AISC LRFD 1.pdf

30 BUILT-UP MEMBERS [Sect. E4.Open sides of compression members built up from plates or shapes shall be providedwith continuous cover plates perforated with a succession of access holes.The unsupported width of such plates at access holes, as defined in Section B5.1, isassumed to contribute to the design strength provided that:(1) The width-thickness ratio conforms to the limitations of Section B5.1.(2) The ratio of length (in direction of stress) to width of hole shall not exceed two.(3) The clear distance between holes in the direction of stress shall be not less thanthe transverse distance between nearest lines of connecting fasteners or welds.(4) The periphery of the holes at all points shall have a minimum radius of 1 1 2-in.(38 mm).As an alternative to perforated cover plates, lacing with tie plates is permitted ateach end and at intermediate points if the lacing is interrupted. Tie plates shall be asnear the ends as practicable. In main members providing design strength, the end tieplates shall have a length of not less than the distance between the lines of fastenersor welds connecting them to the components of the member. Intermediate tie platesshall have a length not less than one-half of this distance. The thickness of tie platesshall be not less than one-fiftieth of the distance between lines of welds or fastenersconnecting them to the segments of the members. In welded construction, the weldingon each line connecting a tie plate shall aggregate not less than one-third thelength of the plate. In bolted and riveted construction, the spacing in the direction ofstress in tie plates shall be not more than six diameters and the tie plates shall beconnected to each segment by at least three fasteners.Lacing, including flat bars, angles, channels, or other shapes employed as lacing,shall be so spaced that l / r of the flange included between their connections shall notexceed the governing slenderness ratio for the member as a whole. Lacing shall beproportioned to provide a shearing strength normal to the axis of the member equalto two percent of the compressive design strength of the member. The l / r ratio forlacing bars arranged in single systems shall not exceed 140. For double lacing thisratio shall not exceed 200. Double lacing bars shall be joined at the intersections.For lacing bars in compression, l is permitted to be taken as the unsupported lengthof the lacing bar between welds or fasteners connecting it to the components of thebuilt-up member for single lacing, and 70 percent of that distance for double lacing.The inclination of lacing bars to the axis of the member shall preferably be not lessthan 60º for single lacing and 45º for double lacing. When the distance between thelines of welds or fasteners in the flanges is more than 15 in. (380 mm), the lacingshall preferably be double or be made of angles.For additional spacing requirements, see Section J3.E5. CONNECTIONS FOR PIN-CONNECTED COMPRESSION MEMBERSPin connections of pin-connected compression members shall conform to therequirements of Sections D3.1 and D3.2, except Equations D3-1 and D3-2 do notapply.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION