debaivaloigiai thep

8/2/2019 debaivaloigiai thep

1/31

1

N=120KN

e=100

N=120

320

12

12

286

12

Hnh 2.12

Chng 2: Lin kt

V d 2.1:

Kim tra kh nng chu lc cho lin kt hn i u ni 2 bn thp c kch thc (320x12)mm

nh hnh v 2.12. Bit lin kt chu lc ko N=120KN c t lch tm 1 on e = 10cm. S dng vt

liu thp CCT34s c f=2100daN/cm2; que hn N42 c fwt = 1800 daN/cm2; C=1;

Bi lm:

Do lc trc t lch tm 1 on e = 10cm, sinh ra mmen:

M = Ne = 120.10 = 1200 KNcm = 120000 daNcm.

Chiu di tnh ton ca ng hn:

lw = b 2t = 32 2.1,2 = 29,6 cm;

Mmen khng un ca ng hn:

)(23,1756

2,1.6,29

6

222

cmhl

Wfw

w ===

Din tch ca ng hn:

Aw = lw.t = 29,6.1,2 = 35,52 (cm2

)Kh nng chu lc ca ng hn:

)/(1800)/(65,102252,35

12000

23,175

120000 22 cmdaNfcmdaNA

N

W

Mcwt =


2/31

2

T (1) v (2), ta c lc ln nht tc dng ln lin kt l:

Nmax = min (N1, N2) = 909 KN

V d 2.3:

Kim tra kh nng chu lc cho lin kt hn gc cnh ni 2 bn thp c kch thc (320x12)mm,

lin kt s dng 2 bn ghp c kch thc (300x8)mm nh hnh v 2.13. Bit lc ko tnh ton N = 1800

KN, chiu cao ng hn hf=10mm; chiu di thc t ca ng hn ltt = 400mm; S dng vt liu thp

CCT34 c f=2100 daN/cm2; que hn N42 c fwf= 1800 daN/cm2; fws=1500daN/cm

2; f=0,7; s= 1; C=1;

N=180KNN

b2=

320

t2=

12

t1=10

t1

ltt=400 50 ltt=400

b1=

300

Hnh 2.13

Bi lm:

a, Kim tra bn cho bn ghp:

Abg = 2.0,8.30 = 48 (cm2) > A = 32.1,2 = 38,4 (cm2)

Vy bn ghp m bo iu kin bn.

b, Kim tra kh nng chu lc cho lin kt:

Chiu di tnh tan ca 1 ng hn: lf= ltt 1 = 40 -1 = 39 (cm)Din tch tnh ton ca cc ng hn:Af= lf. hf= 4.39.1 = 156 (cm

2)

Ta c: (fw)min = min (ffwf; s fws) = min (1800.0,7; 1500.1) = 1260 (daN/cm2)

Kh nng chu lc ca lin kt:

( ) )/(1260)/(85,1153156

180000 2min

2cmdaNfcmdaN

A

Ncw

f

====

Vy lin kt m bo kh nng chu lc.

V d 2.4:

Thit k lin kt hn gc cnh ni 2 bn thp c kch thc (320x12)mm, lin kt s dng 2 bn

ghp c kch thc (300x10)mm nh hnh v 2.14. Bit lc ko tnh ton N = 1200 KN. S dng vt

liu thp CCT34 c f=2100 daN/cm2; que hn N42 c fwf = 1800 daN/cm2; fws = 1500 daN/cm

2; f=0,7;

s= 1; C=1;

Bi lm:

a, Kim tra bn cho bn ghp:Abg = 2.1.30 = 60 (cm2) > A = 32.1,2 = 38,4 (cm2)


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3


b, Xc nh chiu di ng hn:

Vi chiu dy tm thp c bn l 12mm v thp bn

ghp l 10mm, chn chiu cao ng hn h f = 10mm

m bo iu kin:

hfmin =6(mm) < hf=10 (mm) < hfmax =1,2tmin = 12 (mm).

Ta c: (fw)min = min (ffwf; s fws) = min (1800.0,7; 1500.1) = 1260 (daN/cm2) Hnh 2.14

Tng chiu di cn thit ca ng hn lin kt:

( )( )

)(24,951.1.1260

120000

min

mincm

hf

Nlf

hl

N

A

N

fcw

fcw

fff

====

Chiu di thc t ca 1 ng hn: lf= (lf/4) + 1 =95,24/4 + 1 25 (cm)

V d 2.5:

