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tng cng ty t & pt nh h ni
Chn ba ng cc :
Tu theo nng lc trang thit b hin c, iu kin a cht cng trnh, quy nh ca Thit k v chiu su h cc v chi quy nh Nh thu c th la chn thit b h cc ph hp. Nguyn tc la chn ba nh sau:
a) C nng lng h cc n chiu su thit k vi chi quy nh trong thit k, xuyn qua cc lp t dy k c tng kp cng;
b) Gy nn ng sut ng khng ln hn ng sut ng cho php ca cc hn ch kh nng gy nt cc;
c) Tng s nht p hoc tng thi gian h cc lin tc khng c vt qu gi tr khng ch trong thit k ngn nga hin tng cc b mi;
d) chi ca cc khng nn qu nh c th lm hng u ba.
La chn ba ng cc theo kh nng chu ti ca cc trong thit k v trng lng cc. Nng lng cn thit ti thiu ca nht ba p E c xc nh theo cng thc:
E = 1.75 a P (1)
trong : E - Nng lng p ca ba, kGm;
a - h s bng 25 kG.m/tn
P - kh nng chu ti ca cc, tn, quy nh trong thit k.
Loi ba c chn vi nng lng nht p Ett phi tho mn iu kin:
(2)
trong :k - h s quy nh trong bng 2;
Qn - trng lng ton phn ca ba, kG;
q - trng lng cc (gm c trng lng m v m u cc), kG
i vi ba i--zen, gi tr tnh ton nng lng p ly bng:
i vi ba ngEtt = 0.9 QH
i vi ba cnEtt = 0.4 QH
Q - trng lng phn p ca ba, kG;
H - chiu cao ri thc t phn p ba khi ng giai on cui, i vi ba ng H= 2.8 m; i vi ba cn c trng lng phn p l 1250, 1800 v 2500 kG th H tng ng l 1.7; 2 v 2.2 m.
Bng 2- H s chn ba ng
Loi baH s k
Ba i--zen kiu ng v song ng
Ba n ng v i--zen kiu cn
Ba treo6
5
3
Chn s b vi cc 350x350 v 300x300 chn ba 3,5T ;
vi cc 250x250 v 200x200 chn ba 2,5T .
Vi cc 200x200 :
; Vi cc 250x250 :
; Vi cc 300x300 :
; Vi cc 350x350 :
.
Vy ba chn l hp l.
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