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New engineering design processes, updated construction data, and the availability of innovative, sustainable materials have driven the American Concrete Institute to update is structural concrete code, known as ACI 318. The print version of the new code became available on July 9, 2025. The digital version – ACI Plus – is updated “continuously” and is also available.
“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.” -- GPRS Director of Reality Capture, Matt Mikolajczyk, PE (Ohio & Michigan)
What is ACI 318?
The Building Code for Structural Concrete, published by the American Concrete Institute, sets “minimum requirements for the materials, design, and detailing of structural concrete buildings, and, where applicable, nonbuilding structures.”
The organization refers to ACI 318 as its “flagship document,” arrived at “through an extensive consensus process” that covers cast-in-place, precast, shotcrete, plain, non-prestressed, prestressed, and composite construction and structural systems.
Why was ACI 318 Updated?
The last update to ACI 318 took place in 2019 (ACI 318-19). Prior to the 2019 update, the institute released regular updates approximately every three years. However, the anticipated 2022 update was scuttled when the committee instead opted to reapprove the 2019 version, (318-19 (22)), noting that the necessary updates would result in technical changes to the code itself, and that those changes would be incorporated into a subsequent wholesale update, which became ACI 318-25.
The new update, ACI 318-25: Building Code for Structural Concrete – Code Requirements and Commentary was released exclusively to ACI Plus members in the spring, and is now available for anyone to purchase.
What does ACI 318-25 Change from 318-19?
The main updates in 318-25 include:
- Seismic Design
- Shear Friction
- Deep Foundations
- Sustainability
- Performance-Based Wind Design
Seismic Design:
As is often the case, many of the changes in ACI 318-25 are to provide clarity and update existing sections of the 318 codes. New seismic design information that first made its appearance in 2019 caused a raft of clarification questions from California and the Pacific Northwest – some of the most at-risk areas for seismic activity.
“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,” Greg Ziesler, senior engineer and ACI 318 committee secretary, told Engineering News-Record.
Deep Foundations:
Concrete professionals, designers, engineers, and developers will also find an expanded section on deep foundations, building on work begun in 318-19, which was the first time deep foundations were mentioned in the code, when the institute attempted to include provisions from the International Building Code. ACI 318-25 consolidates the IBC and ACI deep foundation standards into one document.
Shear Friction:
Another update provides guidance on shear friction. 318-19 prompted a federal agency to reach out regarding the roadblocks it presented, so ACI’s committee strove to clarify the standards to avoid too broad an application and to “address discrepancies,” according to Ziesler.
Structural engineers are hailing the updates to deep foundation and shear guidance, particularly the sections on pile caps and rafts on piles: included in clause 13.4.6.8 with the exemption from the size effect – under specific conditions – for two-way shear, with specifications on center-to-center spacing measurements for rafts on piles and pile caps, 13.4.6.1’s minimum edge distance and 13.4.6.3’s embedment depths for piles. Plus, a simplification of the one-way shear equation in 13.4.6.8.
And Structure Magazine cites important changes in chapter 17 & 25’s concrete anchoring specification updates. They tagged five “major updates” in anchorage:
- Updates to safety factors
- Introduction of a beneficial overturning moment term
- Beneficial separation of concrete and steel failure modes in interaction equations
- Permissible use of new Chapter 25 factors on existing reinforcement
- Clarifications on the use of reinforcing bars as anchor reinforcement
Some items in the anchoring updates are administrative – moving sections and some equations for document consistency, and others update equations for concrete failure modes, and include an important differentiation between redundant and non-redundant fastenings, “providing a capacity benefit for fastenings that are considered redundant.”
There is also a new strength-increasing factor and equation in section 17.6.2.7 regarding concrete breakout in tension to account for “the positive influence of the compressive toe of an overturning connection moment.” While related to concrete strut behavior, its function differs.
And updates to that clarify the use of reinforcing bars as anchor reinforcements allow you to omit concrete breakout calculations by replacing them with steel calculations for special reinforcing bars, and changes in 17.5.2.1.1 and 17.5.2.1.2 create anchor reinforcement subsections regarding tension and shear breakout. 17.5.2.1.3 clarifies requirements for anchor reinforcements that are not parallel to the load, and 17.5.2.1.4 gives specific requirements on when to use shear friction calculations included in section 22.9. There are also multiple changes to the connection between “concrete structural members” regarding design requirements and updated hooked-bar and headed-bar development length equations.
Sustainability:
Perhaps the most talked-about update in ACI 318-25 is the supplemental sustainability guide. Rather than provide guidance for sustainable material use and best practices, the supplement focuses on meeting state and local ordinances and requirements.
“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 said.
In the supplement, you will find items about meeting low-carbon, and carbon-neutral goals in the design & planning phase. It also includes additional guidance for building more resilient concrete structures – to withstand natural disasters – and provides suggestions as to which types of structures may be best suited to do so. This guidance varies from what already exists in the code, to provide background for those planning in the maze of sustainability initiatives.
“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 Are Not Dismissed
While ACI-323 (part of the 318-25 update) does cover materials, specifically low-carbon concrete, ACI was searching for a way to provide sustainability guidance that did not require new standards, according to ACI’s Mike Tholen. Tholen told ENR that “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.”
Performance-Based Wind Design:
Like the sustainability updates, including performance-based wind design guidance is not part of the code standard, but acts as a primer for those building tall and supertall concrete structures.
The American Society of Civil Engineers (ASCE) provided a more formal “pre-standard” for the 2019 code, whereas the ACI’s appendix on the matter is less structured. For instance, it does not require wind tunnel or computer simulations, which add costs. Ziesler noted that when you’re putting a tall or supertall design in a wind tunnel, you’re most likely going to pivot to a performance-based design. ACI’s purpose in offering what ENR refers to as “an optional standard for wind,” is making sure everyone involved in a design can feel confident of its ability to perform, specifically regarding detailing requirements that would only come into play for tall and supertall construction.
“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 shared. It’s not an appendix to the code; it's not in main body of code; it only applies when you do it.”
GPRS’ Mikolajczyk, who is a structural engineer licensed in Ohio and Michigan, shared that, “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.”
The Building Code for Structural Concrete provides you with the specific and technical requirements, specifications, and guidelines for building with concrete. GPRS provides you with the concrete scanning, imaging, and reality capture solutions you need to cut, core, and anchor your concrete structures safely and give you the accurate as-builts you need to renovate, expand, or maintain your buildings through their entire life cycle – from preconstruction through demolition.
Concrete scanning & imaging services are just one of the ways GPRS Intelligently Visualizes The Built World® to help you plan, build, and manage better.
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