Xc nh lc ln nht tc dng ln lin kt hn gc u ni 2 bn thp c kch thc

(450x16)mm, lin kt s dng 2 bn ghp c kch thc (450x12)mm nh hnh v 2.15. Bit lc kotnh ton N (KN) c t lch tm 1 on e = 10 cm. S dng vt liu thp CCT34 c f=2100 daN/cm 2;

que hn N42 c fwf= 1800 daN/cm2; fws = 1500 daN/cm

2; f=0,7; s= 1; C=1;

t2=16

t1=12

t1

b=450

N=?N

e=100

Hnh 2.15

Bi lm:

a, Kim tra bn cho bn ghp:Abg = 2.1,2.45 = 108 (cm2) > A = 45.1,4 = 72 (cm2)


b, Xc nh ni lc ln nht:

Vi chiu dy tm thp c bn l 16mm v thp bn ghp l 12mm, chn chiu cao ng hn h f =

14mm m bo iu kin:

hfmin =6(mm) < hf=14 (mm) < hfmax =1,2tmin = 14,4 (mm).


Chiu di thc t ca 1 ng hn:lw(tt) = b- 1 = 45 1 = 44 (cm)

Din tch tnh ton ca cc ng hn trong lin kt: Af=lw hf=2.44.1,4 = 123,2 (cm2)

Mmen khng un ca cc ng hn trong lin kt:

=== )(5,9036

4,1.44.2

6

.3

22

cmhl

Wf

f

f

Do lc trc t lch tm 1 on e = 10cm, sinh ra mmen:

N=120N

b2=320

t2=12

t1=10

t1

ltt=? 50 ltt=?

b1=300


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4

M = Ne = N.10 = 10N (KNcm) = 1000N (daNcm).

T iu kin bn cho lin kt:

( )cw

ffff

fW

eN

A

N

W

M

A

N

min

.+=+=

Ta c, lc ln nht tc dng ln lin kt:( )

)(657)(65677

5,903

10

2,123

1

1.1260

1min KNdaN

W

e

A

fN

ff

cw

++

=

+

V d 2.6:

Thit k lin kt hn gc cnh ni 2 thp gc L 100x75x8, lin kt cnh di, vi bn thp c

chiu dy t=10mm. Bit lc ko tnh ton N = 400(KN). S dng vt liu thp CCT34 c f=2100

daN/cm2; que hn N42 c fwf=1800daN/cm2; fws = 1500 daN/cm

2; f=0,7; s= 1; C=1;

N=400KN L100x75x8

ls

f

lm

f

t=10

N

Hnh 2.16

Bi lm:

Vi chiu dy tm thp l 10mm v thp gc ghp l 8mm, chn chiu cao ng hn h fs = 8mm, hf

m =

6mm m bo iu kin:

hfmin =4(mm) < hfs

=8 (mm) < hfmax =1,2tmin = 9,6 (mm).hfmin =4(mm) < hf

m =6 (mm) < hfmax =1,2tmin = 9,6 (mm).


Ni lc ng hn sng chu: Ns = kN = 0,6N = 240 (KN)

Ni lc ng hn mp chu: Nm = (1-k)N = 0,4N = 160 (KN)

Tng chiu di tnh ton ca ng hn sng:

( )= cm

hf

Nl

s

fcw

ss

f40

8,0.1.1260

24000

min

Tng chiu di tnh ton ca ng hn mp:

( ) = cm

hf

Nl

m

fcw

mm

f 226,0.1.1260

16000

min

Vy, chiu di thc t ca 1 ng hn sng: lfs= ( lf

s)/2 + 1 = 21 (cm)

Chiu di thc t ca 1 ng hn mp: lfm= ( lf

m)/2 + 1 = 12 (cm)

V d 2.7:

Kim tra kh nng chu lc cho lin kt bulng ni 2 bn thp c kch thc (400x16)mm, lin

kt s dng 2 bn ghp c kch thc (400x12)mm nh hnh v 2.17. Bit lc ko tnh ton N = 2000


5/31

5

KN c t lch tm 1 on e=5cm. S dng vt liu thp CCT34 c f=2100 daN/cm2; s dng bulng

thng c cp bn 4.6 c fvb = 1500 daN/cm2; fcb = 3950 daN/cm

2; ng knh bulng d=22mm;

C=1;

Bi lm: Hnh 2.17

a, Kim tra bn cho bn ghp:

Abg = 2.1,2.40 = 96 (cm2) > A = 1,6.40 = 64 (cm2)



Kh nng chu ct ca 1 bulng trong lin kt:

[N]vb=n v. Ab.b. fvb=2.3,8.0,9.1500=10260 (daN)

Kh nng chu p mt ca 1 bulng trong lin kt:

[N]cb=d.(t)min.b. fcb=2,2.1,5.0,9.3950=11731,5(daN)

Kh nng chu lc nh nht ca bulng:

[N]bmin = min([N]vb, [N]cb) = 10260 (daN)

Do lc trc t lch tm 1 on e = 5cm, sinh ra

mmen:

M = Ne = N.5 = 2000.5 (KNcm) = 100000 (daNcm).

