Prestressing of Strand in Concrete Beam and Then Release of Strands 1

[Zain_117]

Hello,
I am trying to apply prestressing to strands in a concrete beam. The idea is:
1. I need to pull the strand by a force of 35 Kip (Loading Step).
2. Then cast the concrete and wait for 1 day so that the concrete beam is hardened enough.
3. After one day, the strands released by prestressed force transfer to the concrete beam (Unloading Steps).
I need to know the stresses, strains, and any cracking patterns after releasing the strands.
How I can assign BCs? Should BC be an initial step?
Should I need two steps for loading/pulling strands and unloading/Releasing of strands separately?
Anyone helps me to model all the above systems in ABAQUS?

 

[FEA way]

In the initial step you can only define fixed boundary conditions (but they can be modified in analysis steps). In this case, it would indeed be best to define two steps - one with loading and one with unloading. Use the BC and load managers to control those step-dependent features in subsequent steps.

 

[Zain_117]

Can you please explain in steps, how to create the interaction between strands and concrete?

 

[FEA way]

It depends on how you model them, what kind of behavior you want to represent and how they are connected in real life. In most cases it would be contact with cohesive behavior. You can use general contact (no need to define pairs manually) and just specify the values for the cohesive behavior. Check the article "Accurate finite element modeling of pretensioned prestressed concrete beams" by O. Yapar.

 

[Zain_117]

I got a new error:
THE *CONTACT PAIR pair (ASSEMBLY_GIRDER-1_SURF-3_DUCT, ASSEMBLY_STRAND-1_SURF-2_STRAND) HAS BEEN PROCESSED BEFORE. REMOVE DUPLICATE PAIR. -- THE SAME PAIR OF SURFACES CANNOT BE SPECIFIED MORE THAN ONCE FOR *TIE AND *CONTACT PAIR. ONCE A PAIR OF SURFACES IS USED FOR *TIE, IT CANNOT BE USED AGAIN FOR *CONTACT PAIR AND VICE VERSA.

 

[Zain_117]

FYI, I don't have a tie constraint in the model.

 

[FEA way]

Try with general contact instead of contact pairs.