ACI 318-19, "Building Code Requirements for Structural Concrete," raised the long-standing yield-strength cap and now permits Grade 100 (100,000 psi, 690 MPa) deformed reinforcement in defined structural roles, while leaving the 60,000 psi shear/torsion ceiling in place [S3][S1].
The Grade 100 permission applies to ASTM A1035/A1035M low-carbon chromium bars (per the 2004 inaugural spec, first cited in ACI 318-08) and to confined-grids, boundary elements, shear walls, and some longitudinal column bars where calculations are run at 80,000 psi [S1][S3].
Code Limits by Member Type: Compression, Shear, Longitudinal
Compression reinforcement is capped at 80,000 psi for applications outside special seismic systems because, at the 0.003 extreme-fiber concrete strain assumed at crushing, the maximum usable steel stress is 87,000 psi under linear-elastic behavior (ACI 22.2.2.1), so a higher grade buys no extra capacity [S1]. Grade 100 longitudinal bars are allowed in columns only when the design calculation uses 80,000 psi as the effective yield [S1].
Shear and torsion reinforcement stays at a 60,000 psi ceiling, a limit set to control inclined crack widths in beams and diaphragms; ACI R20.2.2.4 references supporting research for 100,000 psi bars in lateral support of longitudinal bars and concrete confinement, including special seismic systems [S1].
For a working background on how deformed bar geometry and grade are defined for design, the rebar encyclopedia entry lays out the standard terminology used throughout ACI 318. When shop drawings call for bending Grade 100 bars, equipment selection has to match: a rebar bender rated for the higher yield class avoids the under-rated mandrel failures that show up when 60-grade tooling is mistakenly used on 100-grade stock.
Special Seismic Systems: Grade 80 in SMF, Up to Grade 100 in Walls
Under ACI 318-14, only Grade 60 steel was permitted in special seismic systems (special moment frames, special structural walls, coupling beams, wall piers) for flexure, axial, and shrinkage/temperature effects; the cap existed because higher-grade test data was not yet in the code record [S1]. ACI 318-19 changed the map: special moment frames may now use Grade 60 or Grade 80, and shear walls may use Grade 60, 80, or 100, with Grade 100 special seismic permission grounded in the NIST GCR 14-917-30 (2014) test programme funded through the ACI Foundation and the Charles Pankow Foundation [S1][S3].
ASTM A706 Grade 80 deformed bars (the 2009 editions of A615/A706 first added Grade 80, adopted in ACI 318-11) are the seismic-grade choice because of their controlled tensile-to-yield ratio and elongation, both required for inelastic strain demand [S1]. For projects transitioning from 60 to 80 or 100 grade, design teams should expect updated development and splice length provisions, two-way slab, beam, column, wall, diaphragm, and foundation requirements, concrete compressive-strength limits, and strength-reduction factors, all revised in the 2019 cycle [S4].
On the fabrication side, threaded rebar coupler systems qualified for Grade 100 must meet the same ACI 318 development-length and splice-strength provisions as the parent bar; mismatching a Grade 60 mechanical splice onto a Grade 100 bar is one of the most common shop-floor errors when HSRB first lands on a project.
ASTM Material Standards Behind the Permission
Three ASTM specifications carry the load. ASTM A1035/A1035M, "Deformed and Plain, Low-carbon, Chromium, Steel Bars for Concrete Reinforcement," covers Grade 100 in its inaugural 2004 edition, with the 2007 revisions first referenced in ACI 318-08 and tied to ACI ITG-6R-10, "Design Guide for the Use of ASTM A1035/A1035M Grade 100 (690) Steel Bars for Structural Concrete" [S1][S3].
ASTM A615 covers the common Grade 40, 60, 80, and 100 carbon-steel bars, while ASTM A706 covers the low-alloy, weldable seismic bars, both specifications adding Grade 80 in their 2009 revisions and being adopted in ACI 318-11 [S1]. ACI defines "high-strength reinforcing bar" (HSRB) as any bar with yield strength greater than 60,000 psi, a category that began with Grade 75 in ASTM A955 (2001) and extended to Grade 100 in ASTM A1035 (2004) [S1].
