Bài Giảng Kết Cấu Thép

Chng m au

AI CNG VE KET CAU THEP

Khai niem Ket cau thep (KCT) dung e ch nhng ket cau chu lc cua cac cong trnh xay dng lam bang

thep hoac kim loai khac noi chung.

0.1. U VA KHUYET IEM CUA KET CAU THEP

0.1.1. u iem

Kha nang chu lc ln, o tin cay cao; Kha nang chu lc ln: vat lieu thep co cng o ln;

o tin cay cao: cau truc thuan nhat cua vat lieu, s lam viec an hoi va deo cua vat lieu gan sat

nhat vi cac gia thiet tnh toan.

Trong lng nhe; 1

Ket cau thep nhe nhat trong so cac ket cau chu lc nh:

BTCT, gach a, go.

(0.1)

Trong o:

: trong lng rieng thep;

f: cng o tnh toan thep;

oi vi thep: c=3.7*10-4 1/m

oi vi be tong: c=2.4*10-3 1/m

oi vi go: c=5.4*10-4 1/m

Tnh cong nghiep hoa cao;

Tnh c ong trong van chuyen, lap rap;

Tnh kn.

2

cf

0.1.2. Nhc iem

B an mon;

Chu la kem.

Thep khong chay nhng nhiet o t=(500600)0C, thep

chuyen sang deo, mat kha nang chu lc, ket cau b sup

o de dang.

0.2. PHAM VI NG DUNG

+ Nha cong nghiep.

+ Nha nhp ln.

+ Khung nha nhieu tang.

+ Cau ng bo - ng sat.

+ Ket cau thap cao.

+ Ket cau ban.

+ Ket cau di ong.

3

0.3. YEU CAU OI VI KET CAU THEP

Yeu cau ve s dung.

Thoa man cac yeu cau ve chu lc e ra do ieu kien s dung;

am bao o ben lau thch ang cua cong trnh;

ep, ac biet quan trong oi vi nha cong cong co ket cau lo ra ngoai;

Yeu cau ve kinh te.

Tiet kiem vat lieu;

Tnh cong nghe khi che tao;

Lap rap nhanh;

ien hnh hoa KCT;

4

Chng 1

VAT LIEU VA S LAM VIEC CUA KET CAU THEP

1.1. THEP XAY DNG

1.1.1. Phan Loai Thep Xay Dng

+ Thep va gang la hp kim en cua Fe va C, ngoai ra

con cac chat khac co t le khong ang ke nh: O, P, Si,

v.v

+ Qua trnh luyen gang va thep

T quang sat (Fe2O

3 , Fe

3O

4 ) luyen trong lo cao

gang (hp kim Fe, C vi lng C chiem tren 1,7%)

qua lo luyen thep e kh bt C trong gang thep.

5

a. Theo thanh phan hoa hoc cua thep

+ Thep cacbon, vi lng C

+ Thep tnh: trong qua trnh nguoi khong co hi boc ra

nh thep soi, do a c them nhng chat kh oxy nh

Si, Al, Mn, v.v Loai thep nay chu lc ong tot, kho b pha hoai gion.

+ Thep na tnh: la trung gian gia thep tnh va thep soi,

trong o oxy khong c kh hoan toan.

1.1.2. Cau Truc Va Thanh Phan Hoa Hoc Cua Thep

a. Cau truc cua thep

Thep co cau truc tinh the, thep gom co hai to chc

chnh:

+ Ferit (la sat nguyen chat), chiem 99% the tch, mau

sang, co tnh mem va deo.

+ Xementit, la hp chat Fe3C, rat cng va gion.

7

b. Thanh phan hoa hoc cua thep

Thep cacbon, ngoai hai thanh phan chnh la sat va

cacbon, con co cac thanh phan phu khac nh Mn, Si, P,

S, v.v

+ Mn, lam tang cng o va o dai cua thep. Neu ham

lng Mn vt qua 1.5%, thep tr nen gion.

+ Si, lam tang cng o cua thep nhng lam giam tnh

chong g, tnh de han. Ham lng Si khong qua 0.3%

oi vi thep cacbon thap.

+ P, lam giam tnh deo va o dai va cham cua thep,

ong thi lam thep tr nen gion nguoi (gion nhiet o

thap).

+ S, lam thep tr nen gion nong (gion nhiet o cao),

nen de b nt khi han va ren.

8

1.2. QUY CACH THEP CAN DUNG TRONG XAY

DNG

Ket cau xay dng c che tao t cac thep tam, thep

hnh co nhieu loai kch thc khac nhau. Thep can nong

bao gom cac loai thep sau:

+ Thep hnh;

+ Thep tam;

+ Thep hnh dap, can nguoi;

+ Thep pho thong;

9

10

x x

y

y

x 0

0 x y

0

y 0

b b

z 0

d

B

x y

y

b

0

y d

u

x 0

Hnh 1.2.a : thep goc eu canh Hnh 1.2.b : thep goc khong eu canh

y

Hnh 1.2.c : thep ch I

y

x x

b

h

d

t

y

x

y

z 0

b

h

d

Hnh 1.2.d : thep ch

d

Hnh 1.2.e : thep ong

D

1.2.1. Thep Hnh

a. Thep goc

Co 2 loai: eu canh va khong eu canh, vi t le hai canh khoang 1:1.5 en 1:2.

Thep goc eu canh gom 50 loai tiet dien t nho nhat la L20x20x3 en ln nhat la L250x250x35.

Thep goc khong eu canh gom 72 loai tiet dien t nho nhat la L30x20x3 en ln nhat la L200x150x25.

ac iem: canh co hai mep song song vi nhau, tien cho viec cau tao lien ket, chieu dai thanh thep goc t

413m.

Pham vi s dung: thanh cua dan, thanh cua he giang, lien ket vi cac loai thep khac e tao nen cac cau kien

to hp nh ghep vi cac ban thep thanh tiet dien cot

rong, tiet dien dam ch I,v.v

11

b. Thep ch I

Gom co 23 loai tiet dien, chieu cao t 100600mm

K hieu I30 (cao 30cm), I30a (cao 30cm, canh rong va day hn I30), chieu dai t 413m.

Co o cng theo phng truc x rat ln so vi phng truc y.

Pham vi s dung: lam dam chu uon, hoac cot (nen tang o cng oi vi truc y bang cach m rong them canh hoac ghep

hai thep I lai).

c. Thep ch

Gom co 22 loai tiet dien, t 5 en 40. Ky hieu 22 (cao 22cm), chieu dai t 413m.

Thep ch co mot mat bung phang va cac canh vn rong nen tien lien ket vi cac cau kien khac.

Pham vi s dung: lam dam chu uon, ac biet hay dung lam xa go mai chu uon xien hoac c ghep thanh thanh tiet dien

oi xng, dung lam cot, lam thanh dan cauv.v.

12

d. Thep ong

Co hai loai: khong co ng han doc va co ng han doc.

Thep ong co tiet dien oi xng, vat lieu nam xa truc trung hoa nen o cng tang, chu lc khoe, ngoai ra

chong g tot.

Pham vi s dung: dung lam cac thanh dan, ket cau cot thap cao.

1.2.2. Thep Tam

c dung rong rai v tnh chat van nang, co the tao ra

cac loai tiet dien co hnh dang va kch thc bat ky. Co

cac loai sau:

+ Thep tam pho thong, co be day =460mm, rong

B=1601050mm, dai L=612m. Thep tam pho thong co

bon canh phang nen s dung rat thuan tien.

13

+ Thep tam day, co =4160mm, B=6003000mm, L=48m. Thep tam day co be rong ln nen hay dung

cho ket cau ban.

+ Thep tam mong, co =0.24mm, B=6001400mm, L=1.24m. Thep tam mong dung e tao cac thanh

thanh mong bang cach dap, can nguoi, dung lp

mai,v.v.

1.2.3. Thep Hnh Dap, Can Nguoi

ay la loai thep hnh mi so vi thep can. T cac thep

tam mong, day =216mm, mang dap, can nguoi ma thanh.

+ Co cac loai tiet dien: thep goc eu canh-khong eu

canh, thep ch , thep tiet dien hop, v.v.

+ Thep hnh dap, uon nguoi co thanh mong, nen nhe

hn nhieu so vi thep can nong.

14

+ Pham vi s dung: dung chu yeu cho cac loai ket cau

thep nhe, cho nhng cau kien chu lc nho nhng can

co o cng ln.

+ Khuyet iem: Co s cng nguoi nhng goc b uon,

chong g kem. Cha co tieu chuan cho loai thep nay,

can tham khao them cac tieu chuan cua Nga, Anh,

Eurocode, v.v.

1.2.4. Thep Pho Thong

+ Co ng knh t 680mm.

+ Co 2 loai: trn va co gan.

+ Pham vi s dung: thanh cang cua vom, boulone neo,

boulone chu lc. Thng dung trong ket cau be tong

cot thep.

15

1.3. S LAM VIEC CUA THEP CHU TAI

TRONG

1.3.1. S Lam Viec Chu Keo Cua Thep

a. Bieu o ng suat bien dang khi keo (thep C thap)

16

tl

c

21

24

38

40

0

0 4 22 %16

b

B

C D

E

Hnh 1. Bieu o quan he gia ng suat va bien dangHnh 1.3.1. Bieu o ng suat bien dang khi keo

kN/cm2

ng suat =P/A, kN/cm2;

Bien dang t oi: =l/l, %;

Trong o:

P: tai trong;

A: tiet dien ban au cua mau;

L: chieu dai ban au cua mau;

l: o dan dai cua mau ng vi tng cap

tai trong;

+ oan t 0 en B: (, ) co quan he tuyen

tnh, =E, giai oan t le, tl (

h);

E: module an hoi;

Vi thep cacbon thong thng, E=2.06e6 daN/cm2;

17

l

l+

l

l

Hnh 1.3.2. Chieu dai mau trc

va sau khi keo

+ oan t B en C: (, ) co quan he phi tuyen, thep

khong con lam viec an hoi na, giai oan an hoideo;

+ oan t C en D: hau nh la oan nam ngang, giai

oan chay deo. tang, =const, gii han chay c;

+ oan t D en E: thep khong chay na, giai oan

cung co, gii han ben b ,

0=2025%;

b. Cac ac trng c hoc chu yeu cua thep

+ Gii han t le, tl h ;

+ Gii han chay c, o la ng suat ln nhat co the co

trong vat lieu, khong c phep vt qua (=0.2%);

+ Gii han ben b : con goi la cng o tc thi cua

thep, xac nh mot vung an toan d tr gia trang thai

lam viec va trang thai pha hoai;

18

+ Bien dang khi t 0

: ac trng cho o deo, o dai

cua thep;

+ Module an hoi E;

Tuy thuoc vao tr so cua , co the ap dung cac l thuyet tnh toan sau:

Khi tl: dung l thuyet an hoi, vi E=const;

Khi tl

* S lam viec chu nen cua thep khong khac s lam viec

chu keo, cung E, tl,

h,

c. Ch co trong giai oan cung

co th khong xac nh c b. Do o, trong giai oan

lam viec an hoi va an hoi deo, cac ac trng c hoc

tnh toan cua thep chu keo chu nen lay giong nhau.

