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CH¦¥NG iv: Kü thuËt an toµn khi sö dông m¸y x©y dùng
1 më ®Çu
-C¬ giíi ho¸ c¸c c«ng viÖc trong x©y dùng kh«ng nh÷ng n©ng cao n¨ng suÊt lao ®éng mµ cßn gi¶m chÊn th−¬ng tai n¹n do c¸c ®iÒu kiÖn lµm viÖc cña c«ng nh©n ®−îc gi¶m nhÑ vµ an toµn h¬n
.-C¸c m¸y mãc thi c«ng th−êng dïng trªn c«ng tr−êng: m¸y lµm ®Êt (m¸y ®µo, ñi, c¹p), m¸y n©ng chuyÓn (cÇn trôc, thang t¶i, b¨ng chuyÒn), m¸y s¶n xuÊt vËt liÖu (m¸y ®Ëp, nghiÒn, sµng ®¸, m¸y trén BT), m¸y gia c«ng kim lo¹i, gç, m¸y ®ãng cäc, m¸y khoan phôt v÷a, m¸y lu, m¸y san, m¸y ph¸t ®iÖn, biÕm ¸p, m¸y b¬m,... HÇu hÕt c¸c lo¹i m¸y mãc trªn ®Òu cã c¸c lo¹i phô tïng nh− d©y c¸p, curoa, rßng räc, puli, mãc cÈu, xÝch,...
-Khi sö dông c¸c m¸y mãc vµ c¸c phô tïng cña chóng nÕu kh«ng hiÓu biÕt hÕt c¬ cÊu vµ tÝnh n¨ng ho¹t ®éng, kh«ng n¾m v÷ng quy tr×nh vËn hµnh, kh«ng tu©n theo néi quy an toµn khi sö dông cã thÓ g©y ra nh÷ng sù cè vµ tai n¹n lao ®éng.
2 c¸c nguyªn nh©n chÝnh g©y ra sù cè, tai n¹n lao ®éng
-Nguyªn nh©n sù cè, tai n¹n khi sö dông m¸y mãc, thiÕt bÞ bao gåm thiÕt kÕ, chÕ t¹o, l¾p ®Æt vµ sö dông. ë ®©y chØ xem xÐt vµ ph©n tÝch nh÷ng nguyªn nh©n chñ yÕu vÒ l¾p ®Æt vµ sö dông.
1. M¸y sö dông kh«ng tèt:
a) M¸y kh«ng hoµn chØnh:
· ThiÕu thiÕt bÞ an toµn hoÆc cã nh÷ng ®· bÞ háng, ho¹t ®éng thiÕu chÝnh x¸c, mÊt t¸c dông tù ®éng b¶o vÖ khi lµm viÖc qu¸ giíi h¹n tÝnh n¨ng cho phÐp.
· ThiÕu c¸c thiÕt bÞ tÝn hiÖu ©m thanh, ¸nh s¸ng (®Ìn, cßi, chu«ng).
· ThiÕu c¸c thiÕt bÞ ¸p kÕ, v«n kÕ, ampe kÕ, thiÕt bÞ chØ søc n©ng cña cÇn trôc ë ®é v−¬n t−¬ng øng...
b) M¸y ®· h− háng:
C¸c bé phËn, chi tiÕt cÊu t¹o cña m¸y ®· bÞ biÕn d¹ng lín, cong vªnh, r¹n nøt, ®øt
g·y.
· Hép sè bÞ trôc trÆc lµm cho vËn tèc chuyÓn ®éng theo ph−¬ng ngang, ph−¬ng ®øng,
xoay kh«ng chÝnh x¸c theo ®iÒu khiÓn cña ng−êi vËn hµnh.
· HÖ thèng phanh ®iÒu khiÓn bÞ gØ mßn kh«ng ®ñ t¸c dông h·m.
2. M¸y bÞ mÊt c©n b»ng æn ®Þnh:
· §©y lµ nguyªn nh©n th−êng g©y ra sù cè vµ tai n¹n.
· Do m¸y ®Æt trªn nÒn kh«ng v÷ng ch¾c: nÒn yÕu hoÆc nÒn dèc qu¸ gãc nghiªng cho
phÐp khi cÈu hµng hoÆc ®æ vËt liÖu.
· CÈu n©ng qu¸ träng t¶i.
· Tèc ®é di chuyÓn, n©ng h¹ vËt víi tèc ®é nhanh g©y ra m«men qu¸n tÝnh, m«men ly
t©m lín. §Æc biÖt h·m phanh ®ét ngét g©y ra lËt ®æ m¸y.
An toµn lao ®éng: Ch−¬ng IV:Kü thuËt an toµn khi sö dông m¸y x©y dùng![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image001.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image001.gif)
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· M¸y lµm viÖc khi cã giã lín (trªn cÊp 6), ®Æc biÖt ®èi víi m¸y cã träng t©m cao.
