AISC LRFD 1.pdf

242 BOLTS AND THREADED PARTS [Comm. J3.fasteners, and the distance from the edge of the part to the center line of the nearestfastener. Tests have shown (Kulak et al., 1987) that a linear relationship existsbetween the ratio of critical bearing stress to tensile strength (of the connectedmaterial) and the ratio of fastener spacing (in the line of force) to fastener diameter.The following equation affords a good lower bound to published test data for single-fastenerconnections with standard holes, and is conservative for adequatelyspaced multi-fastener connections:FpcrFule=d(C-J3-1)whereF pcr = critical bearing stress, ksi (MPa)F u = tensile strength of the connected material, ksi (MPa)l e = distance, along a line of transmitted force, from the center of a fastener tothe nearest edge of an adjacent fastener or to the free edge of a connectedpart (in the direction of stress), in. (mm)d = diameter of fastener, in. (mm)The provisions of Section J3.3 are concerned with l e as hole spacing, whereas SectionJ3.4 is concerned with l e as edge distance in the direction of stress.Section J3.10 establishes a maximum bearing strength. Spacing and/or edge distancemay be increased to provide for a required bearing strength, or bearing forcemay be reduced to satisfy a spacing and/or edge distance limitation.It has long been known that the critical bearing stress of a single fastener connectionis more dependent upon a given edge distance than multi-fastener connections(Jones, 1940). For this reason, longer edge distances (in the direction of force) arerequired for connections with one fastener in the line of transmitted force thanrequired for those having two or more. The recommended minimum distance transverseto the direction of load is primarily a workmanship tolerance. It has little, ifany, effect on the strength of the member.5. Maximum Spacing and Edge DistanceLimiting the edge distance to not more than 12 times the thickness of an outsideconnected part, but not more than six in. (150 mm), is intended to provide for theexclusion of moisture in the event of paint failure, thus preventing corrosionbetween the parts which might accumulate and force these parts to separate. Morerestrictive limitations are required for connected parts of unpainted weatheringsteel exposed to atmospheric corrosion.6. Design Tension or Shear StrengthTension loading of fasteners is usually accompanied by some bending due to thedeformation of the connected parts. Hence, the resistance factor , by which R n ismultiplied to obtain the design tensile strength of fasteners, is relatively low. Thenominal tensile strength values in Table J3.2 were obtained from the equationRn = 075 . AbFu(C-J3-2)This tensile strength given by Equation C-J3-2 is independent of whether the boltLRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION