sa lap IQc my vao nhu cdu chang thAm d€ chQn, thu<'mg chQn 2 d€n 3 lap (khong k€ lap da ngoai, n€u c6), chi~u day mai lap thu<'mg ti:r 10+20cm.
- Thanh phAnh(lt cUa cac lap IQcnguQ'cco the chQnoou sau:
+De dAtduQ'Chao v~ khong hi cu6n troi ho\ic h(lt cUa lap h(lt 000 khoJg hi cu6n VIIO ke rdng cUa lap h(lt 16nkB c~: 01, ~ 5
d" .
+De dam hao kha nang thoat nuac thfun: 01, >5 dIS -
D, d la duang kiOOh(lt cua lap h(lt 16n va lap h(lt 000 ke OOauho\ic cua dAt duQ'chao v~ vm lap IQclien ke; chi s6 dum la chi s6 phAntrlim trQng lugng m~u hi IQtxu6ng duai m~t sang dang xet.
+V~t li~u trong I lap IQcphai co cAp ph6i hgp Iy, dam hao khong hi tach lap, phan tAngkhi v~ chuyen va kha nang nen ch\it t6t. De dam bao dieu ki~n nay thi h~ s6 khong deu h(lt cUa I lap phai thoa man dieu ki~n : " = :'0 ~20
10
Ngoai ra con cAnkh6ng chB ham lugng h(lt min cUa v~t li~u lam tAng IQcco duang kiOO000 han ho\ic hfulg 0,074mm khong duQ'cvugt qua 5% trQng lugng. 2.3.4. Thiit ki thiit bi bao v~
41 1 . w. •. . • "'X\ . .:" . " ....,' ~.' ~... :. Hinh 2-6.
1. Baa v~mai thu{rng
a. Ly do cdnbaa v~mai thu(fl1g
Mai thugng co the hi pba hO(li do OOieu nguyen OOan: Song lam S(lt la mai, n~g lam nUt mai, mua lam hao mon mai, dong thAm nguQ'c trong ~p lam truQ't mai... trong do tac d\lllg cua song la nguy hiem ooAt. Vi v~y de bao v~ mai cAnchQnIO(lithiSt bi co the dam bao an toan cho cit ca cac truang hgp tren, OOung lAy ysu t6 song lam chu d(lo.
ThiSt hi thuang duQ'cSlrd\lllg hi~n nay la lam theo hinh thuc tAngIQcnguQ'c va thuang lam 3 lap (hiOO2-6): Lap ngoai coog (1) co tac dt,mgchi! ySu la ch6ng song, ch6ng hao mon do nuac mua va ch6ng nUt do n~g cho maioLap ngoai cung thuang dugc lam h~ng da d6, da xSp, be tong tfun lat.-Lap (2) va (3) (gQi la lap d~m) la cac lap da dam ho\ic soi va cat. Cac lap nay vila co tiOOchAtla lap d~m de n6i tiSp lap ngoai coog vm dAt mai ~p (4), vtra co tac d\lllg ch6ng tac d\lllg CUa
song qua khe ha cua lap ngoai cling va ch6ng xoi ngAmdo dong thfun ngm;rctrong thiin ~p gay ra.
Vai cac h6 chua nho, d~p th~p thuang song yeu nen co the kh6ng can co lap bao v~ mai thugng.
b. Thiit ki lap baav~mai thu(TI1g
*Ph{lmvibaa *PhAn bao v~ chinh la vling mai chiu tac d\l11gClla song. Cac phAncon I~icua mai chi can gia c6 nh~ (hinh 2-7).
Gi6'i h~ phAnbao v~ chinh I~y nhu sau:
- Gim h~ tren I~y den het chieu cao song leo cao nh~t tren mal d~p ho(ic den dinh d~p.
- Gim h~n dum I~y th~p han ml,lc nuac chet I do~ th~ng dUng b~ng '\2
bAng 2,50m vm d~p dp III tra len va 1,5Omvm d~p c~p IV, V ( theo TCXDVN 285:2002)
LOp bao v~ nbc;
vMNC
il,
LOp bao v~ nbc;
HInh 2-7. Ph~m vibaav~ mai th\IOIlg
* Thiit ki lap ngoai
- Mai d{lp lam biing da db, da x~ khan (da xip):
Da d6 co the dling lo~i da co chQn IQCde cac vien da co kich thuac tuang d6i gi6ng nhau, ho(ic kh6ng chQn IQc vai kich thuac khac nhau. Neu dling da kh6ng chQn IQc can dam bao s6 lugng nhUng vien da bAng ho(ic Ian han duang kinh vien da tinh toan chiem han 50% trQng lugng toan bi). Neu dling da co chQn IQc can dam bao s6 lugng nhUng vien da bAngho(ic Ian han duang kinh vien da tinh toan chiem han 75% trQng lugng toan bi). Chieu day lap da d6 kh6ng duQ'cbe han 2 Ian duang kinh vien da tinh toan.
( 2-5 )
(2-6 )
Da x6p cAn dam bao hinh d\Ulg vien da ilikh6i chi!' nh~t co chieu dai vien da khoang 2 IAn chieu rQng va kich thuac cac vien da xftp xi nhau. Khi x6p cAn x6p vien da thllng goc vrn mai d6c Clla d~p. Chieu day kh6i da co th~ b6 tri 1 lap ho~c 2 lap my vao kich thuac, trQng Iugng vien da.
DUCmgkinh vien da co th~ tinh theo cac cong thuc sau: +Cong thuc Clla P.A. Sankin:
D=_I_ . .JI+m' A.h Y.-I m(m +2)
+Cong thuc clla B.A. Puskin cho mai bllng da xay khan : D=O,178k._I_.~.h
Y. -I m