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D1.A.6 Design Parameters

Design per AISC 360-05, 360-10, and 360-016 (Unified) specifications is requested by using the CODE parameter. Other applicable parameters are summarized in the following Table. These parameters communicate design decisions from the engineer to the program and thus allow you to control the design process.

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.

Table 1. AISC 360-05, 360-10, and 360-16 Design Parameters
Parameter Name Default Value Description
CODE AISC UNIFIED

Used to designate this code (default is the 2016 edition).

CODE AISC UNIFIED (2016)
CODE AISC UNIFIED 2010
CODE AISC UNIFIED 2005
ALH

(AISC 360-16 only)

0.5 Distance of applied point torsion from start of member as a fraction of member length. Represented by " α " in the torsional case options in Appendix B of AISC Design Guide 9.

To be used with TND values of 3, 6, or 9. (0<ALH<1). Set TORSION 1 to enable Torsion check as per DG9.

BEAM 1.0

See Note 9 below.

  • 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.
BRC

(AISC 360-05 and 360-10 only)

1

Specifies the bracing type for the member used for seismic provision checks:

  • 1 = Relative bracing
  • 2 = Nodal bracing
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 2 1.0 Coefficient Cb per Chapter F. If Cb is set to 0.0, it will be calculated by the program. Any other value will be directly used in the design. See Note 2 below.
CSPACING 12 in Spacing between connectors in current length units. Refer to Section E6.1 and E6.2 of AISC 360.
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 1000.0 mm Maximum allowable depth for member selection.
DMIN 0.0 mm Minimum allowable depth for member selection.
DUCT

(AISC 360-16 only)

0 The ductile category of the member as per AISC 341-16:
  • 0 = non-ductile
  • 1 = moderately ductile
  • 2 = highly ductile
FLX 1

Parameter for specifying the lateral-torsional restraint condition for a single angle. Refer to Section F10 of AISC 360-05, 360-10, and 3601-16.

  • 1 = Member does not have continuous lateral-torsional restraint along the length.
  • 2 = Member has continuous lateral-torsional restraint along the length.
  • 3 = Lateral-torsional restraint is provided at the point of maximum moment only.
AISC 360-16: If FLX 2 is used, then any values assigned to parameters UNB, UNL, UNR, or UNT are ignored and zero is used for the member length for lateral torsional buckling.
FRM

(AISC 360-05 and 360-10 only)

0

Specifies the seismic force-resisting system used in seismic provision checks:

  • 0 = Ordinary Moment Frame (OMF)
  • 1 = Intermediate Moment Frame (IMF)
  • 2 = Special Moment Frame (SMF)
FU 400 MPa Ultimate strength of steel.
AISC 360-16: This value is ignored if SGR specified other than 0.
FYLD 250 MPa Yield strength of steel. The program considers a valid range of input values between 10 ksi - 100 ksi (69 MPa - 689 MPa).
AISC 360-16: This value is ignored if SGR specified other than 0.
KX 1.0 K value for flexural-torsional buckling.
INTERACTION 0

Directs the program which interaction equations to check per section H1:

  • 0 = Checks both H1.1 and H1.3 and reports the lower ratio as critical
  • 1 = Check both H1.1 and H1.3 and reports the higher ratio as critical
  • 2 = Always checks per H1.1 even when H1.3 may be applicable
  • 3 = Checks H1.3 in lieu of H1.1 when applicable
KY 1.0 Effective length factor to calculate slenderness ratio for compression buckling about local y-axis. Usually this is the minor axis.
KZ 1.0 Effective length factor to calculate slenderness ratio for compression buckling about local z-axis. Usually this is the major axis.
LBRC

(AISC 360-16 only)

1

Type of flange lateral bracing:

  • 0 = none
  • 1 = panel bracing
  • 2 = point bracing
  • 3 = special bracing

Used to calculate bracing requirements as per seismic provisions in AISC 341-16.

LEG 0

This parameter is meant for plain angles (Section E5).

  • 0 = The angle is connected by the longer leg.
  • 1 = The angle is connected by the shorter leg.
LX Member Length Length for flexural-torsional buckling. See Note 8 below.
LY Member Length Length to calculate slenderness ratio for buckling about local y-axis.
LZ Member Length Length to calculate slenderness ratio for buckling about local z-axis.
MAIN 200 Allowable slenderness limit for compression members.
METHOD LRFD Used to specify LRFD or ASD design methods.
MTYP 1

Specifies whether the member is a beam or column. Used for seismic provisions checks.