1.3.2. S Pha Hoai Gion Cua Thep

S pha hoai gion la s pha hoai bien dang nho, kem

theo vet nt, vat lieu lam viec trong giai oan an hoi.

a. Hien tng cng nguoi

o la hien tng tang tnh gion cua thep sau khi b bien

dang deo nhiet o thng. Thep sau khi b bien dang

deo th tr nen cng hn, gii han an hoi cao hn va

bien dang khi pha hoai nho hn.

20

+ S cng nguoi xay ra khi gia cong nguoi cac cau kien:

uon nguoi, cat bang may cat, ot lo, v.v

b. Thep chu trang thai ng suat phc tap - s tap trung

ng suat

Trng hp hay gap cua trang thai ng suat phc tap la

trng hp ng suat cuc bo, gay bi cac bien oi ot

ngot cua hnh dang cau kien.

+ Khi cau kien co lo khuyet, ranh cat th ng lc (quy

ao cac ng suat chnh) se khong con song song eu

an, ma uon cong xung quanh cho cat. ng lc tap

trung chng to ng suat cho o tang cao va tai o ton tai

ng suat theo hai phng x va

y lam thep tr nen gion.

+ Ket cau chu tai trong ong lc th s tap trung ng

suat la nguy hiem v lam cho thep de b pha hoai gion.

21

22

Hnh 1.3.3. Cac quy ao ng suat khi keo

1.3.3. Thep Chu Tai Trong Lap

+ Khi thep chu tai trong lap, no co the b pha hoai ng

suat nho hn gii han ben o la s moi cua thep.

+ S pha hoai ve moi mang tnh chat pha hoai gion,

thng xay ra ot ngot va kem theo vet nt.

+ ng suat pha hoai moi cua thep goi la cng o moi ff,

ff phu thuoc vao so chu ky lap, tnh chat thay oi cua tai

trong va mc o tap trung ng suat. Gia tr cua ff, tra

bang.

1.3.4. S hoa gia cua thep

+ Theo thi gian, tnh chat cua thep thay oi dan: c,

b

tang len, o gian va o dai va ap giam i, thep tr nen

gion hn.

23

+ Nguyen nhan: trong cac tinh the ferit van con cac chat

C, N hoa tan. Cac chat nay dan dan tach ra va tao nen

cac lp cng gia cac hat ferit.

1.3.5. Anh hng cua nhiet o

+ nhiet o t=2003000C: tnh chat cua thep thay oi

rat t;

+ nhiet o t=3003300C: thep tr nen gion hn;

+ nhiet o t>3300C:

c,

b giam rat nhanh;

+ nhiet o t=6006500C:

c=0;

+ nhiet o t>15000C: thep bat au chuyen sang the

long;

+ nhiet o t

1.4. TNH TOAN CAU KIEN

1.4.1. Cau Kien Chu Keo ung Tam

Cau kien chu keo c kiem tra ben theo cong thc:

Trong o:

+ N: noi lc doc do tai trong tnh toan;

+ An: dien tch thc cau kien (a tr i cac giam yeu);

+ c: he so ieu kien lam viec, tra bang;

+ f: cng o tnh toan cua thp ly theo gii hn chy;

+ ft: cng o tnh toan cua thp ly theo sc bn ko t;

25

ben han gii theo

chay han gii theo

-

-

u

ct

c

nf

f

A

N

(1.1)

(1.2)

+ u =1.3, he so an toan;

1.4.2. Cau Kien Chu Uon

a. Tnh cau kien chu uon trong giai oan an hoi

Trong o:

+ M, V: moment uon va lc cat do tai trong tnh toan;

+ Wn: moment chong uon cua tiet dien thc;

+ I: moment quan tnh cua tiet dien nguyen;

+ S: moment tnh (nguyen) cua phan tiet dien trt oi

vi truc trung hoa;

26

c

n

fW

M

cvfIt

VS

(1.3)

(1.4)

+ t: be day thanh cau kien;

b.Tnh cau kien chu uon co bien dang deo

Trong o:

+ Wd

= 2S: moment chong uon deo;

Tiet dien ch nhat: Wd=1.5W;

Tiet dien ch I: Wd=1.12W;

+ : ng suat tiep;

27

c

d

fW

M

ctf 1513 22 ,

(1.5)

(1.6)

c.Tnh toan cau kien theo TTGH th hai

: o vong;

: o vong gii han cho phep, tra bang;

1.4.3. Cau Kien Nen ung Tam

a.Tnh ve ben

b.Tnh ve on nh

: he so uon doc, tra bang;

28

(1.7)

c

n

fA

N (1.8)

cfA

N (1.9)

1.4.4. Cau Kien Chu Keo Lech Tam Va Nen Lech Tam

a.Tnh cau kien chu keo lech tam va nen lech tam

+ Kiem tra o ben trong giai oan lam viec an hoi theo

cong thc:

+ Khi xet en bien dang deo:

He so c tuy thuoc vao dang tiet dien, tra bang;

29

c

n

fM

A

N

nW(1.10)

1

2/3

cncn fcW

M

fA

N

(1.11)

b.Tnh ve on nh cua thanh nen lech tam

+ Kiem tra on nh trong mat phang uon:

e: he so giam cng o tnh toan;

cr

e: ng suat ti han;

+ Kiem tra on nh ngoai mat phang uon:

y: he so uon doc khi nen ung tam;

30

ce fA

N (1.12)

f

e

cre

(1.13)

c

y

fAc

N

(1.14)

Chng 2

LIEN KET

Hien nay, trong ket cau thep dung hai phng phap lien

ket chnh la:

+ Lien ket han;

+ Lien ket boulone;

2.1. LIEN KET HAN

La s lien ket gia cac phan t cua cac kim loai b nong

chay (kim loai can han va que han).

2.1.1. u iem

+ Giam cong che tao va khoi lng kim loai;

+ Hnh thc cau tao lien ket n gian;

+ Ben, co tnh kn cao;

31

2.1.2. Nhc iem

+ Gay bien hnh han va ng suat han trong lien ket lam

tang tnh gion cua vat lieu;

+ Kho kiem tra chat lng ng han;

2.1.3. Cac Phng Phap Han Trong Ket Cau Thep

a. Han ho quang ien bang tay

32

Hnh 2.1. S o han ho quang ien bang tay

Tay cam

Nguon

ien

Day dan

Que han

Ho quang

Thep c

ban

+ Nguyen ly

Di tac dung cua dong ien ho quang ien lam

nong chay mep cua thep c ban va que han. Hai kim

loai long hoa lan vi nhau, nguoi lai tao thanh ng

han.

+ Que han (TCVN 3223:1994)

Dung que han (chieu dai L=200450mm) loi kim loai

(ng knh D=1.66mm) co thuoc boc day t=11.5mm

(thuoc han, gom khoang 80% la CaCO3).

b. Han ho quang ien t ong

+ Nguyen ly

Thuoc han c rai trc thanh lp day tren ranh han.

Day han c t ong nha dan theo toc o di chuyen

eu cua may han.

33

+ u iem

Toc o han nhanh (gap 510 lan han tay);

Chat lng ng han tot;

+ Nhc iem

Ch han c cac ng han nam thang hoac tron;

Khong han c cac ng han ng, ngc;

34

Hnh 2.2. S o han ho quang ien t

ong

Ong hut thuoc han

Day han tran

May han

Pheu rai thuoc

han

Ho quang

chm

Thuoc han

c. Cac yeu cau chnh khi han va phng phap kiem tra

chat lng ng han

+ Cac yeu cau chnh khi han

Lam sach g tren mat ranh han;

Cng o dong ien phai thch hp;

Gia cong mep ban thep ung qui nh;

Chon que han phu hp;

Phong nga bien hnh han;

+ Cac phng phap kiem tra chat lng ng han

Kiem tra bang mat;

Dung cac phng phap vat ly nh sieu am, ien t, v.v

35

2.1.4. Cac Loai ng Han Va Cng o Tnh Toan

a. ng han oi au

+ Cau tao

La ng han lien ket trc tiep hai cau kien cung nam trong mot mat phang;

ng han oi au co the thang goc hoac xien goc vi truc cua cau kien;

36

Hnh 2.3. ng han oi au

+ u va nhc iem

u iem

Truyen lc tot;

Lam viec giong nh thanh c ban;

Nhc iem

Gia cong mep ban thep (khi ban thep day, t = > 8mm);

+ Cng o tnh toan cua ng han oi au

Khi chu nen (khong phu thuoc vao phng phap kiem tra chat lng ng han)

fwc

= f (f, cng o tnh toan cua thep c ban);

Thep CCT34, fwc

= 2100daN/cm2;

C, nhom C;

CT, cacbon thng;

fu = 34kN/cm

2, cng o tieu chuan cua thep theo sc

ben keo t;

37

Khi chu keo

- Dung phng phap vat ly kiem tra chat lng

ng han

fwt

= f, thep CCT34, fwt

= 2100daN/cm2;

- Dung cac phng phap khac

fwt

= 0.85f, thep CCT34, fwt

= 1785daN/cm2;

Khi chu cat

fwv

= fv, thep CCT34, f

wv = 1200daN/cm

2;

fv, cng o tnh toan khi chu cat cua thep c ban;

38

b. ng han goc

+ Cau tao

La ng han nam goc vuong tao bi hai cau kien can han;

Tiet dien ng han la mot tam giac vuong can, canh cua tam giac goi la chieu cao ng han h

f;

39

Hnh 2.3. ng han goc

+ Chieu cao ng han

hfmax

1.2tmin

tmin

: chieu day nho nhat trong so cac ban thep c lien

ket;

40

Phng

phap

han

hfmin

khi chieu day cua ban thep tmax

, mm

46 610 1116 1722 2332 3340 4180

Tay 4 5 6 7 8 9 10

T

ong 3 4 5 6 7 8 9

Bang 2.1. Chieu cao nho nhat cua ng han goc

hfmin

, mm

Tuy theo v tr cua ng han so vi phng cua lc tac

dung ma chia ra:

ng han goc canh la ng han goc song song vi phng cua lc tac dung;

ng han goc au la ng han goc vuong goc vi phng cua lc tac dung;

41

ng han goc canh ng han goc

au

Hnh 2.4. Cac loai ng han goc

N

N

N N

+ S lam viec cua ng han goc canh

ng suat phan bo khong eu theo chieu rong, chieu dai ban thep;

Hai mut cua ng han chu max

;

42

Hnh 2.5. S phan bo ng suat trong ng han goc canh

Chu ong thi ca ng suat cat va uon. Trong tnh toan coi nh chung ch chu cat quy c va pha hoai theo hai

dang sau:

- mot trong hai tiet dien doc theo kim loai ng han

(tiet dien 1);

- theo bien nong chay cua thep c ban (tiet dien 2);

43

Hnh 2.6. Dang pha hoai va tiet dien lam viec cua ng

han goc canh

dang pha hoai cac tiet dien lam viec

+ S lam viec cua ng han goc au

Truyen lc eu theo be rong cua lien ket;

