-
118
5.6.1.Chn loi, hnh dng, kch thc i cc v cc.
i y CT; s cc ; b tr cc Cc t nn; ti trng; phng tin thi cng
Chn chiu su h cc: Nu lp tt nm khng su cc nn c tit din ngang ln h
vo lp tt. Nu lp tt nm su dng cc ma st chn chiu di v tit din phc tp
hn. Cc ngm vo lp t tt chu lc 1 on t nht 3 5 ln /k cc.
0,5m , t to ht. 1,0m t cht. 1,5m cht va.
5.6.2.Xc nh SCT: Pvl; Pn chn Pmin( Pvl; Pn) a vo th/k.
C gng la chn chnh lch ny khng qu ln. Tuy nhin: vi cc nhi ta c th
thit k P u vl P u n
Vi cc ng, p trnh b ph hoi cc (nht l u hoc mi cc) trong qu trnh h
cc, th cn thit k nh sau: P u = P u n
P u vl >>P u n(Pu vl phi ln hn nhiu so vi Pun) theo 190:
1996 lc p cc bng 1,5 (t dnh) n 2 (t ri) sc chu ti cho php ca
cc.
do c th thit k P u vl (2 3)P u n 5.6.3 Xc nh s lng cc trong
mng:
PN
n = = h s k/nghim k n nh hng ca m men v trng lng i. = (1 2)
B tr cc tho mn 2 yu cu: thi cng d.
chu lc tt, cc v nhm cc b tr im t ti trng truyn xung mng gn trng
tm nhm cc nht + Thi cng d:
Cc ng hoc p h cc n su th/k kh/cch gia trc cc cc nh sau: mt phng
y i khng nh hn 1,5d mt phng mi cc khng nh hn 3,0d
+ Chu lc tt: B tr trn mt bng: hnh hoa mai hoc vung.
-
119
B tr trn mt ng:
thng, nghing, nng. hoc b tr khng u nhau nu ti lch tm nhiu. Theo
TC 205: Khong cch gia trc cc cc ng thng ng khng: < 3d vi cc ma
st < 2d vi cc chng 5.6.4 Tnh ton kim tra: TTGH I: Ti ln cc. SCT
t mi cc. Tnh ton i cc, tnh cc khi vn chuyn v treo ln gi ba. TTGH
II: ln MC. Cc gi thit: - Trong tnh ton MCT thng g/thit rng ti trng
ngang do ton b t t y i tr nn tip nhn nn mun tnh ton theo MCT cn phi
tho mn /k sau:
h 0,7hmin; h: su chn su y i.
bH
tgh o
=
)2
45(min
, = gc ni ma st v trng lng th tch ca t t y i tr ln H = tng ti
trng nm ngang b = cnh y i vung gc vi H
Cng thc rt ra t /k cn bng tng lc ngang v p lc b ng ca t t y i tr
ln.
-
120
- SCT cc trong mng c xc nh nh i vi cc n (khng k nh hng nhm
cc)
- Ti CT qua i ch truyn ln cc khng ln t di y i. - Kim tra t di mi
cc coi nh mng khi quy c. - Tnh ton mng quy c nh mng nng ( tc l b
qua ma st mt bn mng
v l v cc di nh vy mng chn rt su) xem xt chuyn ngi ta gim mt phn
m men do ti trng ngoi gy ra ti y mng khi quy c bng cch ly gi tr m
men ti y i.
- i cc xem nh tuyt i cng v ch truyn ti N; M ln cc cc cc cc ch
chu nn hoc chu ko
/k:
1. Kim tra ti ln cc: [ ]no Pp max ; [ ]ko Pp min
max
opminop = cc chu nn nhiu nht v cc chu nn t nht (hoc chu ko)
[ ]nP ; [ ]kP = sc chu ti cho php ca cc khi chu nn v chu ko. /k
hp l v ti trng ln cc l: [ ] [ ]PpP o %10max
Cc chu nn nhiu nht:
==
+
+=n
ii
n
x
n
ii
n
yo
y
yM
x
xMn
Np
1
2
max
1
2
maxmax
Tng t vi cc chu nn t nht hoc chu ko:
==
=
n
ii
n
x
n
ii
n
yo
y
yM
x
xMn
Np
1
2
max
1
2
maxmin
Chng minh kt qu ti ln cc:
/s nn trong tit din cc ti mc y i tnh nh sau: J
MxN i+=
max ;
trong : tng din tch tit din cc trong mng Fn.= F = din tch tit
din 1 cc
J = m men q/tnh ca tit din so vi trc i qua trng tm ca tt c cc
cc.
