8/20/2019 Aluminum Design Reference http://slidepdf.com/reader/full/aluminum-design-reference 1/24 6-i SECTION 6:ALUMINUM DESIGNTABLE OF CONTENTS6 6.1—SCOPE..................................................................................................................................................................................6-16.2—NOTATION..........................................................................................................................................................................6-1 6.3—MATERIAL—ALUMINUM ALLOY................................................................................................................................6-36.4—NONWELDED MEMBERS ...............................................................................................................................................6-36.4.1—Local Buckling Stress ..............................................................................................................................................6-116.4.2—Allowable Bending Stress........................................................................................................................................6-126.4.2.1—Effect of Local Buckling on Beam Strength ..................................................................................................6-136.4.3—Allowable Tension Stress ........................................................................................................................................6-136.4.3.1—Slenderness Limit ..........................................................................................................................................6-136.4.4—Allowable Compression Stress ................................................................................................................................6-136.4.4.1—Effect of Local Buckling on Column Strength.................................................................................................6-146.4.4.2—Slenderness Limit ..........................................................................................................................................6-146.4.5—Allowable Shear Stress ............................................................................................................................................6-146.4.5.1—Torsion and Shear in Tubes...........................................................................................................................6-146.4.6—Bearing .....................................................................................................................................................................6-146.5—WELDED MEMBERS ......................................................................................................................................................6-156.5.1—Filler Wire ................................................................................................................................................................6-156.5.2—Members with Longitudinal Welds .........................................................................................................................6-166.5.3—Members with Transverse Welds ............................................................................................................................6-176.6—CASTING ALLOYS..........................................................................................................................................................6-176.7—COMBINED STRESSES...................................................................................................................................................6-18 6.7.1—Vertical Cantilever Pole-Type Supports ..................................................................................................................6-186.7.2—Other Members.........................................................................................................................................................6-196.7.2.1—Axial Compression, Bending, and Shear ......................................................................................................6-196.7.2.2—Axial Tension, Bending, and Shear...............................................................................................................6-196.8—DETAILS OF DESIGN .....................................................................................................................................................6-206.8.1—Minimum Thickness of Material .............................................................................................................................6-206.8.2—Dimensional Tolerances...........................................................................................................................................6-206.9—WELDED CONNECTIONS .............................................................................................................................................6-206.10—BOLTED CONNECTIONS AND ANCHOR BOLTS ..................................................................................................6-20 6.11—PROTECTION .................................................................................................................................................................6-206.11.1—Galvanic Corrosion (Contact with Dissimilar Materials)......................................................................................6-216.11.2—Overall Painting .....................................................................................................................................................6-226.11.3—Cleaning and Treatment of Metal Surfaces ...........................................................................................................6-226.11.4—Anodizing ...............................................................................................................................................................6-226.12—REFERENCES .................................................................................................................................................................6-22
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6.4—NONWELDED MEMBERS ...............................................................................................................................................6-3
6.4.2.1—Effect of Local Buckling on Beam Strength..................................................................................................6-13
6.4.4.1—Effect of Local Buckling on Column Strength.................................................................................................6-14
6.4.5.1—Torsion and Shear in Tubes...........................................................................................................................6-14
6.5—WELDED MEMBERS ......................................................................................................................................................6-15
6.5.2—Members with Longitudinal Welds .........................................................................................................................6-16
