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Bonded VS. Unbonded Post Tensioned Systems

Understanding Post-Tensioned Systems

(Structural)

(OP)

3 Dec 18 14:08

The discourse surrounding bonded versus unbonded post-tensioned systems lacks definitive answers. However, my personal inclination leans towards unbonded systems due to their superior post-flexural capacity, which allows them to withstand two to three times the factored load before failure. Nevertheless, I have heard claims that bonded systems excel in terms of serviceability and crack control. I am eager to gather some perspectives, acknowledging once again that a definitive answer may be elusive.

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Contributions on the Analysis of Post-Tensioned Systems

(Structural)

3 Dec 18 22:10

Yousef AA

It’s important to consider that unbonded tendons might fail to manage any expected load if the strands slip at the anchorages, as they rely solely on friction grip.

Further Insights on Bonded Systems

(Structural)

(OP)

4 Dec 18 07:30

Thank you, Rapt. Are you implying that bonded systems possess a better friction grip for the strands?

Exploring Long-Term Implications

(Structural)

4 Dec 18 21:29

No, what I mean is that bonded tendons, after the grout achieves its required strength, do not depend on friction grip for long-term performance. If you were to remove the anchorages from a bonded tendon, only a short length of development might be compromised. Conversely, if the same were done with an unbonded tendon, it would mean an absolute loss of the tendon.

Final Thoughts on Bonded vs. Unbonded Systems

(Structural)

16 Dec 18 23:00

Quote (OP)

The pursuit of an answer to which system is superior remains challenging.

In my professional opinion, bonded systems outperform unbonded systems across various performance metrics, including crack control. The sole edge that unbonded PT systems might hold is economic viability in certain markets. Furthermore, within contexts where unbonded PT floors are in use, it is not unusual for engineers to utilize bonded systems in critical applications like transfer girders to enhance reliability.

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Unbonded and Bonded Steel Strand Defined

Unbonded steel strands come with a protective layer of grease and a plastic sheath, ensuring they remain isolated from the concrete. This design allows for free movement, hence the term "unbonded." In some construction projects, galvanized unbonded strands may be employed, featuring an additional layer of grease and plastic sheathing to enhance corrosion resistance.

On the contrary, bonded steel strands lack this protective coating.

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