AISC LRFD 1.pdf

Comm. E4.] BUILT-UP MEMBERS 205TABLE C-E3.1Limiting Proportions for TeesShapeRatio of FullFlange Width toProfile DepthRatio of FlangeThickness to Webor Stem ThicknessBuilt-up tees 0.50 1.25Rolled tees 0.50 1.10E4. BUILT-UP MEMBERSRequirements for detailing and design of built-up members, which cannot be statedin terms of calculated stress, are based upon judgment and experience.The longitudinal spacing of connectors connecting components of built-up compressionmembers must be such that the slenderness ratio l/rof individual shapesdoes not exceed three-fourths of the slenderness ratio of the entire member. Additionalrequirements are imposed for built-up members consisting of angles. However,these minimum requirements do not necessarily ensure that the effective slendernessratio of the built-up member is equal to that for the built-up member actingas a single unit. Section E4 gives formulas for modified slenderness ratios that arebased on research and take into account the effect of shear deformation in the connectors(Zandonini, 1985). Equation E4-1 for snug-tight intermediate connectors isempirically based on test results (Zandonini, 1985). Equation E4-2 is derived fromtheory and verified by test data. In both cases the end connection must be welded orslip-critical bolted (Aslani and Goel, 1991). The connectors must be designed toresist the shear forces which develop in the buckled member. The shear stresses arehighest where the slope of the buckled shape is maximum (Bleich, 1952).Maximum fastener spacing less than that required for strength may be needed toensure a close fit over the entire faying surface of components in continuous contact.Specific requirements are given for weathering steel members exposed toatmospheric corrosion (Brockenbrough, 1983).The provisions governing the proportioning of perforated cover plates are basedupon extensive experimental research (Stang and Jaffe, 1948).LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION