The purpose of this article is to discuss some of the most important changes introduced in ACI 318-19 compared to ACI 318-14. Once the NCEES exam specifications are updated in 2027, ACI 318-19 will become the referenced standard for concrete design questions on the Civil PE exam.
ACI 318, “Building Code Requirements for Structural Concrete,” establishes the minimum requirements for the design and construction of structural concrete used in buildings and other structures. It covers materials, structural systems and analysis, strength and serviceability requirements for individual members such as beams, columns, walls, slabs, footings, and diaphragms, and detailing provisions for structures assigned to different seismic design categories, along with anchoring to concrete.
Although the overall scope of ACI 318 has remained largely unchanged, several important procedures have been revised in the 2019 edition. Some changes are relatively minor and involve modifications to coefficients or numerical values in certain equations, while others fundamentally change the procedures used to determine the required strength of concrete members.
Summary of the Major Changes
In the following sections, we will discuss some of the important changes introduced in ACI 318-19. We will not cover every single modification in detail. Instead, we will focus on the high-level changes that may affect the relevant Civil PE Exams. The goal is to provide a high-level overview of the changes and highlight areas that may become important for future structural PE exam takers – also the construction PE exams, since this reference has recently been added to the Construction Civil PE reference list.
High-Strength Reinforcement
One of the most notable additions in ACI 318-19 is the introduction of design provisions for high-strength deformed reinforcement, with yield strengths of 80 ksi and 100 ksi. In ACI 318-14, design provisions were largely developed around Grade 60 reinforcement (fy ≤ 60,000 psi). ACI 318-19 extends several chapters, including development length, minimum reinforcement, and shear design, to explicitly address these higher-strength bars.
This is a good example of a new item, as described in the second section of this article, rather than a simple numerical revision. PE Candidates should not expect every problem to use 80- or 100-ksi reinforcement, but should understand that the code now formally accounts for it, and that certain equations now include a reinforcement grade factor as a result.
Minimum Reinforcement Requirements
The minimum flexural reinforcement requirements for nonprestressed slabs were simplified in ACI 318-19. In ACI 318-14, the minimum reinforcement ratio depended on the reinforcement grade, using a two-tier approach. In ACI 318-19, a single ratio applies to slabs regardless of reinforcement grade, as summarized below.
| Provision | ACI 318-14 | ACI 318-19 |
|---|---|---|
| Minimum flexural reinforcement, As,min (nonprestressed slabs) | fy < 60,000 psi: As,min = 0.0020 Ag fy ≥ 60,000 psi: greater of 0.0018(60,000/fy)Ag or 0.0014 Ag | As,min = 0.0018 Ag (§7.6.1.1), regardless of reinforcement grade |
The development length provisions in Chapter 25 of ACI 318-19 were revised to accommodate the new high-strength reinforcement discussed above. The most notable addition is a new reinforcement grade factor, ψg, which did not exist in ACI 318-14.
| Reinforcement Grade | ψg (Reinforcement Grade Factor) |
|---|---|
| fy ≤ 60 ksi | 1.00 |
| fy = 80 ksi | 1.15 |
| fy = 100 ksi | 1.30 |
Interpolation is used for reinforcement grades between 60 ksi and 100 ksi. The tension development length equation for deformed bars, found in Table 25.4.2.3 of ACI 318-19, now directly incorporates this grade factor, along with the previously existing factors for reinforcement coating, size, and casting location. A similar concrete strength factor, ψc, was also added to the hooked bar development length equation in §25.4.3.1.
Shear Design Provisions
The shear design provisions in Chapter 22 experienced one of the most significant procedural changes between the two editions. In ACI 318-14, a single simplified equation was commonly used to determine the nominal shear strength provided by concrete, Vc, for nonprestressed members without significant axial load.
ACI 318-14 (simplified equation):
\(V_c=2\lambda\sqrt{f_c^{‘}}b_wd\)
ACI 318-19 replaces this single equation with a set of three equations in Table 22.5.5.1. Which equation governs now depends on whether the area of shear reinforcement provided, Av, meets or exceeds the minimum required area, Av,min.
| Condition | ACI 318-19 Equation (Table 22.5.5.1) |
|---|---|
| Av ≥ Av,min — Equation (a) | \(V_c=2\lambda\sqrt{f_c^{‘}}b_wd\) |
| Av ≥ Av,min — Equation (b) | \(V_c=8\lambda(\rho_w)^{1/3}\sqrt{f_c^{‘}}b_wd\) |
| Av < Av,min — Equation (c) | \(V_c=\left[8\lambda_s\lambda(\rho_w)^{1/3}\sqrt{f_c^{‘}}+\dfrac{N_u}{6A_g}\right]b_wd\) |
The size effect factor, λs, introduced in §22.5.5.1.3, is the key new variable candidates should recognize:
\(\lambda_s=\sqrt{\dfrac{2}{1+\dfrac{d}{10}}}\leq1.0\)
This factor only applies to members without at least the minimum required shear reinforcement, such as slabs, footings, and lightly reinforced deep beams, and it only reduces Vc once the effective depth, d, exceeds 10 inches. Physically, it accounts for experimental observations showing that the shear strength per unit area does not increase in direct proportion with member depth once a member has little or no shear reinforcement.