3. ThiÕu c¸c thiÕt bÞ che ch¾n, rµo ng¨n nguy hiÓm:
· Vïng nguy hiÓm khi m¸y mãc ho¹t ®éng lµ kho¶ng kh«ng gian hay xuÊt hiÖn mèi
nguy hiÓm cho søc khoÎ vµ tÝnh m¹ng con ng−êi. Trong vïng nµy th−êng x¶y ra c¸c
tai n¹n sau:
M¸y kÑp, cuén quÇn ¸o, tãc, ch©n tay ë c¸c bé phËn truyÒn ®éng.
C¸c m·nh dông cô vµ vËt liÖu gia c«ng v¨ng b¾n vµo ng−êi.
Bôi, h¬i, khÝ ®éc to¶ ra ë c¸c m¸y gia c«ng vËt liÖu g©y nªn c¸c bÖnh ngoµi da,
¶nh h−ëng c¬ quan h« hÊp, tiªu ho¸ cña con ng−êi.
C¸c bé phËn m¸y va ®Ëp vµo ng−êi hoÆc ®Êt ®¸, vËt cÈu tõ m¸y r¬i vµo ng−êi
trong vïng nguy hiÓm.
Khoan ®µo ë c¸c m¸y ®µo, vïng ho¹t ®éng trong tÇm víi c¶u cÇn trôc.
4. Sù cè tai n¹n ®iÖn:
· Dßng ®iÖn rß rØ ra vá vµ c¸c bé phËn kim lo¹i cña m¸y do phÇn c¸ch ®iÖn bÞ háng.
· Xe m¸y ®Ì lªn d©y ®iÖn d−íi ®Êt hoÆc va ch¹m vµo ®−êng d©y ®iÖn trªn kh«ng khi
m¸y ho¹t ®éng ë gÇn hoÆc di chuyÓn phÝa d−íi trong ph¹m vi nguy hiÓm.
5. ThiÕu ¸nh s¸ng:
· ChiÕu s¸ng kh«ng ®Çy ®ñ lµm cho ng−êi ®IÒu khiÓn m¸y mãc dÔ mÖt mái, ph¶n x¹
thÇn kinh chËm, l©u ngµy gi¶m thÞ lùc lµ nguyªn nh©n gi¸n tiÕp g©y chÊn th−¬ng,
®ång thêi lµm gi¶m n¨ng suÊt lao ®éng vµ h¹ chÊt l−îng s¶n phÈm.
· ChiÕu s¸ng qu¸ thõa g©y hiÖn t−îng m¾t bÞ chãi, b¾t buéc m¾t ph¶i thÝch nghi. §iÒu
nµy lµm gi¶m sù thu hót cña m¾t, l©u ngµy thÞ lùc gi¶m.
· ThiÕu ¸nh s¸ng trong nhµ x−ëng hoÆc lµm viÖc vµo ban ®ªm, s−¬ng mï lµm cho
ng−êi ®iÒu khiÓn m¸y kh«ng nh×n râ c¸c bé phËn trªn m¸y vµ khu vùc xung quanh
dÉn tíi tai n¹n.
6. Do ng−êi vËn hµnh:
· Kh«ng ®¶m b¶o tr×nh ®é chuyªn m«n: ch−a thµnh thôc tay nghÒ, thao t¸c kh«ng
chuÈn x¸c, ch−a cã kinh nghiÖm xö lý kÞp thêi c¸c sù cè.
· Vi ph¹m c¸c ®iÒu lÖ, n«Þ quy, quy ph¹m an toµn: sö dông m¸y kh«ng ®óng c«ng cô,
tÝnh n¨ng sö dông.
· Kh«ng ®¶m b¶o c¸c yªu cÇu vÒ søc khoÎ: m¾t kÐm, tai nghÔnh ng·ng, bÞ c¸c bÖnh vÒ
tim m¹ch,...
· Vi ph¹m kû luËt lao ®éng: rêi khái m¸y khi m¸y ®ang cßn ho¹t ®éng, say r−îu bia
trong lóc vËn hµnh m¸y, giao m¸y cho ng−êi kh«ng cã nghiÖp vô, nhiÖm vô ®iÒu
khiÓn...
7. ThiÕu sãt trong qu¶n lý:
· ThiÕu hoÆc kh«ng cã hå s¬, lý lÞch tµi liÖu h−íng dÉn vÒ l¾p ®Æt, sö dông b¶o qu¶n
m¸y.
· Kh«ng thùc hiÖn ®¨ng kiÓm, kh¸m nghiÖm, chÕ ®é trung tu b¶o d−ìng, söa ch÷a
theo ®Þnh kú.
· Ph©n c«ng tr¸ch nhiÖm kh«ng râ rµng trong viÖc qu¶n lý sö dông.
