BTCT 1 - Phan cau kien co ban.pdf

M U 1

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KT CU B TNG CT THEPPHN CU KIN C BAN

M U 2

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KT CU B TNG CT THEPPHN CU KIN C BAN

M U.Chng 1:

Chng 2: TNH NNG C LY CUA VT LIU.

Chng 3: NGUYN LY CU TAO & TNH TOAN BTCT.

Chng 4: CU KIN CHU UN.

Chng 5: SAN PHNG.

Chng 6: CU KIN CHU NEN.

Chng 7: CU KIN CHU KEO.

Chng 8: CU KIN CHU UN XON.

Chng 9: TNH TOAN CU KIN BTCT THEO TTGH TH II.

Chng 10: B TNG CT THEP NG LC TRC.Tai liu: -Kt cu BTCT-phn cu kin c ban, Phan Quang Minh (chu bin).

-Kt cu B tng v BTCT-Tiu chun thit k TCXDVN 356-2005.

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1. BN CHT CA B TNG CT THPM U.

1.1. BN CHT CA B TNG CT THP:

B tng ct thep la vt liu xy dng phc hp do BT va ct thep cung cng tacchu lc:B tng la a nhn tao c ch tao t cac vt liu ri ( Cat, soi,...goi la ct liu) vacht kt dnh (Xi mng hoc cac cht deo).Chu nen tt, chu keo kem.Ct thep: chu keo, nen u tt.Xt th nghim n gian sau:- Un mt dm b tng (khng ct thep):

pha hoai kha sm do vt nt xut hin vung b tng chu keo. Nh vy kha nngchu lc cua BT vung nen cha c tndung ht

- Cung dm tng t nh vy nhngnu t mt lng ct thep thch hpvao vung b tng chu keo:

Keo

Nen

Keo

Nen

Dm BTCT ch b pha hoai khi BT vung nenb ep v hoc ct thep chu keo b t. Mc khac thep chu keo va nen u tt nnco th t thep vao ca vung chu nen.

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Vy thc cht b tng ct thep la mt vt liu xy dng hn hp ma trong o btng va ct thep a lin kt hp ly vi nhau cung lam vic trong mt kt cu.S d b tng va ct thep co th cung lam vic c la do:

- Lc dnh bam gia BT va ct thep: B tng khi ninh kt dnh cht vi ct thepnn ng lc co th truyn t BT sang ct thep va ngc lai, nh o co th khai thac htkha nng chu lc cua ct thep, han ch b rng khe nt...

- Gia b tng va thep khng xay ra phan ng hoa hoc: B tng bao boc baov ct thep khng b han r va ngn nga tac dung co hai cua mi trng i vi thep.

- B tng va thep co h s gian n nhit gn bng nhau (ct= 1,2.10-5; b=10-51,5.10-5). Nn khi nhit thay i trong pham vi thng thng di 1000C thng sut ( ban u ) xay ra trong vt liu khng ang k.

1.2. PHN LOI BTCT: 1.2.1 Phn loi theo phng php ch to : a. B tng ct thp ton khi (BTCT ti ch):Tin hanh ghep van khun, t ct thep va BT ngay tai v tr thit k cua kt cu.

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2. PHN LOI BTCT1.2. PHN LOI BTCT: 1.2.1 Phn loi theo phng php ch to : a. B tng ct thp ton khi (BTCT ti ch):Tin hanh ghep van khun, t ct thep va BT ngay tai v tr thit k cua kt cu.

* u im: - Cac cu kin lin kt toan khi nn kt cu co cng ln, chutai trong ng tt.

- Co th ch tao cac cu kin theo hnh dang tuy y.* Nhc im: - Tn vt liu lam van khun, a giao.

- Thi cng chu anh hng thi tit.

b. B tng ct thp lp ghp (cu kin BTCT ch tao sn):Phn kt cu thanh cac cu kin ring bit co th ch tao sn ri em lp ghep laithanh kt cu tai v tr thit k. PP nay khc phuc phn nao nhc im cua BT toan khi.

* u im: - Co iu kin Cng nghip hoa trong thi cng xy dng.- Tit kim vt liu lam van khun.- Rut ngn thi gian thi cng, am bao cht lng.. ..

* Nhc im: - Cn co cac phng tin vn chuyn, cu lp.- X ly cac mi ni phc tap.- cng cua kt cu khng ln.

M U 6

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P1.. P2.. P3.. P4.. P5..B TNG CT THP TON KHI B TNG CT THP LP GHP

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c. B tng ct thp na lp ghp :Theo PP nay, ngi ta tin hanh lp ghep cac cu kin c ch tao sn cha hoanchnh, sau o t thm ct thep, ghep van khun va BT hoan chnh kt cu.

* u im: - cng cua kt cu ln.- Giam khi lng van khun, co th loai bo ct chng.

* Nhc im: - Cn giai quyt tt lin kt ga BT cu va mi.- T chc thi cng phc tap.

1.2.2. Phn loi theo trng thi ng sut:a. B tng ct thp thng:Khi ch tao cu kin, ct thep trang thai khng co ng sut. Ngoai cac ni ng sut do co ngot va nhit , trong BT va ct thep ch xut hin ng sut khi co tai trong

b. B tng ct thp ng lc trc (BTCT d ng lc) :Khi ch tao cu kin, ct thep ban u c keo cng, lin kt cht vi BT, khi bung ract thep co lai gy nen trong BT.

1.2.3. Phn loi theo ct thp :- B tng co ct mm. (d40mm, thep hnh).

1.2.4. Phn loi theo trng lng th tch:- B tng nng co 1800 kg/ m3 (2500).- B tng nhe co < 1800 kg/ m3.

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3. U NHC IM CU BTCT1,3. U NHC IM CU BTCT:1.3.1 u im:S dung vt liu a phng (cat, soi, a..) tit kim thep. Re tin hn so vi thepkhi kt cu co nhp va va nho, cung chu tai nh nhau.Chu lc tt hn kt cu g va gach a.Chu la tt hn g va thep. B tng bao v cho ct thep khng b nung nong sm.Tui tho cua cng trnh cao, chi ph bao dng t. BT co cng tng theothi gian, chu tac ng cua mi trng tt, ct thep c BT bao boc bao v khng b g.Vic tao dang cho kt cu thc hin d dang. Va BT khi thi cng dang nhaoco th vao cac khun co hnh dang bt ky, ct thep u deo un theo hnh dang cuakt cu.1.3.2 Nhc im :Trong lng ban thn ln nn gy kho khn cho vic xy dng kt cu co nhp lnbng BTCT thng. Khc phuc: Dung BT nhe, BTCT LT B tng ct thep d co khe nt vung keo khi chu lc. Cn phai ngn ngahoc han ch khe nt kt cu trong mi trng xm thc, cac ng ng hay b chacht long.. (Tnh toan han ch khe nt, s dung BTCT LT.. )

(2) (3), kt cu vo mong ,...

Cach m va cach nhit kem hn g va gach a. Co th s dung kt cu co lrng, kt cu nhiu lp, BT xp..

Thi cng phc tap, kho kim tra cht lng. Khc phuc: BTCT lp ghep..Kho gia c va sa cha. Thit k cn phai phu hp yu cu s dung hin tai va dkin phat trin m rng.

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4. PHM VI NG DNG1.4. PHM VI NG DNG CA B TNG CT THP:

Xy dng dn dung, cng nghip: Kt cu chu lc nha 1 tng va nhiu tng [1][2], ng khoi, bun ke, xi l [3], mong may, hanh lang vn chuyn v.v.. Cng trnh cpthoat nc [4] [5]... (Hnh nh), (Hnh nh KC mi)..Xy dng cng trnh giao thng: Cu, ng, ta vet, u tau, cu tau, vo hm...(Hnh nh cng trnh ng), (Hnh nh cng trnh cu), (Hnh nh tunnel)..

Xy dng cng trnh thuy li: Tram bm, mang dn nc, p thuy in,...(Hnh nh cng trnh thy li), (Hnh nh cng trnh thy in, p)..

Xy dng cng trnh truyn thng, thng tin; Cac cng trnh c bit

Xy dng cng trnh quc phong: Cng s kin c, doanh trai,...

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5. S LC LCH S PHT TRIN1.5. S LC LCH S PHT TRIN:Qua trnh phat trin chia thanh 3 giai oan:- Giai oan phat minh va mo mm trong thc tin, b tr ct thep theo cam tnh.

1848: Lambot (Phap) ch tao chic tau bng li st ngoai trat vi thuy [1.5.1],... Va nm 1855 ng c trao bng sang ch cho cac ban ve dm BTCT va ctc gia c bng 4 thanh thep xung quanh.

1850: Monier (chu vn m Phap) co cac th nghim vi cac chu BT cgia c bng li thep. Va ti p theo la cac bng sang ch vi cac ng va b cha c giac, tm san, cu thang..- Giai oan nghin cu l lun va s dung rng rai (sau 1880), nghin cu vcng cua BT va ct thep, lc dnh gia BT va ct thep, giai thch s lam vic chunggia chung.

1886: Koenen (Trng thanh tra XD cua Ph) xuat ban cun sach v phngphap tnh toan bn cua BTCT.

T nm 1890 n 1920 cac ky s thc hanh a dn dn nm c kin thc vc hoc cua BTCT. Cac cun sach, bai bao, tiu chun a th hin cac ly thuyt tnh toan.

- Giai oan phat trin hin tai: XD cac phng phap tnh toan theo ng sut chophep da trn c s cua mn SBVL, tnh theo giai oan pha hoai co xet n tnh bindang deo cua vt liu, tnh theo trang thai gii han. Nghin cu va ch tao thanh cngBTCT LT [5.2].

TNH NNG C LY CUA VT LIU 1

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2.1. B tngTNH NNG C LY CUA VT LIU.

2.1. B tng:- Tnh nng c hoc cua BT la ch cac c trng c hoc nh: cng va bin dang.- Tnh nng vt ly la tnh co ngot, t bin, kha nng chng thm, cach nhit, ... cua BT.

2.1.1. Thanh phn, cu truc va cac loai b tng:2.1.1.1 Vt liu, thanh phn cua b tng:BT la loai a nhn tao c ch tao t cac vt liu ri (cat,a, soi) va cht kt dnh.Vt liu roi c goi la ct liu, gm cac c hat khac nhau, loai be la cat 1-5mm, loai ln la soi, a dm 5-40mm. Cht kt dnh thng la XM trn nc hoc cac cht deo khac.2.1.1.2 Cu truc cua b tng:BT co cu truc khng ng nht v hnh dang, kch thc cac hat ct liu khac nhau, s phn b ct liu va cht kt dnh khng u, co cac l rng.2.1.1.3 Cac loai b tng:Theo cu truc co: BT c, BT co l rng (dung t cat), BT t ong.Theo khi lng ring: BT nng thng co khi lng ring 22002500kG/m3; BT ct liu be 18002200kG/m3; BT nhe 2500kG/m3;Theo thanh phn: BT thng thng, BT ct liu be, BT chen a hc.Theo pham vi s dung: BT lam kt cu chu lc, BT chu nong, BT cach nhit, BT chng xm thc..


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2.1.2. Cng cua b tng2.1.2. Cng cua b tng:Cng la ch tiu c hoc quan trong, la mt c trng c ban cua BT, phan anh kha nng chu lc cua vt liu. Thng cn c vao cng phn bit cac loai b tng.2.1.2.1 Cng chu nen:Chun b mu th:

a

a

a

Ban nenP

Mu

D

h =2D

aa

h = 4a

Mu khi lng tru.

Th nghim trn may nen, tng tai dn khi mu b pha hoai. Goi P la lc phahoai mu.Cng nen cua mu: )12(;

AP =R

A la din tch TD ngang cua mu.

B tng thng co R=5 30MPa. BT co R>40MPa la loai cng cao. Ngi ta a ch tao c loai BT c bit co R80MPa.


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S pha hoai cua mu chu nen:

Kt qua cho thy trng hp 1 mu co cng ln hn. Thp 2: Khng co ma sat

Bi trn

Bin dang ngangkhng u

Thp 1: Co ma sat trn mt tip xuc

Khi b nen ngoai bin dang theo phng lc tac dung, mu con n ngang. Chnh s nngang qua mc lam cho BT b pha v do ng sut keo (kha nng chu keo cua BT kem hn chu nen nhiu ln). Lc ma sat gia ban nen va mu th can tr s n ngang anh hng n cng BT khi nen.

Kch thc mu th: Mu kch thc nho co cng ln hn mu th co kch thcln. Hnh dang mu th: Mu lng tru co cng be hn mu khi vung co cung kchthc ay Rlt= (0.7-0.8)R...


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2.1.2.2 Cng chu keo: R .(t)

bh=b(=15cm)

4h

P

a

aa (10cm)

4a

PP

Trong o: P, M: Lc va mmen un lam pha hoai mu.B tng thng co R(t)= 1040 kG/cm2.2.1.2.3 Quan h gia cng chu keo R(t) va cng chu nen R:

Mu chu keo trung tm:

)22(;AP

)( aR t =Mu chu keo khi un:

)22(;bh

3.5M2)( bR t =

Mu tru tron chu nen che:P

)22(;l.D.

2.P)( cR t =

Cng thc dung quan h ng cong: )32(;)( aRR tt =

Cng thc dung quan h ng thng: )32(;06.06.0)( bRR t +=Trong o t c ly phu thuc vao loai BT va n v cua R. Voi BT nng thng thng van v cua R la MPa t = 0.280.30.

Cng thc dung quan h ng cong theo h s Ct: )32(;.)( cRCR tt =Vi n v cua R la MPa, H s Ct: )42(;130060

150 ++=

RRCt


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2.1.2.4 Cac nhn t anh hng n cng cua BT:* Thanh phn va cach ch tao BT: y la nhn t quyt nh cng BT.- Cht lng va s lng xi mng:

- cng, sach, cp phi cua ct liu:

- T l N/X hp ly.

