Torsional section properties of steel shapes

Updated February 21, 2017

The torsional section property of a steel shape refers to the amount of rotating or twisting force that a section of steel can withstand before failing. Different shapes of steel sections possess different torsional properties. Structural engineers use multiple mathematical formulas to calculate the torsional section properties of these steel shapes to determine the steel structures to use and additional bracing requirements, if any.

St. Venant Constant

The St. Venant torsional section refers to a constant in the equation that determines the stress of a section of steel and the buckling moment resistance for unsupported beams that run sideways. Flexural-torsional buckling of compression members refers to the simultaneous bending and twisting of an upright load-bearing section of steel. "J" is used to denote the torsional constant in the calculation.

Warping Constant

The warping property refers to the nonuniform or warping torsion of a steel section or beam and how it is calculated when determining a steel section's warping capabilities. "Cw" is used in the calculation to represent this mathematical torsional constant.

Monosymmetry and HSS

An I-beam with its top section larger than its bottom is defined as a beam with monosymmetry torsional properties and incorporates properites of these beams loaded symmetrically. The torsional constant in the calculation used to determine this torsional section property is denoted by "βX."

The HSS (hollow beams) torsional sectional property denotes the sheer stress as the result of an applied torque to a steel beam. Engineers use "C" in the calculation for this torsional constant.

Shear Center

The shear centre is the point in the plane where the twisting occurs. The shear centre is needed for determining the warping torsional and monosymmetry constants in the equation. Additionally, the shear centre is needed to find the destabilising effect of gravity loading beneath or above the shear centre. The shear center's coordinates are figured in accordance with the centroid.

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