An toµn lao ®éng: Ch−¬ng IV:Kü thuËt an toµn khi sö dông m¸y x©y dùng![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image001.gif)
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§3 kü thuËt an toµn khi sö dông c¸c m¸y thi c«ng
I.§¶m b¶o sù cè ®Þnh cña m¸y:
-C¸c m¸y x©y dùng ph¶i ®¶m b¶o æn ®Þnh khi lµm viÖc, di chuyÓn vµ c¶ khi kh«ng ho¹t ®éng.
-Sù mÊt æn ®Þnh do:
· M¸y nghØ hoÆc lµm viÖc ë n¬i qu¸ dèc.
· NÒn kh«ng ch¾c ch¾n.
· Lµm viÖc qu¸ t¶i träng cho phÐp.
· Lùc qu¸n tÝnh vµ lùc ly t©m lín hoÆc gÆp khi giã lín...
-HÖ sè æn ®Þnh ®Æc tr−ng cho møc ®é an toµn khái lËt cña m¸y lµ tû sè gi÷a tæng m«men cña
c¸c lùc gi÷ vµ tæng m«men c¸c lùc g©y lËt ®èi víi ®iÓm lËt hoÆc ®−êng lËt:
K =
∑ M
∑ M
g
l
> 1
(4.1)
Trong ®ã:
+K: hÖ sè æn ®Þnh.
+Mg: m«men gi÷.
+Ml: m«men lËt.
-HÖ sè æn ®Þnh K ®−îc tÝnh khi cã t¶i träng K1 vµ khi kh«ng cã t¶i träng K2.
1.æn ®Þnh cña cÇn trôc tù hµnh:
a/Khi cã t¶i:
K1 =
H×nh 4.1: S¬ då tÝnh æn ®Þnh cÇn trôc
[G(b + c) cosá − Gh1 sin á ] − M 1 − M 2 − M 3 − M 4 − M 5 − M 6
Q(a − b)
> 1.15 (4.2)
Trong ®ã:
+G: träng l−îng m¸y cÇn trôc, ®iÓm ®Æt t¹i träng t©m (kg).
+Q: träng l−îng vËt cÈu tèi ®a (kg).
+Gc: träng l−îng tay cÇn, ®Æt ë ®Çu tay cÇn (kg).
+M1: m«men do t¸c dông ly t©m khi quay cÇn cã t¶i träng
An toµn lao ®éng: Ch−¬ng IV:Kü thuËt an toµn khi sö dông m¸y x©y dùng![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image001.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image002.gif)
M 1 =
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2
900 − n 2 × H
+M2: m«men do lùc qu¸n tÝnh khi phanh h¹ vËt
M 2 =
Q × v × (a − b)
g × t
+M3: m«men t¹o ra khi di chuyÓn ®Çu tay cÇn theo ph−¬ng ngang
M 3 =
(Qc + Q) × v1 × h
g × t1
+M4: M«men t¹o ra khi thay ®æi ®é víi tay cÇn
M 4 =
(Qc + Q) × v2 × (a − b)
g × t 2
+M5=WxP: m«men do lùc giã t¸c dông lªn cabin cÇn trôc
+M6=W1xh: m«men do lùc giã t¸c dông lªn vËt cÇn cÈu
+a: kho¶ng c¸ch tõ trôc quay cña cÇn cÈu ®Õn träng t©m vËt cÈu trªn mÆt ph¼ng
ngang (m).
+b: kho¶ng c¸ch tõ trôc quay ®Õn ®−êng lËt(m).
+c: kho¶ng c¸ch tõ trôc quay ®Õn träng t©m cÇn trôc (m).
+H: kho¶ng c¸ch tõ ®Çu tay cÇn ®Õn träng t©m vËt cÈu (m).
+h: kho¶ng c¸ch tõ ®Çu tay cÇn ®Õn mÆt ®Êt (m).
+h1: kho¶ng c¸ch tõ träng t©m cÇn trôc ®Õn mÆt ®Êt (m).
+P: kho¶ng c¸ch tõ lùc giã lªn cabin ®Õn mÆt ®Êt (m).
+v: tèc ®é n©ng vËt (m/s).
+v1: tèc ®é di chuyÓn ngang cña ®Çu tay cÇn (m/s).
+v2: tèc ®é di chuyÓn ®øng cña tay cÇn (m/s).
+n: sè vßng quay cÇn trôc trong 1 phót.
+t: thêi gian khëi ®éng, h·m c¬ cÊu n©ng (s).
+t1: thêi gian khëi ®éng, h·m c¬ cÊu quay cÇn trôc (s).
+t2: thêi gian khëi ®éng, h·m c¬ cÊu thay ®æi ®é víi tay cÇn (s).
+W, W1: lùc giã t¸c dông lªn cabin, vËt cÈu (®−îc tÝnh an toµn víi ®iÓm ®Æt ®Çu tay
cÇn).
+á: gãc nghiªng mÆt ®Êt so víi ph−¬ng ngang.
+g: gia tèc träng tr−êng, lÊy b»ng 9.81m/s2.