“The introduction of the size effect factor, λs, is one of the most exam-relevant procedural changes in ACI 318-19, since it can noticeably reduce Vc for slabs and footings compared to ACI 318-14.”
The maximum shear strength:
\(V_c=5\lambda\sqrt{f_c^{‘}}b_wd\)
This factor only applies to members without at least the minimum required shear reinforcement, such as slabs, footings, and lightly reinforced deep beams, and it only reduces Vc once the effective depth, d, exceeds 10 inches. Physically, it accounts for experimental observations showing that the shear strength per unit area does not increase in direct proportion with member depth once a member has little or no shear reinforcement.
“The introduction of the size effect factor, λs, is one of the most exam-relevant procedural changes in ACI 318-19, since it can noticeably reduce Vc for slabs and footings compared to ACI 318-14.”
The maximum shear strength:
\(V_c=5\lambda\sqrt{f_c^{‘}}b_wd\)
This equation was retained in §22.5.5.1.1 as an upper bound regardless of which equation governs. The shear strength equations for ordinary and special reinforced concrete shear walls were also coordinated in ACI 318-19, and new hanger reinforcement provisions were introduced for members supporting other members in tension.
Anchoring to Concrete
ACI 318-19 introduces design provisions for two new anchor types that did not exist in ACI 318-14: screw anchors and shear lugs. Candidates preparing for questions on anchoring to concrete, found in Chapter 17, should be aware that these are now recognized anchor types with their own design provisions, in addition to the cast-in and post-installed anchors already covered in ACI 318-14.
Foundations
The foundations chapter received extensive additions in ACI 318-19. ACI 318-14 addressed shallow foundations in relatively limited detail. ACI 318-19 significantly expands this chapter to include deep foundation design provisions, importing concepts previously found only in the IBC and ASCE 7. This is important since it broadens the overlap between ACI 318 and geotechnical design topics such as pile caps and drilled shafts.
It is worth noting that the size effect factor, λs, discussed in the shear design section above, also applies to one-way shallow foundations and two-way isolated and combined footings, which can meaningfully reduce the calculated shear capacity of a footing compared to an ACI 318-14 design.
Shotcrete Provisions
ACI 318-19 also introduces new shotcrete provisions, which were not addressed as a distinct construction method in ACI 318-14. These were part of IBC 2018, now they are removed from IBC 2024. While this topic is less likely to be tested in depth on the Civil PE exam, candidates should be aware that shotcrete is now explicitly recognized as a placement method within the code.
Seismic Provisions
Chapter 18, which governs the design of structures assigned to intermediate and special seismic design categories, experienced some of the most significant changes in ACI 318-19. The following is a high-level summary of the major changes. This list is intentionally kept short for convenience; however, we encourage you to use it as a starting point to review the changes in more detail:
- Important changes to the design of special shear walls, including coordination with the general shear strength equations discussed above.
- Additional changes to seismic detailing requirements for special moment frames.
- Coordination between the shear strength equations for ordinary and special shear walls, which were previously treated somewhat independently.
- Updated development length and hooked bar provisions, discussed earlier in this article, which also apply to seismic detailing of beam-column joints.
When considering all of these changes together, Chapter 18 requires significant attention from candidates preparing for both the Structural Civil PE Exam and the California Seismic Principles Exam, given the combined impact of these updates on concrete seismic-force-resisting systems.
Deflection Calculations
ACI 318-19 also introduces a new equation for the effective moment of inertia, Ie, used in deflection calculations for nonprestressed members. This is a more incremental change compared to the shear and seismic provisions discussed above, but candidates should be aware that the Ie equation referenced on the exam should match the edition of the code specified in the exam specifications at the time of testing.
Additional Changes at a Glance
Here is a table that includes most of the other important changes covered in ACI 318-19. We recommend going through it item by item and referring to the relevant section of ACI 318-19 for each one, since reading the actual code language alongside this summary will help with retention. This table is important and should not be skipped.
