NORTH AMERICAN SPECIFICATION FOR THE DESIGN OF COLD-FORMED
F. TESTS FOR SPECIAL CASES
Tests shall be made by an independent testing laboratory or by a testing laboratory of a manufacturer.
The provisions of Chapter F shall not apply to cold-formed steel diaphragms. Refer to Section D5.
F1 Tests for Determining Structural Performance
F1.1 Load and Resistance Factor Design and Limit States Design
Any structural performance that is required to be established by tests shall be evaluated in accordance with the following performance procedure:
(a) Evaluation of the test results shall be made on the basis of the average value of test data resulting from tests of not fewer than three identical specimens, provided the deviation of any individual test result from the average value obtained from all tests does not exceed
±15 percent. If such deviation from the average value exceeds 15 percent, more tests of the same kind shall be made until the deviation of any individual test result from the average value obtained from all tests does not exceed ±15 percent or until at least three additional tests have been made. No test result shall be eliminated unless a rationale for its exclusion is given. The average value of all tests made shall then be regarded as the nominal strength [nominal resistance], Rn, for the series of the tests. Rn and the coefficient of variation VP of the test results shall be determined by statistical analysis.
(b) The strength of the tested elements, assemblies, connections, or members shall satisfy Eq. F1.1-1a or Eq. F1.1-1b as applicable.
ΣγiQi ≤ φRn for LRFD (Eq. F1.1-1a)
φRn ≥ ΣγiQi for LSD (Eq. F1.1-1b)
where
ΣγiQi = Required strength [factored loads] based on the most critical load combination determined in accordance with Section A5.1.2 for LRFD or A6.1.2 for LSD. γi and Qi are load factors and load effects, respectively.
φ = Resistance factor =
2 Q 2 P P 2 F 2
o VM V C V V
m m mF P )e M
(
Cφ -β + + + (Eq. F1.1-2)
where
Cφ = Calibration coefficient = 1.52 for LRFD
= 1.6 for LRFD for beams having tension flange through-fastened to deck or sheathing and with compression flange laterally unbraced
= 1.42 for LSD
= 1.42 for LSD for beams having tension flange through-fastened to deck or sheathing and with compression flange laterally unbraced
Mm = Mean value of material factor, M, listed in Table F1 for type of component involved
Fm = Mean value of fabrication factor, F, listed in Table F1 for type of component involved
= 1.0
e = Natural logarithmic base = 2.718
βo = Target reliability index
= 2.5 for structural members and 3.5 for connections for LRFD
= 1.5 for LRFD for beams having tension flange through-fastened to deck or sheathing and with compression flange laterally unbraced
= 3.0 for structural members and 4.0 for connections for LSD
= 3.0 for LSD for beams having tension flange through-fastened to deck or sheathing and with compression flange laterally unbraced
VM = Coefficient of variation of material factor listed in Table F1 for type of component involved
VF = Coefficient of variation of fabrication factor listed in Table F1 for type of component involved
CP = Correction factor
= (1+1/n)m/(m-2) for n ≥ 4 (Eq. F1.1-3)
= 5.7 for n = 3 where
n = Number of tests m = Degrees of freedom = n-1
VP = Coefficient of variation of test results, but not less than 6.5 percent VQ = Coefficient of variation of load effect
= 0.21 for LRFD and LSD
= 0.43 for LRFD for beams having tension flange through-fastened to deck or sheathing and with compression flange laterally unbraced
= 0.21 for the LSD for beams having tension flange through-fastened to deck or sheathing and with compression flange laterally unbraced
Rn = Average value of all test results
The listing in Table F1 shall not exclude the use of other documented statistical data if they are established from sufficient results on material properties and fabrication.
For steels not listed in Section A2.1, values of Mm and VM shall be determined by the statistical analysis for the materials used.