( ) += n io xFJJ1
2. ; Jo = m men qun tnh ca mi tit din cc so vi trc i qua
trng tm ca n, Jo thng rt nh so vi 2
. ixF nn J ly gn ng nh sau:
=n
ixFJ1
2. Thay vo ta c:
+=
n
i
i
xF
xMnFN
1
2max
.
+=
n
i
i
x
xMn
NF
1
2max
.
. ; .F chnh l ti ln cc.
-
121
Bi 6
Kim tra ti trng tc dng ln cc p BTCT tit din (25 25) cm2 di 12m B
tng cc M# 300; Ct dc gm 4 thanh 16 AII . Bit Mng gm 12 cc b tr nh
hnh v. Sc chu ti tnh ton ca cc theo t nn [ ]nP = 33T i cc chn su
1,0m v c kch thc BLH = (23,20,7)m
3 Ti trng tiu chun di ct No=300T; Mo=35Tm; Qo=5T
Bi lm
Xc nh sc chu ti ca cc: Theo vt liu:
)...( aabtbtvl FRFRmP += m = h s /k lm vic ph thuc loi cc v s cc
trong i: i thp; s cc =12 nn chn m =1
B tng cc M#300 2/1300 mTRb =
Thp AII 2/28000 mTRa = 2 2 2 4 21.(1300 / .0, 25.0, 25 28000 /
.8,04.10 ) 104vlP T m m T m m T= + =
Theo t nn: [ ]nP = 33T
Vy sc chu ti tnh ton ca cc l: [ ] TPn 33=
Ti ti y i l :
TmTHFNN ddo
8,3128,123002.1.2,3.2300/2.. 3
=+=+=
=+=
TmmTTmHQMM doo 401.535. =+=+=
Ti trng tc dng ln cc:
==
=n
ii
iyn
ii
ixi
x
xM
y
yMn
NP
1
2
1
2
T
P
)45,41,26(12,12
541,26)2,082,1(635,1.401,26
)45,035,1.(635,1.40
128,312
22minmax,
=
==+
=
=
+=
Vy TP 31max ; Tp 22min [ ] TPTP n 3331max =
-
122
Bi 7: Chn s cc v b tr di tng bit: Cc tit din (25 25)cm2; chiu di
L=8m; sc chu ti ca cc [ ] TP 22=
Ti trng tiu chun di tng: N=30 T/m M=5,5Tm/m
y i cch chn tng: H = 1m Bi lm:
Ln 1:
+=
n
ix
xMn
NP
1
2
max.
Th b tr khong cch 2 hng l 1m kim tra: TmtG 5,2/2125,11 3 ==
maxmax 2
2
1
30 2,5 5,5 0,375 16, 25 7,32 2 2 (0,375 )n
i
MxN G T T Tm mPm
x
+ + = + = + = =
TP 55,23max = ; v TP 25,9min = [ ] TP 22= khng t yu cu
Ln 2: Ly: 93,055,23
22=
B tr khong cch 2 hng cc = 0,9m kim tra: TmTG 25,2/2125,19,0 3
==
mTmTN /27/309,0 == mTmmTmM /95,4/5,59,0 ==
maxmax 2
2
1
27 2,25 4,95 0,375 14,6 6,6 21,22 2 2 (0,375 )n
i
MxN G T T Tm mP Tm
x
+ + = + = + = =
TP 2,21max = ; TP 8min = TP 2,21max = < [ ] TP 22= t yu
cu.
2.Kim tra cng t nn: Xem nh mng khi quy c:
( )( ) LtgBLtgAFqu 22 11 ++=
4tb = ;
...
..
21
2211
++
++=
llll
tb
li = chiu dy lp t m cc i qua. i = gc ma st trong ca lp t th i.
Sau tnh ton kim tra nh mng nng (S 1o) trn nn thin nhin tr s:
1000
1250
220
250 250
L
A1+2L.tag
B1+2L.tag
A1
B1
900
1250
220
250 250
-
123
ququ
dWM
FN
+=max ; ququ
dWM
FN
=min
Nd = tng ti trng thng ng ti y mng khi quy c. M = m men so vi trc
i qua trng tm y i l do xt n s c mt ca t quanh mng khi quy c nn M
truyn n y mng khi gim i nhiu nn cho php ly M y i. Mt s dng mng khi
khc:
B +2L/3.tg30
L
3030
L/3
2L/3
B
30
B +2L/3.tg30L
30
L/3
2L/3
B
B +2L/3.tg30
L
3030
L/3
2L/3
B
-
124
Bi 8:
Cho mng cc nh hnh sau: Cc tit din (25 25)cm2 , Khong cch gia cc
cc l 1m. Kim tra iu kin chn su ca i. V mng khi quy c, kim tra iu
kin p lc v ln ca mng khi. Bit nn t gm 2 lp : Lp trn dy 8m, st pha B
=1,2 w= 1,75T/m3 Lp di ct nh qc=750T/m
2; w= 1,8T/m3; =30o; o= 0,3 Ti trng tiu chun di ct :
No=250T; Mo=35Tm; Qo=5T Bi lm: 1. Kim tra h: h = 1,5m
min7,0 hhd ; bH
tgh o.
)2
45(min
=
Vi B =1,2 coi gn ng o0=
Vy mtgh o 1,15,2.75,1
5)2045(min ==
V mmhd 77,01,1.7,0 = vy mhd 5,1= l tha c th gim i. 2. Kim tra
cng t nn di mi cc: Chiu di cc: Lc= 12m ngm vo i 0,4m
h= 1,5m Vy h q = 1,5+(12-0,4) = 1,5+11,6=13,1m Chiu di cc nm
trong lp ct: L2=13,1-8 = 5,1m Lq=3,25+2.1,7.tg30
o = 3,25+2.1,7.0,5774 = 3,25+1,96 = 5,2m Bq =
2,25+2.1,7.tg30
o = 2,25+2.1,7.0,5774 = 2,25+1,96 = 4,2m ng sut di y mng khi quy
c:
dqd
FNp =
284,212,42,5 mBLF ququdq ===
3500
2500
975
975
400
600
12000
4200
250
250
5200
2250
3250
3030
tc
Qo
tc
No
tc
Mo
1100500
0.000
-1.500
-8.000
-11.400
-13..100
975975
5200
3250 975975
-
125
M men chng un ca Fdq l: 2 2
34, 2 5,2 18,936 6
qu quB LW m
= = =
Ti tiu chun thng ng ti y mng khi quy c: ThFN ququtbotc
822)1,13.84,21.2(250)..( =+=+=
ng sut ln y mng khi quy c:
2/64,3784,21
822mT
FNp
dqd
===
; WMpp +=
max
M men ti y i:
;5,425,1.535. TmhQMM dotcotc =+=+= 2
max
/88,3924,26,3793,185,4264,37
mTWMpp
=+
=+=+=
Cng t nn ti y mng khi quy c: Gn ng coi l ti thng ng, p dng cng
thc ca Terzaghi:
cccqqqqugh NcisNqisNBisP ...........5,0 ++= o30= tra bng:
8,21=N ; 4,18=qN ; 1,30=cN cq sss ;; : h s hnh dng.
84,02,52,4
.2,01.2,01 ===lb
s ; 1=qs ; 16,12,52,4
.2,01.2,01 =+=+=lb
sc
H s iu chnh nghing ca ti trng: 2
1
=
i 2
21
==
pi
cq ii
gn ng coi l ti thng ng ( tc = 0) nn 1=== cq iii
dqhq .
=
321
2211 /77,11,1318,914
1,581,5.8,18.75,1..
mThh
hh=
+=
+
+=
+
+=
0,5. . .. . . . . . . . 0,5.0,84.1,8.4,2.21,8 1.1,77.13,1.18,4
0gh qu q q q c c cP s i B N s i q N s i c N= + + = + + =
2/93,49564,42622,69 mT=+=
2/93,2472
86,495mT
FP
Rs
gh===
2/64,3784,21
822mT
FNp
dqd
===
-
126
ln: o
oqugl E
BpS21
..