Chu ong thi ca ng suat cat, keo va uon. Trong tnh toan coi nh chung ch chu cat quy c va b pha hoai

theo tiet dien 1 va 2 giong ng han goc canh;

+ Cng o tnh toan cua ng han goc

ng vi tiet dien 1: cng o tnh toan chu cat cua thep ng han f

wf;

44

Loai que han theo TCVN 3223 : 1994 fwf

(daN/cm2)

N42, N42 - 6B 1800

N46, N46 - 6B 2000

N50, N50 - 6B 2150

Bang 2.2. Cng o tnh toan chu cat cua thep

ng han fwf

ng vi tiet dien 2: cng o tnh toan chu cat cua thep c ban f

ws = 0.45f

u;

fu: cng o tieu chuan cua thep theo sc ben keo t;

c. Cac cach phan loai ng han khac

+ Theo cong dung

ng han chu lc (e truyen lc);

ng han khong chu lc (e cau tao);

+ Theo v tr

ng han nam;

ng han ng;

ng han ngc;

+ Theo a iem che tao

ng han nha may;

ng han cong trng;

45

+ Theo tnh lien tuc cua ng han

ng han lien tuc;

ng han khong lien tuc;

Khoang cach ln nhat gia hai ng han, amax

:

amax

15tmin

: cau kien chu nen;

amax

30tmin

: cau kien chu keo hoac cac bo phan cau

tao;

tmin

: chieu day cua ban thep mong nhat;

46

47

Bang 2.3. Ky hieu cac loai ng han

2.1.5. Cac Loai Lien Ket Han Va Phng Phap Tnh

Toan

a.Lien ket oi au

+ Khi chu lc truc

Kiem tra ben:

(2.1)

48

Hnh 2.7. Lien ket han oi au thang chu lc truc

cwc

cwt

ww

wf

f

tl

N

A

N

b

Trong o:

N: lc keo hoac nen;

Aw: dien tch tnh toan cua ng han oi au;

t: be day tnh toan cua ng han, bang be day cua thep c ban (t = t

min);

lw: chieu dai tnh toan cua ng han, l

w = b - 2t;

b: chieu dai thc te cua ng han, chnh la chieu rong thep c ban;

c: he so ieu kien lam viec;

fwt

: cng o tnh toan cua ng han oi au khi chu

keo;

fwc


nen;

49

Khi cng tnh ton chu ko ca ng hn fwt

< f (f, cng

o tnh toan cua thep c ban), dung ng han xien;

(2.2)

50

Hnh 2.8. Lien ket han oi au xien chu lc truc

cwv

w

w

cwc

cwt

w

w

ftl

N

f

f

tl

N

cos

sin

Trong o:

w,

w: ng suat phap va ng suat tiep trong ng

han;

: goc nghieng cua ng han so vi phng cua lc truc N;

lw: chieu dai tnh toan cua ng han xien;

(2.3)

fwv


cat;

+ Khi chu M;

(2.4)

51

tb

lw 2sin

cwt

w

w fW

M

Trong o:

Ww: moment khang uon cua tiet dien ng han;

(2.5)

+ Khi chu M, V;

(2.6)

He so 1.15 ke en s phat trien cua bien dang deo

trong ng han.

52

6

2

w

w

tlW

ww

w

ww

w

cwtwwtd

tl

V

A

V

tl

M

W

M

f

2

22

6

15.13

b.Lien ket ghep chong dung ng han goc

+Tnh toan lien ket ghep chong chu lc truc

53

Hnh 2.9. Lien ket ghep chong

N N

a5tmin; t=25mm

t2 t1

Hnh 2.10. Cac tiet dien

lam viec

Tiet dien 1 (theo vat lieu ng han)

(2.7)

Tiet dien 2 (theo vat lieu cua thep c ban)

(2.8)

Trong o:

+ hf: chieu cao ng han goc;

+ lw: tong chieu dai tnh toan cua cac ng han;

+ f,

s: cac he so chieu sau nong chay cua ng han

ng vi cac tiet dien 1 va 2;

+ fwf

, fws

: cng o tnh toan chu cat quy c cua thep

ng han va thep c ban;

54

cwf

wff

flh

N

cws

wfs

flh

N

Khi thiet ke nen chon trc hf,

(2.8)

(fw)min

= min(ffwf

; sfws

);

lwmin

4hf va l

w 40mm;

lw 85

fh

f (ng han goc canh);

55

cwf

wfh

Nl

min)(

56 Bang 2.4. He so f va

s cua ng han goc

57

Bang 2.5. He so phan phoi noi lc N khi lien ket cac

thep goc vi thep ban

Loai thep goc Cach lien ket k 1 - k

eu canh 0.7 0.3

Khong eu canh

han theo canh

ngan

0.75 0.25

Khong eu canh

han theo canh

dai

0.6 0.4

c.Lien ket co ban ghep

e cac ban ghep truyen c lc, yeu cau:

Abg A (2.9)

Trong o:

Abg

: tong dien tch tiet dien cac ban ghep;

A: dien tch tiet dien cau kien c ban;

Tnh toan tng t lien ket ghep chong.

58

Hnh 2.12. Lien ket co ban ghep

Ban ghep

d.Lien ket hon hp

La lien ket oi au co them cac ban ghep vi cac ng

han goc.

+ Tnh toan

ieu kien ben:

(2.10)

59

Hnh 2.13. Lien ket hon hp

Ban ghep

N N

ccwt

bg

w fAA

N )(

fwt(c)


keo (nen);

Lc truyen qua ban ghep:

Nbg

= wA

bg (2.11)

Tong chieu dai can thiet cua ng han goc e lien ket mot ban ghep mot pha cua lien ket:

(2.12)

(fw)min

= min(ffwf

; sfws

);

e.Tnh toan lien ket han vi ng han goc chu moment

va lc cat

60

cwf

bg

wfh

Nl

min)(

+ Khi ch co M tac dung

Tnh theo vat lieu ng han (tiet dien 1)

(2.13)

Tnh theo vat lieu cua thep c ban (tiet dien 2)

(2.14)

Trong o:

(2.15)

(2.16)

Wwf(s)

: moment khang cua ng han theo tiet dien 1, 2;

61

cwf

wf

M fW

M 1

cws

ws

M fW

M 2

6

2

w

ffwf

lhW

6

2

w

fsws

lhW

+ Khi ch co V tac dung


(2.17)


(2.18)

Awf

, Aws

: dien tch tnh toan cua tiet dien ng han

tng ng vi cac tiet dien 1, 2;

Awf

= fh

flw (2.19)

Aws

= sh

flw (2.20)

+ Khi co M, V tac dung ong thi

62

cwf

wf

V fA

V 1

cws

ws

V fA

V 2


(2.21)


(2.22)

63

cwf

wfwf

td fA

V

W

M

22

cws

wsws

td fA

V

W

M

22

B. LIEN KET BOULONE

2.5. CAC LOAI BOULONE DUNG TRONG KET

CAU THEP

2.5.1. Cau Tao Chung Cua Boulone

a. Cau tao

64

Hnh 2.14. Cau tao cua boulone

d d0

Mu boulone

D

Phan b ren

l0

l

Than boulone: oan thep tron, d= 12 48mm; boulone neo co d 100mm;

d0: ng knh trong cua phan b ren;

Chieu dai cua phan ren: l0 2,5d;

Chieu dai boulone : l = 35 300 mm;

65

ecu (ai oc)

long en (em)

Hnh 2.15. Lien ket boulone

Thep c ban

Mu, ecu (ai oc) thng co hnh luc giac;

Long en (em): hnh tron phan phoi ap lc cua ecu len mat thep c ban;

b. Cac loai boulone

Tuy theo cach san xuat, vat lieu, tnh chat lam

viec cua boulone, co cac loai sau:

Boulone tho;

Boulone thng;

Boulone tinh;

Boulone cng o cao;

v.v

66

2.5.2. Boulone tho va boulone thng

c san xuat t thep cacbon bang cach ren, dap;

ng knh than boulone phai nho hn ng knh lo (lo loai C) t 2 3mm;

B bien dang nhieu khi lam viec chu trt;

ng dung:

Dung boulone (tho, thng) khi chung lam viec chu keo hoac e nh v cac cau kien khi

lap ghep;

Khong nen dung chung khi thep c ban co gii han chay f

y > 3800daN/cm

2;

67

2.5.3. Boulone tinh

Lam t thep cacbon, thep hp kim thap bang cach tien, o chnh xac cao;

ng knh than boulone phai nho hn ng knh lo (lo loai B) 0.3mm;

Khe h gia boulone va lo nho nen lien ket chat;

Co the lam viec chu cat;

ng dung:

Do tnh phc tap khi san xuat va lap at boulone

vao lo (phai dung bua go nhe) nen loai boulone

nay t dung.

68

2.5.4. Boulone cng o cao

c lam t thep hp kim, sau o gia cong nhiet;

e am bao kha nang chu lc cua lien ket boulone cng o cao, can gia cong mat cac

cau kien lien ket e tang tnh ma sat;

ng dung:

De che tao, kha nang chu lc ln, lien ket t bien dang nen c dung rong rai;

Thay the cho lien ket inh tan trong cac ket cau chu tai trong nang, tai trong ong;

69

2.6. S LAM VIEC CUA LIEN KET BOULONE

VA KHA NANG CHU LC CUA BOULONE

2.6.1. S Lam Viec Chu Trt Cua Lien Ket

Boulone (tho thng tinh)

a. Kha nang lam viec chu cat cua boulone

70


71

Hnh 2.15. S pha hoai do cat cua boulone


Khi ng knh boulone nho, ban thep day, boulone co the b pha hoai do cat ngang than;

Kha nang chu cat cua mot boulone c tnh theo cong thc:

[N]vb

=fvb

bAn

v (2.23)

Trong o:

fvb

: cng o tnh toan chu cat cua vat lieu

boulone;

b: he so ieu kien lam viec cua lien ket

boulone;

A: dien tch tiet dien ngang cua than boulone;

72

a.Kha nang lam viec chu cat cua boulone

nv: so lng mat cat tnh toan cua boulone, phu

thuoc vao so lng cau kien chu lc c lien

ket;

Khi co hai cau kien: nv = 1;

Khi co ba cau kien: nv = 2;

73

74

Bang 2.5. Cng o tnh toan chu cat fvb

va keo ftb cua

boulone

Trang

thai

lam

viec

Ky

hieu

Cap o ben

4.6 4.8 5.6 5.8 6.6 8.8 10.9

Cat fvb

150 160 190 200 230 320 400

Keo ftb

170 160 210 200 250 400 500

n v tnh: N/mm2

75

Bang 2.6. He so ieu kien lam viec b

76

Bang 2.7. Dien tch tiet dien cua boulone A, Abn

, cm2

(TCVN 1916:1995)

d, mm 16 18 20 22 24 27 30 36 42 48

p, mm 2 2.5 2.5 2.5 3 3 3.5 4 4.5 5

A 2.01 2.54 3.14 3.8 4.52 5.72 7.06 10.17 13.85 18.09

Abn

1.57 1.92 2.45 3.03 3.52 4.59 5.6 8.16 11.2 14.72

p: bc ren;

Abn

: dien tch thc cua tiet dien than boulone (a

tr giam yeu do ren);

b. Kha nang lam viec chu ep mat cua boulone

77

Hnh 2.16. S lam viec ep mat cua boulone

b. Kha nang lam viec chu ep mat cua boulone

Neu khoang cach gia cac lo boulone hoac t lo boulone en mep ban thep qua ngan th ban

thep co the b pha hoai trt (cat t theo cac

ng trt 2-3) do tac dung ep mat cua

boulone len thanh lo;

x,

y: cac ng suat trong ban thep;

Kha nang chu trt cua ban thep khi xem chieu dai trt l = a,

S = 2atfv (2.24)

Trong o:

a: khoang cach t trong tam lo boulone en

mep ban thep;

78

t: chieu day ban thep;

fv: cng o tnh toan chu cat cua thep lien ket;

Kha nang chu ep mat cua mot boulone c tnh theo cong thc:

[N]cb

= fcb

bd(t)min (2.25)

Trong o:

fcb

: cng o tnh toan chu ep mat cua boulone;

(t)min : tong chieu day nho nhat cua cac ban

thep cung trt ve mot pha;

79

80

Bang 2.8. Cng o tnh toan chu ep mat fcb

cua boulone

2.6.2. S Lam Viec Chu Trt Cua Lien Ket

Boulone Cng o Cao

Lc ma sat gia cac ban thep hoan toan tiep nhan lc trt do ngoai lc gay nen;

Boulone ch chu keo do s xiet chat ecu;

81

Hnh 2.17. S lam viec chu trt cua boulone cng o

cao

Kha nang chu trt cua mot boulone c tnh theo cong thc:

[N]b

= fhb

b1A

bn(/

b2)nf (2.26)

Trong o:

fhb

: cng o chu keo tnh toan cua vat lieu

boulone, fhb

= 0.7fub

;

fub

: cng o tc thi tieu chuan cua vat lieu

boulone;

: he so ma sat;

nf: so lng mat phang ma sat tnh toan;

Khi co hai ban thep lien ket: nf = 1;

Khi co ba ban thep lien ket: nf = 2;

82

b1

: he so ieu kien lam viec cua lien ket

boulone, gia tr phu thuoc vao so lng boulone

chu lc na;

b1

= 0.8 neu na < 5;

b1

= 0.9 neu 5 na < 10;

b1

= 1 neu na 10;

b2

: he so o tin cay cua lien ket;

83

84

Bang 2.9. He so ma sat va he so o tin cay b2

2.6.3. S Lam Viec Cua Boulone Khi Chu Keo

Kha nang chu keo cua mot boulone c tnh theo cong thc:

[N]tb

= ftb

Abn

(2.27)

ftb

: cng o tnh toan cua vat lieu boulone khi

lam viec chu keo;

85

Hnh 2.18. S lam viec chu keo cua boulone

2.7. TNH TOAN LIEN KET BOULONE

2.7.1. Tnh toan lien ket boulone chu lc truc

86

Hnh 2.19. Lien ket boulone chu lc truc

a. Chon ng knh boulone va kch thc cac

ban ghep

Cong trnh thong thng: d = (20 24)mm;

Cong trnh nang: d = (24 30)mm;

Kch thc ban ghep:

Abg A (2.28)

Trong o:

Abg

: tong dien tch tiet dien ngang cua cac ban

ghep;

A: dien tch tiet dien cua cau kien c lien ket;

Nen bo tr boulone theo phng vuong goc vi phng cua lc;

87

b. Tnh toan so lng boulone theo ieu kien

chu cat va ep mat

oi vi boulone (tho, thng, tinh), so lng boulone can thiet c tnh theo cong thc:

(2.28)

Trong o:

[N]minb

= min([N]vb

, [N]cb

);

Cau kien c ban b giam yeu do lo boulone, kiem tra ben cac ban thep theo cong thc:

(2.29)

88

cbNN

nmin

bl

n

fA

N

Trong o:

An: dien tch tiet dien thc cua ban thep c lay

nh sau:

oi vi boulone (tho, thng, tinh)

89

Hnh 2.20. Kiem tra ben ban thep

Khi boulone bo tr song song, tiet dien kiem tra la tiet dien 1-1:

An = A A

1 (2.30)

Trong o:

A1: dien tch giam yeu do cac lo boulone gay ra;

A1 = mtd

1 (2.31)

m: so lng lo tren mot hang boulone;

t: chieu day cau kien mong nhat;

d1: ng knh lo boulone;

Khi boulone bo tr so le th,

A1 = max(A

15; A

12345 s2t/4u) (2.32)

90

Trong o:

A15

: dien tch giam yeu do cac lo xep tren ng

15;

A12345

: dien tch giam yeu do cac lo xep tren

ng 12345;

91

Hnh 2.21. Cach xac nh dien tch thc

s: bc lo so le;

t: chieu day thanh thep co lo;

u: khoang cach ng lo;

bl: he so ieu kien lam viec, c lay nh sau;

+ bl = 1.1: dam ac, cot, ban noi;

+ bl = 1.05: ket cau thanh cua mai va san;

oi vi boulone cng o cao, so lng boulone can thiet c tnh theo cong thc:

(2.33)

[N]b: kha nang chu lc trt cua mot boulone;

92

cba

N

Nn

Kiem tra ben cac ban thep theo cong thc:

(2.34)

Khi chu tai trong tnh: An = A neu A

n 0.85A;

Khi An < 0.85A, tnh theo dien tch quy c

Ac = 1.18A

n;

Khi chu tai trong ong: An ;

bl = 1;

2.7.2. Tnh toan lien ket boulone khi chu keo

(2.35)

93

bl

n

fA

N

ctbNN

n

Trong o:

N: lc keo tac dung vao lien ket;

[N]tb

: kha nang chu keo cua mot boulone;

c: he so ieu kien lam viec;

2.7.3. Tnh toan lien ket boulone chu moment

va lc cat

M = Nili = N

1l1 + N

2l2 + + N

ili (2.36)

Trong o:

N1: lc tac dung len day inh ngoai cung;

Ni: lc tac dung len day inh th i;

li: canh tay on cua cac cap ngau lc N

i;

94

95

Hnh 2.22. Lien ket boulone chu moment va lc cat

Ni = N

1li/l

1 (2.37)

(2.38)

(2.39)

lmax

= l1: khoang cach gia hai day boulone

ngoai cung;

Goi m, so lng boulone tren mot day mot

pha cua lien ket;

Lc tac dung len mot boulone do M: (2.40)

96

2

1

122

2

2

1

1

1 ... ii ll

Nlll

l

NM

2

max

max1

il

MlNN

cbi

blM Nlm

Ml

m

NN min2

maxmax

oi vi boulone (tho, thng, tinh)

[N]minb

= min([N]vb

, [N]cb

); (2.41)

oi vi boulone cng o cao

[N]minb

= [N]b (2.42)

Lc tac dung len mot boulone do V:

NblV

= V/n (2.43)

n: so lng boulone tren mot na lien ket;

Lc tac dung len mot boulone do M, V: (2.44)

97

cbblVblMbl NNNN min22

98

Bang 2.10. Quy nh bo tr boulone

2.8. BO TR BOULONE

Khoang cach min

99

Hnh 2.23. Bo tr boulone dang song song

Khoang cach min

100

Hnh 2.24. Bo tr boulone dang so le

Khoang cach max (cau kien chu keo)

101

Hnh 2.25. Bo tr boulone cho cau kien chu keo

Khoang cach max (cau kien chu nen)

102

Hnh 2.26. Bo tr boulone cho cau kien chu nen

103

Hnh 2.27. Bo tr boulone cho thep goc

Chng 3

DAM THEP

3.1.AI CNG VE DAM VA HE DAM

3.1.1.Phan Loai Dam

Dam la mot loai cau kien c ban, chu uon la chu yeu;

Dam co cau tao n gian;

Dam dung lam dam san cong tac, dam cau chay, dam mai, dam cau, v.v

Chia dam lam hai loai: dam hnh, dam to hp;

104

a.Dam hnh

La dam c lam t mot thep hnh, tiet dien ch , ch , ch Z;

Dam ch co tiet dien oi xng theo ca hai truc, co W

x kha ln nen thng s dung cho

nhng dam chu uon phang nh lam dam san

nha, dam san cong tac, v.v

105 Hnh 3.1. Tiet dien dam hnh

Dam hnh ch , co tiet dien khong oi xng theo phng truc y-y;

Khi dam chu uon phang hien tng xoan;

Khi dam chu uon xien hp ly;

Dung lam xa go mai, dam tng,v.v

b.Dam to hp

La tiet dien c tao thanh t cac thep ban, thep hnh;

Dam to hp han boulone inh tan;

106

107

Hnh 3.2. Tiet dien dam to hp

3.1.2. He Dam Thep

a.He dam n gian

La he ch co mot he thong cac dam bo tr song song vi canh ngan cua o san;

Ban san lam viec nh ban ke hai canh;

108

Hnh 3.3. He dam n gian

b.He dam pho thong

109

Hnh 3.4. He dam pho thong

La he gom hai he thong dam at vuong goc vi nhau va song song vi hai canh cua o ban;

Ban san lam viec nh ban ke bon canh;

Dung he dam pho thong khi (L x B 36 x 12m) hoac khi san chu tai trong q 3000daN/m2;

c.He dam phc tap

Dung khi san chu tai trong q > 3000daN/m2;

Cac dam trong he dam c lien ket vi nhau bang ba cach:

Lien ket chong

Lien ket bang mat

Lien ket thap

110

111

Hnh 3.5. He dam phc tap

Lien ket chong

Lam tang chieu cao kien truc cua he san;

Ban san ch c goi len hai canh nen o cng va kha nang chu lc cua san khong cao;

112

Hnh 3.6. Lien ket chong

Lien ket bang mat

Giam chieu cao kien truc cua he san hoac co the tang c chieu cao cua dam;

Ban san ch c goi len bon canh nen o cng va kha nang chu lc cua san cao;

113

Hnh 3.7. Lien ket bang mat

Lien ket thap

Ban san ch c goi len hai canh nen o cng va kha nang chu lc cua san khong cao;

114

Hnh 3.8. Lien ket thap

3.1.3. Cau Tao Va Tnh Toan Ban San Thep

Khoang cach cac dam va chieu day ban san thep EJ, kha nang chu lc cua ban san;

Tnh toan ban san thep

Xac nh chieu day thep ban lam ban san t;

Nhp ban san l;

Tnh toan thiet ke cac dam ban san;

Thong ke vat lieu cho ban san, he dam;

115

Bieu thc gan ung gia l, t:

(3.1)

116

Bang 3.1. Quan he gia tai trong tac dung len

san va chieu day ban san thep

cqn

En

t

l4

0

10 72115

4

Trong o:

n0 = [l/];

= 0.3, he so Poisson cua thep;

117

21 1

EE

S o tnh toan ban san thep

118 Hnh 3.9. S o tnh toan ban san thep

Moment ln nhat gia nhp ban c xac nh theo cong thc:

