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D3.B.6 Design Parameters

Available design parameters to be used in conjunction with BS5950 are listed in table 2B.1 along with their default values.

Note: Once a parameter is specified, its value stays at that specified number till it is specified again. This is the way STAAD works for all codes.
Table 1. British Steel Design BS5950:2000 Parameters
Parameter Name Default Value Description

Must be specified as BS5950

準拠する設計コード。「TR.48.1 パラメータの設定」を参照してください。

AD Depth at end/2 Distance between the reference axis and the axis of restraint. See G.2.3
BEAM 3.0

Beam divisions

  • 0. Design only for end moments or those locations specified by the SECTION command.
  • 1. Calculate forces and moments at 12th points along the member. Establish the location where Mz is the maximum. Use the forces and moments at that location. Clause checks at one location.
  • 2. Same as BEAM = 1.0 but additional checks are carried out for each end.
  • 3. Calculate moments at 12th points along the member.  Clause checks at each location including the ends of the member.

Deflection check method. See Note 1 below.

  • 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 note below)
CB 1

Specifies the method used to calculate Mb.

  • 1. Value of Mb from Clause 4.3.6 is used (default).
  • 2. Value of Mbs from Clause 4.7.7 is used.
DFF None(Mandatory for deflection check, TRACK 4.0)

"Deflection Length" / Maxm. allowable local deflection

See Note 1d below.

DJ1 Start Jointof member

Joint No. denoting starting point for calculation of "Deflection Length."

See Note 1 below.

DJ2 End Joint of member

Joint No. denoting end point for calculation of "Deflection Length."

See Note 1 below.

DMAX * 100.0cm Maximum allowable depth
DMIN * 0.0 cm Minimum allowable depth

Clauses and

  • 0.0 =  Fail ratio uses MIN of, and Annex I1 checks.
  • 1.0  =  Fail ratio uses MAX of, and Annex I1 checks.
KY 1.0 K factor value in local y - axis. Usually, this is the minor axis.
KZ 1.0 K factor value in local z - axis. Usually, this is the major axis.
LEG 0.0 Valid range from 0 – 7 and 10. The values correspond to table 25 of BS5950 for fastener conditions. See note 2 below.

Maximum of Lyy

and Lzz(Lyy is a term

used by BS5950)

Used in conjunction with LEG for Lvv as per BS5950 table 25 for double angles. See note 6 below.
LY * Member Length Length in local y - axis (current units) to calculate (KY)(LY)/Ryy slenderness ratio.
LZ * Member Length Length in local z - axis (current units) to calculate (KZ)(LZ)/Rzz slenderness ratio.
MLT 1.0 Equivalent moment factor for lateral torsional buckling as defined in clause
MX 1.0 Equivalent moment factor for major axis flexural buckling as defined in clause
MY 1.0 Equivalent moment factor for minor axis flexural buckling as defined in clause
MYX 1.0 Equivalent moment factor for minor axis lateral flexural buckling as defined in clause
NSF 1.0 Net section factor for tension members.
PNL * 0.0

Transverse stiffener spacing ("a" in Annex H1)

0.0  =  Infinity

Any other value used in the calculations.

PY * Set according to steel grade (SGR) Design strength of steel
MAIN 0.0

Slenderness limit for members with compression forces, effective length/ radius of gyration, for a given axis:

  • 0.0 =  Slenderness not performed.
  • 1.0 =  Main structural member (180)
  • 2.0 =  Secondary member. (250)
  • 3.0 =  Bracing etc (350)
RATIO 1.0 Permissible ratio of the actual capacities.
SAME** 0.0

Controls the sections to try during a SELECT process.

  • 0.0  =  Try every section of the same type as original
  • 1.0  =  Try only those sections with a similar name as original, e.g., if the original is an HEA 100, then only HEA sections will be selected, even if there are HEM’s in the same table.
SBLT 0.0

Identify Section type for section classification

  • 0.0 =  Rolled Section
  • 1.0 =  Built up Section
  • 2.0 =  Cold formed section
SWAY none Specifies a load case number to provide the sway loading forces in clause (See additional notes)
SGR 0.0

Steel Grade per BS4360

  • 0.0 =  Grade S 275
  • 1.0 =  Grade S 355
  • 2.0 =  Grade S 460
  • 3.0 =   As per GB 1591 – 16 Mn
TB 0.0

LImit of moment capacity in Cl

0 = Mc limit 1.5pyZ

1= Mc limit 1.2 pyZ


Output details

  • 0.0 =  Suppress all member capacity info.
  • 1.0 =  Print all member capacities.
  • 2.0 =  Print detailed design sheet.
  • 4.0 =  Deflection Check (separate check to main select / check code)
UNF 1.0 Factor applied to unsupported length for Lateral Torsional Buckling effective length per section of BS5950.
UNL * Member Length Unsupported Length for calculating Lateral Torsional Buckling resistance moment section of BS5950.