=
Trong : co qE = Tra bng: 2 2/15002.750 mTEo ==
23,12,42,5
==
qu
quBL
tra bng: 08,1=const
cmmS 4,4044,01500
3,0108,1.2,4.45,14
2
=
=
3.Kim tra cc khi vn chuyn v cu lp: V tr v ng knh ct thp mc cu c
tnh t 2 s trn sao cho Mmen trn v di chnh lch nhau t m bo s lm vic
tt. Cc gi tr m men dng kim tra cng ca cc c xc nh theo ti trng l
trng lng bn thn cc c nhn vi h s ng lc bng 1,5. Cc c chiu di khong
m76 nn b tr 2 mc cu; m7> nn b tr 3 mc cu. Khi ch to ngi ta thng
t mt cht thp 6 nh du im C, trnh tnh trng cc b nt do on CD qu di khi
dng cc. a; b c xc nh t iu kin cn bng m men dng v m men m, cc gi tr
m men dng kim tra cng ca cc. 5.6.5.Tnh ton i cc: Tnh ton m thng ca
ct. Tnh ton cng trn tit din nghing theo lc ct. Tnh ton i chu un chu
un. 1. Tnh ton m thng ca ct: C th dng cng thc cho mng nng tuy nhin
do gc nghing y khng phi 45o do vy v phi c tng ln
theo t s c
ho nhng khng ln hn 2.
ha
ohc
c h1 c
cbc
2
c1
A B
a a
L
a,
M=0,0214ql2
CD
BC
A
D
L
b
b,
M=0,0432ql2
-
127
( ) ( )[ ] cctkoccct PRhchcbP =+++ .1221 P = lc m thng bng tng
phn lc ca cc nm ngoi phm vi ca thp m thng. Rk = cng tnh ton chu ko
ca b tng.
2
11 15,1
+=
c
ho ; 2
22 15,1
+=
c
ho
Lm cho cc dy: Khi ohc >1 hoc ohc >2
Th phi ly 11
=
c
ho hoc 12
=
c
ho tnh, tc l coi thp m thng c gc
nghing 45o khi 1 hoc 12,22 = . Khi : ohc 5,01 < hoc ohc 5,02
< th ly ohc 5,01 = hoc ohc 5,02 = tnh vi
ch rng: s tng ca kh nng chng ct theo gc nghing ca thp m thng cng
l c gii hn, khi 1 hoc 35,32 = 2.Tnh ton m thng ca cc gc: Cng dng
cng thc mng nng v c xt n s tng kh
nng chng ct theo t s c
ho
3, Tnh ton cng trn tit din nghing theo lc ct.
iu kin cng c vit:
ko RhbQ ... Q= tng phn lc ca cc cc nm ngoi tit din nghing
- h s khng th nguyn 2
1.7,0
+=
c
ho Khi c < 0,5 ho; c tnh theo c = 0,5ho Khi c > ho
c
ho= nhng khng nh hn 0,6.
Lu : Chiu cao i - hp l - l kh nng chng ph hng khng ln hn 10% lc
ph hng
b1 c1
c1
aho
hc
cb
22
c1
c2
b
-
128
4.Tnh ton i chu un: Tnh ton theo tr s mmen ti cc tit din thng ng
ca i mp ct hoc v tr i c chiu cao thay i.
ctoct Rh
MF9.0
=
M I = M men un tit din I I M II = M men un tit din II-II * Nu i
c chiu dy cmH 80 nn b tr thm li thp mt trn i 200;10 =a chng nt cho
b tng i. Lu : Ti ti cc nh cc trong tnh ton i b qua phn trng lng bn
thn i; (ging nh mng nng)
Bi 9 Tnh ton kim tra chiu cao i cc v chn ct thp cn thit b tr
trong i ca Mng cc sau, bit: B tng i M# 200, lp bo v ct thp y i l
10cm, cc tit din ( ) 225 25 cm Tit din ct (40 60)cm2, trng tm ct
trng vi trng tm i. Ti trng tnh ton ti cos 0,0 l: TmMTN oo 40;330 ==
Bi lm: Ti trng tc dng ln cc khng k trng lng bn thn cc v lp t ph t y
i tr ln:
==
=n
ii
iyn
ii
ixoi
x
xM
y
yMn
NP
1
2
1
2;
TP 5,3145,27)5,05,1.(65,1.40
12330
221 =+=++=
TP 8,283,15,27)5,05,1.(65,0.40
12330
222 =+=++= ;
TP 2,263,15,27)5,05,1.(65,0.40
12330
223 ==+=
TP 5,2345,27)5,05,1.(65,1.40
12330
224 ==+=
tt
Qo
tt
No
tt
Mo
11
2
2
aho
-
129
a, Tnh ton m thng ca ct:
( ) ( )[ ] koccct RhchcbP .1221 +++ ctP = lc m thng bng tng phn
lc ca cc nm ngoi phm vi ca thp m
thng. kR = cng tnh ton chu ko ca b tng.