  • 1 = Beam
  • 2 = Column
For AISC 360-16 only:
  • 3 = Beam-column
NBRC

(AISC 360-16 only)

1 Number of braced points within the span. Represented by "n" in Appendix 6.3.2(a) of AISC 360-16. Required for Seismic Provisions.
NSF 1.0 Net Section Factor for tension members, equal to An/Ag ,used to account for reduction in section used for tension checks (clause B 4.3b.) combined with the SLF parameter to determine the rupture strength. (see also SLF parameter)
PROFILE   Used in member selection. Refer to TR.48.1 Parameter Specifications for details.
RATIO 1.0 Permissible ratio of actual load to allowable strength.
SEISMIC 0 Used to instruct the program to add additional checks per the AISC 341, Seismic Provisions for Structural Steel Buildings.
  • 0 = Do not check seismic provisions

AISC 360 – 05, check according to AISC 341 – 05

AISC 360 – 10, check according to AISC 341 – 10

AISC 360 – 16, check according to AISC 341 – 16

See section D1.A. American Codes - Steel Design per AISC 360 Unified Specification for more detials.

  • 1 = Check seismic provisions

See D1.A.9 Seismic Provision Checking per AISC 341 for details.

Note: These additional parameters that should be set when using the seismic option:
  • AISC 360-05 and AISC 360-10
    • MTYPE
    • FRM
    • BRC
  • AISC 360-16
    • MTYPE
    • DUCT
SGR

(AISC 360-16 only)

Select ASTM steel grades:
  • Custom
  • 1 = A36
  • 2 = A53 Gr.B
  • 3 = A500 Gr.B (HSSRect)
  • 4 = A500 Gr.B (HSSRound)
  • 5 = A500 Gr.C (HSSRect)
  • 6 = A500 Gr.C (HSSRound)
  • 7 = A501 Gr.A
  • 8 = A501 Gr.B
  • 9 = A529 Gr.50
  • 10 = A529 Gr.55
  • 11 = A709 Gr.36
  • 12 = A1043 Gr.36
  • 13 = A1043 Gr.50
  • 14 = A572 Gr.42
  • 15 = A572 Gr.50
  • 16 = A572 Gr.55
  • 17 = A572 Gr.60
  • 18 = A572 Gr.65
  • 19 = A618 Gr.I(a)/Gr.I(b)/Gr.II
  • 20 = A618 Gr.III
  • 21 = A709 Gr.50
  • 22 = A709 Gr.50S
  • 23 = A709 Gr.50W
  • 24 = A913 Gr.50
  • 25 = A913 Gr.60
  • 26 = A913 Gr.65
  • 27 = A913 Gr.70
  • 28 = A992
  • 29 = A588
  • 30 = A847
  • 31 = A1085

The yield stress and ultimate stress will be auto-calculated based on the grade selected. Note that any SGR value greater than 0 will take priority when calculating the yield stress and ultimate stress over any supplied FYLD and FU value.

Note: "HSS Rectangle A1085" and "HSS Round A1085" profiles steel grade will always be considered as A1085 irrespective of any value assigned to SGR.
SLF 1.0 Shear Lag Factor, value " U " normally taken from table D3.1, combined with the NSF parameter to determine the net effective area used to calculate the section rupture strength. (see also NSF parameter)
SNUG 1

Type of connection for the built-up members:

  • 0 = Welded or pretensioned bolts
  • 1 = Bolted snug-tight
SOE

(AISC 360-16 only)

0 Second Order Effects have been considered in analysis forces or not:
  • 0 = Have not been considered
  • 1 = Have been considered

By default, Second Order Effects are not considered in the analysis forces. This is related to Torsion checks as per DG9. Set TORSION 1 to enable Torsion check as per DG9.

STFB

(AISC 360-16 only)

0.0 Stiffener width for one-sided web stiffeners, twice the individual stiffener width for pairs of stiffeners. Represented by "bs" in Appendix 6.3.2(a) of AISC 360-16. Required for Seismic Provisions.
STFT

(AISC 360-16 only)

0.0 Thickness of web stiffeners. Represented by "tst" in Appendix 6.3.2(a) of AISC 360-16. Required for Seismic Provisions.
STIFF Member Length or depth of beam, whichever is greater Spacing of stiffeners for plate girder design.
STP 1.0 Section Type used for design
  • 1 = Rolled section
  • 2 = Welded section
Note: If a UPT Wide flange section with different top & bottom flange dimensions have been specified for a member, the AISC360-16 module will ignore the value of STP and consider the section as a Welded/Built-Up section.
TBRC

(AISC 360-16 only)

Type of torsional bracing:

  • 0 = None
  • 1 = continuous bracing
  • 2 = point bracing
  • 3 = special bracing

Used to calculate bracing requirements as per seismic provisions in AISC 341-16.

TFA

(AISC 360-16 only)

0 Tension field action to be considered in shear design:
  • 0 = do not consider
  • 1 = consider
TMAIN 300 Allowable slenderness limit for tension members.
TND

(AISC 360-16 only)

1

Torsion loading and end condition as in Table in Appendix C.4 of AISC Design Guide 9:

  • 1 = Equal concentrated end torques. Both ends free.
  • 2 = Equal concentrated end torques. Both ends fixed.
  • 3 = Concentrated Torque. Both ends pinned.
  • 4 = Uniformly distributed torque. Both ends pinned.
  • 6 = Concentrated Torque. Both ends fixed.
  • 7 = Uniformly distributed torque. Both ends fixed.
  • 9 = Concentrated Torque. One end fixed, another end free.
  • 10 = Partial uniformly distributed torque. One end fixed, another end free.
  • 12 = Uniformly distributed torque. One end fixed, another end pinned.