When distortions interfere with the proper functioning of the specimen in actual use, the load effects based on the critical load combination at the occurrence of the acceptable distortion shall also satisfy Eq. F1.1-1a or Eq. F1.1-1b, as applicable, except that the resistance factor φ shall be taken as unity and the load factor for dead load shall be taken as 1.0.
(c) The mechanical properties of the steel sheet shall be determined based on representative samples of the material taken from the test specimen or the flat sheet used to form the test specimen. Mechanical properties reported by the steel supplier shall not be used in the evaluation of the test results. If the yield stress of the steel from which the tested sections are formed is larger than the specified value, the test results shall be adjusted down to the specified minimum yield stress of the steel that the manufacturer intends to use. The test results shall not be adjusted upward if the yield stress of the test specimen is less than the minimum specified yield stress. Similar adjustments shall be made on the basis of tensile
strength instead of yield stress where tensile strength is the critical factor.
Consideration shall also be given to any variation or differences between the design thickness and the thickness of the specimens used in the tests.
TABLE F1
Statistical Data for the Determination of Resistance Factor
Type of Component Mm VM Fm VF
Transverse Stiffeners Shear Stiffeners Tension Members Flexural Members Bending Strength
Lateral-Torsional Buckling Strength
One Flange Through-Fastened to Deck or Sheathing Shear Strength
Combined Bending and Shear Web Crippling Strength
Combined Bending and Web Crippling Concentrically Loaded Compression Members Combined Axial Load and Bending
Cylindrical Tubular Members Bending Strength
Axial Compression
Wall Studs and Wall Stud Assemblies Wall Studs in Compression
Wall Studs in Bending
Wall Studs with Combined Axial load and Bending Structural Members Not Listed Above
1.10 1.00 1.10
1.10 1.00 1.10 1.10 1.10 1.10 1.10 1.10 1.05
1.10 1.10
1.10 1.10 1.05 1.00
0.10 0.06 0.10
0.10 0.06 0.10 0.10 0.10 0.10 0.10 0.10 0.10
0.10 0.10
0.10 0.10 0.10 0.10
1.00 1.00 1.00
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
1.00 1.00
1.00 1.00 1.00 1.00
0.05 0.05 0.05
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
0.05 0.05
0.05 0.05 0.05 0.05 Continued
TABLE F1 (Continued)
Statistical Data for the Determination of Resistance Factor
Type of Component Mm VM Fm VF
Welded Connections Arc Spot Welds
Shear Strength of Welds Tensile Strength of Welds Plate Failure
Arc Seam Welds
Shear Strength of Welds Plate Tearing
Fillet Welds
Shear Strength of Welds Plate Failure
Flare Groove Welds Shear Strength of Welds Plate Failure
Resistance Welds Bolted Connections Shear Strength of Bolt Tensile Strength of Bolt
Minimum Spacing and Edge Distance Tension Strength on Net Section Bearing Strength
1.10 1.10 1.10
1.10 1.10
1.10 1.10
1.10 1.10 1.10
1.10 1.10 1.10 1.10 1.10
0.10 0.10 0.08
0.10 0.10
0.10 0.08
0.10 0.10 0.10
0.08 0.08 0.08 0.08 0.08
1.00 1.00 1.00
1.00 1.00
1.00 1.00
1.00 1.00 1.00
1.00 1.00 1.00 1.00 1.00
0.10 0.10 0.15
0.10 0.10
0.10 0.15
0.10 0.10 0.10
0.05 0.05 0.05 0.05 0.05 Continued
F1.2 Allowable Strength Design
Where the composition or configuration of elements, assemblies, connections, or details of cold-formed steel structural members are such that calculation of their strength cannot be made in accordance with the provisions of this Specification, their structural performance shall be established from tests and evaluated in accordance with Section F1.1, except as modified in this section for allowable strengthdesign.
The allowable strength shall be calculated as follows:
R = Rn/Ω (Eq. F1.2-1)
where
Rn = Average value of all test results Ω = Safety factor
= φ
6 .
