Background

The LIN3DUSERDEFINED (or LIN2DUSERDEFINED) class creates a line Section class that is represented its geometrical properties given by the user. Therefore, the cross-sectional properties such as area, shear area, inertias and so on must be provided. The figure shows a representation of the Lin2DAngle and Lin3DAngle respectively. The properties in grey squares are used in 2D.

The section properties to be given are:

Area properties: \(A \,, \; As_2\,, \; As_3\) (in 3D) or \(A \,, \; As_2\) (in 2D)
Inertia properties: \(J\,, \; I_{22}\,, \; I_{33}\,, \; I_{23}\) (in 3D) or \(I_{33}\) (in 2D)

REFERENCE:

MIDAS Civil User's Manual: analysis for civil structures, Area Moment of Inertia, Pages 77-78
MIDAS Civil User's Manual: analysis for civil structures, Effective Shear Areas, Pages 68-69

Pre-Analysis

The python Pre-Analysis in the 01-Pre_Process/Method/Attach.py file provides with an interface to populate the Entities dictionary. This file contains several functions to populate specific fields. For example, to create a Lin2DUserDefined or Lin3DUserDefined section using json format, use:

addSection(tag, name='Lin3DUserDefined', model='Plain', attributes):
- tag : The identifier of this section, i.e., tag > -1
- name : Seismo-VLAB section class name
- model : model of the section, i.e., model=plain,fiber
- attributes : Specific properties for the created section, for example
  - 'A' : is the cross section area.
  - 'As2' : is the shear area over the local 2-axis.
  - 'As3' : is the shear area over the local 3-axis.
  - 'J' : is the section polar moment of inertia about the local 1-axis.
  - 'I22' : is the section inertia about the local 2-axis.
  - 'I33' : is the section inertia about the local 3-axis.
  - 'I23' : is the section product of inertia.
  - 'theta' : is The section rotation angle about axis 1.
  - 'material' : is the material identifier the cross section is made out of.
Example

A LIN3DUSERDEFINED section can be defined using the python interface as follows:
SVL.addSection(tag=1, name='Lin3DUserDefined', model='Plain', attributes={'A': 0.40, 'As2': 0.333333, 'As3': 0.333333, 'J': 0.0386667, 'I22': 0.00533333, 'I33': 0.0333333, 'I23': 0.0, 'material': 1})

A LIN2DUSERDEFINED section can be defined using the python interface as follows:
SVL.addSection(tag=1, name='Lin2DUserDefined', model='Plain', attributes={'material': 1, 'A': 0.2, 'As2': 0.166667, 'I33': 0.0166667})

Application
Please refer to the D01-ST_Lin_2DBernoulli_Elastic_Frame2.py file located at 03-Validations/01-Debugging/ to see an example on how to define a Lin2DRectangular section.

On the contrary, the 01-Pre_Process/Method/Remove.py file provides with an interface to depopulate the Entities dictionary. For example, to remove an already define Section, use:

delSection(tag):
- tag : The identifier of the section to be removed, i.e., tag > -1

Run-Analysis

The C++ Run-Analysis in the 02-Run_Process/03-Sections/01-Plain/Lin3DUserDefined.cpp file provides the class implementation. A Lin3DUserDefined section is created using the built-in json parse-structure provided in the Driver.hpp. A Lin3DRectangular is defined inside the "Sections" json field indicating its "Tag" as follows,

{
    "Sections": {
        "Tag": {
            "name" : "LIN3DUSERDEFINED",
            "model" : "PLAIN",
            "attributes": {
                "A": double,
                "As2": double,
                "As3": double,
                "J": double,
                "I22": double,
                "I33": double,
                "I23": double,
                "theta": double,
                "material": int
            }
        }
    }
}

Variable	Description
`Tag`	Unique Section object identifier.
`A`	The the cross section area.
`As2`	Theshear area over the local 2-axis.
`As3`	The shear area over the local 3-axis.
`J`	The section polar moment of inertia about the local 1-axis
`I22`	The the section inertia about the local 2-axis.
`I33`	The the section inertia about the local 3-axis.
`I23`	The section product of inertia.
`theta`	The section rotation angle, see Local Axes.
`material`	Material object identifier.

Attention: The LIN3DUSERDEFINED / LIN2DUSERDEFINED Section object is made of one Material.; The LIN3DUSERDEFINED / LIN2DUSERDEFINED Section is assumed to be used in linearized and finite deformations.; The stress/strain coordinates at Section::GetStrainAt() or Section::GetStressAt() are evaluated without knowledge of the section geometry.; If not specified theta=0.0

Example

A LIN2DUSERDEFINED section of made of material 1 is defined:
{ "Sections": { "1": { "name" : "LIN2DUSERDEFINED", "model": "PLAIN", "attributes": { "A": 0.4, "As2": 0.333333 "I33": 0.0333333, "material": 1, "theta": 0.0 } } } }