Page 263 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.43

CRITERIA FOR BUILDING DESIGN

CRITERIA FOR BUILDING DESIGN 5.43

these purposes, but fillet welds are usually preferred. The effective shearing area of plug and slot
welds is the nominal cross-sectional area of the hole or slot in the plane of the faying surface. See
the AISC Specification for limitations on size and spacing.

5.9.3 Design of Welds for Strength
The design strength φR n and the allowable strength R n /Ω of welds is the lower value of the base mate-
rial strength and the weld metal strength. These are determined as follows for the limit states of ten-
sile rupture, shear rupture, or yielding:
For the base material,
(5.141)
R n = F BM A BM
For the weld metal,
(5.142)
R n = F w A w
where F BM = nominal strength of the base material per unit area, ksi (MPa)
F w = nominal strength of the weld metal per unit area, ksi (MPa)
2
2
A BM = cross-sectional area of the base material, in (mm )
2
2
A w = effective area of the weld, in (mm )
The values of φ, Ω,F BM , and F w and limitations thereon are given in Table 5.7. The AISC
Specification also gives alternative rules that may result in greater strengths.
If two or more types of welds (groove, fillet, plug, or slot) are combined in a single joint, the
strength of each should be calculated separately with reference to the axis of the group to determine
the strength of the combination.
5.9.4 Filler Metal for Welds

The choice of electrode for use with complete-joint-penetration groove welds subject to tension nor-
mal to the effective area should comply with the requirements for matching filler metals given in
specifications of the American Welding Society, AWS D1.1. Also, the AISC Specification requires
filler metal with a specified Charpy V-notch (CVN) toughness of 20 ft⋅lb (27 J) at 40°F (4°C) to be
used for the following joints when subject to tension normal to the effective area: (1) CJP groove-
welded tee and corner joints with steel backing left in place, unless the joints are designed using the
nominal strength and resistance factor or safety factor for a PJP weld, and (2) CJP groove-welded
splices in heavy sections (see Art. 5.9.1). When Charpy V-notch toughness is specified, the process
consumables for all weld metal deposited in a joint, including tack welds, root pass, and subsequent
passes, must be compatible to assure notch toughness in the completed weld.

5.9.5 Design Considerations for Bolted Connections
High-strength bolts should conform to the provisions of the RCSC Specification (“Specification for
Structural Joints Using ASTM A325 or A490 Bolts,” Research Council on Structural Connections,
One East Wacker Dr., Suite 3100, Chicago, IL 60601-2001) as well as the AISC Specification, which
takes precedence should differences occur. High-strength bolts typically used include those desig-
nated as ASTM A325 and A490, as well as ASTM F1852, a “twist-off” tension-control bolt–
nut–washer assembly.
1
Where bolt lengths exceeding 12 diameters or diameters exceeding 1 / 2 in (38 mm) are required,
bolts or threaded rods conforming to ASTM A354 or A449 should be used. These are treated as
threaded rods for strength calculations. If used in slip-critical connections, the bolt geometry, includ-
ing head and nut, should be equal to or proportional to that provided by ASTM A325 or A490 bolts.
Installation should comply with all applicable requirements of the RCSC Specification with modifi-
cations as required for increased diameter or length.

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