Trong tr−êng hîp m¸y cÈn trôc lµm viÖc trªn mÆt ®Êt n»m ngang, nÕu kh«ng kh«ng xÐt ®Õn
c¸c thµnh phÇn lùc ly t©m, qu¸n tÝnh, giã,...th× hÖ sè æn ®Þnh t¶I träng K1 lµ:
K1 =
G × (b + c)
Q × (a − b)
≥ 1.4
(4.3)
An toµn lao ®éng: Ch−¬ng IV:Kü thuËt an toµn khi sö dông m¸y x©y dùng![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image001.gif)
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K 2 =
G × [(b − c) cosá −h1 sin á ]
W2 × h2
≥ 1.15 (4.4)
H×nh 4.2: S¬ då tÝnh æn ®Þnh cÇn trôc khi
kh«ng t¶i
2/BiÖn ph¸p an toµn khi sö dông m¸y x©y dùng:
-§Ó ®¶m b¶o æn ®Þnh cho cÇn trôc khi vËn hµnh ph¶i thùc hiÖn:
· Kh«ng cÈu qu¸ t¶i lµm t¨ng m«men lËt.
· Kh«ng ®Æt cÇn trôc lªn nÒn hoÆc ray cã ®é dèc lín h¬n quy ®Þnh.
· Kh«ng phanh ®ét ngét khi h¹ vËt cÇn cÈu.
· Kh«ng quay cÇn trôc hoÆc tay cÇn nhanh.
· Kh«ng n©ng h¹ tay cÇn nhanh.
· Kh«ng lµm viÖc khi cã giã lín (cÊp 6).
· §èi víi cÇn trô th¸p th−êng cã träng t©m cao gÊp 1.5-3 lÇn chiÒu réng ®−êng ray,
cho nªn ®é nghªng cña ®−êng ray ¶nh h−ëng rÊt lín ®Õn æn ®Þnh cÇn trôc th¸p. V× thÕ
kh«ng cho phÐp ray cã ®é dèc ngang, ®é dèc däc cã thÓ lµ 1-2.5% tøc kho¶ng 0o35-
1o30.
II.An toµn khi di chuyÓn m¸y:
-Sö dông c¸c m¸y mãc x©y dùng ë trªn c¸c c«ng tr−êng x©y dùng cã liªn quan ®Õn viÖc vËn
chuyÓn chóng trªn ®−êng s¾t vµ c¸c ®−êng vËn chuyÓn kh¸c. §Ó ng¨n ngõa sù dÞch chuyÓn
cña nh÷ng m¸y ®ã th−êng ®−îc buéc chÆt vµo toa tµu.
-Lùc t¸c dông lªn cÇn trôc hoÆc m¸y ®µo khi vËn chuyÓn ph¸t sinh kh«ng lín. Nã phô thuéc
vµo ®iÒu kiÖn di chuyÓn cña tµu vµ t¸c dông cña giã. Nguy hiÓm nhÊt lµ lùc g©y ra sù tr−ît
däc,®ã lµ lùc qu¸n tÝnh khi t¨ng tèc vµ h·m.
1. Lùc qu¸n tÝnh khi h·m tµu:
Tqt =
Q × v 2
3.6 2 × g × l
(4.5)
Trong ®ã:
+Q: träng l−îng m¸y ®−îc di chuyÓn (kg).
+v: tèc ®é di chuyÓn cña tµu khi b¾t ®Çu h·m (km/h).
+g: gia tèc träng tr−êng, 9.81m2/s.
+l: chiÒu dµi ®−êng h·m (m).
2. Lùc ly t©m:
Tlt =
Q × v 2
3.6 2 × g × R
(4.6)
Trong ®ã:
+F: diÖn tÝch høng giã cña m¸y ®−îc di chuyÓn trªn tµu (m2).
+q: ¸p lùc giã ®¬n vÞ lÊy b»ng 100kg/m2.
+k: hÖ sè khÝ ®éng häc, lÊy 1.0-1.4
§4 kü thuËt an toµn khi sö dông c¸c thiÕt bÞ n©ng h¹
-Trªn c«ng tr−êng th−êng dïng c¸c lo¹i thiÕt bÞ bèc dì nh− cÇn trôc «t«, cÇn trôc b¸nh xÝch,
cÇn trôc th¸p,... hoÆc c¸c lo¹i m¸y cÇn trôc ®¬n gi¶n nh− kÝch têi, pal¨ng,...®Ó n©ng h¹, vËn
chuyÓn hµng ho¸, vËt liÖu, c¸c cÊu kiÖn...
-Khi sö dông c¸c lo¹i m¸y nµy, nhiÒu tr−êng hîp ®· x¶y ra tai n¹n do nhiÒu nguyªn nh©n
nh−ng nguyªn nh©n chñ yÕu th−êng gÆp lµ do tÝnh to¸n, sö dông hoÆc ®iÒu khiÓn c¸c thiÕt bÞ
n©ng h¹ cña c¸c lo¹i m¸y mãc kh«ng ®óng môc ®Ých hoÆc kh«ng theo quy ph¹m an toµn.
