ANDREW TAYLOR, PHD, S.E., FACI

GREG ZEISLER

The American Concrete Institute (ACI) recently published the 2025 edition of ACI CODE-318, “Building Code Requirements for Structural Concrete—Code and Commentary.” This latest version includes numerous changes, such as refinement of the one-way shear provisions introduced in ACI CODE-318-19, alignment with other ACI codes (e.g., ACI/PCI CODE-319-25, ACI/PTI CODE-320-25, ACI CODE-440.11-25), coordination with ASCE/SEI 7-22, and improved and clarified construction requirements.

There’s a new appendix for sustainable and resilient design, a new appendix for performance-based wind design, improvements to development length equations for hooked and headed bars, refinements to strut-and-tie modeling, updated prestressed concrete provisions, modified structural integrity requirements, post-installed reinforcing bar provisions, and clarifications to anchor reinforcement requirements.

Major Revisions

One major revision in ACI CODE-318-25 was to clarify and improve the efficiency of the one-way shear equations introduced in ACI CODE-318-19. The revisions in ACI CODE-318-25 added a lower bound for the value of the concrete contribution to shear strength. This revision aligns the design equations more closely with the extensive research data used for development of the one-way shear equations. A related change is the reversion to familiar ACI CODE 318-14 one-way shear equations for certain classes of concrete members: cantilever retaining walls, basement walls, pile caps supported on closely spaced piles and shallow foundations that can reasonably be assumed to be rigid.

Another significant revision is related to the equation introduced in ACI CODE-318-19 for development lengths of hooked bars. Two actions were taken by the committee. The first was a comprehensive review of hooked-bar test data, coupled with a review of in-service performance of hooked bars that was designed using earlier versions of ACI CODE-318. Second, the committee reviewed new test data for hooked No. 14 and No. 18 bars. The committee concluded that hooked-bar development length equations from ACI CODE-318-14 and earlier were appropriate, except the older equations didn’t adequately represent the data for No. 10 and larger bars. Thus, ACI CODE-318-25 contains the hooked-bar development length equation from ACI CODE-318-14 with a new modifier for bar size.

Like the major revision for hooked-bar development length, the committee reviewed test data for headed-bar development length. The headed-bar development length equation from ACI CODE-318-19 was adjusted in ACI CODE-318-25, which slightly reduced the headed-bar development length.

Sustainability, Resilience and Wind

In addition, a new appendix on sustainability and resilience was developed. The new appendix is intended to be used as a voluntary framework on projects where an owner or building authority wishes to implement improved sustainable design and construction practices. The appendix doesn’t include quantified limits on equivalent atmospheric carbon emissions, as those limits are better determined on a regional or local basis. However, the appendix commentary provides many useful references on sustainable design and construction practices for reinforced concrete structures.

A new appendix for performance-based wind design (PBWD) is included in ACI CODE-318-25. This optional appendix provides the designer with guidelines and requirements for reinforced concrete structures designed using the “ASCE Prestandard for Performance-Based Wind Design.”

Changes to the Analysis Section

These changes clarify the cracked concrete section properties that should be used for analysis. Simplifications for determining the design depth from extreme compression fiber to center of reinforcement for non-square column sections also are included. New requirements for application of patterned live loads on elevated slabs that contain large internal voids (e.g., embedded ducts) have been added to the new code.

Detailing requirements for members designed using strut-and-tie modeling were revised to help the designer determine reinforcement requirements in areas outside the assumed strut-and-tie model (i.e., when the member is larger than the size of the model used to design the section).

Additional Concrete Concerns

Numerous changes were made in the prestressed concrete sections of the code, with the main two being changes in the required concrete strength at initial transfer of prestress and removal of the approximate shear method. Both changes were made to align the code with current construction and design practice.

Structural integrity requirements evolved based on laboratory data for perimeter beams that suggested improved detailing would reduce the chance of disproportionate collapse if a perimeter column were lost.

Provisions for headed deformed stirrups also were added to the code. Requirements include rules for detailing headed deformed stirrups and definitions of locations where headed deformed stirrups may be used.

Splice and Anchorage Provisions

Major changes to the mechanical and welded splice provisions were made in several locations in the code. These changes primarily affect seismic detailing of mechanical and welded splices. However, some of the changes may affect mechanical and welded splices in non-seismic applications.

Regarding anchorage to concrete, clarifications have been added to the provisions for supplemental reinforcement at anchors. The provisions for shear and tension interaction of anchors also have been clarified. Anchor capacity calculations now include a modifier that may increase the capacity of an anchor when the anchor is located within a concrete compression field. Strength-reduction factors for anchors were migrated to Chapter 21, where all other strength-reduction factors are listed.

Related to the topic of anchorage to concrete, provisions have been added that require checking for a tension breakout cone failure of a group of closely spaced reinforcing bars when the group is loaded in tension. Post-installed reinforcement systems must now be qualified in accordance with ACI CODE-355.5-24: “Post-Installed Reinforcing Bar Systems in Concrete—Qualification Requirements and Commentary.”

Interface shear and shear friction provisions have been clarified at several locations in the code, with the aim of improving the consistency of the provisions. The provisions for steel-fiber-reinforced concrete have been updated to align them with the modified shear provisions adopted in ACI CODE-318-25.

Deep Foundations and Seismic Design

Continuing a process that started with the 2019 edition of the code, provisions for concrete deep foundations have been expanded and clarified. The objective of these changes is to provide a unified, complete and consistent set of design and detailing provisions for all types of concrete deep foundations within ACI CODE-318-25.

In ACI 318 CODE-318-25, numerous changes were made to seismic design provisions to clarify requirements that were added in ACI CODE-318-19. The most significant of these include design strength of diaphragms, detailing of special moment frames, seismic shear force amplification requirements for special walls, special wall reinforcement detailing requirements, special wall shear strength calculations and redistribution of shear forces among coupling beams in ductile coupled shear walls.

Andrew Taylor, PhD, S.E., FACI, is technical director, KPFF Consulting Engineers, and chair, ACI 318 building code committee for ACI CODE 318-25; email: [email protected]. Greg Zeisler is engineer, ACI, secretary ACI 318 building code committee for ACI CODE 318-25; email: [email protected].