* Thi gian (tui cua BT):

- Cht lng cua vic trn va BT, m va bao dng BT.

Cng cua b tng tng theo thi gian, luc u tng nhanh sau tng chm dn.Vi cng chu keo s tng cng theo thi gian nhanh hn so vi cng chu nen.

R

Rt

R28

t 28

t

Cng b tng tng theo thi gian c xac nh theo cng thc thc nghim:

Cng thc cua Sec (1926): Rt=R1+(R10- R1).lgt.

;lg7.0lg28lgt

2828 tRRRt =Cng thc cua Nga (1935), (Skramtaep): (vi t = 7-300 ngay)

Cng thc cua Vin nghin cu BT My ACI theo quy lut hyperbn: ;

b.tat

28 += RRt Trong o h s a, b phu thuc loai XM. Thng thng a=4; b=0.85. Voi XM ng cng nhanh a=2.3; b=0.92.


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* Tc gia tai va thi gian tac dung:Khi tc gia tai chm cng at khoang 0.850.9 tr s thng thng va khi gia tai nhanh cng cua mu co th tng 1.151.2 ln. Khi th nghim phai tun theo quy trnh TN vi tc gia tai 0.2MPa/s.

2.1.3. Gia tr trung bnh va gia tr tiu chun cua cng :2.1.3.1 Gia tr trung bnh:Th nghim n mu th cua cung mt loai BT thu c cac gia tr cng cua mu th laR1, R2.. Rn. Gia tr trung bnh cng cua cac mu th ky hiu la Rm, goi tt la cng trung bnh:

)62(;n

Rn

1ii

==

mR

2.1.3.2 lch qun phng, h s bin ng:t i = |Ri - Rm| goi la lch. Vi s lng mu u ln (n 15) tnh lch qun phng: )72(;

1n

2i

= H s bin ng c tnh: )82(; =

mR

2.1.3.3 Gia tr c trng:Gia tr c trng cua cng cua BT (goi tt la cng c trng) c xac nh theo xac sut am bao la 95% va c tnh: ( ) )92(;.1 = SRR mchTrong o S la h s phu thuc xac sut bao am. Vi xac sut bao am 95% th S=1,64.


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2.1.3.4 Gia tr tiu chun:Gia tr tiu chun cua cng cua BT (goi tt la cng tiu chun) c ly bng cng c trng cua mu th Rch nhn vi h s kt cu KC.Cng tiu chun v nen Rbn, v keo Rbtn: )92(;. aRR chKCbn = H s KC xet n s lam vic cua BT trong kt cu co khac vi s lam vic cua mu th, c ly bng 0,7-0,8 tuy thuc vao Rch. .

Gia tr cua Rbn va Rbtn c cho TCXDVN 356:2005 (Bang 12 trang 35)2.1.4. Cp bn va mac cua b tng:La tr s cua cac c trng c ban v cht lng cua BT. Tuy theo tnh cht va nhim vucua kt cu ma quy nh mac hoc cp bn theo cac c trng khac nhau.

2.1.4.1 Mac theo cng chu nen: K hiu M

B tng nng: M100, 150, 200, 250, 300, 350, 400, 500, 600.B tng nhe: M50, 75, 100, 150, 200, 250, 300.

2.1.4.2 Cp bn chu nen: K hiu BTCXDVN 356:2005 (trang 4) quy nh phn bit cht lng BT theo cp bn chu nen:Cp bn chu nn ca b tng: k hiu bng ch B, l gi tr trung bnh thng k ca cng chu nn tc thi, tnh bng n v MPa, vi xc sut m bo khng di 95%, xc nh trn cc mu lp phng kch thc tiu chun (150 mm x 150 mm x 150 mm) c ch to, dng h trong iu kin tiu chun vth nghim nn tui 28 ngy.


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Cp bn chu nn ca b tng: k hiu bng ch B, l gi tr trung bnh thng k ca cng chu nn tc thi, tnh bng n v MPa, vi xc sut m bo khng di 95%, xc nh trn cc mu lp phng kch thc tiu chun (150 mm x 150 mm x 150 mm) c ch to, dng h trong iu kin tiu chun v th nghim nn tui 28 ngy.TCXDVN 356:2005 (Bang 9 trang 30) quy nh:BT nng co cp bn chu nen B3,5; B5; B7,5; B10; B12,5; B15; B20; B25; B30; B35; B40; B45; B50; B55; B60. BT nhe co cp bn chu nen B2,5; B3,5; B5; B7,5; B10; B12,5; B15; B20; B25; B30; B35; B40.Tng quan gia mac M va cp bn B cua cung mt loai BT th hin bng biu thc:Trong o la h s i n v t kG/cm2 sang MPa; co th ly bng 0,1.

la h s chuyn i t cng trung bnh sang cng c trng (vi =0,135 th = (1-S.) = 0,778).

)102(;.. = MB

2.1.4.3 Mac theo cng chu keo: K hiu K.B tng nng: K10, 15, 20, 25, 30, 40.B tng nhe: K10, 15, 20, 25, 30.2.1.4.4 Cp bn chu keo: K hiu Bt.Khi s chu lc cua kt cu c quyt nh chu yu bi kha nng chu keo cua BT, kt cu co yu cu chng nt.TCXDVN 356:2005 (trang 4) quy nh cp bn chu keo:Cp bn chu ko ca b tng: k hiu bng ch Bt, l gi tr trung bnh thng k ca cng chu ko tc thi, tnh bng n v MPa, vi xc sut m bo khng di 95%, xc nh trn cc mu ko tiu chun c ch to, dng h


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Cp bn chu ko ca b tng: k hiu bng ch Bt, l gi tr trung bnh thng k ca cng chu ko tc thi, tnh bng n v MPa, vi xc sut m bo khng di 95%, xc nh trn cc mu ko tiu chun c ch to, dng h trong iu kin tiu chun v th nghim ko tui 28 ngy.BT co cp bn chu keo doc truc Bt0,8; Bt1,2; Bt1,6; Bt2; Bt2,4; Bt2,8; Bt3,2.2.1.4.5 Mac theo cac yu cu khac:Mac theo kha nng chng thm la con s ly bng ap sut ln nht (tnh bng atm) ma mu chu c nc khng thm qua. Cp chng thm cua BT: W2; W4; W6; W8; W10; W12.W cn quy nh cho cac kt cu co yu cu chng thm hoc c cht cua BT nhcac cng trnh thuy li, thuy in...

Mac theo khi lng ring trung bnh D (kha nng cach nhit): - BT nhe D800; D900; D1000; D1100; D1200; D1300; D1400; D1500; D1600; D1700; D1800; D1900; D2000.- BT t ong D500; D600; D700; D800; D900; D1000; D1100; D1200.- BT rng D800; D900; D1000; D1100; D1200; D1300; D1400.


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2.1.5. Bin dang cua b tng2.1.5. Bin dang cua b tng:2.1.5.1 Bin dang do co ngot:

Co ngot la hin tng BT giam th tch khi ninh kt Mc co ngot khi ng cng trong khng kh (3 - 5).10-4 . Khi ng cng trong nc BT n ra =1/5-1/2 mc co, mc tti a (6 - 15).10-5 .Cac nhn t anh hng n bin dang co ngot:- S lng va loai XM: lng XM co ngot , XM co hoat tnh cao co ngot .- T l N/X tng co ngot tng.- Cat nho hat, ct liu rng co ngot tng.- Cht phu gia lam BT ninh kt nhanh co ngot tng.Co ngot la mt hin tng co hai:- Lam thay i hnh dang va kch thc cu kin.- Gy mt mat ng sut trong ct thep ng lc trc. - Gy ra khe nt trn b mt BT, lam thay i cu truc cua BT, giam kha nng chu lc va tui tho cua cng trnh.Cac bin phap khc phuc:- Chon thanh phn ct liu, t l N/X hp ly.- m cht BT, bao dng BT thng xuyn m trong giai oan u.- Cac bin phap cu tao nh b tr khe co dan, t ct thep cu tao nhng ni cn thit chu ng sut do co ngot gy ra, mach ngng khi thi cng hp lyv.v..


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2.1.5.2 Bin dang do tai trong tac dung ngn han:Th nghim nen mu th hnh lng tru vi tc tng tai t t, o va lp c th gia ng sut va bin dang nh hnh ve.

Khi con be th t cong nhng khi thcong nhiu.

2P1

l

b

RltD

Cb1 (1)

O

*bb

plel

0(2)

pl el-im D ng vi luc mu b pha hoai: ng sut at Rlt va bin dang cc ai *b.Bin dang cua BT gm 2 phn: phn khi phuc c la bin dang an hi (1el), phn khng khi phuc la bin dang deo (2pl): b= el+ pl; (2-11)Do vy BT la vt liu an hi-deo. Mun an hi ban u Eb:

Mun bin dang deo cua BT Eb:

)122(;. 0 === tgEEel

bbelbb

)132(;. '' === tgEEb

bbbbb

t goi la h s an hi b

el = )142(;.' = bb EE


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Khi BT chu keo cung co bin dang an hi va bin dang deo: Eb= t.Eb.Bin dang cc han khi keo kha be 0,00015.

;25.0

*b

t

b

tb E

RE

R ==Th nghim cho thy khi BT chu keo sp nt th t 0,5 nnMun chng ct vi h s Posson = 0,2 vi moi loai BT:

b v2

v1v3

b

el plb

Tc gia tai khac nhau th cacng biu din quan h - khacnhau.

bb

b EEG 4,0

)1(2+=

2.1.5.3 Bin dang do tai trong tac dung dai han - T bin:

Hin tng bin dang deo tng theo thi gian goi la hin tng t bin cua BT.Phn bin dang deo tng ln do tai trong tac dung dai han goi la bin dang tbin.

P b Pc

b

O 2b

c 2b

t

c


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* Cac nhn t anh hng n bin dang t bin:

Hin tng bin dang deo tng theo thi gian goi la hin tng t bin cua BT.Phn bin dang deo tng ln do tai trong tac dung dai han goi la bin dang tbin.

- ng sut trong BT ln bin dang t bin ln.- Tui BT luc t tai ln bin dang t bin be.- m mi trng ln bin dang t bin be.- T l N/X ln, cng ct liu be bin dang t bin ln.- Lng X tng bin dang t bin tng.

* Co th biu din t bin qua mt trong hai ch tiu sau:- c trng t bin: = C/ el. (la ai lng khng th nguyn)- Sut t bin: C= C/ b (MPa-1 hoc cm2/kG).

Cac ch tiu , C u tng theo thi gian, va at n gii han n nh la 0, C0.* Tac hai cua hin tng t bin:

- Lam tng vong cua cu kin.- Lam tng un doc cua cu kin chu nen.- M rng khe nt trong BT.- Gy tn hao ng sut trong ct thep ng lc trc.


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Nu tai trong tac dung ln kt cu lp i lp lai nhiu ln (t vao ri d ra nhiu ln) thbin dang deo se c tch luy dn, nu tai trong ln se gy hin tngmoi cho kt cu .

2.1.5.4 Bin dang do tai trong lp lai:

b

b

b

b

bmaxbmin

2.1.5.5 Bin dang nhit:y la loai bin dang th tch khi nhit thay i, xac nh theo h s n vnhit cua BT t. H s t phu thuc vao loai XM, ct liu, m co gia tr khoang (0,7-1,5)x10-5/. Thng thng khi nhit trong khoang t 0-1000 C ly t =1x10-5 tnh toan.


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2.2. Ct thep:2.2.1. Yu cu i vi thep dung trong B tng Ct thep:

2.2. Ct thep

- am bao cng theo thit k.- Phai co tnh deo cn thit.- Phai dnh kt tt va cung chu lc c vi BT trong moi giai oan lam vic cua kt cu.- D gia cng: d un, ct, va han c ...- Tn dung ht kha nng chu lc cua ct thep khi kt cu b pha hoai.- Tit kim thep va tn t sc L.

2.2.2. Cac loai ct thep:Theo thanh phn hoa hoc cua thep: thng ch dung mt s mac thep cac bon thp va thep hp kim thp.Theo phng phap luyn thep: - Ct thep can nong:- Ct thep keo ngui:- Ct thep gia cng nhit:Theo hnh thc ct thep: Thep thanh tit din tron mt ngoai nhn (tron trn), hoc mt ngoai co g (cac g co tac dung tng dnh bam vi BT). Cung coth dung thanh thep hnh, o la ct cng co th chu lc c khi thi cng.


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2.2.3. Cac tnh cht c ban cua ct thep:2.2.3.1 Biu ng sut-bin dang:Biu ng sut-bin dang co phn thng ng vi giai oan an hi, phn cong ng vi giai oan co bin dang deo. `

pl

C

O

*S

Byel A

DThep deo: Biu _ gm mt oan thng xin OA ng vi giai oan lam vic an hi.oan nm ngang c goi la thm chay, thep trang thai chay deo. Luc nay xac nh c gii han chay cua thep y. oan cong CD la giai oan cung c cua ct thep, ng sut va bin dang tip tuc tng cho n khi ct thep b t, vigii han bn B va bin dang cc han *S. Thep rn (gion): Biu _ gm mt oan thng xin OA ng vi giai oan lam vic an hi, oan cong AD la giai oan ct thep co bin dang deo. Khi keo t xac nh c gii han bn B va bin dang cc han *S.

O

B

el

pl *S

A CDy

0,2%2.2.3.2 Bin dang an hi va bin dang deo:Nu keo thep trong giai oan an hi ri giam tai th toan b bin dang c phuc hi.Khi keo thep vt qua gii han an hi (co bin dang deo) ri giam tai th biu khng v theo ng cu va co mt bin dang d la pl.


