What’s Changed in the American Concrete Institute 318 Code Update?
ACI’s “flagship” concrete building codes are updated with sustainability, seismic, shear friction, deep foundation, and performance-based wind design guidance.
A GPRS Project Manager conducts a concrete scan as part of the rehab of a 38-story skyscraper in Jacksonville, Florida.
ACI 318-25 Marks the First Significant Structural Concrete Code Revision in Eight Years
Advancements in engineering design, evolving construction practices, and the emergence of sustainable building materials and practices have prompted the American Concrete Institute (ACI) to release a comprehensive update to its structural concrete code, ACI 318. The print edition of ACI 318-25 became available on July 9, 2025. A continuously updated digital version, ACI Plus, is also accessible.
“As codes evolve, so must our understanding of existing structures. GPRS plays a vital role in this process by delivering accurate subsurface and structural visualization to inform smarter, safer design modifications and rehabilitation projects.”
— Matt Mikolajczyk, PE (Ohio & Michigan), GPRS Director of Reality Capture
What Is ACI 318?
ACI 318, the Building Code for Structural Concrete, outlines the minimum standards for materials, design, and detailing of structural concrete buildings and, where applicable, nonbuilding structures.
ACI refers to this document as its “flagship,” developed through a rigorous consensus process. It encompasses cast-in-place, precast, shotcrete, plain, non-prestressed, prestressed, and composite construction methods and structural systems.
Why Was ACI 318 Updated?
The previous version, ACI 318-19, was released in 2019. Historically, ACI issued updates every three years. However, the expected 2022 revision was postponed when the committee opted to reapprove the 2019 edition as 318-19 (22). The decision was based on the scope of technical changes required, which were instead incorporated into the full-scale revision now known as ACI 318-25.
ACI 318-25: Building Code for Structural Concrete – Code Requirements and Commentary was initially released to ACI Plus members in the spring and is now available for general purchase.
What Has Changed in ACI 318-25?
Key updates include:
• Seismic Design
• Shear Friction
• Deep Foundations
• Sustainability
• Performance-Based Wind Design
New York City experienced an earthquake on August 3, 2025. The quake’s center was located in Hasbrouck Heights, New Jersey and was measured at a 3.0 magnitude and was felt in New Jersey, New York, and Pennsylvania. 318.25 clarifies design requirements for seismic engineering.
Seismic Design
Many revisions in ACI 318-25 aim to clarify existing provisions. Seismic design updates respond to questions raised after the 2019 release, particularly from engineers in California and the Pacific Northwest, regions with elevated seismic risk.
“The changes in seismic design for 318-25 include a great deal of detailed clarifications on what was in 318-19. [A lot of what] we changed in 318-25 will help seismic engineers in those high seismic regions get some designs that are a little more efficient,” said Greg Ziesler, senior engineer and ACI 318 committee secretary, in an interview with Engineering News-Record.
Deep Foundations
ACI 318-25 expands on deep foundation provisions first introduced in 318-19. That version marked the initial inclusion of deep foundations in the code, drawing from the International Building Code. The new edition consolidates IBC and ACI standards into a unified framework.
Shear Friction
Clarifications to shear friction guidance address concerns raised by a federal agency regarding the broad application of the 318-19 provisions. Ziesler noted that the committee worked to resolve inconsistencies and refine the standards.
Structural engineers have welcomed the updates, particularly those related to pile caps and rafts on piles. Clause 13.4.6.8 introduces an exemption from the size effect for two-way shear under defined conditions, along with specifications for center-to-center spacing, minimum edge distances (13.4.6.1), and embedment depths (13.4.6.3). The one-way shear equation in 13.4.6.8 has also been simplified.
Structure Magazine highlights significant changes in chapters 17 and 25 concerning concrete anchorage. Five major updates include:
• Revised safety factors
• Introduction of a beneficial overturning moment term
• Separation of concrete and steel failure modes in interaction equations
• Use of Chapter 25 factors for existing reinforcement
• Clarifications on reinforcing bars as anchor reinforcement
Some anchorage updates are administrative, involving the relocation of sections and equations for consistency. Others revise equations for concrete failure modes and distinguish between redundant and non-redundant fastenings, offering capacity benefits for the latter.
Section 17.6.2.7 introduces a strength-enhancing factor and equation for concrete breakout in tension, accounting for the compressive toe of an overturning moment. Though related to strut behavior, its function is distinct.
Additional updates clarify the use of reinforcing bars as anchor reinforcement. These allow engineers to bypass concrete breakout calculations by substituting steel calculations for specific reinforcing bars. Changes in 17.5.2.1.1 and 17.5.2.1.2 establish subsections for tension and shear breakout. Section 17.5.2.1.3 addresses anchor reinforcements not aligned with the load, while 17.5.2.1.4 specifies when shear friction calculations from section 22.9 should be applied. Multiple revisions also affect design requirements for connections between concrete structural members, including updated equations for hooked-bar and headed-bar development lengths.
Sustainability
One of the most discussed additions to ACI 318-25 is the sustainability supplement. Rather than prescribing sustainable material practices, it provides a framework for meeting local and state mandates.
“This is more that the local jurisdiction says you must [meet] this GWP [Global Warming Potential], so how do you meet that? We now have a framework to meet those requirements,” Ziesler explained.
The supplement includes guidance for achieving low-carbon and carbon-neutral goals during design and planning. It also offers recommendations for constructing resilient concrete structures capable of withstanding natural disasters. These recommendations differ from existing code provisions and serve as a reference for navigating sustainability regulations.
“These are different types of loads, not in the body of the code. So now if someone says you have to do this, you have a body of knowledge to do it,” Ziesler told ENR.
Materials
Although ACI 323, part of the 318-25 update, addresses materials such as low-carbon concrete, the institute aimed to provide sustainability guidance without introducing new standards.
“We still lean on local jurisdictions to set the limits, but there are some default options in there, based on the size of the project and what sort of targets you have to meet for GWP. One reason it’s in a separate standard is that it’s not the law of the land until a local jurisdiction adopts it,” said ACI’s Mike Tholen.
Performance-Based Wind Design
Similar to the sustainability supplement, the performance-based wind design guidance is not part of the core code. It serves as a resource for engineers designing tall and supertall concrete structures.
Unlike the American Society of Civil Engineers’ formal pre-standard for the 2019 code, ACI’s appendix does not mandate wind tunnel or simulation testing, which can be cost-prohibitive. Ziesler noted that such testing often leads to performance-based design decisions.
“Performance-based wind design… is a response to the industry from committee members. We have a lot of committee members who do tall and supertall buildings,” Ziesler said. “It’s not an appendix to the code; it's not in main body of code; it only applies when you do it.”
Mikolajczyk emphasized the importance of understanding the updates:
“Structural engineers need to be aware of the information contained in this concise, high-level summary of the critical updates in ACI 318-25: particularly regarding anchorage, seismic detailing, deep foundations, and sustainability considerations.”
ACI 318 provides the technical specifications and requirements for concrete construction. GPRS delivers the scanning, imaging, and reality capture services necessary to safely cut, core, and anchor concrete structures. These services support accurate as-built documentation for renovation, expansion, and lifecycle management – from preconstruction through demolition.
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