chuong 1 - dai cuong ve ket cau thep

CHNG 1
I CNG V KT CU THP
u v khuyt im ca Kt cu thp:
a. Kh nng chu lc ln v tin cy cao.

b. Trng lng nh: c = /f

c. Tnh cng nghip ha cao

d. Tnh c ng trong vn chuyn, lp rp

e. Tnh Kn

f. B n mn

g. Chu la km

2. Phm vi ng dng

Nh cng nghip

Nh nhp ln

Khung nh nhiu tng

Cu ng b, ng st

Kt cu thp cao

Kt cu bn

Cc loi kt cu di ng

* So snh cc phng n TK

3. Yu cu i vi kt cu thp

Yu cu v s dng: an ton, bn, p

Yu cu v kinh t: Tit kim, cng ngh ch to, thi cng nhanh, in hnh ha kt cu thp

4. Vt liu thp xy dng

Thp (gang) = Fe + C

Fe2O3, Fe3O4 gang(trn 1.7% C) kh bt C thp

Thp Carbon: C

5. Cc mc thp dng trong XD

Thp Carbon thp cng thng:

Nhm A: cht ch v tnh cht c hc

Nhm B: cht ch v thnh phn ha hc

Nhm C: c hai

Gii hn chy: 2200 2700daN/cm2

Gii hn bn: 3300 5400 daN/cm2

b. Thp cng kh cao:

C thp, hp kim thp

fy = 3100 4000 daN/cm2

ft = 4500 5400 daN/cm2

Gi thnh cao hn thp C

c. Thp cng cao:

fy > 4400daN/cm2

ft > 5900daN/cm2

Tit kim vt liu 25 30%

6. S lm vic ca thp khi chu ti trng

Cc c trng c hc ch yu: ng sut gii hn, bin dng gii hn, module n hi.

Thp carbon cao khng c thm chy do r rt gii hn chy ly bao nhiu?

Cc c trng c hc ch yu

Gii hn t l tl , gii hn chy c , gii hn bn b , bin dng khi t 0 v module n hi E.

Khi < tl : l thuyt n hi, E=const.

tl < < c : l thuyt n hi do, E const.

= c : l thuyt do.

Cc c trng c hc ch yu (tt)

b: cng tc thi.

0: bin dng khi t, c trng cho do dai. 0 ln hn h 200 ln. Kh b ph hoi do.

Khi kt cu thp chu nn: ging nhau trong giai on trc cng c. Kh xc nh b thp c C thp.

S ph hoi gin
L s ph hoi bin dng nh, km theo vt nt, vt liu lm vic trong giai on n hi.Mt s iu kin gy ph hoi gin: ha gi, bin cng, chu ng sut cc b d gy sp hn khi b ph hoi do.

S ph hoi gin (tt)

S ph hoi gin (tt)
Hin tng cng ngui l hin tng tng gii hn n hi ca thp do bin dng do trc lm thp gin, gy bt li.Cng ngui khi: gia cng ngui, un ngui, ct bng my ct, t l.

Thp chu ng sut phc tp, tp trung ng sut

Thp chu ng sut phc tp, tp trung ng sut (tt)
S chy ca vt liu ch yu l do s trt di tc dng ca ng sut tipKhi 1 = 2 th = 0, s chy khng xut hin, s ph hoi l t gin.Thng gp: trng hp ng sut cc b do bin i hnh dng t ngt: l khot, rnh ct, ng lc.

Thp chu ti trng lp
Gy mi, ng sut ph hoi < b.Ph hoi gin, t ngt, km theo vt nt.

S ha gi ca thp
Tnh cht ca thp thay i dn theo thi gian. gin v dai va p gim i, thp tr nn gin hn.Thp tr nn cng hn nhng km do hn.

dai va p
nh gi mc thp d chuyn sang gin v nh hng ca ng sut tp trung. dai va p c gi tr bng cng ph hoi mu chia cho din tch tit din mu.

7. Quy cch thp cn dng trong xy dng

Thp hnh:

Thp gc u cnh, khng u cnh.

Thp ch I

Thp ch [

Thp I cnh rng

Thp ng

Thp ch T

Thp ray

Thp vung

Thp trn

b. Thp hnh dp, cn ngui
Thnh mng, nh, dng cho kt cu thp nh, chu lc nh nhng cn cng ln.C s cng ngui nhng gc un, chng g km.

NGUYN TC TNH TON KCT
Lp s kt cu:Qui m: kch thc, ti trng, mc ch, tui th.iu kin nn mng, mi trng.Tnh hnh cung cp vt t.K k thut, kh nng ch to, vn chuyn, lp dng.Module v thng nht ha, tn dng thit k nh hnh, TK mu.nh hng n gi thnh.

