Fiber Division of Section – MIDAS Support

Function

In order to carry out a nonlinear analysis using fiber elements, beam cross-sections are appropriately divided into fiber cells. Such fiber cells are assigned various nonlinear material properties representing stress-strain hysteresis models for concrete, steel, etc. For a reinforced concrete structure, cover concrete, core concrete, reinforcing steel, etc. can be assigned to the sections.

Call

From main menu, select [Properties] tab > [Inelastic Properties] group > [Inelastic Material] > [Fiber Division of Section]

Input

Define the properties of section division to which a fiber model is applied.

Define Fiber Division of Section dialog box

Name

Fiber model name

Section

(Conventional) Section name to which fiber elements are applied

Add

Add or define a new section to which fibers and fiber material properties will be assigned.

Modify/Show

Modify or check a section, which has been assigned fibers and fiber material properties.

Delete

Delete previously defined fiber model sections.

Fiber Division of Section dialog box

Name

Fiber model name

Section Name

Select a (conventional) section name to which fiber elements will be applied.

: Select a (conventional) section name to which fiber elements will be applied.

: Delete the (conventional) section shape already recalled.

: Recall the rebar information defined for the section in Design.

: Delete all the rebar information recalled.

: When (conventional) sections need to be defined in the midst of defining a Fiber section, additional (conventional) sections can be defined.

Fiber Material Property

A maximum of 6 nonlinear concrete and steel material properties, which were previously defined for fiber elements, can be assigned to fiber cells.

: After assigning materials to the section cells, each material can be displayed with a color. The colors can be changed by the user.

Create Fiber

Divide the section into cells, and assign nonlinear materials to the cells. Concrete cover and confined core can be separately defined. (Place and modify rebar on the Create Rebar tab.)

On the Create Fiber tab, divide a new section and assign nonlinear fiber material properties or edit the previously divided fiber section using Editing Fibers.

The general procedure for dividing a new section and assigning nonlinear fiber material properties is as follows:

1. The Drawing Object feature is used when you want to import or add lines with additional thickness to a basic section shape. For example, if you want to input the outer concrete thickness to a basic rectangular section, you can specify the additional thickness in the "Offset Distance From Boundary" option. If there is no need for additional thickness, you can skip this step.

2. The "Selecting Object" function allows you to select the lines that form the section to be divided. If the section to be divided is composed of a single line, you can select that line and activate it as a thick red line. If the section to be divided is enclosed by multiple lines, you need to select all those lines and activate them as thick red lines. Once the selection is complete, press the Enter button, and the lines will be displayed as thick blue lines, indicating the activation. This completes the step. If you want to cancel the selection, you can press the Clear button and start the selection again.

3. The "Setting Region" step is where you select the section area enclosed by the previously selected lines. You need to select the blue activated lines that surround the target area and activate them as red. Press the Enter button, and the selected section will be shaded, indicating the completion of the preparation for division. If you want to cancel the selection, you can press the Clear button and start selecting the region again.

4. In the "Dividing Section" step, you can appropriately divide the selected section and assign a nonlinear fiber material model to it. Depending on the type of section, you can choose between the "Rectangular" method and the "Radial" method. Specify the desired number of divisions in the "Number of Division" field. The left preview window will show a preview of the divided shape based on the specified number of divisions.

Once you have determined the division status, select the appropriate nonlinear fiber material model in the "Material ID" field. After confirming your selection, click the "Divide" button to perform the division. You can use the "Undo" and "Redo" buttons to undo or redo the respective operations.

For a section with multiple divided regions, you can perform additional steps similar to b. ~ d. to perform division across the entire section.

When there is a need to modify the previously divided fiber sections, you can use the "Editing Fibers" feature. Please refer to the relevant section below for a detailed explanation of this feature.

Create Fiber dialog box

Drawing Object

Import Cover Thickness : Import the Cover Thickness of the section defined in the Design function.

Offset Distance from Boundary : When you need to specify additional boundaries on a general section shape, you can select a reference Polygon and create a new Polygon at a specific distance away from it. This can be useful when defining the outer concrete boundaries, as the nonlinear behavior of the external and internal concrete may differ. Additionally, you can create additional boundaries without any limit in number to define the division regions when there is a need for other additional boundaries.

Entering a positive value will create the boundary lines inside the section, while entering a negative value will create the boundary lines outside the section.

First, select the reference boundary line in the left window and activate it by turning it red. Enter the offset distance and click the Add button to create additional boundary lines. You can use the Undo and Redo buttons to cancel or redo these actions.

: This function is an independent feature that automatically calculates the distance between two arbitrary points on the sectional shape diagram. When you enter a number, it divides the distance between the selected two points into the specified number of segments and automatically determines the distance values. To use this feature, select two points in the left window and activate them by turning them red. Then enter the number of divisions and click the button. The calculated distance values when dividing the distance between the two points into the desired number of segments will be automatically determined and displayed next to "Offset Distance from Boundary". You can use these values for subsequent inputs.

Select Object

This step is about selecting the boundary lines of the area to be divided using Fiber Cells. If there are additional boundary lines defined, they can be recognized as one boundary line.