(3.2)

Trong o:

l: nhp tnh toan cua ban;

: o vong gia nhp ban do tai trong tieu

chuan qc va lc keo H gay ra;

(3.3)

0: o vong gia nhp ban do tai trong tieu

chuan qc gay ra;

119

1

1

80

2

max MHql

M

1

10

(3.4)

: ty so gia lc keo H va lc ti han le Ncr

,

xac nh theo phng trnh sau:

(3.5)

H: lc keo tac dung tai goi ta ban;

(3.6)

(3.7)

Q: he so o tin cay cua tai trong;

120

x

c

IE

lq

1

4

0384

5

2

02 31

t

tEl

H

l

EIH

Q

x

1

22

2

2

4

Kiem tra o vong va o ben cua cau kien chu keo uon ong thi:

(3.8)

Trong o:

A, Wx: dien tch, moment khang uon oi vi truc

x-x cua dai ban day t, rong mot n v (1m);

[]: o vong gii han cho phep;

f: cng o tnh toan chu keo cua thep;

ng han goc co chieu dai mot n v, chieu cao h

f phai u chu lc keo H:

121

; fW

M

A

H

c

x

max

(3.9)

(f)min

= min[(f, f

wf); (

s, f

ws)]

f,

s, f

wf , f

ws : cac he so va cng o tnh toan

cua ng han goc;

3.2.CAC KCH THC CHNH CUA DAM

3.2.1. Chieu Dai Dam, Nhp Dam

Khoang cach nh v L gia hai goi ta nhp danh ngha;

L0: khoang thong thuy;

L1: chieu dai che tao, L

1 = L -

122

cf

f

Hh

min

123 Hnh 3.10. Kch thc chnh cua dam

: sai so che tao, = (5 10)mm;

l: nhp tnh toan, l = L;

3.2.2. Chieu Cao Cua Tiet Dien Dam

Chieu cao tiet dien dam, h:

hmin

h hmax ; h hkt (min)

hmin

: chieu cao am bao cho dam u cng trong

suot qua trnh s dung;

hmax

: chieu cao cho phep u e bo tr he dam va

ban san;

Xac nh chieu cao hmin

o vong ln nhat tai gia dam

124

(3.10)

Trong o:

gc, p

c: tnh tai va hoat tai tieu chuan tac dung

tren mot n v chieu dai dam;

l: nhp dam;

EI: o cng chong uon cua tiet dien dam;

Moment uon

M = (gc

g + p

cp)l

2/8 (3.11)

(3.12)

125

EI

lpg cc

384

5 4

)(48

5 2

p

c

g

c

cc

pgEI

pgMl

Quan he M = fW, I = Wh/2

(3.13)

tb

: he so vt tai trung bnh;

Cho = []

T (3.13) (3.14)

Xac nh chieu cao kinh te, hkt

(3.15)

126

tbEh

fl

24

5 2

p

c

g

c

cc

tb pg

pg

1

l

E

flh

tb24

5min

w

ktt

Wkh

Trong o:

k: he so phu thuoc vao cau tao tiet dien dam;

k = 1.15 1.2 dam to hp han;

k = 1.2 1.25 dam to hp boulone (inh tan);

tw: chieu day ban bung dam;

Xet anh hng cua chieu cao dam, hw va

chieu day ban bung dam, tw

(3.16)

w = h

w/t

w: o manh cua ban bung dam;

127

3

2

3 Wh wkt

128

Bang 3.2. Ty so chieu cao va chieu day ban

bung san thep

3.3. THIET KE DAM THEP HNH

3.3.1. Chon Tiet Dien Dam

Moment khang uon yeu cau

(3.17)

Khi ke en s phat trien cua bien dang deo cua thep cho phep tang kha nang chu M

(3.18)

Cac ieu kien ap dung khi s dung he so c1

Tai trong tnh

129

c

xyc

xf

MW

max

c

xyc

xfc

MW

1

max

3.3. THIET KE DAM THEP HNH


Thep lam dam co fy 53kN/cm2

Tiet dien khong oi

ieu kien on nh tong the c am bao

ng suat tiep, 0.9f

Chon Wx W

x

yc

130

131

Loi tit

din Hnh dng tit din c1

1

0,25

0,5

1,0

2,0

1,19

1,12

1,07

1,04

2

0,5

1,0

2,0

1,40

1,28

1,18

3

0,25

0,5

1,0

2,0

1,19

1,12

1,07

1,04

Bang 3.3. He so c1

w

f

A

A

y

y

x x

Af Aw

Af

x x

y

y

x x

y

y

Af

Aw 0,5Af

Af

Af 0,5Aw

x x

y

y

132

Loi tit

din Hnh dng tit din c1

4

0,5

1,0

2,0

1,40

1,28

1,18

5 - 1,47

6

0,25

0,5

1,0

2,0

1,47

0,5Aw

Af

0,25Af

y

y

x x

y

y

xx

y

x x

y

a) b)

y

x x

y

Af

0,5Aw 0,5Aw

w

f

A

A

Bang 3.3. He so c1 (tiep theo)

3.3.2. Kiem Tiet Dien Dam a Chon Theo ieu

Kien Cng o

a.Kiem tra ieu kien ben ve uon

(3.19)

Trong o:

M: moment uon tai tiet dien kiem tra;

Wnx

: moment khang uon cua tiet dien thc oi

vi truc x-x;

133

c

nx

c

nx

fWc

M

fW

M

1


Kien Cng o

b.Kiem tra ieu kien ben ve cat

(3.20)

Trong o:

V: lc cat tai tiet dien can kiem tra;

S: moment tnh cua phan tiet dien nguyen ben

tren th can tnh ng suat cat oi vi truc x-x;

Ix: moment quan tnh cua tiet dien nguyen oi

vi truc x-x;

fv: cng o tnh toan ve cat cua thep lam dam;

tw: chieu day ban bung cua thep hnh a chon;

134

cv

wx

ftI

VS


Kien Cng o

Trng hp tai tiet dien kiem tra, ban bung b giam yeu do khoet lo (inh tan, boulone)

(3.21)

= a(a d) (3.22)

Trong o:

a: khoang cach tam hai lo (inh tan, boulone);

d: ng knh lo inh;

135

cv

wx

ftI

VS


Kien Cng o

c.Kiem tra ban bung dam chu ng suat cuc bo

136

Hnh 3.11. S o xac nh chieu dai quy c

chu tai cuc bo cua ban bung dam


Kien Cng o

Khi ben tren canh dam co tai tap trung;

Ban bung khong co sn cng gia cng;

Kiem tra ieu kien ben cua ban bung

(3.23)

Trong o:

p: ng suat cuc bo;

F: gia tr cua tai trong tap trung phan bo trc tiep

tren chieu rong b;

lz: chieu dai phan bo quy oi cua tai trong tap

trung F;

137

c

zw

p flt

F


Kien Cng o

Khi dam khao sat la dam thep hnh

lz = b + 2h

y = b + 2(t

f + r) (3.24)

Trong o:

tf: chieu day canh dam;

r: ban knh cong chuyen tiep t bung sang canh;

d.Kiem tra tiet dien dam chu ong thi (, , p )

Kiem tra ben theo cong thc

(3.25)

138

cpptd f 15.13222

d.Kiem tra tiet dien dam chu ong thi (, , p )

Trong o:

(3.26)

, p: mang dau (+) neu la keo, dau (-) neu la

nen;

Inx

: moment quan tnh cua tiet dien thc;

y: khoang cach t bien tren cua chieu cao tnh

toan cua bung dam en truc trung hoa;

139

yI

M

nx

3.3.3. Kiem Tra o Vong Cua Dam

(3.28)

/l: gia tr o vong tng oi cua dam, do to hp

cac tai trong tieu chuan gay ra;

140

ll

141

Loi cu kin vng cho php

Dm ca sn nh v mi:

1. Dm chnh

2. Dm ca trn c trt va, ch tnh vng cho ti trng tm thi

3. Cc dm khc, ngoi trng hp 1 v 2

4. Tm bn sn

L /400

L /350

L /250

L /150

Dm c ng ray:

1. Dm sn cng tc c ng ray nng 35 kg/m v ln hn

2. Nh trn, khi ng ray nng 25 kg/m v nh hn

L /600

L /400

X g:

1. Mi lp ngi khng p va, mi tm tn nh

2. Mi lp ngi c p va, mi tn mi v cc mi khc

L /150

L /200

Dm hoc gin cu trc:

1. Cu trc ch lm vic nh, cu trc tay, palang

2. Cu trc ch lm vic va

3. Cu trc ch lm vic nng v rt nng

L /400

L /500

L /600

Sn tng:

1. Dm tng xy

2. Dm tng nh (tn, fibr ximang), dm ca knh

3. Ct tng

L /300

L /200

L /400

Ghi chu: L l nhp ca cu kin chu un. i vi dm console th L ly bng 2 ln vn ca

dm.

Bang 3.4. o vong cho phep cua cau kien chu uon

3.3.4. Kiem Tra On nh Tong The Cua Dam

Kiem tra on nh tong the dam theo cong thc

(3.29)

Trong o:

Wc: moment khang uon cua tiet dien nguyen

cho th bien cua canh chu nen;

c = 0.95: he so ieu kien lam viec;

b: he so, phu thuoc vao tham so

1

(3.30)

: he so, phu thuoc dang tai trong he so ,v.v;

142

c

cb

fW

M

2

0

2

1lfI

hEI

x

y

143 Bang 3.5. He so cho dam I co hai truc oi xng

3.3.4. Kiem Tra On nh Tong The Cua Dam

Vi thep I can nong,

(3.31)

h: chieu cao tiet dien dam;

It: moment quan tnh xoan cua dam;

lo: chieu dai tnh toan ngoai mat phang dam cua

canh nen;

He so b lay nh sau

Neu 1 0.85, lay

b =

1

Neu 1 > 0.85,

b = 0.68 + 0.21

1 1 (3.32)

144

2

054.1

h

l

I

I

y

t

3.4. THIET KE DAM TO HP


145 Hnh 3.12. Tiet dien ngang dam to hp han



a.Xac nh chieu cao dam

Chieu cao tiet dien dam, h:

hmin

h hmax ; h hkt

b.Xac nh chieu day ban bung dam

Chieu day nho nhat cua ban bung, tw c xac

nh theo ieu kien ban bung u chu Vmax

(3.33)

Khi h = (1 2)m (3.34)

146

cvw

wfh

Vt

2

3 max

1000

37

htw



Neu khong dung sn e gia cng ban bung dam

(3.35)

c.Xac nh cac kch thc cua tiet dien canh

dam

Xac nh tiet dien canh dam han: tf, b

f

(3.36)

147

E

fht ww

5.5

122

23

max

2

ww

cfk

ff

ht

f

hM

htb



Cac yeu cau cau tao

tf = (12 24)mm

bf 30mm

e thoa man ieu kien on nh cuc bo cua ban canh nen

(3.37)

e ng suat phap phan bo eu tren chieu rong canh keo va am bao on nh cuc bo cho

canh nen, chon:

bf 30t

f (3.38)