-Khi dïng m¸y bèc dì ph¶i ®Æc biÖt chó ý ®Õn ®é bÒn d©y c¸p, d©y xÝch vµ ®é tin cËy cña
phanh h·m.
I.C¸c tiªu chuÈn vµ an toµn khi sö dông c¸p:
1.Ph−¬ng ph¸p buéc kÑp ®Çu d©y c¸p:
-§Ó buéc chÆt ®Çu d©y c¸p, mèi nèi bÖn kh«ng ®−îc ng¾n h¬n 15 lÇn ®−êng kÝnh d©y c¸p vµ
300mm
-NÕu kÑp chÆt b»ng bul«ng th× sè bul«ng ph¶i tÝnh to¸n nh−ng kh«ng ®−îc Ýt h¬n 3 vµ bul«ng
ph¶i Ðp 2 nh¸nh d©y c¸p l¹i víi nhau. Kho¶ng c¸ch gi−ac 2 bul«ng phô thuéc vµo sè l−îng
bul«ng kÑp vµ ®−êng kÝnh d©y c¸p.
-Ngoµi ra nÕu kh«ng cã ph−¬ng ph¸p ch»ng buéc tèt th× vËt dÔ bÞ r¬i. Cã mét sè c¸ch buéc
c¸p nh− sau:
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-TÝnh to¸n c¸c lo¹i d©y c¸p theo c«ng thøc sau:
P
k
Trong ®ã:
+P: lùc kÐo ®øt d©y c¸p (kg).
+S: lùc kÐo thùc tÕ d©y c¸p (kg).
+k: hÖ sè dù tr÷ søc bÒn, ®èi víi lo¹i c¸p thÐp lÊy nh− sau:
· C¸p uèn treo ®Ó n©ng vËt t¶i träng ®Õn 50 tÊn → k=8
· C¸p uèn treo ®Ó n©ng vËt t¶i träng nÆng h¬n 50 tÊn → k=6
· C¸p buéc chÆt vËt nÆng treo trªn mãc cÈu hoÆc vßng treo → k=6
· C¸p kÐo, d©y ch»ng, d©y gi»ng cã xÐt ®Õn lùc giã → k=3.5
· Pal¨ng víi têi tay → k=4.5
· Pal¨ng víi têi ®iÖn → k=5
a/Khi d©y c¸p ë vÞ trÝ th¼ng ®øng:
Q
m × k
Trong ®ã:
+Q: khèi l−îng vËt nÆng (kg).
+Sn: lùc kÐo thùc tÕ trªn nh¸nh d©y c¸p (kg).
+m: sè nh¸nh d©y.
+k: hÖ sè dù tr÷ søc bÒn.
b/Khi d©y c¸p ë vÞ trÝ n»m nghiªng:
-Kh¶ n¨ng n©ng vËt cña nã gi¶m v× sù t¨ng lªn gãc nghiªng th× lùc kÐo ë c¸c nh¸nh còng t¨ng
lªn
- 36 -
-Lùc kÐo trong mçi nh¸nh ®−íc x¸c ®Þnh theo c«ng thøc:
S n =
1
cosá
×
Q
m
= c ×
Q
m
(4.10)
Trong ®ã:
+Q: khèi l−îng vËt nÆng (kg).
+c: hÖ sè phô thuéc gãc nghiªng cña c¸p, cã thÓ lÊy nh− sau
3.X¸c ®Þnh ®é dµi cña nh¸nh d-Trong tr−êng hîp cã ≥4 nh¸nh d©y th× ®é dµi d©y cña c¸c nh¸nh ®ång ®Òu nh− nhau cã ý
nghÜa rÊt quan träng v× ®¶m b¶o sù ph©n bè ®ång ®Òu t¶i träng lªn c¸c nh¸nh, nÕu kh«ng sÏ
cã nh¸nh chÞu v−ît t¶i lµm gi¶m tuæi thä cña d©y vµ cã khi g©y tai n¹n.
-ChiÒu dµi cña mçi nh¸nh d©y ®−îc x¸c ®Þnh theo c«ng thøc sau:
2
L = ⎜ ⎟ + h 2
⎝ 2 ⎠
(4.11)
Trong ®ã:
+L: ®é dµi cña nh¸nh d©y c¸p (m).
+h: chiÒu cao tam gi¸c t¹o thµnh bëi c¸c nh¸nh(m).
+b: kho¶ng c¸ch gi÷a c¸c ®iÓm cè ®Þnh d©y c¸p theo ®−êng chÐo (m).
4.Lo¹i bá d©y c¸p trong qu¸ tr×nh sö dông:
-Trong qu¸ tr×nh sö dông c¸p ph¶i th−êng xuyªn kiÓm tra sè sîi ®øt hoÆc møc ®é gØ cña c¸p
mµ lo¹i bá.
