Civil Engineering Reference
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Points of inflection
(b) Mode1,
Q
2
=0
Points of inflection
Q
1
Q
2
Q
1
(c) Mode 2,
Q
1
=0
L
1
L
2
L
1
(a) Elevation
(d) Mode 3, zero interaction
Figure 6.21
Buckling modes for a symmetrical three span continuous beam.
Q
2
L
2
2
/ (
EI
z
GI
t
) for zero interaction 3
60
Q
2
L
2
2
/ (
EI
z
GI
t
) for span
L
1
unloaded 2
50
Q
1
Q
2
Q
1
40
Q
1
L
1
2
/ (
EI
z
GI
t
)
for zero interaction 3
L
2
L
1
L
1
30
(
2
EI
w
/GI
t
L
2
) = 0
K
=
20
(a) Three span beam
10
Q
1
L
1
2
/ (
EI
z
GI
t
) for span L
2
unloaded 1
0 0.2 0.4 0.6 0.8 1.0 0.8 0.6 0.4 0.2 0
L
1
/
L
2
Span ratios
L
2
/
L
1
(b) Significant buckling loads
Figure 6.22
Significant buckling loads of symmetrical three span beams.
case the restraint parameters [12] are given by
1
1
+
3
L
2
/
2
L
1
R
1
=
R
2
=
R
4
=
(6.63)
approximately. Some dimensionless buckling loads (for beams of narrow rectan-
gularsection)determinedbyusingtheserestraintparametersinthetabulationsof
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