Member Check Parameters

This window is displayed when you select Member Check from the Compute menu, and the active window is a section. After you enter the appropriate values, press the OK button and the Member Check output will be displayed.

Unbraced Lengths

Lx, Ly, LtThe unbraced lengths of the member for buckling about the X axis (in the Y direction), buckling about the Y axis (in the X direction), and torsional buckling, respectively. For lateral-torsional buckling of beams symmetrical about the X axis and bending about the X axis, Ly and Lt are the controlling unbraced lengths.
Kx, Ky, KtThe effective length factors applied to the respective unbraced lengths. A value of 0 indicates a fully braced condition, where internal forces resulting from loads in that direction are set to 0.
LmThe distance along the length of the member between discrete rigid restraints that restrict distortional buckling. If there are no discrete restraints for distortional buckling, leave this as a large value (such as the span length) and CFS will calculate the distortional buckling wavelength. If the member is fully restricted against distortional buckling, use Lm = 0. If the shape does not have a distortional buckling failure mode, the value of Lm has no effect.

In cases where rotational stiffness is provided to the braced flange by connection to sheathing, Lm does not represent the spacing between fasteners. It is the distance between rigid restraints against distortional buckling, if they exist.

Coefficients

Cbx, CbyThe bending coefficients used to determine the elastic critical moments for the member about the X axis and Y axis, respectively. The value is dependent on the moment gradient throughout the unbraced length. You may conservatively use the default value of 1. For bending about a non-symmetric axis, you must enter the reciprocal of CTF as the value of Cb, which may also be conservatively set to 1.
Cmx, CmyThe moment coefficients used in the combined compressive axial load and bending interaction equation, for moments about the X axis and Y axis, respectively. You may conservatively use the default value of 1.
Braced FlangeFor members having one flange fastened to deck, sheathing, roof system, or other continually connected system, select the flange that is attached: Bottom, Top, Left, or Right. Otherwise, select None.
Reduction Factor, RIf there is a braced flange, enter the moment reduction factor as defined in the AISI or ASCE Specification for your situation. For example:
R=0.70 for continuous span Z sections
R=0.60 for continuous span C sections
R=0.70 for simple span C or Z section, depth 6.5"
R=0.65 for simple span C or Z section, 6.5" < depth 8.5"
R=0.50 for simple span Z section, 8.5" < depth 12"
R=0.40 for simple span C section, 8.5" < depth 12"
Stiffness, kf The rotational stiffness provided to the braced flange by connection to the bracing material (deck, sheathing, etc.). This stiffness is incorporated in the distortional buckling calculations for the flange which is braced (bottom, top, left, or right). The units for this input are moment/radian/unit length (such as k-in/rad/in) which is then reduced to a force (such as k). Refer to the AISI Specification and Commentary for more information on determining what value to use.
Mx and My include
P-δ effects
Choosing this option will prevent moment amplifiers from being applied due to axial compression load.

Internal Forces

PThe axial force (factored for LRFD) applied to the section. Positive loads are compression and negative loads are tension.
ex, eyThe axial load eccentricity in the X and Y direction, measured from the origin of the section. Positive ex is horizontal to the right of the origin and positive ey is vertically above the origin. The combination of the axial load and these eccentricities produces additional bending moment if the unbraced length is greater than zero.
MxThe moment (factored for LRFD) about the X axis applied to the section. Positive moments produce compression above the X axis.
VyThe shear force (factored for LRFD) in the Y direction applied to the section. This generally accompanies a moment about the X axis.
MyThe moment (factored for LRFD) about the Y axis applied to the section. Positive moments produce compression to the right of the Y axis.
VxThe shear force (factored for LRFD) in the X direction applied to the section. This generally accompanies a moment about the Y axis.
BThe torsional bimoment (factored for LRFD) applied to the section. The sign of the bimoment is very important when combined with bending. For a C section with a vertical web, a positive bimoment causes tension in the upper-right and lower-left quadrants of the section, and causes compression in the upper-left and lower-right quadrants of the section.