Fiber Division of Section

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.

From the Main Menu select Properties > Inelastic Properties > Inelastic Material > Fiber Division of Section

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

Name: Fiber model name

Section: (Conventional) Section name to which fiber elements are applied

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

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

: Delete previously defined fiber model sections.

Name

Fiber model name

Section Name

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

: Recall the (conventional) section shape previously defined.

: 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:

a.   Drawing Object can be used to import a boundary with additional thickness or thickness can be added to the basic section shape. For  example, in order to add cover thickness to the basic rectangular section, enter the cover thickness in "Offset Distance from Boundary"  If it is not necessary to add cover thickness, this step can be ignored.

b.   Selecting Object can be used to select the lines comprising a section to be divided. When the section to be divided consists of a single line, selecting the single line and it will turn bold and red. When the section to be divided consists of two or more lines, select all the constitutive lines and they will turn bold and red. After the selection, click Enter. Then the activated lines will turn blue and the selection will be completed. To cancel the selection click Clear, and re-select.

c.   Setting Region can be used to select the region encompassed by the lines selected in the previous step. Select the blue lines. When the blue lines turn red, click Enter. Then the activated region is shaded. Now the region is ready to divide. To cancel the selection click Clear, and re-select.

d.   Dividing Section can be used to divide the selected region and assign nonlinear fiber material properties. Depending on the section type, select either Rectangular or Radial and enter Number of Divisions. According to the Number of Divisions, the division of section will be previewed on the diagram. After the division of section is fixed, select a nonlinear fiber material property from the Material ID combo box. After it is confirmed, click Divide to execute the division. Use Undo and Redo to cancel or restore the division.

In case the section has two division regions or more, repeat steps b ~ d.   

When it is necessary to modify the previously divided fiber section, use Editing Fibers. More details on this function will appear later on this page

Draw the boundary line delineating the cover and core parts of concrete.

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

Offset Distance from Boundary: After selecting the section, if additional boundary needs to be defined, select a reference polygon, and enter a distance from the boundary. Click Add to create an offset polygon. The concrete inside the main rebar and the concrete outside the main rebar are characterized differently. This function is usually used to enter the boundary of the outside concrete. Besides that, it is used to create a number of additional boundaries.

+ values will create a boundary inside the section, and ?values will create a boundary outside the section.

Select the reference boundary on the diagram and the selected boundary turns red. Enter the offset distance and click Add to create a boundary. Use Undo and Redo to cancel or revive the action.  

: When new boundaries need to be created, and the offset distances can not be readily calculated, distances are automatically calculated between two points selected on the section shape diagram. The two points are divided by the number entered here, and the distances are automatically calculated. Select two points on the diagram. Then the selected points turn red. After that, enter the number of division and click thebutton so as to divide the distance between the two points by the number of division entered. The auto-calculated distance will appear to the right of   "Offset Distance from Boundary"

After selecting a shape, click Enter to define an object, which defines a region.

Enter: A general shape is a polygon consisted of a number of points and boundaries. Among these, we select a boundary zone, which will be divided into fiber cells. Any other defined boundaries are also recognized as individual objects.

Clear: Selected boundary is cancelled.

A completely closed area is selected on preferential basis with reference to the selected boundary.

Set the fiber model regions, which will be applicable to the cover concrete and core concrete. First, select the shape of the core or cover region, and click Enter to determine the region.

Enter: The face of the region, which will be divided into fiber cells, will be selected. At this point, only the polygon regions

composed of the selected boundaries in Selecting Object will be activated. The activated region for division is shaded.

Clear: Cancel the selected region.

Enter the number of section divisions for the defined region. Each divided cell becomes a fiber. The properties of the cover and core can be reflected into each fiber.  

Note

Fiber cell division has direct relation to the analysis time, so it is cautioned. The number of divisions is not always directly proportional to the accuracy of analysis.  A common rule of thumb is to use 100~200 cells, which guarantees sufficient accuracy. In midas Gen, a section can be divided into a maximum of 1000 cells.

It is common to densely divide the outer part of the section in which maximum strain occurs and to sparsely divide the inner part of the section in order to satisfy the analysis speed as well as the accuracy.

Division Type: The region selected in Setting Region can be divided in a rectangular or radial pattern.    

Rectangular: Division by rectangular pattern

Number of Divisions: Number of divided cells

Ny: Number of divided cells in the y-axis direction (Enter 2 or more.)

Nz:Number of divided cells in the z-axis direction (Enter 2 or more.)

Once the Number of Divisions is entered, fiber division status is previewed on the diagram.

Radial: Division by circular or elliptical pattern

Number of Divisions:   

Center Point (y,z):Enter the coordinates of the center.

: Two points are selected on the diagram if the mid point of the two points needs to be selected as the center of the circle for radial division.

Nt: Number of divisions in the circular direction

Nr: Number of divisions in the radius direction

Once the Number of Divisions is entered, fiber division status is previewed on the diagram.

Material ID: Select a Fiber Material Property ID, which will be assigned to the divided cells.

 After the above inputs, click Divide and confirm that the cells that were assigned fiber material properties are divided as intended.

Use Undo and Redo to cancel or revive the action.

Edit the fiber cells already divided.

First, select the cells to be modified. The selected cells turn red.

: Select a number of cells, and Merge them into a cell.  

: Delete selected cells.

, : The above cell editing is cancelled or revived.

 Create Rebar

Specific rebars can be defined in the section. Rebars can be defined in three ways, Point, Liner and Circular. All the placed rebars are classified and tabulated by rebar designation, Number and total area.

Type: Point
Each rebar is individually defined in the section.

Material ID: Select a steel material defined in Fiber Material Property.

Center Point(y,z): Enter the location of the rebar. The coordinates can be directly entered, or the center point can be selected on the section diagram after clicking on the entry field.

Area: Cross-sectional area of a single rebar, which can be selected from the rebar DB. Or the user may directly enter the area.  

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

Material ID: Select a steel material defined in Fiber Material Property.

Starting Point(y,z): First rebar location on a line - the coordinates can be directly entered, or the point can be selected on the section diagram after clicking on the entry field.  

End Point(y,z): Last rebar location on the line - the coordinates can be directly entered, or the point can be selected on the section diagram after clicking on the entry field.  

Number of Rebars: Specify the number of rebars to be placed on the line.

Area: Cross-sectional area of a single rebar, which can be selected from the rebar DB. Or the user may directly enter the area.

Type: Circular
Define rebars in the section placed in a circular pattern.

Material ID: Select a steel material defined in Fiber Material Property.

Starting Point(y,z): First rebar location on a circle - the coordinates can be directly entered, or the point can be selected on the section diagram after clicking on the entry field. In order to place rebars accurately, Starting Point and Center of Arc must be lined up horizontally. For placement of rebars in an elliptical or arc pattern, line up Starting Point and Center of Arc horizontally and adjust Angle..

Center of Arc(y,z): Center of the circle on which rebars are placed - the coordinates can be directly entered, or the point can be selected on the section diagram after clicking on the entry field. In order to place rebars accurately, Center of Arc must be located horizontally to the left of Starting Point.

Central Angle of Arc: Angle of circular placement of rebars. The default of 360o places rebars in a full circle. Use Angle less than 360o to place rebars in an arc pattern.

Number of Rebars: Number of rebars in a circular placement

Area: Cross-sectional area of a single rebar, which can be selected from the rebar DB. Or the user may directly enter the area.