Post-tensioned cable

Post-tensioned cable

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Use the Post-tensioned cable for bars tool or Post-tensioned cable for shells tool to define a tendon system along the relevant element.

When you select Post-tensioned cable for bars or Post-tensioned cable for shells, a tool palette opens.

Main tools

• Define - place a new post-tensioned cable along a bar
• Properties - check or edit properties of an existing cable. Opens the Default settings dialogue for the selected cable
• Default settings - set the default parameters for cable shape, strand type, jacking and stress loss (read below in more detail)

Main settings

Available when the Define tool is selected. These settings define the vertical profile of the cable within spans.

• Parabolic shape by axes - if selected, the cable shape follows a parabolic path based on grid axes. If unselected, the shape will be straight
• Reverse shape - reverse the direction of the parabolic shape
• Auto calc. min. position - if selected, automatically calculates the minimum base point locations for outer and inner spans
• A/Lo (infl.) - numeric field for outer span’s first inflection point ratio (relative to outer span length)
• B/Lo (min.) - numeric field for outer span’s minimum base point ratio (relative to outer span length)
• C/Lo (infl.) - numeric field for outer span’s second inflection point ratio (relative to outer span length)
• D/Li (infl.) - numeric field for inner span’s inflection point ratio (relative to inner span length)
• E/Li (min.) - numeric field for inner span’s minimum base point ratio (relative to inner span length)

info

The inner and outer spans refer to the automatically recognized areas created by building axes that cross the post-tensioning cable. You can also customize the shape later. See the Shape wizard in Default settings dialogue for more.

tip

If you hover over the numeric fields, a pop-up graph will show the meaning of the letters.

Definition methods

Available when using the Define tool.

• Straight line - draw a straight cable path between two points
• Line by selection - select an existing line in the model to define the cable path
• Layout wizard - only available for shells. Opens a new dialogue window where you can generate a pattern of post-tensioned cables across a shell element, based on applied loads, strand limits, and layout preferences (read below in more detail)

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Post-tensioned cable layout wizard

When you press the Layout wizard button (available when defining post-tensioned cables for shells), a new dialogue window opens.

Load settings

These values define how the tendon pattern should respond to structural loading.

• Considered load - numeric field where you can manually enter the design load
• Struc. dead load! - button that automatically fills the field above with the shell’s calculated dead load
• Balance ratio of the load - numeric field to define what ratio of the considered load should be balanced by the cable layout
• Maximal deviation - maximum allowable deviation from the target balance

Unequal loading

Configure how the layout adapts to irregular spans or variable loading.

• Column span load ratio - numeric field to define load variation between spans
• Column span width ratio - numeric field to define span width variation
• Different strand number - checkbox that allows strand count to vary between cables

Direction and shape settings

Control which directions are considered and how the tendon profiles are shaped.

• Used direction - two checkboxes to enable layout along the x′ and y′ axis directions
• Minimal strand number - numeric fields for minimum number of strands in x′ and y′ directions
• Maximal strand number - numeric fields for maximum number of strands in x′ and y′ directions
• Top - numeric fields defining distance from the top surface in x′ and y′ directions
• Bottom - numeric fields defining distance from the bottom surface in x′ and y′ directions
• Shape wizard using height instead of physical model - checkbox to override the model geometry when generating parabolic shapes and a numeric field for custom height used in the shape definition
• Minimal distance between the considered axes using shape wizard - numeric field that defines the minimum spacing between axes used to generate cables. Axes closer than this value are ignored

Placement

These parameters define how the cables are spaced and filtered for final layout.

• PTC - PTC minimal distance - minimum spacing between adjacent cables
• PTC - PTC maximal distance - maximum spacing between adjacent cables
• PTC - Column minimal distance - minimum clearance from cables to column edges
• Minimal length - shortest allowed cable length. Shorter cables will not be created
• Prefer less cable with more strands - if checked, generates fewer cables but with higher strand counts

Global option

At the bottom of the dialogue there are two more options:

• Delete the previously defined cables from the shell - if checked, all cables previously placed on the shell will be removed when applying the new layout
• Generate - use the button to start the calculation for required cables. After the during the calculation the Layout calculation dialogue is displayed

Layout calculation dialogue

When you press the Generate button, a new dialogue window opens.

After the calculation is finished, you can see the load and layout results.

At the bottom you have two buttons:

• Apply - apply the generated cables (even if the analysis ended with errors)
• Cancel - do not apply anything (even if the calculation was successfully finished)

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Default settings dialogue

When you press the Default settings button, a dialogue window opens.

This dialogue contains four tabs: General, Shape, Results, and Manufacturing. These tabs define the default geometric, analytical, and practical behavior of post-tensioned cables for bar elements.

Common for every tab

At the bottom of the Default settings dialogue, regardless of the selected tab, there is a graph and two buttons:

• The smaller graph shows the cable’s vertical profile along its length for quick reference and consistency across tabs.

• Add to documentation - opens a dialogue to include current cable settings in project documentation (read below in more detail)

• ? - opens the relevant article in the User Manual for post-tensioned cables

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General tab

This tab sets the fundamental parameters for cable strands, jacking strategy, and stress losses.

• Identifier - optional name or label for the cable

The other controls are grouped into parameter blocks:

Strands

• Type - select a predefined strand type from the drop-down menu. In the menu, there is also Edit Library function.
  • Edit library - open the Strand library dialogue to manage and create custom strand types (read below in more detail)
• Number - define the number of strands in the cable

Jacking

• Jacking side - choose the jacking method from the drop-down menu:
  • Start
  • End
  • Start then end
  • End then start
• Jacking stress - define the jacking stress value as a numeric input

Short term losses (T0)

• Curvature coef. - coefficient for loss due to cable curvature, μ, according to [G1]EN 1992-1-1 5.10.5.2 (1)
• Wobble coef. - coefficient for unintentional deviations in the duct path, k, according to [G1]EN 1992-1-1 5.10.5.2 (1)
• Anchorage set slip - loss due to slip at the anchorage
• Elastic shortening loss - loss due to elastic shortening of the concrete member
• Estimate ES... - opens a dialogue to estimate elastic shortening loss (read below in more detail)

Long term losses (T8)

• Creep stress loss - loss due to creep of concrete
• Shrinkage stress loss - loss due to shrinkage of concrete
• Relaxation stress loss - loss due to steel relaxation
• Estimate T8... - opens a dialogue to estimate long-term losses (read below in more detail)

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Strand library dialogue

When you select the Edit library option in the Strands ➔ Type drop-down list of the General tab, the Strand library dialogue window opens.

This dialogue allows you to define, modify or delete strand material types used in post-tensioned cables.

The layout is divided into two main sections. On the left side, a list of all currently available strand materials is shown. On the right side, detailed properties of the selected strand material are displayed.

• Name - name of the strand material
• f pk - characteristic tensile strength of the strand
• A p - cross-sectional area of the strand
• E p - elastic modulus of the strand material
• ρ - density of the strand material
• Relaxation class - drop-down menu with three relaxation classes
• ρ 1000 - stress relaxation value at 1000 hours

Buttons at the bottom

• New - create a new strand material
• Modify - update the properties of the selected strand
• Delete - remove the selected strand from the library
• Import - load a strand material library from an external file
• Export - save the current strand material library to a file

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Estimate Elastic Shortening Loss dialogue

When you press the Estimate ES... button in the Short term losses (T0) group of the Default settings dialogue, a new dialogue window opens.

This tool calculates the expected elastic shortening loss using the formula [G1]EN 1992-1-1 (5.44), as defined in clause [G1]EN 1992-1-1 5.10.5.1 (2)..

The dialogue contains two main parameter groups:

Data to apply EC2 5.10.5.1.(2) (formula 5.44)

These inputs are required for the calculation:

• Number of strand on the structure (Plate: on 1m) - number of strands in the structural section (or per meter in case of slab-type elements)
• Average stress in the strand - mean tensile stress in the post-tensioning strands (stated in [G1]EN 1992-1-1 as σ_p)
• E cm,t - secant modulus of elasticity of concrete at the time of stressing (stated in [G1]EN 1992-1-1 as E_cm(t))
• A c - cross-sectional area of the concrete section (stated in [G1]EN 1992-1-1 as A_c)
• I c - moment of inertia of the concrete section (stated in [G1]EN 1992-1-1 as I_c)
• z cp - distance from the centroid of the cross-section to the centroid of the stressing tendons (stated in [G1]EN 1992-1-1 as z_cp)

Calculated stress values

• Average stress in structure - computed average compressive stress in the concrete
• Elastic shortening stress loss according to different jacking time - resulting loss depending on whether jacking is applied before or after other post-tensioning operations

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Estimate Long Term Losses dialogue

When you press the Estimate T8... button in the Long term losses (T8) group of the Default settings dialogue, a new dialogue window opens.

This tool calculates expected long-term stress losses using the [G1]EN 1992-1-1 (5.46), as defined in [G1]EN 1992-1-1 5.10.6 (2).

The dialogue contains two main parameter groups:

Data to apply EC2 5.10.6.(2) (formula 5.46)

These inputs are used to calculate creep, shrinkage, and relaxation losses:

• Δ σ pr - change in steel stress from jacking to final time (stated in [G1]EN 1992-1-1 as Δσ_pr)
• σ c,QP - mean concrete compressive stress at the level of the tendon (stated in [G1]EN 1992-1-1 as σ_c,QP)
• ε cs - shrinkage strain of concrete (stated in [G1]EN 1992-1-1 as ε_cs)
• φ (t,t₀) - creep coefficient of concrete (stated in [G1]EN 1992-1-1 as φ(t, t₀))
• Number of strand on the structure (Plate: on 1m) - number of strands in the section (or per meter in slabs)
• E cm - modulus of elasticity of concrete (stated in [G1]EN 1992-1-1 as E_cm)
• A c - cross-sectional area of the structural element (stated in [G1]EN 1992-1-1 as A_c)
• I c - moment of inertia of the section (stated in [G1]EN 1992-1-1 as I_c)
• z cp - distance from the centroid of the cross-section to the centroid of the cable (stated in [G1]EN 1992-1-1 as z_cp)

Calculated long term losses (T8)

T8 refers to a time where all losses have been accounted for (similar to the concept of t_∞)

• Creep stress loss - calculated loss due to creep
• Shrinkage stress loss - calculated loss due to shrinkage
• Relaxation stress loss - calculated loss due to steel relaxation

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Shape tab

Shape tab allows you to define the cable profile using a list of Base points and Inflection places, as well as adjust vertical limits and analyze geometric properties.

Base points and inflection places

The table on the left lets you define and edit the control points that shape the cable’s curve.

• Type - drop-down menu to set the row as either a Base point or Inflection place
• x′ - local x-coordinate of the control point along the element
• z′ - local z-coordinate of the point (only available for Base points)
• Tangent - slope of the curve at the base point (only available for Base points)

info

Inflection places only require an x′ value. Their vertical position (z′) is computed automatically by the program.

Shape tools and settings

On the right side of the tab, several settings and utility buttons are available:

• Top - numeric field for the maximum allowed vertical position of the cable
• Bottom - numeric field for the minimum allowed vertical position of the cable
• Shape wizard... - opens a dedicated dialogue to generate the cable shape automatically based on height or axis layout (read below in more detail)
• Sort by x - sort all rows in the table based on their x′ coordinate
• Display physical element - checkbox to toggle the visibility of the physical member’s centerline. This is especially useful for bar elements

Shape analysis

Three informational readouts provide feedback about the geometry:

• Equilibrium status of equivalent transversal loads - displays OK! if the cable geometry satisfies equilibrium conditions
• Summated / Accumulated forces - displays the calculated forces acting on the cable
• Minimal radius of curvature - displays the tightest radius of curvature found in the current cable shape

Shape profile graph

At the bottom of the tab, a dynamic graph shows the cable’s vertical profile along its length with added details relevant in the Shape tab:

• Base points - marked as squares
• Inflection places - marked as circles

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Shape wizard dialogue

When you press the Shape wizard... button in the Shape tab of the Default settings dialogue, a new window opens.

This dialogue allows you to generate the cable's shape automatically using parabolic logic based on the position of grid axes. It is especially useful when the profile needs to align with the structural spans defined by these axes.

At the top of the dialogue, two diagrams illustrate the meaning and reference positions for all the shape-defining ratios:

• A, B, C - distances for the Lo (outer) spans
• D, E - distances for the Li (inner) spans

These visuals help clarify how the ratios are applied to the geometry of the tendon path.