2
11 15,1
+=
c
ho ; 2
22 15,1
+=
c
ho
Lm cho cc dy cc. *Trng hp 1:
075,01 =c ; 675,02 =c ; y 075,01 =c < 45,05,0 =oh
nn ta ly 35,31 =
5,2675,09,01.5,115,1
22
22 =
+=
+=
c
ho
TPct 3305,2332,2638,2835,313 =+++= ( ) ( )[ ]
[ ] TRhchcb kocc
35675.9,0)075,06,0.(5,2)675,04,0.(35,3.1221
=+++=
=+++
TPTP cctct 356330 = 9,0=oh Nn ta ly 12,21 =
5,2675,09,01.5,115,1
22
22 =
+=
+=
c
ho
TPct 2755,2332,2628,2825,313 =+++=
( ) ( )[ ][ ] T
Rhchcb kocc43675.9,0)075,16,0.(5,2)675,04,0.(12,2
.1221
=+++=
=+++
TPTP cctct 436275 =
-
130
b, Tnh cng trn tit din nghing theo lc ct:
iu kin cng c vit:
ko RhbQ ... Q= tng phn lc ca cc cc nm ngoi tit din nghing = h s
khng th nguyn
21.7,0
+=
c
ho Khi c < 0,5 ho; c tnh theo c = 0,5ho Khi c > ho
c
ho= nhng khng nh hn 0,6
*Trng hp 1:
075,01 =c ; y 075,01 =c < 45,05,0 =oh c tnh theo ohc 5,01
=
56,19,0.5,0
9,01.7,02
=
+=
k kim tra:
ko RhbQ ... 3 31,5 3 28,8 181Q T= + =
TRhb ko 26375.9,0.5,2.56,1... == TTQ 263181 9,0=oh
84,0075,1
9,02
===
c
ho k kim tra:
ko RhbQ ... TQ 5,945,313 == ; TRhb ko 14275.9,0.5,2.84,0...
==
TTQ 1425,94
-
131
c, Tnh ton ct thp:
ctoct Rh
MF9.0
=
M I = m men un tit din I I M II = m men un tit din II-II M I tnh
thp theo phng cnh di:
TmM I
13028,174,1132,08,2832,15,313
=+=
=+=
22 570057,028000.9,0.9,0
1309.0
cmmRh
MF
cto
IctI ====
M II tnh thp theo phng cnh ngn:
TmM II
88)5,232,268,285,31(8,0
=
=+++=
22 390039,028000.9,0.9,0
889.0
cmmRh
MF
cto
IIctII ====
Mt s ch : Ma st m: Lm gim kh nng chu ti ca cc, nht
l i vi cc nhi. Cc lm vic trong cc trng hp sau: - t p dy hn 2m -
H mc nc ngm - Ti ph thm: CT ln cn, ti trng kho bi - S tng cht ca t
ri di tc dng ca ng lc - S ln t ca t khi b ngp nc. - S c kt ca t cha
kt thc. - S gim th tch ca t do cht hu c phn hu Th ln ca cc lp t ny
c th ln hn, lu hn so vi ln ca cc Tnh ton:
i
R R
PP
Ma st m
Ma st dng
100
900
75
3500
2500
1300
300
250
1200
800
1
2
0.000
-1.300
1
2
250
400
1050
2506001450
250
7575 600
1000 1000 1000 250250
3500
-
132
y l vn phc tp c th dng mt s cng thc thc nghim nu trong cc ti liu
chuyn .
Theo TCXD 189: 1996 lc ma st m ln cc: =
=
m
iinin lfuP
1..
