AISC LRFD 1.pdf

124 DESIGN FOR CYCLIC LOADING (FATIGUE) [App. K3.4. Bolts and Threaded PartsThe range of stress at service loads shall not exceed the stress range computed asfollows.(a) For mechanically fastened connections loaded in shear, the maximum range ofstress in the connected material at service loads shall not exceed the designstress range computed using Equation A-K3.1 where C f and F TH are taken fromSection 2 of Table A-K3.1.(b) For high-strength bolts, common bolts, and threaded anchor rods with cut,ground or rolled threads, the maximum range of tensile stress on the net tensilearea from applied axial load and moment plus load due to prying action shallnot exceed the design stress range computed using Equation A-K3.1 orA-K3.1M. The factor C f shall be taken as 3.9 10 8 (as for category E). Thethreshold stress, F TH shall be taken as 7 ksi (48 MPa) (as for category D). Thenet tensile area is given by Equation A-K3.5 and A-K3.6M.At20.9743öç db÷p æ= -4 ènø(A-K3.5)æMetric bolts : A p ( 0.9382 ) 2 öç t= db- Pè4÷ø(A-K3.6M)whereP = pitch, mm per threadd b = the nominal diameter (body or shank diameter), in. (mm)n = threads per in.For joints in which the material within the grip is not limited to steel or joints whichare not tensioned to the requirements of Table J3.1 or J3.1M, all axial load andmoment applied to the joint plus effects of prying action (if any) shall be assumed tobe carried exclusively by the bolts or rods.For joints in which the material within the grip is limited to steel and which aretensioned to the requirements of Table J3.1 or J3.1M, an analysis of the relativestiffness of the connected parts and bolts shall be permitted to be used to determinethe tensile stress range in the pretensioned bolts due to the total service live load andmoment plus effects of prying action. Alternatively, the stress range in the boltsshall be assumed to be equal to the stress on the net tensile area due to 20 percent ofthe absolute value of the service load axial load and moment from dead, live andother loads.5. Special Fabrication and Erection RequirementsLongitudinal backing bars are permitted to remain in place, and if used, shall becontinuous. If splicing is necessary for long joints, the bar shall be joined with completepenetration butt joints and the reinforcement ground prior to assembly in thejoint.In transverse joints subject to tension, backing bars, if used, shall be removed andthe joint back gouged and welded.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION