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Excerpt
nameGirder Tendon

Layout

Girder Tendon is used to model post-tensioning tendons. In OpenBrIM, tendons are modeled as loads, and the following process is applied to determine the structural effects:

  • Tendon loads are determined by the forces that act along the tendon layout and affect the selected structure. When calculating the forces, prestress losses are also taken into account.

  • Tendon loads are discretized into smaller segments, specifically at every foot. The tendon loads within each segment are statically distributed to the nodes of the selected structural element.

The main factors affecting the distribution of stress are as follows:
Short-term losses: Friction Losses - Anchorage Set Loss
Long-term losses: Elastic Shortening - Concrete Creep - Concrete Shrinkage - Steel Relaxation - Posttension Losses from Structure

Girder: Select the girder that tendon is applied. Tendon loads are distributed to the this structure.

Section Reference Edge[Top/Bottom]: Select a reference edge of the Girder. This selection affects the reference line chosen during the definition of the tendon geometry.

Layout Input Method[Path Data/ Tabular Data]: There is two possible ways to input tendon geometry: Tabular Data and Path Data. Both of these methods take their reference from the selected structural object, the Girder’s reference line. User needs to specify points on each row and these points are combined by OpenBrIM to create a tendon line.

Tabular Data: This cell is activated when Layout Input Method is selected as Tabular Data. If Layout Input Method is selected as Path Data this cell is displayed as “N/A”.
This definition allows user to define points with transverse and vertical offsets with respect to the reference line of Girder. Additionally, the user can enter the radius of an arc at the corresponding point.

To view the inputs, click the three-dot menu, then select "Edit…". The description of the inputs is listed below.

Tendon Layout Tabular Data

Reference Support Line

Select a reference support line.

Longitudinal Distance[ft]

Set the station difference along PGL from Reference Support Line.

Transerverse Offset[ft]

Set the transverse offset according to Section Reference Edge of Girder.

Vertical Offset[ft]

Set the vertical offset according to Section Reference Edge of Girder.

Radius[ft]

Set the point’s radius of curve.

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Transverse Tendon Path: This cell is activated when Layout Input Method is selected as Path Data. If Layout Input Method is selected as Tabular Data this cell is displayed as “N/A”.
This definition allows user to define a transerve offset with respect to the reference line of Girder. With the use of this tool curve with different type of variations [None/Linear/Parabola/Circular/Polynomial Fit] can be assigned between points.

Vertical Tendon Path: This cell is activated when Layout Input Method is selected as Path Data. If Layout Input Method is selected as Tabular Data this cell is displayed as “N/A”.
This definition allows user to define a vertical offset with respect to the reference line of Girder. With the use of this tool curve with different type of variations [None/Linear/Parabola/Circular/Polynomial Fit] can be assigned between points.

To view the inputs, click the three-dot menu, then select "Edit…". The description of the inputs of both Transverse Tendon Path and Vertical Tendon Path is listed below.

Tendon Layout Transverse/Vertical Path Data

Reference Support Line

Select a reference support line.

Longitudinal Offset Along the PGL[ft]

Set the station difference along PGL from Reference Support Line.

Transverse Offset/ Vertical Offset[in]

Set the transverse or vertical offset according to Section Reference Edge of Girder.

Variation Type(from next point)

Set the type of variation between the point in the current row and the point in the next row.

Curvature Type(for Parabola and Circular)

[Concave Up/Concave Down] Set the curvature type of the variation. This option is applicable to Parabola/Circular variation types.

Radius(for Circular)

Set the radius of the arc of the circle that is inserted between the point in the current row and the point in the next row. This option is applicable to Circular variation type, only.

Start Grade (%) (for Polynomial Fit)

Set the initial grade of the fitted polynomial line between the point in the current row and the point in the next row. This option is applicable to Polynomial Fit variation type, only.

End Grade (%) (for Polynomial Fit)

Set the end grade of the fitted polynomial line between the point in the current row and the point in the next row. This option is applicable to Polynomial Fit variation type, only.


Local Coord. X Offset [in]: X offset in local coordinates of the selected object.

Local Coord. Y Offset [in]: Y offset in local coordinates of the selected object.

Local Coord. Z Offset [in]: Z offset in local coordinates of the selected object.

Using Local Coord. Offsets would be beneficial when multiple tendons use the same layout definition.

Duct Outer Diameter [in]: Set the outer diameter of tendon duct. This parameter only affects the 3D visualization of tendons.

Properties

Material: Set the material for the tendon.

Post-tension Type[Bonded/Unbonded]: Specify the post-tension type, Bonded or Unbonded.

Exposure[Internal/External]: Set the type of exposure of tendon, Internal or External.

Anchor Set Length [in]: Anchor set length is user defined parameter.

Wobble Friction Coefficient [1/ft]: Enter the wobble friction coefficient.

Curvature Friction Coefficient [1/rad]: Enter the curvature friction coefficient.

Jacking

# of Strands: Enter the number of strands for the tendon.

Strand Type: Enter the strand type for the tendon. The strand type can be imported from the Properties section.

Jacking Method[Start/End/Start then End/ End then Start]: Specify the jacking method that is applied to the tendon. In the case of Girder, start and end refer to downstation and upstation directions with respect to PGL.

Jacking Force From Start [kip]: Enter the start jacking force that is applied to the tendon. It must be specified, unless Jacking Method is selected End.

Jacking Force From End [kip]: End jacking force that is applied to the tendon. It must be specified, unless Jacking Method is selected Start.

FEA Settings

In OpenBrIM, short-term losses are calculated automatically. The effect of these losses can be observed from clicking the three-dot menu of any cell and selecting “Prestressing Details…”. (Note: FEM generation needs to be activated).

Load Dist. Elem. Type[FENodes/FELines]: This input affects the type of finite elements loads are distributed. FELines are used for beam elements.

Percent Loss(%): Set the percent loss for the long-term losses. This is an optional input. Users can leave this input as 0 and let OpenBrIM calculate the long-term losses using the CEB-FIB 1990 curve by running the time-dependent analysis. Alternatively, users can set an approximate value for the Percent Loss (%) to account for long-term losses, which will reduce the Jacking Force values of the tendon.