Lc ln nht tc dng ln dy bulng ngoi cng do mmen gy ra:

==

2

1.

i

bMl

lMN )(5,23809

61830

30.1000000222

daN=++

Lc ln nht tc dng ln 1 bulng trong lin kt:

=+=n

N

n

NN bMb

1

[ ] )(10260)(952436

100000

6

6,23809min daNNdaN b = A = 1,6.40 = 64 (cm2)


b, Thit k lin kt:

Chn bulng c ng knh d=20mm.


e=50

N=2000KNN

60 60 60 60 60

60

60

60

60

60

50

50

60 60


6/31

6

[N]vb = n v. Ab.b. fvb= 2.3,14.0,9.1500 = 8478 (daN)


[N]cb = d.(t)min.b. fcb= 2.4.0,9.3950 = 28440 (daN)


S lng bulng cn thit trong lin kt:

[ ]

6,10

8478

90000

min

===bN

Nn

Chn 12 bulng v b tr nh hnh v.

N=1000KNN

50 50 5050

50

100

100

1

00

50

t2=16

t1=12

t1

Hnh 2.18

Kim tra bn cho bn ghp:

Ahn = A -Agy = 40.1,6 4.2,2.1,6 = 49,92 (cm2)

)/(2100)/(9,180292,49

90000 22cmdaNfcmdaN

A

Nc

hn

= A = 1,6.40 = 64 (cm2)



N=4000KNN

50 50 50 50 5050

50

100

100

100

50

t2=16

t1=12

t1


7/31

7

Kh nng chu ko ca 1 bulng cng cao trong lin kt: [N] b = n f. Abn.b1. fhb

2b

Ta c: fhb = 0,7 fub= 0,7.11000 = 7700 (daN/cm2)

b1 =1 (do s lng bulng trong lin kt na>10);

b2 =1,17; =0,35; n f=2; Abn = 2,45 (cm2)

[N]b = 2.2,45.1.7700.

17,1

35,0= 11287(daN)

Lc ln nht tc dng ln 1 bulng trong lin kt:

)(11287][)(1000020

200000daNNdaN

n

NN bb = A = 1,6.40 = 64 (cm2)


b, Xc nh lc ln nht tc dng ln lin kt:


[N]vb = n v. Ab.b. fvb= 2.3,14.0,9.1500 = 8478 (daN)


[N]cb =d.(t)min.b. fcb= 2.1,5.0,9.3950 = 10665 (daN)


[N]bmin = min([N]vb, [N]cb ) = 8478 (daN) Hnh 2.21

Ngoi lc ln nht tc dng ln lin kt:

[ ] )(3052)(30520836.8478.min KNdaNnNN b ===

NN

60 60 60 60 60

60

60

60

60

60

50

50

60 60


8/31

8

Chng 3: Dm thp

V d 3.1:

Kim tra kh nng chu lc cho dm ch IN036 c s dm n gin nhp l = 6m, chu ti trng

phn b u qc= 2500 daN/m nh hnh v 3.7. Bit cc c trng hnh hc ca thp IN 036: Wx = 743

cm3; Ix = 13380 cm4; h = 36cm; Sx = 423 cm

3; tw = 12,3 mm; b qua trng lng bn thn dm. S dng

thp CCT34 c f =2100 daN/cm2; fV =1250 daN/cm2; vng [/l] = 1/250; C=1; q=1,2.

l=6m

q

M

V

ql /82

ql/2

ql/2

y

xh

I No36

Hnh 3.7

Bi lm:

Ti trng tnh ton tc dng ln dm:

qtt = qcq= 2500.1,2 = 3000 (daN/m)

Mmen ln nht tc dng ln dm:

)(135008

6.3000

8

22

max daNmlq

M tt ===

Lc ct ln nht tc dng ln dm:

)(90002

6.3000

2max daN

lqV tt ===

Kim tra bn cho dm hnh:

)/(2100)/(1817743

10.13500 222

max cmdaNfcmdaNW

Mc

x

=


9/31

9

Thit k tit din dm ch I nh hnh cho dm c s dm n gin nhp l = 6m, chu ti trng

phn b u qc= 1000 daN/m nh hnh v 3.8. S dng thp CCT34 c f =2100 daN/cm2; fV =1250

daN/cm2; vng [/l]=1/250; C=1; q=1,2.

l=6m

q

M

V

ql /82

ql/2

ql/2

y

xh

I No?

