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Code checks on tube

Five code checks are implemented for tubes:

  • API-RP-2A-WSD-2007
  • API-RP-2A-LRFD-1993
  • ISO-19902-2007
  • NORSOK-N-004-2004
  • NORSOK-N-004-2013
  • DNVGL-ST-0126-2021

The two last NORSOK-N-004-2013 and DNVGL-ST-0126-2021 differ only by the expression of the material factor \(\gamma_M\):

  • formula (6.22) in the NORSOK-N-004-2013 regulation,
  • § 4.5.1.6 in the DNVGL-ST-0126-2021 regulation.

Note

The names used for code checks by DeepLines are those which are listed in the Study tab. To see which regulation (or part of regulation) these names correspond to, you must refer to the section Theory/Structural Code Check.

Parameters

The Parameters tab for the code checks on tubes has the following form:

Parameters can have a specific value for each tube which is a segment. The two tables below give the meaning of each of these parameters.

There are two types of parameters:

  • parameters which identify a tube and set its properties,
  • parameters used by the code checks formulas.

The list of the first type parameters is given in the next table.

NameMeaningCommentary
LineLine containing the segment to which the code check calculation is performed.The line has been selected in the Selection tab by the user.
SegmentSegment of the line where the code check calculation is performed which has tube properties.The segment has been selected in the Selection tab by the user.
Section Local section whose properties are defined as a Structure property/Circular hollow section. Local section specified to the segment in the model.
Can be changed by the user to use reinforced section.
Steel material Material whose properties are defined as a Structure property/Steel material. Material specified to the segment in the model.
Can be changed by the user.
LengthActual length of the segment specified in the model.Cannot be changed by the user.

This second table lists the parameters used by the code checks formulas. Not all the code checks on tubes need all the parameters: for each parameter, the last column indicates the code checks concerned by this parameter and, in parentheses, the formulas which use the parameter.

Name Meaning Default Formulas
LXRBuckling length around the local X axis0.WSD (3.2.2-1, 3.2.2-2, 3.3.1-4)
LRFD (D.2.2-2c, D.2.5-5)
ISO (13.2-7, 13.3-5, 13.3-6)
NORSOK (6.5, 6.29)
LYRBuckling length around the local Y axis0.Same as LXR.
KXBuckling coefficient for bending around the local X axis.1.WSD (Same as LXR)
LRFD (D.2.2-2c)
KYBuckling coefficient for bending around the local Y axis.1.Same as KX.
WEBSTClear distance between ring stiffeners for allowable hoop stress computing. If no value is input, the program will take: WEBST = Min(LXR, LYR), with L = length between nodes, member end joint sizes being accounted for. If a negative value < -0.9 is specified, then the distance between ring stiffeners is taken as D=L/(-WEBST).ComputedWSD (3.2.5-5)
ISO (13.2.6.2)
NORSOK (6.3.6.1)
CMXDetermines the reduction coefficient Cm to be used for the bending around the local X axis.
  • if 0. ≤ CMX ≤ 0.85, Cm = CMX
  • if CMX = 1, formula 3.3.1e(a) is used : Cm = 0.85
  • if CMX = 2, formula 3.3.1e(b) is used. (See Remark 1 below)
  • if CMX = 3, formula 3.3.1e(c) is used.
  • if CMX = 4, formula c.ii in AISC, chapter H1: Cm = 1.
0.85WSD (3.3.1-4)
LRFD (D.3.2-1)
ISO (13.4-14)
NORSOK (6.27)
CMYSame as CMX around the local Y axis.0.85Same as CMX.

Remark 1: this option should be used only if the physical member is not cut down into several members. Otherwise, wrong start and end moments M1 and M2 may be used.

Note that none of these parameters are being used for the code checks on joints.

Options

The code checks options have the same value throughout the code checks study.

