MT-1620 al.2002 But t is constant around the section. This can be seen by cutting out a piece of the wall AB Figure 12.11 Representation of infinitesimal piece of wall of thin closed section under torsion Z c X-y plane Use∑F=0 to give τ,t,dz+τ nt dz=0 B in general: tt =constant Paul A Lagace @2001 Unit 12-15MIT - 16.20 Fall, 2002 But τ t is constant around the section. This can be seen by cutting out a piece of the wall AB. Figure 12.11 Representation of infinitesimal piece of wall of thin closed section under torsion z x-y plane Use ∑Fz = 0 to give: −τ t dz + τ B tB dz = 0 AA ⇒ τ t AA = τ B tB in general: τ t = constant Paul A. Lagace © 2001 Unit 12 - 15