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Then
V σ T E 1 σ + σ T E 1
1
2
δ =
p T u dS
δ σ )
dV
S u δ
V δ
σ T dV
p T u dS
=
S u δ
=
0
(2)
δ
W i δ
W e =
This expression is the same as
0 of Eq. (2.78). For the beam, using the
notation of Example 2.6,
x δ
0 x
γ
κ
u 0
w
θ
dx
δ =
[ NVM ]
δ
[ NVM ]
(3)
S u
[ NVM ] T . In order to
where σ and p of (2) are replaced by the stress resultants s , with s
=
derive the proper relations, it is necessary to add the identity
00
x
s T D u u dV
s T D u u dV
V δ
V δ
=
0 ,
D u
=
0
1
(4)
x
00
x
to the right-hand side of (3). This leads to
δ =
u 0 ) + δ
w θ) + δ
θ )
[
δ
N
(
V
M
] dx
0 x
x
δ
θ L
Nu 0 + δ
(w + θ) + δ
θ ] dx
+
[
δ
V
M
N u 0 + δ
V
w + δ
M
0 =
0
(5)
x
S u
where the terms due to (4) are indicated by an underline. Integration by parts of the second
integral gives
Nu 0 + δ
(w + θ) + δ
θ ] dx
[
δ
V
M
x
δ
θ L
N u 0 + δ
V w +
M δ
=
Nu 0 + δ
V
w + δ
M
0
[
δ
V
] dx
(6)
x
S u
N =
V =
M
Since for equilibrium (Chapter 1, Section 1.8.3)
δ
0 ,
δ
0 ,
δ(
V
) =
0 along x , (6)
becomes
δ
θ L
0
Nu 0 + δ
(w + θ) + δ
θ ] dx
[
δ
V
M
=
Nu 0
+ δ
V
w + δ
M
(7)
x
S u
δ in the form
Substitution of (7) into (5) gives
δ =
u 0 ) + δ
w θ) + δ
θ )
[
δ
N
(
V
M
] dx
0 x
x
L
0
δ
N
(
u 0
u 0
) + δ
V
(w w) + δ
M
θ)
(8)
S u
or
δ =
s T
p T
V δ
(
)
S u δ
(
)
=
D u u
u
u
dS
0
(9)
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