NGUYN TC TNH TON KCT (tt)
M hnh thc t v m hnh tnh ton:Phn nh kh nng lm vic ch yu nht, khai thc ti a kh nng chu lc, lm vic an ton.n gin, thun tin trong thit k.

NGUYN TC TNH TON KCT (tt)
Cc giai on tnh ton: Gi nh trc cc thng s v hnh hc, tit din, cng.Xc nh ni lc v kim tra tit din gi nh. Nu khng t, tr li iu chnh giai on 1.

8. Phng php tnh KCT
Phng php trng thi gii hn (TTGH).TTGH: ti kt cu thi khng tha mn cc yu cu ra khi s dng, thi cng.

Nhm trng thi gii hn 1
Mt kh nng chu lc hoc khng cn s dng c na.Ph hoi v bn, mt n nh, mt cn bng v tr, bin i hnh dng.N SN: ni lc trong cu kin ang xt. C gi tr ln nht c th xy ra trong sut thi gian s dng.S: Ni lc gii hn m cu kin c th chu c.

Nhm trng thi gii hn 1 (tt)

N = Pic Qn nc

f = S = A f c

ft = S = A ft c

Dng ti trng tnh ton

Nhm trng thi gii hn 2
Lm cho kt cu khng s dng bnh thng c na hoc gim tui th.Vng, ln, rung, nt.
Dng ti trng tiu chun

Cng tiu chun v cng tnh ton
Thp Carbon & thp cng kh cao: fy = ci vi thp cng cao:
fu = b
Cng tnh ton:
f = fy/M ft = fu/ M

M: h s an ton vt liu

M = 1,05 i vi thp cng thng v cng kh cao.

Vi cc dng chu lc khc, nhn thm h s chuyn i

c : h s iu kin lm vic
Xt n nh hng trong qu trnh s dng: ti trng tc dng, gi thit gn ng, m, nhit , n mn.Ch p dng cho 1 s cu kin c iu kin s dng ring.
Bng I.14, ph lc 1, trang 306 (Phm Vn Hi)

n : h s an ton v s dng
Nhn vo ti trng hoc ni lc.Ph thuc vo mc quan trng, cp bn ca cng trnh.S dng trong mi tnh ton.
Cp c bit: n = 1

Cp thng thng: n = 0,98

Cp t quan trng: n = 0,9

TI TRNG V TC NG
Theo TCVN 2737:1995.Ti trng thng xuyn: khng bin i gi tr, v tr, phng chiu.Ti trng tm thi:Tm thi di hn.Tm thi ngn hn.Ti trng c bit.

Q : h s tin cy v ti trng
Do s bin thin ti trng khc thng.Vt liu thp: Q = 1,05Ti trng gi: Q =1,2Ti trng tm thi trn sn: Q = 1,2 hoc 1,3

T HP TI TRNG
TH c bn: TX + DH + NHTH c bit: TX + DH + NH + 1 BH s t hp nc : th hin xc xut xy ra ng thi nhiu ti trng u vi tr s ln nht l t.

T HP TI TRNG (tt)
Khi trong TH c bn ch c 1 ti trng ngn hn : nc = 1Khi trong TH c bn c nhiu ti trng ngn hn: nc = 0,9TH c bit: mi ti trng ngn hn nhn vi nc = 0,8TX v DH khng nhn nc

9. TNH TON CU KiN

Cu kin chu ko ng tm:

Cu kin chu un:

n hi:

b. Tnh cu kin chu un
C xt n bin dng do:

b. Tnh cu kin chu un (tt)
Moment un gii hn:
Wd = 2S : moment chng un do

Wd = 1,5Wn i vi tit din ch nht

Wd = 1,2Wn i vi tit din ch I

b. Tnh cu kin chu un (tt)
Ti im c v tc dng ng thi kh ln s lm tng bin dng do

c. Tnh cu kin theo TTGH 2
[]

3. Cu kin nn ng tm

Tnh v bn: thanh ngn

Tnh n nh: khi N t ti Ncr th thanh bt u cong.

