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Trong 66 :

'P- (1) Khi bo'ong trdn d$u cot chSng la boong tren cung thi Po = 0 (2) Khi tr&n 48x1 cQt ch6ng c6 nhie"u tang boong thi tr/ s6 P llIy bhng cot ch6ng

phia tren ngm cung mot dub.ng th&ng dinq. (3) NGu cot ch6ng phia tr6n khdng n&m cbng tren mot d~rirng t h h g dGng

thi Pe tinh theo sv phhn bb l ~ c . Vi du : @

12 P, b cot ch6og I # t h i Ps0 = - 10

11 Po b cot ch6ng 2 # thi P". - - - lo

' #+

S - KhoAng cAch tinh b&ng rn, do giGn hai tiim '

H/hh 24 cot chdng phia trubc v,& phia sau (hinh 25).

b - Khoing cich ttr m ~ t C o t c h b g den cot c h h g hai bCn trdi phhi, ho$c dgn m$t trong slrbll tinh bBng m (xem hinh 25) nhvng nzu khoHng each 66 kh6ng b&ng 115 B thi c b g 1 % ~ b&ng 115 B.

V#,, .y ,. 5 .

I - -

hi;X 25 h - Chibu cao c&t nubc tuong duang tinh b%ng m. Tri sb giang nh

thirc (6) vA (7). Chi& day t c&a t8n lam cot ch6ng rang khbng d ~ q c . pup &nh & c6ng thfrc (14).

t = 0,022d + 3mm (14)

32 . .

. . 'S' , ~a

- .5t,.r.-.

.:, 7* ,< -- . -- - I.. . , -'.:*y%*-, , , I. . , . * .. . ' . ~ . . .;- :,:~.y&+.;

lu & cbng nh8 han

Trong ao: d - 8 u h g kinh ngoAi cfia cot ch6ng rang tinh biing mm.

8

BiGu 39 - Cot ch6ng dsc :

Hubng kinh ngoai d cot ch6ng dijc khong dvqc nh6 hon quy djnh b ~Bng rhuc (15),

Trong do : 1-ChiE?u dAi cot ehiing tinh b a n g - a

P - Tinh the0 c6ng t hirc (13).

C H V O N G V I I I

V A C H -

Bidu 40 - Quy djnh chung :

b b"a ccir t8u nho, d e b sdng 1115i khdng nh6 hao O,05L d6u phHi dat vhch kin nvbc phong va t h h g (vach miii) chay su6t tir dhy tau l&n dbq boong chinh 1ii.n tuc 6 1ai cCing phHi dgt mQt vtlch kin nvirc (vAch lhi) chay sudt ti? day thu Icn qua dub.ng mwn nvirc ch& hang va d8n t@n boong chinh.li8n tvc.

Tau c6 buang mAy b gWa, vhcll kin nubc kh6ng duqc Khon 4 vbch, b u b g ,

may b sau lhi, vhch kin nubc kh6ng duqc it han 3 vdeh.

Khohng ~Ach vAcb ngakg khBng duqcltrn hm G llin chi$u cao t&u, nhvng ndu duqc s~ dang y c&a Bang kigm, d& cho viec x%p d& hang duqc ti&n lqi thi khohng cach vach cO th8 phli hgn chb; Nhvny d b dHm bAo sirc b&n ngang thhh tau,

\

cir cdch 4 khoing swan dat miit strhn k i d $ vh mot rA ngaug kh6e (xem diku $6 va di6u 33). -%

Tau d8i dubi am, n8u dwqc sg dang 4 ciia Blng ki8m thi cO th8 gihm b6t s6 lwffng vAch kin ntrbc.

VBoh kin nvirc. 6 miii LhBng duqc khokt cira va 16 nguisi chui. Ndu b cac vach kin du6.c khhc c o khoet c&a thi phii dHm b&o kin ouirc, dang thiri co bien yhhp dong kin c&a & hai phia. Tiit cH ctic Zlng di qua vhch kin nvtrc phHi c6 m@t bich ho@c bien phAp khac c6 djnh d$ dHm bHo cho Zing xuykn qua vitch dvqc kin nwac. Khi c6 day dien di qua thi cBng dung bien phap tren dB b&o dhm dwgc kin nwbc.

BiBu 41 - Vach ham miii, 1Bi va hffm nuh.c sau: nep v8ch ham miii, ham 1ai bht the0 chiau thing dirng. Kholhg cach .giGa chc nep khong dvqc lirn hun 600rn. MB men khang W cfia nep viich b ham mfii, ham ltii co dHi t8n lien kdt kh6hg duqc nh6 han quy djnh b cdng thirc (16).

W = K12 S (h + 0,051) cm3 (16)