Creating a Road Map for Code Adoption of High-Strength Steel Reinforcing Bars

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The shift from Grade 40 to Grade 60 reinforcing steel reshaped masonry construction decades ago. A comparable shift toward Grade 80 (550 MPa) reinforcement has been underway in reinforced concrete, and masonry is positioned to follow. High-strength steel reinforcing bars (HSRBs) carry a higher specified yield strength, which lets designers carry the same force with less steel. The payoff for masonry is direct: fewer and smaller bars, less reinforcement congestion in grouted cells, easier handling and placement of bars by masons, and a smaller embodied-carbon footprint.

Reinforced concrete already capitalizes on these benefits. ACI 318 Building Code Requirements for Structural Concrete permits HSRBs across axial, flexural, and shear applications, a position built on decades of testing showing that members reinforced with Grade 80 bars develop strength and deformation capacities comparable to Grade 60 members. Masonry design has lagged for one reason: supporting analytical and experimental data did not exist. As a result, TMS 402/602-22 Building Code Requirements and Specification for Masonry Structures caps reinforcement at Grade 60. Allowable stress design limits the reinforcement stress to 32,000 psi, and strength design limits flexural reinforcement to a specified yield strength of 60,000 psi. Both thresholds exclude higher grades.

A research program at the University of Houston set out to close that data gap and give The Masonry Society the evidence needed to act. The program pairs large-scale experiments with high-fidelity finite element modeling and translates the results into specific, balloted code language. The sections that follow trace that road map from first feasibility study to proposed code revision.

The road map began with a question of economics and constructability: does Grade 80 reinforcement pay off in masonry under current design rules? A 2023 feasibility study answered through design case studies of common masonry members, including lintel beams, pilasters, out-of-plane walls, and shear walls, evaluated under both the allowable stress and strength design procedures of TMS 402 Building Code Requirements for Masonry Structures.

For tension-controlled members, substituting Grade 80 for Grade 60 reduced the required area of tension steel by roughly 25 percent, with carbon-footprint reductions reaching 33 percent. A full building design made the case solid. A single-story, high-bay retail prototype redesigned with Grade 80 bars cut total reinforcement cost by about 25 percent, driven largely by the out-of-plane load-bearing walls, where smaller bars replaced larger ones at the same spacing.
The study also flagged the limits of the benefit. Gains concentrate in tension-controlled members designed by the strength method; for compression-controlled members and heavily loaded sections, the steel grade has little effect because masonry crushing governs. The balance point for Grade 80 sits lower than for Grade 60, which constrains how much high-strength steel a section can use effectively. These findings set the agenda for the experimental work: confirm the savings and resolve the provisions that stand in the way.

The clearest obstacle to Grade 80 adoption is bond. A higher yield strength demands a longer development and lap-splice length to transfer the larger bar force into the surrounding grout. The penalty is not proportional, and it grows with bar size.
Twenty-two contact lap-splice tests and parametric finite element analyses in concrete and clay brick masonry quantified the demand for Grade 80 bars, with bar size, splice length, and bar standard as the variables. The tests showed that Grade 80 bars require lap lengths as much as 53 percent greater than Grade 60 bars, with the largest penalties for No. 5 bars and larger. To reproduce this in design, the research introduced a grade factor applied to the existing TMS lap-length formula, set to 1.15 for Grade 80 bars, mirroring the approach ACI 318 already uses for high-strength steel.

Two findings sharpened the recommendation. First, the bar standard matters: ASTM A706 (Standard Specification for Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement) bars consistently developed the code-required splice stress, while the less tightly controlled ASTM A615 (Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement) bars fell short of the conventional 125-percent-of-yield criterion in TMS 402. Because A615 bars serve regions where seismic demand is unlikely to govern, a relaxed 115-percent criterion proved sufficient and reasonable for them. Second, the required factor appeared to depend on bar size, a dependence that should belong to the bar-size factor rather than the grade factor, exposing known conservatism in the TMS 402 size factor for smaller bars. The size factor, therefore, becomes an item for future code revisions.

In special circumstances, longer splices may erode the constructability advantage of Grade 80 steel. Because bond failure in masonry is governed by splitting of the grout around the bar, adding steel fibers to the grout mix offers a way to bridge those splitting cracks, confine the bar, and shorten the splice. The idea is well established in other cementitious materials but rarely used in masonry grout.

A program of lap-splice tests, out-of-plane wall testing, and companion material tests evaluated steel hooked fibers at 1 and 2 percent by volume in the coarse grout of No. 7 Grade 80-reinforced specimens. A dosage of 1 percent fibers allowed a 26 percent reduction in the required lap length while still meeting the code splice-stress criterion. Increasing the dosage from 1 to 2 percent gave no further improvement, a plateau explained by the failure mode: the splice still split longitudinally because the surrounding masonry units and mortar joints carry no fiber reinforcement and continue to govern panel response.