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2.2.3.3 S cng ngui:o la hin tng tng gii han chay khi gia cng ngui ct thep. Ly ct thep deo em keo ngui cho qua gii han chay ri giam tai se co c ct thep keo ngui. Ct keo ngui nay co gii han chay cao hn ct thep ban u. Sau vai ln keo hoc chut thm chay se bin mt, ct thep tr thanh rn vi cng tng cao va bin dang cc han giam.

2.2.3.4 Cng tiu chun cua ct thep:Gia tr tiu chun v cng cua ct thep c goi tt la cng tiu chun, k hiu Rsn c ly bng cng gii han chay (thc t hoc quy c) vi xac sut bao am khng di 95%.Vi my la gia tr trung bnh cua gii han chay khi th nghim mt s mu thep th: ( ) )152(;.1 = SR mysn2.2.3.5 Mun an hi cua ct thep ES:Mun an hi cua ct thep, k hiu ES c ly bng dc cua oan OA trn biu ng sut bin dang. Gia tr cua ES phu thuc loai thep va khoang (17 - 21)x104 MPa, xem TCXDVN 356:2005 (Bang 28 trang 53)2.2.3.6 deo cua ct thep:

2.2.3.7 Tnh han c:Tnh han c phu thuc vao thanh phn cua thep va cach ch tao. Cac thep can nong bng thep cha t cac bon va thep hp kim thp co tnh han c tt. Khng c phep han i vi cac thep a qua gia cng ngui hoc gia cng nhit.


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2.2.4. Phn loai (nhom) ct thep:2.2.4.1 Phn loai ct thep theo TCVN:Theo TCVN 1651:1985, c cc loi ct thp trn trn CI v ct thp c gn (ct thp vn) CII, CIII, CIV.

2.2.4.2 Phn loai ct thep theo mt s tiu chun khac:Theo TC Nga: - Cn nng: trn trn nhm A-I, c g nhm A-II v AC-II, A-III, A-IV, A-V, A-VI;- Gia cng bng nhit luyn v c nhit luyn: c g nhm AT-IIIC, AT-IV, AT-IVC, AT-IVK, AT-VCK, AT-VI, AT-VIK v AT-VII.Ct thep cua Trung Quc chia thanh cac cp I, II, III, IV va cac loai si keo ngui.Ct thep cua Phap c ghi theo gii han chay nh: FeE230, FeE400, FeE500.2.2.4.3 Tng quan gia mac thep va nhom (loai) thep:Mac thep c nh ra va k hiu chu yu da vao thanh phn hoa hoc va cach luyn, v du CT3, CT5, 182C, 25X2C.. Nhom ct thep c phn chia theo tnh nng c hoc.Hai cach phn chia nay la khac nhau nhng lin quan vi nhau v tnh nng cua thep lado thanh phn quyt nh. Ct thep nhom CI, A-I ch tao t thep cac bon mac CT3; Ct thep nhom CII, A-II ch tao t thep cac bon mac CT5;


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2.3. B tng ct thep2.3. B tng ct thep:2.3.1. Lc dnh gia b tng & ct thep:2.3.1.1 Cac nhn t tao nn lc dnh:- Lc ma sat do co ngot khi ng cng BT ep cht vao ct thep.- S bam do b mt g gh cua ct thep.- Lc dan do keo xi mng co tac dung nh mt lp h dan BT vao ct thep

Mu th nghim xac nh lc dnh:2.3.1.2 Th nghim xac nh lc dnh:

Cng trung bnh cua lc dnh:

P

lnmax C

P

ln

maxC

)162(;..

=l

P

Trong o: P la lc keo (nen) tut ct thep. la ng knh ct thep.l la chiu dai oan ct thep chn vao BT.

Lc dnh cc ai: )172(;.1...max

== lP

Trong o: la h s hoan chnh biu lc dnh. ( < 1)

;.max mRbn =)182(;

.max = m

RbnTr s lc dnh cc ai:Trong o: m la h s phu thuc b mt: thep trn m=56; thep co g m=33,5;

la h s phu thuc trang thai chu lc: chu keo =1; chu nen =1,5;


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)182(;.max = mRbnTr s lc dnh cc ai:

Trong o: m la h s phu thuc b mt: thep trn m=56; thep co g m=33,5; la h s phu thuc trang thai chu lc: chu keo =1; chu nen =1,5;

2.3.1.3 Cac yu t anh hng n lc dnh:Khi BT ct thep thng ng lc dnh ln hn ct thep nm ngang.Ct thep chu nen co lc dnh ln hn ct thep chu keo.Khi thay i chiu dai oan l tr s max khng i nhng tr s trung bnh thay i, khi tng l h s hoan chnh biu giam.Nu co cac bin phap han ch bin dang ngang cua BT lc dnh tng.


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2.3.2. Anh hng cua ct thep n co ngot va t bin cua b tng:2.3.2.1 Anh hng n co ngot:Do s dnh kt gia BT va ct thep ma ct thep cantr bin dang co ngot cua BT: ct thep b nen lai conBT b keo ra, o la ng sut ban u do co ngot trongBTCT.

0

(1)Bin dang cng bc trong BT: 0 - 1 t = (0 - 1).t.Eb.Bin dang cng bc trong ct thep: 1. S = 1.ES.

Nu khng co ct thep, BT t do co co ngot 0;Do ct thep can tr BT co co ngot 1< 0 bngbin dang cua ct thep a=1.

1< (=

(2)

Ab

AS

0

a)

Hp lc trong BT: Nt = t.Ab; trong ct thep: NS = S.AS.

ng sut keo do co ngot ln khi ham lng thep ln;

V la lc ni tai nn chung cn bng nhau: Nt = NS;

Suy ra: ;1.

.0+=

St

SS n

E ;

.11

.. 0

St

btt

n

E

+= ;;

b

S

bt

SSt A

AEEn ==

ng sut keo do co ngot va ng sut keo do tai trong gy ra lam BT b nt sm hn so vi khi khng co anh hng cua co ngot, nhng khi a co khe nt th anh hng cua co ngot giam va n giai oan pha hoai th khng con anh hng n kha nng chu lc cua cu kin. Trong kt cu siu tnh lin kt tha ngn can co ngot cua BT nn xut hin ni lc phu.


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2.3.2.2 Anh hng n t bin:

Ab

AS

NXet cu kin chu lc n gian nh hnh ve:

C

N

Trong BT: ;.

;..b

bbb E

E ==

Trong CT:)192(;..

.. === bSS

b

bSS nEE

E

Vi la h s tng ng ( 8-20).b

SS E

En.=

T iu kin cn bng lc, co:( ) )202(;.... +=+= SSbbSSbb AnAAAN t Ared = Ab + nS.AS goi la din tch cua tit din tng ng (qui i).

1

N

;.;;.. red

SS

redb

redb ANn

AN

AEN === ng sut, bin dang cua cu kin:

Khi chu lc lu dai, BT co bin dang t bin. Ct thep cung anh hng n bin dang tbin cua BT.

Nu khng co ct thep, vi ng sut b bin dang t bin cua BT la C = C.b; Ct thep se can tr bin dang cua BT, va bin dang tng thm se la: 1


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2.3.3. S pha hoai va h hong cua BTCT:2.3.3.1 S pha hoai do chu lc:- Vi thanh chu keo: Sau khi BT b nt, ct thep chu toan b lc keo. Pha hoai khi ngsut trong ct thep at gii han chay.- Vi ct chu nen: Pha hoai khi ng sut nen trong BT at n cng chu nen.- Vi dm chu un: Pha hoai khi ng sut trong ct thep chu keo at gii han chayhoc khi ng sut trong BT vung nen at n cng chu nen.

2.3.3.2 S huy mon cua b tng & cac bin phap bao v:B tng b n mon la do: Tac dung c hoc (ma, dong chay, s ong va tan bng lin tip..),Tac dung sinh hoc (rong ru, ha, vi khun sng, bin..) hoa tan va cun i lam BT trnn xp,Tac dung hoa hoc (cac cht axt, kim..) xm thc b mt hoc thanh phm cua cacphan ng hoa hoc co th tch ln hn th tch cac cht tham gia phan ng, lam nt nekhi BT.


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2.3.3.2 S huy mon cua b tng & cac bin phap bao v:B tng b n mon la do: Tac dung c hoc (ma, dong chay, s ong va tan bng lin tip..),Tac dung sinh hoc (rong ru, ha, vi khun sng, bin..) hoa tan va cun i lam BT trnn xp,Tac dung hoa hoc (cac cht axt, kim..) xm thc b mt hoc thanh phm cua cacphan ng hoa hoc co th tch ln hn th tch cac cht tham gia phan ng, lam nt nekhi BT.Ct thep b huy mon, b g tao ra cac Oxyt hoc mui st co th tch ln hn th tch ban u, lam cho lp BT bao quanh ct thep b v bong.Bin phap bao v: B tng cn co cng cao va c chc b mt cua kt cu.Khi thit k cac cng trnh co mi trng n mon:Khi cn dung cac bin phap c bit: Cn cao sach bui g trn ct thep trc khi s dung. am bao chiu day lp BT bao v.


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NGUYN LY CU TAO & TNH TOAN 1

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NGUYN LY CU TAO & TNH TOAN KT CU BTCT.Thit k kt cu BTCT gm 2 vic chnh: tnh toan va cu tao.Ni dung tnh toan gm:- Xac nh tai trong va tac ng; - Xac nh ni lc do tng loai tai trong va cac t hp cua chung; - Tnh toan tit din xac nh kha nng chu lc cua kt cu hoc ct thep.

Cac yu cu cu tao gm:- Chon vt liu (mac BT va nhom ct thep) phu thuc mi trng s dung, tnhcht chu lc, tnh cht cua tai trong, vai tro cua kt cu..,- Chon kch thc tit din, B tr ct thep.- Lin kt gia cac b phn va chon giai phap bao v chng xm thc.


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3.1. NGUYN L TNH TONNGUYN LY CU TAO & TNH TOAN KT CU BTCT.3.1. NGUYN L TNH TON KT CU B TNG CT THP:3.1.1 Ti trng, tc ng:- Theo tnh cht:

Tai trong thng xuyn (tnh tai):Tai trong tam thi (hoat tai):Tai trong c bit:

- Theo phng, chiu:

Tai trong ng:Tai trong ngang:

- Theo tr s khi tnh theo PP trang thai gii han:

Tr s tiu chun (Tai trong tiu chun):Tai trong tnh toan: TT TT = TT TC.n (3 1)

- Theo thi gian tac dung cua tai trong:Tai trong tac dung dai han.Tai trong tac dung ngn han.


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3.1.2 Ni lc3.1.2 Ni lc:S tnh: S kt cu la c s xac nh s tnh toan kt cu chu lc. Vi kt cu tnh nh:

Vi kt cu siu tnh (dm lin tuc, khung, vo mong..): Tnh theo s an hi hoc theo s deo tnh ni lc va thc hin t hp ni lc cn thanh lp mt s s tnh:

- Mt s tnh vi tnh tai (cho ni lc Sg).- Mt s s tnh vi cac trng hp co th xay ra cua hoat tai (Sij).Ni lc tnh toan la t hp cua Sg va cac Sij: S= Sg + . Sij (3 - 2) la h s t hp, theo TCVN 2737-1995 ly =1 khi ch xet mt hoat tai,


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3.1.3 Tnh tit din BTCT3.1.3 Tnh ton tit din BTCT: 3.1.3.1 Phng php tnh theo ng sut cho php: iu kin tnh toan: []. (3 - 4)

Gia thit tnh toan:[ ] ;

kR=

Trong o: - : ng sut ln nht trong vt liu do tai trong s dung.- []: ng sut cho phep cua vt liu.

c Gia thit TD phng:d Xem BT va CT la vt liu an hi.

- S ng sut cua min BT chu nen la tuyn tnh: (Khng xet BT chu keo) - Quy i tit din gm B tng & Ct thep thanh TD tng ng ch co BT:


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Da vao iu kin bin dang cua Ct thep & BT tai v tr Ct thep o la bng nhau:

;.. btSbtb

SS

b

btbt

S

SS nE

EEE

=====Tc la qui i vi mt din tch ct thep chu keo tng ng thanh ns ln din tch BT hay din tch ct thep AS quy i thanh nS.AS din tch BT.

Xet dm chu un TD ch nht:

Khng xet BT chu keo ( vung keo ch co din tch BT quy i cua ct thep chu keo)

Tit din quy i va s ng sut:

V tr truc trung hoa:b

h

M

bmax

Db

Da AS

ng sut ln nht cua BT chu nen:

ng sut keo trong BT tng ng:

Vy ng sut trong ct thep :

x

a

h0 h

bnSAS

( ) ;xh..An3

b.xJ 20SS3

red +=

( ) 0;xh..An2

b.xS 0SS2

red ==[ ];.max b

redb xJ

M =( );. 0red

bt JxhM =

[ ];. SbtSS n =


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3.1.3 Tnh ton tit din BTCT: 3.1.3.2 Phng php tnh theo ng sut cho php:iu kin tnh toan: []. (3 - 4)

Gia thit tnh toan:[ ] ;

kR=

Trong o: - : ng sut ln nht trong vt liu do tai trong s dung.- []: ng sut cho phep cua vt liu.

c Gia thuyt TD phng:d Xem BT va CT la vt liu an hi.

- Quy i tit din gm B tng & Ct thep thanh TD tng ng ch co BT: - S ng sut cua min BT chu nen la tuyn tnh: (Khng xet BT chu keo)

u im:- Ra i sm nht cho nn giup cho ngi thit k co khai nim tng i ro rt v s lamvic cua kt cu- Kt cu co an toan kha cao.