Hnh 3.8

Bi lm:

Ti trng tnh ton tc dng ln dm:

qtt = qcq= 1000.1,2 = 1200 (daN/m)

Mmen ln nht tc dng ln dm:

)(54008

6.1200

8

22

max daNmlq

M tt ===

Lc ct ln nht tc dng ln dm:

)(36002

6.1200

2max daN

lqV tt ===

T iu kin m bo tra bn cho dm hnh:

)(1,2572100

10.5400 32

maxmax cmf

MWf

W

M

c

xc

x

==


10/31

10

)/(2100)/(1913289

10.5529 222

max cmdaNfcmdaNW

Mc

x

=


11/31

11

)/(11242,1

7,1348

)/(7,134810.5,4

289.2100

5,4

.)/(2100

1

2

2max

1

1

mdaNq

q

mdaNWf

qcmdaNfW

M

q

tt

xcc

x

c

tt

==

===


12/31

12

18

10

16

1200

16

2

0

f

200.

200

18

tf

C1

Hnh 3.11

Bi lm:

Xc nh tit din sn gi t iu kin p mt t u:

)(3,311.3200

100000 2maxmax cmf

VAf

A

V

cc

scc

s

==

Chn bs = bf= 20 (cm)

Chiu dy sn gi:

)(6,120

3,31cm

b

At

s

ss =

Kim tra chiu dy sn theo iu kin n nh:

)(65,06,31

20

6,316,31

2100

10.1,26

cmb

tf

E

t

b s

ss

s ====

Vy, chn sn c kch thc bS.tS = 20.1,8 (cm)

Kim tra n nh tng th:

Ta c: c1 = 0,65tW. )(54,20210010.1,2.1.65,06

cmfE ==

A = AS + Aqu = 1,8.20 + 1.20,54 = 56,54 (cm2)

IZ = )(120212

1.20

12

54,20.1

12

.

12

. 4333

1

3

cmtbct

ssw =+=+

61,454,56

1202===

A

Ii zz (cm)

2661,4

120===

z

wz

i

h . Tra bng ta c = 0,949.

)/(2100)/(1864949,0.54,56

100000 22max cmdaNfcmdaNA

Vc =


13/31

13

Kim tra kh nng chu lc cho vng dm gn gi ta ca dm I t hp hn c kch thc bn

bng (1200x10)mm, bn cnh (200x16)mm c s nh hnh v 3.12. Vmax= 1500 KN. S dng thp

CCT34 c f =2100 daN/cm2; fc=3200daN/cm2; Bit c1 = 0,65tW. fE

C 181 C1.

120

0

16

16

.

.

.

200.

10.

Hnh 3.12

Bi lm:

Tnh c1 = 0,65tW. )(54,20210010.1,2.1.65,06

cmfE ==

A = AS +2 Aqu = 1,8.20 + 2.1.20,54 = 77,08 (cm2)

IZ = )(120412

1.2012

54,20.1.212

.12.2 4

333

1

3

cmtbct ssw =+=+

95,308,77

1204===

A

Ii zz (cm)

38,3095,3

120===

z

wz

i

h . Tra bng ta c = 0,936.

)/(2100)/(2080936,0.08,77

150000 22max cmdaNfcmdaNA

Vc= A = 1.120 = 120 (cm

2

)Vy bn ghp m bo iu kin bn.


14/31

14

MM xx

Vx

Vx

1100

1200

16

16

.

.

.

200.

200.

Hnh 3.13

Chn chiu cao ng hn hf=8(mm) tha mn iu kin:

hfmin = 6(mm) < hf=8(mm) < hfmax =1,2tmin = 9,6 (mm).

Chiu di tnh tan ca 1 ng hn:

lf= ltt 1 = 110 -1 = 109 (cm)

Din tch tnh ton ca cc ng hn:

Af= lf. hf= 2.109.0,8= 174,4 (cm2)

M men khng un ca cc ng hn:

Wf= lf2. hf/6= 2.109

2.0,8/6 = 3168,3 (cm2)

Mmen un m mi hn ni bng phi chu:

)(5,21305,0.2000380599

144000.300. KNmeV

I

IMM x

d

wxw

=+=+=

Trong :

I =

++

4122

12

233

fff

ffwh

tbbtth

w

=

++

46,121.20.2

12

20.6,12

12

1.120 233

= 380599 (cm4)

IW =12

3

wthw =12

1.1203

= 144000(cm4)


Kh nng chu lc ca lin kt:22

+

= fw

f

x

W

M

A

V

( ) )/(1260)/(8,11463,3564

100.21350

4,174

200000 2min

2

22

cmdaNfcmdaN w =


15/31

15

Chng 4: Ct

V d 4.1.Chn tit din ct c chu nn ng tm (I nh hnh ). Bit ct c c chiu di l = 5 m.