| Topic | Clause | Effect on PE Candidate |
|---|---|---|
| Two-way slab analysis methods | §6.2.4.1 | DDM/EFM no longer mandatory, but still usable — don’t assume removal |
| Slab tension-controlled requirement | §7.3.3.1, Table 21.2.2 | Replaces flat εt ≥ 0.004; use tension-controlled table instead |
| Minimum flexural reinforcement, slabs | §7.6.1.1 | Single value As,min = 0.0018Ag, all grades — easy recall item |
| Shrinkage & temp. reinforcement | §24.4 | Reduction for fy > 60,000 psi removed — more steel required than before |
| Structural integrity reinf., one-way slabs | §7.7.7 | New requirement — know the 1/4 rule and anchorage/splice rules |
| Two-way slab min. thickness table | Table 8.3.1.1 | Updated for Grade 80 bars — check which fy column applies |
| Opening effect on two-way shear | §8.5.4.2 | Exclusion distance cut from 10h to 4h — more openings trigger a shear check |
| Minimum flexural reinf., two-way slabs | §8.6.1, §8.6.1.2 | New equation applies when shear stress exceeds threshold — extra calc step |
| Shearheads | (removed, was §22.6.9) | No longer a valid design option — don’t select it as an answer |
| Cantilever retaining walls | §11.1.4 | New explicit design path via Ch. 22–13 |
| Wall/floor intersecting elements | §11.2.4.2 | New min. f’c check at floor-wall joint (0.8f’c of wall) |
| Wall shear strength upper bound | §11.5.4.5 | Revised Vc cap — new value to remember |
| Foundation scope | §13.1 | Expanded to include retaining walls — clarifies applicability |
| Size effect factor exemption, footings | §13.2.6.2 | λs may be neglected for shallow foundations — raises allowable Vc |
| Deep foundations | §13.4 (new) | Entirely new design section |
| Post-installed anchor resetting | §17.1.3 | New prohibition — cannot remove/reset a mechanical anchor |
| Adhesive anchor install timing | §17.2.2 | New min. concrete age of 21 days before installation |
| Reinforcement used as anchorage | §17.1.6 | Must check breakout or provide anchor reinforcement (§17.5.2.1) |
| Screw anchors | §17.3.4 | New anchor type — same method as expansion/undercut anchors, new parameters |
| Shear lugs | §17.5.2.6, §17.11 | New anchor type — min. 4 separate anchors required for tension |
| Lightweight concrete factor λ | §19.2.4.1 | New simplified option based on density |
| Water exposure classes | Table 19.3.2.1 | W0 split into W0/W1; old W1 renamed W2 — know new terminology |
| Sulfate exposure, Class S3 | Table 19.3.2.1 (Option 2) | New stricter alternative (lower w/cm, higher f’c) |
| Shotcrete durability provisions | Ch. 19 (new) | First-time recognition of shotcrete as a material |
| No. 20 reinforcing bars | §20.2.1.3 | Excluded from use despite ASTM listing — don’t specify these |
| A615 reinforcement in high-seismic use | §20.2.2.5 | Grade 80/100 A615 still NOT permitted in high-seismic applications |
| Cover for deep foundation members | Table 20.5.1.3.4 (new) | New reference table |
| One-way shear strength, Vc | Table 22.5.5.1 | 3 new equations replace 8 — major new procedure, learn it well |
| Size effect factor λs | §22.5.5.1.3 | Key new variable — reduces Vc when d > 10 in. and Av < Av,min |
| Torsional strength, Tn | §22.7.6.1(b) | Equation corrected — verify exact form in code text |
| Reinforcement grade factor ψg | Table 25.4.2.5 | New factor in straight-bar development length calc |
| Hooked bar development length | §25.4.3.1(a) | db raised to power 1.5; new ψo, redefined ψc, modified ψr |
| Headed bar development length | §25.4.4 | Clear spacing cut from 4db to 3db; new ψp, ψo, ψc factors |
| Excess reinforcement factor | §25.4.10.1, 25.4.10.2 | No longer allowed for hooked/headed/mechanical anchorage or SDC C–F |
| Splices, Grade 100 reinforcement | §25.5.1.5 | New transverse reinforcement requirement |
| Test load combinations | §27.4.6 (new) | Three new load combinations aligned with ACI 437.2 |
| Deflection waiver, load testing | §27.5.3.6 | New threshold (larger of 0.05 in. or lt/20,000) |
Summary
Although ACI 318-19 includes many revisions, the most significant changes are the procedural changes introduced in the shear design, development length, and seismic detailing provisions, along with the seismic requirements in Chapter 18. Regardless of whether these procedural changes are simple or complex, they require engineers to familiarize themselves with the new methodology. It’s important to note that, for PE exam preparation, these procedures should be practiced beforehand rather than learned for the first time during the exam.
In addition to these procedural updates, ACI 318-19 also introduces several other changes, including revised minimum reinforcement requirements, new anchor types, new shotcrete provisions, and an expanded foundations chapter. While many of these changes are relatively straightforward, candidates should still become familiar with them before the examination.
Overall, ACI 318-19 represents an evolution and refinement rather than a complete redesign of the standard. Understanding where the major procedural changes occurred, while being aware of the smaller revisions throughout the code, will help engineers transition more confidently from ACI 318-14 and be better prepared for both engineering practice and future PE examinations.
As always, Petro Publications will continue updating our PE exam preparation material as the 2027 NCEES code-reference update takes shape, so that candidates are always studying from the most current, exam-relevant version of these updated codes.
