K3Cyclic tests for qualification of buckling-restrained braces

AISC 341-22, Seismic Provisions for Structural Steel Buildings

Last Updated 29 Oct 2026

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K3.1 Scope

This section includes requirements for qualifying cyclic tests of individual buckling-restrained braces and buckling-restrained brace subassemblages, when required in these Provisions. The purpose of the testing of individual braces is to provide evidence that a buckling-restrained brace satisfies the requirements for strength and inelastic deformation by these provisions; it also permits the determination of maximum brace forces for design of adjoining elements. The purpose of testing of the brace subassemblage is to provide evidence that the brace-design is able to satisfactorily accommodate the deformation and rotational demands associated with the design. Further, the subassemblage test is intended to demonstrate that the hysteretic behavior of the brace in the subassemblage is consistent with that of the individual brace elements tested uniaxially.

Alternative testing requirements are permitted when approved by the engineer of record and the authority having jurisdiction (AHJ). This section provides only minimum recommendations for simplified test conditions.

K3.2 Subassemblage Test Specimen

The subassemblage test specimen shall satisfy the following requirements:

(a) The mechanism for accommodating inelastic rotation in the subassemblage test specimen brace shall be the same as that of the prototype. The rotational deformation demands on the subassemblage test specimen brace shall be equal to or greater than those of the prototype.
(b) The axial yield strength of the steel core, $P_{y s c}$ , of the brace in the subassemblage test specimen shall not be less than $90 \%$ of that of the prototype where both strengths are based on the core area, $A_{s c}$ , multiplied by the yield strength as determined from a coupon test.
(c) The cross-sectional shape and orientation of the steel core projection of the subassemblage test specimen brace shall be the same as that of the brace in the prototype.
(d) The same documented design methodology shall be used for design of the sub-assemblage as used for the prototype, to allow comparison of the rotational deformation demands on the subassemblage brace to the prototype. In stability calculations, beams, columns, and gussets connecting the core shall be considered parts of this system.
(e) The calculated margins of safety for the prototype connection design, steel core projection stability, overall buckling, and other relevant subassemblage test specimen brace construction details, excluding the gusset plate, for the prototype, shall equal or exceed those of the subassemblage test specimen construction. If the qualification brace test specimen required in Section K3.3 was also tested, including the subassemblage requirements of this section, the lesser safety factor for overall buckling between that required in Section K3.3a(a) and that required in this section may be used.
(f) Lateral bracing of the subassemblage test specimen shall replicate the lateral bracing in the prototype.
(g) The brace test specimen and the prototype shall be manufactured in accordance with the same quality control and assurance processes and procedures.

Extrapolation beyond the limitations stated in this section is permitted subject to qualified peer review and approval by the AHJ.

K3.3 Brace Test Specimen

The brace test specimen shall replicate as closely as is practical the pertinent design, detailing, construction features, and material properties of the prototype.

K3.3a Design of Brace Test Specimen

The same documented design methodology shall be used for the brace test specimen and the prototype. The design calculations shall demonstrate, at a minimum, the fol- lowing requirements:

(a) The calculated margin of safety for stability against overall buckling for the prototype shall equal or exceed that of the brace test specimen.
(b) The calculated margins of safety for the brace test specimen and the prototype shall account for differences in material properties, including yield and ultimate stress, ultimate elongation, and toughness.

K3.3b Manufacture of Brace Test Specimen

The brace test specimen and the prototype shall be manufactured in accordance with the same quality control and assurance processes and procedures.

K3.3c Similarity of Brace Test Specimen and Prototype

The brace test specimen shall meet the following requirements:

(a) The cross-sectional shape and orientation of the steel core shall be the same as that of the prototype.
(b) The axial yield strength of the steel core, $P_{y s c}$ , of the brace test specimen shall not be less than $50 \%$ nor more than $150 \%$ of the prototype where both strengths are based on the core area, $A_{s c}$ , multiplied by the yield strength as determined from a coupon test.
(c) The material for, and method of, separation between the steel core and the buckling restraining mechanism in the brace test specimen shall be the same as that in the prototype.

Extrapolation beyond the limitations stated in this section is permitted subject to qualified peer review and approval by the AHJ.

K3.3d Connection Details

The connection details used in the brace test specimen shall represent the prototype connection details as closely as practical.

K3.3e Materials

K3.3e.1 Steel Core

The following requirements shall be satisfied for the steel core of the brace test specimen:

(a) The specified minimum yield stress of the brace test specimen steel core shall be the same as that of the prototype.
(b) The measured yield stress of the material of the steel core in the brace test specimen shall be at least 90% of that of the prototype as determined from coupon tests.
(c) The specified minimum ultimate stress and strain of the brace test specimen steel core shall not exceed those of the prototype.