API-RP-2A-WSD-2007 on tubes

Option Default Meaning
Modulation of the allowable stresses Operating
Operating Allowable stresses are not increased
Extreme Allowable stresses are increased by 1/3
Seismic Allowable stresses are multiplied by 1.7
Blast This option allows the user to define a multiplying coefficient α to be applied to the allowable stresses.
The allowable stresses are limited to the following values: \begin{array}{llll} {\small\textsf{Axial }}&: {\small\alpha_\textsf{axial }} &{\small\textsf{F_y}\qquad\textsf{Default:}\quad\alpha_\textsf{axial }} &{\small\textsf{= 1.265}}\\ {\small\textsf{Bending X}}&: {\small\alpha_\textsf{bendingX}} &{\small\textsf{F_y}\qquad\textsf{Default:}\quad\alpha_\textsf{bendingX}} &{\small\textsf{= 1.265}}\\ {\small\textsf{Bending Y}}&: {\small\alpha_\textsf{bendingY}} &{\small\textsf{F_y}\qquad\textsf{Default:}\quad\alpha_\textsf{bendingY}} &{\small\textsf{= 1.265}}\\ {\small\textsf{Shear }}&: {\small\alpha_\textsf{shear }} &{\small\textsf{F_y}\qquad\textsf{Default:}\quad\alpha_\textsf{shear }} &{\small\textsf{= 1.265 / $\sqrt{3}$}}\\ \end{array} The default value for \({\small\alpha}\) is \({\small\alpha \textsf{= 2.108 = 1.265 / 0.6 = 1.10} \times \textsf{1.15 / 0.6}}\)
Where 1.10 is the strain hardening and 1.15 is the percentage of plastic section.
General This option allows the user to define the multiplying coefficient to be applied to the allowable stresses. Any positive coefficient \({\small\alpha_\textsf{general}}\) may be input.
The preceding options are in fact particular cases of this one: \begin{array}{ll} {\small\textsf{Operating}} & {\small\textsf{is equivalent to $\alpha_\textsf{general} = 1$}}\\ {\small\textsf{Extreme }} & {\small\textsf{is equivalent to $\alpha_\textsf{general} = 4/3$}}\\ {\small\textsf{Seismic }} & {\small\textsf{is equivalent to $\alpha_\textsf{general} = 1.7$}}\\ \end{array}
Hydrostatic pressure False If this option is checked, the hydrostatic pressure is taken into account.
Three options are available for the Hydrostatic pressure computation: see explanation for the API-RP-2A-LRFD-1993 below.
For the option From geometric depth, the hydrostatic head used is Hz = -z(section) and the design pressure is taken as PSd = ρ g Hz.
Note that the static and dynamic loads and the effect of the wave profile are neglected.
The user can impose the safety factors defined in § 3.3.4.: \begin{array}{lll} {\small\textsf{Safety factor for axial compression }} & {\small\textsf{is SFac}} & {\small\textsf{Default: SFac = 2 /} \alpha_\textsf{general}} \\ {\small\textsf{Safety factor for axial tension }} & {\small\textsf{is SFat}} & {\small\textsf{Default: SFat = 1.67 /} \alpha_\textsf{general}} \\ {\small\textsf{Safety factor for bending }} & {\small\textsf{is F_y / (SFb.Fb)}} & {\small\textsf{Default: SFb =} \alpha_\textsf{general}} \\ {\small\textsf{Safety factor for hoop compression }} & {\small\textsf{is SFh }} & {\small\textsf{Default: SFh = 2 /} \alpha_\textsf{general}} \\ \end{array}

API-RP-2A-LRFD-1993 on tubes

Option Default Meaning
Blast case False With the Blast option the phi resistance factors are set equal to 1
Hydrostatic pressure False If this option is checked, the hydrostatic pressure is taken into account.
Three options are available for the Hydrostatic pressure computation:
  • From geometric depth:
    The hydrostatic head used is Hz = -z(section) and the design pressure is taken as PSd = ρ g Hz.
    Note that the static and dynamic loads and the effect of the wave profile are neglected.
  • From static and dynamic vertical position in the database:
    The design pressure is PSd = ρ g (γG zstat + γE (zdyn - zstat))
    where:
    • the coefficients γG = CStat and γE = CDyn are, respectively, the permanent and environmental loads factors which can be chosen by the user on the same dialog box below;
    • zstat and zdyn are the post-processing variables vertical position wrt sea level computed from the results of the, respectively, static and dynamic solver analyses.
  • From static and dynamic pressure in the database:
    The design pressure is PSd = γG (Pext - Pint)stat + γE ((Pext - Pint)dyn (Pext - Pint)stat)
    where:
    • the coefficients γG = CStat and γE = CDyn are, respectively, the permanent and environmental loads factors which can be chosen by the user on the same dialog box below;
    • (Pext - Pint)stat and (Pext - Pint)dyn are computed from the results of the, respectively, static and dynamic solver analyses.
The user choice is recalled is the header of the listing .lst: 
****************************************************************************************************************************
*                                                                                                                          *
*                          Code checking of tubes according to NORSOK N-004 Rev. 3, February 2013.                         *
*                                                CodeCheck API version 1.8.0                                               *
*                                                                                                                          *
*                                                                                                                          *
*                                              Output results for all the tubes                                            *
*        Water depth : 0.000 m ( = 0.000 ft ) - Hydrostatic pressure computation: From vertical position in database       *
*                                                                                                                          *
****************************************************************************************************************************
The detailed listing .pun indicates the effective pressure used by the code check computation: 
Loading : s100    loading pattern : signed 1

Section forces and pressure:
/---- Fx ----/---- Fy ----/---- Fz ----/---- Mx ----/---- My ----/---- Mz ----/-- PSd (MPa) --/
 -7.05278e+03  4.82352e+02  6.12205e+02 -3.61369e+06 -4.52722e+06  1.76391e+06  5.18383852e-02
Only if the model contains a multi-structure floater, the following check box is present:
For multistructure floater lines, from Hull dynamic pressure.
If the box is checked, the hydrostatic pressure for lines belonging to the floater is computed as a Hull dynamic pressure.

ISO-19902-2007, NORSOK-N-004-2004, NORSOK-N-004-2013 and DNVGL-ST-0126-2021 on tubes

Option Default Meaning
Hydrostatic pressure False If this option is checked, the hydrostatic pressure is taken into account.
Sub-option Default Meaning
Capped-end action Excluded Specify if the capped-end compressive forces due to the external hydrodynamic pressure are included or not in the analysis forces. If not included, the corresponding stresses are computed and added to the analysis stresses. For details, see: NORSOK-N-004-2013 regulation, §6.3.9.
Three options are available for the Hydrostatic pressure computation: see their descriptions in the API-RP-2A-LRFD-1993 options above.