Cng thc Euler:

K: E = const , tl

3. Cu kin nn ng tm (tt)
mnh nh nht vn dng c cng thc Euler:Khi nh hn, s mt n nh xy ra khi c bin dng do:

Thc t c lch tm nh: lch tm ngu nhin, cong ban uH s un dc: H s tra bng II.1 ph lc II, hoc cng thc sau:

4. Cu kin ko, nn lch tm
Va chu lc dc (ko, nn) va chu moment.Lc dc t lch tm so vi trc.Quan h gia lch tm v moment un:

4. Cu kin ko, nn lch tm (tt)

Cu kin chu ko lch tm, cu kin ngn chu nn lch tm (tnh theo bn):

Tnh n nh thanh chu nn lch tm (nn-un):

Ngay khi t ti, thanh b cong do moment:

M = N.e

Khi N tng, bin dng tng khng tuyn tnh vi N, do moment: M = N.(e+f)

ng sut ti hn cre ph thuc vo: mnh ca thanh. lch tm e ca lc dc.Hnh dng ca tit din.Kim tra n nh trong mt phng unH s gim cng tnh ton un lch tm, nn un (tra bng II.2):

Kim tra n nh trong mt phng vung gc vi mt phng un:

CHNG 2
LIN KT
Lin kt hn: Gim cng ch to, khi lng kim loi.Hnh thc cu to lin kt n gin.Bn v kn.Nhit cao, gy gin vt liu, chu ti trng ng km.Kh kim tra cht lng ng hn.

Lin kt bu lng
Tn cng v vt liu nhiu.Chu c ti trng ng.Thun tin trong tho, lp, c th ch s dng th cng.

A. LIN KT HN

Cc phng php hn:

- Hn h quang in bng tay

- Hn h quang in t ng v na t ng di lp thuc hn.

- Hn h quang in trong lp kh bo v
Hn Hi

NG HN I U

NG HN I U (tt)
Cng tnh ton ca ng hn:Khi chu nn: fwc = fKhi chu ko: fwt = f hay fwt = 0,85fKhi chu ct : fwv = fv

Cng thc kim tra bn

Cng thc kim tra bn (tt)
Hn i u thng gc chu ko, nn:ng hn xinchu ko, nn:

Cng thc kim tra bn (tt)
i u thng gc chu moment:i u thng gc chu M v V:

NG HN GC

Cng chu ct tnh ton ca thp ng hn : fwf
- Cng tnh ton chu ct ca thp c bn trn bin nng chy: fws = 0,45fu

Tnh ton lin kt ghp chng chu lc dc trc:

Tnh ton lin kt ghp chng chu lc dc trc (tt):

Lin kt c bn ghp

Lin kt c bn ghp (tt)

Tnh ton Lin kt c bn ghp

Thit k bn ghp: chn trc din tch bn ghp, tnh chiu di cn thit ca ng hn.

Lin kt hn hp
Kim tra iu kin bn:

Lin kt hn hp (tt)
Thit k: chn trc chiu rng bn ghp gn bng chiu rng thp c bn b tr ng hn i u tnh lc truyn qua bn ghp:
Tnh tng chiu di cn thit ca ng hn:

ng hn gc chu moment v lc ct:

ng hn gc ch chu moment
Theo tit din 1:Theo tit din 2:

ng hn gc ch chu lc ct

ng hn gc chu M v V ng thi

LIN KT BULONG
ng knh : 12 - 48 mmng knh Bulong neo: 100mmChiu di phn ren: l0 2,5dChiu di bulong: l = 35 300mm

LIN KT BULONG (tt)

Bulong th v thng
Sn xut t thp C bng cch rn, dp.ng knh thn nh hn ng knh l 2 3mm.Khng nn dng trong cc cng trnh quan trng vi thp c bn c cng fy > 3800daN/cm2

Bulong tinh
SX t thp C, thp hp kim bng cch tin, chnh xc cao.ng knh l ln hn ng knh bulong khng qu 0,3mm. bn tng t bu long th v bulong thng.

Lm vic chu trt

Bulong b p mt

Bulong chu ko

Bulong cng cao
Lm t thp hp kim, sau cho gia cng nhit. chnh xc ging bulong thng.Lc xit mnh, to ma st ln, chu lc cao hn.

Cu to lin kt bulong
i vi thp tm: lin kt c 1 bn ghp v LK chng c lch tm nn chu moment un ph, cn tng s bulong thm 10% so vi tnh ton.i vi thp hnh: Khi LK khng i xng vi cu kin mm, cn tng s bulong thm 10% so vi tnh ton.

B tr bulong

B tr bulong (tt)

TNH TON LIN KT BULONG
LK bulong chu lc dc trc:Thng thng dng loi c d=20-24mmCc cng trnh nng: dng loi c d=24 30mmKch thc bn ghp: Abg ANn b tr s bulong theo hng ti a truyn lc u theo chiu ngang cu kin (vung gc vi phng ca lc)

LK bulong chu lc dc trc:

Tnh ton s lng bulong theo chu ct v p mt

Tnh ton s lng bulong theo K chu ko

Tnh ton s lng bulong theo K moment v lc ct

Tnh ton s lng bulong theo K moment v lc ct (tt)

Tnh ton s lng bulong theo K moment v lc ct (tt)

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chuong 1 - dai cuong ve ket cau thep

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