K3.3e.2 Buckling-Restraining Mechanism

Materials used in the buckling-restraining mechanism of the brace test specimen shall be the same as those used in the prototype.

K3.3f Connections

The welded, bolted, and pinned joints on the test specimen shall replicate those on the prototype as close as practical.

K3.4 Loading History

K3.4a General Requirements

The test specimen shall be subjected to cyclic loads in accordance with the requirements prescribed in Sections K3.4b and K3.4c. Additional increments of loading beyond those described in Section K3.4c are permitted. Each cycle shall include a full tension and full compression excursion to the prescribed deformation.

K3.4b Test Control

The test shall be conducted by controlling the level of axial or rotational deformation, $\Delta_{b}$ , imposed on the test specimen. As an alternate, the maximum rotational deformation is permitted to be applied and maintained as the protocol is followed for axial deformation.

K3.4c Loading Sequence

Loads shall be applied to the test specimen to produce the following deformations, where the deformation is the steel core axial deformation for the test specimen and the rotational deformation demand for the subassemblage test specimen brace:

(a) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=\Delta_{b y}$
(b) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=0.50 \Delta_{b m}$
(c) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=1.0 \Delta_{b m}$
(d) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=1.5 \Delta_{b m}$
(e) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=2.0 \Delta_{b m}$
(f) Additional complete cycles of loading at the deformation corresponding to $\Delta_{b}=$ $1.5 \Delta_{b m}$ , as required for the brace test specimen to achieve a cumulative inelastic axial deformation of at least 200 times the yield deformation (not required for the subassemblage test specimen)

where

$\Delta_{b m}=$ value of deformation quantity, $\Delta_{b}$ , at least equal to that corresponding to the design earthquake displacement, in. (mm)

$\begin{aligned} \Delta_{b y} & =\text { value of deformation quantity, } \Delta_{b} \text {, at first yield of test specimen, in. } \\ & \text { (mm) }\end{aligned}$

The frame drift at the design earthquake displacement shall not be taken as less than 0.01 times the story height for the purposes of calculating $\Delta_{b m}$ . Other loading sequences are permitted to be used to qualify the test specimen when they are demonstrated to be of equal or greater severity in terms of maximum and cumulative inelastic deformation.

K3.5 Instrumentation

Sufficient instrumentation shall be provided on the test specimen to permit measurement or calculation of the quantities listed in Section K3.7.

K3.6 Materials Testing Requirements

K3.6a Tension Testing Requirements

Tension testing shall be conducted on samples of steel taken from the same heat of steel as that used to manufacture the steel core. Tension test results from certified material test reports shall be reported but are prohibited in place of material specimen testing for the purposes of this section. Tension test results shall be based upon testing that is conducted in accordance with Section K3.6b.

K3.6b Methods of Tension Testing

Tension testing shall be conducted in accordance with ASTM A6/A6M, ASTM A370, and ASTM E8/E8M, with the following exceptions:

(a) The yield stress that is reported from the test shall be based upon the yield strength definition in ASTM A370, using the offset method of 0.002 strain.
(b) The loading rate for the tension test shall replicate, as closely as is practical, the loading rate used for the test specimen.
(c) The coupon shall be machined so that its longitudinal axis is parallel to the longitudinal axis of the steel core.

K3.7 Test Reporting Requirements

For each test specimen, a written test report meeting the requirements of this section shall be prepared. The report shall thoroughly document all key features and results of the test. The report shall include the following information:

(a) A clear description of the test specimen, including key dimensions, boundary conditions at loading and reaction points, and location of lateral bracing, if any.
(b) The connection details, including member sizes, grades of steel, the sizes of all connection elements, welding details including filler metal, the size and location of bolt or pin holes, the size and grade of connectors, and all other pertinent details of the connections.
(c) A listing of all other essential variables as listed in Section K3.2 or K3.3.
(d) A listing or plot showing the applied load or displacement history.
(e) A plot of the applied load versus the deformation, $\Delta_{b}$ . The method used to determine the deformations shall be clearly shown. The locations on the test specimen where the loads and deformations were measured shall be clearly identified.
(f) A chronological listing of test observations, including observations of yielding, slip, instability, transverse displacement along the test specimen, and rupture of any portion of the test specimen and connections, as applicable.
(g) The results of the material specimen tests specified in Section K3.6.
(h) The manufacturing quality control and quality assurance plans used for the fabrication of the test specimen. These shall be included with the welding procedure specifications and welding inspection reports.