Nhc im:

- BTCT khng phai la vt liu ng cht, BT co bin dang deo va co nt trong vung keo...- H s nS thay i theo tr s ng sut trn tit din, tuy thuc s hiu thep va BT.- H s an toan k=R/[] cua BT & ct thep khng ging nhau th h s nao la h s an toan cua kt cu.


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3.1.3.2 Phng php tnh theo ni lc ph hoi: Ni dung c ban cua phng phap la: Xac nh ni lc ln nht do tai trong tai TD tnh toan ri so sanh vi kha nng chu lc cua TD o.

iu kin kim tra: Sc Sph /k hay k.Sc Sph. (3 - 5)Trong o:

Sc: Ni lc do tai trong tiu chun gy ra tai TD xet.Sph: Kha nng chu lc cua TD ( Con goi la ni lc pha hoai).k >1: H s an toan cua kt cu. (k = 1.52.5)

Xac nh kha nng chu lc cua TD theo cac gia thit sau:- ng sut trong BT chu nen at Rb va phn b ch nht (u).- ng sut trong ct thep chu keo at gii han chay RS.

AS T = RS.AS

C = Rb.b.x

Rb


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Th du vi cu kin chu un:

Phng trnh cn bng mmen vi truc qua trong tm Db:

b

x

a

h0 h

AS

MphDb

RS.AS

b=Rb

( ) ;05,0..0 0 == xhARMM SSphDbCo c: Mph = RS.AS.(h0 - 0.5x).

Chiu cao vung BT chu nen xac nh theo phng trnh hnh chiu cac lc lnphng truc cu kin: X= 0 RS.AS=Rb.b.x.iu kin (3-5) la: k.M Mph.


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3.1.3.2 Phng php tnh theo ni lc ph hoi: Ni dung c ban cua phng phap la: Xac nh ni lc ln nht do tai trong tai TD tnh toan ri so sanh vi kha nng chu lc cua TD o.

iu kin kim tra: Sc Sph /k hay k.Sc Sph. (3 - 5)Trong o:

Sc: Ni lc do tai trong tiu chun gy ra tai TD xet.Sph: Kha nng chu lc cua TD ( Con goi la ni lc pha hoai).k >1: H s an toan cua kt cu. (k = 1.52.5)

Xac nh kha nng chu lc cua TD theo cac gia thit sau:- ng sut trong BT chu nen at Rb va phn b ch nht (u).- ng sut trong ct thep chu keo at gii han chay RS.

u im: - a xet n s lam vic cua vt liu giai oan deo nn tit kim vt liu.- Cho khai nim ro rang hn v an toan cua kt cu .Nhc im: - H s an toan k= Sph / Sc gp chung lai nh vy la cha thoa ang v an toan cua ktcu phu thuc rt nhiu yu t nh tai trong, vt liu, iu kin lam vic v.v.. V vykhng th anh gia an toan bng mt h s duy nht c.- Cha xet n bin dang va nt cua kt cu la hai vn cung rt cquan tm.


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3.2. PHNG PHP TNH THEO TTGH3.2. PHNG PHP TNH CU KIN THEO TRNG THI GII HN: 3.2.1 Cc trng thi gii hn (TTGH): - TTGH la trang thai ma t o tr i kt cu khng thoa man cac yu cu ra cho no (do chu lc qua sc,do mt n nh, do bin dang qua ln hoc do khent xut hin va m rng v.v..)

- Kt cu BTCT c tnh theo 2 nhom TTGH: TTGH th I (TTGH v cng ) va TTGH th II (TTGH v iu kin s dung)3.2.2 Tnh theo TTGH v cng (TTGH I): TTGH th I c qui nh ng vi luc kt cu bt u b pha hoai, b mt nnh v hnh dang va v tr, b hong do moi do tac dung ng thi cua taitrong va mi trng.iu kin tnh toan: S Sgh. (3 - 6)S: La ni lc ln nht co th phat sinh tai TD do tai trong tnh toan gy ra.Sgh: La gii han be nht v kha nng chu lc cua TD xac nh theo cng tnh toancua vt liu.

- Tnh theo TTGH th I la cn thit i vi moi kt cu cung nh cac bphn.- Tnh theo TTGH th I cho moi giai oan: ch tao, vn chuyn, cu lp, s dung, sa cha.. (mi giai oan vi s tnh phu hp).


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3.2.3 TNH THEO TTGH 23.2.3 Tnh theo TTGH v iu kin s dng (TTGH II): Tnh theo TTGH th II v bin dang: f fgh. (3 7a)f: bin dang hoc chuyn v do tai trong tiu chun fgh: bin dang hay chuyn v ti a ma qui pham cho phep:

Tnh theo TTGH th II v nt:- Nu kt cu c phep nt: acrc agh. (3 7b)acrc: b rng khe nt do tai trong tiu chun. agh: b rng khe nt gii han ma qui pham cho phep;Gii han cho phep cua b rng khe nt va bin dang am bao iu kin lam vic bnh thng: agh ly theo Bang 1, Bang 2 trang12, fgh ly theo Bang 4 trang 14 TCXDVN 356:2005.- Nu kt cu khng cho phep nt: Sc Scrc. (3 7c)Sc: ni lc do tai trong tiu chun. Scrc: Ni lc ti a ma TD co th chu c khi sp nt (kha nng chng nt).

(Co th xem Sc la ng sut keo ln nht trong BT, Scrc la cng chu keo cua BT)TCXDVN 356:2005 iu 4.2.2 trang 10 qui inh: Tnh ton kt cu v tng th cng nh tnh ton tng cu kin ca n cn tin hnh i vi mi giai on: ch to, vn chuyn, thi cng, s dng v sa cha. S tnh ton ng vi mi giai on phi ph hp vi gii php cu to chn.Cho php khng cn tnh ton kim tra s m rng vt nt v bin dng nu qua thc nghim hoc thc t s dng cc kt cu tng t khng nh c: b rng vt nt mi giai on khng vt qu gi tr cho php v kt cu c cng giai on sdng.


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3.2.2 Cng tnh ton3.2.2 Cng tnh ton ca vt liu :

Trong o bc va bt la h s tin cy cua BT khi nen va khi keo. Khi tnh theo TTGH I bc=1,3-1,5 va bt=1,3-2,3 -TCXDVN 356:2005 Bang 11

trang 34.bi la h s iu kin lam vic cua BT (i=1, 2, .., 10) -TCXDVN 356:2005 Bang

15 trang 37.

Cng tnh toan cua ct thep v keo RS c xac nh nh sau:

3.2.2.1 Cng tnh ton ca BT: Cng tnh toan cua BT v nen Rb va v keo Rbt c xac nh nh sau:

)83(;.;. ==bt

btnbibt

bc

bnbib

RRRR

3.2.2.2 Cng tnh toan cua ct thep:

;s

sns

RR =)93(;. =

s

snsiS

RR

Trong o S la h s tin cy cua ct thep. Khi tnh theo TTGH th nht s=1,05-1,2 tuy thuc loai thep. TCXDVN 356:2005 Bang 20 trang 46.

si la h s iu kin lam vic cua ct thep (i=1, 2, .., 9). TCXDVN 356:2005 Bang 23 trang 49.


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3.3. NGUYN L CU TO3.3. NGUYN L CU TO: 3.3.1 Chon kch thc tit din cac cu kin:Khi thit k kt cu BTCT thng phai chon kch thc TD cac cu kin xac nh tai trong, tnh ni lc va ct thep. S hp ly cua TD chon theo yu cu chu lc c anh gia qua ham lng thep (mi loai cu kin co mt khoang hp ly cua ).Chon TD con phai quan tm n yu t thm my (yu cu tao dang cua kin truc) va iu kin ch tao (thng nht van khun, b tr thep va BT..). 3.3.2 Khung v li ct thp:Ct thep trong cu kin BTCT c lin kt thanh khung, li :

- Gi v tr ct thep khi thi cng.- Cac ct thep cung chu lc, tranh cac pha hoai cuc b.- Chu cac ng sut phc tap ma tnh toan khng xet n.

Lin kt cac ct thep bng cach buc hoc han.

Khung ct thep: gm ct doc, ct ngang, ct thi cng. Thng b tr cac cu kin dang thanh nh ct, dm.Li ct thep: Thng s dung cho cac cu kin dang ban nh ban san, ban mong.


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Khung ct thep: gm ct doc, ct ngang, ct thi cng. Thng b tr cac cu kin dang thanh nh ct, dm.Li ct thep: Thng s dung cho cac cu kin dang ban nh ban san, ban mong.3.3.2.1 Khung li buc: Buc bng si thep 0,8 1.

BucBuc

Van khun

* u im: Chu tai trong ng tt. (co deo cao)B tr ct thep linh ng.Khng cn thit b han.* Nhc im:

Mc lin kt khng tt bng han. Thi cng chm, kho c gii hoa.

3.3.2.2 Khung li hn:Co th ch tao sn cac khung phng ri ghep thanh khung khng gian bng cac thanh ngang (ct thi cng)

Thanh ni ngang(1-3 thanh/m).

Co th la li phng hoc cun nhng am bao mi cun G 500 kg phu hp cn cu thiu nhi khi thi cng.


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3.3.3 Ct chu lc v ct cu to3.3.3 Ct chu lc v ct cu to:- Ct chu lc: Dung chu cac ng lc phat sinh do tai trong, c xac nh theo tnh toan.- Ct cu tao: Lin kt cac ct chu lc thanh khung hoc li, giam s co ngot khng u cua BT, chu ng sut do co ngot va thay i nhit , giam b rng khe nt, han ch bin dang (vong), phn b tac dung cua tai trong tp trung..3.3.4 L p BT bo v:Lp BT bao v ct doc chu lc TCXDVN 356:2005 qui inh:iu 8.3.2 trang 122: i vi ct thp dc chu lc (khng ng lc trc, ng lc trc, ng lc trc ko trn b), chiu dy lp b tng bo v cn c ly khng nh hn ng knh ct thp hoc dy cp v khng nh hn:- Trong bn v tng c chiu dy:

+ t 100 mm tr xung: 10 mm (15 mm)+ trn 100 mm: 15 mm (20 mm)

- Trong dm v dm sn c chiu cao:+ nh hn 250 mm: 15 mm (20 mm)+ ln hn hoc bng 250 mm: 20 mm (25 mm)

- Trong ct: 20 mm (25 mm)- Trong dm mng: 30 mm- Trong mng:

+ lp ghp: 30 mm+ ton khi khi c lp b tng lt: 35 mm+ ton khi khi khng c lp b tng lt: 70 mm

c2

c2c1

c2c1


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3.3.4 L p BT bo v3.3.4 L p BT bo v:Lp BT bao v ct cu tao TCXDVN 356:2005 qui inh:iu 8.3.3 trang 122: Chiu dy lp b tng bo v cho ct thp ai, ct thp phn b v ct thp cu to cn c ly khng nh hn ng knh ca cc ct thp ny v khng nh hn:- khi chiu cao tit din cu kin nh hn 250 mm: 10 mm (15 mm)- khi chiu cao tit din cu kin bng 250 mm tr ln: 15 mm (20 mm)

ch thch:1. Gi tr trong ngoc (...) p dng cho kt cu ngoi tri hoc nhng ni m t.2. i vi kt cu trong vng chu nh hng ca mi trng bin, chiu dy lp b tng bo v ly theo quy nh ca tiu chun hin hnh TCXDVN 327 : 2004.Trong kt cu mt lp lm t b tng nh v b tng rng cp B7,5 v thp hn, chiu dy lp b tng bo v ct thp dc chu lc cn phi khng nh hn 20 mm, cn i vi cc panen tng ngoi (khng c lp trt) khng c nh hn 25 mm.i vi cc kt cu mt lp lm t b tng t ong, trong mi trng hp lp b tng bo v khng nh hn 25 mm.Trong cc cu kin lm t b tng nh, b tng rng c cp khng ln hn B7,5 v lm t b tng t ong, chiu dy lp b tng bo v cho ct thp ngang ly khng nh hn 15 mm, khng ph thuc chiu cao tit din.


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3.3.5 B tr ct thp3.3.5 B tr ct thp v khong cch gia cc ct thp:- Nu ct thep nm ngang hoc nghing khi BT:

- Nu ct thep t ng khi BT: t0 50.t0 1.5d

t0 50

t0 30d

t0 30d

t0

t0 25d

t0 25d

(t0 la khoang h gia cac mep cua cacct thep-khoang cach thng thuy)

Ngoai ra khoang cach gia cac ct thep cung khng nn qua ln nhm tranh cac vt ntdo co ngot, thay i nhit , tranh s pha hoai cuc b va n nh cua khung (li) ctthep khi thi cng.. Trong moi trng hp t0 400.


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3.3.6 Neo ct thp3.3.6 Neo ct thp: Neo ct thep nhm bao am phat huy ht kha nng chu lc cua ct thep, tranh pha hoaicuc b do tut.

Chiu dai oan neo: c xac nh theo kha nng truyn lc gia BT va ct thep (lcdnh):

Neo co un moc u: Ct thep tron trntrong khung buc phai co moc neo hai u.

2,5dUn may

3,25d

Un tay

6,25d

3d 2,5d

45-900

Trng hp khi thanh cn neo c din tch tit din ln hn din tch yu cu theo tnh ton bn vi ton b cng tnh ton, chiu di lan theo cng thc (3-10) cho php gim xung bng cch nhn vi t s din tch cn thit theo tnh ton v din tch thc t ca tit din ct thp.

nhng khng nh hnTrong an, an, an cng nh gi tr cho php ti thiu lan c xc nh theo TCXDVN 356:2005 Bng 36 (tr. 125).