Ct c lin kt theo phng x hai u khp; theo phng y 1 u ngm, mt u khp. Ti trng tc

dng N = 3500 kN. Vt liu l thp CCT38 c f = 2300 daN/cm2; []= 120, =1 .

Bi lm:

f = 2300 daN/cm2=23 kN/cm

2.

Chiu di tnh ton ca ct

ly = 0,7.5= 3,5 (m); lx=1.5=5 (m)

Chn sb mnh =40 tra bng c gi tr=0,900.

Din tch tit din ct cn thit l:

Ayc = N/(f. . c)=3500/(23.0,9)= 169,1 (cm2).

Bn knh qun tnh

ixyc = lx/ = 500/40= 12,5 (cm).

iyyc = ly/ = 350/40= 8,75 (cm).

Chiu rng v chiu cao tit din ct:

byc = iyyc/y =8,75/0,24= 36,5 (cm);

hyc = ixyc/x =12,5/0,42= 29,8 (cm).

T bng tra chn thp I cnh rng 40K1 c:

A=175,8 cm2; h= 393 mm; b= 400 mm; d=11mm; t=16,5

mm; r=22 mm; Ix= 52400 cm4; Wx =2664 cm

3; ix= 17,26

cm; Sx=1457 cm3;

Iy= 17610 cm4; Wx =880 cm

3; ix= 10 cm; g=138 kG/m.

mnh y= ly/ iy = 350/10= 35 ;

x= lx/ ix = 500/17,26= 28,97max=35 =0,918.

Kim tra

= N/( A.)= 3500/(175,8.0,918)= 21,7 (kN/cm2) < f. c = 23 kN/cm2.

n nh tng th ct chn tha mn. (k cn kim tra cc b vi tit din nh hnh)

V d 4.2. Chn tit din ct c chu nn ng tm (I t hp ). Bit ct c c chiu di l = 6,5 m.

Ct c lin kt theo phng x hai u khp; theo phng y 1

u ngm, mt u khp. Ti trng tc dng N = 4500 kN.Vt liu l thp CCT38 c f = 2300 daN/cm2; []= 120, =1

.

Bi lm:


2.

Chiu di tnh ton ca ct

ly = 0,7.6,5= 4,55 (m); lx=1.6,5=6,5 (m)


16/31

16

Chn sb mnh =40 tra bng c gi tr=0,900.

Din tch tit din ct cn thit l:

Ayc = N/(f. )=4500/(23.0,9)= 217,3 (cm2).

Bn knh qun tnh

ixyc = lx/ = 650/40= 16,25 (cm).

iyyc = ly/ = 455/40= 11,35 (cm).

Chiu rng v chiu cao tit din ct:

byc = iyyc/y =11,35/0,24= 47,4 (cm);

hyc = ixyc/x =16,25/0,42= 38,7 (cm).

Chn tit din ct: cnh- 2.48.1,8=172,8 (cm2)

bng 217,3- 172,8= 44,5 (cm2)

hw =38,7-2.1,8=35,1 cm chn 36 cm;

tw44,5/36= 1,24 (cm); chn hw =38 cm; tw= 1,2 cm.

Kim tra n nh

-c trng hnh hc: Iy =2.1,8.483/12+38.1,23/12= 33183 cm4;

A=2.1,8.48+1,2.38=218,4 (cm2)

iy =4,218

33183=

A

Iy=12,3 (cm)

y= ly/ iy = 445/12,3= 36,2 ;

Ix =48.41,63/12- (48-1,2).38

3/12= 73964 cm

4;

ix =4,218

73964=

A

Ix =18,4 (cm)

x= lx/ ix = 650/18,4= 35,3max=36,2 =0,912.-kim tra n nh tng th

= N/( A.)= 4500/(218,4.0,912)= 22,6 (kN/cm2) < f. c = 23 kN/cm2.

( -f.c)/ f.c= 1,8%< 5% tha mn.

-kim tra n nh cc b bn bng

410.1,2

232,36==

E

f =1,2


17/31

17

Vy tit din chn tha mn iu kin n nh tng th, n nh cc b cnh v bng.

V d 4.4. Xc nh kh nng chu lc ca ct chu nn ng tm c cc s liu sau. Ct c tit

din ch I t hp, bn cnh ( 480x18)mm, bn bng (450x12) mm. Ct c chiu di l=6,5 m , hai u

lin kt khp. Cng thp f=2300daN/cm2, [] =120

Bi lm:

Chiu di tnh ton ca ct lx=ly = 0,7.6,5= 4,55 (m).

A=2.1,8.48+1,2.45=226,8 (cm2)

Iy =2.1,8.483/12 + 45.1,2

3/12= 33182 cm

4;

Ix =48.48,63/12- (48-1,2).45

3/12= 103778 cm

4;

iy =8,226

33182=

A

Iy=12,09 (cm); y= ly/ iy = 445/12,09= 36,8

ix =

8,226

103778=

A

Ix =21,4 (cm); x= lx/ ix = 445/21,4=20,8

max= y=36,8 =0,911.

