4.5.2.Tinh toan cac h~s8An djnh cho than iI~p
1. Tinh h~ s66n ajnhvJ tr!C(J1 phting KT
T6ng quat: KT b~ng t6ng l\fc ch6ng truqt (h,rc rna sat va h,rc diOO)tren m~t truqt AB chia cho t6ng h,rc gay truqt tren m~t AB,( h,rc co chieu song song vm AB)
K - LQ~~
T- LQ~~
L:Q~ =L:QI - LQ2 :T6ng h,rc gay truqt len m~t truqt AB. L Q~ la h,rc xo ngang co chieu huang ve phia hfi.luu
LQ~ :T6ng h,rc ch6ng truqt tren m~t truqt AB.
Dodo:
LQ~ =(LP - LW ).f+ C.F
_ (Lp-LW}f +C.F
KT- LQ (4-19)
F: Dien tich clla m~t truqt AB. Khi dt bang I met d~ tiOOthi F = Bm. Bmla chieu rQng clla day mongo la chieu rQng clla day mongo
f,.C : He s6 rna sat va h,rc diOOtren m~t truqt. N6u truqt tren m~t nen, sabQ co the Idy OOusau;
+Nen da t6t : f= 0,75; C = 40 +20 T/m2•
Khi n~n Iii <!Atvii m(it tnrqt tnrqt tren m(it n~n nhu hinh (4-2Ia) thi lAy C =o.
~Q =~Ql-~Q2
Khi n~n Iii dAt vii m(it tnrqt c~t qua dAt n~n nhu hinh (4-21b) thi lAy C bfulg h,rc dinh cua <!Atn~n.
Ghi ehu : Vm eong thue (4-19) ehi viit cho truimg h(1JJmqt tru(J1AS song song vm mqt ph{mg nlim ngang. Khi AS nghieng vm mqt phJng nlim ngang thi ttit ca cac l(rc If'. LW, L!]l. L!]2 pMi chiiu chUng len phttang song song va vuong goc vm mqt AS r6i mui xet cac l(rc hinh chdu cua chung la l(rc ch6ng tru(J1 hay gay tru(J1,tJi tinh KT.
2. Tinh h~ s66n tJinhva l(lt KL
T6ng quat: KL bfulg t6ng mo men ch6ng I~t ( ngugc kim d6ng h6 tren hinh 4-20) chia cho t6ng mo men gay I~t ( th~n kim d6ng h6 tren hinh 4-20 ) vai mm
I~tB.
(4-20)
3. Tinh h~ s6 6n tJinhva tJdyn6i KJn
T6ng quat: Kdn b~ng t6ng h,rc th~ng dUng (len m(it AB) co chi~u di xu6ng chia cho t6ng h,rcthkg dUng co chi~u di len.
(4-21)
4.5.3. Tinb toan eae b~s8 An djnb tU'img cli~n dit va eae bQ ph"n kbae