Torsional resistance

Torsional resistance is calculated on the basis of a thin-walled closed section. Solid sections are replaced by an idealized equivalent thin-walled section. Sections of complex shape are divided into sub-sections with each sub-section treated as an equivalent thin-walled section. The torsional resistance is taken as the sum of the torsional resistances of the sub-sections.

The torsional moment, carried by each sub-section according to elastic theory, may be found on the basis of the St Venant torsional stiffness. Division of the section into sub-sections should be so arranged as to maximize the calculated stiffness.

For this example the section will be divided into the sub-sections shown in Figure 3.14.

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