Tendon Property

Define the tendon properties such as tendon area and instantaneous prestress losses.

From the Main Menu select Load > Temp./Prestress > Prestress Loads > Tendon Property.

To define new or additional tendon properties

Click in the Tendon Property dialog box and enter the following:

Tendon Name

tendon name being defined

Tendon Type

Define the tendon type among Pre-Tension, Post-Tension and External.

Internal (Pre-Tension): Prestressing tendons prior to casting concrete, which transmits prestress through bonding between concrete and tendons

Internal (Post-Tension): Post-tensioning tendons through hardened concrete members - tendons are gradually stressed and anchored to the members.

External: Tendons are placed external to concrete members and stressed.

Note 1
Depending on the Tendon Type (Pre-Tension, Post-Tension and External), the entry fields for variables related to tension losses in tendons and duct diameter are either activated or inactivated.

Note 2
If the tendon placement location is External, the tendon is displayed as a straight line in Display.

Material

Select the material properties of the tendon. Click to the right to add new or modify/delete previously defined tendon properties.

Total Tendon Area

Specify the total area of the tendon. You may either directly specify the cross-sectional area or click to enter the standard cross-sectional area and the number of strands for auto-calculation of the total area.

Duct Diameter

When the Tendon Type is Post-Tension, input for the diameter of duct is required. Based on the tendon area, the duct diameter is automatically calculated, which is then referred to for duct diameter input.

Strand Diameter

When the Tendon Type is Pre-Tension, the diameter of strand should be entered. The program automatically calculates the diameter of strand corresponding to the specified Total Tendon Area. The diameter of the strand is used to compute Transfer Length.

Relaxation Coefficient: C

Select Magura or CEB-FIP for the method of applying relaxation. To ignore the steel relaxation, uncheck the box.

• When Magura is selected

  Select 10 or 45 for Relaxation Coefficient (C), which relates to the product. Relaxation coefficients of 10 and 45 may be used for general steel and low-relaxation steel respectively.  Losses due to steel relaxation are determined from the following equation:

   

  

   

  where,  ,fsi: initial stress,fs:  stress at time t after loading, fy: yield stress (0.1% Offset Yield Stress), C: Relaxation Coefficient (general steel: 10, low-relaxation steel: 45)

• When CEB-FIP(2010) is selected

  Enter the loss ratio after 1000 hours steel relaxation. Prestress loss due to steel relaxation is determined from the following equation:

   

  

   

  where,fsi: initial stress, r: loss ratio after 1000 hours due to steel relaxation, ki: progress of steel relaxation at the last time step

   

   

  The progress of steel relaxation with time is as follows:

   

  Time in hour	1	5	20	100	200	500	1000
  Slow Development	20	35	45	65	75	85	100
  Mean Development	30	45	55	70	80	90	100
  Rapid Development	40	55	65	75	85	95	100

   

  Following formula is applied:

   

  

   

  where ρt: the relaxation after t hours,  ρ1000: the relaxation after 1000 hours, k =log(ρ1000/ρ100)

   

   

  Note

  For Relaxation Coefficient (C), 10 for general steel and 45 for low-relaxation steel may be entered. Check off the box to ignore Relaxation.

• When CEB-FIP(1990) is selected

  Enter the loss ratio after 1000 hours steel relaxation. Prestress loss due to steel relaxation is determined from the following equation:

   

  

   

  where,fsi: initial stress, r: loss ratio after 1000 hours due to steel relaxation, ki: progress of steel relaxation at the last time step

   

   

  The progress of steel relaxation with time is as follows:

   

   

  Time in hour	1	5	20	100	200	500	1000
  Relaxation losses at percentage of losses  in 1000 hours	25	45	55	70	80	90	100

   

  For an estimation of relaxation up to 30 years, the following formula is applied

  

  where ρt: the relaxation after t hours,  ρ1000: the relaxation after 1000 hours, k to be 0.12.

   

   

  Note

  For Relaxation Coefficient (C), 10 for general steel and 45 for low-relaxation steel may be entered. Check off the box to ignore Relaxation.

