150 RESISTANCE OF MATERIALS 



outside plates except in special cases hereafter noted. In the 

 flanges of beams and girders, where plates more than 12 in. wide 

 are used, an extra line of rivets with a pitch not greater than 9 in. 

 should be driven along each edge to draw the plates together. 



At the ends of compression members the pitch should not ex- 

 ceed 4 diameters of the rivet for a length equal to twice the width 

 or diameter of the member. 



In the flanges of girders and chords carrying floors the pitch 

 should not exceed 4 in. 



For plates in compression the pitch in the direction of the line of 

 stress should not exceed 16 times the thickness of the plate, and 

 the pitch in a direction at right angles to the line of stress should 

 not exceed 32 times the thickness, except for cover plates of top 

 chords and end posts, in which the pitch should not exceed 40 times 

 their thickness. 



The distance between the edge of any piece and the center of the 

 rivet hole should not be less than li in. for |-in. and |-in. rivets, 

 except in bars less than 2^ in. wide ; when practicable it should 

 be at least 2 diameters of the rivet for all sizes, and should not 

 exceed 8 times the thickness of the plate. 



Typical illustrations of riveted connections in structural steel 

 work are shown in Figs. 106 and 107. 



93. Unit stresses. In structural-steel work it is customary to 

 proportion the various members on the basis of certain specified 

 unit stresses. The following specifications for the greatest allow- 

 able unit stresses represent the best American practice: 



Axial tension, net section 



Axial compression, gross section, but not to exceed 17,000 



Ib./in. 



18,000 Ib./in. 5 



16,000-17- 

 l = length of member in inches, 



r = least radius of gyration of member in inches. 



Compression in flanges of deck plate girders and built or 

 rolled beams, but not to exceed 17,000 Ib./in. 2 



Compression in flanges of through plate girders, but not to 

 exceed 17,000 Ib./in. 2 



I unsupported length of flange in inches, \1T)W 



r least radius of gyration of flange section laterally 



in inches, 



18,000-70- 

 r 



18,000- 70- 



