Page 279 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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Source: STRUCTURAL STEEL DESIGNER'S HANDBOOK

CHAPTER 6

DESIGN OF BUILDING MEMBERS

Ali A. K. Haris, Ph.D., P.E.
President
Haris Engineering, Inc.
Overland Park, Kansas
Kaise Haris
Structural Engineer
Haris Engineering, Inc.
Overland Park, Kansas

Steel members in building structures can be part of the floor framing system to carry gravity loads,
the vertical framing system, the lateral framing system to provide lateral stability to the building and
resist lateral loads, or two or more of these systems. Floor members are normally called joists,
purlins, beams, or girders. Roof members are also known as rafters.
Purlins, which support floors, roofs, and decks, are relatively close in spacing. Beams are floor
members supporting the floor deck. Girders are steel members spanning between columns and usu-
ally supporting other beams. Transfer girders are members that support columns and transfer loads
to other columns. The primary stresses in joists, purlins, beams, and girders are due to flexural
moments and shear forces.
Vertical members supporting floors in buildings are designated columns. The most common steel
shapes used for columns are wide-flange sections, pipes, and tubes. Columns are subject to axial
compression and also often to bending moments. Slenderness in columns is a concern that must be
addressed in the design.
Lateral framing systems may consist of the floor girders and columns that support the gravity
floor loads but with rigid connections. These enable the flexural members to serve the dual function
of supporting floor loads and resisting lateral loads. Columns, in this case, are subject to combined
axial loads and moments. The lateral framing system also can consist of vertical diagonal braces or
shear walls whose primary function is to resist lateral loads. Mixed bracing systems and rigid steel
frames are also common in tall buildings.
Most steel floor framing members are considered simply supported. Most steel columns support-
ing floor loads only are considered as pinned at both ends. Other continuous members, such as those
in rigid frames, must be analyzed as plane or space frames to determine the members’ forces and
moments.
Other main building components are steel trusses used for roofs or floors to span greater lengths
between columns or other supports, built-up plate girders and stub girders for long spans or heavy
loads, and open-web steel joists. See also Chap. 7.
This chapter addresses the design of these elements, which are common to most steel buildings.
Design is based on the “Specification for Structural Steel Buildings,” American Institute of Steel

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