To use this feature, first select the boundary lines in the left window and activate them by turning them red. If the area to be divided is surrounded by multiple boundary lines, select all of them and activate them in red. Once the selection is complete, press the Enter key to activate them in blue, and this step will be completed.

Clear : Cancel the selected region.

Setting Region

This step is about selecting the faces of the area to be divided using Fiber Cells.

To use this feature, reselect the previously selected and activated boundary lines from the "Selecting Object" step and turn them red. Select all the boundary lines of the area you want to divide, and then press the Enter button. The selected area to be divided will be shaded. If you need to make modifications, you can cancel by pressing the Clear button and start again.

When selecting the area, priority is given to completely closed regions based on the boundary lines.

Dividing Section

This step involves dividing the selected section and assigning a nonlinear fiber material model.

Dividing the fiber cells is directly related to the analysis time, so careful attention is required from the user. The number of divisions does not always directly correspond to the accuracy of the analysis. For general sections, it is known that a division of around 100-200 cells is sufficient to ensure reasonable accuracy. In midas Civil, you can divide up to 1000 cells in a single section.

As a general guideline, it is recommended to divide the outer parts of the section, where the maximum deformation occurs, into smaller cells, while the internal parts can be divided into larger cells. This approach helps improve analysis speed while maintaining accuracy.

Type Division : In the Setting Region, the selected section can be divided using either the Rectangular or Radial method.

Rectangular : This method is used to divide sections with a rectangular shape as the base.

Ny = Enter the number of cells to be divided in the y-direction of the section. (Enter 2 or more)

Nz = Enter the number of cells to be divided in the z-direction of the section. (Enter 2 or more)

Once you enter the numbers, the left picture window will show a preview of the section after division.

Radial : This method is used to divide sections with a circular or elliptical shape.

Center Point (y,z) = Enter the coordinates of the center point for circular division.

: If you want to use the midpoint between two selected points as the center point, select the two points, and pressing this button will automatically assign the midpoint coordinates as the center point for radial division.

Nt = Enter the number of divisions in the angular direction for circular division.

Nr = Enter the number of divisions in the angular direction for circular division.

Once you enter the numbers, the left picture window will show a preview of the section after division.

Material ID : Assign the material properties from the Inelastic Material Property list to the divided cells.

After completing the above steps, pressing the Divide button will divide the selected section according to the assigned nonlinear fiber materials.

You can use the Undo and Redo buttons to undo or redo the division operation.

Editing Fibers

This feature allows you to edit already divided fiber cells. Please note that this function can only be applied to sections that have already been divided.

To use this feature, select the cells you want to edit from the drawing window and activate them in red.

Merge : Select multiple cells and merge them into a single cell.

Delete : Delete the selected cells.

Undo, Redo : Undo or redo the cell editing actions.

Create Rebar

You can define arbitrary rebars in the section. There are three methods available: Point, Linear, and Circular. All the defined rebars will be organized in a table format, including the rebar name, number, and total area.

Create Rebar dialog box (Point Type)

Type : Point

In this mode, you can place individual rebars in the section.

Material ID : Select the type of material for the rebars from the defined steel materials in the Inelastic Material Property.

Center Point(y,z) : Enter the coordinates for the rebar's location. You can either enter the values directly or select them from the section drawing.

Area : Enter the area for each individual rebar. For standard rebars, you can select from a list of available diameters (DB). Alternatively, you can manually enter the area using the user-defined (User) input method.

Crate Rebar dialog box (Linear Type)

Type : Linear

Select a line on which rebars will be located. Rebars are located on a line by line basis.

Material ID : Select the type of material for the rebars from the defined steel materials in the Inelastic Material Property.

Starting Point(y,z) : Enter the coordinates for the starting position of the rebar line. You can either enter the values directly or select them from the section drawing.

End Point(y,z) : Enter the coordinates for the end position of the rebar line. You can either enter the values directly or select them from the section drawing.

Number of Rebar : Enter the total number of rebars in the line.

Create Rebar dialog (Circular Type)

Type : Circular

Define rebars in the section placed in a circular pattern.

Material ID : Select the type of material for the rebars from the defined steel materials in the Inelastic Material Property.

Starting Point(y,z) : Enter the starting position of the rebar for circular reinforcement. You can either enter the values directly or select them from the section drawing. For circular reinforcement, the starting point and the center of the arc should be aligned on the horizontal plane for accurate placement. For elliptical reinforcement or partial arc shapes, ensure that the starting point and the center of the arc are aligned, and adjust the angle appropriately for efficient reinforcement.

Center of Arc(y,z) : Enter the starting position of the rebar for circular reinforcement. You can either enter the values directly or select them from the section drawing. For circular reinforcement, the starting point and the center of the arc should be aligned on the horizontal plane for accurate placement. For elliptical reinforcement or partial arc shapes, ensure that the starting point and the center of the arc are aligned, and adjust the angle appropriately for efficient reinforcement.

Central Angle of Arc : Enter the central angle of the arc when performing partial arc reinforcement. For circular reinforcement, the default value is 360 degrees. By using a value less than 360 degrees, you can achieve partial arc reinforcement.

Number of Rebar : Enter the number of rebars for circular reinforcement.