SPECIFICATIONS. 211 



41 . Maximum Diameter. The diameter of the rivets in any angle carrying calculated stress 

 sh.ill inn r\. cv<l Din- -quarter the width of the leg in which they are driven. In minor parts J-in. 

 rivri-^ may be used in 3-in. angles, and J-in. rivets in 2}-in. angles. 



4^. Long Rivets. Rivets carrying calculated stress and whose grip exceeds four diameters 

 >hall In- iniTiMsi-d in number at least one per cent for each additional A-in. of grip. 



43. Pitch at Ends. The pitch of rivets at the ends of built compression members shall not 

 r\ivrd four diameters of the rivets, for a length equal to one and one-half times the maximum 

 width of nu'inber. 



44. Compression Members. In compression members the metal shall be concentrated as 

 much as possible in webs and flanges. The thickness of each web shall be not less than one- 

 t hirt it-t h of the distance between its connections to the flanges. Cover plates shall have a thickness 

 nut less than one-fortieth of the distance between rivet lines. 



45. Minimum Angles. Flanges of girders and built members without cover plates shall have 

 a minimum thickness of one-twelfth of the width of the outstanding leg. 



46. Tie-Plates. The open sides of compression members shall be provided with lattice and 

 shall have tie-plates as near each end as practicable. Tie-plates shall be provided at intermediate 

 points where the lattice is interrupted. In main members the end tie-plates shall have a length 

 not less than the distance between the lines of rivets connecting them to the flanges, and inter- 

 mediate ones not less than one-half this distance. Their thickness shall not be less than one- 

 fiftieth of the same distance. 



47. Lattice. The latticing of compression members shall be proportioned to resist the 

 shearing stresses corresponding to the allowance for flexure for uniform load provided in the 



column formula in paragraph 16 by the term 70 - . The minimum width of lattice bars shall be 



2j in. for J-in. rivets, 2} in. for f-in. rivets, and 2 in. if f-in. rivets are used. The thickness shall 

 not be less than one-fortieth of the distance between end rivets for single lattice, and one-sixtieth 

 for double lattice. Shapes of equivalent strength may be used. 



48. Three-fourths-inch rivets shall be used for latticing flanges less than 2$ in. wide, and 

 |-in. for flanges from 2 J to 3 J in. wide; $-in. rivets shall be used in flanges 3$ in. and over, and 

 lattice bars with at least two rivets shall be used for flanges over 5 in. wide. 



49. The inclination of lattice bars with the axis of the member shall be not less than 45 degrees, 

 and when the distance between rivet lines in the flanges is more than 15 in., if single rivet bar is 

 used, the lattice shall be double and riveted at the intersection. 



50. Lattice bars shall be so spaced that the portion of the flange included between their 

 connections shall be as strong as the member as a whole. 



51. Faced Joints. Abutting joints in compression members when faced for bearing shall be 

 spliced on four sides sufficiently to hold the connecting members accurately in place. All other 

 joints in riveted work, whether in tension or compression, shall be fully spliced. 



52. Pin Plates. Pin-holes shall be reinforced by plates where necessary, and at least one 

 plate shall be as wide as the flanges will allow and be on the same side as the angles. They shall 

 contain sufficient rivets to distribute their portion of the pin pressure to the full cross-section of 

 the member. 



53. Forked Ends. Forked ends on compression members will be permitted only where 

 unavoidable; where used, a sufficient number of pin plates shall be provided to make the jaws of 

 twice the sectional area of the member. At least one of these plates shall extend to the far edge 

 of the farthest tie-plate, and the balance to the far edge of the nearest tie-plate, but not less than 

 6 in. beyond the near edge of the farthest plate. 



54. Pins. Pins shall be long enough to insure a full bearing of all the parts connected 

 upon the turned body of the pin. They shall be secured by chambered nuts or be provided with 

 washers if solid nuts are used. The screw ends shall be long enough to admit of burring the 

 threads. 



55. Members packed on pins shall be held against lateral movement. 



56. Bolts. Where members are connected by bolts, the turned body of these bolts shall be 

 long enough to extend through the metal. A washer at least J-in. thick shall be used under the 

 nut. Bolts shall not be used in place of rivets except by special permission. Heads and nuts 

 shall be hexagonal. 



57. Indirect Splices. Where splice plates are not in direct contact with the parts which 

 they connect, rivets shall be used on each side of the joint in excess of the number theoretically 

 required to the extent of one-third of the number for each intervening plate. 



58. Fillers. Rivets carrying stress and passing through fillers shall be increased 50 per cent 

 in number; and the excess rivets, when possible, shall be outside of the connected member. 



59. Expansion. Provision for expansion to the extent of i-in. for each 10 ft. shall be made 

 for all bridge structures. Efficient means shall be provided to prevent excessive motion at any 

 one point. 



