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American Steel Design
Section 2
2-10
Methodology
If the user were to request design for torsion, the torsional
properties required for calculating the warping normal stresses,
warping shear stresses and pure shear stresses are first determined.
These depend of the ”boundary” conditions that prevail at the ends
of the member. These boundary conditions are defined as “Free”,
“Pinned” or “Fixed”. They are explained below:
Free : “Free” represents the boundary condition such as that which
exists at the free end of a cantilever beam. It means that there is no
other member connected to the beam at that point.
Pinned : “Pinned” represents the condition that corresponds to
either a pinned support defined at the joint through the Support
command or a release of any of the moments at the joint through a
Member Release specification.
Fixed : “Fixed” represents the condition where a fixed support
exists at the joint. In the absence of a support at that joint, it
represents a condition where a rigid frame connection exists
between the given member and at least one other member
connected to that joint. Also, no member releases should be
present at that joint on the given member.
After the boundary conditions are determined, the normal and
shear stresses are determined. The guidelines specified in the
publication T114 for concentrated torsional moments acting at the
ends of the member are used to determine these stresses.
The warping normal stresses are added to the axial stresses caused
by axial load. These are then substituted into the interaction
equations in Chapter H of the AISC 89 code for determining the
ratio. The plane shear and warping shear stresses are added to the
shear stresses causes by actual shear forces and compared against
the allowable shear stresses on the cross section.