp ly phai thit k nhiu phng an ri chon phng an thoa man c cac yu cu ma co gia thanh re nht.

    1.3. Xac nh trong lng ban thn cua kt cu Cn phai xac nh trc trong lng ban thn cua kt cu chu lc : - Tnh lc tac dung

    - So sanh trong lng Trong lng ban thn cua kt cu c xac nh s b theo cng thc kinh nghim:

    Kbt= )(.1000

    bt

    bt

    ggplg++

    (6.1)

    p,g: Hoat tai va tnh tai tac dung ln kt cu tnh trn 1m2 din tch nha hay trn 1m dai cua nhp (N/m2, N/m)

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    Trang 50

    gbt: Trong lng ban thn kt cu ( N/m2 hay N/m) l: Nhp kt cu (m) 1000: H s quy c cho kbt co tr s nguyn. Kbt: h s biu th s lng n v vt liu g dung cho kt cu tnh vi mt n v tai trong va trn

    mt n v din tch hay mt n v chiu dai nhp

    1

    .1000

    +=

    lK

    gpg

    bt

    bt (6.2)

    Sau khi thit k, tnh trong lng ban thn thc t cua kt cu, nu gbt sai khac 30% th phai tnh toan lai kt cu.

    2. DM G TIN DIN NGUYN Nhp ti a L = 5 6 m S thng gp: - Dm n gian

    - Dm lin tuc tng kha nng chu lc hoc giam - Dm co on vong

    2.1. Dm n gian:

    1. Cu tao va tnh toan: - Tit din dm: Ch nht, tron

    c chon theo qui cach g. - Kim tra dm: V bn va vong nh cu kin chu un thng thng. - Gi dm: + bn trn gi ta trung gian (ct, dm chnh), hai nhp dm c k sat u vao nhau (h.a) hay chng 2 u vat cheo ln nhau (h.b) va dung cht c nh dm. + Ch u dm gi vao tng gach phai co bin phap bao v cho g khoi b muc. + Khi t dm phu ln dm chnh: giam chiu cao kin truc cua h dm co th ct khac bn di u dm (h.d). tranh ng sut cuc b ln co th lam g b tach ngang th,

    qua thc nghim ngi ta qui nh ch ct khc tuy theo tr s ng sut ct trong bnh hb

    A.

    :

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 51

    hacmkghb

    A

    hacmkghb

    A

    hacmkghb

    A

    5,0/5,2.

    25,0/4.

    1,0/6.

    2

    2

    2

    A: phan lc gi ta H > 18 cm th a 0,3 h

    H = 18 12 cm th a 0,4 h H < 12 cm th a 0,5 h

    + Gn gi ta co lc tp trung ln th khng c ct khc. + tit din khoi thay i t ngt nn ct khc theo ng vat cheo i = 1/4 + Chiu dai mt ta c h

    2. ng dung - San nha, trn treo, mai nha, tng hm mai,...

    2.2. Dm co on

    1. Cu tao va tnh toan: a. Cu tao on :

    - Tit din xp x tit din dm. - on : Lin kt vao u ct va bt bulng vi dm; lam tng kha nng chu lc cua dm, giup lin kt dm vi ct chc chn hn.

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    - Chiu dai ln nht a cua 1/2 on theo ly thuyt a = (0,11 0,18) l : Tuy theo t l tit din dm va on

    a = 0,17 l : Tit din dm = tit din on - Chiu dai thc t a2 cua 1/2 on ( co u din tch ep mt u on) a2 = a + 10 cm

    b. Ni lc tnh toan - Mmen ln nht trong on la khi co tai trong toan b 2 bn nhp:

    Mon = ( ) alpg

    2+ (6.3)

    - Mmen ln nht trong dm xay ra khi ch trn nhp dm ang xet co hoat tai, con 2 nhp 2 bn khng co. Do tai khng i xng, dm b quay i, im tip xuc gia dm va on d v pha co hoat tai lui vao gn gi ta hn (a1 < a), pha bn kia th im tip xuc la u on (a2 = a + 10 cm). Nhp tnh toan cua dm: l1 = l - 2a1

    Mdm = ( )

    282 21

    21 qaQlq (6.4)

    a1 c xac nh theo iu kin cn bng cua on:

    qgaa

    aglaql

    .

