Plastic Analysis in Staad

8/10/2019 Plastic Analysis in Staad

1/6

International Codes

British Codes - Steel Design Per BS5950:2000

2B.6 Design Parameters

Available design parameters to be used in conjunction with BS5950 are listed in table 2B.1 along with their default values. Thefollowing items should be noted with respect to their use.

1. (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 functionof cross sectional thickness for a particular steel grade (SGR parameter) and particular element considered. Generally speaking thisoption is not required and the program should be allowed to ascertain the appropriate value.

2. (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 alongwith or instead of UNF, KY and KZ (which are factors, not lengths) to define lateral torsional buckling and compression effectivelengths 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 forcompression checks.

3. (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 ormember selection) in kilonewtons per square metre.

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

An example of each TRACK setting follows:-

TRACK 0.0 OUTPUT STAAD CODE CHECKING - (BSI )

--------------------------- ******************************

ALL UNITS ARE - KNS METR (UNLESS OTHERWISE NOTED)

MEMBER TABLE RESULT/ CRITICAL COND/ RATIO/LOADING/

FX MY MZ LOCATION=================================================================

1 ST UB686X254X170 PASS BS-4.8.3.2 0.0363

86.72 C 0.00 -22.024.50

---------------------------------

TRACK 1.0 OUTPUT STAAD CODE CHECKING - (BSI )

--------------------------- ******************************

ALL UNITS ARE - KNS METR (UNLESS OTHERWISE NOTED)


FX MY MZ LOCATION

=================================================================

1 ST UB686X254X170 PASS BS-4.8.3.2 0.0363

86.72 C 0.00 -22.024.50

TRACK 2.0 OUTPUT STAAD.Pro CODE CHECKING - (BSI )

--------------------------- ***************************

ALL UNITS ARE - KN METE (UNLESS OTHERWISE NOTED)


CALCULATED CAPACITIES FOR MEMB 1 UNIT - KN,M SECTION CLASS 4

MCZ= 1141.9 MCY= 120.4 PC= 3451.5 PT= 5739.9 MB= 1084.1 PV=

1597.5

BUCKLING CO-EFFICIENTS M AND N : M = 1.000 N = 1.000

PZ= 5739.90 FX/PZ = 0.02 MRZ= 1141.9 MRY=

120.4

Page 1 of 62B.6 Design Parameters

05-07-2013mk:@MSITStore:C:\SProV8i\STAAD\Help\International_Codes_2007.chm::/British_Codes/BS_595...


2/6

_________________________

4. (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 forMX, 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 GROUPcommand (see the Technical Reference Manual section 5.16 Listing of Members/Elements/Joints by Specification of GROUPS). Thenodes 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 Usetting 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:

FX MY MZ LOCATION

===================================================================

1 ST UB533X210X92 PASS BS-4.3.6 0.902 100

0.00 0.00 585.410.00

===================================================================

MATERIAL DATA

Grade Of Steel = S 275

Modulus Of Elasticity = 205 KN/Mm2

Design Strength (Py) = 275 N/Mm2

SECTION PROPERTIES (Units - Cm)

Member Length = 325.00

Gross Area = 117.00 Net Area = 117.00

Major Axis Minor Axis

Moment Of Inertia : 55229.996 2389.000

Plastic Modulus : 2360.000 356.000

Elastic Modulus : 2072.031 228.285

Shear Area : 58.771 53.843

DESIGN DATA (Units - KN,M) BS5950-1/2000

Section Class : PLASTIC

Major Axis Minor Axis

Moment Capacity : 649.0 94.2

Reduced Moment Capacity : 649.0 97.9

Shear Capacity : 969.7 888.4

BUCKLING CALCULATIONS (Units - KN,M)

(Axis Nomenclature As Per Design Code)

LTB Moment Capacity (KNm) And LTB Length (M): 649.00, 0.001

LTB Coefficients & Associated Moments (KNm):

MLT = 1.00 : Mx = 1.00 : My = 1.00 : Myx = 1.00

Mlt = 585.41 : Mx = 585.41 : My = 0.00 : My = 0.00CRITICAL LOADS FOR EACH CLAUSE CHECK (Units- KN,M):

CLAUSE RATIO LOAD FX VY VZ MZ MY

BS-4.2.3-(Y) 0.329 100 - 292.3 - - -

BS-4.3.6 0.902 100 - 292.3 - 585.4 -

BS-4.8.3.2 0.814 100 0.0 68.0 0.0 585.4 0.0

BS-4.8.3.3.1 1.027 100 0.0 - - 585.4 0.0

BS-4.8.3.3.2 0.902 100 0.0 - - 585.4 0.0

Annex I.1 0.902 100 0.0 - - 585.4 0.0

Torsion And Deflections Have Not Been Considered In The Design.




3/6


4/6

Lb = KZ * LZ

The slenderness calculated for the v-v axis is then used to calculate the compression strength pcfor 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 compressionstrength p

cfor 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 usertables, (Technical Reference Manual section 5.19) 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.