1.0 closed

2.0 open

Weld Type

  • 1.0  =  Closed sections.  Welding on one side only (except for webs of wide flange and tee sections)
  • 2.0  =  Open sections.  Welding on both sides (except pipes and tubes)

* current units must be considered.

**For angles, if the original section is an equal angle, then the selected section will be an equal angle and vice-versa for unequal angles.

Note: There was an NT parameter in STAAD.Pro 2005 build 1003 which is now automatically calculated during the design as it is load case dependent.

D3.B.6.1 Notes

  1. CAN, DJ1, and DJ2 – Deflection

    1. When performing the deflection check, you can choose between two methods. The first method, defined by a value 0 for the CAN parameter, is based on the local displacement. 局所変位の詳細については、「TR.44 メンバーに関する断面変位の出力」を参照してください。

      If the CAN parameter is set to 1, the check will be based on cantilever style deflection. Let (DX1, DY1, DZ1) represent the nodal displacements (in global axes) at the node defined by DJ1 (or in the absence of DJ1, the start node of the member). Similarly, (DX2, DY2, DZ2) represent the deflection values at DJ2 or the end node of the member.

      Compute  Delta = SQRT((DX2 - DX1)2 + (DY2 - DY1)2 + (DZ2 - DZ1)2)

      Compute Length = distance between DJ1 & DJ2 or, between start node and end node, as the case may be.

      Then, if CAN is specified a value 1, dff = L/Delta

      Ratio due to deflection = DFF/dff

    2. If CAN = 0, deflection length is defined as the length that is used for calculation of local deflections within a member.  It may be noted that for most cases the “Deflection Length” will be equal to the length of the member. However, in some situations, the “Deflection Length” may be different. A straight line joining DJ1 and DJ2 is used as the reference line from which local deflections are measured.

      D = メンバー1、2、3の最大局所変位。
      DFF 300. ALL
      DJ1 1 ALL
      DJ2 4 ALL
    3. If DJ1 and DJ2 are not used, "Deflection Length" will default to the member length and local deflections will be measured from original member line.

    4. It is important to note that unless a DFF value is specified, STAAD will not perform a deflection check.  This is in accordance with the fact that there is no default value for DFF.

    5. The above parameters may be used in conjunction with other available parameters for steel design.

  2. LEG – follows the requirements of BS5950 table 28. This table concerns the fastener restraint conditions for angles, double angles, tee sections and channels for slenderness. The following values are available:

    Table 2. LEG Parameter values
    Clause Bold Configuration Leg LEG Parameter

    Single Angle

    (a) - 2 bolts short leg 1.0
    long leg 3.0
    (b) - 1 bolts short leg 0.0
    long leg 2.0 Double Angles (a) - 2 bolts short leg 3.0
    long leg 7.0
    (b) - 1 bolts short leg 2.0
    long leg 6.0
    (c) - 2 bolts long leg 1.0
    short leg 5.0
    (d) - 1 bolts long leg 0.0
    short leg 4.0 Channels (a) - 2 or more rows of bolts 1.0
    (b) - 1 row of bolts 0.0 Tee Sections (a) - 2 or more rows of bolts 1.0
    (b) - 1 row of bolts 0.0

    The slenderness of single and double angle, channel and tee sections are specified in BS 5950 table 25 depending on the connection provided at the end of the member.  To define the appropriate connection, a LEG parameter should be assigned to the member.

    The following list indicates the value of the LEG parameter required to match the BS5950 connection definition:

    Clause Single Angle:
    1. 2 Bolts: Short leg = 1.0, Long Leg = 3.0
    2. 1 Bolt: Short Leg = 0.0, Long Leg = 2.0
    For single angles, the slenderness is calculated for the geometric axes, a-a and b-b as well as the weak v-v axis.  The effective lengths of the geometric axes are defined as:

    La = KY × LY

    Lb = KZ × LZ

    The slenderness calculated for the v-v axis is then used to calculate the compression strength pc for the weaker principal axis (z-z for ST angles or y-y for RA specified angles).  The maximum slenderness of the a-a and b-b axes is used to calculate the compression strength pc for the stronger principal axis.

