62 



STEEL ROOF TRUSSES AND MILL BUILDINGS. 



CHAP. I. 



105. Main tension members shall preferably be made of 2 angles, 2 angles and a plate, or 2 

 channels laced. Secondary tension members may be made of a single shape. 



106. Eye-Bars. Heads of eye-bars shall be so proportioned as to develop the full strength 

 of the bar. The heads shall be forged and not welded. 



107. Pins. Pins must be turned true to size and straight, and must be driven to place by 

 means of pilot nuts. 



The diameter of pin shall not be less than f of the depth of the widest bar attached to it. 

 The several members attached to a pin shall be packed so as to produce the least bending 

 moment on the pin, and all vacant spaces must be filled with steel or cast iron fillers. 



1 08. Bars or Rods. Long laterals may be made of bars with clevis or sleeve nut adjustment. 

 Bent loops shall not be used. 



109. Spacing Trusses. Trusses shall preferably be spaced so as to allow the use of single 

 pieces of rolled sections for purlins. Trussed purlins shall be avoided if possible. 



no. Purlins and Girts. Purlins and girts shall preferably be composed of single sections 

 channels, angles or Z-bars, placed with web at right angles to the trusses and posts and legs turned 

 down. 



in. Fastening. Purlins and girts shall be attached to the top chord of trusses and to columns 

 by means of angle clips with two rivets in each leg. 



112. Spacing. Purlins for corrugated steel without sheathing shall be spaced at distances 

 apart not to exceed the span as given for a safe load of 30 lb., and girts for a safe load of 25 Ib. 

 as given in Fig. 18. 



113. Timber Purlins. Timber purlins and girts shall be attached and spaced the same as 

 steel purlins. 



114. Base Plates. Base plates shall never be less than f in. in thickness, and shall be of 

 sufficient thickness and size so that the pressure on the masonry shall not exceed the allowable 

 pressures in 30. 



115. Anchors. Columns shall be anchored to the foundations by means of two anchor 

 bolts not less than i in. in diameter upset, placed as wide apart as practicable in the plane of the 

 wind. The anchorage shall be calculated to resist one and one-half times the bending moment 

 at the base of the columns. 



1 1 6. Lateral Bracing. Lateral bracing shall be provided in the plane of the top and bottom 

 chords, sides and ends; knee braces in the transverse bents; and sway bracing wherever necessary. 

 Lateral bracing shall be designed for an initial stress of 5,000 lb. in each member, and provision 

 must be made for putting this initial stress into the members in erecting. 



117. Temperature. Variations in temperature to the extent of 150 degrees F. shall be 

 provided for. 



MATERIAL AND WORKMANSHIP. 



MATERIAL. 



1 1 8. Process of Manufacture. Steel shall be made by the open-hearth process. 



1 19. Schedule of Requirements. 



The yield point, as indicated by the drop of beam, shall be recorded in the test reports. 



* See paragraph 128. 



t See paragraphs 129, 130 and 131. 



j See paragraph 132. 



