debaivaloigiai thep
Transcript of debaivaloigiai thep
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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 =
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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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Vy bn ghp m bo iu kin bn.
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)
Vy bn ghp m bo iu kin bn.
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).
Ta c: (fw)min = min (ffwf; s fws) = min (1800.0,7; 1500.1) = 1260 (daN/cm2)
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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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).
Ta c: (fw)min = min (ffwf; s fws) = min (1800.0,7; 1500.1) = 1260 (daN/cm2)
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
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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)
Vy bn ghp m bo iu kin bn.
b, Kim tra kh nng chu lc cho lin kt:
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)
Vy bn ghp m bo iu kin bn.
b, Thit k lin kt:
Chn bulng c ng knh d=20mm.
Kh nng chu ct ca 1 bulng trong lin kt:
e=50
N=2000KNN
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60
60
60
60
60
50
50
60 60
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[N]vb = n v. Ab.b. fvb= 2.3,14.0,9.1500 = 8478 (daN)
Kh nng chu p mt ca 1 bulng trong lin kt:
[N]cb = d.(t)min.b. fcb= 2.4.0,9.3950 = 28440 (daN)
Kh nng chu lc nh nht ca bulng:
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)
Vy bn ghp m bo iu kin bn.
b, Kim tra kh nng chu lc cho lin kt:
N=4000KNN
50 50 50 50 5050
50
100
100
100
50
t2=16
t1=12
t1
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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)
Vy bn ghp m bo iu kin bn.
b, Xc nh lc ln nht tc dng ln lin kt:
Kh nng chu ct ca 1 bulng trong lin kt:
[N]vb = n v. Ab.b. fvb= 2.3,14.0,9.1500 = 8478 (daN)
Kh nng chu p mt ca 1 bulng trong lin kt:
[N]cb =d.(t)min.b. fcb= 2.1,5.0,9.3950 = 10665 (daN)
Kh nng chu lc nh nht ca bulng:
[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
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60
60
60
60
60
50
50
60 60
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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
=
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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
==
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)/(2100)/(1913289
10.5529 222
max cmdaNfcmdaNW
Mc
x
=
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)/(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
==
===
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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 =
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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.
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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)
Ta c: (fw)min = min (ffwf; s fws) = min (1800.0,7; 1500.1) = 1260 (daN/cm2)
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 =
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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:
f = 2300 daN/cm2=23 kN/cm
2.
Chiu di tnh ton ca ct
ly = 0,7.6,5= 4,55 (m); lx=1.6,5=6,5 (m)
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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
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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.
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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
f = 2100 daN/cm2=21 kN/cm
2.
x= lx/ ix=250/2,6=96,2
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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.
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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.
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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:
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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.
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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 =
==
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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
=
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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%
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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
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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.
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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.
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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
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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.
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Fth = 16 x (18 2 x 1,8) = 230,4 cm2
22 /76958,0/7,474,230
11000cmkGRmcmkG
F
Nkk
th
k ==