;.dl anan =)103(;

+= d

RRl anb

sanan


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3.3.6 Neo ct thp: Chiu dai oan neo: c xac nh theo kha nng truyn lc gia BT va ct thep (lcdnh):

nhng khng nh hnTrong an, an, an cng nh gi tr cho php ti thiu lan c xc nh theo TCXDVN 356:2005 Bng 36 (tr. 125).

;.dl anan =)103(;

+= d

RRl anb

sanan

Neo bng cach han cac thep neo u:4d2d

d

d4d 10mm 2.5d


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3.3.7 Un ct thp3.3.7 Un ct thp: Tai ch un cong, ct thep khi chu lc se epcuc b vao BT.

F

F

d

r 10d

F

F

3.3.8 Ni ct thp: 3.3.8.1 Ni chng (ni buc):Khi d 36. Khng nn ni buc ct thep trong vung keo tai TD tn dung htkha nng chu lc.

lan

Khng c ni buc khi d > 36 hoc khi cu kin chu keohoan toan (Thanh chu keo cua dan, thanh treo cua khung..).

oan lan xac nh theo cng thc tnh oan neo va:Keo: lan 250 mm.Nen: lan 200 mm.

Tuy thuc mac BT va loai ct thep

3.3.8.2 Ni hn : Han i u:

d10

lh lh8d lh4d

d20.85 d210 mmd1

lh

d8

lh10d lh5d

Han i u co nep:Han ghep (chng):

phn b lc nen ep u vao BT, ct thepc un cong vi ban knh cong r 10d.

Han trong mang:

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1. C IM CU TOCU KIN CHU UN.

Cu kin chu un la cu kin chu M hay ng thi M & Q.P

M&Q Q = 0

P

M&QCu kin chu un la loai cu kin c ban rt quan trong c s dung rng rai va trong nhiu b phn cua cng trnh nh dm, san, cu thang, ... Co th quy v hai loai c ban: ban va dm.

h

4.1. C IM CU TO:4.1.1 Bn:Ban la loai kt cu phng co chiu day kha beso vi chiu dai va chiu rng.Trong kt cu nha ca ban co kch thc mt bngthng bng 26m.

Ct thep trong ban gm co ct chu lc va ct phn b (CI, CII i khi CIII )a. Ct thp chu lc: ChChuu mm men men uunn. . BB trtr trongtrong vuvungng kekeoo.Chon va b tr theo tnh toan.

Ct phn b

Ct chu lc

Chiu day ban chon theo yu cu chu lc va cng (bin dang, vong, goc xoay.. San nha thng khoang t 620 cm, trong cac kt cu khac cac kch thc o co th ln hn hoc be hn ). B tng cua ban thng chon co cp bn t B12.5 n B25.

CU KIN CHU UN 2

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ng knh d=612 mm, khoang cach gia cac ct thep a=720 cm. Tai gi ct mu chu M(-) th a 100 tin BT; Tai ni co M ln th: a 200 khi chiu day ban h 150,

a 1.5h khi chiu day ban h > 150,Tai ni co M be th ti thiu phai co 3 thanh/1m dai ban.

b. Ct thp phn b (cu to):Tac dung: gi v tr ct chu lc khi thi cng, chu ng lc do co ngot, thay inhit , phn phi anh hng cua lc tp trung ra cac ct chu lc ln cn.

4.1.2 Dm:

Lng ct phn b khng t hn 10% s lng ct chu lc tai TD co m men un ln nht.

Ct phn b

Ct chu lc

ng knh d=48; Cach khoang a=200300 (a 350). c

c15 khi d10c1,5d khi d>10

lan10d

Dm la cu kin chu un co kch thc TD (b rng va chiu cao) kha beso vi chiu dai (nhp).

lb

hHnh dang tit din: Tit din dm thng co dang chnht, I, T, hp, khuyn, ...

CU KIN CHU UN 3

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b

h

Hnh dang tit din:

Kch thc tit din:

Chiu cao nhp;

=201

81h - Bi s cua 50 khi h 600.- Bi s cua 100 khi h > 600.

Phai thun tin vi qui cach van khun va tiu chun hoa kch thc dm.

Chiu rng b = h;

41

21 - 100, 120, 150, 180, 200, ...

- Bi s cua 50 khi b >250.

Ct thep: a. Ct dc chu lc:

Chu M, xac nh theo tnh toan. ng knh d = 10-32B tr trong vung keo, i khi co ca trong vung nen;Co th b tr 1, 2 hay nhiu lp (khi b 150 phai co t nht 2 thanh)

Ct xin Ct ai Ct doc ct

Ct docchu lc ai 2 nhanh ai 4 nhanh

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Ct xin Ct ai Ct doc ct

Ct docchu lc ai 2 nhanh ai 4 nhanh

b. Ct dc cu to: ng knh 10 14. Ct gia: la ct doc t trong vung BT chu nen (tai cac goc cua ct ai).Ct thep phu: Khi dm co chiu cao ln h > 700. Lng thep 0.1% din tch BT sn.Co tac dung gi n nh ct ai, chu ng lc co ngot va nhit .c. Ct ai: chu lc ct, lin kt ct doc thanh khung, gn vung BT chu keo va vungBT chu nen vi nhau chu m men.Tnh toan theo lc ct.ng knh ct ai: d 6mm; khi h 800 d 8mm.d. Ct xin: chu lc ct (thng kt hp a ct doc ln chu M(-) mep trn).Goc nghing = 450 khi h 800;

= 600 khi h > 800. = 300 khi dm thp va ban.

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3. TRNG THI US-BD4.2. S LM VIC CA DM:

Nh vy vic tnh toan va cu tao cac cu kin chu un theo iu kin cng nhm:- Khng b pha hoai trn TD thng goc: Tnh toan theo cng trn TD thng goc.- Khng b pha hoai trn TD nghing: Tnh toan theo cng trn TD nghing.

Quan sat mt dm BTCT chu tai cho nluc b pha hoai:

Khe ntthng goc

Khe ntnghing

Tai khu vc gia dm ni M ln co vtnt thng goc vi truc dm; Tai khu vc gn gi ta co Q ln th vtnt nghing.

4.3. TRNG THI NG SUTBIN DNG TRN TIT DIN THNG GC: Din bin cua trang thai US - BD trn TD thng goc co th phn thanh 3 giai oan sau:

4.3.1 Giai on I: Khi tai trong be vt liu lam vic an hi.

Tai trong tng bin dang deo trong BT phat trin (nht la vung keo). S ng sut trong BT cong i.Khi bt=Rbt BT vung keo sp sa nt: Trang thai Ia.

I b

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4.3.2 Giai on II:Tai trong tng BT chu keo nt. Taikhe nt toan b lc keo do ct thepchu. Min BT chu nen co bin dang deo khaln s ng sut b cong nhiu.

Nu lng ct thep chu keo kha nhiu, khi tai trong tng tit din b pha hoaikhi BT chu nen at Rb trong khi S< RS. y la trng hp pha hoai th 2 (pha hoai gion).

Nu lng ct thep chu keo khng nhiu lm, khi tai trong tng ng suttrong ct thep at gii han chay RS (S=RS): Trang thai IIa.4.3.3 Giai on III:Ct thep trang thai chay deo, tai trongtng Khe nt m rng va phat trindn ln pha trn, min BT chu nenthu hep dn. Khi ng sut trong BT chu nen at Rbb pha hoai: trng hp pha hoai thnht (pha hoai deo).

IIa b

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4. TNH TON THEO CNG TRN TIT DIN THNG GC4.4. TNH TON THEO CNG TRN TIT DIN THNG GC: 4.4.1 Tnh cu kin c TD ch nht:Co 2 trng hp b tr ct doc chu lc:- Ch co ct thep chu keo goi la b tr ct n; - Co ct thep ca trong vung keo ln vung nen : Ct kep. 4.4.1.1 Tnh tit din ch nht c ct n: a) S ng sut: S ng sut TTGH I trn c scua trng hp pha hoai deo:- ng sut trong vung BT chunen: at cng chu nen Rb. (ng sut vung nen phn b dangch nht)- ng sut trong ct thep chukeo at cng chu keo RS.

x/2x/2

h

x

AS

b

Rb

Mgh Rbbxh0h

h0-x/2

a

RSAS

b) Cng thc c ban:Phng trnh hnh chiu cac lc ln phng truc dm:

Tng m men vi truc qua trong tm ct thep chu keo va vung goc vi mp un :)14(;...0 == xbRARX bss

)24(;2

...0 0

== xhxbRMM bghAs

CU KIN CHU UN 8

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iu kin cng (am bao cho TD khng vt qua TTGH th I) la:

)14(;...0 == xbRARX bss)24(;

2...0 0

== xhxbRMM bghAs

)34(;2

...; 0

xhxbRMMM bgh)34(;

2.. 0 a

xhARM SS

Kt hp (4-1) & (4-3): c) iu kin han ch:Kt qua thc nghim cho thy trng hp pha hoai deo xay ra khi:

)44(;

1,111

,

00

+===

usc

S

RR Rh

xhx

Trong o: - c trng tnh cht bin dang cua vung BT chu nen: - H s phu thuc loai BT, =0,85 vi BT nng.Rb, RS tnh bng MPa.sc,u - ng sut gii han cua ct thep trong vung BT chu nen (khi BT

at ti bin dang cc han), sc,u =500MPa vi tai trong thng xuyn, .. sc,u =400MPa vi tai trong c bit.

)64(;R

.b.h.RR.b.xR.b.xR.R maxs,

S

0bR

S

bSbSS === AAA T (4-1) & (4-4):

0

Sb.hA=Goi la ham lng ct thep th ham lng cc ai 4(;

RR.

b.hA

S

b

0

maxS,max == R

CU KIN CHU UN 9

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)64(;R

.b.h.RR.b.xR.b.xR.R maxs,

S

0bR

S

bSbSS === AAA T (4-1) & (4-4):

Ct thep qua t cung b pha hoai gion, v vy: min ;

0

Sb.hA=Goi la ham lng ct thep th ham lng cc ai:

)74(;R

.b.h S0

max == R RA bmaxS,

d) Cac bai toan ap dung: tin s dung, ta tin hanh mt s phep bin i:t , Cac cng thc trn vit lai nh sau:

0hx=

T (4 - 1) )84(;.... 0 = hbRAR bss T (4 - 3) ( ) )94(;....5,01.... 2020 = hbRhbRM bmb

( ) )104(;....5,01... 00 = hARhARM SSSS T (4 3a) Trong o m= .(1 - 0,5. ), = (1 - 0,5.); iu kin han ch R m R;Bai toan 1: Bit kch thc TD b, h, mmen M, cp bn cua BT, loai ct thep (Rb, RS). Tnh ct thep cn thit AS ?Giai:- Cn c cp bn cua BT, loai ct thep: (tra bang) Rb, RS, theo (4-4) tnh R, theo (4-7) tnh max..

T h h h V h A h i i h 1 20 i b

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- T phng trnh (4 - 9) xac nh m:

Giai:- Cn c cp bn cua BT, loai ct thep: (tra bang) Rb, RS, theo (4-4) tnh R, theo (4-7) tnh max.- Tnh h0 = h - a. V cha co AS nn phai gia thit trc a: a = 15-20 vi ban,

a = 30-60 vi dm. )124(;

.b.hRM

20b

=m

- Kim tra m theo iu kin han ch:*Nu m R tra bang co

)134(;h.R

M0S

= SATnh AS t phng trnh (4-10):

min0

Sb.hA =Kim tra ham lng thep:

**Nu m > R th hoc tng kch thc TD.tng cp bn cua BT.t ct thep vao vung nen (t ct kep).

Bai toan 2: Bit M, cp bn cua BT, loai ct thep. Yu cu chon b, h, va tnh ct thep AS ?Giai:- Cn c loai BT, ct thep: Rb, RS, theo (4-4) tnh R, theo (4-7) tnh max.Ap dung cac cng thc (4 - 8) & (4 - 9) bai toan vi 2 phng trnh cha 4 n: b, h, va AS. giai cn chon trc 2 n: (tin nht la chon trc b & )

CU KIN CHU UN 11

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giai cn chon trc 2 n: (tin nht la chon trc b & )*Chon trc b (theo kinh nghim, theo yu cu cu tao, theo kin truc..)*Chon : = 0,25 0,35 i vi dm.

= 0,1 0,25 i vi ban.- Chiu cao lam vic cn thit cua TD h0: )144(;bR

M.1bm

0 = hSau khi co bxh hp ly th vic tnh AS tin hanh theo nh bai toan 1.

Bai toan 3 (BT kim tra): Bit b, h, AS, cp bn cua BT, loai ct thep. Tnh kha nng chu lc cua tit din Mgh (Mtd)Giai: - Cn c cp bn cua BT, loai ct thep: (tra bang) Rb, RS, theo (4-4) tnh R..- Cn c vao cach b tr ct thep xac nh c a ri tnh h0 = h - a.Bai toan vi 2 phng trnh cha 2 n , Mgh nn hoan toan xac nh.

;.b.hRAR

0b

SS=- T (4 - 8) - Kim tra theo iu kin han ch:

*Nu R: tra bang co m th vao (4 - 9) ;... 20hbRM bmgh =**Nu > R chng to AS qua nhiu, kha nng chu lc c tnh theo kha

nng cua vung nen, tc ly = R hay m = R ;... 20hbRM bRgh =

CU KIN CHU UN 12

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4.1.2 Tnh tit din ch nht c ct kp:4.4.1.2 Tnh tit din ch nht c ct kp: Cac ly do chu yu b tr ct thep chu nen trong dm (cu kin chu un):c Giam vong do t bin khi chu tai trong dai han.d Tng tnh deo cua cu kin.e D thi cng.

* iu kin t ct kep:

Vic t ct kep khng phai luc nao cung la kinh t. Kt qua nghin cu chothy ch nn t ct kep khi m 0,5 nu m >0,5 th nn tng kch TD.