    Alternatively for single angles where the connection is not known or Table 25 is not appropriate, by setting the LEG parameter to 10, slenderness is calculated for the two principal axes y-y and z-z only.  The LVV parameter is not used.

    For double angles, the LVV parameter is available to comply with note 5 in table 25. In addition, if using double angles from user tables, (refer to TR.19.4 ダブルアングル) an eleventh value, rvv, should be supplied at the end of the ten existing values corresponding to the radius of gyration of the single angle making up the pair.

  3. PY – Steel Design Strength

    The design parameter PY should only be used when a uniform design strength for an entire structure or a portion thereof is required. Otherwise the value of PY will be set according to the stipulations of BS5950 table 9 in which the design strength is seen as a function of cross sectional thickness for a particular steel grade (SGR parameter) and particular element considered. Generally speaking this option is not required and the program should be allowed to ascertain the appropriate value.

  4. UNL, LY, and LZ – Relevant Effective Length

    The values supplied for UNL, LY and LZ should be real numbers greater than zero in current units of length. They are supplied along with or instead of UNF, KY and KZ (which are factors, not lengths) to define lateral torsional buckling and compression effective lengths respectively. Please note that both UNL or UNF and LY or KY values are required even though they are often the same values. The former relates to compression flange restraint for lateral torsional buckling while the latter is the unrestrained buckling length for compression checks.

  5. TRACK – Control of Output Formats

    When the TRACK parameter is set to 0.0, 1.0, or 2.0, member capacities will be printed in design related output (code check or member selection) in kilonewtons per square meter.

    TRACK 4.0 causes the design to carry out a deflection check, usually with a different load list to the main code check.  The members that are to be checked must have the parameters DFF, DJ1, and DJ2 set.


  6. MX, MY, MYX, and MLT – Equivalent Moment Factors

    The values for the equivalent moment factors can either be specified directly by the user as a positive value between 0.4 and 1.0 for MX, MY and MYX and 0.44 and 1.0 for MLT.

    The program can be used to calculate the values for the equivalent moment factors by defining the design member with a GROUP command (refer to TR.16.1 グループ設定によるエンティティのリスト). The nodes along the beam can then be defined as the location of restraint points with J settings.

    Additionally for the MLT parameter, the joint can be defined as having the upper flange restrained (positive local Y) with the a U setting or the lower flange restrained (negative local Y) with a L setting.

    For example, consider a series of 5 beam elements as a single continuous member as shown below:

    To enable the steel design, the beam needs to be defined as a group, called MainBeam:

    _MainBeam  11 2 38 12 3
    Note: This can be done in the User Interface by selecting Tools > Create New Group….

    Therefore, this 5 beam member has 6 joints such that:

    • Joint 1 = Node 3
    • Joint 2 = Node 1
    • Joint 3 = Node 33
    • Joint 4 = Node 14
    • Joint 5 = Node 7
    • Joint 6 = Node 2
    1. Consider MX, MY and MYX

      Say that this member has been restrained in its’ major axis (local Y) only at the ends.  In the minor axis (local Z) it has been restrained at the ends and also at node number 33 (joint 3).  For local flexural buckling, it has only been restrained at its ends.  Hence:

      For the major axis, local Y axis:

      MX _MainBeam J1 J6

      For the minor axis, local Z axis:

      MY _ MainBeam J1 J3 J6

      For the lateral flexural buckling, local X axis:

      MYX _ MainBeam J1 J6

    2. Consider MLT

      Say that this member has been restrained at its’ ends against lateral torsional buckling and the top flange has been restrained at node number 33 (joint 3) and only the lower flange at node number 7, (joint 5).  Hence:

      MLT _MainBeam J1 T3 L5 J6

      To split the beam into two buckling lengths for Ly at joint 14:

      MY _groupname J1 J4 J6

  7. SWAY – Sway Loadcase

    This parameter is used to specify a load case that is to be treated as a sway load case in the context of clause This load case would be set up to represent the kam pMs mentioned in this clause and the steel design module would add the forces from this load case to the forces of the other load case it is designed for.

    Note that the load case specified with this parameter will not be designed as a separate load case.  The following is the correct syntax for the parameter:

    Parameter Name Default Value Description
    SWAY (load case number)


    MEMBER (member list)

    _(group name)


    SWAY  5 MEM 1 to 10
    SWAY  6 _MainBeams