    .2

    .2

    21

    21

    =

    = (6.5)

    - nhp bin on cung quay t do vi dm nn khng lam giam nhp tnh toan cua dm. Nhp tnh toan cua dm la: l - a1

    2. ng dung: Dung lam dm cu hay dm chu tai trong ln.

    2.3. Dm lin tuc: Dm lin tuc co mmen nho nn tit din nho nhng lai cu tao phc tap. Co 2 loai: - Dm nhiu nhp tnh nh. - Dm lin tuc ghep i.

    1. Dm tnh nh nhiu nhp - Dm bao gm: Cac nhp mut tha va nhp treo xen ke nhau .

    - Ch ni ni phai bao am quay c (M=0), co th lam kiu ct vat co mt bulng o gia tnh cht khp.

    - Chiu dai x cua mut tha: + Thng chon Mgi = Mnhp, vi tai trong phn u th x = 0,1465 l = 0,15 l va:

    16

    2qlMM nhg == (= 1/2 M dm n gian) (6.6)

    EJqlfma

    4

    .3842

    = (= 40% vong cua dm n gian) (6.7)

    + Chon vong tai cac nhp bng nhau th x = 0,21l

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    ;

    12

    .3841

    2

    4

    max

    qlM

    EJqlf

    g =

    = (6.8)

    24

    2qlM nh =

    -

    - ng dung: Ch dung khi nhp l 3 (v phai dung thanh g dai l thanh g thng 4,5 m ((1,4 1,5)l) va chu tai trong tnh phn b u.

    2. Dm lin tuc ghep i

    Hnh V5 Dm lin tuc ghep i

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    - Dm gm: Hai na la 2 thanh van t ng, ong inh vao nhau trn sut chiu dai dm theo cu tao cach nhau 40 50 cm.

    - u ni mi bn van b tr sole nhau hai pha gi ta va v tr ni khoang co M 0tc la cach gi x = 0,21 l.

    - Dm c tnh toan nh dm lin tuc: + Khi tai trong u va cac nhp bng nhau th:

    Mmen gi th 2: Mg2 = ql2/10 (6.9) Mmen cac gi khac: Mg = ql2/12 (6.10)

    Mg: ni lc dung chon tit din dm ( nhp bn phai m to tit din dm bng cach ghep thm mt tm van th ba) + Khi tai trong u va nhp bin con 0,8l th mmen cac gi u bng nhau Mg = ql2/12 va khng cn gia cng cho nhp bin. - Ch u ni thanh van c ong nh vao nhau chu c lc ct (h.c)

    xM

    Q gid 2= (6.11)

    Goi T la kha nng chu lc cua mt inh th s inh cn thit mi bn u ni:

    Tx

    MTQn goid

    .2== (6.12)

    3. DM T HP Dm t hp la loai dm ngn (di 4 5 m) co tin din do nhiu thanh g ghep lai

    theo phng ngang bng cac loai lin kt nh cht, chm, inh ... Cac lin kt dung trong dm t hp u la lin kt mm, co bin dang nn dm t hp

    oc tnh toan nh cu kin t hp mm a nu chng trc. Dm t hp c dung thay th cho dm nguyn khi tai trong ln oi hoi tit din

    ln vt qua tit din qui cach.

    3.1 Dm cht ban: 1.Cu tao: - Dm gm 2,3 thanh g hp xp chng ln nhau dung cht ban lin kt. - Cht ban b tr cach u nhau sut chiu dai dm, ring khoang 0,2 l gia dm co

    th khng t cht v lc trt nho. - 2 u dm thm 2 bulng xit cht cac thanh g vao nhau.

    - u im: + Khng dung kim loai.

    + Co th ch tao c gii hoa vi thit b n gian. + D ch tao chnh xac, cht che, tao fCT.

    + Cng va khoe (do tnh dai cua cht ban moi cht cung lam vic, khng co lc y nh trong dm t hp chm).

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    2. Tnh toan: a Xac nh tit din:

    - Mmen chng un cn thit cua tit din:

    uw RkMW.

    = (6.13)

    M: Mmen un ln nht do tai trong tnh toan k ca trong lng ban thm dm. tw: H s iu chnh W tra bng

    -Bo qua giam yu do cac ranh cht. Cho trc b rng dm b, tm c b cao:

    h=bW6 (6.14)

    -B cao 1 thanh: h1 = 2h hay

    3h va ly tron theo qui cach.

