.
4.1. RB , EJ (. 4.3, ).
`MB0 |
l |
. 4.3
. B, RB (. 4.3, ).
, () , RB , B , RB (. 4.3, ).
B , : D = (Mp 0 ´ `MB 0), Mp 0 , `MB 0 , B (. 4.3, ). , :
D (P) = (1/ EJ)[(1/2)×(l /2)×(Pl /2)]×[(5/6)× l ] = 5 Pl 3/48 EJ.
D (RB) RB. `MB 0 (. 4.3, ), :
D (RB) = (MRB 0 ´ `MB 0) = (- RB) × (`MB 0 ´ `MB 0) = (- RB) × d BB,
d BB - B , :
d BB = (`MB 0 ´ `MB 0) = (1/ EJ) [(1/2) × l × l ] × [(2/3) × l ] = l 3/ (3 EJ).
B , , P RB, , , :
D (P,RB) = D (P) +D (RB) =5 Pl 3/48 EJ + (- RB)(l 3)/(3 EJ) = 0,
: RB = (5/16) P.
, n , X 1, X 2, , Xn.
, . 4.4, 3 , 2 1 , .
X 1, X 2, X 3, , . 4.4, . , , ,
D1 (X 1, X 2, X 3, P) = 0;
D2 (X 1, X 2, X 3, P) = 0; (4.2)
D3 (X 1, X 2, X 3, P) = 0,
D i (X 1, X 2, X 3, P) Xi Xi : X 1, X 2, X 3 . :
d11 X 1 + d12 X 2 + d13 X 3 + D1 p 0 = 0;
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d21 X 1 + d22 X 2 + d23 X 3 + D2 p 0 = 0; (4.3)
d31 X 1 + d32 X 2 + d33 X 3 + D3 p 0 = 0,
d ij Xi Xi Xj = 1, D ip 0 Xi Xi .
, :
d ij = (`Mi 0 ´ `Mj 0) = Sò (`Mi 0 × `Mj 0 / EJ) ds, (4.4)
D ip 0= (`Mi 0 ´ Mp 0) = Sò (`Mi 0 × Mp 0 / EJ) ds, (4.5)
`Mi 0 Mp 0 Xi = 1 .
. 4.4
(3.10), (4.4) , :
d ij = d ji.
(4.3) . , . . : X 1, X 2, X 3, .
n :
S d ij Xj + D ip 0= 0; (i = 1,2,, n). (4.6)
X 1, X 2, , Xn, , .
. EJ, .
4.2. (. 4.5, ), EJ .
.
1. : = 3 = 3×1 1 = 2 , X 1 X 2 (. 4.5, ).
(4.4) :
d11 X 1 + d12 X 2 + D1 p 0 = 0; ()
d21 X 1 + d22 X 2 + D2 p 0 = 0.
2. (. 4.5, ).
3. ():
d11 = 8/3 EJ;
d12 = - 4/ EJ;
d22 = 32/3 EJ;
D1 p 0= 2/ EJ;
D2 p 0 = - 8/3 EJ.
4. ():
(8/3) X 1 4 X 2 = - 2;
- 4 X 1 + (32/3) X 2 = 8/3,
: X 1 = - (12/14) ; X 2 = - (1/14) .
5) :
S MA = 0; _ MA = 3/7;
S X = 0; _ XA = - 8/7;
S Y = 0; _ YA = 2/7.
X 1 X 2 , (. 4.5, ):
MA = 3/7; XA = - 8/7; YA = 2/7; XB = - 6/7; YB = - 1/14.
1. , , , .
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2. (4.4) (4.5) , d ij i ¹ j D ip 0 , . d ii, (4.3), .
3. , , .
4. , EJ - (4.6).