Vic tnh toan vi trng hp t ct kep con co th gp khi do yu cu cu taotrong vung nen co mt lng thep ang k, cn xet n anh hng cua no.

As

Ab

Rsc A's Rb Ab

Rs As

h

b

h

0

a

a

'

M

A's

x

V vy iu kin tnh ct kep la ;5,0.b.hRM

20b=< mR

CU KIN CHU UN 13

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a) S ng sut: n TTGH v cng , s ng sut:

- Ct thep chu keo AS at RS

b) Cng thc c ban:Phng trnh hnh chiu cac lc ln phng truc dm:

iu kin cng (am bao cho TD khng vt qua TTGH th I):

Cung dung cac ky hiu nh trng hp ct n:

- Ct thep chu nen AS at RSC

- B tng vung nen at Rb.x

h

ba

h0

AS

AS

a'

h0Mgh

Rb RSCAS

RSASa

Tng m men vi truc qua trong tm ct thep AS va vung goc vi mp un cua dm:)154(;'....0 +== sscbss ARxbRARX( ) )164(;'.'.

2...0 00 +

== ahARxhxbRMM sscbghAs

( ) )174(;'.'.2

... 00 +

ahARxhxbRMMM sscbgh

m= .(1 - 0,5. ), = (1 - 0,5.);;0hx=

Cac cng thc trn vit lai nh sau:T (4-15) T (4-16)

)184(;'..... 0 += sscbss ARhbRAR ( ) )194(;'.'.... 020 + ahARhbRM sscbm

CU KIN CHU UN 14

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Cac cng thc trn vit lai nh sau:

c) iu kin han ch:- cu kin khng b pha hoai gion t BT chu nen:

x R.h0 hoc R hay m R. (4 - 20)- ng sut nen trong AS at n RSC phai thoa man iu kin: x 2a. (4 - 21)

T (4-15) T (4-16)

)184(;'..... 0 += sscbss ARhbRAR ( ) )194(;'.'.... 020 + ahARhbRM sscbm

d) Cac bai toan ap dung:Bai toan 1: Bit M, b, h, cp bn cua BT, loai ct thep. Tnh AS, AS ?Giai:- Cn c cp bn cua BT va nhom ct thep Rb, RS, RSC, tnh R.- Xac nh h0 = h - a (a va a c chon trc nh trng hp t ct n).

Bai toan vi hai phng trnh (4 - 18), (4 - 19) cha 3 n s , AS, AS nn phai loai bt n s bng cach chon trc = R tc m= R.( li dung ht kha nng chu nen cua BT nn ct thep AS, AS co (AS + AS) be nht).

- Kim tra iu kin cn thit tnh ct kep :

Thay m= R vao (4-19) tm c:

Khng qun kim tra lai a, a a gia thit!

Th AS vao (4-18) c:

)224(;5,0.b.hRM

20b

=< mR

)234(;)'(hR

.b.hR-M'0sc

20bR = aA S

)244(;'... 0 += ss

sc

s

bRs AR

RR

hbRA

CU KIN CHU UN 15

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Bai toan 2: Bit M, b, h, cp bn cua BT, loai ct thep va AS. Tnh AS?Giai:- Cn c cp bn cua BT va nhom ct thep Rb, RS, RSC, tnh R.- Xac nh h0 = h - a (a va a c chon trc nh trng hp t ct n).Bai toan xac nh v co hai phng trnh cha 2 n s.

- Kim tra iu kin han ch:Nu m R: tra bang x = .h0.

T (4-19) tnh m:

Nu x < 2a: ng sut trong ct thep chu nen SC< RSC. Xem hp lc cuavung nen trung vi trong tm AS (ly x = 2a).

Nu x 2a:

S ng sut luc o co dang:

)254(;.b.hR

)'.('.R-M20b

0ssc = ahAm

)264(;'... 0 += ss

sc

s

bs AR

RR

hbRA

( ) )274(;'..0 0' == ahARMM ssghsAT iu kin M Mgh ( ) )284(;'0 = ahR

MAs

s

Rb.b.xa

h0 Mgh

a

aRS.AS

SC.AS

Nu m > R: ct thep AS a cho la cha u am bao kha nng chu lc cua vung nen nn ta xem AS la cha bit va tnh theo bai toan 1(Tnh AS, AS).

CU KIN CHU UN 16

Chng 4

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Bai toan 3: Bit b, h, cp bn cua BT, loai ct thep, AS, AS. Kim tra khanng chu lc cua TD (Mgh = ?).Giai:- Cn c cp bn cua BT va nhom ct thep Rb, RS, RSC, tnh R.- Xac nh a, a, h0 = h a.Bai toan vi 2 phng trnh cha 2 n s la va Mgh nn hoan toan xac nh.

Kim tra iu kin han ch:

T (4 - 18)

Nu > R ly = R hay m = R tnh Mgh:

;.b.hR

A'RAR0b

SSCSS =

Rha 0

'2Nu T m: );'.('.... 020 ahARhbRM SSCbmgh +=

Nu (tc x < 2a) ly x = 2a tnh Mgh theo (4-27);0

'2ha

Chng to ct thep chu keo AS qua nhiu, xac nh kha nng chu lc cua tit din theo kha nng cua vung nen, tc ly = R hay m = R.

);'.('.... 020 ahARhbRM SSCbRgh +=

CU KIN CHU UN 17

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4.2 Tnh ton cu kin c TD ch T

4.4.2.1 c im lam vic cua TD ch T: 4.4.2 Tnh ton cu kin c TD ch T:

Tit din ch T gm canh va sn.

bf

hfh

ba) c)

bf

hfh

b

bf

h

b)

h

b

bf

b

h

hf

h

bf

bsbs

d)

hf

h

bf

Trng hp a): Canh ch T nm trong vung nense tng thm din tch BT vung nen, tng kha nngchu un cua TD.

Canh nm trong vung keo khng anh hng n kha nng chu lc cua TD nn c tnhnh TD ch nht b*h.

Trng hp b):

Trng hp c):Canh nm trong vung nen, truc TH qua canh, kha nng chu lc cua TD tng ngnh TD ch nht bf*h.

Trng hp d) Tnh nh tit din ch T vi b rng sn bng tng cac sn.Nh vy theo quan im tnh toan kha nng chu un cac dm c xp vao loai co TD ch nht khi vung nen co hnh ch nht, va la TD ch T khi vung nen co hnh ch T.

CU KIN CHU UN 18

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B rng canh dung trong tnh toan c xac nh theo vn SC quy nh lynh sau: TCXDVN 356:2005 iu 6.2.2.7 trang 62 qui inh:Gi tr bf dng tnh ton c ly t iu kin: b rng mi bn cnh SC, tnh t mp bng dm khng c ln hn 1/6 nhp cu kin v ly khng ln hn:-khi c sn ngang hoc khi hf 0,1h: 1/2 khong cch thng thy gia cc sn dc;khi khng c sn ngang hoc khi khong cch gia chng ln hn khong cch gia cc sn dc, hf < 0,1h: 6hf;

b'f

SC

h'f

h

bSC

khi cnh c dng cng xn: + trng hp hf 0,1h: 6hf + trng hp 0,05h hf < 0,1h: 3hf + trng hp hf < 0,05h: cnh khng k n trong tnh ton.

S S

SC

b'f

SC

Tit din ch T co th t ct n hoc ct kep. Nhng TD ch T t ct kep (theo tnh toan) t khi dung v khng kinh t (TD ch T do a co vung chu nen ln).

CU KIN CHU UN 19

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4.4.2.2 Tnh ton tit din ch T: (t ct n)a) S ng sut:

- Nu truc TH qua canh TD ch T c tnh nh TD ch nht bf xh.

b'f

x h'f

h h0 AS

ba

Rb

MghRS.AS

xh0h

ab

b'f

h'f

AS

Rb

MghRS.AS

- Nu truc TH qua sn tnh toan theo TD ch T. phn bit truc TH qua canh hay sn, goi Mf la m men un khi truc TH i qua mepgia canh va sn (x= hf): ( ) )294(;50...0 0 == fffbfA h',hh'b'RMM SNu M Mf: truc TH qua canh, tnh toan theo TD ch nht bfxh. Nu M > Mf: truc TH qua sn, tnh toan theo TD ch T.b) Cng thc c ban:

CU KIN CHU UN 20

Chng 4

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4.4.2.2 Tnh ton tit din ch T: (t ct n)a) S ng sut:b) Cng thc c ban: x

h0h

ab

b'f

h'f

AS

Rb

MghRS.AS

;0= X ( ) )304(;'.'... += ffbbss hbbRxbRAR;0=

SAM

( ) ( ) ( ) )314(;.5,0.'.'..5,0... 00 += fffbbgh hhhbbRxhxbRMiu kin cng : M MghHay ( ) ( ) ( ) )324(;'.5,0.'.'..5,0... 00 + fffbb hhhbbRxhxbRMCung dung cac ky hiu nh trng hp TD ch nht:

m= .(1 - 0,5. ), = (1 - 0,5.);;0hx=

Cac cng thc trn vit lai nh sau:

T (4-30) T (4-31)

( ) )334(;'.'..... 0 += ffbbss hbbRhbRAR ( ) ( ) )344(;'.5,0.'.'.... 020 + fffbbm hhhbbRhbRM c) iu kin han ch:- cu kin khng b pha hoai gion t BT chu nen:

x R.h0 hoc R hay m R.

CU KIN CHU UN 21

Chng 4

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( ) )334(;'.'..... 0 += ffbbss hbbRhbRAR ( ) ( ) )344(;'.5,0.'.'.... 020 + fffbbm hhhbbRhbRM x R.h0 hoc R hay m R.

d) Tnh toan tit din: Tnh ct thep: Bit b, bf, hf, h, M; cp bn cua BT, loai ct thep. Tnh AS?Giai:T (4-34), tnh m:

* Nu m R: tra bang c . T (4-33)

( ) ( ))354(;

..

'.5,0.'.'.20

0 =hbR

hhhbbRM

b

fffbm

Kim tra iu kin han ch: ( )( ) )364(;'.'.. 0 += ffs

bs hbbhbR

RA Kim tra ham lng ct thep cua TD (ch tnh cho phn sn, tc =[AS/(b.h0)]).* Nu m > R: phai t ct kep hoc tng kch thc TD, cp bn cua BT.Bai toan kim tra: Bit b, bf, hf, h, cp bn cua BT, ct thep AS. Tnh Mgh?Giai:

* Nu R tra bang co m, t (4 - 34):T (4-33) xac nh :

( ))374(;

..'.'..

0=

hbRhbbRAR

b

ffbss( ) ( );'.5,0.'.'.... 020 fffbbmgh hhhbbRhbRM +=

* Nu > R th ly = R tc m = R tnh Mgh.

CU KIN CHU UN 22

Chng 4

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5. TNH TON THEO CNG TRN TIT DIN NGHING4.5. TNH TON THEO CNG TRN TIT DIN NGHING: 4.5.1 c im ph hoi trn tit din nghing (TDng): Trn TDng chu tac dung ng thi m men va lc ct. S pha hoai theo TD nghingthng theo 2 kiu:

Kiu 1: Hai phn dm nay quay xung quanh vung nen, vung nen thu hep lai cui cung b pha huy. Luc o ct thepchu keo at gii han chay hay b keo tut v neo khng u.Kiu 2: Khi ct thep chu keo kha nhiu va neo cht th squay cua 2 phn dm b can tr. Dm b pha hoai khi minBT chu nen b pha v do tac dung chung cua lc ct va lcep. Hai phn dm co xu hng trt ln nhau va tut xungso vi gi ta.

QM M

Q

4.5.2 Tnh toan theo kha nng chu ng sut nen chnh (K han ch):Kt qua thc nghim chng to, BT khng b pha v v ng sut nen chnh cu kin cn phai thoa man iu kin:

)394(;.....3,0 011 hbRQ bbw Trong o w1 - H s k n anh hng cua ct ai t vung goc vi truc cu kin, c xac nh theo cng thc: w1= 1+5..w 1,3; (4 - 40)Vi ;

.;

sbA

EE sw

wb

S == Asw- din tch tit din ngang cua cac nhanh ct ai t trong mt mt phng vung goc vi truc cu kin va ct qua TD nghing

CU KIN CHU UN 23

Chng 4

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4.5.2 Tnh toan theo kha nng chu ng sut nen chnh (K han ch):Kt qua thc nghim chng to, BT khng b pha v v ng sut nen chnh cu kin cn phai thoa man iu kin:

)394(;.....3,0 011 hbRQ bbw Trong o w1 - H s k n anh hng cua ct ai t vung goc vi truc cu kin, c xac nh theo cng thc: w1= 1+5..w 1,3; (4 - 40)Vi ;

.;

sbA

EE sw

wb

S == Asw- din tch tit din ngang cua cac nhanh ct ai t trong mt mt phng vung goc vi truc cu kin va ct qua TD nghing.b - Chiu rng cua TD ch nht; Chiu rng sn cua TD ch T va ch I.s - Khoang cach gia cac ct ai theo chiu doc cu kin.

b1- H s xet n kha nng phn phi lai ni lc cua cac loai BT khac nhau:)414(;11 = bb R

- H s ly nh sau:+ i vi b tng nng, b tng ht nh, b tng t ong: 0,01;

+ i vi b tng nh: 0,02;Rb tnh bng MPa.

iu kin (4 - 39) nu khng thoa man phai tng kch thc tit din hoc tng cp bn BT.

