Girder Tendon [SPIG]

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.
  

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.

Tabular Data:

Transverse Tendon Path:

Vertical Tendon Path:

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]:

Exposure[Internal/External]:

Anchor Set Length [in]:

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 endstation respectively.

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 and 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 (Concrete Creep - Concrete Shrinkage - Steel Relaxation). This is an optional input. User can leave this input as 0 and let OpenBrIM calculate the long-term losses by CEB-FIB 1990 curve by runing the time-dependent analysis. Alternatively, user can set an approximate Percent Loss(%) value for long-term losses which reduces to the Jacking Force values of the tendon.