Lc ln nht ct c th chu :

Nmax = A. .f. c =226,8.0,911.23.1= 4752 kN.


18/31

18

Chng 5:Dn

V d 5.1. Kim tra kh nng chu lc ca thanh dn ghp t hai thp gc c s hiu L 125x90x10,

chu lc nn N =500 KN. Bit chiu di tnh ton ca thanh lx=250 cm, ly =400 cm. Din tch tit din 1

thp gc Ag=20,6 cm2. Bn knh qun tnh tra bng ix =3,95 cm, iy = 2,6 cm; ix2 = 5,95 cm. Thp CCT34

c f = 2100 daN/cm2, []=120.

Bi lm: ix= iy (tra bng) = 2,6 cm; iy = ix2 (tra bng) = 5,95 cm


2.

x= lx/ ix=250/2,6=96,2


19/31

19

Phn kt cu gNn ng tm

Bi 1: Kim tra mt thanh nn ng tm 2 u lin kt khp c kch thc nh hnh

v. Bit lc nn tnh ton Ntt= 10T; Rn= 130 kg/cm2; []= 150.

Gii:

Kim tra v cng :Theo cng thc: = Ntt/Ath.

Ath= Ang - Agy= 18.15- 6.15= 180 cm2.

= Ntt/Ath= 10000/180= 55,6 kg/cm2

< Rn= 130 kg/cm2.

Vy thanh g tha mn iu kin chu lc v cng .

b) Kim tra vn nh

Agy= 6.15= 80 cm2.

Ang= 18.15= 270 cm2.

Agy/Ang= 80/270= 33%> 25% nn

Att= 4/3Ath= 4/3.180= 240 cm2.

rmin= 0,289.b= 0,289.15= 4,34 cm.

l0= l=420 cm.

max= ltt/rmin= 420/4,34= 97 < []= 150 tha mn.

= 3100/ 2= 3100/ 972= 0,33.

= Ntt/(.Ath)= 10000/(0,33.240)= 126 kg/cm2< Rn= 130 kg/cm

2.

Vy thanh gm bo iu kin vn nh.

Tcc kt qu trn thy rng vic kim tra n nh thng c tnh cht quytnh.

Bi 2: Chn tit din mt ct g chu nn ng tm trong mt kt cu chu lc lu

di bit chiu di tnh ton ltt= 5 m, ti trng tnh ton Ntt= 10 T.

Gi

i:Gi thit >75.

Dng tit din trn: A= 2278130

10000.

75,15

500.

75,15cm

R

Nl

n

tt ==

d= 1,135A

= 1,135278

= 18,9 cm.


20/31

20

Chn g c d= 20 cm, th li mnh max = 500/(0,25.20)= 100 >75 dng ng

cng thc.

b) Nu dng tit din vung :

A= 2282130

10000.

16

500.

16cm

R

Nl

n

tt ==

a=A

=282

= 16,8 cm.

Dng tit din vung c cnh 18x18 cm, th li mnh max = 500/(0,289.18)=

93,7 >75 dng ng cng thc.

Nu max 15cm, h / b < 3,5, khi mu = 1,15.

Gi thit b = 0,8h.


21/31

21

32

max 6,88912015,1

106,1227cm

Rm

MW

uu

ct =

==

4

5

323

23,1186525010

45010400

384

5

384

5cm

f

l

E

lqJ

tc

ct =

=

=

cmhbcmW

h ct 04,158,188,08,08,182

6,88915

2

1511

331

======

cmhbcmJhct

4,165,208,08,05,2023,151186515 2244

2 ======

Chn b = 18cm, h = 20cm.

Tnh li cc thng stit din chn.

5,318

20 15cm mu = 1,15

33

22

688912006

2018

6cm,Wcm

bhW

ct=>=

==

44

33

23118651200012

2018

12cm,Jcm

bhJ

ct=>=

==

Kim tra li tit din chn.

Gi thit v mu: b v h > 15cm, nn gi thit v mu l ng.

Bn un: Do khng c gim yu v gi thit v mu l ng nn khng cn kim tra.

Bn ct: Do l / h = 450 / 20 = 22,5 > 5 nn khng cn kim tra bn ct.

vng: Khng cn kim tra.

Bi 2: chn tit din mt dm g, bit: nhp 3,6 m; ti trng Ptc= 2T; h s vt ti

1,2; g c Rn= 130 kg/cm2; [f/l]= 1/250.

Gii:


22/31

22

Mmax= Ptt.l/4= (2000.1,2).360/4= 216000 kgcm.