Trong :
nif - ma st m gii hn tc dng ln cc ti lp t i trn phn thn cc chu
ma st m, kN/m2
m - s lp t gy ma st m. u- chu vi ngoi ca tit din cc. Ch thch: -
Gi tr ti a ca ma st m gii hn:
'. vn Ff = F = h s ly bng 0,3
'
v = ng sut hu hiu theo phng thng ng
- i vi cc chng, phn chiu di cc chu ma st m ly bng chiu su cc gp
lp t cng ta cc
- i vi cc ma st trong nn ng nht, phn chiu di cc chu ma st m ly
bng 0,7L Bin php hn ch: Chn cc c b mt cng nhn cng tt Gim ma st tip
sc t cc: ph cc bng bitum ph cc bng bentonit Tham kho: 20TCN 21-86;
TCXD 205, TCXD 189: 1996; 20TCN 112-84 4 Chn lc p u cc v ba ng
cc
Phng php p:
cc t c sc chu ti cho php [ ]P th lc p gii hn ti thiu min)( epP
theo kinh nghim c ly nh sau:
- ct [ ]PPep )25,1()( min > - st, st: [ ]PPep )5.12,1()( min
> Tuy nhin xc nh chnh xc min)( epP cn thit xuyn qua cc lp trung
gian l kh khn. Trong mi trng hp c th, nn lm th nghim p th v th
nghim nn tnh c th xc nh ng dn gi tr min)( epP yu cu ph hp vi thc t
nn t cng trnh.
Gi tr lc p ti thi im cui cng khng nh hn lc p ti thiu v cng khng
ln hn lc p ln nht cho php.
Cc c cng nhn l p xong khi tho mn ng thi 2 /k sau:
Chiu di: maxmin LLL c
Lc p: maxmin )()()( epepep PPP
-
133
Phng php ng:
Loi ba rt nh hng hiu qu cng tc ng cc
Chn ba da vo: gc; lc; [ ]P ; /k thi cng Theo kinh nghim: PE 25
Trong :
E = g2v.Q 2
; (g- gia tc trng trng) nng lng ca ba ( ly theo h chiu),
Nm; mk
PP o.
= (kN)
oP - sc chu ti tnh ton ca cc theo t nn.kN
k = h s ng nht ca t ( thng ly bng 0,7 0,8)
m = h s /k lm vic, s lng cc, cu to b mng, m thng ly bng 1
Sau kim tra li h s hiu dng ca ba theo cng thc:
max.81,9 KEqQK +=
Q = ton b trng lng ba, kg;
q = trng lng cc, m cc, m ba v cc m, kg
Bng: H s hiu dng ln nht ca ba.
Vt liu cc Loi ba
G Thp BTCT
1. Ba kp, ba izen loi ng
2. Ba n, ba loi 2 a
3. Ba trng lc
5,0
3,5
2,0
5,5
4,0
2,5
6,0
5,0
3,0
Nn chn K nh hn cc tr s cho trong bng , nu khng hoc ba cha nng so
vi ton b trng lng cc v m hiu qu s km v tc chm c khi cc khng xung ni
ti su thit k hoc v u cc.
Nhng nu ba qu nng cc s xung nhanh v mun t chi thng phi ng su hn
thit k, lng ph
H cc c kt qu khi dng ba hi 1 chiu v ba izen kiu 2 thanh
T s: qQ < 1,5 t cht
qQ 1,5 cht va
qQ = 1 yu, bo ho
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134
T s ny cng ln: on cc nh ln v s cc ng khng ln ht cng nh
Ba izen kiu ng ly thp hn: c th 0,7 0,8.
h ng v tr: lc u h khong 1,5 2m nng ba 0,3 0,4m. Nhn xt phng php
tnh
Gi thit 1: Chp nhn c khi Q0 khng ln khc phc bng cch tnh ton theo
nguyn l trong phn cc i cao
Gi thit 2: Khng ng cho d l ng cc tha Gi thit 3: Khng k n s lm
vic ca t di i lng ph. y
chnh l s n gin ho vic tnh ton mng cc i thp khi tnh i cao. Gi
thit 4;5: rt khng r rng nhng tnh ton n gin, v kinh nghim cho
thy l an ton. 5.7. Mt s ch khi tnh ton: 1. Trng hp mng lch : M =
M0 + N0. e0 M men lch tm ln v c phn phi cho ging, cc, ct. Lc ging
phi c cng kh ln chu phn ln m men lch tm trnh cho ct v cc ph hoi do
un C th coi ging v cc l nhng dm trn nn n hi c ghp ni vi ct trong mt
nt l i. Sau dng cc phng php trong CHKC phn phi m men ti nt cho cc
cu kin quy t vo nt. + Ging y c tit din ln hn ch khc. 2. Trng hp ct
i: Hp cc lc Noi , Moi v trng tm cc u cc ti mc y i v tnh ton nh ni
trn.
