Design of Building Members

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 usually 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 supporting 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 Sec. 8. This section addresses the design of these elements, which are common to most steel buildings, based on allowable stress design (ASD) and load and resistance factor design (LRFD). Design criteria for these methods are summarized in Sec. 6.


—–7.1. [aa:Tension Members]
—–7.2. [aa:Comparative Designs of Double-Angle Hanger]
—–7.3. [aa:Example LRFD for Wide-Flange Truss Members]
—–7.4. [aa:Compression Members]
—–7.5. [aa:Example LRFD for Steel Pipe in Axial Compression]
—–7.6. [aa:Comparative Designs of Wide-Flange Section with Axial Compression]
—–7.7. [aa:Example LRFD for Double Angles with Axial Compression]
—–7.8. [aa:Steel Beams]
—–7.9. [aa:Comparative Designs of Single-Span Floorbeam]
—–7.10. [aa:Example LRFD for Floorbeam with Unbraced Top Flange]
—–7.11. [aa:Example LRFD for Floorbeam with Overhang]
—–7.12. [aa:Composite Beams]
—–7.13. [aa:LRFD for Composite Beam with Uniform Loads]
—–7.14. [aa:Example LRFD for Composite Beam with Concentrated Loads and End Moments]
—–7.15. [aa:Combined Axial Load and Biaxial Bending]
—–7.16. [aa:Example LRFD for Wide-Flange Column in a Multistory Rigid Frame]
—–7.17. [aa:Base Plate Design]
—–7.18. [aa:Example LRFD of Column Base Plate]

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