When a project mixes grades on the same deck, traceability matters: a rebar cutter and a rebar straightener shared between Grade 60 and Grade 100 stock should be reset for the higher yield, or operators risk hardened-blade chipping and inconsistent camber.
Quantifying the Allowable Stress Across Member Types
For routine selection, the 2019 rules can be condensed into a four-row decision grid that ACI 318-19 users can pull straight off the table. [S4]
Compression reinforcement outside special seismic systems: allowable fy = 80,000 psi; Grade 100 bars may be present in a column, but design runs at 80,000 psi (ACI 22.2.2.1) [S1]. Shear and torsion: allowable fy = 60,000 psi; the 100,000 psi cap is reserved for lateral tie / confinement use (ACI R20.2.2.4) [S1]. Longitudinal bars in special moment frames: allowable grades 60 and 80; Grade 100 is excluded [S3]. Longitudinal bars in special structural walls (including coupling beams and wall piers): allowable grades 60, 80, and 100 [S3]. Confinement reinforcement (spirals, hoops, cross-ties in special seismic systems and in non-seismic columns where used as confinement): Grade 100 permitted, with the 2008 ACI 318-05/318-08 lineage for 100,000 psi confinement explicitly carried forward into the 2019 edition [S1][S3].
The 87,000 psi usable-stress ceiling at 0.003 strain, the 80,000 psi compression cap, and the 60,000 psi shear/torsion cap together explain why Grade 100, even where permitted, often gets a project-specific economiser study against Grade 80 rather than a blanket upgrade [S1].
Research Base and Funding Behind the 2019 Shift
The permission did not appear in a vacuum. Through 2022, 15 research projects had been completed under the joint ACI Foundation, Charles Pankow Foundation (CPF), Concrete Reinforcing Steel Institute (CRSI), Precast/Prestressed Concrete Institute (PCI), and Magnusson Klemencic Associates (MKA) Foundation programme, demonstrating acceptable performance of special seismic members reinforced with Grade 100 bars [S3]. Jack Moehle, FACI, Chair of ACI Committee 318 for the 2019 cycle, called the rule change "a generational move" because the prior comprehensive update on reinforcing bar strength had been in 1971, capping Grade 60 in seismic and Grade 80 in general use for nearly 50 years [S3].
The last comprehensive update related to reinforcing-bar strength was made in 1971; ACI 318-19 then raised the limits on specified strengths and disallowed Grade 40 for flexural reinforcement in seismic applications, a change set documented in the December 2022 Concrete International recap [S3].
Where ACI 318-19 Still Says No
Three exclusions matter for spec writers. First, Grade 40 is no longer permitted for flexural reinforcement in seismic applications under ACI 318-19 [S3]. Second, Grade 100 longitudinal bars are excluded from special moment frames, where only Grade 60 and Grade 80 are allowed [S3]. Third, shear and torsion design must run at 60,000 psi even if the rest of the member uses Grade 100 longitudinal stock, so stirrups and torsional closed ties on a Grade 100 beam remain a 60-ksi detailing problem, not a 100-ksi one [S1].
For shop planning, the rebar tool reference page consolidates which cutter, bender, straightener, and coupler families are typically qualified for which grade class; mismatched tool ratings remain a leading source of NCRs when HSRB first lands on a project.
The training pipeline is catching up: ICC's 1-hour continuing-education webinar "Use of Grade 80 and Grade 100 Reinforcing Bars in ACI 318-19" (SK2023SWL0025, 2024-04-02) covers the new bar types, development and splice lengths, two-way slabs, beams, columns, walls, diaphragms, foundations, concrete compressive-strength limits, and strength-reduction factors, and is scheduled for 2026-08-05 as a live session [S4]. Trackable signals for the rest of 2026 include the next ICC offering date and any state-wide Department of Transportation amendments that adopt ACI 318-25, which will be the first code cycle to build on the 2019 HSRB permission rather than introduce it.
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