Qo2
No2
Mo2Qo1
No1
Mo1
No
Mo
NM
eo
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135
3. B tr cc khng i xng (khng u): - Thng dng vi lch tm c nh v M
tng i ln (cu, cng, nh cng nghip...) - B tr cc dy v pha lch (sao cho
din chu ti mi hng gn bng nhau). - Tm trc trng tm ca tt c cc cc,
chuyn cc lc v gc to trng tm. Sau tnh ton nh trn. 4. i bng di
tng
Theo phng di c th coi l cng, theo phng b rng th tnh ton nh trn.
Cc c th b tr hnh vung hoc hoa mai. - Khi cc cch nhau tha 6D, v chiu
cao i khng ln coi l i cng tnh ton i mm. Vic gii bi ton i mm rt phc
tp i hi c s tr gip ca my tnh. Khi coi i l phn t shell hoc Solid, cc
l cc phn t Frame lin kt cng vi i cc, c th s dng cc chng trnh phn mm
nh SAP2000 5. i vi mng cc tre
y l bin php p dng kh rng ri trong xy dng nh gia nh, nh lm vic t
tng, cng trnh thu li, ng, cu nh ...trn nn t c lp t bn trn thuc loi
dnh yu, bo ho nc thng xuyn (trong iu kin ngp nc, cc tre c th ti rt
lu, v d nh th Pht dim hn 100 nm nay cc tre vn xanh)
Cu to:
Cc tre c gi di 1-2,5m, c ng vi mt thng l (cc 20 20; 25 25cm)
162025 cc/m2. u cc c lin kt bi gch v, hay b tng mc thp.
C gng b tr cc tre trn ra ngoi mng.
BT. gch v mc 75#
Qo
No
Mo
-
136
Tiu chun: ng cc tre bng v hay t. Khi trnh lm v cc bng cch chp m
u cc hay chng buc u bng dy cao su. Ngi ta ch my m t thnh dng c rung
ng cc tre rt tt. Cng dng: - Lm cht t - Truyn ti xung di lp di mi cc
(c rng hn y mng nhiu) Thit k cc tre:
- Tnh ton cc, c nhiu quan im: + Coi cc tre lm cht t nh cc ct
(gia c nn) + Coi cc tre thuc loi cc cng (theo nguyn l nh cc btct
trn).
C th tnh nh sau: cc lm vic c coi nh 1 b, c din tch y bng din tch
ca mng, v chiu di bng chiu di ca cc, mng khi quy c (b cc tre) lm
vic nh mi v lc bm dnh xung quanh. T xc nh c kh nng chu ti v ln ca
mng.
Ch : Sau gia c phi c th nghim bn nn tnh cm cc tre hoc cc th
nghim hin trng khc kim tra hiu qu gia c. 5.8. Tnh ton mng cc i cao
- Khi i pha trn b mt t hoc cha chn su trong t khi c ti trng ngang
ln cc chu un. - Thng dng ni ngp nc (cu, cng), on cu vt, mng thu li
vt, nh thu ta. - So vi i thp th km n nh hn do cc chu un, chuyn v
ngang ca mng
fs=c
qm
s tnh cc tre
Mo
No
Qo
on cc t do
Qo ln Mo
No
h nh
-
137
thng dng tit din cc ln. Nguyn l tnh ton: thng thc hin theo cc
hng sau
1. Phng php gii tch:
Phi gii quyt 2 bi ton c bn sau Bi ton 1: Phn phi ti ln cc. y l
kt cu siu tnh bc cao. Thng dng phng php chuyn v vi mt s gi thit n
gin bi ton. V d h c bn vi gi thit h phng v i tuyt i cng.(xem hnh
bn), trong cc ngm vi i v cc ngm n hi vi t hoc ngm cng trong . K
hiu:
+ Ti trng phn phi ln u cc th i trong mng: Ni, Qi , Mi + Chuyn v
ti O trong h c bn: v, u, (n s) + Phn lc n v ca cc kin kt ti O: rik
