Page 222 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.2

CRITERIA FOR BUILDING DESIGN

5.2 CHAPTER FIVE

Hot-rolled structural shapes: A36, A529, A572, A588, A709, A913, and A992
Structural tubing: A500, A501, A618, A847
Pipe: A53 (Grade B)
Plates: A36, A242, A283, A514, A529, A572, A588, A709, A852, A1011
Bars: A36, A529, A572, A709
Sheets: A606, A1011 (Grades SS, HSLAS, and HSLAS-F)

The AISC Specification treats structural tubing (round, square, and rectangular) and pipe collectively
as HSS, hollow structural sections.
The AISC Specification also specifies the materials to be used for other components such as bolts
and nuts, anchor rods, shear studs, filler metal and flux for welding, and steel castings.
To minimize the likelihood of an undesirable premature fracture, Charpy V-notch impact
testing and minimum toughness requirements apply to certain thick sections. Included are hot-
rolled shapes with a flange thickness exceeding 2 in (50 mm) used as members subject to primary
tensile forces due to tension or flexure, and spliced using complete-joint-penetration groove
welds that fuse through the thickness. Also included are cross sections built up from plates with
a thickness exceeding 2 in (50 mm) subject to similar usage. In such cases, the impact test must
meet a minimum average value of 20 ft⋅lb (27 J) absorbed energy at +70°F (+21°C). Some
exceptions apply.

5.1.2 Design Methods

Under the AISC Specification, members and connections may be designed according to the provi-
sions of either load and resistance factor design (LRFD) or allowable strength design (ASD). The
strength required of structural members and connections must be determined by structural analysis
for the appropriate factored loads and load combinations stipulated in the applicable building code
(see Chap. 4). In the absence of a building code, the loads and load combinations should be accord-
ing to American Society of Civil Engineers (ASCE), ASCE 7, “Minimum Design Loads for
Buildings and Other Structures.” Note that the loads, load factors, and load combinations for LRFD
and ASD are generally different.
Design is based on the principle that no applicable strength or serviceability limit state is exceeded
when the structure is subjected to all appropriate load combinations. Strength limit states are related
to safety and maximum load-carrying capacity. Serviceability limit states are related to performance,
such as deflection or vibration considerations, under normal service conditions.

LRFD Strength Requirements. A design satisfies the strength requirements of the AISC Specification
when the design strength of each structural component equals or exceeds the required strength
determined on the basis of the LRFD load combinations. This is expressed as

(5.1)
R u ≤ φR n
where R u = required strength (LRFD)
R n = nominal strength (as given in the Specification)
φ= resistance factor
φR n = design strength

ASD Strength Requirements. A design satisfies the strength requirements of the AISC
Specification when the allowable strength of each structural component equals or exceeds the
required strength, determined on the basis of the ASD load combinations. This is expressed as

R ≤ R n (5.2)
Ω
a

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