Aluminium Design and Construction John Dwight

Figure 9.8 Torsional buckling of a type-R section strut.
1. Box or tubular sections (always much stiffer in torsion than a
comparable open section);
2. Any type-R section that would be classified as compact for local
buckling;
3. Conventional bisymmetric I-sections (with unreinforced flanges);
4. Conventional skew-symmetric Z-sections (with unreinforced flanges).
9.6.5 Basic calculation
As with column buckling, the basic expression for the calculated resistance
Pc is as follows:
Pc =Apb (9.8)
where pb is now the torsional buckling stress, allowing for interaction
with flexure if necessary, and A is the gross section area as before.
9.6.6 Torsional buckling stress
The buckling stress p b depends on the torsional buckling slenderness
parameter � and may be read from one of the families of curves (T1,
T2) given in Figure 9.9. Alternatively, it may be calculated from the
relevant formula (Section 5.4.2). The appropriate family is chosen as
follows, the T2 curves being the more favourable:
Type-R sections T2
All other sections T1
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