Additional documents, data, and discussion of the test specimen or test results are permitted to be included in the report.

K3.8 Acceptance Criteria

At least one subassemblage test that satisfies the requirements of Section K3.2 shall be performed. At least one brace test that satisfies the requirements of Section K3.3 shall be performed. Within the required protocol range, all tests shall satisfy the following requirements:

(a) The plot showing the applied load versus displacement history shall exhibit stable, repeatable behavior with positive incremental stiffness.
(b) There shall be no rupture, brace instability, or brace end connection failure.
(c) For brace tests, each cycle to a deformation greater than $\Delta_{b y}$ , the maximum tension and compression forces shall not be less than the nominal strength of the core.
(d) For brace tests, each cycle to a deformation greater than $\Delta_{b y}$ , the ratio of the maximum compression force to the maximum tension force shall not exceed 1.5.

Other acceptance criteria are permitted to be adopted for the brace test specimen or subassemblage test specimen subject to qualified peer review and approval by the AHJ.

End of chapter · NextCommentary — Appendix 1 Design verification using nonlinear response history analysis

K3Cyclic tests for qualification of buckling-restrained braces

AISC 341-22, Seismic Provisions for Structural Steel Buildings

Last Updated 29 Oct 2026

Hover any section to copy its link or text, ask Copilot about it, or bookmark it.

K3.1 Scope

K3.2 Subassemblage Test Specimen

The subassemblage test specimen shall satisfy the following requirements:

(a) The mechanism for accommodating inelastic rotation in the subassemblage test specimen brace shall be the same as that of the prototype. The rotational deformation demands on the subassemblage test specimen brace shall be equal to or greater than those of the prototype.
(b) The axial yield strength of the steel core, $P_{y s c}$ , of the brace in the subassemblage test specimen shall not be less than $90 \%$ of that of the prototype where both strengths are based on the core area, $A_{s c}$ , multiplied by the yield strength as determined from a coupon test.
(c) The cross-sectional shape and orientation of the steel core projection of the subassemblage test specimen brace shall be the same as that of the brace in the prototype.
(d) The same documented design methodology shall be used for design of the sub-assemblage as used for the prototype, to allow comparison of the rotational deformation demands on the subassemblage brace to the prototype. In stability calculations, beams, columns, and gussets connecting the core shall be considered parts of this system.
(e) The calculated margins of safety for the prototype connection design, steel core projection stability, overall buckling, and other relevant subassemblage test specimen brace construction details, excluding the gusset plate, for the prototype, shall equal or exceed those of the subassemblage test specimen construction. If the qualification brace test specimen required in Section K3.3 was also tested, including the subassemblage requirements of this section, the lesser safety factor for overall buckling between that required in Section K3.3a(a) and that required in this section may be used.
(f) Lateral bracing of the subassemblage test specimen shall replicate the lateral bracing in the prototype.
(g) The brace test specimen and the prototype shall be manufactured in accordance with the same quality control and assurance processes and procedures.

Extrapolation beyond the limitations stated in this section is permitted subject to qualified peer review and approval by the AHJ.

K3.3 Brace Test Specimen

The brace test specimen shall replicate as closely as is practical the pertinent design, detailing, construction features, and material properties of the prototype.

K3.3a Design of Brace Test Specimen

The same documented design methodology shall be used for the brace test specimen and the prototype. The design calculations shall demonstrate, at a minimum, the fol- lowing requirements:

(a) The calculated margin of safety for stability against overall buckling for the prototype shall equal or exceed that of the brace test specimen.
(b) The calculated margins of safety for the brace test specimen and the prototype shall account for differences in material properties, including yield and ultimate stress, ultimate elongation, and toughness.

K3.3b Manufacture of Brace Test Specimen

The brace test specimen and the prototype shall be manufactured in accordance with the same quality control and assurance processes and procedures.

K3.3c Similarity of Brace Test Specimen and Prototype

The brace test specimen shall meet the following requirements:

(a) The cross-sectional shape and orientation of the steel core shall be the same as that of the prototype.
(b) The axial yield strength of the steel core, $P_{y s c}$ , of the brace test specimen shall not be less than $50 \%$ nor more than $150 \%$ of the prototype where both strengths are based on the core area, $A_{s c}$ , multiplied by the yield strength as determined from a coupon test.
(c) The material for, and method of, separation between the steel core and the buckling restraining mechanism in the brace test specimen shall be the same as that in the prototype.

Extrapolation beyond the limitations stated in this section is permitted subject to qualified peer review and approval by the AHJ.

