STRUCTURE
UNSTABLE
TRACTION
STABLE
BRIDGE
SHELL
H
S
J
E
F
O
P
I
I
J
U
H
H
X
L
F
E
J
U
U
V
N
E
E
E
B
R
I
D
G
E
O
V
L
L
P
R
O
M
I
P
I
V
A
B
L
W
H
U
O
L
T
A
F
E
A
O
I
X
Z
T
C
I
A
F
C
T
A
U
O
M
A
C
O
E
V
F
S
R
W
L
R
X
W
U
C
E
A
N
G
O
T
M
Y
I
F
R
B
Y
U
L
A
U
I
I
E
Z
R
T
L
E
A
O
N
E
L
B
A
T
S
S