6. (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 4.8.3.3.4. This loadcase would be set up to represent the k

ampM

s 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 syntaxfor the parameter:-

Example

Parameter Name Default Value Description

SWAY (load case number) ALL

MEMBER (member list)

_(group name)

SWAY 5 MEM 1 To 10

SWAY 6 _MainBeams

Table 2B.1 - British Steel Design BS5950:2000 Parameters

Parameter

NameDefault Value Description

CODE BS5950 Design Code to follow. See section 5.47.1 of the Technical Reference

Manual.

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

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

PY * Set according to

steel grade (SGR)

Design strength of steel

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.

LY * Member Length Length in local y - axis (current units) to calculate (KY)(LY)/Ryyslenderness ratio.

LZ * Member Length Length in local z - axis (current units) to calculate (KZ)(LZ)/Rzz

slenderness ratio.

UNF 1.0 Factor applied to unsupported length for Lateral Torsional Buckling

effective length per section 4.3.6.7 of BS5950.

UNL * Member Length Unsupported Length for calculating Lateral Torsional Buckling resistance

moment section 4.3.6.7 of BS5950.

NSF 1.0 Net section factor for tension members.

SBLT 0.0 Identify Section type for section classification

0.0 = Rolled Section

1.0 = Built up Section

2.0 = Cold formed section

MAIN 0.0 Slenderness limit for members with compression forces, effective length/

radius of gyration, for a given axis:-




5/6

0.0 = Slenderness not performed.

1.0 = Main structural member (180)

2.0 = Secondary member. (250)

3.0 = Bracing etc (350)

RACK 0.0 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)

BEAM 3.0 0.0 = Design only for end moments or those locations specified by the

SECTION command.

1.0 = 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.

2.0 = Same as BEAM = 1.0 but additional checks are carried out for

each end.

3.0 = Calculate moments at 12th points along the member. Clause

checks at each location including the ends of the member.

LEG 0.0 Valid range from 0 7 and 10. See section 2B.6.5 for details. The values

correspond to table 25 of BS5950 for fastener conditions.

LVV * 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, note 5.

CB 1.0 1.0 = BS5950 per clause B.2.5 (continuous) to calculate Mb.

2.0 = To calculate Mbs (simple) as per Clause 4.7.7 as opposed to Mb.

DFF None

(Mandatory for

deflection check,

TRACK 4.0)

"Deflection Length" / Maxm. allowable local deflection

DJ1 Start Joint

of member

Joint No. denoting starting point for calculation of "Deflection

Length" (See Note 1)

DJ2 End Joint of

member

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

Note 1)

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 note below)ESTIFF 0.0 Clauses 4.8.3.3.1 and 4.8.3.3.2

0.0 = Fail ratio uses MIN of 4.8.3.3.1, 4.8.3.3.2. and Annex I1 checks.

1.0 = Fail ratio uses MAX of 4.8.3.3.1, 4.8.3.3.2. and Annex I1 checks.

WELD 1.0 closed

2.0 open

Weld Type, see AISC steel design

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)

B 0.0 0.0 = Elastic stress analysis

1.0 = Plastic stress analysis

PNL * 0.0 ransverse stiffener spacing (a in Annex H1)

0.0 = Infinity

Any other value used in the calculations.




6/6

Once a parameter is specified, its value stays at that specified number till it is specified again. This is the way STAAD works forall codes.

* 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 unequalangles.

There was an NT parameter in STAAD.Pro 2005 build 1003 which is now automatically calculated during the design as it is loadcase dependant.

NOTES:

1. When performing the deflection check, the user can choose between two methods. The first method, defined by a value 0 for

the CAN parameter, is based on the local displacement. Local displacement is described in section 5.43 of this manual.If the CAN parameter is set to 1, the check will be based on cantilever style deflection. Let (DX1, DY1, DZ1) represent the nodaldisplacements (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 benoted 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. For example, refer to the figure below where a beam has been modeled using four jointsand three members. The Deflection Length for all three members will be equal to the total length of the beam in this case.The parameters DJ1 and DJ2 should be used to model this situation. Also the straight line joining DJ1 and DJ2 is used as thereference line from which local deflections are measured. Thus, for all three members here, DJ1 should be "1" and DJ2 shouldbe "4".

3. If DJ1 and DJ2 are not used, "Deflection Length" will default to the member length and local deflections will be measured fromoriginal 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 accordancewith the fact that there is no default value for DFF (see Table 2.1).

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

Related Topics

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 HEMs in the same table.

MX 1.0 Equivalent moment factor for major axis flexural buckling as defined in

clause 4.8.3.3.4

MY 1.0 Equivalent moment factor for minor axis flexural buckling as defined in

clause 4.8.3.3.4MYX 1.0 Equivalent moment factor for minor axis lateral flexural buckling as

defined in clause 4.8.3.3.4

MLT 1.0 Equivalent moment factor for lateral torsional buckling as defined in

clause 4.8.3.3.4

SWAY none Specifies a load case number to provide the sway loading forces in clause

4.8.3.3.4 (See additional notes)

DMAX * 100.0cm Maximum allowable depth

DMIN * 0.0 cm Minimum allowable depth

RATIO 1.0 Permissible ratio of the actual capacities.


Documents

Plastic Analysis in Staad