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D1.C.6 Design Parameters

Design per LRFD specifications is requested by using the CODE parameter. Other applicable parameters are summarized in Table 2-4. These parameters communicate design decisions from the engineer to the program and thus allow the engineer to control the design process to suit an application's specific needs.

The default parameter values have been selected such that they are frequently used numbers for conventional design. Depending on the particular design requirements, some or all of these parameter values may be changed to exactly model the physical structure.

The parameters DMAX and DMIN are applicable for member selection only.

Table 1. AISC LRFD (2nd and 3rd Ed.) Design Parameters
Parameter Name Default Value Description
CODE -

Must be specified LRFD or LRFD3 for 3rd Edition.

Must be specified LRFD2 for 2nd Edition.
AXIS 1

1 = Design single angles for bending about their principle axis.

2 = Design single angles for bending about their geometric axis.
BEAM 1.0
  • 0.0 = design at start and end nodes and those locations specified by the SECTION command.
  • 1.0 = design at 13 evenly spaced points (i.e., 1/12th points) along member length, including start and end nodes.
Note: See D1.A.6 Design Parameters.
CAN 0

0 = deflection check based on the principle that maximum deflection occurs within the span between DJ1 and DJ2.

1 = deflection check based on the principle that maximum deflection is of the cantilever type (see D1.B.1.2 Design Parameters)
CB** 1.0 Coefficient Cb per Chapter F of AISC LRFD. If Cb is set to 0.0, it will be calculated by the program. Any of value will be used directly in design.
DFF None (Mandatory for deflection check) "Deflection Length" / Maximum allowable local deflection
DJ1 Start Joint of Member Joint No. denoting starting point for calculation of "Deflection Length" (see D1.B.1.2 Design Parameters)
DJ2 End Joint of Member Joint No. denoting end point for calculation of "Deflection Length" (see D1.B.1.2 Design Parameters)
DMAX 45.0 in. Maximum allowable section depth.
DMIN 0.0 in. Minimum allowable section depth
FLX 1

1 = Single angle member is not fully braced against lateral torsional buckling.

2 = Single angle member is fully braced against lateral torsional buckling.

3 = Single angle member is braced against lateral torsional buckling at the point of maximum moment.
FYLD 36.0 ksi Yield strength of steel.
FU 60.0 ksi Ultimate tensile strength of steel.
KX 1.0 K value for flexural-torsional buckling.
KY 1.0

Effective length factor to calculate slenderness ratio for buckling about local y-axis. Usually this is the minor axis.

KZ 1.0

Effective length factor to calculate slenderness ratio for buckling about local z-axis. Usually this is the major axis.

LX Member Length Length used for flexural-torsional buckling.
LY Member Length Length to calculate the slenderness ratio for buckling about the local y-axis.
LZ Member Length Length to calculate the slenderness ratio for buckling about the local z-axis.
MAIN 0.0

0.0 = check for slenderness

1.0 = suppress slenderness check

Any value greater than 1 = Allowable KL/r in compression.
NSF 1.0 Net section factor for tension members.
PROFILE   Used in member selection. Refer to TR.48.1 Parameter Specifications for details.
RATIO 1.0 Permissible ratio of actual load effect to design strength.
STIFF Member Length or depth, whichever is greater Spacing of stiffeners for beams for shear design.
STP 1

Section type to determine Fr (compressive residual stress in flange) per 3rd Ed. LRFD spec., p 16.1-97.

  • 1 = Rolled section (Fr = 10 ksi)
  • 2 = Welded section (Fr = 16.5 ksi)
TMAIN 300 Any value greater than 1 = Allowable KL/r in tension.
TRACK 0.0

Specified the level of detail included in the output.

  • 0.0 = Suppress all design strengths
  • 1.0 = Print all design strengths
  • 2.0 = Print expanded design output
UNB Member Length Unsupported length (Lh) of the bottom* flange for calculating flexural strength. Will be used only if flexural compression is on the bottom flange.
UNT Member Length Unsupported length (Lh) of the top* flange for calculating flexural strength. Will be used only if flexural compression is on the top flange.

*Top and Bottom represent the positive and negative side of the local Y axis (local Z axis if SET Z UP is used).  

Note: For a description of the deflection check parameters DFF, DJ1, DJ2, and CAN, see the D1.B.1.2 Design Parameters of this manual. 

The STIFF parameter represents the term “a” as defined in Section F2, page 6-113 of the LRFD 2nd edition manual.

** Non-default values of CB must be re-entered before every subsequent CHECK CODE or SELECT command.

Parent topic: D1.C. American Codes - Steel Design per AISC LRFD Specification
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