CU KIN CHU UN 24

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4.5.3 Tnh toan theo kha nng chu ct cua tit din BT (cu kin khng b tr ct ngang chu ct):Kt qua thc nghim chng to rng khi dm chu ct thun tuy, se khng xut hin khe nt nghing nu ng sut tip thoa iu kin:

;.5,2. 0

btkc RhbQ ==

Tc kha nng chu ct ln nht cua tit din BT: )424(;...5,2 0max = hbRQ btbVy iu kin cng theo lc ct ln nht cua cu kin khng co ct thep ngang la: )424(;...5,2 0max ahbRQ bt TCXDVN 356:2005 iu 6.2.3.4 trang 81 qui inh:i vi cu kin BTCT khng c ct thp ai chu lc ct, m bo bn trn vt nt xin cn tnh ton i vi vt nt xin nguy him nht theo iu kin:( ) )434(;...1. 204 +

chbRQ btnb

V phi ca cng thc (4 - 43) ly theo khng ch: ( ) ( ) )444(;...1....1....5,2 03

204

0 ++ hbRchbRhbR btnbbtnbbt

Trong c chiu di hnh chiu ca TDng trn trc dc cu kin tnh t mp gi ta. c cmax = 2.h0; Q - Lc ct c xc nh t ngoi lc t mt pha ca TDng ang xt.H s b3, b4 ph thuc loi BT;

CU KIN CHU UN 25

Chng 4

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4.5.3 Tnh toan theo kha nng chu ct cua tit din BT (cu kin khng b tr ct ngang chu ct):TCXDVN 356:2005 iu 6.2.3.4 trang 81 qui inh:i vi cu kin BTCT khng c ct thp ai chu lc ct, m bo bn trn vt nt xin cn tnh ton i vi vt nt xin nguy him nht theo iu kin:( ) )434(;...1. 204 +

chbRQ btnb

V phi ca cng thc (4 - 43) ly theo khng ch: ( ) ( ) )444(;...1....1....5,2 03

204

0 ++ hbRchbRhbR btnbbtnbbt

Trong c chiu di hnh chiu ca TDng trn trc dc cu kin tnh t mp gi ta. c cmax = 2.h0; Q - Lc ct c xc nh t ngoi lc t mt pha ca TDng ang xt.H s b3, b4 ph thuc loi BT;H s n xt n nh hng lc dc;

H s n xt n nh hng lc dc, c xc nh nh sau:Khi chu lc nn dc, xc nh theo cng thc: i vi cu kin ng lc trc, trong cng thc (4-45) thay N bng lc nn trc P; khng xt nu lc nn dc trc gy ra m men un cng du vi tc dng ca ti trng.Khi chu lc ko dc trc, xc nh theo cng thc: nhng gi tr tuyt i ca v phi ca (4-46) khng ln hn 0,8.

)454(;5,0..

1,00

=hbR

Nbt

n

)(;bhR

N,bt

n 464200

=

CU KIN CHU UN 26

Chng 4

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5.4 iu kin cng TDng c ct ngang

4.5.4 iu kin cng trn tit din nghing ca dm c ct ngang:4.5.4.1 S ng lc trn tit din nghing: Gia thit:Ni lc trong cac ct ngang la lc keo doc theo truc cua no.

c

s s s s s s

c0

Qb

Rsw Asw

Rsw Asw Rsw Asw

Rsw As, inc

Giai thch cac ai lng trong s ng lc:s: Khoang cach gia cac ct ai.RSW: Cng tnh toan cua ct thep ngang.ASW: Din tch tit din ngang cua cac nhanh ct ai t trong mt mt phng vung goc vi truc cu kin (goi la 1 lp).AS,inc(i): Din tch tit din ngang cua cac lp ct xin (i=1, 2,..).Zs: Khoang cach t trong tm ct thep doc chu keo n trong tm vung nen.Zsw(i): Khoang cach t cac lp ct ai n trong tm vung nen.Zs,inc(i): Khoang cach t cac lp ct xin n trong tm vung nen.

CU KIN CHU UN 27

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4.5.4 iu kin cng trn tit din nghing ca dm c ct ngang:4.5.4.1 S ng lc trn tit din nghing:

Ms

Nb+RSCAS

Qb

RswAswRSAS+ RSPASPQ

c0

Zs,inc2

ZS

Zsw1Z sw2

Zs,inc1

s RswAs,inc1

x

c

Giai thch cac ai lng trong s :s: Khoang cach gia cac ct ai.RSW: Cng tnh toan cua ct ngang.ASW: Din tch tit din ngang cua cac nhanh ct ai t trong mt mt phng.AS,inc(i): Din tch tit din ngang cua cac lp ct xin (i=1, 2,..).Zs: Khoang cach t trong tm ct thep doc chu keo n trong tm vung nen.Zsw(i): Khoang cach t cac lp ct ai n trong tm vung nen.Zs,inc(i): Khoang cach t cac lp ct xin n trong tm vung nen.

4.5.4.2 iu kin cng trn TDng theo lc ct:i vi cu kin chu un co t ct thep ngang, iu kin cng trn TDng theo lc ct nh sau: )474(;, ++ incsswb QQQQTrong o: QSW: Kha nng chu lc ct cua ct ai.

Qs,inc: Kha nng chu lc ct cua ct xin. Qb: Kha nng chu lc ct cua BT c xac nh theo cng thc thc nghim:

CU KIN CHU UN 28

Chng 4

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4.5.4.2 iu kin cng trn TDng theo lc ct:i vi cu kin chu un co t ct thep ngang, iu kin cng trn TDng theo lc ct nh sau: )474(;, ++ incsswb QQQQTrong o: QSW: Kha nng chu lc ct cua ct ai.

Qs,inc: Kha nng chu lc ct cua ct xin. Qb: Kha nng chu lc ct cua BT c xac nh theo cng thc thc

nghim: ( ))(;

c.b.hR

Q btnfbb 4841. 202 ++=

H s b2 xt n nh hng ca loi b tng.H s f xt n nh hng ca cnh chu nn trong tit din ch T, ch I.( ) ;5,11 ++ nf Trong mi trng hp phi khng ch gi tr:Gi tr Qb tnh theo (4-48) ly khng nh hn:( ) )504(;..1. 03min ++= hbRQQ btnfbbb Kha nng chu ct cua BT phai am bao Qb Qbmin. T (4-48) va (4-50) suy ra:

a)(;hcb

b 50403

2

ng thi phai am bao Qb Qbmax. T (4-48) va (4-42) suy ra:( ) b)(;.h,

c nfb 504152 02 ++

CU KIN CHU UN 29

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4.5.4.3 iu kin cng trn TDng theo m men: am bao cng trn TDng theo m men, cn tnh toan vi TDng nguy him nht theo iu kin: )514(;, ++ incssws MMMMTrong o: M -M men cua tt ca ngoai lc t mt pha cua TDng i vi truc i qua hp lc cua vung nen va thng goc vi mt phng un.

Ms, Msw, Ms,inc -tng m men i vi truc noi trn cua cac ni lc tng ng trong ct thep doc, ct ai va ct xin ct qua TDng.4.5.5. Tnh toan ct ai khi khng t ct xin:4.5.5.1 iu kin cng trn TD nghing khi khng t ct xin:Khi khng dung ct xin, iu kin (4-47) tr thanh:

)524(; + swb QQQQu

Qumin

c0 c

Trong o lc ct do ct ai chu co th vit lai nh sau:

Cung vi (4-48), iu kin cng trn TDng (4-52) tr thanh:

)534(;..

Vi:

== cqARQ swswswsw)(;

s.ARq swswsw 544 =

( ))(c;q

c.b.hR

QQ swbtnfb

u 554.1. 202 +++=

4.5.5.2 Tit din nghing nguy him nht: Tr s c0 tng ng vi Qu nho nht (Qumin). tm c0:

)564(;020

==cMq

dcdQ b

swu Trong o: ( ) )(;.b.hR.M btnfbb 5741 202 ++=

CU KIN CHU UN 30

Chng 4

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4.5.5.2 Tit din nghing nguy him nht: Tr s c0 tng ng vi Qu nho nht (Qumin). tm c0:

)564(;020

==cMq

dcdQ b

swu Trong o: ( ) )(;.b.hR.M btnfbb 5741 202 ++=

)(;qMc

sw

b 5840 = ;qMQ swbu ..2min =Tm c:

Nh vy, khi tnh ct ai gi tr Qsw c xc nh theo cng thc:)594(;. = oswsw cqQ

Ct thp ai xc nh theo tnh ton phi tho mn iu kin:( ))604(;

.22..1.

0

min3 =++h

QbRq bbtfnbsw

Khi tnh toan ct ai cn phai tnh vi nhiu TDng khac nhau vi gia tr c khng vt quakhoang cach t gi ta n TD co gia tr m men cc ai va khng vt qua gia tr tnh theo (4-50a).

TCXDVN 356:2005 iu 6.2.3.3 trang 80 qui nh:i vi cu kin b tng ct thp c ct thp ngang cng cn m bo bn theo tit din nghing trong khong gia cc ct thp ai, gia gi v ct thp xin, gia cc ct thp xin vi nhau.Chiu di c0 ca hnh chiu vt nt xin nguy him ln trc dc cu kin c xc nh t iu kin cc tiu ca biu thc (Qb + Qsw + Qs,inc). Trong cng thc xc nh Qb thay gi tr c bng c0, gi tr c0 ly khng ln hn 2.h0 v khng ln hn gi tr c, ng thi c0khng nh hn 2.h0 nu c > h0.

CU KIN CHU UN 31

Chng 4

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4.5.5.3 Tnh cu kin chu tai trong phn b u:

Ms

Nb+RSCAS

Qb

RswAsw

RSAS+ RSPASPQ c

ZSs

x

q1

qsw

qsw

V phai cua (4-55) co thm q1:( );..

1.1

202 cqcq

c.b.hR

Q swbtnfb

u ++++=

( ) )(c;qqc

MQ swbu 614.1 ++=Va TDng nguy him nht c0:

)(;qq

Mcsw

b 6241

0 +=iu kin cng theo lc ct se la:

( ) )(c;qqc

MQQ swbu 634.1max ++=Theo thc nghim:- Khi q1 0,5.qsw th c0 tnh theo cng thc:- Khi q1 > 0,5.qsw th c0 tnh theo cng thc (4-62);iu nay co ngha khi q1 be, gia tr c0 khng phu thuc vao s b tr ct ai.

)(;q

Mc b 6441

0 =

Trong tnh toan thit k, tnh ct ai (qsw) nh sau: * Khi )(QQ b 664;

6,01

max Trong o: )(qMQ bb 674;..2 11 =

Th )(M

QQqb

bsw 684;4

21

2max =

Th)(QQQ

hM b

bb 694;

6,01

max10

>>+ ( ) )(M

QQqb

bsw 704;

21max =* Khi

CU KIN CHU UN 32

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4.5.5.3 Tnh cu kin chu tai trong phn b u:Trong tnh toan thit k, tnh ct ai (qsw) nh sau:

* Khi )(QQ b 664;6,01

max Trong o: )(qMQ bb 674;..2 11 =

Th )(M

QQqb

bsw 684;4

21

2max =

Th)(QQQ

hM b

bb 694;

6,01

max10

>>+ ( ) )(M

QQqb

bsw 704;

21max =* Khi

Trong ca hai trng hp trn, ly ;.2 0

1maxh

QQq bsw

)(QhMQ bb 714;1

0max + )724(;

0

1max =h

QQq bswTh

Nu tnh c th phai tnh lai qsw theo cng thc sau:

* Khi

0

min.2 h

Qq bsw qsw1 - qsw2 th:

;qMcswi

bi =0

Trong o

- Khi q1 qsw1 - qsw2 th:

)(;qq

cqQcqc

M

clswsw

swb

744..

21

1max0111

++=

( ) )754(;. 032

211= hqqq

Mcb

b

swsw

b

( ) )(;cq

cqQQl swb 764. 011

012minmax1 +=

Trong oan ct ai c giam (nm ngoai oan l1) gia tr qsw2 khng bt buc phai thoa iu kin (4-60).4.5.5.5 Tnh cu kin chu tai trong tp trung:Trong trng hp nay cn tnh toan vi tt ca cac TDng ci xut phat t mep gi nhng khng vt qua TD co m men ln nht. c1

s

F1

s

F2

CU KIN CHU UN 34

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4.5.5.5 Tnh cu kin chu tai trong tp trung:

c1c2

s

F1

s

F2

Q1Q2= Q1- F1

Trong trng hp nay cn tnh toan vi tt ca cac TDng ci xut phat t mep gi nhng khng vt qua TD co m men ln nht.Gia tr qsw xac nh theo h s:

)774(; =bi

biii Q

QQTrong o )784(; =

i

bbi c

MQ

* Nu th: 0

0min0 .2

.h

cQ

Qbi

bii =< )794(;1. 0

0

0)( += i

iiisw c

Qq

* Nu th: 0

0 cci

ii < )804(;0

)( = cQQq biiisw

* Nu th: 00 h

ccc i

ii < ( ) )814(;2)( =

b

biiisw M

QQq

* Nu th: 0h

cii > )824(;

0)( = h

QQq biiisw

y: c0 ly bng ci nhng khng ln hn 2.h0;Cui cung ly gia tr qsw(i) ln nht xac nh ct ai.