K3.3d Connection Details

The connection details used in the brace test specimen shall represent the prototype connection details as closely as practical.

K3.3e Materials

K3.3e.1 Steel Core

The following requirements shall be satisfied for the steel core of the brace test specimen:

(a) The specified minimum yield stress of the brace test specimen steel core shall be the same as that of the prototype.
(b) The measured yield stress of the material of the steel core in the brace test specimen shall be at least 90% of that of the prototype as determined from coupon tests.
(c) The specified minimum ultimate stress and strain of the brace test specimen steel core shall not exceed those of the prototype.

K3.3e.2 Buckling-Restraining Mechanism

Materials used in the buckling-restraining mechanism of the brace test specimen shall be the same as those used in the prototype.

K3.3f Connections

The welded, bolted, and pinned joints on the test specimen shall replicate those on the prototype as close as practical.

K3.4 Loading History

K3.4a General Requirements

K3.4b Test Control

K3.4c Loading Sequence

(a) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=\Delta_{b y}$
(b) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=0.50 \Delta_{b m}$
(c) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=1.0 \Delta_{b m}$
(d) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=1.5 \Delta_{b m}$
(e) 2 cycles of loading at the deformation corresponding to $\Delta_{b}=2.0 \Delta_{b m}$
(f) Additional complete cycles of loading at the deformation corresponding to $\Delta_{b}=$ $1.5 \Delta_{b m}$ , as required for the brace test specimen to achieve a cumulative inelastic axial deformation of at least 200 times the yield deformation (not required for the subassemblage test specimen)

where

$\Delta_{b m}=$ value of deformation quantity, $\Delta_{b}$ , at least equal to that corresponding to the design earthquake displacement, in. (mm)

$\begin{aligned} \Delta_{b y} & =\text { value of deformation quantity, } \Delta_{b} \text {, at first yield of test specimen, in. } \\ & \text { (mm) }\end{aligned}$

K3.5 Instrumentation

Sufficient instrumentation shall be provided on the test specimen to permit measurement or calculation of the quantities listed in Section K3.7.

K3.6 Materials Testing Requirements

K3.6a Tension Testing Requirements

K3.6b Methods of Tension Testing

Tension testing shall be conducted in accordance with ASTM A6/A6M, ASTM A370, and ASTM E8/E8M, with the following exceptions:

(a) The yield stress that is reported from the test shall be based upon the yield strength definition in ASTM A370, using the offset method of 0.002 strain.
(b) The loading rate for the tension test shall replicate, as closely as is practical, the loading rate used for the test specimen.
(c) The coupon shall be machined so that its longitudinal axis is parallel to the longitudinal axis of the steel core.

K3.7 Test Reporting Requirements

(a) A clear description of the test specimen, including key dimensions, boundary conditions at loading and reaction points, and location of lateral bracing, if any.
(b) The connection details, including member sizes, grades of steel, the sizes of all connection elements, welding details including filler metal, the size and location of bolt or pin holes, the size and grade of connectors, and all other pertinent details of the connections.
(c) A listing of all other essential variables as listed in Section K3.2 or K3.3.
(d) A listing or plot showing the applied load or displacement history.
(e) A plot of the applied load versus the deformation, $\Delta_{b}$ . The method used to determine the deformations shall be clearly shown. The locations on the test specimen where the loads and deformations were measured shall be clearly identified.
(f) A chronological listing of test observations, including observations of yielding, slip, instability, transverse displacement along the test specimen, and rupture of any portion of the test specimen and connections, as applicable.
(g) The results of the material specimen tests specified in Section K3.6.
(h) The manufacturing quality control and quality assurance plans used for the fabrication of the test specimen. These shall be included with the welding procedure specifications and welding inspection reports.

Additional documents, data, and discussion of the test specimen or test results are permitted to be included in the report.

K3.8 Acceptance Criteria

(a) The plot showing the applied load versus displacement history shall exhibit stable, repeatable behavior with positive incremental stiffness.
(b) There shall be no rupture, brace instability, or brace end connection failure.
(c) For brace tests, each cycle to a deformation greater than $\Delta_{b y}$ , the maximum tension and compression forces shall not be less than the nominal strength of the core.
(d) For brace tests, each cycle to a deformation greater than $\Delta_{b y}$ , the ratio of the maximum compression force to the maximum tension force shall not exceed 1.5.

Other acceptance criteria are permitted to be adopted for the brace test specimen or subassemblage test specimen subject to qualified peer review and approval by the AHJ.

End of chapter · NextCommentary — Appendix 1 Design verification using nonlinear response history analysis