148

f

E

t

b

f

f



Nham am bao ieu kien on nh tong the cua dam va de lien ket vi cac cau kien khac,

bf = (0.2 0.5)h; b

f 180mm; b

f 0.1h

Xac nh tiet dien canh dam inh tan (boulone)

Chon tiet dien thep goc canh dam

(3.39)

tg = t

w; (3.40)

149

hbg

12

1

9

1

gg bt

11

1

10

1

150

Hnh 3.13. Tiet dien dam to hp inh tan



Chon tiet dien ban phu canh dam

Id = I I

w I

g (3.41)

(3.42)

Id = 0.5n

1b

th

2 (3.43)

Trong o:

Ig: moment quan tnh cua tiet dien mot thep

goc oi vi truc x-x;

Ag: dien tch tiet dien cua thep goc a chon;

151

ggogwwxd AaIhthW

I 23

4122



Iog

: moment quan tnh cua tiet dien mot thep goc

oi vi truc trong tam cua chnh no, tra bang;

ag: khoang cach t truc trong tam thep goc en

truc trung hoa;

Id: moment quan tnh cua tiet dien cac ban phu

hai canh dam oi vi truc x-x;

n1: so lng ban phu moi canh dam;

h: khoang cach trong tam cac ban phu hai

canh dam, h = h (12 24)mm;

152



Chieu rong can thiet cua ban phu

b 2b

g + t

w (3.44)

Khoang cach t tam inh tan ngoai cung en mep ban phu, a

1

a1 15t

(khi canh dam dung mot ban phu)

a1 8t

(khi canh dam dung hai ban phu)

3.4.2. Kiem Tra o Ben, o Vong Cua Dam To

Hp (tng t nh dam hnh)

153

3.4.3. Thay oi Tiet Dien Dam Theo Chieu Dai

Dam

154

Hnh 3.14. Cac cach thay oi tiet dien dam

Hnh 3.4.3.a Bien oi chieu cao dam theo bieu o M

Hnh 3.4.3.b Bien chieu day ban canh dam

Hnh 3.4.3.c Bien oi be rong ban canh dam

i

3.4.3. Thay oi Tiet Dien Dam Theo Chieu Dai

Dam

Giam tiet dien tai v tr co moment be;

Thay oi tiet dien dam bang cac cach sau

Giam chieu cao bung dam v tr au dam

Giam chieu day canh dam

Giam chieu rong canh dam

Cau tao chieu rong mi cua ban canh, bf1

bf1

180mm;

bf1

0.5bf;

bf1

0.1h

155

3.5. ON NH TONG THE CUA DAM THEP

3.5.1. Hien Tng Va Nguyen Nhan

156

Hnh 3.15. Mat on nh tong the cua dam

3.5.2. Tnh Toan Dam Theo ieu Kien On nh

Tong The

a. Kiem tra on nh tong the dam theo cong thc

(3.45)

Vi dam to hp han ch

(3.46)

Trong o:

hf: khoang cach trong tam hai canh dam;

a = 0.5hf;

157

c

b

fW

M

ff

w

ff

w

tb

at

bh

tl 32

0 18


Tong The

b. Khi dam co mot trong cac ieu kien sau th

khong can kiem tra on nh tong the

Co ban san BTCT hoac ban san thep u cng lien ket mot cach chac chan vi canh nen cua

dam;

(3.47)

(neu bf/t

f


Tong The

c. Bien phap tang cng on nh tong the

S dung ban san (BTCT, thep);

Hieu chnh cac ty so bf/t

f , b

f/h

f ;

Giam l0 bang cach bo tr them he giang, thanh

chong ngang;

159

3.6. ON NH CUC BO CUA BAN CANH, BAN

BUNG DAM TO HP

Ban canh nen chu tac dung cua ng suat nen;

Vung ban bung au dam chu tac dung cua ng suat cat;

Vung ban bung gia dam chu tac dung cua ng suat uon;

Cac ng suat tren ban canh, ban bung b venh ra ngoai mat phang cua no mat on nh

cuc bo cua dam.

160

3.6.1. On nh Cuc Bo Cua Ban Canh Nen

161

Hnh 3.16. Mat on nh cuc bo cua canh dam


ieu kien ben cua ban canh nen dam

(3.48)

Chieu rong b0f = b

0 c lay nh sau

162

f

E

t

b

f

f5.0

0

163


Bang 3.6. Gia tr gii han [b0/t

f]

164

hw

bo

o

r r

bo

hw

r ao

bo

hw

r

r r

bo

bo

r ao

ao

bo

bo

Hnh 3.17. S o tiet dien ngang cua nh hnh cong


a.Mat on nh cuc bo do tac dung cua ng suat

tiep

165

3.6.2. Mat On nh Cuc Bo Cua Ban Bung Dam

Hnh 3.18. Mat on nh cuc bo cua ban bung

dam do ng suat tiep,


tiep

166

e am bao on nh cuc bo, ban bung cua dam to hp phai c tang cng bang cac

sn cng theo cac quy nh sau

o manh quy c cua ban bung

(3.49)

Neu > 3.2 khi dam chu tai trong tnh;

Neu > 2.2 khi dam chu tai trong ong;

Ban bung phai c tang cng bang cac

sn cng ngang;

E

f

t

h

w

ww

w

w


tiep

Khoang cach gia cac sn cng ngang

a 2hw khi > 3.2

a 2.5hw khi 3.2

Chieu rong sn

Khi bo tr cap sn oi xng

bsn

= bs = h

w/30 + 40mm (3.50)

Khi bo tr cac sn mot ben cua ban bung

bsn

= bs = h

w/24 + 50mm (3.51)

Chieu day sn, (3.52)

167

w

w

E

fbt ss 2

168

Hnh 3.19. S o dam c tang cng bang cac sn

cng

b.Mat on nh cuc bo cua ban bung dam do tac

dung cua ng suat phap

169

Hnh 3.20. Mat on nh cuc bo cua ban bung dam do tac




Di tac dung cua , phan chu nen cua ban bung b phong len tao thanh cac song vuong

goc vi ban bung dam hien tng mat on

nh cuc bo cua ban bung dam do tac dung cua

ng suat phap;

Neu > 5.5, th ngoai sn cng ngang con phai tang cng ban bung bang cac sn cng

doc;

Kch thc sn cng doc

(3.53)

170

w

wsd tt 75.0

wsd tb 10



Khong can kiem tra on nh cuc bo cua ban bung dam khi

3.5, trong trng hp khong co ng suat cuc bo;

2.5, trong trng hp co ng suat cuc bo;

171

w

w

c.On nh cua ban bung dam do ,

172

(3.54)

(3.55)

(3.56)

, : ng suat (phap, tiep) cua th mep ban

bung tai tiet dien kiem tra;

(3.57)

(3.58)

M, V: gia tr trung bnh cua moment uon va lc

cat trong o kiem tra;

cr

, cr

: ng suat phap va ng suat tiep ti han

cua ban bung dam;

173


Wh

Mhw

wwth

V

174


(3.59)

175


Bang 3.7. He so ccr

oi vi dam to hp han

Bang 3.8. He so

176


(3.60)

177


Hnh 3.21. S o dam c tang cng bang cac

sn cng

a, b) Lc F at canh chu nen, chu keo

178


(3.61)

(3.62)

c,cr

: ng suat phap cuc bo ti han;

179


(3.63)

(3.64)

(3.65)

180 Bang 3.9. He so c

1

181


(3.66)

182 Bang 3.10. Gia tr

c /

183

Bang 3.11. He so c2

Trong moi trng hp cr

eu c tnh theo

kch thc thc cua o ban;

3.7.1. Lien Ket Canh Dam Vi Ban Bung

184

3.7. CAU TAO VA TNH TOAN CAC CHI TIET

CUA DAM

Hnh 3.22. S lam viec cua lien ket canh vi bung

dam to hp


Khi dam chu uon, ban canh co xu hng trt tng oi so vi ban bung, ng han phai chu

c lc trt o;

Goi T la lc trt tren mot n v chieu dai dam

Trong o:

V: lc cat tnh toan;

Ix: moment quan tnh cua tiet dien oi vi truc

trung hoa x-x;

185

x

f

wI

VStT (3.67)

Sf: moment tnh cua phan tiet dien b trt oi

vi truc trung hoa x-x;

Kha nang chu lc cua ng han

2hf(f

w)min

c T = VS

f/I

x (3.68)

(fw)min

= min[(ffwf

), (sfws

)];

Chieu cao can thiet cua ng han

(3.69)

Khi tren canh dam han co lc tap trung F

186


cxwf

fIf

VSh

min

2

(3.70)

Vi dam to hp inh tan (boulone)

Lc trt moi inh phai chu

(3.71)

Kha nang chu lc cua mot inh tan

(3.72)

187

cw

zx

f

ff

l

F

I

VS

h

min

22

2


aI

VSTaT

x

f

b

aI

VSTN

x

f

bcb min

Bc inh, a

(3.73)

188


f

xcb

VS

INa

min

a. Dam thep hnh

189

3.7.2. Cau Tao Va Tnh Toan Moi Noi Dam

Hnh 3.23. Noi dam hnh dung ng han oi au

Noi bung dam trc, noi cac ban canh dam sau (e giam ng suat han bien hnh han);

o ben chu keo cua ng han oi au ch lay bang 85% o ben chu keo cua thep lam

dam;

noi dam nhng tiet dien co M 0.85Mmax

190

a. Cau Tao Va Tnh Toan Moi Noi Dam Thep

Hnh

191


Hnh

Noi dam nhng tiet dien co M > 0.85Mmax

Hnh 3.24. Noi dam hnh dung ng han oi au va ban noi

bf bbn

Cac ng han oi au va ban noi phai chu toan bo M tai tiet dien noi, hnh 3.24c;

Moment do tiet dien ng han oi au noi canh va bung dam phai chu

Mw = W

wfwt

c (3.74)

Ww: moment khang uon cua tiet dien ng han

oi au;

fwt

: cng o chu keo cua ng han oi au;

Moment ma ban noi canh dam phai chu

Mbn

= M - Mw (3.75)

192


Hnh (M > 0.85Mmax

)

Dien tch tiet dien ban noi

(3.76)

hbn

: khoang cach trong tam hai ban noi hai

canh, hbn

= h + (12 20)mm (3.77)

Chieu rong ban noi

bbn

= bf - (16 20)mm (3.78)

Chieu day ban noi

tbn

= Abn

/bbn

(3.79)

193


Hnh (M > 0.85Mmax

)

cbn

bnbn

fh

MA

ng han goc lien ket ban noi vi canh dam phai u chu lc truyen qua ban noi, N

bn

Nbn

= Mbn

/hbn

(3.80)

Tong chieu dai ng han lien ket mot na ban noi vi canh dam

(3.81)

Thng chon trc hf t

bn

194


Hnh (M > 0.85Mmax

)

fcw

bnf

hf

Nl

min

195

bf bbn


Hnh (M > 0.85Mmax

)

Hnh 3.25. Noi dam hnh dung ng han oi au va ban noi

Xet hnh 3.24d, cac quan niem

Moment tac dung tai tiet dien noi do cac ban noi canh dam chu;

Lc cat tac dung tai tiet dien noi do cac ban noi bung dam va cac ng han goc chu;

Dien tch can thiet cua tiet dien ban noi canh

(3.82)

Chieu rong, chieu day ban noi, chieu dai ng han xac nh tng t nh s o hnh

3.24c;

196


Hnh (M > 0.85Mmax

)

cbn

bnbn

fh

MA

Chng 4

COT THEP

4.1. KHAI QUAT CHUNG

4.1.1. ac iem Chung

Cot la ket cau thang ng lam nhiem vu cac ket cau khac nh dam, dan, v.v va truyen tai trong t cac ket cau o xuong mong.

Cot co ba bo phan chnh

au cot;

Than cot;

Chan cot;

197


4.1.2. Cac Loai Cot

Theo s dung

Cot nha cong nghiep;

Cot nha khung nhieu tang;

Cot san cong tac;

Cot ng day tai ien;

v.v

Theo cau tao

Cot ac;

Cot rong;

198

Theo cau tao

Cot tiet dien khong oi;

Cot tiet dien thay oi;

v.v

Theo s o chu lc

Cot nen ung tam;

Cot nen lech tam;

Cot nen uon;

199


4.1.2. Cac Loai Cot

a.S o tnh

S o tnh cua cot la truc doc cua cot co cac

lien ket chan cot va au cot theo cac phng.

b.Chieu dai tnh toan

Chieu dai tnh toan cua cot l0 phu thuoc vao s

o tnh va noi lc doc trong cot.

oi vi cot tiet dien khong oi hoac cua cac oan cot bac, l

0

l0 = l (4.1)

201

4.1.3. S o Tnh, Chieu Dai Tnh Toan Va o

Manh Cua Cot

Trong o:

l: chieu dai hnh hoc cua cot;

: he so chieu dai tnh toan;

oi vi cot tiet dien thay oi, l0

l0 =

jl (4.2)

j: he so chieu dai tnh toan bo sung;

202


Manh Cua Cot

204

S hnh dang cot l1/l Khi t s Imin/Imax bng

0,01 0,1 0,2 0,4 0,6 0,8 1,0

- - 1,35 1,24 1,14 1,08 1,02 1,0

- - 1,66 1,45 1,24 1,14 1,06 1,0

0,0 1,69 1,35 1,25 1,14 1,08 1,03 1,0

0,2 1,45 1,22 1,15 1,08 1,05 1,02 -

0,4 1,23 1,11 1,07 1,04 1,02 1,01 -

0,6 1,07 1,03 1,02 1,01 1,01 1,00 -

0,8 1,01 1,00 1,00 1,00 1,00 1,00 -

Imin Imax

ImaxImin

l1

l

ImaxImin

c.o manh cua cot

(4.3)

Trong o:

ix, i

y: cac ban knh quan tnh cua tiet dien cot

tnh theo truc x, y;

Cot nen ung tam: x =

y (4.4)

Cot lam viec bnh thng: max

[] (4.5)

205


Manh Cua Cot

y

y

y

x

xx

i

l

i

l

a.Tiet dien dang ch H

207

4.2. COT AC CHU NEN UNG TAM

4.2.1. Hnh Thc Tiet Dien

a.Tiet dien dang ch H

De lien ket vi cac ket cau;

Thoa man cac yeu cau ve kien truc;

Hnh thc n gian, de che tao;

b.Tiet dien dang ch thap

208

Cau tao n gian;

Lien ket vi cac ket cau khac phc tap;

Kho thoa man cac yeu cau ve kien truc;

c.Tiet dien kn

209

b.Tiet dien dang ch thap

Co ban knh quan tnh ln hn tiet dien h cung dien tch;

ap ng c x

y

Hnh thc tiet dien gon;

Kho bao dng c mat ben trong cua tiet dien;

210

c.Tiet dien kn

a.Tnh toan ve ben

(4.6)

Trong o:

N: lc doc tnh toan;

An: dien tch tiet dien thc (a tr cac giam yeu);

f: cng o tnh toan cua vat lieu thep;

c: he so ieu kien lam viec cua cot;

211


4.2.2. Tnh Toan Cot ac Chu Nen ung Tam

c

n

fA

N

b.Tnh toan ve on nh tong the

(4.7)

Trong o:

A: dien tch tiet dien nguyen (cha tr phan

giam yeu);

min

: he so uon doc nho nhat;

Cac cach xac nh min

Tnh theo cong thc

212



cfA

N

min


Khi

(4.8)

Khi

Khi

(4.10)

213



5.20

E

f53.5073.01

5.45.2

2

53.50275.03.27371.01347.1

E

f

E

f

E

f

5.4

51

3322


Trong o:

: o manh quy c, (4.11)

c.Tnh toan ve on nh cuc bo

Trong cac ban thep co ng suat phap nen, n;

n [

n] ban thep b bien dang ra ngoai mat

phang cot b mat on nh cuc bo;

e kha nang chu lc cua cot khong b han che bi ieu kien on nh cuc bo, [

cb] [

tt]

214



E

f

(4.12)

Trong o:

hw: chieu cao tnh toan cua ban bung;

tw: chieu day ban bung;

[hw/t

w]: o manh gii han cua ban bung;

hw/t

w 2[h

w/t

w] t

w = const (neu cot am bao

ieu kien on nh tong the);

Khi o phan ban bung ch co oan 2c1 cung

tham gia lam viec vi canh;

215


c.1.ieu kien on nh cuc bo cua ban bung

w

w

w

w

t

h

t

h

216

Hnh 4.5. Tiet dien cot ac to hp han

c1: phan ban bung hu dung;

(4.13)

Khi h > 1m ma ieu kien on nh cuc bo cua ban bung khong thoa gia cng bung cot

bang mot cap sn doc;

Kch thc cua sn doc

217



w

ww

t

htc 5.01

wsd tt 75.0

wsd tb 10

218

Hnh 4.6. Sn gia cng ban bung cot

219

Bang 4.3. o manh gii han [hw/t

w] cua ban bung cot

ac nen ung tam

Khi bo tr sn doc th cac sn nay phai c ke vao tiet dien tnh toan cua cot;

gia tr o manh gii han cua ban bung cot la:

Tr so c xac nh nh sau:

Khi Isd

6hwtw

3

(4.14)

220



w

w

t

h

3

3

3

1.01

4.01

ww

sd

ww

sd

th

I

th

I

Khi Isd

> 6hwtw

3 = 1

Isd

: moment quan tnh cua sn doc oi vi truc

bung cot vuong goc vi canh bsd

;

hw: chieu cao tnh toan cua bung cot khi cha

at sn doc;

Khi

can gia cng ban bung bang cac oi sn

ngang e cot khong b mat on nh cuc bo di

tac ong cua ng suat tiep, .

221



f

E

t

h

w

w 3.2

Kch thc cua sn ngang

: khi bo tr cap sn oi xng

: khi bo tr sn mot ben

c.2.ieu kien on nh cuc bo cua ban canh

(4.15)

222

E

fbt snsn 2

mmh

b wsn 4030

mmh

b wsn 5024



ff t

b

t

b 00

b0: chieu rong tnh toan cua phan ban canh nho

ra;

tf: chieu day ban canh;

[b0/t

f]: o manh gii han cua phan ban canh nho

ra;

223


c.2.ieu kien on nh cuc bo cua ban canh

224

Bang 4.4. o manh gii han [b0/t

f] cua phan ban

canh nho ra

Kha nang theo ieu kien ben

[N]b = A

nf

c (4.16)

Kha nang theo ieu kien on nh tong the

[N] = minAfc (4.17)

Kha nang chu nen ung tam cua cot

[N] = min {[N]b; [N]} (4.18)

225

d.Kha nang chu nen ung tam cua cot ac

a.Chon tiet dien cot ( to hp)

Xac nh dien tch can thiet cua tiet dien cot

(4.19)

: he so uon doc c gia thiet trc hoac c xac nh theo

gt;

gt

= 100 120, khi N 1500kN;

gt

= 70 100, khi N = 1500 3000 kN;

gt

= 50 70, khi N = 3000 4000 kN;

gt

= 40 50, khi N 4000 kN;

226

4.2.3. Xac nh Tiet Dien Cot ac Chu Nen

ung Tam

c

ycf

NA

Xac nh kch thc tiet dien ban canh va ban bung

(4.20)

x,

y: cac he so, tra bang;

Theo yeu cau cau tao

h = (1 1.15)b

tf = (8 40)mm

tw = (6 16)mm

227

a.Chon tiet dien cot ( to hp)

gty

y

yc

lb

gtx

xyc

lh

Kiem tra ben; Kiem tra on nh tong the; Kiem

tra on nh cuc bo; Kiem tra o manh;

c.Xac nh tiet dien cot theo o manh

Xac nh Ayc

, byc

, hyc

; gt

= []

Kch thc tiet dien c chon

A Ayc

; ix i

xyc; i

y i

yyc

Trong o:

229

b.Kiem tra tiet dien cot

y

yyc

xxyc

li

li

Lien ket canh va bung cot to hp c lay theo cau tao

ng han dai suot chieu dai cot;

hf = (6 8)mm;

230

d. Lien ket canh va bung cot

231

4.3. COT RONG CHU NEN UNG TAM

4.3.1. Cau Tao Than Cot

Cot rong co he thanh bung (thanh giang) cot rong thanh giang;

Cot rong co cac ban giang cot rong ban giang;

Kch thc tiet dien cau tao cua ban giang

tb = (6 12)mm; t

b = (1/10 1/30)d

b; t

b 1/50b

b

db = (0.5 0.8)h

Trong o:

bb: chieu dai cua ban giang;

h: be rong mat rong cua cot;

233


4.3.1. Cau Tao Than Cot

a.S lam viec cua cot rong oi vi truc thc y-y

o manh cua cot oi vi truc thc y-y

(4.21)

Ban knh quan tnh cua tiet dien cot

(4.22)

Trong o:

Af: dien tch tiet dien nhanh; A

f = A/2

234


4.3.2. S Lam Viec Cua Cot Rong

y

y

yi

l

0

00

2

2y

f

y

f

y

y iA

I

A

Ii

iy0

, Iy0

: ban knh quan tnh va moment quan tnh

cua tiet dien nhanh oi vi truc y0 (y

0 trung y);

b.S lam viec cua cot rong oi vi truc ao x-x

o manh ban au cua cot oi vi truc ao x-x

(4.23)

(4.24)

o manh thc (o manh tng ng), 0

0 =

x

t (4.25)

235


a.S lam viec cua cot rong oi vi truc thc y-y

x

xx

i

l

A

Ii xx

t: he so ke en anh hng bien dang cua he

bung rong;

(4.26)

1: goc trt cua tiet dien cot do V = 1 n v gay

ra;

236


b.S lam viec cua cot rong oi vi truc ao x-x

2

2

11x

t

EA

237

c. o manh tng ng 0 cua cot rong ban

giang

= 1

= 1

Gia thiet: iem gia chieu dai cac oan nhanh

va ban giang co M = 0 va xem la khp.

