The September 15th dinner event was held at the Chapter Certification Center in Sacramento. The theme of the evening was a "Taco Truck Takeover", with food provided by the amazing folks from California Street Tacos.
Delicious food from California Street Tacos.
The evening's guest speaker was Chapter member Ali Banaeipour, PhD, PE with AECOM. Recent updates to ACI 318 address shear design, reinforcement anchorage, seismic walls, mechanical splices, sustainability, and performance-based wind design. ACI 318-25 introduces a broad set of changes that will affect how structural engineers design and detail concrete members. In a presentation titled “ACI 318-25: Key Changes Practicing Engineers Need to Know,” Ali Banaeipour, PhD, PE, with AECOM, organized the revisions around several practical design decisions, with particular emphasis on shear, development length, anchorage, seismic design, and reinforcement detailing.
Ali Banaeipour, PhD, PE
New Shear Provisions Affect Member and Foundation Design
One of the most significant updates concerns one-way shear. ACI 318-25 retains the size-effect and longitudinal-reinforcement factors introduced in the 2019 edition but adds a lower-bound provision for the concrete contribution to shear strength. The change is intended to prevent the combined effects of member size and low reinforcement ratios from producing a disproportionately low calculated concrete shear capacity.
The lower-bound provision does not apply to members subjected to net axial tension or to members designated for special seismic-frame applications. Engineers must therefore determine whether those exceptions apply before using the revised calculation.
The code also adds provisions for certain shallow foundations that are continuously supported by soil and may be analyzed as rigid. Under specified conditions, the new provisions may also apply to pile caps or pile mats with closely spaced piles. The change recognizes that continuous support alters the load path compared with the free-spanning specimens that formed the basis of earlier shear provisions.
A simplified example presented during the discussion illustrated the potential effect. For a lightly reinforced member, the calculated concrete shear contribution increased from approximately 28.2 kips under the 2019 provisions to 45.5 kips under the 2025 lower-bound provision. When the shallow-foundation conditions were also assumed to apply, the calculated contribution increased to approximately 91.1 kips. The example was intended to demonstrate the significance of the change, not to replace required checks for flexure, punching shear, crack control, or other applicable limit states.
Development Length Rules Change for Hooked and Headed Bars
ACI 318-25 also revises the development-length provisions for hooked bars. The code returns to an equation like the expression used in ACI 318-14, while adding a new bar-size factor. The factor increases for larger bars, reflecting test data indicating that larger bars may require longer development lengths.
The revised provisions also retain a benefit for confining reinforcement, but that benefit remains limited to No. 11 bars and smaller. The presentation noted that experimental work involving larger bars indicated improved anchorage behavior when confinement was provided, even when the confinement did not meet all current prescriptive requirements. That behavior is not fully reflected in the current provisions for No. 14 and No. 18 bars.
For headed bars, the new code modifies the development-length equation and changes the treatment of parallel ties. Rather than the previous all-or-nothing penalty, ACI 318-25 uses a bar-spacing-based factor that provides designers with greater flexibility. However, the provisions still do not fully incorporate the cited research involving larger headed bars.
New Requirements for Groups of Bars in Tension
Another major addition addresses the anchorage of groups of bars in tension, particularly in foundations and similar connections. The new provisions require engineers to check concrete breakout strength in addition to development length.
When tensioned bars are closely spaced, their individual breakout surfaces can overlap, reducing the effective concrete breakout capacity of the group. The revised approach therefore treats the strength of the group as a combination of concrete breakout resistance and qualified steel reinforcement contributions.
Reinforcement may count toward the steel contribution only when it satisfies specified requirements. The presentation referenced configurations such as hooked, or “candy cane,” bars with defined geometry and spacing. For seismic applications, the discussion identified a lower strength-reduction factor of 0.65, reflecting the limited available data on the cyclic behavior of these connections.
Post-Installed Reinforcing Bars and Anchors
ACI 318-25 references ACI 355.5 as a qualification basis for post-installed reinforcing-bar systems. The code distinguishes between systems intended to transfer anchor forces and those intended to develop reinforcing bars, recognizing that the qualification requirements should reflect the intended load-transfer mechanism.
The code also changes the interaction checks for anchors subjected to combined tension and shear. Under the previous approach, tension and shear failure modes involving different materials could be combined in a single interaction check. The revised provisions separate concrete interaction from steel interaction so that each calculation better corresponds to the failure mechanisms acting together.
Additional anchor provisions recognize reliability and redundancy in connection design. Engineers must consider whether a viable load path remains after the failure of an anchor. The code also provides relief for certain connections subjected to overturning moments when the geometry allows compression to help restrain potential concrete breakout surfaces.
Revisions to Seismic Wall Design
Several updates affect seismic design, particularly reinforced-concrete structural walls. ACI 318-25 changes the basis for amplifying shear demand: instead of applying amplification to the final shear demand, engineers are directed to apply it to the horizontal earthquake shear component. The revised approach uses separate factors for flexural overstrength and dynamic response.
The code also adds an exception that may permit a strength-reduction factor of 0.75 instead of 0.60 when specified overstrength and amplification conditions are satisfied. The change is intended to improve consistency between amplified design demands and capacity-design procedures.
Other wall provisions address compression flanges, including a cap on the concrete compressive strength used in a specified calculation and an additional factor that can account for the beneficial effects of a compression flange under defined geometric conditions.
The presentation further noted updates affecting high-strength materials and cyclic loading. These revisions reflect the need to account for modern concrete and reinforcing steel strengths as well as the behavior of walls subjected to repeated displacement demands during earthquakes.
New Classification System for Mechanical Splices
ACI 318-25 replaces the previous Type 1 and Type 2 designations for mechanical splices with three new classes. Class L is intended for limited applications without anticipated yielding of the splice or coupler. Class G covers general use with limited inelastic demand, while Class S addresses substantial inelastic and cyclic demands.
The revised classifications are based in part on reverse-load testing that showed differences in the performance of mechanical couplers under cyclic demands. The new system is intended to provide a clearer connection between the expected behavior of a splice and the application in which it may be used.
Additional Materials and Design Options
The new edition expands material options by recognizing additional cementitious materials, including ground-glass pozzolans. It also adds sustainability and resilience provisions in Appendix C. Those provisions apply when invoked by the owner or authority having jurisdiction; they do not impose a universal carbon limit.
Appendix B adds a framework for performance-based wind design of concrete structures. The provisions establish explicit performance objectives and include requirements related to advanced analysis and independent review. They are intended to work with the structural loading provisions of ASCE 7.
What Engineers Should Review
The ACI 318-25 changes will require engineers to revisit several recurring design workflows. Key areas for review include one-way shear calculations, shallow-foundation and pile-cap assumptions, development lengths for large hooked and headed bars, breakout checks for groups of bars in tension, post-installed reinforcing-bar qualifications, seismic wall shear amplification, and mechanical-splice classifications.
Although some provisions may increase calculated capacity or provide additional design flexibility, the updates also introduce new checks and qualification requirements. Engineers should therefore evaluate the complete load path and confirm that all applicable requirements—including strength, detailing, seismic, anchorage, and serviceability provisions—are satisfied.
Technical updates and tasty cuisine were provoided to event attendees.
The Chapter would like to thank California Street Tacos, guest speaker Ali Banaeipour, and all those in attendance for making this a sucessful and enjoyable evening.