5 Key Changes in the ACI-PTI 320-25 Code You Need to Know
By Don Kline
The release of the ACI-PTI 320-25 Code marks a defining moment for post-tensioned (PT) concrete design.
For the first time, the industry now has a standalone building code dedicated exclusively to post-tensioned concrete systems. Prior to this, PT design provisions were embedded within ACI 318, a general concrete code that has guided the industry for over 100 years.
The ACI-PTI 320-25 Code (2025) represents a major step forward, aligning modern PT design with decades of research and field performance. And this is just the beginning. The committee is already actively working on the next round of updates targeted for 2028, continuing to advance the state of practice.
At KLINE, we’ve broken down the five most impactful changes shaping the future of PT design, constructability, and performance:
1. Dual Banded Tendon Layouts Now Permitted
For the first time, dual-banded tendon layouts in two-way slabs are explicitly allowed by code.
Why it matters:
Expands design flexibility for architects and engineers
Eliminates historic tendon spacing limitations
Improves constructability and construction speed
Reduces risk during future slab penetrations
This change represents one of the most significant evolutions in PT slab design in over 50 years—unlocking more efficient and adaptable structural systems.
2. Headed Shear Studs Approved for Anchorage Zones
The code now formally recognizes headed shear studs as an alternative to traditional reinforcement in PT anchorage zones.
Why it matters:
Reduces reinforcement congestion at anchor locations
Improves concrete placement and consolidation
Enhances resistance to bursting and spalling forces
Aligns design with modern reinforcement systems
This update provides engineers with a more buildable and efficient detailing option, especially in highly congested regions.
3. Clearer Requirements for Shrinkage & Temperature Tendons
ACI-PTI 320-25 introduces explicit guidance for shrinkage and temperature (S&T) effects in one-way PT slabs, including a minimum 100 psi precompression requirement.
Why it matters:
Improves crack control and serviceability performance
Reduces ambiguity in PT slab detailing
Aligns design intent with construction and inspection practices
Leads to more predictable long-term slab behavior
This change reinforces consistent performance expectations across PT systems.
4. Removal of 0.70fpu Stress Limit at Anchorage
The previous requirement limiting tensile stress at the anchorage to 0.70fpu immediately after stressing has been removed.
Why it matters:
Aligns code provisions with real-world stressing practices
Reflects that typical stressing levels (~0.8fpu) are already standard
Maintains safety, as anchorage hardware is tested up to 0.95fpu
Eliminates unnecessary design constraints
This update reduces confusion while maintaining the same level of safety and performance.
5. Corner Restraint Reinforcement No Longer Required in PT Slabs
The code clarifies that corner restraint reinforcement is not required in PT two-way slabs, even when corners are supported by stiff elements.
Why it matters:
Eliminates unnecessary reinforcement
Reduces steel congestion and simplifies detailing
Improves constructability and efficiency
Aligns with over 50 years of successful PT slab performance
This change reflects the fundamental behavior of PT systems, where precompression inherently mitigates cracking and restraint effects.
What This Means for the Industry
These updates don’t redefine how post-tensioning works; they codify what decades of successful performance have already proven.
Collectively, they:
Improve design efficiency and clarity
Enhance constructability and field execution
Reduce unnecessary conservatism and ambiguity
Expand opportunities for architectural flexibility
KLINE’s Perspective
As active contributors to PT industry standards and design practice, KLINE sees ACI-PTI 320-25 as a major step forward in aligning code requirements with real-world behavior.
With leadership from experts like Don Kline, these changes reflect a deeper understanding of how PT systems perform, not just in theory, but in the field.
Looking Ahead
As adoption of the new code accelerates, engineers, architects, and contractors who understand these changes will be better positioned to deliver:
More efficient designs
Faster construction timelines
Higher-performing structures
If you’re attending the convention or interested in learning how these updates impact your projects, now is the time to start the conversation.
