Civil Engineering Reference
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Q
Q
Q
L
L
L
(a) Continuously braced
(Free torsion)
(b) Centrally braced
(Free torsion)
(c) Unbraced
(Destabilising torsion)
e
e
Q
Q
(i) Free torsion
(ii) Destabilising torsion
(d) Eccentric load
Figure 10.33
Beams in torsion and bending.
1 . 4
e
Q
Q
1 . 2
( )
Approximate
equation 10.82
M
M
zx
Accurate
[25]
py
L
1 . 0
0.5
1.0
1.41
0 . 8
0 . 6
0 . 4
0 . 2
0
0
0 . 2
0 .4
0.6
0.8
1.0
1.2
1. 4
Dimensionless torque 1/
x
Figure 10.34
Interaction between lateral buckling and torsion for unbraced beams.
10.5.2 Plastic design of fully braced members
ThemembermustbeClass1.Plasticcollapseanalysesshouldbeusedtodetermine
the plastic collapse load factors
α
i
for in-plane bending (Section 5.5) and
α
x
for
torsion (Section 10.3.3.3).
The member should satisfy the circular interaction equation
1
/α
i
+
1
/α
x
≤
1
(10.81)
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