• When CEB-FIP(1978) is selected

  Enter the final loss ratio due to steel relaxation. Prestress loss due to steel relaxation is determined from the following equation:

   

  

   

  where,fsi: initial stress, r: final loss ratio due to steel relaxation, ki: progress of steel relaxation at the last time step

   

   

  The progress of steel relaxation with time is as follows:

   

   

  Progress of relaxation (k)	Lapse
  k=1/16 ln{ (t-to)/10+1 }	0 ≤ (t-to) ≤ 1000
  k={ (t-to)/(0.5x0^6) }0.2	1000 ≤ (t-to) ≤ 0.5x106
  k=1. 00	(t-to) ≥ 0.5 x106

   

  where to: the timing of pre-stressing,  t: the time when tendon loss due to relaxation is evaluated

   

   

  Note

  For Relaxation Coefficient (C), 10 for general steel and 45 for low-relaxation steel may be entered. Check off the box to ignore Relaxation.

• When JTG04 is selected

  If the user selects JTG04 standard in the Material Data and selects JTG04 for Relaxation Coefficient in the Tendon Property, the Characteristic Value of Strength (fpk) is automatically entered as per the JTG04 code. If the user does not select JTG04 standard in the Material Data, the user can directly enter the Characteristic Value of Strength (fpk).

   

  In case Steelbar540, Steelbar785 or Steelbar930 is selected in the Material Data, the Application of Overstress Reduction Factor is ignored.

• When TB05 is selected

  If the user selects TB05 standard in the Material Data and selects TB05 for Relaxation Coefficient in the Tendon Property, the Characteristic Value of Strength (fpk) and the Tendon Relaxation Coefficient (ξ) are automatically entered as per the TB05 code. If the user does not select TB05 standard in the Material Data, the user can directly enter the Characteristic Value of Strength (fpk) directly.

   

  Note

  Calculation of Tendon Relaxation Coefficient (ξ) and loss due to Relaxation Tendon Relaxation

• When INDIA(IRC:112-2011) is selected

   

  Relaxation loss at 1000 days is as follows (at 20 °C ± 2 °C ):

   

  Initial Stress	Relaxation loss for Normal relaxation steel (%)	Relaxation loss for Low relaxation steel (%)
  0.5 fp	0	0
  0.6 fp	2.5	1.25
  0.7 fp	5.0	2.5
  0.8 fp	9.0	4.5

   

  Relaxation loss, in relation to time, is as follows:

   

  Time (hour)	1	5	20	100	200	500	1000
  Relaxation loss (%)	15	25	35	55	65	85	100

   

• When INDIA(IRC:18-2000) is selected

   

  Relaxation loss at 1000 days is as follows (at 20 °C ± 2 °C ):

   

  Initial Stress	Relaxation loss for Normal relaxation steel (%)	Relaxation loss for Low relaxation steel (%)
  0.5 fp	0	0
  0.6 fp	2.5	1.25
  0.7 fp	5.0	2.5
  0.8 fp	9.0	4.5

   

  Relaxation loss, in relation to time, is as follows:

   

  Time (hour)	1	5	20	100	200	500	1000
  Relaxation loss (%)	15	25	35	55	65	85	100

   

• When European is selected

• When User Defined is selected

  Select the user defined relaxation function in hour/day and loss ratio due to steel relaxation relation.

  Click [...] button to add/modify User Defined Relaxation Function.

   

Ultimate Strength

Yield Strength

Curvature Friction Factor

to account for friction loss due to the curvature of tendons

Wobble Friction Factor

To account for straightness/length effect (imperfection in alignment along the length of tendon, regardless of straight or draped alignment)

Anchorage Slip (Draw in)

Tendon slippage at the anchor

Begin: slippage at the beginning of tendon if tensioned here

End: slippage at the end of tendon if tensioned here

 Bond Type

Bonded: Section properties reflect the duct area after grouting

Unbonded: Section properties exclude the duct area.

To modify the previously entered tendon data

Select the tendon from the list in the Tendon Property dialog box and click to change any relevant data.

To delete the previously entered tendon data

Select the tendon from the list in the Tendon Property dialog box and click to eliminate any relevant data.

Q1. What are the considerations in the program regarding external tendons?

Q2. What is the Wobble Friction Factor and how does it relate to the "unintentional angular displacement"-factor (k)?

Q3. What is the consideration in the software for relaxation loss calculation when Eurocode is selected?