To bring this into design, the research proposed a fiber-grout factor that multiplies the lap-length requirement, with a recommended value of 0.74 corresponding to the validated 26-percent reduction for Grade 80 No. 7 bars.

Lap-splice panels isolate bond, but walls reveal how Grade 80 reinforcement behaves in flexure. Eleven out-of-plane wall tests, the first such dataset in the literature, used hollow concrete and clay brick units across a range of variables: bar size and standard, partial and full grouting, tension- through compression-controlled responses, and continuous versus lap-spliced bars.
Walls reinforced with Grade 80 bars performed comparably to their Grade 60 counterparts. Tension-controlled walls developed large deflections and good ductility; compression-controlled walls failed by face shell crushing that progressed into a diagonal strut, as expected when masonry crushing governs. Measured strengths consistently exceeded the TMS 402-based design strengths in every wall, confirming that the existing provisions, extended with the grade factor, deliver adequate conservatism for Grade 80 flexural design.

Two practical lessons emerged. Walls with Grade 80 bars deflect more at service level loading because fewer bars reduce the cracked section stiffness, though all walls remained well within the TMS 402 deflection limit. Lap-spliced walls behaved differently from those with continuous bars: the spliced bars engaged more effective steel area than design assumes at the allowable stress limit state, and splitting along the splice could limit ductility. These behaviors point to splice detailing, not flexural capacity, as the item to watch.

Out-of-plane flexure is only part of the picture. Masonry shear walls resist combined axial and lateral load, and their design hinges on a ductile, flexure-controlled response that avoids brittle diagonal cracking. Whether Grade 80 reinforcement supports that behavior is the next frontier on the road map, and current provisions raise specific concerns that the in-plane studies set out to resolve.

Analytical shear-wall studies using the TMS 402 procedures show the same tension-controlled benefit seen in other members: a meaningful gain in moment and axial capacity for Grade 80 over Grade 60 below the balance point. The complication lies in the reinforcement limits. The maximum flexural-tension reinforcement ratio is inversely tied to the yield strength, so the cap on Grade 80 steel is markedly lower than for Grade 60, and it tightens further for special shear walls where ductility demand is highest. Because that limit was calibrated without high-strength data, its accuracy for Grade 80 bars is unverified. An experimental campaign is currently underway to characterize the use of Grade 80 bars as transverse reinforcement in partially and solid grouted walls. Figure 6 shows some highlights from the campaign.

The value of this evidence lies in what changes in the code. The lap-splice findings translated directly: in 2025, TMS committee ballots approved a revised lap-splice length expression for Grade 80 bars that adopts a grade factor of 1.15 and recognizes the narrower strength distribution of these bars through a reduced minimum splice-stress requirement for low-seismic applications. The flexural data support extending the allowable-stress and strength-design provisions to Grade 80 bars, with a recommended allowable stress of 42,000 psi, a proportional increase from the 32,000-psi value for Grade 60.

Table 1 summarizes the proposed design parameters that the research supports.

Work remains. The bar-size factor in the lap-length expression carries conservatism that future cycles should refine. The maximum reinforcement ratio for Grade 80 shear walls needs experimental validation that is being addressed in the aforementioned experimental campaign. Hooked steel fiber-grout factors are established but not yet adopted by TMS 402, and the service-deflection formulas deserve improvement. Even so, the road map is clear: feasibility established the value, lap-splice and flexural testing supplied the evidence, fiber-reinforced grout addressed the chief drawback, and the first code changes are now in the standard. Grade 80 reinforcement gives masonry designers expanded flexibility, material savings, and better constructability, and the path to its full adoption by TMS 402 is well underway. ■

This research was supported by the National Concrete Masonry Association (NCMA), the Western States Clay Products Association (WSCPA), and the Brick Industry Association (BIA). In-kind support was provided by the Texas Masonry Council and its professional masons, BarSplice Products Inc., Concrete Reinforcing Steel Institute, Interstate Brick, Best Block Construction Materials, Nucor Harris Rebar, D’Ambra Construction, and Veazey Enterprises. The author acknowledges graduate research assistants Muhammad Waleed Khan, Samvid Parajuli, and Omar Khalid, as well as industry advisor John Hochwalt, PE, SE.

This article is dedicated to the memory of John Chrysler, a valued member of the masonry community who dedicated three decades of his professional life to the Masonry Institute of America (MIA).

Dimitrios Kalliontzis, Ph.D., is an Assistant Professor in the Department of Civil and Environmental Engineering at the University of Houston, where he directs the Structural Performance and Fluid-Structure Interaction Laboratory ([email protected]).