6.5.3—Members with Transverse Welds ............................................................................................................................6-17
6.7.2.1—Axial Compression, Bending, and Shear ......................................................................................................6-19
6.7.2.2—Axial Tension, Bending, and Shear...............................................................................................................6-19
6.8—DETAILS OF DESIGN .....................................................................................................................................................6-20
6.8.1—Minimum Thickness of Material .............................................................................................................................6-20
6.11.3—Cleaning and Treatment of Metal Surfaces ...........................................................................................................6-22
6-2 STANDARD SPECIFICATIONS FOR STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
F a = allowable compressive stress for a member considered as an axially loaded column (MPa, ksi)
a = average compressive or tensile stress on cross-section produced by an axial load (MPa, ksi)
F a0 = allowable compressive stress of an axially loaded member considered as a short column (MPa, ksi)
F b = allowable stress for members subjected to bending only (MPa, ksi)
b = maximum bending stress produced by transverse loads or bending moments (MPa, ksi)
F bu = bearing ultimate strength (MPa, ksi)
F buw = bearing ultimate strength within 25 mm (1 in.) of a weld (MPa, ksi)
bx = bending stress about the major axis (MPa, ksi)
F bx = allowable bending stress about the major axis (MPa, ksi)
by = bending stress about the minor axis (MPa, ksi)
F by = allowable bending stress about the minor axis ( Article 6.7.2.1) (MPa, ksi)
F by = bearing yield strength (Tables 6-1 and 6-3) (MPa, ksi)
F byw = bearing yield strength within 25 mm (1 in.) of a weld (MPa, ksi)
F c = allowable compressive stress (MPa, ksi)
F cast = allowable compressive or shear stress on slender element for casting (MPa, ksi)
(F cast )t = allowable tensile or compressive stress for casting from Table 6-9 (MPa, ksi)
F cr = local buckling stress for element (MPa, ksi) F cy = compressive yield strength (MPa, ksi)
F cyw = compressive yield strength across a butt weld (0.2 percent offset in 250 mm (10 in.) gage length) (MPa, ksi)
F e = elastic buckling stress divided by nu (MPa, ksi)
F ec = for columns, elastic critical stress (Article 6.4.4.1) (MPa, ksi)
F ec = for beams, allowable elastic lateral buckling stress of beam calculated assuming that the elements are not buckled
(Article 6.4.2.1) (MPa, ksi)
F n = allowable stress for cross-section 25 mm (1 in.) or more from a weld (MPa, ksi)
F pw = allowable stress on cross-section, part of whose area lies within 25 mm (1 in.) of a weld (MPa, ksi)
F rb = allowable stress for beam with buckled element (MPa, ksi)
F rc = allowable stress for column with buckled element (MPa, ksi)
s = shear stress on cross-section caused by torsion or transverse shear loads (MPa, ksi)
F s = allowable shear stress for members subjected only to shear or torsion (MPa, ksi)
F su = shear ultimate strength (MPa, ksi)
F suw = shear ultimate strength within 25 mm (1 in.) of a weld (MPa, ksi)
F sy = shear yield strength (MPa, ksi)
F syw = shear yield strength within 25 mm (1 in.) of a weld (MPa, ksi)
F t = allowable tensile stress for axial load only (MPa, ksi)
F tu = tensile ultimate strength (MPa, ksi)
F tuw = tensile ultimate strength across a butt weld (MPa, ksi)
F ty = tensile yield strength (MPa, ksi)
F tyw = tensile yield strength across a butt weld (0.2 percent offset in 250 mm (10 in.) gage length) (MPa, ksi) F w = allowable stress on cross-section if entire area were to lie within 25 mm (1 in.) of weld (MPa, ksi)
F y = either F ty or F cy, whichever is smaller (MPa, ksi)
h = clear height of shear web (mm, in.)
I y = moment of inertia of a beam about axis parallel to web (mm4, in.4)
J = torsion constant (mm4, in.4)
k = effective length factor by rational analysis. k shall be taken larger than or equal to unity unless rational analysis
justifies a smaller value
k 1 = coefficient for determining slenderness limit S 2 for sections for which the allowable compressive stress is based on
k 2 = coefficient for determining allowable compressive stress in sections with slenderness ratio above S 2 for which the
allowable compressive stress is based on ultimate strength
k c = coefficient for compression members
k t = coefficient for tension members
L = unsupported length in plane of bending. Bracing points are the points at which the compression flange is restrained
against lateral movement or twisting (mm, in.)
Lb = length of the beam between bracing points or between a brace point and the free end of a cantilever beam (mm, in.) Lt = length of tube between circumferential stiffeners (mm, in.)
na = factor of safety on appearance of buckling
nu = factor of safety on ultimate strength
n y = factor of safety on yield strength
R = mid-thickness radius of round tubular column or maximum mid-thickness radius of oval tubular column (mm, in.)
r = radius of gyration of the column about the axis of buckling (mm, in.)
Rb = mid-thickness radius of curvature of curved plate and tubular beam element (mm, in.)
Ro = for torsion and shear, outside radius of round tube or maximum outside radius of oval tube (mm, in.)
r y = radius of gyration about axis parallel to web (mm, in.)
S = slenderness ratio of section
S 1, S 2 = slenderness limits
S c = section modulus of a beam, compression side (mm3, in.3)
t = thickness (mm, in.)
6.3—MATERIAL—ALUMINUM ALLOY
For principal materials used for structural members,
minimum mechanical properties for nonwelded aluminum
alloys shall be as given in Table 6-1, and for welded
aluminum alloys in Table 6-2. Applicable ASTM
specifications are Designations B 209, B 210, B 211, B 221,
B 241, B 247, B 308, and B 429.
For aluminum alloys not found in Tables 6-1 and 6-2,
reference should be made to the Aluminum Design Manual ,
“Specifications for Aluminum Structures—Allowable Stress
Design.”
6.4—NONWELDED MEMBERS
Allowable stresses for nonwelded aluminum alloy
members shall be determined in accordance with the
formulas shown in Table 6-3, except as indicated in
Articles 6.4.1, 6.4.2.1, and 6.4.4.1. When more than one
formula is given, the smallest of the resulting stresses shall
be used.
Allowable stresses for commonly used alloys are
tabulated in Appendix B in accordance with the formulas o
Table 6-3. Tabulated allowable stresses for additional alloys
are provided in the Aluminum Design Manual , “Design
Aids.”
The safety factors for the basic allowable stresses shall
follow those specified for building-type structures. The
safety factors nu, n y, and na shall be taken as follows:
nu = 1.95
n y = 1.65
na = 1.20
Equations for buckling constants B, C , and D and values
of k 1 and k 2 shall be as given in Tables 6-4 and 6-5. Values
of coefficients k t and k c shall be as given in Table 6-6.
Tabulated values of buckling constants for aluminum
alloys are provided in the Aluminum Design Manual , “Design