Settings

• Reverse parabola - checkbox to flip the parabolic curve vertically
• Auto calculation minimum position - automatically determine the base point locations for smooth curvature
• A/Lo (infl.) - distance ratio to the first inflection point in the outer span
• B/Lo (min.) - distance ratio for the minimum base point location in the outer span
• C/Lo (infl.) - distance ratio to the second inflection point in the outer span
• D/Li (infl.) - distance ratio to the inflection point in the inner span
• E/Li (min.) - minimum base point distance in the inner span
• Minimal distance between the considered axes - if the distance between axes is less than this value, they are ignored during shape generation

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Results tab

The Results tab allows you to inspect the effects of friction, anchorage, short-term and long-term losses, and equivalent forces on the strand or the full cable.

Selectable result functions

Use the drop-down menu at the top of the tab to choose which result to display:

• Radius of curvature
• Angular deviation function
• Stress function with friction losses
• Stress function with anchorage set slip losses
• Stress function with elastic shortening losses (T0)
• Stress function with all time dependent losses (T8)
• Equivalent force for 1 strand (T0)
• Equivalent force for 1 strand (T8)
• Equivalent force for PTC (T0)
• Equivalent force for PTC (T8)

Display options

• Display stress functions in f pk ratio - available for stress results only. If checked, stress-related functions are shown as a ratio of the strand's characteristic tensile strength. If unchecked, the unit is in project's stress units

Result graph

The selected result is shown in the central result graph area. This visualizes how the value varies along the cable’s length.

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Manufacturing tab

This tab includes functions to adjust and export the geometry for real-world production, along with precise control over coordinate generation.

Position adjustment settings

• x′ shift - numeric field to shift all coordinate points in the x′ direction
• z′ shift - numeric field to shift all coordinate points in the z′ direction.

info

The z′ shift is filled by default. It is useful since the software reference is usually at mid-height or top (analytical model), but manufacturing requires distances from the bottom of the element.

Export and editing functions

• Export - export the current shape and coordinate data as a DWG file for use in CAD or manufacturing workflows
• Generate points - opens the Generate points dialogue to insert intermediate points along the cable curve for greater precision in manufacturing (read below in more detail)
• Edit points > - opens the Edit points dialogue to manually review and edit the generated point list (read below in more detail)

Shape graph

The main graph displays the cable with all currently defined and generated coordinate points. This visual guide reflects all shifts and additions made.

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Generate points dialogue

When you press the Generate points button in the Manufacturing tab of the Default settings dialogue, a new window opens.

This dialogue helps you add extra points to the cable geometry to ensure accurate manufacturing. These points are used when exporting the shape or editing it numerically.

Settings

• Apply Base points - include all existing base points in the output
• Apply inflection places - include automatically calculated inflection points
• Apply regular division - insert intermediate points along the cable at fixed intervals. Use numeric field next to the checkbox to define the regular spacing between generated points

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Edit points dialogue

When you press the Edit points > button in the Manufacturing tab of the Default settings dialogue, a new window opens.

This dialogue allows you to directly edit the generated points of the cable profile. A table is displayed with all generated points, listing their x′ coordinates.

• Users can manually adjust the x′ values in the table to fine-tune the shape
• Sort - button to reorder all rows in the table based on ascending x′ values

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Add to documentation dialogue

When you press the Add to documentation button at the bottom of the Default settings dialogue, a new dialogue window opens.

This window defines which cable-related data is added to the documentation module and how it should appear in the output.

Content

Use the checkboxes to select which information to include in the documentation:

• General data
• Radius of curvature
• Angular deviation
• Stress function with friction losses
• Stress function with anchorage set slip losses
• Stress function with short term losses (T0)
• Stress function with long term losses (T8)
• Equivalent force for 1 strand (T0)
• Equivalent force for 1 strand (T8)
• Equivalent force for cable (T0)
• Equivalent force for cable (T8)
• Manufacture drawing

Appearance

Define how the information will be presented in the document:

• Graphs width - numeric field to define graph width in millimeters
• Graphs height - numeric field to define graph height in millimeters
• Text - opens the Text dialogue to insert optional caption or description (read below in more detail)
• Graph - opens the Text dialogue to name the graph or add a title (read below in more detail)
• Display stress functions in f pk ratio - if checked, displays stress function graphs in relation to the strand’s characteristic strength

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Text dialogue

The Text dialogue is used by both the Text and Graph buttons in the Add to documentation window.

• Font - select the font family
• Size - change the text height
• Width factor - control the horizontal scaling of the text
• B, I, U - apply bold, italic or underline formatting
• ab - display the text with a strike-through effect
• Get default arrow button - restore all the settings to their default values

A live preview is shown in the Sample text field.