# Cap/Bent Tendon \[SPIG]

## Layout

Cap/Bent 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: Concrete Creep - Concrete Shrinkage - Steel Relaxation - Posttension Losses from Structure

**Cap/Bent:** Select the Cap/Bent that tendon is applied. Tendon loads are distributed to the this structure.

**Section Reference Edge \[Top/Bottom]:** Select a reference edge of the **Cap/Bent**. This selection affects the reference line chosen during the definition of the tendon geometry. The reference line starts at the right edge of the **Cap/Bent** with respect to PGL.

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230720-135426.png?api=v2)

**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 **Cap/Bent**'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 **Cap/Bent**. 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 |                                                                                    |
| -------------------------- | ---------------------------------------------------------------------------------- |
| **Longitudinal Distance**  | Set the distance of the point from right edge of the **Cap/Bent**.                 |
| **Transerverse Offset**    | Set the transverse offset according to **Section Reference Edge** of **Cap/Bent**. |
| **Vertical Offset**        | Set the vertical offset according to **Section Reference Edge** of **Cap/Bent**.   |
| **Radius**                 | Set the point’s radius of curve.                                                   |

## Tabular Data

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230718-160812.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/RadiusofArc.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230720-140448.png?api=v2)

**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 **Cap/Bent**. 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 **Cap/Bent**. 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   |                                                                                                                                                                                               |
| --------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Distance**                                  | Set the distance of the point from the right edge of the **Cap/Bent**.                                                                                                                        |
| **Transverse Offset/ Vertical Offset**        | Set the transverse or vertical offset according to **Section Reference Edge** of **Cap/Bent**.                                                                                                |
| **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.     |

## Path Data

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230718-143325.png?api=v2)

## Transverse Path Data

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230718-143906.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230720-130910.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230720-131002.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230718-145010.png?api=v2)

## Vertical Path Data

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230718-151930.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230720-131116.png?api=v2)

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

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

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

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

![](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20230718-145727.png?api=v2)

## 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:** Anchor set length is user defined parameter.

**Wobble Friction Coefficient:** Enter the wobble friction coefficient.

**Curvature Friction Coefficient:** 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 **Cap/Bent**, start and end refer to right and left directions with respect to PGL.

**Jacking Force From Start:** 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:** 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.

{% hint style="info" %}
There are two methods for calculating tendon losses in OpenBrIM. The first method, the approximate method, involves defining the Percent Loss (%) of the tendon objects on the FEA tab, as outlined above. The second method, the detailed method, is as follows:

1. **Defining Time-Dependent Material Properties** for tendon materials:\
   Refer to **Properties-Materials** for parameters such as:

* Steel Relaxation Effect
* PT Losses from Structure

2. **Defining CEB-FIB 1990 Parameters** of the materials:\
   Refer to **Properties-Materials** for defining parameters such as:

* Steel Relaxation Class

3. **Making Construction Stage Definitions**:\
   Refer to **Construction-Construction Stages** for making stage definitions by:

* Construction Day
* Code
* Steel Relaxation Effect
* PT Losses from Structure

4. **Defining the Associated Result Extraction Cases**: refer to screenshot below for example case definitions. ![image-20241218-130057.png](https://openbrim.atlassian.net/wiki/download/attachments/2226389032/image-20241218-130057.png?api=v2)
   {% endhint %}