D kin chn dm tit din ch nht c cnh 15 cm, h/b 3,5 mu= 1,15.

uu

th

n RmW

M.= Wct=

31445

15,1.130

216000

.cm

mR

M

uu

==

=

l

f

IE

lP

l

f tc

.48

.2

Ict =4

5

22

13500250.10.48

360.2000.

48

.cm

f

l

E

lPtc ==

.

Gi thit k= h/b= 1,25 b= 0,8h W= bh2/6= 0,8h3/6; I= bh3/12= 0,8h4/12.

Ta c: 0,8h3/6= 1445; 0,8h

4/12= 13500 h= 22,1 cm; h= 21,2 cm.

Chn bxh= 18x22 cm h/b= 22/18= 1,2< 3,5 vy gi thit ban u l ng.

W= bh2/6= 18.22

2/6= 1452 cm

3> Wct= 1445 cm

3.

I= bh3/12= 18.22

3/12= 15972 cm

4> Ict= 13500 cm

4.

Vy tit din chn tha mn yu cu.

Un xin

Bi 1: Chn tit din x g ca mt sn mi nh c dc = 250. Chiu di nhp

x g 3,6m. qtc = 130kG/m, qtt = 180kG/m. vng cho php200

1=

l

f. S ca

dm l dm n gin.

Bit cos = 0,906; sin = 0,423.

G nhm VI, Nm 18%, nhit 20C.

Li gii.

Ly cc thng su bi.

G nhm VI, Nm 18%, nhit 20C nn Ru = 130kG/cm2.

Gi thit mu = 1,15.


23/31

23

Phn ti trng theo 2 phng.

mkGqq

mkGqq

tctc

tctc

y

x/99,5425sin.130sin

/78,11725cos.130cos

0

0

===

===

mkGqq

mkGqq

tttt

x

tttt

y

/14,7625sin.180sin

/08,16325cos.180cos

0

0

===

===

Tnh ni lc.

cm.kGm.kG,,,lq

M

tt

y

x2641818264

8

6308163

8

22

==

==

cm.kGm.kG,,,lq

Mtt

x

y1233434123

8

631476

8

22

==

==

Hai m men ln nht ny cng xut hin trn cng 1 tit din gia dm.

Tnh Wctv chn b, h.

Chn k = 1,2, vi tga = 0,423 / 0,906 = 0,46.

T: uux

x mRtgkW

M+ ).1(

ct

uu

x

xWcm,),,(

,)tg.k(

mR

MW ==+

=+ 31297460211

151120

264181

cm,,,kWhx

91212972166 33 ===

b = 12,9 / 1,2 = 10,75cm

Chn h = 14cm, b = 12cm.

Tnh cc thng stit din chn.

322

3926

1412

6cm

bhWx =

==


24/31

24

322

3366

1214

6cm

hbWy =

==

433

274412

1412

12cm

bhJx =

==

4

33

201612

121412

cmhbJy ===

Kim tra tit din chn.

Gi thit v mu: Do c hai cnh tit din u nh hn 15cm nn mu = 1,0.

Bn un:

2

1203104336

12334

392

26418

cm/kGRm,W

M

W

Muu

y

y

x

x

maxymaxxmax ==+=+=+=

Tit din chn m bo yu cu cng .

vng:

cm,,

EJ

lqf

y

tc

x

x5960

201610

360109954

384

5

384

5

5

424

=

==

cm,0,

EJ

lqf

x

tc

y

y939

274410

3601078117

384

5

384

5

5

424

=

==

Hai vng ln nht ny cng xut hin trn mt tit din gia dm, v th:

cmfff yx 11,1939,0596,02222 =+=+=

200

1

324

1

360

1,11

=


25/31

25

Gii: Phn ti trng theo 2 phng:

qxtc= qtc.cos= 130 cos250= 117,8 kg/m; qytc= qtc.sin= 130 sin25

0= 54,9 kg/m.

qxtt= qxtc.n= 117,8.1,3= 153 kg/m;

qytt= qytc.n= 54,9.1,3= 71,4 kg/m.

Mmen un ln nht:

Mx= qxtt.l2/2= 153.1,22/2= 110,16 kg.m;

My= qytt.l2/2= 71,4.1,2

2/2= 51,4 kg.m.

Gi thit k= h/b= 1,2 v c tg250= 0,466.

Theo iu kin cng ta c:

Wx=3

132130.1

)466,0.2,11.(11016

.