o cng n v, n cua cac oan nhanh cot va ban giang

(4.27)

Trong o:

Ix0

: moment quan tnh cua tiet dien nhanh oi

vi truc x0-x

0;

Ib: moment quan tnh cua ban giang

Ib = t

bd

b

3/12 (4.28)

238


giang

aI

CIn

b

x0

C: khoang cach trong tam hai nhanh cot;

a: khoang cach trong tam cac ban giang;

Goc trt, 1 do V = 1 n v gay ra

(4.29)

Trong o:

1 a/i

x0 : o manh cua nhanh (4.30)

ix0

: ban knh quan tnh cua tiet dien nhanh oi

vi truc x0 ;

He so, t

239


giang

EA

n

12

1211

(4.31)

o manh tng ng, 0 cua cot rong ban

giang hai nhanh

(4.32)

Khi n 1/5, EIb

(4.33)

240


giang

2

2

1182.01x

t n

nx 182.02

1

2

0

2

1

2

0 x

241

d. o manh tng ng 0 cua cot rong thanh

giang

Goc trt, 1

(4.34)

Trong o:

: bien dang doc truc cua thanh bung xien do lc cat V = 1 n v gay ra cho ca hai mat rong;

(4.35)

Nb: tong lc doc cua cac thanh bung xien hai

mat rong tren cung mot tiet dien do V = 1 gay

ra;

242


giang

sincos1

dla

1d

db

EA

lN

(4.36)

(4.37)

Trong o:

Ad1

: tong dien tch tiet dien cua cac thanh bung

xien hai mat rong;

Ad1

= 2At (vi he thanh bung tam giac);

At: dien tch tiet dien cua mot thanh bung xien;

: goc nghieng cua truc thanh bung xien vi truc nhanh cot;

243

sin

1bN


giang

2

1

1sincos

1

dEA

(4.38)

(4.39)

Trong o:

ld: chieu dai truc thanh bung xien;

o manh tng ng cua cot rong hai nhanh

(4.40)

244


giang

2

1

11xd

tA

A

2

3

2

2

1

10

cossin aC

ld

1

12

0

d

xA

A

(4.41)

An = 2A

fn

Afn

: dien tch tiet dien thc cua nhanh cot;


(4.42)

min

xac nh theo max

= max{0;

y}

c.Tnh toan ve on nh cuc bo (nh cot ac)

245

4.3.3.Tnh Toan Cot Rong Chu Nen ung Tam

a.Tnh toan ve ben

c

n

fA

N

cfA

N

min

max

[]

o manh cua cac nhanh cot, 1 (4.42a)

Cot rong ban giang, 1 < 40 va

1 <

y

Cot rong thanh giang, 1 80 va

1

y

e. Kha nang chu nen ung tam cua cot rong

(tnh toan nh cot ac)

246

4.3.3.Tnh Toan Cot Rong Chu Nen ung Tam

d. Cac yeu cau ve o manh

a.Chon tiet dien cot

Xac nh dien tch tiet dien nhanh cot

(4.43)

y c xac nh theo

ygt = 40 90

Xac nh ban knh quan tnh yeu cau

(4.44)

247

4.3.4. Xac nh Tiet Dien Cot Rong Chu Nen

ung Tam

cy

fycf

NA

2

ygt

y

yyc

li

Chon nhanh cot va kiem tra cot theo truc thc

T Afyc

, iyyc

chon thep hnh lam nhanh cot sao cho thoa man ieu kien:

(4.45)

Trong o:

A = 2Af

y xac nh theo

y (theo tiet dien a chon);

iy = i

y0: ban knh quan tnh cua tiet dien nhanh

oi vi truc y0;

248

4.3.4. Xac nh Tiet Dien Cot Rong Chu Nen ung

Tam


y

y

y

c

y

i

l

fA

N

Xac nh khoang cach hai nhanh, C

Can c vao s lam viec cua cot oi vi truc ao x-x;

ieu kien hp ly 0 =

y ;

Cot rong ban giang (n 1/5)

(4.46)

1: chon s bo theo (4.42a);

Cot rong thanh giang

(4.47)

249

2

1

2 yxyc

1

12

d

yxycA

A


Tam


S bo chon trc thep goc lam thanh bung xien

1 va A

d1;

Xac nh ixyc

(4.48)

Khoang cach yeu cau hai nhanh

(4.49)

(4.50)

ix0

: ban knh quan tnh cua nhanh oi vi truc x0;

250

xyc

xxyc

li

2

0

22 xxycyc iiC

x

xyc

yc

ih


Tam


He thanh giang va ban giang c tnh toan vi lc cat, V

f sinh ra khi cot b uon doc quanh truc ao;

(4.51)

Trong o:

N: lc doc tnh toan cua cot;

= f(0);

Lc cat, Vs tac dung tren mot mat rong cua cot

Vs = V

fn

r (4.52)

nr = 0.5 : cot rong hai nhanh;

251


ung Tam

b. Tnh toan ban giang va thanh bung

N

f

EeV f

233015.7 6

252


ung Tam

b.1. Tnh toan ban giang

Chon db, t

b , khoang cach cac ban giang a;

Chieu dai tnh toan lf;

Xem cac ban giang va hai nhanh

cot nh mot khung mot nhp nhieu

tang chu bien dang trt do Vf;

Moment uon, lc cat trong ban

giang

Mb = 0.5aV

s (4.53)

Tb = aV

s/C (4.54)

253


ung Tam


Kiem tra ben ban giang va tnh toan lien ket ban giang vi nhanh cot (M

b, T

b);

b.2. Tnh toan thanh bung

254


ung Tam


Lc doc trong thanh bung xien

(4.55)

Trong o:

nt = 1, he thanh bung tam giac;

nt = 2, he thanh bung hnh thoi;

He thanh bung ch thap co thanh ngang

(4.56)

255


ung Tam


sint

sd

n

VN

fu

t

sd N

n

VN

sin

Nfu

: lc doc phu trong thanh xien;

(4.57)

Nf: lc doc trong mot nhanh cot;

(4.58)

Chon tiet dien thanh bung

Gia thiet max

= gt

150 min

;

(4.59)

256


ung Tam


f

tfd

fuA

ANN

33

2

2Cl

al

d

dd

gt

dyc

lii

min

Dien tch tiet dien yeu cau cua thanh bung xien

(4.60)

T Atyc

, iyc

tra bang chon tiet dien

Kiem tra thanh bung

(4.61)

Tnh toan lien ket thanh xien vao nhanh (Nd);

257


ung Tam


c

dtyc

f

NA

min

c

t

d fA

N

min

258

4.4. COT CHU NEN LECH TAM, NEN UON

4.4.1. Cau Tao

Kch thc tiet dien: b, h

h = (1/8 1/14)lc : cot rong;

h = (1/10 1/15)lc : cot ac;

b = (0.3 0.5)h

b = (1/20 1/30)lc

lc: chieu dai cot;

4.4.2. Tnh Toan Cot ac Chu Nen Lech Tam,

Nen Uon

a.Tnh toan ve ben

259

4.4. COT CHU NEN LECH TAM, NEN UON

4.4.1. Cau Tao


Nen Uon

a.Tnh toan ve ben

Tiet dien cot giam yeu;

o lech tam tnh oi me > 20;

cot mat kha nang chu lc

Me = m (4.62)

Trong o:

m: o lech tam tng oi;

(4.63)

: he so ke en anh hng cua hnh dang tiet dien en s phat trien bien dang deo;

260

cNW

MAm

ieu kien ben cua cot

(4.64)

Khi cot khong chu trc tiep tai trong ong;

0.5fv; f

y 5300daN/cm2;

N/Anf > 0.1

ke en s phat trien bien dang deo;

(4.65)

nx, c

x, c

y: cac he so phu thuoc dang tiet dien;

261


Nen Uon

a.Tnh toan ve ben

c

ny

y

nx

x

n

fxI

My

I

M

A

N

1minmin

nycy

y

nxcx

x

n

n Wfc

M

Wfc

M

fA

Nc

b.1.Cot chu (N, Mx)

Tnh toan oi vi truc x

(4.66)

e = f(

x, m

e) - tra bang;

Tnh toan oi vi truc y

(4.67)

c: he so ke en anh hng cua Mx va hnh dang

tiet dien;

262


Nen Uon


c

e

fA

N

c

y

fcA

N

Khi mx 5,

(4.68)

, : cac he so;

Khi mx 10,

(4.69)

Khi 5 < mx

264

Bang 4.9. He so ,

b.2.Cot chu (N, My)

(4.71)

b.3.Cot chu (N, Mx, M

y)

(4.72)

(4.73)

exy

xac nh nh e;

265


Nen Uon


c

x

fA

N

43 4.06.0 cceyexy

c

exy

fA

N

c.1.Cac ieu kien on nh cuc bo cua ban canh

(4.74)

Cot co tiet dien khong la hnh hop

[b0/t

f], phu thuoc va xac nh nh cot nen

ung tam;

Cot co tiet dien hnh hop

[b0/t

f], phu thuoc va m;

266


Nen Uon


ff t

b

t

b 00

Khi m 0.3, [b0/t

f] lay nh tren;

Khi m 1 va 2 + 0.04m

(4.75)

Khi m 1 va > 2 + 0.04m

(4.76)

Khi 0.3 < m < 1, [b0/t

f] c noi suy;

267

c.1.Cac ieu kien on nh cuc bo cua ban canh

f

E

t

b

f

0

mf

E

t

b

f

01.013.04.00

Cot tiet dien ch H, hnh hop co Ix > I

y va kha

nang chu lc cua cot c quyet nh bi ieu

kien on nh tong the trong mat phang uon;

Theo bang tra (4.10)

Cot tiet dien ch H, hnh hop co Ix > I

y va kha

nang chu lc cua cot c quyet nh bi ieu

kien on nh tong the ngoai mat phang uon;

[hw/t

w] = f(m, , )

(4.77)

268

c.2. Cac ieu kien on nh cuc bo cua ban bung

1

(4.78)

(4.79)

Trong o:

y: khoang cach t truc x en th chu nen nhieu

nhat cua ban bung;

y1: khoang cach t truc x en th xa nhat cua

ban bung chu keo do Mx;

269


yI

M

A

N

x

x

11 yI

M

A

N

x

x

Khi 0.5

[hw/t

w], lay theo bang (4.10);

Khi 1

(4.80)

Trong o:

= 1.4(2 - 1)/ (4.81)

= V/hwtw (4.82)

Khi 0.5 < < 1, [hw/t

w] c noi suy;

270


fEE

t

h

w

w 8.342

1235.4

22

Thng chon cot tiet dien ch H (oi xng hoac

khong oi xng);

b. Xac nh tiet dien cot H (oi xng)

Chon b, h

h = (1/10 1/15)lc;

b = (1/20 1/30)lc; b = (0.3 0.5)h

Xac nh dien tch tiet dien cot

(4.83)

272

4.4.3. Xac nh Tiet Dien Cot ac Chu Nen

Lech Tam, Nen Uon

a. Chon dang tiet dien cot

ce

ycf

NA

e: xac nh theo

x va m

x = e

x/

x = M

x/N

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