(cc h s)
Ta c h phng trnh chnh tc:
=+++
=+++
=+++
0r .u r .vr0r .u r .vr0r .u r .vr
uv
uuuv
vvuvv
MQN
u
+ Gi ik v ik l phn lc, chuyn v n v ti u cc + Gi oik v oik l phn
lc, chuyn v n v ti cao trnh mt t ca
cc + i(N, Q, M) chuyn v ca cc theo cc phng ng, ngang v
xoay. Trong : ik , ik lin quan ti oik v oik - c xc nh t iu kin
lin kt ca cc vi lp t ti mi cc (ngm hay gi n hi) Cc h s rik c xc nh
t quan h rik =f1(ik) , ik li c xc nh theo quan h vi ik , tip tc nh
vy ta c:
rik =f1(ik) = f1(f2(ik)) = f1(f2(f3(ik))) =
f1(f2(f3(f4(oik)))
Qo
No
MoMo
No
Qo
MNQ
uvO
-
138
MiQi
PiPi
MiQi
Bng cch a vo mt s gi thuyt th vic xc nh rik tr nn n gin. - Gii h
phng trnh chnh tc xc nh c v, u, t xc nh c N, M, Q sau l Ni, Qi, Mi
v i = f(v, u, ) v:
Ni = ik. N Qi = QQ. Q - QM. M Mi = MM. M - QM. Q
Gii ra ti trng tc dng ln u cc th i: Pi, Qi, Mi (Vi i thp Qi = Mi
= 0
Pi =
+
+ 2
i
iy2i
ix
x
xMy
yMn
N)
- Bi ton 2: Cc chu un (Pi, Qi, Mi ) Xt cc th i: thanh chu un vi
ti trng tc dng u cc l (Pi, Qi, Mi) thng gi thit bin dng ca cc nh, p
dng nguyn l cng tc dng th bi ton ny tr 2 bi ton:
+ Cc chu lc dc trc Pi + Cc chu lc ngang trc Qi, Mi
Bi ton cc chu ti ngang v m men (cn tm zy )
Thng thng ngi ta phn bit bi ton cc chu ti trng ngang v mmen
:
+ Cc cng. + Cc c cng hu hn.
Cc phng php gii bi ton tng t nh bi ton tng c. + Phng php gi thit
cc cng v xoay ti O, ti trng tc dng ln mt bn
cc l p lc ch ng v b ng. + Phng php tng t nh dm trn nn n hi (i vi
cc c cng hu
hn):
- Phng trnh ca vng theo phng y
- M hnh nn: quan h y v zy
Gii ra c yz ni lc (M,Q), chuyn v ngang t : + Kim tra nn: theo
phng ng v phng ngang ( SCT, chuyn v). + Kim tra cc chu un v mt cng
.
S tnh
y
Phn lc ca t ln cc
Qi Mi
z
Qi
i
Mi
y
-
139
2. Phng php phn t hu hn M hnh ho h kt cu cc v i cc thnh cc phn t
hu hn, cc l cc phn t Frame, i cc l phn t Shell hoc solid, nh hng ca
nn v d c thay th bng gi n hi, cng ca cc gi n hi theo phng ngang v
phng ng K c th xc nh theo mt s cng thc: Terzaghi, Vesic, Poulos
Theo Terzaghi:
= 2
124
165,0
s
s
pp
s EIEdE
dK
Trong : ppIE = cng khng un ca cc.
d = ng knh hay cnh cc. s = h s n hng.
sE = moduyn n hi.
vic gii bi ton trn c th p dng chng trnh SAP 2000.
Sau khi tm c ni lc chuyn v ca cc v i cc ( M,Q), y thc hin cc cng
vic nh sau:
Kim tra SCT ca cc theo phng ngang ca t. C ni lc (M,Q) kim tra ct
thp cc. Kim tra SCT ca cc theo phng ngang.
Tm li: Vic thit k mng cc i cao khc i thp c bn cc phn - Bi ton 1
- Bi ton tnh ton kim tra cc theo phng ngang trong bi ton 2. (Kim
tra [ ],yy,R ngz maxy v kim tra cng cc chu un ngang. Cn
li ging i thp)
a) Trng hp i t cao hn mt t
S tnh ton mng cc theo phng php tng qut
b) Trng hp i t thp hn mt t
h
n
m
m
n
h
-
140
-
141