-ViÖc lo¹i bá c¨n cø vµo sè sîi ®øt trªn ®o¹n dµi 1 b−íc bÖn, còng nh− dùa vµo sù h− háng bÒ
mÆt hoÆc mßn gØ c¸c sîi. (*B−íc bÖn c¸p lµ kho¶ng c¸ch däc trªn mÆt c¸p trong ®ã chøa tÊt
c¶ sè sîi c¸p trong tiÕt diÖn ngang↔t−¬ng tù nh− b−íc xo¾n*).
-C¸c quy ®Þnh:
· Tiªu chuÈn quy ®Þnh lo¹i bá c¸p phô thuéc vµo kÕt cÊu d©y c¸p, ph−¬ng ph¸p bÖn (tr¸i
chiÒu hay cïng chiÒu) vµ hÖ sè dù tr÷ søc bÒn ®−îc x¸c ®Þnh trong b¶ng sau![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image006.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image007.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image008.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image009.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image010.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image011.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image012.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image013.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image014.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image015.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image016.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image012.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image014.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image010.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image017.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image018.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image019.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image020.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image021.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image022.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image023.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image024.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image025.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image026.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image027.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image028.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image029.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image030.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image031.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image032.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image033.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image017.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image034.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image035.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image036.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image037.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image038.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image039.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image028.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image040.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image041.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image042.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image043.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image044.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image045.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image046.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image047.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image048.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image022.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image049.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image050.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image051.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image052.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image053.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image054.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image055.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image056.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image057.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image058.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image059.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image024.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image060.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image061.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image062.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image063.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image064.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image065.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image066.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image067.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image068.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image046.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image069.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image070.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image071.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image072.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image073.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image074.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image075.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image076.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image077.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image078.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image079.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image047.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image080.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image048.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image081.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image067.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image068.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image069.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image082.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image083.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image084.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image072.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image073.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image001.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image096.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image097.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image097.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image098.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image099.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image100.gif)
HÖ sè
an toµn
ban ®Çu
HÖ sè
an toµn
ban ®Çu
HÖ sè
an toµn
ban ®Çu
chiÒu
HÖ sè
an toµn
ban ®Çu
|
Sè sîi cã trong tiÕt diÖn ngang cña c¸p
|
6*19=114 |
6*37=222
|
6*61=366
|
18*19=342
|
Sè sîi ®øt trong 1 b−íc bÖn c¸p khi c¸p cã d¹ng xo¾n |
Tr¸i |
Cïng
chiÒu
|
Tr¸i
chiÒu
|
Cïng
chiÒu
|
Tr¸i
chiÒu
|
Cïng
chiÒu
|
Tr¸i
chiÒu
|
Cïng
chiÒu
|
≤6
|
12
|
6
|
22
|
11
|
36
|
18
|
36
|
18
|
6-7
|
14
|
7
|
26
|
13
|
38
|
19
|
38
|
19
|
>7
|
16
|
8
|
30
|
15
|
40
|
20
|
40
|
20
|
|
|
Gãc á (®é)
|
0
|
30
|
45 60
|
HÖ sè c
|
1
|
1.15
|
1.42 2
|
|
|
- 37 -
· C¸p cña nh÷ng m¸y n©ng dïng cÈu ng−êi, vËn chuyÓn c¸c kim lo¹i nãng, nÊu ch¶y,
c¸c chÊt ®éc, dÔ næ, dÔ ch¸y th× ph¶i lo¹i bá ®i khi sè sîi ®øt Ýt h¬n 2 lÇn so víi lo¹i
d©y c¸p kh¸c.
· Khi mÆt c¸p bÞ mßn hoÆc gØ th× sè sîi ®øt ph¶i gi¶m ®i t−¬ng øng so víi phÇn tr¨m tiªu
chuÈn quy ®Þnh.
· Khi d©y c¸p bÞ mßn hoÆc gØ ®Õn 40% kÝch th−íc ®−êng kÝnh ban ®Çu hoÆc bªn ngoµi
bÞ x©y x¸t th× coi nh− bÞ bá ®i.
II.Quy ®Þnh ®èi víi tang quay vµ rßng räc:
1.§−êng kÝnh cña tang quay, puli, rßng räc:
-§−êng kÝnh cña tang quay, puli vµ rßng räc cã ý nghÜa thiÕt thùc ®èi víi sù lµm viÖc an toµn
cña c¸p khi sö dông c¸p thÐp trong nh÷ng thiÕt bÞ n©ng h¹.
-§Ó ®¶m b¶o ®é bÒn mßn cña c¸p vµ tr¸nh cho c¸p khái biÕn d¹ng th× ®−êng kÝnh cña nã ph¶i
tÝnh theo ®−êng kÝnh cña c¸p bÞ uèn trong ®ã.
-§−êng kÝnh cho phÐp nhá nhÊt cña räng räc hoÆc tang cuén c¸p x¸c ®Þnh theo c«ng thøc:
D ≥ d (e − 1) (4.12)
Trong ®ã:
+D: ®−êng kÝnh cña tang quay hoÆc rßng räc ë chç c¸p tiÕp xóc (®o theo ®¸y r·nh)
cña thiÕt bÞ n©ng h¹ (mm).
