- Uu di6m cua cftu mang:
b. Than mang bang betong cbt thep
D\Ia vao hinh thuc k€t du chia than mang thilnh 2 lo~i: Mang thanh m6ng (co chi~u day thilnh mang khoang (2+5)cm) va mang thilnh day (chi~u day thilnh mang
~ IOcm).
Hinh d~ng m(it dt ngang long mang thu<'mgla chfr nh~t hay hinh parabol. Long mang co th~ lam kin, hCrhoan toan hay ha m(>tphftn.
Long mang ha co m(it c~t la hinh cM nh~t hay hinh vuong g6m co cac b(>ph~n: Day mang, thilnh mang, phia tren thilnh mang lam tai mang (co th~ lam dili xUng hay khong dili xUng) theo ki~u dftm cong son. Tai mang hai ben thilnh mang dugc nili vm nhau b~ng cac thanh gi~ng d(it th~ng goc vai trvc Clladong nuac.
Tai mang va thanh gi~ng co m\lCdieh lam tang d(>cUng eua thanh mang va long mang, lilm dftm d6' cae tAmlat m(itcAugiao thOng(Hinh 6.15a, b).
Long mang kin la m(>tilng d&nco m(it e~t vm hinh d~g bAtkyo TAmtren c6 th~ k€t hgp lam cAucong tac hay cftu giao thong (Hinh 6.15e).
Ban m~t
I Lan can Lan can
IT~m nitp Thanh giitng
Tai mang Tai mang
a- b- c-
Thanh mang
Day mang Day mang
Hinh 6.15. Cac lo~i m~t citt long mang belOng c6t thop a, b - Long mang h6 c - Long mang kin
* Kich thlfO'cm~t ciit ngang long mling: Duge xac dinh theo tinh toan thuy l\Ic, du d~ thao qua lUlllugng nuae thi€t k€, khong gay x6i la, b6i I~ng va cantra dong ehay trong mang khi d&nnuae.
D(>vugt eao an toan eua dinh thanh mang tren mve nuac Ian nhAt trong mang tinh theo cong thuc:
h
e=-+15 (cm)
12
(6.1)
Trong do:
e _DO vuqt cao an toim clla dinh thimh mango h _ Chi6u sau Ian nhat trong mango
Cao trinh clla dinh thilnh mang t6i thi6u phili blmg cao trinh ba kenh d6ng thai' khong d~ m~t mang hay thanh gi~ng cantra dong chily trong mangoNoi chung m~t
duai clla thanh gi~ng phili cao hou m\ICnuac Ian nhat trong mang (15 -;-20)cm. Khoang cach giua cac thanh gi~ng (lg) d\Ia theo cau t~o mil dinh. Khi d~t c~u tren thanh gilmg thi khoimg cach 19lay (1,5 -;-2,5)m. N~u dimg tai mang lilm c~u thi tri
56 19co th~ lay Ian hou.
Khi chQn d~ng mang kin, n~u mang dili c~ b6 tri cac 16 co chi6u rOng ~ 0,7m (d~g h6 ga) dQc m~t mang d~ nguai co th~ vilo mang n~o vet bim cat (thuiYng khoimg 10 -;-15m b6 tri 1 16).
Chi6u rOng c~u tren mang phai ~ 0,7m. Hai ben c~u co Ian can bilOv~ co chi6u cao 1m b~ng be tong c6t thep, b~ng thep hay b~ng g6. Khoimg each giua cac cOtIan can thuiYnglay blmg 2m. Cac cOtduqc lien k~t clIng vai tai mang hay tam m~t c~u.
* Kieh thUcJem~t e~tngang ella tAt ea cae eAu ki~nella long mang, ella e~u
va Ian can: Duqc xac dinh theo tinh toan khil nang chiu l\Ic tac d\lng len chung. Xet v6 m~t cau t~o, chi~u dily day mang vii thilnh mang phili? 12cm. a ch6 n6i ti~p giua day mang vii thilnh mang lilm thimh m(it nghieng 45° vii chi6u cao ~ 10cm m\lC dich d~ giiun co h~p m(it c~t clla dong nuac khi chily qua long mango
Chi6u cao thanh gi&nglay ~ ~ chi6u dili d~m, phili ~ chi6u dily thilnh mang vii 15
phili ~ 15cm. Chi~u rOngthanh gi&ngdu d~ lilm g6i do c~u vii ~ 15cm.
