ICC-ES released the AC133 (24) 2nd Edition acceptance criteria in April 2025, governing how manufacturers qualify mechanical splice systems for uncoated deformed steel reinforcing bars in concrete [S1][S4]. The 2025 edition supersedes the prior AC133 (21) and updates Type 1, Type 2, and Type 2HS (high-strain) test protocols used by ICC Evaluation Service (ICC-ES) to issue Evaluation Service Reports such as ESR-3433 and ESR-4572 [S5][S9].
The criteria apply to splices that are field-assembled onto bar ends prepared either in a factory or at the jobsite, and to splices that include components factory-attached to the reinforcing bar, broadening the scope from earlier editions [S1][S3]. Evaluation work under AC133 ties directly to ACI 318-19, Sections 18.2.7.1 and 25.5.7.1, and the structural provisions of the 2021 International Building Code (IBC) and International Residential Code (IRC) [S5].
Splice Types and Where Each One Is Required
AC133 (24) defines three splice performance tiers: Type 1 is a tension- and compression-rated connection for general use, while Type 2 is required where yielding is anticipated in the splice region [S4]. Type 2HS, the high-strain category, is intended for seismic applications where the splice must develop bar fracture in a plastic hinge region, per ACI 318-19, Section 20.2.1.3(b) [S5].
ICC-ES Evaluation Reports list which Tier each proprietary system is qualified for, for example ESR-3433 lists NMB Splice-Sleeve Type U-X and A11W systems as Type 1 and Type 2, with sizes 6U-X, 8U-X, 11U-X, 14U-X, and the A11W also qualified as Type 2HS [S5]. ESR-4572 (Wellsys Metal) similarly cites AC133 (24) 2nd Edition, published April 2025, on its cover page for its cementitious-grouted mechanical connector data [S9].
Bar Grades, Coatings, and the Annex A Grouted Sleeve Path
Typical qualified bar inputs are ASTM A615 Grade 60 and ASTM A706 Grade 60 deformed bars, both of which appear across the recent ICC-ES report holder documents [S5][S7]. A706 is the low-alloy, weldable grade typically specified for seismic splices, while A615 is the standard billet-steel grade used in non-seismic concrete. AC133 (24) explicitly covers uncoated, deformed bars, with coated or stainless variants handled through separate criteria.
Annex A of AC133 (24) covers cementitious grouted sleeve reinforcing bar splice systems, the technology used in NMB Splice-Sleeve and similar grouted coupler products that rely on SS Mortar or equivalent proprietary grout inside a steel sleeve [S4][S5]. ESR-3433 specifies that SS Mortar is supplied with the sleeve and bonds the bar via internal ridges and a rebar stop at the sleeve mid-section [S5]. Independent testing against Annex A is performed at labs such as Wiss, Janney, Elstner Associates (WJE) under the AC133 scope [S3].
Cyclic Loading Stages, Residual Slip, and ISO 15835 Cross-Reference
Stage 1 through Stage 4 cyclic loading plus monotonic tension make up the core performance test in AC133, with residual slip limits tied to the loaded cycles and Type 1 / Type 2 / Type 2HS classifications [S4]. Industry comments filed against the prior AC133-1020-R1 revision pointed out that the proposed residual slip at cycle 20 was more severe than ISO 15835, which loads to 90% of nominal yield for the first 20 cycles and limits residual slip to no more than 0.3 mm (0.012 in) versus an unspliced bar [S2].
AC133 (24) also includes Annex B, which defines the procedure for measuring strain developed during Stage 4 of cyclic loading using marks on the bar, an approach that lets test labs quantify plastic strain in a Type 2HS splice without a clip-gauge setup [S4]. The published April 2025 edition landed after years of task-group debate over whether the slip limits should be bar-size dependent, and whether slip should be subtracted from the unspliced bar elongation before comparison, two items Caltrans Standard Specifications Section 52-6.02B(1) already addressed by allowing an increasing allowable slip as bar size grows [S2].
Comparison Matrix: Type 1 vs Type 2 vs Type 2HS Performance
The three AC133 tiers differ in qualifying tests, seismic eligibility, and ACI 318 code path, and the differences are summarized below. [S5]
Type 1: monotonic tension and compression only, general use, no seismic strain demand requirement, referenced under ACI 318-19, Section 18.2.7.1 and 25.5.7.1. Type 2: monotonic plus cyclic loading per Stages 1 to 4, used where yielding is anticipated in the splice, same ACI 318 sections, qualifies for use in moderate ductility locations. Type 2HS: full high-strain qualification, must show bar fracture clear of the splice affected zone in Stage 4 per Annex B, tied to ACI 318-19, Section 20.2.1.3(b) for seismic detailing in plastic hinge regions [S4][S5].
On cost, Type 1 report holders run the lightest test program, Type 2 adds cyclic and slip measurement, and Type 2HS adds the mark-based strain verification plus tighter quality control, which is why seismic bridge column and shear wall projects that specify Type 2HS typically narrow the bid list to a small number of ICC-ES report holders [S4][S5].
How AC133 Connects to IBC, IRC, and Evaluation Reports
AC133 is an acceptance criteria document, not a code in itself; it is invoked by ICC-ES to issue Evaluation Service Reports (ESRs) that are then cited by the 2021 IBC and 2021 IRC for code compliance [S4][S5]. ESR-3433 was reissued in February 2026 and cites AC133 (21) 2nd Edition, Published March 2025, demonstrating how report holders transition from the prior edition to the April 2025 (24) 2nd Edition as the document is updated [S5].
For engineers, the practical flow is: identify the splice Type required by ACI 318-19 in the section being detailed, confirm the ICC-ES report holder product is qualified for that Type, and then check the ESR's reissue date and AC133 edition reference on the report cover [S5][S7]. ESR-1163 (Aicher Steel Americas), for example, also lists AC133 (21), Published March 2025, on its conditions of use page, showing the report holder community migrating from the (21) edition to the (24) edition in 2025 [S7].
Selection Criteria for Specifiers and Quality Managers
Specifier-side, the four key criteria are splice Type, bar grade and size range, code path, and quality control system. Splice Type must be picked first (Type 1, 2, or 2HS) based on whether the splice falls in a seismic plastic hinge region per ACI 318-19, Section 20.2.1.3(b), or only in a yielding but non-seismic location per Section 18.2.7.1 [S5]. Bar grade is the second filter, since most ICC-ES reports are scoped to ASTM A615 Grade 60 and ASTM A706 Grade 60 only, with size ranges listed by report (for example, U-X sizes 6 through 14 covering #6 to #14 bars) [S5][S7].
Code path is the third filter: the report must be cited under the IBC edition the project is using (2009, 2012, 2015, 2018, or 2021) because each IBC ties to a specific ACI 318 version [S5]. Quality control is the fourth, and AC133 Section 5.0 plus the ICC-ES mark of conformity and quality-control audit are how report holders maintain their listings year over year [S4][S7]. The mechanical seal and coupling vocabulary in process piping is unrelated to rebar couplers, so make sure the procurement spec points to ACI 318-19 and the ICC-ES report number rather than to industrial-piping component catalogues.
Limitations, Open Debates, and Trackable Signals
Open technical debate centers on whether AC133 should reference ISO 15835-1 and 15835-2 (latest 2018 edition) directly for slip criteria, and whether a third option for Type 2HS strain determination via bar break in the reinforcing bar clear of the splice affected zone should be added, a position Caltrans already takes [S2]. The April 2025 (24) 2nd Edition does not yet resolve all of these items, and the task group has signaled more time is needed for industry consensus [S2][S4].
Trackable signals to watch over the next 12 months: (1) reissue dates of ESRs citing AC133 (24) 2nd Edition Published April 2025, (2) any new annexes covering stainless or epoxy-coated bar variants, and (3) whether a future revision adopts Caltrans Ultimate Splice requirements for high-strain qualification [S2][S4]. For projects already underway, couplers vs lap splices remain the structural decision, and the 2025 AC133 edition is the controlling document for qualifying the coupler system on the bid list.
Spec-level background on the components involved: pressure transmitter, and flow meter.