).1(cm

Rm

tgkM

uu

x =+

=+

Wx = bh2/6= h

3/(6k) h= cmkW 8,9132.2,1.66 3

3 ==

b=h/k= 9,8/1,2= 8,2 cm. Chn tit din bxh= 8x10 cm v kim tra li:

+ Theo cng :

22 /130130.1./8,1308.8.10

6.5140

10.10.8

6.11016cmkgRmcmkg

W

M

W

Muu

y

y

x

x ===+=+= f

Sai s= 100%.(130,8-130)/130= 0,6%


26/31

26

Nn lch tm

Bi 1: Chn tit din mt thanh g chu nn lch tm bit l= 3,3m, hai u lin kt

khp, Ntt=12 T t lch tm e= 3cm so vi trc cu kin. Rn= 130 kg/cm2, Ru=150

kg/cm2.

Gii:

V 1


27/31

27

Xc nh thng svt liu.

G nhm V, W = 18%, T = 20C c Rn = Rem = 135kG/cm2, R

90em = 22kG/cm

2, Rtr

= 25kG/cm2.

2

33

90

30 /31,82

30sin122

1351

135

sin11

cmkG

RR

RR

em

em

em

em=

+

=

+

=

Yu cu ti thiu ca hr.

T 1,5h ltr 10hr 30 cm ltr 10hr 3 cm hr

Tnh hr+ hr.

cmbRm

Nhhemem

n

rr 52,52031,820,130cos106,10cos 3''' =

=+

Chn hr , hr.

Tiu kin cu to:

( )

cmh;cmhChn

cm,hh

cm,h

h

cmhh

cmhcmh

''

r

'

r

'

r

''

r

''

r

'

r

''

r

'

r

'

r

63

525

6763

20

3

2

32

==

+

==

+

Xc nh chiu di mt trt 1.

kGNhh

hN n

rr

r

em 33,35331060063

3'''

'' =

+=

+=

kGNN emtr 305230cos33,3533cos'' ===

Trt mt pha: b = 0,25; mt bn khng i xng nn e = h / 2 = 10 cm.


28/31

28

cm

e

NbR

Nl

tr

tr

tr

tr 42,9

10

305225,020258,0

3052

8,0'

'

' =

=

Cu to: 1,5h ltr 10hr 30 cm ltr 30 cm lrr = 30 cm.

Xc

nh chiu di m

t tr

t 2.

kGNN ntr 916930cos10600cos'' ===

cm

e

NbR

Nl

tr

tr

tr

tr 26,26

10

916925,0202515,1

9169

15,1''

''

'' =

=

Cu to: 1,5h ltr 10hr 30 cm ltr 60 cm Chn theo v hnh.

N

N

Hnh 3.15 - Minh ho v d

Bi 2: Tnh ton lin kt mng 2 rng mt gi dn v ko c lc nn cnh trn Nn=

11T, =300. Tit din cc thanh l 20x20 cm. G nhm V, Nm 18% c Rn(Rem)=135

kg/cm2, Rem(90

0)= 25 kg/cm

2,Rtr=25 kg/cm

2.

Gii:

Gi thit hr=3 cm>2 cm; hr=6 cm2 cm.

Tng din tch p mt: Aem= Aem+ Aem

= b(hr

+hr

)/cos= 20.(3+6)/cos300=

208cm2.


29/31

29

2

033

/87

30sin)125

135(1

135

sin)1)90(

(1

)30( cmkg

R

R

RR

em

em

em

em =

+

=

+

=

Kim tra p mt: Nem= Nn= 11000kg


30/31

30

Xc nh kh nng chu lc ca mt mt ct cht.

y l lin kt i xng. cht thp, a = 8 cm, c = 16 cm, d = 1,8 cm.

kGadTa

em 11528,188080 ===

kGcdTc

em

14408,1165050 ===

kGdkGadTu 8108,12502502,711828,11802180222222 ===+=+= Kh

nng chu lc ca mt mt ct cht:

( ) ( ) kG,,;;minT;T;TminTu

c

em

a

em2711271114401152 ===

Slng cht cn thit.

73722711

11000,

,Tn

Nnch

=

== chn 8 cht.

Btr cht.

Do b = 18cm = 10d = 10 x 1,8 nn:

S1 = 6d = 6 x 1,8 = 10,8cm.

S2 = 3d = 3 x 1,8 = 5,4cm.

S3 = 2,5d = 2,5 x 1,8 = 4,5cm.

B tr kiu vung.

S cht theo phng vung gc th:

7,21

4,5

5,42181

2

2

3

1 =+

=+

S

Shn cht

Chn n1 = 2cht, 4 hng. 2 x 4 = 8 cht.

B tr nh hnh v.

Kim tra gim yu do khot l.


31/31

Fth = 16 x (18 2 x 1,8) = 230,4 cm2

22 /76958,0/7,474,230

11000cmkGRmcmkG

F

Nkk

th

k ==

debaivaloigiai thep

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