+d: ®−êng kÝnh c¸p thÐp (mm).
+e: hÖ sè phô thuéc vµo kiÓu d¸ng cña m¸y n©ng h¹ vµ chÕ ®é lµm viÖc cña nã:
§èi víi cÇn trôc cã tay cÇn, e=16-25.
§èi víi pal¨ng ®iÖn, e=20.
§èi víi têi tay, e=16.
§èi víi têi ®Ó n©ng ng−êi, e=25.
-ThÓ tÝch quÊn cña tang quÊn c¸p sÏ ®−îc x¸c ®Þnh tõ ®iÒu kiÖn lµ khi mãc cña cÇn trôc ë vÞ
trÝ thÊp nhÊt th× trªn tang quÊn c¸p cßn l¹i kh«ng ®−îc Ýt h¬n 1.5 vßng c¸p.
2.Quy ®Þnh vÒ tang h·m:
-TÊt c¶ c¸c m¸y vËn chuyÓn vµ n©ng h¹ nhÊt thiÕt ph¶i trang bÞ phanh h·m ®Ó phanh khi n©ng
hoÆc di chuyÓn vËt nÆng.
-Phanh h·m ph¶i tèt. §¸nh gi¸ tr¹ng th¸i phanh h·m b»ng hÖ sè h·m. HÖ sè nµy th−êng lÊy
b»ng 1.75, 2.00 vµ 2.50 t−¬ng øng víi chÕ ®é sö dông m¸y nhÑ, trung b×nh vµ nÆng.
-Khi sö dông têi quay nhÊt thiÕt ph¶i cã 2 phanh h·m: mét phanh ®Ó gi÷ vËt trªn cao vµ cßn
phanh kia ®Ó h¹ vËt tõ tõ. Trong mét sè têi, sù kÕt hîp nµy cã thÓ thùc hiÖn ®−îc dÔ dµng
b»ng c¸ch sö dông tay quay an toµn.
-Pal¨ng cÇn ®−îc trang bÞ lo¹i thiÕt bÞ h·m cã thÓ tù h·m vµ gi÷ vËt ë ®é cao bÊt kú khi n©ng
còng nh− khi h¹. Th−êng cã thÓ truyÒn ®éng b»ng trôc vÝt, b¸nh vÝt hoÆc b¸nh xe cãc.
-ThiÕt bÞ rßng räc ph¶i cã bul«ng ch»ng ®Ó phßng ngõa tr−êng hîp c¸p hoÆc xÝch bÞ tôt vµo
khe vµ kÑt l¹i trong ®ã.
III.æn ®Þnh cña têi:
1.Ph−¬ng ph¸p cè ®Þnh têi:
-§Ó ng¨n ngõa hiÖn t−îng tr−ît vµ lËt cña têi trong khi sö dông th× ph¶i cè ®Þnh chóng mét
c¸ch ch¾c ch¾n. Cã thÓ thùc hiÖn theo c¸c tr−êng hîp sau:![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image006.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image007.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image008.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image009.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image010.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image011.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image012.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image013.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image014.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image015.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image016.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image012.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image014.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image010.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image017.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image018.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image019.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image020.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image021.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image022.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image023.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image024.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image025.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image026.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image027.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image028.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image029.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image030.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image031.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image032.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image033.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image017.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image034.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image035.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image036.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image037.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image038.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image039.gif) 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- 38 -
· §ãng c¸c cäc neo th¼ng ®øng vµo ®Êt ®Ó cè ®Þnh têi b»ng c÷ chÆn vµ ®èi träng.
· Ch«n neo d−íi hè thÕ, tøc lµ dïng 1 c©y hoÆc bã gç ch«n s©u (theo kiÓu n»m ngang)
d−íi ®Êt 1.5-3.5m; dïng c¸p buéc vµo gç, cßn ®Çu kia kÐo lªn mÆt ®Êt xiªn 1 gãc 30o-
45o ®Ó nèi vµo d©y neo têi.
-Trong tÊt c¶ mäi tr−êng hîp, quÊn d©y c¸p vµo trôc têi ph¶i tiÕn hµnh tõ phÝa d−íi tang quÊn
®Ó gi¶m m«men øng lùc trong d©y c¸p.
2.TÝnh to¸n æn ®Þnh têi:
H×nh 4.4: S¬ ®å tÝnh to¸n æn ®Þnh cña têi
a/Tr−êng hîp cã ®èi träng 1 bªn vµ d©y c¸p n»m ngang:
-§iÒu kiÖn æn ®Þnh khi kÐo têi theo ph−¬ng ngang:
G × a + Q × c = P × b
(4.13)
Trong ®ã:
+P: lùc kÐo d©y c¸p.
+G: träng l−îng têi.