CU KIN CHU UN 35

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4.5.5.6 Khoang cach ln nht gia cac ct ai: Co th xay ra trng hp pha hoai theo TD nghing nm gia 2 ct ai.

c=smax

T (4-43) ly c=smax, co:( ) )834(;...1. 204max += QhbRs btnb

H s b4 xet n thiu chnh xac cua khoang cach ai do thi cng, s sai lch v phng cua khe nt nghing do BT khng ng nht.4.5.5.7 Yu cu cu tao i vi ct ai trong dm va ban:

l

l/4

l

l/4 l/4

Khoang cach cu tao cua ct ai uct:oan u dm:

khi h 450 uct 150

2h

khi h > 450 uct 500

3h

oan gia dm (co Q be co th khng cn tnh ct ai):

khi h > 300 uct 500

43h

Vi dm co h

CU KIN CHU UN 36

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5.6 Tnh ton ct ai v ct xin4.5.6 Tnh ton cu kin c ct ai v ct xin:Ct xin co nhim vu chu phn lc ct vt qua kha nng cua ai va BT trong vung coQ>Qu am bao cng trn TDng ct qua BT nm gia mep gi ta va u lp ct xin th nht va gia cac lp ct xin tip theo.

smaxsmaxsmax

F

iu kin cng (4-47) trn TDng c ct qua ca ct ai va ct xin:

)844(;sin... , ++ incsswswb ARcqcMQ

Trong o As,inc -Tng din tch cac lp ct xin ct qua mt ct nghing c.

Khi thit k cn kim tra cng cua tt ca cac mt ct nghing xut phat tmep gi va t cui cua cac lp ct xin.Ngoai ra cn kim tra cng cua cac TDng co im cui tai im t cua lc tp trung nm trong khu vc co ct xin. F

c1c2

c3c0

c

Khi kim tra theo (4-84) cn lu y :- Phai k n tai trong phn b q1.- Khi tnh qsw.ci, nu ci>c0 th phai ly ci=c0; khi ci>2.h0 th phai ly ci=2.h0.

i

bc

M- Khi tnh phai thoa cac yu cu

khng ch (4-50a), (4-50b).

CU KIN CHU UN 37

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4.5.7 Kim tra cng trn TDng chu m men:Tit din nghing chu tc dng ca m men cn c tnh ton ti cc v tr ct hoc un ct thp dc, cng nh ti vng gn gi ta ca dm v u t do ca cng xn. Ngoi ra, tit din nghing chu tc dng ca m men cn c tnh ton ti cc v tr thay i t ngt hnh dng ca cu kin (ct mt phn tit din, v.v...).

Rsw Asw

c

Rsw Asw

Rsw Asw

Nb

Rsw As, inc

zsw

zsw

zsw

zs, inc

Rs As

z

s

s s s

)514(;, ++ incssws MMMMTi cc v tr gn gi ta ca cu kin, m men Ms chu bi cc ct thp dc ct qua vng chu ko ca tit din nghing c xc nh theo cng thc: ;.. ssss zARM =trong : As din tch ct thp dc ct qua tit din nghing;

zs khong cch t hp lc trong ct thp dc n hp lc vng chu nn.M men Msw c chu bi cc ct thp ai vung gc vi trc dc cu kin, c bc khng i trong phm vi vng chu ko ca TDng ang xt, c xc nh theo cng thc: )874(;..5,0 2 = cqM swswKhai trin iu kin (4-51) theo cac ct thep Ms, Msw va Ms,inc c:

)854(;...... ,, ++ incsincsswswswswsss zARzARzARM

CU KIN CHU UN 38

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4.5.7 Kim tra cng trn TDng chu m men:M men Ms chu bi cc ct thp dc: ;.. ssss zARM =M men Msw c chu bi cc ct thp ai: )874(;..5,0 2 = cqM swswiu kin cng trn TDng chu m men :

)854(;...... ,, ++ incsincsswswswswsss zARzARzARMChiu cao vung nen x c xac nh t phng trnh cn bng:

)864(;0cos...'..0 , =+= incsswsssscbb ARARARARXTrong o Ab la din tch vung BT chu nen (nu la TD ch nht th Ab = b.x).

( ) )(;.ac.zz ss,inc 884sincos 1 +=4.5.7.1 Kim tra neo ct thep doc chu keo tai gi ta t do:

la

M

* Trng hp dm co ca ct xin va lc tp trungiu kin (4-85) kim tra trn TDng nguy him nht co:

)934(;sin.. , +

=qq

ARFQc

sw

incsswi

Trong o Q -lc ct TD gi taF, q -Tai trong tp trung va tai trong phn b

trong pham vi TDng.Gia tr c tnh c theo (4-93) khng c ln hn chiu dai phn k gi ta ma pha ngoai oan o thoa man iu kin:

ng vi gia tr c 0,8.cmax (cmax = 2,5.h0).)944(;....8,0

204

chbRQ btb

CU KIN CHU UN 39

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4.5.7.1 Kim tra neo ct thep doc chu keo tai gi ta t do:

la

M

* Trng hp dm co ca ct xin va lc tp trung:

)934(;sin.. , +

=qq

ARFQc

sw

incsswi

Trong o Q -lc ct TD gi taF, q -Tai trong tp trung va tai trong phn b

trong pham vi TDng.Gia tr c tnh c theo (4-93) khng c ln hn chiu dai phn k gi ta ma pha ngoai oan o thoa man iu kin:

ng vi gia tr c 0,8.cmax (cmax = 2,5.h0).)944(;....8,0

204

chbRQ btb

* i vi dm chu tai trong phn b u, khng t ct xin va ct ai comt khng i, iu kin (4-85) c thay bng (4-95):

( )( ) )954(;....2 0 + qqMzARQ swsssTrong o Q -Lc ct TD gi ta; M0 -M men TD mep gi ta.

Cho phep khng phai kim tra cng trn TDng theo m men khi thoa man cac iu kin sau:

)964(;....8,0;...2204

0max chbRQhbRQ btbbt

Trong o Q -Lc ct cui TDng; Qmax -Lc ct ln nht TD mep gi ta.

c: chiu dai hnh chiu TDng xut phat t mep gi ta vi c 2.h0.

CU KIN CHU UN 40

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* Yu cu neo ct thep doc chu keo tai gi ta t do:

C da

lala 5d;da 0,5d;C 15mm khi d 10 mm;C 1,5d khi d > 10mm;

d C

la

da d

la 10d;Trn oan neo phai han hai ct ngang.

Nu thoa man iu kin (4-42a) va (4-43) (TD b tng u chu ct): la 5d; trong khung va li han nu la ct trn th phai co mt ct ngang han vi ct doc cach u mut mt oan C.Nu iu kin (4-42a) va (4-43) khng thoa man (phai b tr ct ngang chu ct): la 10d; trong khung va li han nu la ct trn th trn oan neo phai han hai ct ngang vi ct doc cach u mut mt oan C.

4.5.7.2 Kim tra cng trn TDng theo m men i vi cng xon:

l1

q Fi

c

i vi cng xon chu tai trong tp trungkhe nt nghing se xut phat t im t tai tp trung tai gn u mut cng xon.

CU KIN CHU UN 41

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4.5.7.2 Kim tra cng trn TDng theo m men i vi cng xon:

l1

q Fi

c

* i vi cng xon chu tai trong tp trung khe nt nghing se xut phat t im t tai tp trung tai gn u mut cng xon. TDng nguy him nht:

)974(;sin.. ,1 =

sw

incsswqARQ

c

Trong o Q1 la lc ct tai TD u khe nt nghing.Gia tr c tnh c theo (4-97) khng c ln hn khoang cach t khi im TDng n mep gi ta.Kim tra cng trn TDng theo (4-85) vi: )984(;.

2.. 11 +

+= cFlclqM i

* i vi cng xon chu tai trong phn b q TDng nguy him nht se kt thuc gi ta va co:

( ) )994(;... += qqlzARc

swan

sss

Trong o As la din tch ct doc c keo n u mut cng xon.zs c xac nh vi TD tai gi ta.

Nu c < l-lan th vic kim tra theo cng trn TDng co th bo qua.

* i vi cng xon co chiu cao TD tng dn theo lut bc nht v pha gi ta, khi xac nh TDng nguy him theo (4-97) gia tr cua t s phai c giam i mt lng bng: Rs.As.tg khi mep chu nen nghing;

Rs.As.sin khi mep chu keo nghing; ( la goc nghing so vi phng ngang)

CU KIN CHU UN 42

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4.5.7.3 Kim tra cng trn TDng theo m men khi giam ct doc chu keo:a) Biu bao vt liu: (BBVL) h0/2

am bao cng trn TDng N1-N1 thZs,inc ZS.

Zs,inc ZS

N1

N1ZS

II

III

I B

B

Wb) Un ct dc chu ko:

W

A

MA

O

O

MO

Vy khoang cach t im un ct thep doctrong vung keo (Tit din I-I) n TD ma tai oct doc c s dung ht kha nng chu lc(Tit din tnh toan II-II) phai (h0/2). c) Ct ct dc chu ko: Tai gi lng thep doc mep trn nhiu. Xagi M giam, tai tit din O-O theo tnh toan coth ct bt ct doc (Tai gi la AS, ct bt AS2, con lai AS1: AS = AS1+ AS2).Tit din O-O goi la mt ct ly thuyt.Xet trn TD nghing OA co MA>M0 nhng ct chu keo la AS1 va co thm mt s t ct aise khng u chu m men un MA. khng b pha hoai trn TD nghing do m men ta phai keo ct thep ctgiam ra ngoai mt ct ly thuyt O-O mt oan W na (n im B).

Q: Lc ct tai im ct ly thuyt, ly bng dc cua biu bao mmen.d: ng knh ct doc c ct giam. 5d: oan cn thit ct doc bt u chu lc.

Tit din B-B goi la mt ct thc t.)1004(;20.52.q

Qsw

+= ddW

CU KIN CHU UN 43

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4.5.7.3 Kim tra cng trn TDng theo m men khi giam ct doc chu keo:

c) Ct ct dc chu ko: Tai gi lng thep doc mep trn nhiu. Xagi M giam, tai tit din O-O theo tnh toan coth ct bt ct doc (Tai gi la Fa, ct bt AS2, con lai AS1: AS = AS1+ AS2).

TD O-O goi la mt ct ly thuyt.Xet trn TD nghing OA co MA>M0 ct chu keo la AS1 se khng u chu m men un MA. khng b pha hoai trn TD nghing do m men ta phai keo ct thep ctgiam ra ngoai mt ct ly thuyt O-O mt oan W na (n im B).

Khi trong vung ct thep co ct xin th:

Zs,inc Za

N1

N1

h0/2

Za

II

III

I B

B

W

W

A

MA

O

O

MO

a) Biu bao vt liu: (BBVL)b) Un ct dc chu ko:

Q: Lc ct tai im ct ly thuyt, ly bng dc cua biu bao mmen.d: ng knh ct doc c ct giam. 5d: oan cn thit ct doc bt u chu lc.

Tit din B-B goi la mt ct thc t.)1004(;20.52.q

Qsw

+= ddW

)1014(;20.52.q

Q-Q

sw

incs, += ddWTrong o Qs,inc= Rsw.As,inc.sin vi As,inc la din tch cua ct xin trong vung ct thep. n gian va an toan co th ly As,inc la din tch ct xin trn oan: ;2.q

Q-Q

sw

incs,

KHOA XY DNG DD&CN SAN PHNG 1

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SAN PHNG.5.1. Gii thiu chung

5.1. Gii thiu chung:San BTCT co u im la kha nng chu lc ln, a nng, thit k va thi cng n gian.

5.1.1 Phn loai: a. Theo PP thi cng: co san toan khi, san lp ghep va san na lp ghep. b. Theo s kt cu: co san sn va san khng sn. - San sn toan khi co ban loai dm (ban san lam vic 1 phng).- San sn toan khi co ban k 4 canh.- San sn c.- San sn pa nen lp ghep. 5.1.2 Phn bit ban loai dm va ban k 4 canh: - Khi ban ch co lin kt 1 canh hoc 2 canh idin, tai trong truyn theophng co lin kt. Ta goi la ban loai dm.

q

l l

q

l

q


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- Khi ban co lin kt 4 canh, taitrong c truyn vao lin kttheo ca 2 phng. Ta goi loai nay la ban k 4 canh.

Xet ban k t do 4 canh chu taitrong phn b u;

vong tai im gia cua mi dai:

q1

l1

q2 l2

l1

q1

q2 l21

1

Goi tai trong truyn theo phng l1 la q1, tai trong truyn theo phng l2 la q2.

Ta co: q = q1+ q2. (5 - 1)

+ Theo phng l1: ;E.J.lq.

3845f

411

1 =Ta co: ;.lq.lqff 422

41121 == (5 - 2)

Ct cac dai ban theo 2 phng.

T (5 - 1) va (5 - 2): qll

lq .42

41

42

1 += va ;.424141

2 qlllq +=

(5 - 3)

;. 241

42

1 qllq = (5 - 4)

+ Theo phng l2: ;E.J.lq.

3845f

422

2 =

Vy tai trong truyn theo phng canh ngn nhiu hn.Khi tnh toan thc t, nu l2>2.l1 th co th xem ban lam vic 1 phng.


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5.1.3 Khai nim khp deo-S phn b lai ni lc do khp deo: 5.1.3.1 Khai nim khp deo: Xet 1 dm chu un cho n khi b pha hoai. Gia s dmc cu tao thep sao cho khi b pha hoai co:

Vung BT co bindang deo ln

ct thep chu keo atgii han chay

Tai TD pha hoai xut hin 1 khp deo co m men khp deo Mkd = Mgh.

- ng sut trong ct thep chu keo at gii han chay;- ng sut trong BT vung nen at gii han chu nenva co bin dang deo ln;

Vi kt cu tnh nh, s xut hin khp deo ng thi vi kt cu b pha hoai.Vi kt cu siu tnh xut hin khp deo lam giam 1 bc siu tnh cua h. S pha hoaicua kt cu khi s khp deo u h b bin hnh.

- Trang thai khi xut hin khp deo cui cung trc khi kt cu b pha hoai goila trang thai cn bng gii han.- Phng phap tnh theo s deo (xet s hnh thanh khp deo cho n khi h spb pha hoai) con goi la tnh theo trang thai cn bng gii han.


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5.1.3.2 S phn b lai ni lc: Xe

Documents

BTCT 1 - Phan cau kien co ban.pdf