The number corresponds to the case number of the case chart in Appendix B of DG9. Set TORSION 1 to enable Torsion check as per DG9.

TORSION

(AISC 360-10 and 360-16 only) 

0

Specifies design for torsion per AISC Design Guide 9. See D1.A.5.6 Design for Torsion

  • 0 = Do not perform torsion checks
  • 1 = Perform torsion checks
Note: When torsion checks are performed, TRACK 3 output may be used to provide detailed torsion design output for Design Guide 9 checks.
TRACK 0

Specifies the amount of detail included in design output

  • 0 = Suppress all member capacities
  • 1 = Print all member capacities
  • 2 = Print full member design details
UNB Member Length Unsupported length of the bottom flange for calculating flexural strength. Will be used only if compression is in the bottom flange. See Note 3 below.
UNL Member Length Unsupported length of left extreme flange for LTB that will be used as lateral-torsional buckling length for the section with the vertical axis as major principal axis and where the left extreme fiber is in compression. If member is assigned with any value of UNL and FLX=2 concurrently, LTB length of the member will be treated as zero.
UNR Member Length Unsupported length of right extreme flange for LTB that will be used as Lateral-torsional buckling length for the section with the vertical axis as major principal axis and where the right extreme fiber is in compression. If member is assigned with any value of UNR and FLX=2 concurrently, LTB length of the member will be treated as zero.
UNT Member Length Unsupported length of the top flange for calculating flexural strength. Will be used only if compression is in the top flange. See Note 3 below.
WTYPE

(AISC 360-05 and 360-10 only)

0

Weld type for HSS per Sect. B3.12 (AISC 360-05) or Sect. B4.12 (AISC 360-10):

  • 0 = Electric resistance welding
  • 1 = Submerged arc welding

For HSS Rectangle and Round profiles from AISC databases, the weld type will always be determined based on profile table (grade A1085 or not). WTYP will have no effect on these. For any other hollow profiles (pipe, tube, box, etc.) from AISC databases, all hollow profiles from any other country databases, and User Provided tables, the weld type must be specified using the WTYP parameter.

Notes

  1. For the AISC 360 unified code, an angle is automatically checked for geometric axis bending (in addition to principal axis bending) provided one of the following conditions is met:
    1. The FLX parameter is set to 2 for that member. The section could be an equal or an unequal legged angle.
    2. The angle is equal-legged, has bending moment only about one of its geometric axes, and is not subjected to axial compression.

    The AXIS parameter is only used by the deprecated AISC 360-05 code checking method (CODE AISC UNIFIED OLD). If this code is used, then AXIS 1 specifies design based on principle axes, where AXIS 2 specifies design based on geometric axes.

  2. Non-default values of CB must be re-entered before every subsequent CHECK CODE or SELECT command.
  3. Top and Bottom represent the positive and negative side of the local Y axis (local Z axis if SET Z UP is used).
  4. For a description of the deflection check parameters DFF, DJ1, DJ2 see the Notes section of D1.B.1.2 Design Parameters of this manual.
  5. NSF is the Net Section Factor as used in most of the steel design codes in STAAD.Pro. It is defined as the Ratio of "Net cross section area" / "Gross section area" for tension member design. The default value is 1.0. For the AISC 360 code, it is described in section D.3.2.
  6. SLF is the Shear Lag Factor, as used in Section D.3.3 of the AISC 360-05 code. This factor is used to determine the effective net area by multiplying this factor with net area of the cross section. Please refer to Table D3.1 of the 360 code for a list of acceptable SLF values. In STAAD.Pro, the default value for SLF is 1.0. The effective net area is used to determine the tensile strength for tensile rupture in the net section, as per equation D.2.2.
  7. To summarize, the “Gross Area” (Ag) is multiplied by NSF to get the “Net Area” (An) of the section. The “Net Area” (An) is again multiplied by SLF to get the “Effective Net Area” (Ae) of the section.
  8. For the design of a single angle for flexure, the parameter LX should be used to specify the value of the term "L" in equations F10-4a, F10-4b, F10-5 and F10-6 of AISC 360-05 and the term "Lb" in equations F10-4, F10-5, F10-6a, and F10-6b of AISC 360-10.
  9. When BEAM is 1.0 (default), the design is performed at 13 evenly spaced points along the length of the beam, including start and end points (i.e., 1/12th points or at ends of 12 equal length segments).

    The default sections for design when BEAM 1.0 is used

    When BEAM is 0.0, the start and ends along with up to three locations specified in TR.41 Section Specification are designed.