1 (Eq. F1.2-2)
where
φ = A value evaluated in accordance with Section F1.1
The required strength shall be determined from nominal loads and load combinations as described in Section A4.
F2 Tests for Confirming Structural Performance
For structural members, connections, and assemblies for which the nominal strength [resistance] is computed in accordance with this Specification or its specific references, confirmatory tests shall be permitted to be made to demonstrate the strength is not less than the
TABLE F1 (Continued)
Statistical Data for the Determination of Resistance Factor
Type of Component Mm VM Fm VF
Screw Connections
Shear Strength of Screw Tensile Strength of Screw
Minimum Spacing and Edge Distance Tension Strength on Net Section Tilting and Bearing Strength Pull-Out
Pull-Over
Combined Shear and Pull-Over Connections Not Listed Above
1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10
0.10 0.10 0.10 0.10 0.08 0.10 0.10 0.10 0.10
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
0.10 0.10 0.10 0.10 0.05 0.10 0.10 0.10 0.15
nominal strength [resistance], Rn, specified in this Specification or its specific references for the type of behavior involved.
F3 Tests for Determining Mechanical Properties F3.1 Full Section
Tests for determination of mechanical properties of full sections to be used in Section A7.2 shall be conducted in accordance with this section.
(a) Tensile testing procedures shall agree with ASTM A370.
(b) Compressive yield stress determinations shall be made by means of compression tests of short specimens of the section. See AISI S902.
The compressive yield stress shall be taken as the smaller value of either the maximum compressive strength of the sections divided by the cross-sectional area or the stress defined by one of the following methods:
(1) For sharp yielding steel, the yield stress is determined by the autographic diagram method or by the total strain under load method.
(2) For gradual yielding steel, the yield stress is determined by the strain under load method or by the 0.2 percent offset method.
When the total strain under load method is used, there shall be evidence that the yield stress so determined agrees within 5 percent with the yield stress that would be determined by the 0.2 percent offset method.
(c) Where the principal effect of the loading to which the member will be subjected in service will be to produce bending stresses, the yield stress shall be determined for the flanges only. In determining such yield stress, each specimen shall consist of one complete flange plus a portion of the web of such flat width ratio that the value of ρ for the specimen is unity.
(d) For acceptance and control purposes, one full section test shall be made from each master coil.
(e) At the option of the manufacturer, either tension or compression tests shall be permitted to be used for routine acceptance and control purposes, provided the manufacturer demonstrates that such tests reliably indicate the yield stress of the section when subjected to the kind of stress under which the member is to be used.
F3.2 Flat Elements of Formed Sections
Tests for determining mechanical properties of flat elements of formed sections and representative mechanical properties of virgin steel to be used in Section A7.2 shall be made in accordance with this section.
The yield stress of flats, Fyf, shall be established by means of a weighted average of the yield stresses of standard tensile coupons taken longitudinally from the flat portions of a representative cold-formed member. The weighted average shall be the sum of the products of the average yield stress for each flat portion times its cross-sectional area, divided by the total area of flats in the cross-section. Although the exact number of such coupons will depend on the shape of the member, i.e., on the number of flats in the cross-section, at least one tensile coupon shall be taken from the middle of each flat. If the actual virgin yield stress exceeds the specified minimum yield stress, the yield stress of the flats, Fyf, shall be adjusted by multiplying the test values by the ratio of the specified minimum yield stress to the actual virgin yield stress.
F3.3 Virgin Steel
The following provisions shall apply to steel produced to other than the ASTM Specifications listed in Section A2.1 when used in sections for which the increased yield stress of the steel after cold forming is computed from the virgin steelproperties in accordance with Section A7.2. For acceptance and control purposes, at least four tensile specimens shall be taken from each master coil for the establishment of the representative values of the virgin tensile yield stress and tensile strength. Specimens shall be taken longitudinally from the quarter points of the width near the outer end of the coil.