M(it c~t ngang cua tai mang Iii hinh chit nh~t hay hinh thang, kich thuac m~t c~t lay nhu sau: Chi~u cao lay b~ng chi6u cao clla thanh gi~ng vii ~ ~ khoilng cach25
cau tren mling h6' thuimg dung cac t~m betong c6t thep duc s~n hay g6d~ lat. Chi€u day t~m mi).tc5.u ~ 315chi€u rQng cAu nhung phai ~ Scm (n~u lam bang g6 thi
phai l~y 100 hon).
CQt va tay vin Ian can nen lam mi).t c~t hinh vuong hay chii nh~t co kich thuac m6i c\lnh ~ 10cm.
Mi).ttrong long mling dUng viia xi mang d~ trat, chi€u day laptrat =2cm.
N6i ti~p long mang vai cua vao va cua ra c5.n pMi bao dam 6n dinh v€ th~m ... thuimg keo dai long mling k6 ill mep mai d6c cila ba song vao long kenh d~t mQt do~n ~ 0,7 5m d~ lam tang chi(\u dai duimg vi(\n th~m.
* K~t eftu nhip: Tuy theo di(\u ki~n chiu hfc, tinh hiOO dia ch~t cua n(\n va dia hiOOnai xay d1Jllg. Sa d6 b6 tri OOipthan mang thuimg co cac hiOOthuc sau:
- Than mling d~ng dAm don (HiOO 6.14): Than mling dUQ"cphan thaOOOOi(\udo~va di).ttren cac tl1,ldo, m6i do~n lam vi~c theo huOOg dQc OOumQt dAm don. va di).ttren cac tl1,ldo, m6i do~n lam vi~c theo huOOg dQc OOumQt dAm don.
- Than mang d~ng dAm co milt thua (Hinh 6.16): Phan c5.u mang ra lam nhi(\udo~n, trong m6i do~n than mang lam vi~c theo huOOg dQc la dAm mQt nhip co 2 milt do~n, trong m6i do~n than mang lam vi~c theo huOOg dQc la dAm mQt nhip co 2 milt thua. Chi(\u dai do~n milt thua a=(1,5 +.2,5)m.
cAu mang lo~i nay dUQ"cdung khi qua thung lilng rQng OOung khong sau.
Khen6i , Im~ ~ (10 -;-15)m a ~ (1,5 -;-2,5)m Dfunchinh " " .dk a Milt thira Khe n6i
Hinh 6.16. Than mang d?ng dftm co milt thira
- Than mang ki~u vom va vom treo: Toan bQ than mang co th(\ di).ttren vom(HiOO 6.17a) hay treo aphia duai vom biing cac thanh treo (HiOO 6.17b) t~o thanh (HiOO 6.17a) hay treo aphia duai vom biing cac thanh treo (HiOO 6.17b) t~o thanh mQt nhip cAu.
a- b-
Hinh 6.17. C~u mang nhip vom
a- KiSu vorn b -Ki~u vom treo
*Khe nBi: Nili ti6p thiin mang vai Clla vitO va cua ra thuimg lam tach rai.
Cac khe nili giiia cac dO(ln (OOip) cua than mang, giiia cua vao va cua ra vai than mang d.n phai khong duqc thilm nuac va co dan d6 dang khi OOi~td(>thay d6i hay c~u mang bi lun.
B€ r(>ng cua khe nili 2?: 2cm. (HiOO 6.18) th€ hi~n cfru t(lO khe nili thuimg dung giiia than mang vai clra vao va cua ra, giiia cac dO(ln (OOip).
NhlJa duang Ne the Man Cao su tfun b- Man Maog Bulen ~~(12716)
Hinh 6.18. Cae d~ng khe nbi thuang dung
a-
Lap 16t *' *' .