    -Tnh vong cua dm khi s dung, dung Jm = KJ . Jng (Kj : tra bng) b. Tnh s cht ban:

    - S cht lin kt trn 1/2 nhp cua mi mach:

    TJSM

    nng

    ngma

    .

    .5,1 (6.15)

    + i vi dm gm 2 thanh g hp:

    Tbh

    hbhMn

    ma

    .12

    4.

    2.

    5,1 3 (6.16)

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 56

    ThMn.

    25,2 max (6.17)

    + i vi dm co 3 thanh:

    Th

    Mn.

    2 max (6.18)

    Cht c b tr vi khoang cach nho nht Smin = 9ch .Nu khng u ch b tr cht th phai tng tit din dm va tnh lai.

    c. Tnh vng cu tao: - khi chu tai, truc dm tr thanh thng. Khi ch tao ngi ta un sn dm cho co vng ngc vi vong khi chu tai, vng nay goi la vng cu tao. Thng ly fct = - f va c tnh theo cng thc

    02..hnlf Kct

    = (cm) (6.19)

    l: Nhp dm (cm) NK: S khe; 2 thanh : nk = 1; 3 thanh : nk = 2 h0: Khoang cach gia 2 truc cua cac thanh ngoai cung. : Bin dang trt cua cht ban trong mach, = 92 cm

    =>1

    1,0hlf ct= (cm) (6.20)

    3.2. Dm chm: 1. Cu tao: - Dm gm 2 hay 3 thanh g hp hoc tron xp chng ln nhau roi dung chm hay

    chm cach lin kt lai.

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    Trang 57

    - Cu tao chm, khoang cach chm, bulng xit... nh phn lin kt chm - Ph bin nht la dung chm ch nht, doc hay ngang. Chm ngang biu vat cheo

    ong cht va dm lam vic vng chc hn. Dm chm nghing dung khi chiu tai trong khng i. Dm chm cach dung cho kt cu ngoai tri thng thoang khng ong m. - Dm chm khng lam vng cu tao v rt kho lam nn cho dung khi cng yu cu khng cao hoc cho phep vong nhiu.

    - c im: + Khng ch tao c gii hoa c nhng lai yu cu chnh xac cao nn cn th gioi.

    + Chm khng dai nn d b pha hoai cuc b khi ch tao khng chnh xac.

    Tuy nhin dm chm lai phu hp vi trnh ch tao thu cng nn c dung nhiu chu yu lam dm cu.

    2. Tnh toan: a. Xac nh tit din: - Tnh toan dm chm v cng va vong nh cach tnh cu kin t hp chu un

    va dung cac h s iu chnh KW, KJ

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    Trang 58

    b. Tnh s chm va b tr: 2 cach - Chu y:

    + Giam yu cua ranh khng k n khi tnh toan. + Giam yu cua l bulng phai k n khi tnh v cng nhng co th bo qua khi tnh v vong.

    - Cach 1: + Khi Q qua ln: B tr chm chu lc nh nhau ngha la pha gi t gn nhau hn

    pha gia.

    + S chm trn 1/2 chiu dai dm: chng

    ng

    ch

    l

    TJSM

    TTn

    ..max2/ == (6.21)

    Tl/2 : Tng s lc ct trn 1/2 chiu dai dm

    Sau o chia biu lc ct trn na chiu dai dm ra lam n phn co din tch bng nhau ri t chm vao ung trong tm cua mi phn o.

    V du: Vi biu lc ct hnh tam giac co th dung phng phap biu sau hay dung bang V-1 trang 22.

    - Cach 2: Thng dung hn la b tr chm cach u nhau.

    Tng s chm trn 1/2 nhp dm: ch

    l

    TTn 2/5,1= (6.22)

    4. DM VAN GHEP - Dm van ghep la loai dm t hp do nhiu thanh van ghep lai vi nhau bng inh.

    4.1. c im va pham vi s dung:

    1. c im: - u :

    + Ch tao n gian, khng cn thit b phc tap. + Tn dung g xu lam bung.

    + cao nho so vi dan keo. - Khuyt:

    + Dm cu tao nhiu lp, khng thng thoang nn d b ong m, g chng muc, inh chng r. + Bin dang ln do lin kt inh rt mm.

    2. ng dung: - Lam m mai vt khu ln L = 12m. - Lam dm cu nhp 30 40 m, chiu cao n vai met.