+Q: träng l−îng ®èi träng.
+a, b, c: c¸c c¸nh tay ®ßn c¸c lùc ®èi víi ®iÓm A.
⇒Tõ c«ng thøc trªn, träng l−îng cña ®èi träng lµ :
Q =
P × b − G × a
c
× k
(4.14)
Trong ®ã:
+k: hÖ sè an toµn k=1.3-1.5
b/Tr−êng hîp cã ®èi träng phô vµ d©y c¸p cã ®é nghiªng:
-§iÒu kiÖn æn ®Þnh cña têi khi kÐo xiªn:
P sin á × c = G × c + Q × d + Q1 × l + P cosá × b
⇒Tõ c«ng thøc trªn, träng l−îng cña ®èi träng lµ :
(4.15)
Q1 =
P sin á × c − G × c − Q × d − P cosá × b
l
× k
(4.16)
- 39 -
+Q1: träng l−îng ®èi träng phô.
3.TÝnh to¸n hè thÕ ®Ó cè ®Þnh têi:
-Khi neo b»ng hè thÕ cÇn tÝnh to¸n kiÓm tra c−êng ®é chÞu Ðp cña ®Êt vµ tiÕt diÖn thanh gç
neo.
a/Tr−êng hîp neo kh«ng cã gç gia c−êng:
-KiÓm tra æn ®Þnh cña neo d−íi t¸c dông cña lùc th¼ng ®øng:
Q+T ≥ kN2 (4.18)
Trong ®ã:
+Q: träng l−îng ®Êt t¸c dông lªn neo, tÝnh theo c«ng thøc:
Q =
b1 + b2
2
× H × l × ã
(4.19)
+b1,b2: bÒ réng phÝa d−íi vµ phÝa trªn hè thÕ.
+H: chiÒu s©u ®Æt neo.
+l: chiÒu dµi thanh neo.
+ã: khèi l−îng ®¬n vÞ cña ®Êt.
+T: lùc ma s¸t gi÷a ®Êt vµ gç neo, tÝnh theo c«ng thøc:
T = fN1
+f: hÖ sè ma s¸t gi÷a gç vµ ®Êt, f=0.50
+N1: thµnh phÇn n»m ngang cña lùc S.
+k: hÖ sè æn ®Þnh, k=3.
-KiÓm tra ¸p suÊt cho phÐp lªn ®Êt do lùc ngang N1:
[ó d ]× µ ≥
N1
h × l
(4.20)
Trong ®ã:
+µ: hÖ sè gi¶m ¸p suÊt cho phÐp cña ®Êt v× c−êng ®é chÞu lùc cña ®Êt kh«ng ®ång
®Òu, µ=0.25
+h: chiÒu cao bã gç neo.
-KiÓm tra tiÕt diÖn thanh neo:
· Khi kÐo b»ng 1 d©y, m«men uèn lín nhÊt gÇn ®óng:
- 40 -
· Khi kÐo b»ng 2 d©y víi gãc nghiªng â, thanh neo ®−îc kiÓm tra ®iÒu kiÖn uèn vµ nÐn:
M«men uèn lín nhÊt:
Trong ®ã:
+a: kho¶ng c¸ch tõ ®Çu thanh neo ®Õn chç buéc d©y c¸p.
Lùc däc trong thanh neo:
Trong ®ã:
+â: gãc gi÷a d©y nÐo vµ thanh neo trong mÆp ph¼ng chøa 2 nh¸nh d©y c¸p.
-øng suÊt tÝnh to¸n trong thanh neo:
ó g =
M
W
+
N
F
≤ mR
(4.21)
Trong ®ã:
+W: m«men chèng uèn cña tiÕt diÖn thanh gç neo, W=0.1nd3.
+d,n: ®−êng kÝnh 1 thanh gç vµ sè l−îng thanh gç lµm neo.
+F: diÖn tÝch tiÕt diÖn ngang cña thanh neo.
+m: hÖ sè ®iÒu kiÖn lµm viÖc cña thanh neo.
+R: c−êng ®é tÝnh to¸n cña gç lµm neo.
b/Tr−êng hîp hè thÕ cã gç gia c−êng:
-KiÓm tra tÝnh to¸n t−¬ng tù nh− trªn nh−ng träng l−îng Q cña ®Êt ®−îc tÝnh Q=H.b.l.ã (b: bÒ
réng hè thÕ)
-KiÓm tra ¸p suÊt cho phÐp lªn ®Êt do lùc ngang N1:
[ó d ]× µ ≥
N1
(h1 + h2 )× l
(4.22)
Trong ®ã:
+h1, h2: chiÒu cao cña gç gia c−êng phÝa trªn vµ phÝa d−íi lùc ngang N1.![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image006.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image007.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image008.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image009.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image010.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image011.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image012.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image013.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image014.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image015.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image016.gif) ![](file:///C:\DOCUME~1\Admin\LOCALS~1\Temp\msohtml1\01\clip_image012.gif) 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