Tendon outside section boundary 23'

Hi everyone,

Today, I created a test model to compare external prestress of the cross-section using the Tendon module and cables in linear analysis. To do this, I used the sysp command with ... beta 0 mue 0 sp 0 minr=1e-3 and cs ... ics2 999. The prestress force was 6138*0.774 for both the Tendon and cable models. However, for the cable model, I used a factor of 241347/176470 for consider of elastic deformation .

The model is built as 3 beam which:

  • beam 1: concrete beam prestressed by tendon sysp 1, so do 107
  • beam 2: concrete beam prestressed by tendon sysp 2, so do 1
  • beam 3: concrete beam prestressed cables as finite elements

I have attached the model with a .gra file. The graphic in file are:

  • Graphic 1: The elastic deformation Z of all three models is acceptable.
  • Graphic 2: The elastic deformation X of the third model is slightly higher, which is normal due to elastic deformation of the beam.
  • Graphic 3: The stresses in the tendon are similar, which is acceptable because the prestress force is very similar, but not identical (due to another input…).
  • Graphic 4 and 5: The stresses of the concrete beam are completely wrong when the do value is significant (beam 1).

The difference between beam 2 and beam 3 is acceptable, but concrete stresses in beam 1 are wrong. In my opinion, the problem is that AQB treats the tendon’s ungrounded duct area as negative, even when the duct is outside the section. I tried to find a solution to this issue in the AQB manual, but I was unsuccessful. Is it a bug or did I miss something?

I have also attached the model’s .dwg and .dat files for SOFiSTiK 2023.

Best regards, SB

main.dwg (69.5 KB)
main.dat (1.2 KB)
main.gra (2.4 KB)

Hello SB,
you are absolutely right: SOFiSTiK always subtracts the outer diameter of the duct. If the tendon is outside the cross section, SYSP… DO must therefore always be defined with a small value (e.g. 0.1 mm). There is no other solution for this except your procedure in beam 3 with the external rope.

Best regards,

thank you for confirming my doubts and confirming the provisional solution of beam No. 2. best regards :+1:

Good to know, never noticed that my external cables acts on lesser area. In some extreme situations (many cables) this is unsafe side!!