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    Trang 59

    4.2 Cu tao: 1.Hnh dang:

    - Dm co tit din ch I gm bung la 2 lp van mong xp sat nhau cheo theo 2 phng, canh la 2 tm van hay 2 thanh g hp ong p bn ngoai cac van bung

    - Theo yu cu s dung dm co hnh dang ch nht (canh song song), hai mai dc, mt mai dc.

    - am bao cng chiu cao dm gia nhp, lh91

    i vi dang ch nht va

    lh41

    i vi dang hai mai dc.

    2. Canh va bung: - Canh: mi canh ( trn hay di) gm 2 thanh van day 4 6 cm, rng 15 22 cm m

    ly bn ngoai bung. Canh di chu keo cn chon g tt. Cac van canh c ong inh t hai pha vao bung, phn inh ngp vao canh bn kia sau khi tr cac khe h (3 khe x 2mm) va u nhon 1,5d phai ln 4d.

    - Bung: gm 2 lp van day 1 3 cm, rng 15 cm, t nghing vi canh mt goc 300 450 theo hai chiu cheo nhau. Hai lp van bung cung ong inh vao nhau thanh mt tm phng. inh b tr theo hang ng va ngang sao cho mi van c ong t nht bng 2 inh. Chiu dai t do cua van gia 2 inh 30 van.

    3. Sn ng: - t cach nhau 1/10 l va t bn di tai trong tp trung. - Sn day bng van canh, rng bng 1/2 van canh (van canh xe i). - Sn u dm ln hn (bng tit din canh) m ly pha ngoai hai canh chu phan

    lc ta, gia sn va ban bung co lot 2 tm m cung b rng vi sn ng.

    4. u ni: - Khi chiu dai cua canh ln hn g nguyn ta phai ni. V tr ni tuy theo chiu dai

    thanh g, thng gia nhp dm.

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    Trang 60

    - Canh trn: Ni bng cach t sat hai u van vao nhau, bn ngoai co 2 ban p va t bulng theo cu tao.

    - Canh di: Dung hai ban p va mt ban chm vao gia hai van canh. ch co van m, van bung phai ct t bn ngoai van canh va se c lin kt vi van canh qua hai thanh g vung nho, ong inh ngang vao bung va ong inh xung canh.

    5. Dm ln - i vi dm chu tai trong ln, canh lam bng thanh g hp, khi o mi lp van

    bung se ong inh vao thanh g hp (na canh) t trong ra c hai na dm ring re. Sau o hai na dm c ghep vao nhau bng bulng canh va inh bung.

    4.3. Tnh toan: 1. Chon tit din canh: - Lc keo ln nht trong canh di:

    0max h

    MN = (6.23)

    h0 : Khoang cach gia 2 truc canh ch co Nmax M: Mmen un ch co Nmax. + Vi dm canh song song, h0 = h - hc khng i, tit din co Nmax trung vi tit din co Mmax tc gia dm. + Vi dm co mai c, tit din co Nmax cach tit din gi dm pha co chiu cao nho mt oan x0:

    += 1.1

    0

    00

    g

    g

    hltg

    tgh

    x

    (6.24)

    hog: Khoang cach gia hai truc canh gi dm pha co chiu cao nho. l: Nhp dm.

    : Goc nghing cua canh trn. - Tit din canh di:

    KKc Rm

    NF8,0

    max= (6.25)

    0,8: H s k n phn giam yu cau tit din canh do l cht hay nh (ang chng) - Tit din mi van canh : a x hC = Fc : 2 chon theo qui cach - Tit din canh trn ly bng canh di nhng phai kim tra un doc ra ngoai mt

    phng dm ch co Nmax. Chiu dai tnh toan bng khoang cach gia cac dm phu (xa g) t ln canh trn va tnh mt van ring re chu lc nen Nmax/2 (v anh hng t hp cua inh khng ang k).

  • Bai giang Kt cu g Huynh Minh Sn --------------------------------------------------------------------------------------------------------------

    Trang 61

    Nu khoang cach gia hai dm phu 25a (a: b day mt thanh van) th khng cn th n nh cach trn.

    - Ni canh di: Vi s cht:

    =T

    Nn ni (6.26)

    T: Kha nng chu lc cua mt cht 4 mt ct. Nni: Lc keo trong thanh canh di ch ni.

    Sau khi b tr cht, cn kim tra lai tit din thu hep cua canh.

    2. Tnh lin kt gia canh va bung:

    - inh dung chu lc trt gia canh