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STABILITATEA ŞI DINAMICA CONSTRUCŢIILOR 145<br />

şi<br />

⎧⎛<br />

⎪ ⎜<br />

⎪⎝<br />

⎪<br />

⎪<br />

⎪<br />

EI<br />

39,<br />

90468365<br />

3<br />

a<br />

EI<br />

− 35,<br />

96069821<br />

3<br />

ma<br />

⎞<br />

⋅ 1,<br />

5m<br />

⎟ ⋅ X1,<br />

2 −<br />

⎠<br />

⎨<br />

EI<br />

18,<br />

43878389<br />

3<br />

a<br />

⋅ X1,<br />

2 +<br />

EI<br />

− 18,<br />

43878389<br />

3<br />

a<br />

⋅ X2,<br />

2 = 0<br />

⎛<br />

EI<br />

+<br />

⎜<br />

⎜11,<br />

73870173<br />

3<br />

⎝<br />

a<br />

EI<br />

− 35,<br />

96069821<br />

3<br />

ma<br />

⎞<br />

m<br />

⎟ ⋅ X2,<br />

2<br />

⎠<br />

= 0<br />

⎪−<br />

⎪<br />

⎪<br />

⎪<br />

⎪<br />

⎩<br />

Rezolvând sistemele de ecuaţii ale formelor proprii pentru X2,1=1,<br />

respectiv X2,2=1, stabilim următoarea soluţii:<br />

şi<br />

Matricea modală are forma:<br />

X1,1=0,507494194<br />

X1,2=-1,313643927.<br />

⎡0, 507494194 − 1,<br />

313643927⎤<br />

[ X]<br />

= ⎢<br />

⎥<br />

⎣ 1<br />

1 ⎦<br />

9. Verificarea formelor proprii de vibraţie<br />

Aplicăm condiţia de ortogonalitate:<br />

T { } [ m]{<br />

X } 0<br />

X1 2 =<br />

şi determinăm eroarea absolută şi cea relativă:<br />

ε<br />

a<br />

= X<br />

1,<br />

1<br />

X<br />

1,<br />

2<br />

m<br />

1<br />

= 0,<br />

507494194<br />

+ X<br />

2,<br />

1<br />

X<br />

2,<br />

2<br />

m<br />

2<br />

=<br />

−9<br />

( − 1,<br />

313643927)<br />

⋅ 1,<br />

5m<br />

+ 1 ⋅ 1 ⋅ m = 1,<br />

09 ⋅ 10 m<br />

−9<br />

1,<br />

09 ⋅ 10 ⋅ m<br />

εr<br />

% =<br />

=<br />

1 ⋅ 1 ⋅ m<br />

1,<br />

09<br />

−<br />

⋅ 10<br />

7<br />

< 0,<br />

1.

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